Biological molecules (PROTEINS)

Question 1

Describe the biuret test for proteins

Answer 1

1) Add sodium hydroxide to test solution
2) Add copper sulfate
Positive test result - solution turns from blue to lilac

Question 2

What monomer is the polymer protein formed from

Answer 2

Amino acids

Question 3

Describe the structure of amino acids

Answer 3

Horizontal: N-C-C
Attached to the N - two Hs
Attached to C - one R and one H
Attached to C - double bond O and another OH

Question 4

What makes up an amino acids

Answer 4

Amino group - H2N
Carboxyll group - COOH

Question 5

What does the R mean in an amino acid

Answer 5

Variable group

Question 6

What is a dipeptide

Answer 6

2 amino acids joined together via a condensation reaction

Question 7

What is a polypeptide

Answer 7

2 or more amino acids joined together via a condensation reaction

Question 8

What is the bond called between amino acids

Answer 8

Peptide bond - forms between the OH of carboxyll and H of amino group

Question 9

What are the 4 levels of proteins

Answer 9

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

Question 10

What is the primary structure of a protein

Answer 10

The type, number and sequence of amino acids linked by peptide bonds

Question 11

Describe the secondary structure of a protein

Answer 11

The folding shape that the polypeptide chain forms as a result of hydrogen bonding into either a alpha helix or beta pleated sheet

Question 12

Give the two types of secondary structure

Answer 12

Coil into an alpha helix
Fold into a beta pleated sheet

Question 13

Describe the tertiary structure

Answer 13

The overall specific 3d shape of the polypeptide chains formed by further folding

Question 14

Give the 2 types of tertiary structure proteins

Answer 14

Globular proteins
Fibrous proteins

Question 15

Give the 3 bonds present in the tertiary structure

Answer 15

Hydrogen bonding
Disulphide bonding - form between cysteine molecules (specifically the sulphur atoms)
ionic bonds - form from ionised amine and ionised carboxyll group
Also: hydrophobic interations

Question 16

Describe the quaternary structure
(not all proteins have this, although all proteins have the first 3 structures)

Answer 16

protein made from more than 1 polypeptide chains in the tertiary structure

Question 17

Give an example of a protein that has a quaternary structure

Answer 17

Haemoglobin

Question 18

What happens if the primary structure of an enzyme is changed

Answer 18

Structure is determined by the position of amino acids. If the primary structure is changed, so is the sequence of amino acids in the polypeptide so it will cause the hydrogen/ ionic/ disulphide bonds of tertiary structure to change location so the overall 3d shape changes. This changes the shape of the active site so the enzyme is no longer functional

Question 19

What is an enzyme

Answer 19

Enzymes are tertiary structure proteins which catalyse reactions, providing a lower activation energy
Enzymes are also globular

Question 20

Describe the lock and key model for enzymes

Answer 20

The enzymes active site is complimentary to the substrate.
Enzyme and substrate collide and bond to form an enzyme substrate complex
Substrates bonds get distorted and strained, therefore lowering the activation energy
Products are then formed and released so enzyme returns to its original shape

Question 21

What makes the active site unique in an enzyme

Answer 21

The specific folding and bonding in the tertiary structure of the protein

Question 22

When an enzymes active site bonds to a substrate, what does it form

Answer 22

An enzyme substrate complex

Question 23

Describe the induced fit model of an enzyme

Answer 23

The enzymes active site is initially not complimentary to substrate
Once substrate and enzyme collide and bond to form an enzyme substrate complex, the active site changes shape so its complimentary to the substrate
This puts strain on the substrates bonds, distorting and weakening them, therefore lowering the activation energy
Products are then formed and released so enzyme returns to its original shape

Question 24

Which model is the accepted model for enzyme action

Answer 24

The induced fit model

Question 25

Enzymes are….

Answer 25

Specific - usually only catalyse one type of reaction

Question 26

What happens if the primary structure of an enzyme is changed

Answer 26

The sequence of amino acids within the polypeptide chain of the enzyme will change
This will change the location of the ionic / disulphide / hydrogen bonds within the tertiary structure
This changes the shape of the active site
Therefore enzyme substrate complexes will not be able to form as the substrate is not complimentary to active site shape
Enzyme is no longer FUNCTIONAL

Question 27

Give the effect of temperature on enzyme activity

Answer 27

If temperature is too low - there is not enough kinetic energy for successful collisions between enzyme and substrate so less enzyme substrate complexes form

Optimum temperature - many successful collisions and many enzyme substrate complexes due to more kinetic energy

If temperature is too high - enzymes denature and active site changes shape so enzyme substrate complexes cannot form

Question 28

What happens to the bonds holding the enzyme in shape once an enzyme denatures

Answer 28

They break due to the vibration of the enzyme

Question 29

Give the effect of pH on enzyme activity

Answer 29

Too high OR too low - enzyme can denature, active site change shape and less enzyme substrate complexes forming
—> this is because the changed OH- or H+ ions can interfere with the ionic and hydrogen bonds found in the enzymes tertiary structure

Question 30

Do all enzymes have an optimum pH of 7

Answer 30

No
—> all enzymes have different optimum pH it depends on where they are naturally occurring

Question 31

When do you use the -log[H+] equation

Answer 31

-log[H+] is used to calculate the pH from the hydrogen ion concentration of a solution

Question 32

At low substrate concentration, what is the limiting factor

Answer 32

Substrate concentration - not enough substrate molecules to collide with enzymes

Question 33

Describe the effect of increasing substrate concentration on enzyme activity

Answer 33

Higher the substrate concentration = faster rate of reaction
—> more substrate molecules so more collisions between enzymes active site so more enzyme substrate complexes
—> This is only true up to the ‘saturation point’

Question 34

What happens at the saturation point / V max for a graph investigating the rate of reaction with increasing SUBSTRATE concentration

Answer 34

The line plateaus as enzyme concentration becomes the limiting factor.
—> all the active sites become occupied (CANNOT say used up)

NOTE: in exams, specify this concentration

Question 35

Describe the effect of enzyme concentration on enzyme activity

Answer 35

Increasing enzyme activity increases the rate of reaction as substrates are more likely to collide with enzymes forming enzyme substrate complexes
—> however this is only true for a certain point - if the substrate concentration does not increase then enzyme concentration has no affect on rate or reaction
—> there is empty active sites due to insufficient substrate concentration so less enzyme substrate complexes

Question 36

What does the graph of rate of reaction against increasing ENZYME concentration initially show

Answer 36

Initially shows a linear relationship ( a straight line)
—> can use the gradient to determine the rate of reaction at a specific point

Question 37

What will a graph show if enzyme / substrate concentration increases alongside substrate / enzyme concentration

Answer 37

A straight line -no plateau

Question 38

What do inhibitors do

Answer 38

Stop the enzyme from functioning and producing product

Question 39

What are the two types of inhibitors

Answer 39

Competitive
Non competitive

Question 40

Describe how the competitive inhibitor works

Answer 40

Competitive inhibitor has similar shape to substrate and can bind to active site
This prevents enzyme substrate complexes from forming and reaction from occurring

Question 41

What does increasing substrate concentration do to competitive inhibitors

Answer 41

Reduces the chance of competitive inhibitors from binding to enzymes active site as they can knock them out of the active site
NOTE: on a graph for rate or reaction, the line with no inhibitor and a competive inhibitor must end at the same point

Question 42

Describe how non competitive inhibitors work

Answer 42

Non competitive inhibitors bind to the enzyme AWAY from the active site (called allosteric site)
This causes a change in the tertiary structure
This changes the shape of the active site so the substrate and enzyme can no longer bind as they are not COMPLIMENTARY

Question 43

What happens to the rate of reaction if you increase substrate concentration with non competitive inhibitors

Answer 43

Nothing - there is no effect
regardless of how much substrate you add, the enzymes active site is no longer complimentary so enzyme substrate complexes cannot form

Question 44

In a results table, which way do the dependant and independent variables go

Answer 44

Independent variable ( the one that changes) goes first ( on the left) and the dependant variable ( the actual results ) goes on the right

Question 45

What is it called when an enzyme breaks down the substrate into products

Answer 45

we say the substrate has been HYDROLYSED (or digested) into its products

Question 46

When bread becomes stale, the structure of some of the starch is changed. This changed starch is called retrograded starch.
Scientists have suggested retrograded starch is a competitive inhibitor of amylase in the small intestine.
Assuming the scientists are correct, suggest how eating stale bread could
help to reduce weight gain

Answer 46

The similar shape of the competitive inhibitor stops enzyme substrate complexes from occurring so less hydrolysis of starch into maltose so less digestion of glucose

Question 47

Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how.

Answer 47

It reduces activation energy as substrates bonds become stressed, distorted and bended

Question 48

How to work out initial rate of reaction from a graph

Answer 48

Draw a tangent when t = 0. Work out gradient of tangent. Remember to add unit ( unit will be unit of y divided by unit of x)