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Biology A Level > Enzymes > Flashcards

Enzymes Flashcards

1
Q

Why are enzymes called biological catalysts?

A

They speed up metabolic reactions in the living organisms

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2
Q

How are enzymes made?

A

They are proteins so they are produced by protein synthesis, if the base sequence is edited then the the amino acid sequence will also be edited and the enzyme’s tertiary structure will be altered which could prevent the enzyme from functioning

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3
Q

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

A

A metabolic disorder results

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4
Q

What structural components of an organism do enzymes catalyse?

A

Collagen in bones, cartilage, blood-vessel walls and connective tissue

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5
Q

How many amino acids does the tertiary structure of the active site of an enzyme usually consist of?

A

Around 6-10, the tertiary structure of the active site is crucial as its shape is complementary to the shape of the substrate

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6
Q

Why is each enzyme highly specific?

A

As it can only catalyse reactions involving the specific type of substrate that fits into its active site

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7
Q

How can temperature and pH affect the active site of an enzyme?

A

Changes to temperature and pH can disrupt the bonds holding the tertiary structure of the active site of an enzyme together. If the tertiary structure of the active sight is disrupted then the substrate will no longer be able to bind and therefore the enzyme will no longer be able to catalyse the reaction the involving that substrate

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8
Q

What are the reactants, intermediates and products of a metabolic pathway known as?

A

Metabolites

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9
Q

What is a catabolic process?

A

Where metabolites are broken down into smaller molecules to release energy eg. respiration

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10
Q

What is an anabolic process?

A

Where energy is used to synthesise larger molecules from smaller ones eg. photosynthesis

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11
Q

What is catalase?

A

A very important enzyme that breaks down hydrogen peroxide which is a potentially harmful by-product of many metabolic processes. It breaks down hydrogen peroxide into water and oxygen

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12
Q

Where is catalase found in eukaryotic cells?

A

Enclosed in small vesicles called peroxisomes

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13
Q

When white blood cells ingest pathogens what enzyme do they use to help kill the invading microbe?

A

Catalase

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14
Q

How many polypeptide chains does catalase have?

A

It has four polypeptide chains, each with a haem group attached to them

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15
Q

What is an intracellular enzyme?

A

an enzyme that carries out its function inside the cell

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16
Q

What is an extracellular enzyme?

A

An enzyme that is produced in a cell and is then secreted to carry out its function outside the cell

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17
Q

How does amylase act as an extracellular enzyme?

A
  • It is produced by the salivary glands, and secreted into the mouth where it breaks down the polysaccharide starch into the disaccharide maltose
  • It is also made in pancreatic cells and secreted into the lumen of the small intestine where it catalyses the same reaction as in the mouth
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18
Q

How does trypsin act as an extracellular enzyme?

A

It is produced in the pancreatic cells and secreted into the lumen of the small intestine where it breaks down proteins into smaller polypeptides by hydrolysing peptide bonds, its optimum pH is 7.5-8.5

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19
Q

How do many enzymes act in the gut lumen?

A

Many enzymes are synthesised in and secreted from cells lining the alimentary canal into the gut lumen, here they extracellularly digest large molecules such as proteins, lipids, carbohydrates and nucleic acids

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20
Q

What is a cofactor?

A

A non-protein molecule that is attached to an enzyme to enable it to function properly

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21
Q

What is a prosthetic group?

A

A cofactor that is covalently bonded to an enzyme, for example, carbonic anhydrase requires a Zn2+ cofactor

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22
Q

What is the function of carbonic anhydrase?

A
  • Carbonic anhydrase is found in erythrocytes and catalyses the conversion of carbon dioxide and water to carbonic acid, which is then able to dissociate into HCO3- and H+ ions
  • This reaction is very important as it enables CO2 to be carried from respiring tissue in the blood and into the lungs
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23
Q

What is the cofactor that is covalently bonded to carbonic anhydrase (prosthetic group)?

A

Zn2+

24
Q

How do cofactors that are not permanently bound to the enzyme work?

A
  • Some cofactors may bind to the substrate to and act as co-substrates, this means that the cofactor binds to the substrate to form the correct shape to fit the active site of the enzyme
  • Other cofactors may change the charge distribution on the surface of the substrate molecule or the surface of the enzyme’s active site, this makes the formation of the enzyme-substrate complex easier as it makes the temporary bonds that hold the enzyme-substrate complex together easier to form
  • Amylase will only function if Cl- ions are present, due to the charge distribution being altered by the chloride ions to make the temporary bonds of the enzyme-substrate complex easier to form
25
Q

What is an enzyme substrate complex?

A

During an enzyme catalysed reaction, the enzyme and substrate form temporary bonds to form the enzyme-substrate complex

26
Q

What are coenzymes?

A
  • Non-protein molecules that bind temporarily to the active site of the enzyme at the same time or just before the substrate molecule binds
  • Coenzymes are chemically changed during the reaction and therefore need to be recycled to their original state , sometimes by other enzymes
27
Q

Where are most coenzymes derived from?

A

Water-soluble vitamins that are essential in the diets of humans, if these vitamins are deficient then it can result in certain diseases as there will be a shortage of the coenzyme that is derived from the vitamin that is deficient

28
Q

Describe how an enzyme breaks down a substrate with reference to the lock and key hypothesis

A
  • The substrate molecule fits into the enzyme’s active site, temporary hydrogen bonds hold the two together forming an enzyme substrate-complex
  • The substrate molecule is then broken into smaller molecules that leave the active site
29
Q

Describe how an enzyme joins two substrates together with reference to the lock and key hypothesis?

A
  • The substrate molecules fit into the active site forming an enzyme substrate complex
  • Bonds form between the two substrate molecules forming the enzyme-product complex, the larger product molecule then leaves the active site
30
Q

What is an enzyme-substrate complex?

A

An enzyme molecule with substrate molecule(s) in its active site, the enzyme and substrate are joined together by temporary bonds such as hydrogen bonds

31
Q

What is an enzyme-product complex?

A

An enzyme molecule with product molecule(s) in its active site, the product and enzyme are held together by temporary bonds such as hydrogen bonds

32
Q

How does the lock and key hypothesis work?

A
  • The substrate and enzyme molecules have kinetic energy and are constantly moving randomly
  • If a substrate molecule collides successfully with an enzyme molecule then an enzyme-substrate molecule forms as the substrate molecule fits into the complementary shaped active site on the enzyme molecule
  • Substrate molecules are broken down or built up into the product molecule(s) and these form an enzyme-product complex
  • The product molecule leaves the active site and another substrate molecule can attach to the active site to form another enzyme-substrate complex
  • Therefore a small amount of enzyme molecules can break down a large amount of substrate molecules
33
Q

What is the induced fit theory?

A
  • As the substrate molecule fits into the active site, the active site changes shape slightly to mould itself around the substrate molecule
  • The active site still has a shape complementary to the shape of the substrate molecule, but on binding, the R groups of the amino acids forming the active site change shape slightly to give a more precise conformation that exactly fits the substrate molecule
  • This change in shape allows the substrate to bind more effectively to the active site
  • As the enzyme-substrate complex forms, non-covalent forces such as ionic bonds, Van der Waals and hydrophobic and hydrophilic interactions hold together the enzyme-substrate complex together
  • As the product molecules has a slightly different shape from the substrates, the product molecule detaches and the enzyme is free to catalyse another reaction with a substrate molecule of the same type
34
Q

Summarise the reaction of an enzyme and a substrate using an equation

A

Enzyme + substrate → Enzyme-substrate complex → Enzyme product-complex → Enzyme + product

35
Q

How do enzymes act as catalysts?

A
  • In living cells, temperature cannot be raised too much so that molecules are colliding with an energy greater than or equal to the activation energy, as proteins would denature and lipids would begin to melt
  • This means that enzymes have to act as catalysts, they provide an alternative route for the reaction with a lower activation energy therefore increasing the frequency of successful collisions and therefore increasing the rate of reaction
36
Q

What happens to the rate of enzyme substrate reactions as temperature is increased?

A
  • Both types of molecule will gain more kinetic energy and therefore move faster and also be colliding with an energy greater than or equal to the activation energy and the frequency of successful collisions therefore increases
  • Therefore the rate of formation of ES complexes increases and the rate of reaction increases up until the optimum temperature
  • This is when the rate of reaction is at its maximum
37
Q

What happens as temperature increases past the optimum temperature?

A
  • As the temperature increases, molecules will vibrate, this may break some of the weak bonds, such as hydrogen bonds and ionic bonds that hold the tertiary structure of the active site together
  • This changes the shape of the tertiary structure and the substrate molecules will no longer fit the active site as well and the rate of reaction will therefore decrease
  • As more heat is applied the shape of the enzymes active site changes completely and irreversibly so that its no longer complementary to the shape of the substrate molecule
  • This means that the reaction can’t proceed at all as the enzymes have denatured
38
Q

Which bonds would the active sites of enzymes of organisms living in hot environments have many of?

A

Disulfide bridges, as they’re covalent bonds which can withstand high temperatures and keep enzyme’s active sites specific to the substrate that they break down or build up

39
Q

How does rate of reaction change with temperature?

A

Rate of reaction increases until optimum temperature where enzyme activity and therefore rate of reaction is at its maximum. Rate of reaction increases with temperature as substrate and enzyme molecules have more kinetic energy meaning there are more successful collisions per second and more enzyme-substrate complexes formed per second. After the temperature increases past the optimum point, the rate of reaction rapidly decreases as the tertiary structure of the active site of the enzyme is disrupted by the molecules vibrating as they have more kinetic energy as temperature increases. These vibrations break the bonds holding the tertiary structure of the active site together and therefore change the shape of the active site meaning the substrate is no longer complementary, this means that the frequency of enzyme substrate complexes being formed decreases and therefore the rate of reaction also decreases

40
Q

What is the temperature coefficient?

A

Rate of reaction at (T+10) / Rate of reaction at, this gives you the factor that rate of reaction increases by when the temperature is increased by 10

41
Q

What is the Q10 for most chemical reactions?

A

2, this means that for every 10 degrees that temperature is increased by, the rate of reaction doubles

42
Q

What is a buffer solution?

A

A solution that resists a change in pH, there are many chemicals in the blood that help resist changes in pH to ensure the pH of the blood stays in a range close to 7.4

43
Q

How does a decrease in pH affect tertiary structure of n enzyme’s active site?

A
  • Hydrogen ion concentration is increased as pH is decreased
  • The excess hydrogen ions will interfere with hydrogen bonds and ionic forces that hold the tertiary structure of the active site together, this means that the substrate will no longer be specific to the active site of the enzyme and therefore the frequency of enzyme-substrate complexes being formed decreases and therefore the rate of reaction decreases
  • The charge of the active site of the enzyme molecule will also be altered because H+ ions will cluster around the negatively charged R groups, this interferes with the binding of the substrate molecule to the active site
44
Q

How does an increase in pH affect tertiary structure of an enzyme?

A
  • Hydroxide ion concentration is increased as pH is increased
  • The excess hydroxide ions will interfere with hydrogen bonds and ionic forces that hold the tertiary structure of the active site together, this means that the substrate will no longer be specific to the active site of the enzyme and therefore the frequency of enzyme-substrate complexes being formed decreases and therefore the rate of reaction decreases
  • The charge of the active site of the enzyme molecule will also be altered because OH- ions will cluster around the positively charged R groups, this interferes with the binding of the substrate molecule to the active site
45
Q

What happens to the rate of reaction when the substrate concentration is increased?

A

There are more substrate molecules available, this means that more enzyme-substrate complexes are formed per second

  • As a result, more product molecules are formed per second and the rate of reaction increases
  • Substrate concentration is the limiting factor until substrate concentration is increased to the point where reaction rate reaches its maximum
  • At this point, substrate concentration is no longer the limiting factor as all the enzyme’s active sites are occupied with substrates
  • If more substrate molecules are added they won’t be able to successfully collide with and fit into the enzyme’s active site
46
Q

What happens to the rate of reaction as the concentration of enzyme is increased?

A
  • More enzyme active sites become available
  • This means more successful collisions occur between enzyme and substrates and therefore the frequency of enzyme-substrate complexes being formed increases and the rate of reaction therefore increases
  • Enzyme concentration is the limiting factor at this point, it is still the limiting factor until the enough enzyme is added so that the rate of reaction has reached its maximum
  • Enzyme concentration is no longer the limiting factor and adding more enzyme will no longer increase the rate of reaction as all substrate molecules will be occupying an active site
47
Q

Where is the rate of reaction highest in an enzyme catalysed reaction the highest?

A
  • The initial rate of reaction is the highest as the concentration of substrate is highest, as the reaction proceeds substrate molecules are used up as they’re converted into product molecules
  • The frequency of successful collisions decreases as some enzymes may still collide with product molecules and also there will be less substrate molecules to collide with
48
Q

What are competitive inhibitors?

A
  • Substances that have similar shapes to the substrates that are specific to the enzyme
  • They compete with substrate molecules for a place on the enzyme’s active site, when they bind they form an enzyme-inhibitor complex
  • Most enzyme inhibition by competitive inhibitors is reversible, this means that increasing the concentration of the substrate will reduce the effect of the inhibitor as there will be more chance of an enzyme molecule colliding with a substrate molecule than an inhibitor
49
Q

What is an inhibitor molecule called if it binds irreversibly to the enzyme’s active site?

A

An inactivator

50
Q

What are non-competitive inhibitors?

A
  • Inhibitor molecules that bind somewhere other than the active site
  • Non-competitive inhibitors don’t compete with substrate molecules for a place on the enzyme’s active site, they attach to the enzyme in a region known as the the allosteric site, this disrupts the enzyme’s tertiary structure and change its shape
  • This changes the shape of the enzyme’s active site meaning the substrate molecule is no longer complementary to the enzyme’s active site
51
Q

Where does a non-competitive inhibitor bind to an enzyme?

A

Its allosteric site

52
Q

What is the shape of a graph of an enzyme with a competitive inhibitor against a graph of an enzyme with no inhibitor?

A

The curve of the non-inhibitor reaches its maximum rate with a lower substrate concentration than the the curve of the competitive inhibitor, the curve of the competitive inhibitor reaches the same rate as the enzyme without an inhibitor but at a much higher concentration of substrate, this is because as the concentration of substrate is increased, there is more chance of an enzyme molecule colliding with a substrate molecule than a competitive inhibitor molecule

53
Q

What is the shape of a graph of an enzyme with a non-competitive inhibitor against the shape of a graph with no inhibitor?

A

The curve of the enzyme with the non-competitive inhibitor reaches a much lower maximum rate of reaction than the curve of the enzyme with no inhibitor. This is because adding more substrate won’t increase the rate of reaction if the active sites of the enzymes have changed shape due to the enzyme’s tertiary structure being altered. This means that the rate of reaction of the enzyme with an inhibitor can’t advance beyond a low rate of reaction

54
Q

What is end product inhibition?

A

After an enzyme catalysed reaction has reached completion, the product molecules may stay tightly bound to the enzyme and act as inhibitors. This prevents the cell from forming too much of the product and is an example of negative feedback

55
Q

How are metabolic processes controlled?

A
  • The product of one enzyme controlled reaction becomes the substrate of the next enzyme catalysed reaction
  • The product of the last enzyme catalysed reaction attaches to the allosteric site of the first enzyme, changing the shape of the enzyme and its active site, it acts as a non-competitive inhibitor, the binding of the product to the allosteric site is irreversible
  • When the concentration of the product falls, the product molecules will detach from the first enzyme’s active site restoring the active site to its original shape and therefore enabling the metabolic process to continue

Biology A Level (21 decks)

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