Proteins

Question 1

What elements do proteins contain?

Answer 1

Carbon, hydrogen, oxygen, nitrogen and sometimes sulphur.

Question 2

How many amino acids are there?

Answer 2

20, which can all be arranged in different sequences.

Question 3

What do amino acids consist of?

Answer 3

An amino group.
A carboxylic acid group
A hydrogen atom.
A residue (R group).

Question 4

What does an amino acid look like generally?

Answer 4

R
H        |       O
    \      |     //
     N--C--C
     /      |      \
    H     |       OH
            H

Question 5

What are some of the features of R groups?

Answer 5

Some of the residues carry a charge and so may be involved in hydrogen bonding.
Some are hydrophobic (water hating).
A few contain sulphur.

Question 6

What is formed when two amino acids bond together?

Answer 6

A dipeptide. A condensation reaction is involved and the amino acids are linked by a covalent peptide bond.

Question 7

What is the primary structure of a protein?

Answer 7

Many amino acids are peptide-bonded together to form a polypeptide. This is this sequence of amino acids in the chain. The polypeptide has an amino group (NH2) at one end and a carboxyl group (COOH) at the other.

Question 8

What is the secondary structure of proteins?

Answer 8

Is either an alpha helix or beta pleated sheets. The structures are held in place by hydrogen bonds between peptide links in adjacent parts of the chain.

Question 9

What is the tertiary structure of proteins?

Answer 9

The further folding of proteins in a precise way to produce a specific three dimensional structure. This is due to the interaction between the free r groups of the amino acids. Different r groups produce specific links to each other.

Question 10

What is the quarternary structure of proteins?

Answer 10

This is when two or more polypeptide chains are bonded together.

Question 11

What type of protein is haemoglobin?

Answer 11

A globular protein found in red blood cells. Each molecule consists of four polypeptides, two alpha chains and two beta chains. Each polypeptide has an iron containing haemoglobin attached.

Question 12

What type of protein is collagen?

Answer 12

A fibrous protein. Each molecule consists of three similar polypeptides coiled around each other and held together by hydrogen bonds. Collagen molecules are bonded together to form strong fibres found in the skin, tendons and ligaments.

Question 13

What types of bonds are found in the secondary structure?

Answer 13

Hydrogen bonds between the amino and carboxyl group.

Question 14

What types of bonds are found in the tertiary structure?

Answer 14

Hydrogen bonds.
Ionic bonds, are formed between amino and carboxyl groups in some of the amino acid r groups. They are stronger than hydrogen bonds but are damaged by changes in pH.
Disulphides bridges, are covalent bonds formed between R groups of sulfur containing amino acids. They are very strong.
Hydrophobic interactions, involving amino acids with hydrophobic r groups, which tend to take up positions within the molecule surrounded by other parts of the polypeptide as opposed to water.

Question 15

Give examples of prosthetic groups.

Answer 15

Glycoproteins - carbohydrate
Lipoproteins - lipid
Nucleoprotein - Nucleic acid

Question 16

What are prions?

Answer 16

Malformed proteins which are the agents that cause diseases.

Question 17

What are prions involved in?

Answer 17

Synoptic transmission.

Question 18

What are all the prion diseases and for what animal?

Answer 18

Cows - Bovine Spongiform Encephalopathy or mad cow disease.
Sheep - Scrapie
Humans - Creutzfeldt-Jacob disease.

Question 19

What does a prion protein disease involve?

Answer 19

The replacement of normal, cell surface glycoprotein that is located on the cell surface of a variety of cells, particularly neurones within the brain or spinal cord, with a structurally altered prion form. The secondary structure of normal prions is mostly composed of alpha helices, whereas disease causing prions are rich in beta pleated sheets.

Question 20

How do prion diseases arise?

Answer 20

Transmission through consumption of infected food or via an open wound. There is evidence that sheep prions affect cattle and cattle prions affect humans.
Inheritance of a gene mutation that would have occurred during meiosis in the production of an egg or sperm cell. The mutant gene codes for the synthesis of the misshapen prion protein. These account for 15% of all CJD cases.
Sporadically, whereby the normal protein spontaneously transforms into the disease form. There is no evidence of it being transmitted or being inherited. Sporadic prion disease accounts for 80% of all cases of CJD.