Proteins

Question 1

Proteins

Answer 1

• contain carbon, hydrogen, oxygen and nitrogen
  - some contain sulphur and phosphorus
• made of amino acids.
  - chain of amino acids is a polypeptide

Question 2

Structure of amino acids

Answer 2

attached to a carbon is:
- an amino group – NH2 ( N-terminal)
- a carboxyl group – COOH ( C-terminal )
- a hydrogen atom – H
- the R group – R (which is the variable)

Question 3

Formation of a peptide bond

Answer 3

• proteins are linear sequences of amino acids
• the amino group of one amino acid reacts with the carboxyl group of another, with the elimination of water
  - condensation reaction
  - forms a peptide bond
  - makes a dipeptide

Question 4

Protein structure - primary

Answer 4

• this is the order of amino acids in a polypeptide chain
• the order is decided by the DNA
• the bond between each amino acid is a peptide bond

Question 5

Protein Structure - secondary

Answer 5

• this is the shape that the polypeptide chain forms due to hydrogen bonds
• hydrogen bonds twists and fold the polypeptide forming an alpha helix, or beta pleated sheet

Question 6

Protein structure - tertiary

Answer 6

• the alpha helix is further folded into a more complex, compact 3D structure.
• shape is maintained by disulphide, ionic bonds
• enzymes have a tertiary structure
  - the bonds maintain the shape of the
  enzymes active site

Question 7

Protein structure - quaternary

Answer 7

• comes from a combination of two or more polypeptide chains in tertiary form
• associated with non-polar groups and form large complex molecules, e.g. haemoglobin
  - has four polypeptide chains
  - four gene are needed to code for
  haemoglobin, one gene for each
  polypeptide

Question 8

Fibrous protein

Answer 8

• have long thin molecules
  - makes them insoluble in water
• the polypeptide are in parallel chains, with many cross-links forming long fibres
  - e.g. keratin in hair
• strong and tough
• a single fibre, consists of three identical polypeptide chains twisted around each other. #
  - linked through hydrogen bonds, making
  them very stable

Question 9

Globular protein

Answer 9

• compact
• folded into spherical protein and are soluble in water, and have many functions
  - hormones, enzymes
• haemoglobin is a globular protein
  - four folded polypeptide chains
  - iron-group, haem at the centre

Question 10

Test for protein

Answer 10

• add a few drops of sodium hydroxide and copper(ll) sulphate
• these react to make blue copper hydroxide.
• if a protein is present, the copper hydroxide interacts with the peptide bond in the protein to make buiret
• colour change from blue to purple