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deck_5661106 Flashcards

1
Q

Why are enzymes called biological catalysts?

A

Because they speed up metabolic reactions in living organisms. Their actions affect both structure and function within cells, tissues and organs

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2
Q

What do catalysts do?

A

Speed up chemical reactions and remain unchanged at the end of the reaction and able to be used again. A small amount of catalyst can catalyse the conversion of a large number of substrate molecules into product molecules

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3
Q

What is a turnover number?

A

The number of reactions that an enzyme molecule can catalyse per second

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4
Q

Why are enzymes better than chemical catalysts?

A

Need lower temperatures, neutral pH and normal pressure so they are able to function in conditions that sustain life. Also enzymes are more specific and don’t produce unwanted by-products/rarely make mistakes. Their production and activity is regulated to fit the needs of the cell or the organism

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5
Q

What may enzymes need help from to catalyse some reactions?

A

Cofactors

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6
Q

Where are the instructions for making enzymes?

A

They are encoded in the genes. If the gene has a mutation that alters the sequence of amino acids in the protein then it ma alter the enzyme’s tertiary structure and prevent it from functioning

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7
Q

What happens if an enzyme that catalyses a metabolic reaction is deficient?

A

A metabolic disorder

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8
Q

What do enzymes also catalyse the formation of?

A

Organism’s structural components such as collagen in bone, cartilage, blood-vessel walls, joints and connective tissue

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9
Q

What do some genetic disorder cause?

A

Malformations of connective tissue and can be very harmful

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10
Q

What is an active site?

A

Indented area on the surface of an enzyme molecule, with a shape that is complementary to the shape of the substrate molecule

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11
Q

Why is the tertiary structure of the active site crucial?

A

Its shape is complementary to the shape of the substrate molecule

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12
Q

Why is it a good thing that each type of enzyme is highly specific in its function?

A

It can only catalyse a reaction involving the particular type of substrate molecule that fits into its active site

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13
Q

What can the shape of the enzymes active site, and ability to catalyse a reaction be altered by?

A

Changes in temperature and pH as these affect the bonds that hold proteins in their tertiary structure

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14
Q

Where do enzymes work?

A

Enzymes catalyse a wide range of intracellular and extracellular reactions

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15
Q

Why are intracellular enzymes needed?

A

Within organelles there may be up to 1000 metabolic reactions going on at the same time, each being catalysed by a different enzyme. Some of these reactions are part of a metabolic pathway

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16
Q

What is a metabolic pathway?

A

Each metabolic pathway in a living cell is one of a series of consecutive reactions, every step catalysed by a specific enzyme that produces a specific product

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17
Q

What acts as substrates for specific enzymes?

A

The various reactants and intermediates

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18
Q

What are the reactants, intermediates and products known as?

A

Metabolites

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19
Q

What happens in catabolic metabolic pathways?

A

Metabolites are broken down to smaller molecules and release energy

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20
Q

What happens in anabolic metabolic pathways?

A

Energy is used to synthesise larger molecules from smaller ones

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21
Q

What are respiration and photosynthesis examples of?

A

Complex metabolic pathways with many enzymes involed

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22
Q

Where is catalase found?

A

In nearly all living organisms that are exposed to oxygen

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23
Q

Why is catalase very important?

A

It protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide, a potentially harmful by product of many metabolic reactions, to water and oxygen

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24
Q

What does catalase consist of?

A

Four polypeptide chains and contains a haem group with iron

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25
Q

How fast is catalase?

A

It is the fastest acting enzyme, having the highest turnover known, of about 6million per second

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26
Q

Where is catalase found in eukaryotic cells?

A

Inside small vesicles called peroxisomes

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27
Q

How is catalase used in white blood cells?

A

When white blood cells ingest pathogens, they use catalase to help kill the invading microbe

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28
Q

What is the optimum pH for human catalase?

A

Around pH7, but for other species it varies between pH 4 and 11

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29
Q

What is the optimum temperature?

A

Varies with species, for humans it’s about 45ºC and for some thermophilic archae it’s 90ºC

30
Q

Why are extracellular enzymes needed?

A

Some enzymes are secreted from the cells where they are made and act on their substrates extracellular

31
Q

What is an example?

A

Fungi release hydrolytic enzymes from their thread-like hyphae. The enzymes digest carbohydrates, proteins and lipids, and the products of digestion (glucose, amino acids, glycerol and fatty acids) are absorbed into the fungal hyphae for use in respiration and growth

32
Q

Where are enzymes secreted from in our digestive system?

A

From cells lining the alimentary canal, into the gut lumen. They extracellularly digest large molecules such as proteins, lipids, carbohydrates and nucleic acids found in the food. The products of digestion are then absorbed via epithelial cells of the gut wall, into the bloodstream in order to be used for respiration, growth and tissue repair

33
Q

What is amylase?

A

Produced in salivary glands and acts in mouth to digest the polysaccharides starch to the disaccharide maltose. It is also made in the pancreas, and acts to catalyse the same reaction in the lumen of the small intestine

34
Q

What is trypsin?

A

Made in the pancreas and acts in the lumen of the small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds. Its optimum pH is between 7.5 and 8.5

35
Q

What are cofactors?

A

A substance that has to be present to ensure that an enzyme-catalysed reaction takes place at the appropriate rate

36
Q

What is a prothetic group?

A

A cofactor that is permanently bound, by covalent bonds, to an enzyme molecule

37
Q

What is an example?

A

The enzyme carbonic anhydrase contains a zinc ion permanently bound as a prosthetic group to its active site. This is found in erythrocytes and catalyses the interconversion of carbon dioxide and water to carbonic acid, which then breaks down to protons and hydrogen carbonate ions. It is very important because it enables carbon dioxide to be carried in the blood from respiring tissues to the lungs

38
Q

What happens during an enzyme-catalysed reaction?

A

The enzyme and substrate molecules temporarily bind together to form an enzyme-substrate complex. The presence of certain ions that may temporarily bind to either the substrate or the enzyme molecule may ease the formation of such complexes and so increase the rate of the reaction

39
Q

What can some cofactors act as?

A

Co-substrates-they and the substrate together form the correct shape to bind to the active site of the enzyme. And some change the distribution on the surface of the substrate molecule or on the enzymes active site and make the temporary bonds in the complex easier to form

40
Q

What does the enzyme amylase digest?

A

Starch to maltose, and will only function if chloride ions are present

41
Q

What are coenzymes?

A

Small organic non-protein molecules that bind temporarily to the active site of enzyme molecules, either just before or at the same time that the substrate binds

42
Q

What happens to the coenzymes during and after a reaction?

A

They become chemically charged during, and need to then be recycled to their original state, sometimes by a different enzyme

43
Q

Where are many coenzymes derived from?

A

Water-soluble vitamins

44
Q

What happens if the water soluble vitamins are deficient in the diet of a human?

A

Certain diseases may result

45
Q

What happens if you lack in B12?

A

(coenzyme cobalamin coenzymes) pernicious anaemia (progressive and fatal)

46
Q

What happens if you lack in folic acid?

A

(coenzyme tetrahydrofolate) metabolic anaemia (large, irregularly shaped erythrocytes)

47
Q

What happens if you lack in nicotinamide B3?

A

(coenzyme NAD and NADP) pellagra (diarrhoea, dermatitis and dementia)

48
Q

What happens if you lack in pantothenate B6?

A

(coenzyme A) elevated blood-plasma triglyceride levels

49
Q

What happens if you lack in thiamine B1?

A

(coenzyme thiamine pyrophosphate) beriberi (mental confusion, irregular heartbeat, muscular weakness, paralysis and heart failure)

50
Q

What are NAD and NADP?

A

Hydrogen acceptors, and they are both derivatives of nucleotides

51
Q

What is the lock and key hypothesis?

A

Substrate molecule fits into the active site on the enzyme due to the tertiary structure of the active site, giving it a complementary shape to the substrate (like a lock and key)

52
Q

How does an enzyme substrate complex form?

A

The substrate and enzyme molecules have kinetic energy and are constantly moving around randomly, if they successfully collide, then the complex forms

53
Q

What happens in an enzyme substrate complex?

A

The substrate molecules are even broken down, or built up into the product molecules and these form an enzyme product complex whilst still in the active site

54
Q

What happens when the product molecules leave the active site?

A

The enzyme molecule is able to form another enzyme substrate complex, so a small number of enzyme molecules can convert a large number of substrate molecules into product molecules

55
Q

What does the lock and key hypothesis fail to explain?

A

How the transition state (enzyme substrate complex) is established

56
Q

Who modified the lock and key hypothesis?

A

Daniel Koshland in 1985, by suggesting that the active site isn’t a rigid and fixed structure, but the presence of the substrate molecule in it indices a shape, giving a good fit

57
Q

What is this hypothesis called?

A

The induced fit hypothesis

58
Q

What does the induced fit hypothesis suggest?

A

When substrate fit into active site, active site changes slightly to mould around substrate. Active site is complementary but on binding, the subtle changes of shape of r groups of the amino acids that make up the active site, gives a more precise fit-enabling more effective binding

59
Q

How does the binding happen?

A

When an enzyme substrate complex is formed, forces such as hydrogen bonds, ionic attractions and hydrophobic interactions bind the substrate to the active site

60
Q

What happens when the substrate molecules have been converted to the product and are still in the active site?

A

They form an enzyme product complex

61
Q

Why does the product then leave the active site?

A

They now have a slightly different shape from the substrate molecule and so detach, leaving the enzyme free to catalyse another reaction with another substrate of the same type

62
Q

What is the equation for how an enzyme catalyses a reaction?

A

Enzyme + substrate -> enzyme substrate complex -> enzyme-product complex -> enzyme + product

63
Q

What do enzymes do to reactions?

A

They lower the activation energy which is useful in living things as the temp cant be raised too much without denaturing proteins and melting lipids

64
Q

What happens if a substrate is heated?

A

Extra energy in the form of heat causes molecules to move faster, increases rate of collisions between molecules, also increases force with which they collide as they are moving faster

65
Q

What happens if the reactant mixture, containing enzyme and substrate molecules is heated?

A

Both will gain kinetic energy and move faster, increasing rate of successful collisions, so the rate of formation of ES complexes increases and rate of reaction increases, increasing number of enzyme product complexes up to a point, then at the optimum temperature the rate of reaction is at it’s maximum

66
Q

What also happens to the molecules when temperature is increased?

A

They vibrate more which may break weaker bonds eg hydrogen and ionic bonds that hold tertiary structure of active site, as active site changes the substrate molecules don’t fit as well so rate of reaction decreases, plus more heat means the site is changed completely and irreversibly so its no longer complementary and the reaction can’t happen at all-enzyme is denatured

67
Q

Why is the enzymes primary structure not altered?

A

Because heat doesn’t break the peptide bonds between amino acids

68
Q

What is optimum temperature?

A

The temperature at which the enzyme works best, it is the temperature at which the enzyme has its maximum rate of reaction

69
Q

What is an example of an organism that is adapted to living in cold conditions?

A

Psychrophilic bacteria, which live in very cold conditions, so their enzymes can work at really low temperatures

70
Q

What is an example of an organism that is adapted to living in hot temperatures?

A

Thermophilic bacteria in hot springs, their enzymes are heat stable and have more disulfide bonds that don’t break with heat and keep shape of protein molecule stable-their enzymes have high optimum temperatures

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