Module 1 - Proteins

Question 1

What is a protein?

Answer 1

Proteins are a diverse group of large and complex polymer molecules made up of a long chain of amino acids.

Question 2

They have a wide range of biological roles including:

Answer 2

Structural = main components of body tissue
Catalytic = all enzymes are proteins that catalyse many chemical reactions
Signalling = many hormones and receptors are proteins
Immunological = all antibodies are proteins. Help with immunity

Question 3

What is the ‘R’ group?

Answer 3

Represents a side chain from the centre of the alpha carbon atom, and can be anything from a simple hydrogen to a complex ring sturcture.

Question 4

What are polypeptides?

Answer 4

long chains of amino acids

Question 5

What is the bond formed between two amino acids?

Answer 5

Peptide bond

Question 6

What is the reaction that forms peptides bonds?

Answer 6

Condensation reaction

Question 7

Describe the reaction between 2 amino acids

Answer 7

Condensation reaction between 2 amino acids forming one peptide bond. The reaction site takes place at the carboxylic and the amine group (specifically the reaction between the hydroxyl in the carboxylic group and hydrogen in the amine group).

Question 8

What forms from the condensation of 2 amino acids

Answer 8

Dipeptides

Question 9

Describe the primary structure of proteins

Answer 9

The sequence of amino acids in a polypeptide chain form the primary structure of any protein. Many of the 20 amino acids in a polypeptide chain joined in different sequences, limitless combos and so limitless primary protein structures. Determines shape and function.

Question 10

Describe the secondary structure of proteins

Answer 10

Linked amino acids in a polypeptide bond possess -NH and -C=0 group. H of -NH is positive charge, O of -C=O is negative charge. Form weak bonds, called hydrogen bonds. Causes the long polypeptide to be twisted into a 3D shape (a-helix)

Question 11

Describe the tertiary structure of proteins

Answer 11

The a-helixes of the secondary structure can be twisted even more to form an even more complex structure, 3D shape of a protein. Structure maintained by number of different bonds.

Question 12

The role of hydrogen bonds - teritary sturcture

Answer 12

Makes each protein distinctive and allows it to recognise and to be recognised by other molecules.

Question 13

The role of Ionic bonds - tertiary structure

Answer 13

Formed between carboxyl and amino acid groups that are not involved in forming peptide bonds. Weaker than disulfide bonds and easily broke by change in pH

Question 14

The role of disulfide bonds - tertiary structure

Answer 14

Fairly strong and so are not easily broken

Question 15

Quaternary structure of a protein

Answer 15

Large proteins form complex molecules containing a number of individual polypeptide chains linked in many ways. Non-protein groups associated with the molecules called prosthetic groups

Question 16

What is the name of the test for proteins? What does it detect?

Answer 16

Biuret test. Detects peptide bonds

Question 17

Describe the biuret test in proteins

Answer 17

Place a sample of solution into a test tube and add an equal volume of sodium hydroxide solution at room temp. Add a few drops of very dilute copper sulfate solution and mix gently. Purple colour indicates presence of peptide bonds. If no protein present, colour remains blue

Question 18

What causes the changes in protein structure through the three or four levels of structure?

Answer 18

The primary chains form a-helix and b-pleated sheets which fold onto each other forming the tertiary structure.

Question 19

How does a chaperone work with proteins?

Answer 19

Chaperones assists proteins in folding

Question 20

What are 2 characteristics of globular proteins?

Answer 20

Spherical proteins that are soluble in water

Question 21

How are globular proteins soluble in water?

Answer 21

Globular proteins have hydrophilic amino acids on their surface. This means that hydrophilic ‘R’ group of the amino acid can interact with water. Hydrophobic amino acids in centre of amino acids.

Question 22

Give 3 characteristics of fibrous proteins

Answer 22

They play a structural role, long-rope like molecules and insoluble in water

Question 23

Why are fibrous proteins insoluble in water?

Answer 23

High proportion of amino acids with hydrophobic R groups meaning it repels water and so they are insoluble in water

Question 24

Describe collagen

Answer 24

Strong as polypeptide chains wrap tightly forming triple helix. Large number of hydrogen bonds between polypeptide chains which stabilises quaternary structure forming microfibrils and fibrils.

Question 25

Describe Keratin

Answer 25

Strong and insoluble that are long strained molecules. High amount of amino acid cysteine used to form large number of disulfide bonds.

Question 26

Describe Elastin

Answer 26

Elastic and can stretch. Long strands containing hydrophobic regions. The strands are crosslinked with each other.