Chemicals Of Life

Question 1

Describe the molecular structure of water

Answer 1

• The water molecule comprises two hydrogen atoms and one oxygen atom
• The molecule itself is polar (specifically dipolar) as there is an uneven distribution of charges in it
• The oxygen atom is slightly negative and that of the hydrogen is slightly positive thus making it polar
• Water molecules have weak forces of attraction to each other with opposite charges coming together
• The hydrogen bonds are constantly being formed and broken and although individually weak, their collective effect give water its unusual properties

Question 2

State functions of water

Answer 2

It is a component of cells
➢ It is a solvent and a medium of transport
➢ It is a reagent in hydrolysis
➢ It enables fertilization by swimming gametes
➢ It enables dispersal of seeds, fruits, gametes and larvae stages in aquatic organisms.
➢ It is important in transpiration in plants.
➢ It is important in translocation in plants.
➢ It enables germination to proceed by activating enzymes, transporting hydrolyzed stored food, swelling and
breaking open the testa.
➢ It is involved in Osmo-regulation in animals
➢ It enables cooling by evaporation as a result of sweating and panting.
➢ It is a component of lubricants at joints e.g. the synovial fluid.
➢ It offers support in hydrostatic skeleton.
➢ It offers protection as a component of mucus and tears.
➢ It enables migration to occur as a result of river flow or ocean currents.

Question 3

How do the properties of water relate to its biological role in organisms?

Answer 3

1) Water is transparent and this allows light penetration in aquatic habitats to enable photosynthesis of aquatic
autotrophs and visibility of aquatic animals.
2) Water has a low viscosity and this allows for smooth flow of water and other dissolved substances in an aquatic medium for easy transport.
3) It has a high surface tension providing support to aquatic organisms and allowing movement of living organisms on water surface.
4) Has a high latent heat of vaporization hence a cooling effect on the body surface since evaporation of water from the body of an organism draws out excess heat.
5) It has a high boiling point thus provides a stable habitat and medium since a lot of heat which is not normally provided in the natural environment is needed to boil the water.
6) It has a high latent heat of fusion and hence a low freezing point thus providing a wide range of temperature for survival of aquatic organisms since it prevents freezing of cells and cellular components.
7) It has a high specific heat capacity which minimizes drastic temperature changes in biological systems and provides a constant external environment for many plant cells and aquatic organisms.
8) It has a maximum density at 4o C hence ice floats on top of water insulating the water below hence increasing the chances of survival of aquatic organisms below the ice.
9) Water is liquid at room temperature providing a liquid medium for living organisms and metabolic reactions and a medium of transport.
10) It has high adhesive and cohesive forces creating enough capillarity forces for transport in narrow tubes of biological systems.
11) It is a universal solvent hence providing a medium for biochemical reactions.
12) Water is a polar molecule allowing solubility of polar substances, ionization or dissociation of biochemical
substances.
13) Water is incompressible thus providing support in hydrostatic skeleton and herbaceous stems.
14) Water is neutral hence does not alter the pH of cellular components on their environme

Question 4

State the properties of water

Answer 4

i) It is liquid at room temperature.

ii) It has a high heat capacity therefore much energy is used to raise its temperature because it is used to break the hydrogen bonds which restrict the mobility of the molecules. As a result water is relatively slow to heat up or to cool down thus a high heat capacity.

iii) Water expands as it freezes unlike other liquids which contract on cooling.
iv) Water reaches its maximum density above its freezing point at 4oC hence when water freezes, the ice formed is
less dense than the water and hence floats on top of the surface. In this way, ice insulates water below making it
less dense and able to float hence the water will be warmer than the air above.

v) Water has a high surface tension. Surface tension is the force that causes the surface of a liquid to contract so
that it occupies the least area. It is high due to the fact that molecules are oriented so that most hydrogen bonds
point inwards towards other water molecules.

vi) It has a high latent heat of fusion i.e. much heat must be removed before freezing occurs.

vii) It has high adhesive and cohesive properties preventing it from breaking under tension.

viii) It is colourless and transparent.

ix) It has a low viscosity i.e. water molecules slide over each other very easily.

x) It dissolves more substances than any other liquid i.e. it is a universal solvent.

Question 5

What is an enzyme?

Answer 5

A biological catalyst protein in nature that catalyzes (speeds up) the rate of a biochemical reaction and itself remains unchanged by the end of it

Question 6

What is a substrate?

Answer 6

This is the chemical worked upon by the enzyme.

Question 7

What is a product?

Answer 7

The final result of a chemical reaction

Question 8

What pH is considered neutral?

Answer 8

pH 7

Below 7-acidity

Above 7- alkalinity/basis

(pH 6.9 is slightly acidic, and 7.1 is slightly basic)

Question 9

What is an acid?

Answer 9

A compound which when dissolved in water ionizes to produce hydrogen ions as the only positive charged ions e.g. hydrochloric acid, nitric acid, Sulphuric acids e.t.c.

Question 10

What is a base?

Answer 10

A base is a compound, which can react with acids to produce a salt and water only.

Question 11

What is an alkali?

Answer 11

A substance which when dissolved in a solvent produces hydroxyl ions as the only charged ions.

-Alkalis are bases but not all bases are alkaline.
-Strong alkalis completely ionize e.g. sodium hydroxide
-Weak alkalis don’t ionize completely e.g. ammonium hydroxide

Question 12

Give functions of acids

Answer 12

-They provide a suitable pH for the proper functioning of enzymes e.g. pepsin
-Acids like hydrochloric acids activate organic substances like pepsinogen
-Acids kill bacteria, which may be ingested together with food

Question 13

Give functions of bases

Answer 13

-Provide an optimum pH range for enzyme activity e.g.in the duodenum
-They are buffers in the body

Question 14

What is a buffer?

Answer 14

A buffer is a substance that minimizes/ resists changes in pH of a solution when small amounts of acids or bases are added.

-Most buffers are acid base pairs

Question 15

What is the importance of buffers in the body?

Answer 15

To maintain the narrow range of pH in which enzymes function

Question 16

Give examples of acids in the body

Answer 16

• Nucleic acids
• Hydrochloric acids
  -Amino acids
  -Lactic acids

Question 17

What is a salt?

Answer 17

A compound which is formed when the hydrogen ions in an acid are either partially or fully replaced by a metal ion or ammonium ion

HCL ———> NaCl, KCl etc

Question 18

Give the functions of mineral salts

Answer 18

1. They form body structures
   e.g. the bones, the teeth, etc
2. They form body pigments
   e.g. Haemoglobin contains Iron, chlorophyll contains magnesium.
3. They form chemicals in the body
   e.g. Sulphur and Nitrogen form proteins, nucleic acids, ATP etc.
4. They are metabolic activators. Certain ions activate enzymes
   e.g. magnesium activates enzymes that are
   involved in phosphorylation of glucose.
5. They are constituents of enzymes
   e.g. nitrogen in proteins.
6. Constituents of various chemicals
   e.g. ATP contains phosphorous while thyroxin contains iodine.
7. They are determinants of osmotic pressure. Mineral salts and other solutes determine the osmotic pressure
   of cells and body fluid.

Question 19

Which are the four most common elements in living organisms and why?

Answer 19

• Hydrogen
• Carbon
• Oxygen
• Nitrogen
  (In that order)

Due to their ability to form more stable covalent bonds than any other elements with their valencies

Question 20

What is the name of this chemical group?
-S-H

Answer 20

Sulphydryl group

Question 21

What is the -COOH group responsible for in compounds containing it?

Answer 21

Acidic nature
eg fatty acids, amino acids

Question 22

What is the difference between a saturated and unsaturated compound?

Answer 22

Saturated compounds contain single carbon-carbon bonds while unsaturated compounds contain double or triple carbon-carbon bonds

Question 23

What characteristics of the carbon atom make possible the building of a variety of biological molecules

Answer 23

• It is a relatively small atom with a low mass
• The ability to form four strong, stable covalent bonds
• The ability to form carbon-carbon bonds thus building up large carbon skeletons
• The ability to form multiple covalent bonds with other carbon atoms, nitrogen and oxygen

Question 24

What is the general formula for carbohydrates?

Answer 24

CnH2nOm
(n and m may be either the same or vary)

Question 25

What is the formula of glucose?

Answer 25

C6H12O6

Question 26

What is the general formula of sucrose?

Answer 26

C12H22O11

Question 27

What are the three main groups of carbohydrates?

Answer 27

-Monosaccharides -Disaccharides -Polysaccharides

Question 28

Give differences between sugars and polysaccharides

Answer 28

Sugars: -Small molecules -Sweet -Readily soluble in water -Crystalline Polysaccharides: -Marcomolecules -Not sweet -Insoluble or slightly soluble in water -Non-crystalline

Question 29

What are aldoses/ aldose sugars?

Answer 29

These are sugars containing an aldehyde group (-CHO). Their functional group is at the terminal end of the chain.

Question 30

What are ketoses /keto sugars?

Answer 30

These are monosaccharides containing a ketone group (C=O) Their functional group is anywhere in the middle of the chain.

Question 31

Give examples of aldoses

Answer 31

-Glyceraldehyde (triose sugar) -Ribose, Xylose ,Arabinose (pentoses) -Glucose, Galactose, Mannose ( hexoses)

Question 32

Give examples of ketoses

Answer 32

-Dihydroxyacetone (Triose) -Ribulose,Xylulose (Pentoses) -Fructose, Sorbose (Hexoses)

Question 33

What is the difference between the alpha glucose ring and the beta glucose ring structure?

Answer 33

The -OH group on carbon atom 1 is “down” in alpha glucose and “up” in beta glucose

Question 34

What are isomers?

Answer 34

Compounds with the same molecular formula but different structural formulae

Question 35

By what chemical reaction do monosaccharides combine to form disaccharides?

Answer 35

Condensation reaction (Removal of water)

Question 36

By what chemical reaction do disaccharides break down to form their component monosaccharides?

Answer 36

Hydrolysis reaction (Break down with addition of a water molecule)

Question 37

What is the resultant bond of a condensation reaction?

Answer 37

Glycosidic bond

Question 38

Glucose + Glucose = ?

Answer 38

Maltose Mainly a breakdown product during digestion of starch by amylase enzymes. Common in animals and germinating seeds Applied in brewing beer when barley grain is used as the source of starch. The process is called malting.

Question 39

Glucose + Galactose = ?

Answer 39

Lactose (Milk sugar) Exclusively in milk Energy source for young mammals Digested slowly thus a steady release of energy

Question 40

Glucose + Fructose = ?

Answer 40

Sucrose (Cane sugar) Commonly found in plants

Question 41

Which of the following is not a reducing sugar? a) Lactose b) Maltose c) Sucrose d) Glucose

Answer 41

c) Sucrose Sucrose is the only non- reducing disaccharide All monosaccharides are reducing sugars

Question 42

True or false? “Polysaccharides are reducing sugars”

Answer 42

False

Question 43

What do reducing sugars do to Benedict’s solution?

Answer 43

Reduce copper (ii) ions in Benedict’s solution to copper (I) oxide giving an orange precipitate.

Question 44

Give importances of monosaccharides

Answer 44

-Trioses are intermediates in respiration, photosynthesis and other branches of carbohydrate metabolism -Pentoses are used in synthesis of nucleic acids, ATP etc -Hexoses are a source of energy when oxidized in respiration -Hexoses combine to form disaccharides and polysaccharides

Question 45

What specific monomer makes up the polymer of starch?

Answer 45

Alpha glucose

Question 46

Which of the following are most abundant in plants? a) Starch b) Starch and cellulose c) Cellulose and glycogen d) Starch and glycogen

Answer 46

b) Starch (storage) and cellulose (structure i.e the cell wall)

Question 47

What are the two major components of starch?

Answer 47

-Amylose (20%) -Amylopectin (79%)

Question 48

What is the use of starch in plants?

Answer 48

It is made from excess glucose as a food reserve (storage polysaccharide)

Question 49

Give differences between amylose and amylopectin

Answer 49

Amylose; -Has 1,4-glycosidic bonds only -Made up of unbranched helical chains -Made up of fewer glucose units (300) -Smaller molecular mass Amylopectin; -Has both 1,4 and 1,6 glycosidic bonds -Made up of branched helical chains -Made up of more glucose units(1300) -Larger molecular mass

Question 50

Give similarities between amylose and amylopectin

Answer 50

-Both amylose and amylopectin are made up of alpha glucose molecules -Both amylose and amylopectin have 1,4 glycosidic bonds

Question 51

What are the adaptations of starch to its storage function in plants?

Answer 51

- It is insoluble thus it has no osmotic effect within cells - It is insoluble thus cannot be lost in solution form - It is a compact polymer hence takes up little space in the cell - Made up of glucose thus it can be hydrolyzed by enzymes to provide energy in form of ATP when needed

Question 52

What is the animal equivalent of starch?

Answer 52

Glycogen (Also present in fungi)

Question 53

What monomer makes up the glycogen polymer?

Answer 53

Alpha glucose

Question 54

Where is glycogen mainly stored in animals?

Answer 54

Liver and muscles (Centers of high metabolic activity as it is an energy reserve)

Question 55

Which bonds are present in glycogen?

Answer 55

1,6 glycosidic bonds ( making it highly branched)

Question 56

Which is more soluble, starch or glycogen?

Answer 56

Glycogen (Is more branched)

Question 57

Give adaptations of glycogen to its storage functions.

Answer 57

- It is high branched thus can be broken down into glucose easily to release energy - It is insoluble thus it has no osmotic effect within cells - It is insoluble thus cannot be lost in solution form - It is a compact polymer hence takes up little space in the cell

Question 58

What is the monomer of cellulose?

Answer 58

Beta glucose

Question 59

Which bonds are present in cellulose?

Answer 59

1,4-glycosidic bonds (Unbranched parallel chains)

Question 60

Where is cellulose mainly found?

Answer 60

Cell walls of plant cells

Question 61

Many chains of cellulose form?

Answer 61

Microfibrils (Which form macrofibrils)

Question 62

Give commercial uses of cellulose

Answer 62

-Used in the manufacture of paper -Cellulose in cotton is used to make fabrics

Question 63

Give differences between glycogen and starch

Answer 63

Glycogen: -More soluble in water -More branched -Hydrolyzed more easily than starch -Found in animals Starch: -Less soluble in water -Less branched -Hydrolyzed less easily than starch -Found in plants

Question 64

What is the biological significance of iced water being less dense than liquid?

Answer 64

During the winter, the ice floats thus providing an insulating barrier for aquatic life forms below whose enzymes would otherwise be inactivated leading to death

Question 65

Describe the sequence of events of the action of enzymes

Answer 65

- The enzyme works on a substrate to which it is specific and combines with it forming a short-lived enzyme substrate complex - The proximity of the enzyme to the substrate in the complex greatly increases chances of a reaction occurring - Once the reaction has taken place, the complex breaks up into products and enzyme. - The enzyme remains unchanged by the end of the reaction and is free to interact with more substrate E + S <=> ES (complex) <=> EP (complex) <=> E + P

Question 66

Explain the importance of water as a solvent

Answer 66

- Transport The solvent properties of water mean that it is a transport medium, as it is in blood plasma, tissue fluid, lymph, in mammals and Xylem and Phloem in plants. They are all made up of water and dissolve a number of substances which can then be easily transported. - Excretion Metabolic wastes like ammonia, urea, excess salts require water to be removed from the body in solution form. - Secretion They are transported from their place of secretion in solution form (aqueous form) e.g. most digestive juices have enzymes in solution, tears mainly consist of water, snake venoms have toxins in suspension composed of water.

Question 67

How does a nucleoside differ from a nucleotide?

Answer 67

A nucleoside is a compound formed when sugar joins a nitrogeneous base with the loss of a water molecule (condensation reaction) while a nucleotide the compound formed when a nucleoside joins a phosphate group by loss of another water molecule

Question 68

State the fat soluble vitamins

Answer 68

Vitamin A Vitamin D Vitamin E Vitamin K

Question 69

How do enzymes speed up the rate of a chemical reaction?

Answer 69

They lower the amount of activation energy required to initiate a reaction.

Question 70

Give similarities between glycogen and starch

Answer 70

- Both exist in form of granules - Both are made up of alpha glucose molecules - Both are storage polysaccharides - Both have glycosidic bonds

Question 71

Give differences between cellulose and starch

Answer 71

Cellulose -Made up of beta glucose molecules -Structural polysaccharide -Not easily hydrolyzed -Parallel chains Starch: -Made up of alpha glucose molecules -Storage polysaccharide -Easily hydrolyzed -Folded helical chains

Question 72

Explain the importance of water as a solvent

Answer 72

i. Transport The solvent properties of water mean that it is a transport medium, as it is in blood plasma, tissue fluid, lymph, in mammals and Xylem and Phloem in plants. They are all made up of water and dissolve a number of substances which can then be easily transported. ii. Excretion Metabolic wastes like ammonia, urea, excess salts require water to be removed from the body in solution form. iii. Secretion They are transported from their place of secretion in solution form (aqueous form) e.g. most digestive juices have enzymes in solution, tears mainly consist of water, snake venoms have toxins in suspension composed of water.

Question 73

Give differences between cellulose and glycogen

Answer 73

CELLULOSE - Structural polysaccharide - Made up of beta glucose molecules - Present in plants GLYCOGEN - Storage polysaccharide - Made up of alpha glucose molecules - Present in animals

Question 74

Give adaptations of polysaccharides to their role in food storage

Answer 74

- easily hydrolyzed - Folded into compact shapes - No osmotic effect on the cell

Question 75

True or false Oils exist as liquids and fats exist as solids at room temperature

Answer 75

True

Question 76

What is the determining factor of the chemical and physical properties of a lipid?

Answer 76

The fatty acid

Question 77

Give examples of saturated and unsaturated fatty acids

Answer 77

SATURATED - Stearic acid - Palmitic acid - Cerotic acid UNSATURATED - Oleic acid - Linoleic acid

Question 78

Why can’t triglycerides (lipids) dissolve in water?

Answer 78

They are non-polar thus do not form hydrogen bonds with water molecules and cannot dissolve in water.

Question 79

What type of reaction yields a lipid?

Answer 79

Condensation reaction (Loss of water molecules)

Question 80

What type of bond is present in a triglyceride that joins the fatty acid to the glycerol?

Answer 80

Ester bonds

Question 81

Why are lipids better storage materials in animals than carbohydrates?

Answer 81

- They are lighter than carbohydrates - Lipids are more compact - Insoluble in water - Higher calorific value - Serve secondary functions - Shock absorbers - Buoyancy - Insulation - No osmotic effect

Question 82

Give the structural functions of lipids

Answer 82

- act as shock absorbers - Component of the myelin sheath - Subcutaneous, fat layer in the dermis of the skin - Buoyancy in aquatic organisms - Component of the cell membrane - Component of the waxy cuticle in the exoskeleton of arthropods - Waxy, cuticle in plants

Question 83

Give the physiological functions of lipids

Answer 83

- they are respired to yield a lot of energy - Yield metabolic water on oxidation - Stores, fat, or lipid soluble vitamins ADEK - Synthesis of steroid hormones - Component of brown adipose tissue

Question 84

What is the difference between essential and non-essential amino acids?

Answer 84

Essential amino acids cannot be synthesized by the body, but must be provided in the diet while non-essential amino acids can be synthesized by the body

Question 85

Describe the structure of amino acids

Answer 85

- amino acids have an amino group/ basic group, an alpha carbon atom, a carbonyl group/ acidic group, a hydrogen atom and an R group - The amino group is responsible for the basic properties. Well, the carbonyl is responsible for the acidic properties. - Therefore, the amino acid has both acidic and basic properties. Thus it is known as an amphoteric compound. - The R group is responsible for the uniqueness of each amino acid as it varies from one to another

Question 86

What is a Zwitterion?

Answer 86

A molecule or ion having separate positively and negatively charged groups

Question 87

What happens to an amino acid in basic conditions?

Answer 87

- The carboxyl group dissociates, and the hydrogen atom is lost, which combines with hydroxide ions in the medium, forming water with a neutral pH

Question 88

What happens to an amino acid in neutral conditions?

Answer 88

- The Carbonyl group dissociates, losing a proton and remains negatively charged - The proton is attracted to the basic amino group which becomes positively charged - The amino acid becomes dipolar

Question 89

What happens to an amino acid in acidic conditions?

Answer 89

- hydrogen ions in the medium, are attracted to the amino group that has a higher affinity will hydrogen ions and this neutralizes the solution

Question 90

What is a buffer?

Answer 90

Chemical substances which resist pH changes when small amounts of an acid or base are added to it

Question 91

What type of reaction leads to the formation of a protein?

Answer 91

Condensation reaction (loss of a water molecule)

Question 92

Describe the process of formation of a polypeptide

Answer 92

- First, a dipeptide is formed through - when two amino acids are combined together - A peptide bond joins the two amino acids and a water molecule is lost - A carbonyl group is exposed on one end of the dipeptide and an amino group on the other thus more amino acids may be added to the dipeptide - Addition of more amino acids to the dipeptide forms, a polypeptide chain

Question 93

Describe the bonds that stabilize the protein structure

Answer 93

HYDROGEN BONDS - this form the alpha helix structure - Hydrogen in OH or NH groups becomes slightly positively charged, attracted to a neighboring, O, or N atoms that can occur along the polypeptide chain - Hydrogen bonds are weak, but they provide a strong force because of increased numbers in proteins IONIC BONDS - acidic R groups are negatively charged well basic R groups are positively charged - Thus they can be attracted to each other forming ionic bonds - However, in an aqueous environment ionic bonds are weaker than covalent as they can be broken by changing the pH of the medium DISULPHIDE BONDS/ BRIDGES - these may be intrachain or interchain - They are strong bonds - Neighboring sulphydryl R groups may be oxidized (hydrogen removed) to form a sulphydryl bond HYDROPHOBIC INTERACTIONS - hydrophobic groups come close to exclude water, thus folding - The hydrophobic groups point inwards while the hydrophilic ones point outwards, making the protein soluble - This is how globular proteins are formed

Question 94

Describe the fibrous structure of proteins

Answer 94

- The secondary structure is most conspicuous - Insoluble in water - Physically tough - Long parallel, polypeptide chains, cross-linked at intervals, forming long fibers or sheets

Question 95

Give examples of functions performed by fibrous proteins

Answer 95

- Structural functions; such as collagen, myosin in muscle, silk in spiderwebs and keratin in hair, horns and nails

Question 96

Describe the globular structure of proteins

Answer 96

- The tertiary structure is most conspicuous - Easily soluble in water - Polypeptide chains are tightly folded, to form the spherical shape

Question 97

Give examples of functions performed by globular proteins

Answer 97

- Form enzymes, antibodies and some hormones

Question 98

Give the differences between fibrous and globular proteins

Answer 98

FIBROUS - insoluble - Repetitive regular sequence of amino acids - Polypeptide chains form long, parallel strands - Stable structure - Support and structural functions, for example, collagen and keratin - Sheet like GLOBULAR - Soluble - Irregular sequence of amino acids - Polypeptide chains fold into a spherical shape - Relatively unstable structure - Metabolic functions, for example, enzymes and hormones - Spherical

Question 99

Describe the primary structure of proteins

Answer 99

- this is the linear sequence of amino acids in a polypeptide - It is stabilized by peptide bonds - It is determined by the sequence of bases in the DNA

Question 100

Describe the secondary structure of proteins

Answer 100

ALPHA HELIX - It’s structure is an alpha helix - It is stabilize by hydrogen bonds between the CO and NH2 groups - Examples include keratin which is in hair, horns and hooves BETA PLEATED SHEETS - this is in the form of a beta pleated sheet - The amino acids run, anti-parallel to each other - It is stabilized by hydrogen bonds - Examples include spiderwebs

Question 101

Describe the tertiary structure of proteins

Answer 101

- this is a result of extensive coiling and folding of the polypeptide chain into a compact globular shape - In addition to the hydrogen bond, more bonds, such as Ionic, disulfide, and hydrophobic bonds, stabilize the tertiary structure describe the quaternary structure of proteins - More than one polypeptide chain associate to create a quaternary structure for example, hemoglobin (which has two alpha polypeptide chains and two beta polypeptide chains) - It is stabilized by hydrogen, ionic and hydrophobic interactions

Question 102

What is an enzyme?

Answer 102

A biological catalyst **protein** in nature, which speeds up the rate of a metabolic reaction without itself undergoing a permanent change

Question 103

State the properties of enzymes

Answer 103

- specific in action - Remain chemically unchanged at the end of a reaction - Protein in nature - Possess active sites - Required in small amounts - Activity affected by pH and temperature

Question 104

What is the role of enzymes in chemical reactions?

Answer 104

They provide an alternative pathway of low activation energy required to initiate a chemical reaction

Question 105

Describe the lock and key hypothesis

Answer 105

- The substrate is imagine to be like a key, whose shape is complementary to the enzyme, which is the lock - The site where the substrate binds is the active site and it has a specific configuration - The substrate fits in to the active site, and forms the enzyme substrate complex - The enzyme product complex once formed the products no longer fit into the active site and escape into the surrounding medium, leaving the active site free to receive further substrate molecules (It is based on the fact that enzymes are not used up, but used over and over again)

Question 106

Describe the induced fit hypothesis

Answer 106

- enzymes have active sites which are flexible structures, and can be modified - The active site is modified as the substrate interacts with the enzymes - The amino acids, which make up the active site are molded into a precise shape, which enables the enzyme to perform its catalytic function effectively (It is based on the fact that enzymes are not static, but rather dynamic molecules)

Question 107

Explain the factors affecting enzyme activity

Answer 107

- enzyme concentration - Substrate concentration - Temperature - pH

Question 108

Define enzyme inhibition

Answer 108

This is the slowing down or stopping of enzyme-controlled reactions by inhibitors

Question 109

What is an enzyme inhibitor?

Answer 109

These are substances that reduce the activity of enzymes

Question 110

What is an antidote?

Answer 110

This is a chemical substance that counteracts the effect of an inhibitor or a poison

Question 111

Explain competitive inhibition

Answer 111

- this occurs when a compound, which has a structure similar to that of the normal substrate, prevents it from entering the active site - The inhibitor occupies the active site and prevent the true substrate from entering - Therefore the inhibitor and the substrate to compete for the active site - If the substrate concentration is increased, the rate of reaction increases

Question 112

Explain non-competitive reversible inhibition

Answer 112

- The inhibitor has no structural similarity to the substrate and combines with the enzyme at a point other than its active site - It does not affect the ability of the substrate to bind to the enzyme, but makes it impossible for catalysis to take place - The enzyme loses its three-dimensional structure - The rate of reaction decreases with increasing inhibitor concentration - Once the inhibitor is removed the enzyme, may regain its three-dimensional structure and normal catalysis resumes

Question 113

Describe non-competitive irreversible inhibition

Answer 113

- The inhibitor permanently attaches to the enzyme, their attachment is irreversible - This causes the enzyme to lose its three-dimensional shape. Thus the shape of the active site is completely altered, and the substrate no longer fits into the active site. - The proteins of the enzyme molecule precipitates

Question 114

Give the importance of enzyme inhibitors

Answer 114

- regulate enzyme controlled reactions - have important medical and agricultural uses for example in drugs and pesticides - Enable biochemists to reconstruct metabolic pathways - Provide information about the shapes and properties of active sites

Question 115

Give the categories of enzymes according to the reactions they catalyze

Answer 115

- Oxidoreductases - Transferases - Hydrolases - Lyases - Isomerases - Ligases

Question 116

Explain how end-product inhibition in an enzyme controlled reaction is negative feedback

Answer 116

For biochemical reactions that occur in **series**, **accumulation** of the final product acts as an **allosteric inhibitor** for the first enzyme controlling the first step of the reaction **pathway**. This **temporarily stops** its formation. However, if the final product **reduces**, the inhibition is **reduced** or removed, and more end-products are **formed**

Question 117

Why are enzyme controlled reactions carried out in a step-by-step mechanism?

Answer 117

The body can control the amount of energy produced by the body’s requirement

Question 118

What are enzyme cofactors?

Answer 118

These are non-Protein compounds required for efficient activities of enzymes

Question 119

Define inorganic ions as enzyme activators

Answer 119

These mould the enzyme or substrate into a shape that allows the enzyme-substrate complex to be formed. For example, salivary amylase activity is increased in the presence of chloride ions.

Question 120

Define prosthetic groups

Answer 120

These are organic molecules tightly bound to the enzyme on a permanent basis that assist the catalytic function of the enzyme eg Haem

Question 121

Define coenzymes

Answer 121

These are organic non-protein molecules not bonded to the enzyme. They do not remain attached to the enzyme between reactions. eg NAD, CoA, ATP (They are organic)

Question 122

What is the simplest form of the R on the amino acid molecule?

Answer 122

Hydrogen (H) This is found in glycine making it the simplest