4.9: Perfect Enzymes - Biology

4.9: Perfect Enzymes - Biology

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Now, if we think about what an ideal enzyme might be, it would be one that has a very high velocity and a very high affinity for its substrate. Such enzymes are referred to as being “perfect" because they have reached the maximum possible value. It is safe to say for a perfect enzyme that the only limit it has is the rate of substrate diffusion in water.

Given the “magic" of enzymes alluded to earlier, it might seem that all enzymes should have evolved to be “perfect." There are very good reasons why most of them have not. Speed can be a dangerous thing. The faster a reaction proceeds in catalysis by an enzyme, the harder it is to control. As we all know from learning to drive, speeding causes accident. Just as drivers need to have speed limits for operating automobiles, so too must cells exert some control on the ‘throttle’ of their enzymes. In view of this, one might wonder then why any cells have evolved any enzymes to perfection. There is no single answer to the question, but a common one is illustrated by the perfect enzyme known as triose phosphate isomerase (TPI), which catalyzes a reaction in glycolysis (figure on previous page). The enzyme appears to have been selected for this ability because at lower velocities, there is breakdown of an unstable enediol intermediate that then readily forms methyl glyoxal, a cytotoxic compound. Speeding up the reaction provides less opportunity for the unstable intermediate to accumulate and fewer undesirable byproducts are made.

Enzymes are proteins that act as catalysts. When one substance needs to be transformed into another, nature uses enzymes to speed up the process. In our stomachs for example, enzymes break down food into tiny particles to be converted into energy.

Our customers use enzymes as catalysts to manufacture a variety of everyday products - like sugar, beer, bread and ethanol. They are also used directly in products such as laundry detergent, where they help remove stains and enable low-temperature washing.

Practical Work for Learning

Class practical

Phenolphthalein is an indicator that is pink in alkaline solutions of about pH10. When the pH drops below pH 8.3 phenolphthalein goes colourless. Here, an alkaline solution of milk, lipase and phenolphthalein will change from pink to colourless as the fat in milk is broken down to form fatty acids (and glycerol) thus reducing the pH to below 8.3. The time taken for this reaction to occur is affected by temperature.

Lesson organisation

This investigation could be carried out as a demonstration at two different temperatures, or in a group of at least 5 students with each student working at a different temperature. This would allow students to collect repeat data at their allocated temperature. Or it could be an investigation carried out by one student.

Apparatus and Chemicals

For each group of students:

Measuring cylinder (or syringe), 10 cm 3 , 2

Beaker, 100 cm 3 , 2 (for milk and sodium carbonate solution)

Beaker, 250 cm 3 , 2 (to act as water baths for temperatures below room temperature)

For each temperature:

For the class – set up by technician/ teacher:

Milk, full-fat or semi-skimmed, 5 cm 3 per student per temperature assessed

Phenolphthalein in a dropper bottle (Note 2)

5% lipase solution, 1 cm 3 per student per temperature assessed

Sodium carbonate solution, 0.05 mol dm – 3 , 7 cm 3 per student per temperature assessed

Electric hot water baths set to a range of temperatures, each containing a thermometer, a test-tube rack and a beaker of lipase solution.

Health & Safety and Technical notes

Sodium carbonate solution, 0.05 M. Make with 5.2 g of anhydrous solid, or 14.2 g of washing soda per litre of water. See CLEAPSS Hazcard it is an IRRITANT at concentrations over 1.8 M.

Ethanol (IDA) in the phenolphthalein indicator is described as HIGHLY FLAMMABLE on the CLEAPSS Hazcard (flash point 13 °C) and HARMFUL (because of presence of methanol).

Electric water baths should be safety checked in accordance with your employer’s instructions.

Take care with thermometers and brief students how to react if they are broken.

1 Lipase solution is best freshly made, but it will keep for a day or two in a refrigerator. Don’t try to study different temperatures on different days for the same investigation the activity of the enzyme will change and it will not be a fair test.

2 Phenolphthalein is described as low hazard on CLEAPSS Hazcard. Refer to Recipe card (acid-base indicators): Dissolve 1 g in 600 cm 3 of IDA then make up to 1 litre with water. Label the bottle highly flammable. Suppliers of phenolphthalein solution may not use IDA it also may be diluted. Follow any hazard warning on supplier’s bottles.


SAFETY: Keep the phenolphthalein solution away from sources of ignition.

Wear eye protection and quickly rinse any splashes of enzyme solution or sodium carbonate from the skin.


a Make up lipase solution and suitable quantities of the other solutions.

b Set up the water baths at a range of temperatures and put a beaker of lipase, containing a 2 cm 3 syringe into each water bath. Cover a range of temperatures up to around 60°C. An ice-bath will maintain a temperature of 0°C, until all the ice is melted.


c Label a test tube with the temperature to be investigated.

d Add 5 drops of phenolphthalein to the test tube.

e Measure out 5 cm 3 of milk using a measuring cylinder (or syringe) and add this to the test tube.

f Measure out 7 cm 3 of sodium carbonate solution using another measuring cylinder (or syringe) and add this to the test tube. The solution should be pink.

g Place a thermometer in the test tube. Take care as the equipment could topple over.

h Place the test tube in a water bath and leave until the contents reach the same temperature as the water bath.

i Remove the thermometer from the test tube and replace it with a glass rod.

j Use the 2 cm 3 syringe to measure out 1 cm 3 of lipase from the beaker in the water bath for the temperature you are investigating.

k Add the lipase to the test tube and start the stopclock/ stopwatch.

l Stir the contents of the test tube until the solution loses its pink colour.

m Stop the clock/ watch and note the time in a suitable table of results.

Teaching notes

The quantities used should take approximately 4 minutes to change from pink to white at normal laboratory temperature. If this is not the case, change the concentration of enzyme to alter the speed of the reaction (more enzyme will reduce the time or increase the speed). Students will need to use the same volume at each temperature.

Digestion of fat produces fatty acids (and glycerol) that neutralise the alkali, sodium carbonate, thus lowering the pH and changing phenolphthalein from pink to colourless. You could use a pH probe or data logger, or another indicator.

You could add washing-up liquid to the solution (1 or 2 drops per 250 cm 3 ), to emulsify the fats which will provide a larger surface area for enzyme action. This will demonstrate the effect of bile salts. Or bile salts could be used.

  • This protocol is based on a pH dependent result, so is not suitable for assessing the effect of different pHs on lipase.
  • It would be possible to vary the concentration of the lipase and look at the effect of enzyme concentration on the breakdown of fat in milk.
  • Different types of milk could be used Jersey, full cream, semi-skimmed and skimmed, to explore the effect on the reaction of changing fat concentration (substrate concentration).

Question 6 on the student question sheet opens the doors to a more extensive piece of research on this enzyme.

Basic Characteristics Of Enzymes

What is an enzyme?
The proteins produced by a living body which acts as a catalyst in the metabolic activities are generally termed as enzymes. The characteristics of enzymes have the potential to affect the pace of the biochemical reactions and are very crucial in the sustenance of life. No biochemical reaction could be balanced in the biological body in the absence of the respective enzymes. Whether it is the most crucial process like digestion, or it is a simple act of excretion, the characteristics of enzymes play a large role in every human body process. In simple terms, the enzymes could be termed as biological catalysts.

We hope that you have a basic idea of what is enzyme and its significance in the human body. It is time that we should discuss deeply the role and various aspects of the characteristics of enzymes.

It is a known fact that the biological body is comprised of various inorganic ions, water, carbon, and other organic molecules. The crucial procedures in the biological body like excretions, digestion, metabolic activities, etc. are being initiated and controlled by the characteristics of enzymes. It is by the secretion of various enzymes that the intended activities in the biologically takes place effectively.

Typical characteristics of enzymes

  • It is the role of catalysts in most of the biochemical reactions taking place in a biological body that could be considered as one of the major characteristics of enzymes. However, it has the ability to influence the reaction even if it is not present at the site of the process. Below are provided with some of its distinctive qualities.
    1. It would be impossible to sustain life in a living body without enzymes since the pace of biochemical reaction at the cellular level would become too slow. The reactions should be rapid to support life in the body.
    2. If excluded from the case of certain RNA molecules, every enzyme could be brought under the classification of globular proteins.
    3. The potential of enzymes in a biochemical reaction is very high, and it could accelerate the pace to 10 20 times that of the natural pace of the reaction.
  • It is the three major characteristics that make the enzyme a crucial element in the human body. They are: – self-controlling behaviour if the reaction accelerates more than required, only take part in a specific reaction, and the potential of accelerating the process to multiple times of its natural pace.

How characteristics ofenzymes help in achieving catalytic efficiency?
Below are listed down the way in which the characteristics of enzymes help in achieving the catalytic efficiency in the biochemical reactions.

  • Though the enzymes actively take part in the chemical reaction, they don’t undergo any permanent change and keep on influencing the process.
  • The chemical concepts followed by the enzymes are the same as the catalyst in a chemical reaction. The presence of the enzyme helps the biochemical reaction achieve the equilibrium much faster by lowering the activation energy of the reactants.
  • There is the presence of enzyme various chemical occurrences in the biological environment such as amide formation, alcohol oxidation, hydrolysis,
    1. The presence of enzymes makes it possible to conduct the biochemical reaction at a limited pH level and temperature. Such reactions would not exist naturally at ideal conditions.
    2. With the help of the characteristics of enzymes, various biochemical reactions could be attained in seconds that are even very hard to attain in a laboratory environment.
  • The crucial process in the biological body like the ejection of carbon dioxide from the living body is made possible by the association of carbonic anhydrase. The presence of this enzyme would instigate the combination of water with carbon dioxide resulting in the formation of carbonic acid. The carbonic anhydrase boosts up the biochemical reaction to such a limit that around 36 million molecules per minute.

Specific characteristics ofenzymes
Enzymes won’t take part in every reaction. There is some degree of specificity where the enzymes are allowed to enhance the rate of a biochemical reaction.

Absolute Specificity: The enzyme which has the characteristic of absolute specificity would only take part in a particular reaction.

Relative Specificity: The enzyme which takes parts in the reaction with reactants having the same structural combination and structure are classified under the category of relative specificity (The compounds could be labelled as structurally similar compounds are proteases, lipases, phosphatases hydrolyze phosphate esters, and hydrolyze lipids).

Stereochemical Specificity: The enzymes coming under this category could only enter into reaction with the two specific enantiomers. The perfect example for this is the D-amino acid oxidase enzyme which only enters with the enantiomers like L-amino acids and D-amino acids.

Regulating characteristics ofenzymes
The enzymes play a major role in regulating the rate of various metabolic activities going on in a living body. Thus, it indirectly affects the output of various procedures in the living body. The living cells are comprised of a lot of compounds, and hence there is a large probability that they would react with each other. It is the presence of various enzymes that keep various components of the cell intact. The production of any particular product is regulated by the enzymes, and hence it is very crucial to sustain life.

Induced Fit Theory
The theory of Induced Fit is also termed as lock and key theory in the discipline of biology. This theory suggests that there is a certain level of flexible confirmation in the components of enzymes. The enzymes would get only active in reaction if the active sited of it adopts the complementary component. Only in such a case, the enzyme would affect the ongoing biochemical reaction.

Roughly speaking each molecule of the enzyme consists of a certainly shaped fissure. These fissures are often termed as active sites. It is in this place of the enzyme molecules where the respective reagents approach and activate it. The unique shape of active sites avoids other inappropriate reagents from activating the enzymes. The feature increases the efficiency of the enzyme molecules since it freshens up again when the reagent leaves the active sites.

Allosteric enzymes
Though the procedure is not as simple in the case of an allosteric enzyme. Despite an active site, there is an allosteric site in the compounds of allosteric enzymes. Whereas reagent reacts in the normal case, non-substrate molecules enter into the reaction in the allosteric enzymes. The binding process in allosteric enzymes is very complex since there are several polypeptides that could make the bond with various allosteric. The mechanics enable the enzymes to react to a specified set of compounds in the biological environment.

  • The major role of the enzyme is to make a bond between the activators and substrate in the allosteric site so that the required biological reaction would take place.
  • The structure of the enzyme would transform when an inhibitor would bond in the allosteric site. The allosteric site of the enzyme molecule would get locked after it binds with the inhibitors.

Various types of Inhibitors

Irreversible inhibitors: The inhibitors which bind with the enzymes and changes its composition permanently could be classified under the division of irreversible inhibitors. Such inhibitors permanently block the site of substrates and thus eliminates the catalytic power of the enzyme.

Competitive Inhibitors: The reactants try to bond to the active site of the enzyme to carry out the intended biological reaction. The inhibitors are always trying to attain stability, and hence there is a long rush among the inhibitors to connect the enzyme molecules. The molecule which approaches to the active first would make the bond with the enzyme molecules.

Uncompetitive inhibitors: The uncompetitive inhibitors help to slow down and regulate the pace of the biochemical reaction in the body. The uncompetitive inhibitors bind to the enzyme molecules and take a little effort to get free from its active site. The effective slowdown of the biochemical processes would help in sustaining a chemical balance.

Non- Competitive inhibitors: The non-competitive inhibitors are although not suitable for the active sites of the enzyme molecules. It hampers the natural impact of enzymes over the chemical reaction since the molecular structure of the enzyme gets distorted for a while. Such locking of the substrate on the enzyme would prevent it from entering different processes.

The major role of controlling the metabolic activities in a living body is done by the allosteric enzymes. The biological balance is very crucial to sustain life, and hence allosteric enzymes are very crucial.

Major features of allosteric enzymes

  • The allosteric enzymes could regulate its activity in a reaction by being transforming into a less active and more active variant.
  • Apart from possessing a normal active site, allosteric enzymes retain binding sites.
  • The molecular size of the allosteric enzyme is significantly small and could be labelled under the category of single subunit proteins.

Purpose of an enzyme
It is impossible for a living body to sustain its life enzymes are absent in it. The practicality of enzymes is very wide, and it holds significance in various biological activities. We have listed down some of the significant enzymes of the human body and their respective roles.

Lactase – The enzyme is secreted in the small intestine of the human body while the process of digestion is going on. The sugar present in milk is lactose, and by the help of lactase, it is disintegrated into galactose and glucose.

Lipases – This enzyme would help the process of digestion by disintegrating fatty food.

Trypsin – The disintegration of protein happens in the small intestine of the human body. Trypsin helps to break the protein molecules into simpler amino acids. This helps the effective absorption of protein into the body.

Amylase – The process of digestion starts even from the mouth of the human being. Salivary amylase helps to convert the starch into its simpler forms of sugars while the food is chewed.

Maltase – This enzyme disintegrates large hydrocarbon molecules of maltose into simple glucose molecules.

As mentioned in the previous section of this article, the activation energy required to start a chemical reaction is lowered significantly by an enzyme. Thus by reducing the energy required to conduct a biochemical reaction increases its efficiency to them multiple times. The enzymes provide a convenient circumstance for the reactants which are held together in a way so that the reaction would take place abruptly.

Enzymes are more efficient in biological circumstances since it provides the appropriate nonpolar and acidic conditions. These factors would create a large impact on the overall efficiency of the chemical procedure. One of the best quality of enzymes which sets it apart from the catalysts is that its molecular structure remains intact after entering into a reaction. The same enzyme molecule would take part in the coming cycles of catalysis.

Scientific characteristics of enzymes
The colloidal nature of the enzymes set it apart from another type of protein in the living body. Some of the distinctive factors like change in performance at different pH levels, different temperatures, various inhibitors, turnover numbers, etc. are some decisive factors of enzymes. Let us have a detailed look over the scientific characteristics of enzymes.

  • The change in pH and body temperature would significantly affect the chemical process in which the enzymes are involved.
  • As per the chemical composition and its molecular formulation characteristics of enzymes, it resembles a protein.
  • Every enzyme has it has its numeric turnover and is being indicated by the number of molecules transformed in a decided set of time. The denominations could be denoted in the multiples per 10 3 or 10 2 per second.
  • The enzymes are present in the form of hydrophilic colloids in the protoplasm of the cells.
  • The major ideology behind the initiation of a particular chemical reaction is lowering down the requirement of activation energy.
  • Each enzyme will get activated if it is approached by the appropriate substrates.

We hope that this article on the characteristics of enzymes was quite helpful for you. Please stick with us for similar academic blogs.

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Steroids and Waxes

Unlike the phospholipids and fats discussed earlier, steroids have a ring structure. Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail.

Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It is also the precursor of vitamins E and K. Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells.

Waxes are made up of a hydrocarbon chain with an alcohol (–OH) group and a fatty acid. Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out.

Concept in Action

Biology Notes Form 3

1. Type of leaf Leaf (a) Compound leaves. (b) Type of venation.

Features used to identify animals:

A mature moss plant is obtained.

To examine Pteridophyta

To examine Spermatophyta

A mature twig of either cypress or pinus with cones is obtained.

A mature bean plant with pods is obtained,

A mature maize plant is obtained.

Examination of Arthropoda

The differences in the following are noted:

Examination of Chordata

Features used include:

Concepts and Terms Used in Ecology

Factors in an Ecosystem

Inter-relationships Between Organisms

They occupy different trophic levels as follows:

Interspecific competition.

Energy Flow in an Ecosystem

Examples of Food Chains

lady-bird beetle Green plants

mosquito larva Phytoplankron-eZooplankton

Population Estimation Methods

Capture-recapture method

The total number T can be estimated using the following formula: Total Number =

Hydrophytes (Water plants)

Halophytes (Salt plants)

Effect of Pollution on Human Beings and other Organisms

Sources of Pollutants

Effects of Pollutants to Humans and other organisms

Control of Air Pollution

Causative agent a bacterium Vibrio cholerae.

The bacteria produce a powerful toxin, enterotoxin, that causes inflammation of the wall of the intestine leading to:

Prevention and Control

Amoebic dysentry (Amoebiasis)

They are transmitted through contaminated water and food especially salads.

Prevention and control

Effects of Ascaris lumbricoides on the host

Adaptive Characteristics

Control and Prevention

Adaptive Characteristics

Prevention and Control

Comparison of Root nodules from fertile and poor soils

Estimation of Population using Sampling Methods

Reproduction in Plants and Animals Introduction

There are two types of cell division:

Significance of Mitosis

Second Meiotic Division

Significance of Meiosis

Types of asexual reproduction.

Spore formation in Rhizopus

Spore formation in ferns

Sexual Reproduction in Plants

Structure of a flower

Agents of pollination

Mechanisms that hinder self-pollination

Fertilisation in Plants

After fertilisation the following changes take place in a flower:

Classification of fruits

Marginal placentation:

Parietal placentation:

Free Central placentation.

Methods of fruit and seed dispersal

Self dispersal (explosive) Mechanism

Reproduction in Animals

External fertillsation

Internal fertilisation

Structure of female reproduction system

The female reproduction system consist of the following:

Structure of male reproductive system

The male reproductive system consists of the following: Testis:

Fertilisation in Animals

Production of hormones

Reproductive Hormones

Sexually transmitted infections (STl)

Advantages of Reproduction Asexual

Disadvantages of asexual reproduction

Advantages of sexual reproduction

Disadvantages of sexual reproduction

Examining the stages of mitosis

Examining the stages of meiosis

To observe the structure of Rhizopus

To examine spores on sori of ferns

Examine insect and wind pollinated flowers

Dispersal of fruits and seeds


Study Question 1-State two major differences between growth and development

For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure .

A sigmoid curve may therefore be divided into four parts.

Lag phase (slow growth)

Exponential phase (log phase)

This rapid growth is due to:

(i) An increase in number of cells dividing,2-4-8-16-32-64 following a geometric progression,

(ii) Cells having adjusted to the new environment,

(iii) Food and other factors are not limiting hence cells are not competing for resources,

(iv) The rate of cell increase being higher than the rate of cell death.

The slow growth is due to:

( i) The fact that most cells are fully differentiated.

(ii) Fewer ceils still dividing,

(iii) Environmental factors (external and internal) such as:

This is due to the fact that:

Practical Activity I: Project

To measure the growth of a plant

Plant some seeds in the box and place it in a suitable place outside the laboratory (or plant the seeds in your plot).

Repeat this with four other seedlings. Work out the average height of the shoots for this day.

Growth and Development in Plants

Structure of the Seed

Factors that Cause Dormancy

Ways of Breaking Dormancy

Conditions Necessary for Germination

To investigate conditions necessary for seed germination

These meristems originate from the embryonic tissues. In this growth there are three distinctive regions, the region of cell division, cell ejpngarion and eel] differentiation. See figure 4.7.

In the region of cell elongation, the cells become enlarged to their maximum size by the stretching of their walls.

Vacuoles start forming and enlarging. In the region of ceH differentiation the cells attain their permanent size, have large vacuoles and thickened watt cells.

The seedling is left to grow for sometime (about 24 hours or overnight) and then the ink marks are examined.

When the distance between successive ink marks are measured, it is found that the first few ink marks, especially between the 2nd and 3"1 mark above tip of root have increased significantly.

This shows that growth has occurred in the region just behind the tip of the root.

The difference between the length of each new interval and the initial interval of 2 mm gives the increase in the length of that interval during that period of time.

From this the rate of growth of the root region can be calculated. See figure 4.9.M

To determine the region of growth in roots

In monocotyledons plants there are no cambium cell in the vascular bundles.

The growth in diameter is due to the enlargement of the primary cells.

This forms a continuous cambium ring.

This results in stretching and rupturing of the epidermal cells. In order to replace the protective outer layer of the stem, a new band of cambium cells are formed in the cortex. These cells, called cork cambium orphellogen originate from the cortical cells.

The cork cambium divides to produce new cells on either side. The cells on the inner side of the cork cambium differentiate into secondary cortex and those produced on the outer side become cork cells.

Cork cells are dead with thickened walls. Their walls become coated with a waterproof substance called suberin.

These cells are large, have thin walls and the wood has a light texture. In the dry season, the xylem and trancheids formed are few in number.

They are small, thick-walled and their wood has a dark texture. This leads to the development of two distinctive layers within the secondary xylem formed m a year, called annual rings. See figure 4.13.

It is possible to determine the age of a tree by counting the number of annual rings.

Furthermore climatic changes of the past years can be infered from the size of the ring.

They stimulate cell division and cell elongation in stems and roots leading to primary growth.

Cuttings can be encouraged to develop roots with the help of IAA. If the cut end of a stem is dipped into IAA, root sprouting is faster. IAA is also used to induce parthenocarpy.

This is the growth of an ovary into a fruit without fertilisation. This is commonly u^ed by horticulturalists to bring about a good crop of fruits particularly pineapples.

Auxins are known . to inhibit development of side branches from lateral buds. They therefore enhance apical dominance. During secondary growth auxins Play an important role by initiating cell division in the cambium and differentiation of these cambium cells into vascular tissues.

When the concentration of auxins falls in the plant, it promotes formation of an abscission layer leading to leaf fall. A synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D) induces distorted growth and excessive respiration leading to death of the plant. Hence it can be used as a selective weed killer.

Gibberellins are another important group of plant growth hormone.

Gibberellins are a mixture of compounds and have a very high effect on growth. The most important in growth is gibberellic acid. Gibbereilins are distinguished from auxins by their stimulation of rapid cell division and cell elongation in dwarf varieties of certain plants.

Dwarf conditions are thought to be caused by a shortage of gibberellins due to a genetic deficiency.

They induce the growth of ovaries into fruits after fertilisation.

They also induce parthenocarpy. Gibberellins also promote formation of side branches from lateral buds and breaks dormancy in buds.

This is common in species of temperate plants whose buds become dormant in winter.

In addition, this hormone also inhibits sprouting of adventitious roots from stem cuttings, it retards formation of abscission layer hence reduces leaf fall.

Gibberellins also break seed dormancy by activating the enzymes involved in the breakdown of food substances during germination.

Cytokanins also known as kinetins, are growth substances which promote growth in plants when they interact with auxins. In the presence of auxins, they stimulate cell division thereby bringing about growth of roots, leaves and buds.

They also stimulate formation of the callus tissues in plants.

The callus tissue is used in the repair of wounds in damaged parts of plants.

They also promote formation of adventitious roots from stems and stimulate lateral bud development in shoots. When in high concentration cytokinins induce cell enlargement of leaves but in low concentration they encourage leaf senescence and hence leaf fall.

Ethylene is a growth substance produced in plants in gaseous form. Its major effect in plants is that it causes ripening and falling of fruits.

This is widely applied in horticultural farms in ripening and harvesting of fruits.

It stimulates formation of abscission layer leading to leaf fall, induces thickening of stems by promoting cell division and differentiation at the cambium meristem.

But it inhibits stem elongation. Ethylene promotes breaking of seed dormancy in some seeds and flower formation mostly in pineapples.

Abscisic acid is a plant hormone whose effects are inhibitory in nature.

It inhibits seed germination leading to seed dormancy, inhibits sprouting of buds from stems and retards stem elongation.

In high concentration, abscisic acid causes closing of the stomata.

This effect is important in that it enables plants to reduce water loss.

It also promotes leaf and fruit fall. Another hormone, florigen is produced in plants where it promotes flowering.

This forms the basis of pruning in agriculture where more branches are required for increased harvest particularly on crops like coffee and tea.

Growth and Development in Animals

Growth and Development in Insects

Please insert your question in the form below. Check and ensure that your question has not been asked and answered in the enquiries appearing beneath the form.

Normal Lab Values

AST and ALT are measured in international units per liter (IU/L). The normal levels vary based on a person's body mass index (BMI) as well as the individual lab's reference value. Generally speaking, the normal reference value for adults is:

The high end of the reference range is referred to as the upper limit of normal (ULN). This number is used to establish how elevated your liver enzymes are.

Mild elevations are generally considered to be two to three times the ULN. With some liver diseases, the level can exceed 50 times the ULN. Levels this high are described as deranged.

The 7 Best Digestive Enzymes of 2021, According to a Dietitian

Eliza Savage, MS, RD is Senior Health Commerce Editor at Verywell, a registered dietitian, and a published author.

Ashley Hall is a writer and fact checker who has been published in multiple medical journals in the field of surgery.

Our editors independently research, test, and recommend the best products you can learn more about our review process here . We may receive commissions on purchases made from our chosen links.

First Look

"Ideal for those with sensitivities, the capsule is free of common allergens and includes digestive enzymes for nutrient absorption."

"The cost-effective option is formulated to break down fats and proteins, optimize nutrient availability, and support digestion."

"Tailored to vegans, the formula's packed with 15 plant-sourced enzymes for optimized digestion and absorption."

"Ideal if you need extra help digesting spicy, raw, and processed foods, it features a blend of enzymes, prebiotics, and probiotics."

Best with Stomach-Soothing Herbs: Hum Flatter Me at Amazon

"The proprietary and potent enzyme blend breaks down proteins, carbs, fiber, lactose, and fats, and helps minimize bloating. "

Best for Lactose Intolerance: Lactaid Fast Act Chewable at Amazon

"The lactase supplement is a solid option to keep gas and bloating at bay if you find it difficult to digest lactose meals."

Best for Veggie-Associated Gas: Enzymedica at Amazon

"The high-potency capsules provide 12 enzymes to help digest sugars and proteins from beans, raw veggies, and carbs that create gas."

When your body is functioning properly, it naturally produces digestive enzymes to help digestion by breaking down and absorbing nutrients. These digestive enzymes are naturally produced by the pancreas, which secretes a specific enzyme to break down each macronutrient: amylases to break down carbs, lipases for fats, and proteases for proteins.

However, the body isn’t always able to produce enough to keep up. The result is discomfort in the form of bloating, gas, and digestive distress. A common digestive enzyme deficiency is lactase, which helps break down lactose, or the sugar found in milk. Another common deficiency is an absence of alpha-galactosidase, which can help break down the carbohydrates found in legumes and beans.

Often, the solution is digestive enzymes supplements readily available over the counter. These can be an effective and reliable treatment for various gastrointestinal concerns, like IBS, low stomach acid, or age-related enzyme insufficiency. Still, there is limited research to support adding enzymes as an overall digestive solution, and much of the research to date is done on prescription-only supplements.

Keep in mind: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.

Catalase and Hydrogen Peroxide Experiment

How do living cells interact with the environment around them? All living things possess catalysts, or substances within them that speed up chemical reactions and processes. Enzymes are molecules that enable the chemical reactions that occur in all living things on earth. In this catalase and hydrogen peroxide experiment, we will discover how enzymes act as catalysts by causing chemical reactions to occur more quickly within living things. Using a potato and hydrogen peroxide, we can observe how enzymes like catalase work to perform decomposition, or the breaking down, of other substances. Catalase works to speed up the decomposition of hydrogen peroxide into oxygen and water. We will also test how this process is affected by changes in the temperature of the potato. Is the process faster or slower when compared to the control experiment conducted at room temperature?


What happens when a potato is combined with hydrogen peroxide?



  1. Divide the potato into three roughly equal sections.
  2. Keep one section raw and at room temperature.
  3. Place another section in the freezer for at least 30 minutes.
  4. Boil the last section for at least 5 minutes.
  5. Chop and mash a small sample (about a tablespoon) of the room temperature potato and place into beaker or cup.
  6. Pour enough hydrogen peroxide into the cup so that potato is submerged and observe.
  7. Repeat steps 5 & 6 with the boiled and frozen potato sections.

Observations & Results

Watch each of the potato/hydrogen peroxide mixtures and record what happens. The bubbling reaction you see is the metabolic process of decomposition, described earlier. This reaction is caused by catalase, an enzyme within the potato. You are observing catalase breaking hydrogen peroxide into oxygen and water. Which potato sample decomposed the most hydrogen peroxide? Which one reacted the least?

You should have noticed that the boiled potato produced little to no bubbles. This is because the heat degraded the catalase enzyme, making it incapable of processing the hydrogen peroxide. The frozen potato should have produced fewer bubbles than the room temperature sample because the cold temperature slowed the catalase enzyme&rsquos ability to decompose the hydrogen peroxide. The room temperature potato produced the most bubbles because catalase works best at a room temperature.


Catalase acts as the catalyzing enzyme in the decomposition of hydrogen peroxide. Nearly all living things possess catalase, including us! This enzyme, like many others, aids in the decomposition of one substance into another. Catalase decomposes, or breaks down, hydrogen peroxide into water and oxygen.

Want to take a closer look? Go further in this experiment by looking at a very small sample of potato combined with hydrogen peroxide under a microscope!

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4.9: Perfect Enzymes - Biology

The primary types and functions of proteins are listed in Table 1.

Table 1. Protein Types and Functions
Type Examples Functions
Digestive Enzymes Amylase, lipase, pepsin, trypsin Help in digestion of food by catabolizing nutrients into monomeric units
Transport Hemoglobin, albumin Carry substances in the blood or lymph throughout the body
Structural Actin, tubulin, keratin Construct different structures, like the cytoskeleton
Hormones Insulin, thyroxine Coordinate the activity of different body systems
Defense Immunoglobulins Protect the body from foreign pathogens
Contractile Actin, myosin Effect muscle contraction
Storage Legume storage proteins, egg white (albumin) Provide nourishment in early development of the embryo and the seedling

Two special and common types of proteins are enzymes and hormones. Enzymes, which are produced by living cells, are catalysts in biochemical reactions (like digestion) and are usually complex or conjugated proteins. Each enzyme is specific for the substrate (a reactant that binds to an enzyme) it acts on. The enzyme may help in breakdown, rearrangement, or synthesis reactions. Enzymes that break down their substrates are called catabolic enzymes, enzymes that build more complex molecules from their substrates are called anabolic enzymes, and enzymes that affect the rate of reaction are called catalytic enzymes. It should be noted that all enzymes increase the rate of reaction and, therefore, are considered to be organic catalysts. An example of an enzyme is salivary amylase, which hydrolyzes its substrate amylose, a component of starch.

Hormones are chemical-signaling molecules, usually small proteins or steroids, secreted by endocrine cells that act to control or regulate specific physiological processes, including growth, development, metabolism, and reproduction. For example, insulin is a protein hormone that helps to regulate the blood glucose level.

Proteins have different shapes and molecular weights some proteins are globular in shape whereas others are fibrous in nature. For example, hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein. Protein shape is critical to its function, and this shape is maintained by many different types of chemical bonds. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to loss of function, known as denaturation. Different arrangements of the same 20 types of amino acids comprise all proteins. Two rare new amino acids were discovered recently (selenocystein and pirrolysine), and additional new discoveries may be added to the list.

In Summary: Function of Proteins

Proteins are a class of macromolecules that perform a diverse range of functions for the cell. They help in metabolism by providing structural support and by acting as enzymes, carriers, or hormones. The building blocks of proteins (monomers) are amino acids. Each amino acid has a central carbon that is linked to an amino group, a carboxyl group, a hydrogen atom, and an R group or side chain. There are 20 commonly occurring amino acids, each of which differs in the R group. Each amino acid is linked to its neighbors by a peptide bond. A long chain of amino acids is known as a polypeptide.

Proteins are organized at four levels: primary, secondary, tertiary, and (optional) quaternary. The primary structure is the unique sequence of amino acids. The local folding of the polypeptide to form structures such as the α helix and β-pleated sheet constitutes the secondary structure. The overall three-dimensional structure is the tertiary structure. When two or more polypeptides combine to form the complete protein structure, the configuration is known as the quaternary structure of a protein. Protein shape and function are intricately linked any change in shape caused by changes in temperature or pH may lead to protein denaturation and a loss in function.

Watch the video: Enzymes Updated (October 2022).