2. proteins and enzymes

Question 1

what do all proteins and amino acids contain

Answer 1

Nitrogen (N), Carbon (C), and Hydrogen (H) and
oxygen (O). Some also contain sulphur (S).

Question 2

example of proteins

Answer 2

Haemoglobin,
antibodies
enzymes
actin and myosin,

Question 3

what does Haemoglobin do

Answer 3

transports oxygen

Question 4

what does antibodies do

Answer 4

defend the body against infection,

Question 5

what do enzymes do

Answer 5

are biological catalysts

Question 6

what do actin and myosin do

Answer 6

involved in muscle contraction

Question 7

what does keratin do

Answer 7

found in nails and hooves

Question 8

what does collagen do

Answer 8

is found in tendons

Question 9

what are proteins made up of

Answer 9

monomers called amino acids

Question 10

what is the general formular of an amino acid

Answer 10

H2n - C-H-R - COOH

Question 11

1. Describe the structure of proteins.

Answer 11

1. Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is order of amino acids;
5. Secondary structure is folding of polypeptide
   chain due to hydrogen bonding;
6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic/di-sulfide bonds;
7. Quaternary structure is two or more polypeptide chains;

Question 12

When a pathogen causes an infection, plasma cells secrete antibodies which destroy this pathogen.
Explain why these antibodies are only
effective against a specific pathogen.(2)

Answer 12

1. Antigens (on pathogen) are a specific shape/have specific tertiary / 3D structure;
2. Antibody fits/binds / is complementary to antigen/ antibody-antigen complex forms;
   OR
3. Antibodies are a specific shape / have specific
   tertiary/ 3D structure;
4. Antigens (on pathogen) fit/ bind/ are complementary to antibody / antibody-antigen
   complex forms;

Question 13

Describe & explain how you could use the
biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose(2)

Answer 13

Add Biuret reagent to both solutions) – no mark; Lactase / enzyme will give a purple colour;
OR
Lactose / reducing sugar will not give purple / will remain blue;
Because Lactase is a protein;

Question 14

Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.(3)

Answer 14

1. Lactose has a different
   shape/structure;
2. Does not fit/bind to active site of enzyme/sucrase;
   OR
3. Active site of enzyme/sucrase has a
   specific shape/structure;
4. Does not fit/bind to lactose;

Question 15

Describe one way that the lock and key model
is different from the induced fit model(2)

Answer 15

Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
substrate / (already) fits the substrate / is complementary (before binding);

Question 16

One enzyme will catalyse only one reaction.
Explain why.

Answer 16

1. (Enzyme has) active site;
2. Only substrate fits (the active site);

Question 17

Suggest why a protein can be the substrate for 2 different enzymes.

Answer 17

1. Different parts of the protein have different
   amino acid sequences so are a different shape;
2. Each enzyme active site is a specific shape and
   complementary to a different part of the protein;

Question 18

Diabetes mellitus is a disease that can lead to an increase in blood glucose concentration. Some diabetics need insulin injections. Insulin is a protein so it cannot be taken orally. Suggest why insulin cannot be taken orally.(2)

Answer 18

Broken down by enzymes / digested / denatured
(by pH) /too large to be absorbed;