Enzymes and Enzyme Kinetics Flashcards by Maimoona Latif

What are enzymes and what is their main function?

Globular (spherical) proteins, which are catalysts to speed up biochemical reactions
Also help with nutrient absorption

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What biological processes are enzymes essential for?

Digestion
Respiration
Liver function

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How can the enzyme’s rate of reaction be affected?

If denaturing occurs, which can be caused by pH changes, temperature and substrate concentration

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How can other substances affect the enzyme’s function?

Other substances can either promote or inhibit the enzyme function

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What is a biochemical reaction?

When one molecule is turned into another molecule

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What do enzymes do to behave as a catalyst?

They lower the activation energy needed for the reaction to occur

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How do enzymes and substrates interact?

Induced fit model: the active site and substrate are similar in shape, but when the substrate binds the enzyme’s active site is induced to change shape and become fully complementary with the active site
Lock and key model also

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Why can enzymes be used in diagnosis?

Enzymes can be used as biomarkers- the level/concentration of enzymes in the blood can be used to diagnose disease

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How can enzymes be used therapeutically?

To treat:
Infectious diseases
Genetic diseases
Miscellaneous
Cancer
Metabolic disorders
Blood clotting disorders

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What is the general prefix to identify enzymes?

Enzyme names generally end in ‘-ase’

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What are the six main classes of enzymes?

Transferases: transfer functional groups from one molecule to another
Ligases: join two molecules together
Oxidoreductases: move electrons between molecules
Isomerases: convert one molecule’s isomer into another
Hydrolases: break bonds between molecules using a molecule of water
Lyases: break bonds between molecules without using water or oxidation

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What are some features of enzymes as biological catalysts?

Globular proteins with specific shapes
Control rates of metabolic reactions
Lower EA needed to start reactions
Not consumed in chemical reactions
Substrate specific
Shape of active site determines substrate

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What is a substrate?

The reactant in a biochemical reaction

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What is an active site, and what are its features?

Region where substrate binds & undergoes a chemical reaction
Comprised of:
Binding site
Catalytic site

Has a specific shape
Change in shape affects active site andenzyme activity

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How do enzyme-substrate complexes form?

When the complementary substrate binds to the enzyme’s active site

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What are some features of the Lock and key model?

Developed by Emil Fischer, 1894
Active site has a rigid shape
Only substrates with the matching shape can fit
No change in the active site on binding the substrate

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What are some features of the Induced fit model?

Developed by Daniel Koshland, 1958
Active site is flexible, not rigid
Shapes of the enzyme, active site, and substrate adjust
Maximizes the fit, improves catalysis
Greater range of substrate specificity

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What is the transition period and why is kinetic energy necessary?

The transition period is when not all of the substrate is used up but no product is formed
Kinetic energy is required to increase the likelihood and frequency of substrate and enzymes colliding to form e-s complexes and for product to be formed

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How can temperature affect enzyme activity?

Optimum temperature (mostly 37 degrees Celsius) is when enzyme works best
High temperatures may denature enzyme, so can no longer bind to substrate
Full denaturing occurs roughly at 70 degrees for most enzymes
Enzymes like TAC polymerase are exceptions

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What occurs when an enzyme denatures?

The chemical bonds are overcome, leading to a change in shape, so enzyme-substrate complexes can no longer form

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How does pH affect enzyme activity?

Most enzymes have a pH of 7, but some prefer more acidic or basic conditions
Extreme changes in pH can lead to the enzyme denaturing
Small changes in pH can lead to an affect on substrate binding to enzyme’s active site

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What is the approximate optimum pH levels for pepsin, human amylase and trypsin?

Pepsin~ pH 2
Human amylase~ pH 7
Trypsin~ pH 8

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What is pepsin and pepsinogen?

Pepsin is a protease enzyme in the stomach and so has an optimum temperature of pH 2
Pepsinogen is the deactivated version of pepsin, that requires HCl to activate it to pepsin

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What is trypsin?

Trypsin is an enzyme in the small intestine that is responsible for protein and lipid digestion
Trypsin has an optimum temperature of pH 8 and the deactivated version of trypsin is trypsinogen

How are alkaline conditions achieved?

By pancreatic juices that contain sodium bicarb

Why does acidic material not damage the small intestine lining?

Acidic material is neutralised in the small intestine and this means that there is no lining damage as the epithelium is still intact

What is the relationship between rate of reaction and substrate concentration?

As the [substrate] increases, the rate of reaction also increases

When can maximum enzyme activity be recorded?

When all the enzyme active sites are occupied (saturated)

What is the purpose of an inhibitor?

An inhibitor binds to an enzyme and decreases enzyme activity

What are the two different types of inhibitor?

Competitive inhibitor Non-competitive/allosteric inhibitors

How can the effects of competitive inhibitors be reversed?

Can associate and dissociate with the enzyme to regulate activity

Why are the effects of non-competitive inhibitors not reversible?

Covalent attachment of the inhibitor to the enzyme, therefore this can only be overcome by producing more enzyme

What are some features of competitive inhibitors?

Similar in shape/structure to the substrate Competes with the substrate for the enzyme's active site Effects are reversed when [substrate] increases

What are some features of non-competitive/allosteric inhibitors?

Different in shape/structure to the substrate Binds to enzyme via other (allosteric) binding site Can bind in the absence or presence of substrate Alters shape of the enzyme, so therefore alters the shape of the active site Cannot be reversed by adding more substrate

Why is the active site changing shape so detrimental?

The active site is no longer complimentary to the substrate Enzyme-substrate complexes cannot form, but if they do they are very weakly associated No reaction can occur

What are the job of activators?

Increase enzyme activity by binding to allosteric binding sites on the enzyme

What are some examples of activators and their features?

Cofactors (inorganic): Make some enzymes active Either ions or coenzymes Coenzymes: Molecules that act as cofactors Mostly vitamins

What is metabolism and what are some of the features?

Metabolism is the chemical reactions that occur in a living organism Conversion of one compound to another compound either directly or by a series of reactions

What is the purpose of metabolism?

Energy production Biosynthesis Excretion

What are the organisational units of metabolism?

Biochemical pathways

What is anabolism and some of its features?

Involves the synthesis of larger molecules from smaller molecules Requires energy Provides substances needed for cellular growth and repair

What is catabolism and some of its features?

Breaking down of larger molecules into smaller ones Releases energy Used to decompose lipids, carbohydrates and proteins

What are the three main sources of energy?

Carbohydrates Lipids Proteins

What is glycolysis?

An energy conversion pathway Set off reactions that convert glucose into pyruvic acid Net gain of 2 ATP molecules per glucose molecule

How is the glycolytic pathway tightly controlled?

The rate of conversion of glucose into pyruvate is controlled by: The requirement for the generation of ATP The synthesis of cellular components

How and why does glycogenolysis occur?

Glycogen is converted into G-6-P Requires 3 enzymatic reactions and produces G-6-P which can then enter glycolysis

What is gluconeogenesis?

The creation of glucagon from other molecules such as fatty acids

Why is the TCA cycle important?

Central to all respiratory oxidations

What is the purpose of the TCA cycle?

Oxidises acetyl-coA from glucose, lipid and protein catabolism in aerobic respiration Maximises energy gain

What is oxidative phosphorylation?

Formation of ATP via the transfer of electrons

Why is oxidative phosphorylation important?

Major source of ATP in aerobic organisms

Why are triglycerides important?

Major form of stored energy in the form of fat droplets within adipose tissue

When does lipolysis occur and what happens during lipolysis?

Lipolysis occurs during starvation Switches from 'fast' (carbohydrate) to 'slow' (lipid) energy

What happens to the brain during lipolysis and why?

Only the brain continues to use carbohydrates as an energy source Brain co-ordinates all of the body function, whilst also maximising lipid energy for function

What are the three stages of processing for fatty acids?

Triglycerides degraded to fatty acids and glycerol in adipose tissue and transported to other tissue At these tissues, fatty acids are activated and transported into mitochondria for degradation Fatty acids broken down into 2-carbon acetyl-coA units and fed into TCA cycle

Where does protein degradation begin and end?

Begins in the stomach and ends in the small intestine

What enzymes are involved and where are they located?

Primary proteolytic enzyme of the stomach is pepsin Pancreas secretes zymogens (inactive enzymes)

What is unique about enzymes?

Has a wide range of specificity Substrates are degraded into free amino acids as well as small peptides

What is key about protein turnover?

Protein turnover is constant Metabolic regulation (use) Damaged proteins (source of amino acids)