proteins

Question 1

what are the functions of proteins?

Answer 1

• structural: collagen (connective tissues), keratin (hair, nails, horns)
• signalling: hormone (insulin and FSH- matures egg)
• catalyst: enzymes that speeds up reactions
• transport: haemoglobin transports oxygen

Question 2

what is the structure of amino acids

Answer 2

-there are 20 different amino acids
- all have the same general structure, only the ‘R’ changes

Question 3

describe how amino acids join together

Answer 3

• condensation reaction
• removing a water molecule
• between carboxyl/COOH group of one and amine/ NH2 group of another
• forming a peptide bond
  ( amino acid is the only molecule that can lose a water molecule from a carboxyl group to undergo a condensation reaction)

Question 4

what are dipeptides and polypeptides?

Answer 4

• dipeptide: 2 amino acids joined together
• polypeptide: many amino acids joined together
  A functional protein may contain one or more polypeptides

Question 5

describe the primary structure of a protein

Answer 5

• sequence of amino acids in a polypeptide chain, joined by peptide bonds
• this is determined by your genes

Question 6

describe the secondary structure of a protein

Answer 6

• the initial folding (repeating patterns) of a polypeptide chain into an alpha helix or beta pleated sheet due to hydrogen bonding between amino acids
• between NH (group of one amino acid) and C=O (group)

Question 7

describe the tertiary structure of a protein

Answer 7

-further folding of a polypeptide into a 3D shape held together by hydrogen bonds
-due to interactions between amino acid R groups (dependent on sequence of amino acids)
- forming hydrogen bonds, ionic bonds (occurs between C=O (carboxyl) and N-H (amine groups) and disulfide (strongest) bonds

Question 8

describe the quaternary structure of a protein

Answer 8

more than one polypeptide chains bonded together e.g. haemoglobin and antibodies (hydrogen bonds, ionic bonds and disulfide bonds/bridges)
-There may also be prosthetic (non protein) groups attached to these proteins.

Question 9

describe the test for proteins

Answer 9

1. add biuret reagent (sodium hydroxide + copper (II) sulphate)
2. positive result= blue to a purple/lilac colour (indicating presence of peptide bonds)

Question 10

true or false : dipeptide has a primary structure

Answer 10

false: dipeptides is not a protein so doesn’t have a primary structure

Question 11

true or false: all hydrogen bonds are between R groups

Answer 11

false: in the secondary structure, hydrogen bonds are between NH and C=O groups

Question 12

true or false: all proteins have a quaternary structure

Answer 12

false: only proteins with more than one polypeptide chain possess a quaternary structure e.g. haemoglobin and antibodies

Question 13

What decides the amino acid sequence that determines the primary structure of a protein?

Answer 13

A DNA sequence

Question 14

Describe the ionic bonds that hold the tertiary structure of a protein in place.

Answer 14

-Weaker than disulfide bonds
-Easily broken by changes in pH
-Form between free carboxyl and amino groups in the polypeptide chain

Question 15

Describe the disulfide bonds that hold the tertiary structure of a protein in place.

Answer 15

-Strong
-Not easily broken
-Occur between two cysteine amino acids

Question 16

Name 3 fibrous type proteins

Answer 16

-Collagen
-Keratin
-Silk

Question 17

What is the monomer unit of a protein?

Answer 17

Amino acid

Question 18

What is meant by a fibrous protein

Answer 18

-A protein made from many parallel polypeptide chains. These chains main form an α helix shape.
-Fibrous proteins are usually insoluble in water.

Question 19

What is meant by a globular protein? + examples

Answer 19

-A protein made from few polypeptides, which form a spherical shape.
-They are usually water soluble.
-Enzymes, Hormones, Transport proteins e.g. haemoglobin

Question 20

Describe the hyodrogen bonds that hold the tertiary structure of a protein in place.

Answer 20

-Individually weak and easily broken
-Cumulatively provide some strength

Question 21

How can a polypeptide be broken down into amino acids?

Answer 21

hydrolysis

Question 22

Which type of bond forms between two amino acids?

Answer 22

peptide

Question 23

A change of just 1 amino acid in the primary structure of a protein can cause what to happen?

Answer 23

the shape of the protein and will stop working as well

Question 24

Name the 3 groups present on in an amino acids molecule

Answer 24

-Amino group (NH2)
-Carboxyl group (COOH)
-R-group

Question 25

What is released when two amino acids chemically join together?

Answer 25

water molecules through condensation reaction

Question 26

Give an example of a prosthetic group that is associated with a quaternary protein structure.

Answer 26

The iron containing ‘Haem’ group in the haemoglobin protein.

Question 27

2 proteins have same number and type of AA but different tertiary structure - why?

Answer 27

-different sequence of AA
therefore ionic/H/disulphide bonds form in different places

Question 28

what is the prosthetic group?

Answer 28

non-protein based molecule that aids function