TOPIC 2B — PROTEINS AND GENETICS

Question 1

What are proteins made of?

Answer 1

The monomers of proteins are amino acids. A dipeptide is formed when two amino acids join together.
A polypeptide is formed when more than two mino acids join together. Proteins are made up of one or more polypeptides.

Question 2

What are amino acids made from?

Answer 2

A carboxyl group (-COOH), an amine group (-NH2) and a carbon containing R group.

Question 3

How many amino acids are there in living things?

Answer 3

20 amino acids. The only difference between them is what makes up their carbon-containing R group.

Question 4

How are polypeptides formed?

Answer 4

Amino acids are linked together by condensation reactions to form polypeptides. A water molecule is released during the reaction. The bonds formed between amino acids are called peptide bonds.

Question 5

What is the primary structure?

Answer 5

The sequence of amino acids in the polypeptide chain.

Question 6

What are the four structural levels in a protein?

Answer 6

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

Question 7

What is the secondary structure?

Answer 7

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

Question 8

What is the tertiary structure?

Answer 8

More bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds. Disulphide bonds can also form. For proteins made from a single polypeptide change the tertiary structure forms their final 3D structure.

Question 9

What is the quaternary structure?

Answer 9

Some proteins are made of several different polypeptide chains held together by bonds. The quaternary structure is the way these polypeptide chains are assembled together. For proteins made from more than one polypeptide chain (e.g. haemoglobin, insulin, collagen), the quaternary structure is the protein’s final 3D structure.

Question 9

What are the kind of bonds in the primary structure?

Answer 9

Held together by the peptide bonds between the amino acids.

Question 10

What are the kind of bonds in the secondary structure?

Answer 10

Held together by hydrogen bonds.

Question 11

What are the kind of bonds in the tertiary structure?

Answer 11

Ionic bonds. These are attractions between the negative nd positive charges on different parts of the molecule.
Disulphide bonds. When two molecules of amino acid cysteine come closer together, the sulphur atom in one cysteine bonds to the sulphur in the other cysteine.
Hydrophobic and Hydrophilic interactions. When hydrophobic groups are close together in the protein, they tend to clump together, Meaning that the hydrophilic groups are more likely to be pushed to the outside.
Hydrogen bonds.

Question 12

What are the kind of bonds in the quaternary structure?

Answer 12

Tend to be determined by the tertiary structure of the individual polypeptide chains being bonded together.

Question 13

What does the amino acid sequence of a protein determine?

Answer 13

What bonds will form and how the protein will fold up into its 3D structure, e.g. if there are many cysteines, these will form disulphide bonds with each other, protein will form in a certain way.

Question 14

What does the 3D structure of a protein determine?

Answer 14

Its properties. Properties relate to its function in the body.

Question 15

What is the structure of a globular protein?

Answer 15

Globular proteins are round, compact proteins made up of many polypeptide chains.

Question 16

What is the property of a globular proteins?

Answer 16

Soluble as the chains are coiled up so that the hydrophilic parts of chains are on the outside of the molecule and hydrophobic parts of chains face inwards.

Question 17

What is the function of globular proteins?

Answer 17

E.g. Haemoglobin is a globular protein made of four polypeptide chains. Carries oxygen around the body in blood. It’s soluble so it can be easily transported in blood. Has iron-containing haem groups that bind to oxygen.

Question 18

What is the structure of a fibrous proteins?

Answer 18

Fibrous proteins are made up of long, insoluble polypeptide chains that are tightly coiled around each other to form a rope shape.

Question 19

What is the property of a fibrous protein?

Answer 19

Chains are held together by lots of bonds (e.g. disulphide and hydrogen bonds), which make the protein strong. As they are strong fibrous proteins are often found in supportive tissue.

Question 20

What is the function of a fibrous proteins?

Answer 20

E.g. Collagen is a strong, fibrous protein regar forms connective tissue in animals.

Question 21

What is an enzyme?

Answer 21

Enzymes are proteins which act as biological catalysts and catalyse metabolic reactions. Enzymes can be intracellular (catalyse reactions inside cells) or extracellular (produced and secreted by cells to catalyse reactions outside cells.

Question 22

What happens to the enzyme’s active site?

Answer 22

Enzymes have an active site, which has a specific shape. The active site is the part of the enzyme where the substrate molecules bind to. Enzymes are highly specific due to their tertiary structure.

Question 23

What is the activation energy?

Answer 23

The certain amount of energy that needs to be supplied to the chemicals before the reaction will start. Often provided as heat.

Question 23

What is the relationship between enzymes and the activation energy?

Answer 23

In a chemical reaction, enzymes lower the amount of activation energy that’s needed, often making reaction happen at a lower temperature. This speeds up the rate of reaction.

Question 24

What happens to the enzyme’s substrate?

Question 24

How does an enzyme lower the activation energy?

Answer 24

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 molecules bind breaks up more easily.

Question 25

What is the ‘lock and key’ model?

Answer 25

This is where the substrate fits into the enzymes active site in the same way that a key fits into a lock.

Question 25

What is the ‘induced fit’ model?

Answer 25

Helps to explain why enzymes are so specific and only bind to one particular substrate. Substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way.