Proteins

Question 1

draw a basic structure of an amino acid and label the different parts

Answer 1

-amino group
-carboxyl group
-variable group

Question 2

draw the reaction between 2 amino acids

reaction? products? bond?

Answer 2

-condensation reaction
-water and dipeptide
-peptide bond

Question 3

what is the primary structure of protein?

Answer 3

-the order/sequence of amino acids n the polypeptide chain joined by peptide bonds
-determines shape and function of protein
-around 20 different amino acids making different combinations

Question 4

what is the secondary structure of protein?

Answer 4

-coiling or folding of amino acid chain due to hydrogen bonds
-alpha helix or beta pleated sheets
-hydrogen bonds between c=o carboxyl group of one and H of amino group of the other

Question 5

what is the tertiary structure of protein?

Answer 5

-precise/functional shape, further folding of protein
-globular or fibrous

bonds:
-ionic - R group charged
-disulphide bridges if sulfur in R group present
-hydrogen bonds
hydrophilic or hydrophobic

Question 6

what is the order of bonds/interactions in tertiary structure according to strength?

Answer 6

disulphide-ionic-hydrogen-hydrophilic/phobic

Question 7

what is the quaternary structure of protein?

Answer 7

-a protein made up of more than one polypeptide chains
-e.g haemoglobin or collagen

Question 8

-what is a prosthetic group?
-give an example

Answer 8

-a non protein associated with a protein
-e.g haem group in haemoglobin

Question 9

compare fibrous and globular protein

Answer 9

Fibrous:
-regular repetitive sequence
-usually insoluble due to hydrophobic groups
-very strong
-cross linking of polypeptides chains by hydrogen bonds = fibrous structure
-collagen, elastin, keratin

Globular:
-tend to roll up into almost sphere
-soluble as hydrophilic groups outside on the surface
-much weaker secondary and tertiary bonds = denature
-polypeptide chains are folded in to form their specific shapes
-enzymes, hormones, insulin, haemoglobin

Question 10

describe collagen a fibrous protein
and its function

Answer 10

-fibrous tight triple helix made of three polypeptide chains
-insoluble
-glycine - 1/3 of amino acid= polypeptides can wind tightly round as glycine is the smallest R group.
-no prosthetic group
-mainly left handed helix, triple helical

Functions:
-artery walls prevented from bursting
-tendons and ligaments connecting muscles to bones stretch without snapping
-bones- collagen network hardened
-cartilage and connective tissue

Question 11

describe haemoglobin a globular protein
and its functions

Answer 11

-four polypeptide chains
-globular/round
-soluble
-made of many amino acids
-mainly alpha helix
-carry oxygen around the body
-haem prosthetic group

Question 12

what is the test for protein?

Answer 12

1. add biuret
2. positive test goes from blue to purple/lilac

Question 13

describe function and structure of insulin

Answer 13

-plays a role in blood glucose regulation
-two polypeptide chains linked by disulfide bonds
-bind to specific receptor molecules e.g glycoprotein on outside of muscle and fat cells to increase uptake of glucose from the blood

Question 14

describe the function and structure of pepsin

Answer 14

-one polypeptide chain, has many acidic R groups to withstand acidic conditions in stomach
-protein digesting enzyme to make amino acids made in the stomach

Question 15

describe the function and structure of keratin

Answer 15

-contains very high proportion of cycteine so lots of disulphide bridges
-hydrogen bonding making it very strong
-skin hair and nails where it provides mechanical protection and impermeable barrier to infection and water

Question 16

describe the function and structure of elastin

Answer 16

-in blood arteries so can stretch and recoil
-crosslinking and coiling make it strong and extensible