Protein Structure and Enzymes

Question 1

What are proteins made from?

Answer 1

Long chains of amino acids.

Question 2

What are the monomers of proteins?

Answer 2

Amino acids.

Question 3

What is formed when two amino acids join together?

Answer 3

Dipeptide.

Question 4

What is formed when more than two amino acids join together?

Answer 4

Polypeptide.

Question 5

What is the structure of an amino acid?

Answer 5

Amino acids have the same general formula- a carboxyl group (-COOH), an amine or amino group (-NH2) and a carbon containing R group.

Question 6

How are polypeptides formed?

Answer 6

Amino acids are linked together by condensation reactions between carboxyl group of one amino acid and amino group of another. A molecule of water is released during the reaction and a peptide bond is formed.

Question 7

What four structural levels do proteins have?

Answer 7

Primary
Secondary
Tertiary
Quaternary

Question 8

What is the primary structure of a protein?

Answer 8

The sequence of amino acids in the polypeptide chain.

Question 9

What is the secondary structure of a protein?

Answer 9

Hydrogen bonds form between the amino acids in the chain. This makes it automatically coil up into an alpha helix or fold into a beta pleated sheet.

Question 10

What is the tertiary structure of a protein?

Answer 10

The coiled or folded chain of amino acids is often coiled and folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

Question 11

What is the quaternary structure of a protein?

Answer 11

The quaternary structure is the way these polypeptide chains are assembled together. For proteins made from more than one polypeptide chain, the quaternary structure is the proteins final 3D structure.

Question 12

What does the amino acid sequence of a protein determine?

Answer 12

What bonds will form and how the protein will fold up into it’s 3D structure.

Question 13

What does the 3D structure of a protein determine?

Answer 13

Its properties which relate to its function in the body.

Question 14

What is the structure of globular proteins?

Answer 14

Globular proteins are round, compact proteins made up of multiple polypeptide chains. The chains are coiled up so that the hydrophillic parts of chains are on the outside of the molecule and hydrophobic parts of chain face inwards. This makes the protein soluble so they’re easily transported in fluids.

Question 15

What is the structure of fibrous proteins?

Answer 15

Fibrous proteins are made up of long, insoluble polypeptide chains that are tightly coiled round each other to form a rope shape. The chains are held together by lots of bonds, which will make the proteins strong. Because they’re strong fibrous proteins are often found in supportive tissue.

Question 16

Why are enzymes described as biological catalysts?

Answer 16

They reduce activation energy of biological reactions to increase the rate of the reaction.

Question 17

What is the activation energy?

Answer 17

Minimum amount of energy needed to start a reaction.

Question 18

What are intracellular enzymes?

Answer 18

Enzymes which catalyse reactions inside cells.

Question 19

What are extracellular enzymes?

Answer 19

Enzymes that are produced and excreted by cells to catalyse reactions outside cells.

Question 20

What is formed when a substrate fits into the enzyme’s active site?

Answer 20

Enzyme-substrate complex

Question 21

Why does an enzyme substrate complex lower the activation energy?

Answer 21

If two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily.
If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.

Question 22

What is the active sites shape determined by?

Answer 22

The active site’s shape is determined by the enzyme’s tertiary structure which is determined by the enzymes primary structure.

Question 23

How does enzyme concentration affect the rate of reaction?

Answer 23

The more enzyme molecules there are in a solution, the more active sites are present and therefore the more likely a substrate molecule is to collide with an active site and form an enzyme substrate complex. So increasing the concentration of the enzyme increases the rate of reaction.
But if the amount of substrate is limited, there comes a point when theres more than enough enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect. Substrate concentration has become a limiting factor.

Question 24

How does substrate concentration affect the rate of reaction up to a point?

Answer 24

The higher the substrate concentration, the faster the rate of reaction. More substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be used. This is only true up until a saturation point though. After that, there are so many substrate momecules that the enzymes have about as much as they can cope with, and adding more makes no difference. Substrate concentration decreases with time during a reaction so if no other variables are changed, the rate of reaction will decrease overtime too. This makes the initial rate of reaction the highest rate of reaction.

Question 25

What happens if an enzymes tertiary structure is altered?

Answer 25

If the tertiary structure of an enzyme is altered in any way, the shape of the active site will change. This means substrate won’t fit into the active site and an enzyme substrate complex won’t be formed.

Question 26

What is the tertiary structure of an enzyme determined by?

Answer 26

The tertiary structure of an enzyme is determined by a change in pH or temperature.