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A-level AQA Biology > Chapter 1: Proteins/Enzymes > Flashcards

Chapter 1: Proteins/Enzymes Flashcards

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1
Q

What are monomers of proteins?

A

amino acids

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2
Q

What is formed when two (or more) amino acids are joined together?

A

dipeptide- 2 amino acids

polypeptide- 3 or more amino acids

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3
Q

How are dipeptides/polypeptides formed?

A

amino acids undergo a condensation reaction to form peptide bonds between the amino acids

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4
Q

What is the general structure of an amino acid?

A
  • central carbon
  • carboxyl group
  • amine group (NH₂)
  • variable R group
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5
Q

How many types of naturally occuring amino acids are there?

A

20 naturally occurring amino acids

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6
Q

What makes each amino acid different?

A

the varying R group

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7
Q

What is the primary structure of a protein?

A

a sequence of amino acids in the polypeptide chains

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8
Q

What is the secondary structure of a protein?

A

interactions between amino acids in the chain cause HYDROGEN BONDING to occur
the chain is folded into an alpha helix or a beta pleated sheet

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9
Q

What is the tertiary structure for a protein?

A
  • the chain is folded or coiled even further
  • more bonds formed between different parts of the chain such as hydrogen, ionic and disulfide bonds
  • forms a 3D structure of a protein
  • forms the active site
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10
Q

What does a protein’s shape and structure determine?

A

precise structure determines function

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11
Q

What is a quaternary structure?

A

some proteins have more than one polypeptide chains held together by bonds

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12
Q

What does amphoteric mean?

A

amphoteric: have both positive and negative charges on them

being able to react both like an acid and a base

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13
Q

How is a globular protein formed?

A

proteins are amphoteric so the attraction of these opposite charges form weak electrostatic (hydrogen) bonds which forms a complex 3D structure

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14
Q

What is a globular protein?

A

compact, roughly spherical (circular) in shape and soluble in water
all enzymes and some hormones are globular proteins

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15
Q

What are fibrous proteins made from and what are one of their properties?

A

long parallel chains with cross-links

insoluble

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16
Q

What are examples of structural proteins/fibrous proteins?

A

collagen-tendons

keratin-hair/nails

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17
Q

What is the structure of collagen?

A

1ᵒ- unbranched polypeptide chain
2ᵒ- polypeptide chain is tightly wound up
3ᵒ- chain is twisted into a second helix
4ᵒ- it is made up of 3 polypeptide chains tightly coiled together, which makes it strong

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18
Q

How does denaturation occur?

A

if heated extensively or treated with strong acids/alkalis, the hydrogen bonds are broken

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19
Q

What is the biuret’s test?

A

biuret’s test works by detecting peptide bonds

  1. add a few drops of NaOH
  2. then add copper (II) sulfate solution
  3. solution turns from blue to purple
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20
Q

What is a prosthetic group?

A

a non-amino acid part of a protein

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21
Q

What is an example of a quaternary protein?

A

haemoglobin

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22
Q

What is an enzyme?

A

it is a large, globular protein that speeds up the rate of reaction without being used up in the reaction themselves

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23
Q

What effect do enzymes have on the body?

A

they catalyse anabolic (building up) and catabolic (breaking down) reactions inside and outside of the cells
they can affect structures (e.g-production of collagen) and affect functions (respiration)

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24
Q

What is the only part of the enzyme that is functional and what is it like?

A

the active site which is highly specific due to its tertiary structure
key words: specific/ complementary

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25
Q

What is needed for a reaction to start?

A

particles must collide with sufficient energy to start a reaction (activation energy)

26
Q

How do enzymes lower the activation energy? (3)

A
  • pushing molecules together (forming bonds)
  • stretching molecules (breaking bonds)
  • changing the conditions around molecules
  • creates a transition state between the enzyme and substrate that is much more stable
27
Q

Because enzymes reduce activation energy, reactions can occur at ………?

A

lower temperatures

28
Q

What are the two theories for enzyme function?

A

lock and key

induced fit

29
Q

What is the lock and key model?

A

enzymes only work with the specific substrates that are complementary to the shape of the active site
together, they form an enzyme-substrate complex

30
Q

What is the induced fit model?

A
  • the active site changes shape slightly because the substrate might not be an exact fit
  • as substrate moves into the active site, forces between the two molecules distort the active site
  • so an enzyme-substrate complex is formed
  • enzymes revert to original shape after products are released
31
Q

What are cofactors and the two types?

A

some enzymes have cofactors which are non-protein substances before they catalyze a rxn.

  1. activators
  2. coenzymes
32
Q

What are coenzymes?

A
  • they are organic molecules
  • they bind temporarily to enzyme (transferring a chemical required for the reaction)
  • e.g- vitamin C and ATP
33
Q

What are activators and examples?

A
  • inorganic groups
  • permanently bound to enzyme (type of prosthetic group)
  • e.g-iron, zinc and copper
34
Q

What happens if the tertiary structure of a protein changes?

A
  • shape of the active site is changed
  • so substrate doesn’t fit active site
  • so an enzyme-substrate complex won’t be formed
  • enzyme can no longer carry out its function
35
Q

What is a transition state?

A

unstable middle point of a reaction in a chemical reaction

36
Q

What factors affect the rate of an enzyme controlled reaction? (5)

A
  • pH
  • temperature
  • enzyme concentration
  • substrate concentration
  • presence of inhibitors
37
Q

What effect does temperature have on enzyme reactions?

A

rate increases with temp at first because reactants have more kinetic energy so they are more likely to collide
rate increases up until an optimum temperature
after the optimum, enzyme is denatured

38
Q

How are enzymes denatured by temperature ?

A

the bonds that maintain the 3D structure is broken down by the heat and there is an irreversible change in the shape of the active site

39
Q

How does pH affect rate of enzyme reactions?

A

rate increases until it reaches optimum pH

enzyme is denatured if pH is too LOW or too HIGH

40
Q

How can pH denature enzyme?

A

in highly acidic and alkaline environments, H+ and OH - ions interact with amino acids which breaks bonds and changes the shape of the active site

41
Q

What is the effect of enzyme concentration on rate of reaction?

A

rate of rxn. is directly proportional to enzyme concentration if the substrate is in excess (and as long as there are no other limiting factors)
more enzymes mean more active sites, more collisions
if substrate is limited, quickly levels off because active site outnumbers substrates

42
Q

What are inhibitors?

A

interfere and prevent enzyme activity

43
Q

What are the main 4 classes of inhibitors?

A

competitive
non-competitive
reversible
non-reversible

44
Q

What does the reversibility of an inhibitor depend on?

A

Whether the inhibitory effect on the enzyme is permanent or not

45
Q

What are competitive inhibitors?

A

molecules that have a similar shape of that of the substrate
they compete with the substrate to bind to the active site but no reaction will take place (with an inhibitor), forms and enzyme-inhibitor complex
prevents the normal reaction from taking place

46
Q

What do reversible competitive inhibitors do?

A

they bind to the active site with weak bonds (e.g- hydrogen bonds) that can easily be broken, when inhibitors leave the active site, the substrate can bind again

47
Q

What are non-competitive inhibitors?

A

do not compete with substrate for active site because they have a different shape to substrate
they bond to the allosteric site of the enzyme
this causes the active site to change shape so that substrate mol. can no longer bind to the it

48
Q

What do reversible non-competitive inhibitors do?

A

it can dissociate from the allosteric site which causes the active site to revert to its original shape and the substrate can bind normally

49
Q

Draw the graph comparing enzyme and with non/competitive inhibitors?

A

x-axis- substrate concentration
y-axis- rate of reaction
with just enzyme, normal curve (levels off)
with enzyme + competitive in. rate is slower but eventually reaches same level as enzyme
with enzyme + non-comp. rate is slower and levels off a lot lower (not much increase in rate)

50
Q

How can you mitigate the effects of a competitive inhibitor?

A

by increasing the concentration of the substrate, because it has a higher chance of binding to an active site, increasing conc of substrate increases rate, up to a point

51
Q

How can you mitigate the effects of a non-competitive inhibitor?

A

you cannot

increasing the concentration of the substrate won’t make any difference, enzyme activity will still be inhibited

52
Q

What are some uses of inhibitors?

A

-natural poisons/venom-inhibitors in venom irreversibly
block enzymes and can cause paralysis
- heavy metals are irreversible non-competitive inhibitors for metabolic reactions
-cyanide

53
Q

What is end-product inhibition?

A

when the amount of end-product is higher, non-competitive inhibitors would bind to the enzyme, blocking further production
the end-product itself can act as an inhibitor

54
Q

What is a use of inhibition?

A

enzyme inhibition is important in regulating metabolic pathways (e.g- when there is too much of a product formed)

55
Q

H. pylori cells produce an enzyme that neutralises acid

Suggest an advantage to the H. pylori of producing this enzyme.

A

to stop the cells being damaged by the stomach acid

56
Q

When mentioning a change in the shape of the active site, what must you mention before this?

A

the change in the tertiary structure so no substrates can bind to the enzyme so no enzyme-substrate complexes can form

57
Q

What is the name of a protein in the blood?

A

haemoglobin

58
Q

How do you describe/compare a typical product conc. vs time?

A
  • initial rate of reaction is faster in one graph
  • more kinetic energy
  • so more collisions, more enzyme substrate complexes formed
  • graph plateaus
  • because all substrates are used up
59
Q

Lactose free milk made after hydrolysis with lactase tastes sweeter than cow’s milk containing lactose
Suggest why?

A

because lactose is hydrolysed into glucose and galactose
so MORE sugar molecules are present
(so more receptors are stimulated)

60
Q

Explain why maltase only breaks maltose down and allows this reaction to take place at room temperature?

A

shape of maltose is complementary to shape of active site due to the tertiary structure, or similar shape, as it approaches, forces between the two changes the shape of the active site slightly so they tightly fit together, and forms an enzyme-substrate complex. It reduces the activation energy without being used up. So less energy required, enzymes push substrates together to form bonds or stretching substrates to break bonds

61
Q

Describe competitive/non-competitive inhibition (5)?

A

comp. in. have a similar shape to substrate
when they bind to active site, no substrate can fit so prevents rxn. from occurring
non.comp. bind to allosteric site
changes shape of active site
so no enzyme-substrate complex formed,
adding EXCESS substrate can affect rate of comp. but has no effect with non-comp

A-level AQA Biology (6 decks)

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