Proteins

Question 1

Name the functional groups in an amino acid

Answer 1

COOH- carboxyl group, NH2- amino group, R group

Question 2

What is an R group?

Answer 2

A functional group. This is the section that is different on each of the 20 amino acids and gives them their properties

Question 3

How many naturally occurring amino acids are there?

Answer 3

20

Question 4

What bond is formed by a condensation reaction between amino acids?

Answer 4

Peptide

Question 5

What is primary protein structure and what bonds hold it in place?

Answer 5

A sequence of amino acids linked by peptide bonds

Question 6

What is secondary protein structure and what bonds hold it in place?

Answer 6

Folding of primary structure into an alpha helix or a beta pleated sheet. This is held by hydrogen bonds between H and O that are not in the R groups

Question 7

What is tertiary protein structure and what bonds hold it in place?

Answer 7

Further folding into a complex and specific 3D structure. This is held by disulphide, ionic, hydrogen and hydrophobic bonds between R groups

Question 8

What are ionic bonds in polypeptides between?

Answer 8

Positively and negatively charged R groups

Question 9

What are disulphide bonds in polypeptides between?

Answer 9

They are strong covalent bonds between sulphur atoms in the R groups of two cysteine amino acids

Question 10

What are hydrogen bonds in tertiary structure of polypeptides between?

Answer 10

They are between hydrogen and oxygen atoms in the R groups of two amino acids

Question 11

What are hydrophobic interactions in polypeptides?

Answer 11

Hydrophobic non polar R groups cluster in the centre of a globular polypeptide to stay away from water. Hydrophilic polar R groups will be on the outside. This makes globular proteins soluble.

Question 12

What is quaternary protein structure and what bonds hold it in place?

Answer 12

Two or more polypeptide chains in tertiary form bonded together. This is held by disulphide, ionic, hydrogen and hydrophobic bonds between R groups

Question 13

Are enzymes, antibodies and hormones globular or fibrous?

Answer 13

Globular, as they must be soluble

Question 14

Name a fibrous protein

Answer 14

Collagen, keratin

Question 15

What are the features of fibrous proteins?

Answer 15

Fibrous proteins form long chains. They have regular, repetitive sequences of amino acids. Usually insoluble in water. They tend to have structural roles

Question 16

What are the features of globular proteins?

Answer 16

Compact ball like shape. Hydrophobic R- groups towards the centre of the protein and hydrophilic R -groups on the outside. Contain a wider range of amino acids. They are usually water soluble and end to have a metabolic role

Question 17

Give an example of a globular protein

Answer 17

Haemoglobin

Question 18

What is a prosthetic group?

Answer 18

A non protein functional group within a protein. For example the haem groups in haemoglobin are functional groups containing an iron ion

Question 19

What is the structure of haemoglobin?

Answer 19

Haemoglobin consists of 4 polypeptide chains. There are 2 alpha chains and 2 beta chains. Each chain has a haem group which contains a Fe2+ ion.

Question 20

What is the structure of collagen?

Answer 20

Each molecule contains three identical alpha helices wound around each other to form a triple helix. Every third amino acid is glycine (the smallest R group). The three chains are held together by H-bonds. Molecules have covalent bonds cross linking them to make collagen strong

Question 21

What happens to a protein when you heat it?

Answer 21

Heating a protein increases the kinetic energy in the molecules. This can lead to atoms vibrating and the weak hydrogen bonds may break. This can lead to the whole tertiary structure unravelling and the protein being permanently denatured.