Proteins

Question 1

What is an amino acid?

Answer 1

Monomers from which proteins are made

Question 2

What is formed from the condensation of 2 amino acid?

Answer 2

One water molecule, one peptide bond and a dipeptide.

Question 3

How is a dipeptide form?

Answer 3

A dipeptide is formed through the condensation reaction of 2 amino acids, forming a peptide bond. A molecule of water is formed by the hydroxide ion from the carbonyl group of the first amino acid and the hydrogen from the amino group of the 2nd amino acid.

Question 4

How many amino acids are there and how do they differ?

Answer 4

20 amino acids.
Essential amino acids are those which the body cannot synthesis themselves and must be taken through diet.
The R group is what differs between the amino acids.

Question 5

Functions of proteins:

Answer 5

-building muscle
-making enzymes
-form receptors and antigens on cells
-form structural protein e.g. collagen in the skin
- making hormones
- forms pigments in cells e.g., haemoglobin
Amino acids sequence are determined by genes.

Question 6

Test for proteins

Answer 6

Biuret Test:
1. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide and copper sulfate at room temperature (Biuret Reagent)
Negative - blue (starting colour)
Positive - lilac/purple colouration

Question 7

Describe Primary Structure

Answer 7

Chain of amino acids held together by peptide bonds. Determine by the order of bases (sequences of codons on mRNA)
It is a polypeptide.
Changing one of the bases changes primary structure which effects folding of protein.

Question 8

Describe Secondary Structure

Answer 8

Alpha Helix (usually used for globular structures.) - hydrogen bonds between slightly negative O in C=O and slightly positive H attaché to - NH. Every 4th amino acid. Spiral. H bonds parallel to helical axis
Beta Pleated Sheet (fibrous Proteins) - hydrogen bonds form between adjacent amino acids.

The secondary structure is when polypeptide begins to fold.

Question 9

Describe Tertiary Structure

Answer 9

3D structure formed by further folding of the polypeptide.

Question 10

Bonds in Tertiary Structure:

Answer 10

Hydrogen - Weak but numerous
Ionic - relatively strong bonds between charged R groups
Disulphide Bridges - Strong. Amino acids with sulfur in R group. Covalent S-S bonds.

Question 11

Describe Quaternary Structure

Answer 11

-Functional Proteins may consist of more than one polypeptide chain
- Contain more than one polypeptide chain
- Precise 3D structures
- May have a Prosthetic group (non protein group)

Question 12

Structure and Function of Globular Proteins

Answer 12

• spherical and compact
• Hydrophilic R groups face outwards and hydrophobic R groups face inwards = usually water soluble
• Involved in metabolic processes.

Question 13

Structure and Function of fibrous Proteins

Answer 13

Can form long chains of fibre
Insoluble in water
Structure and Support.

Question 14

Describe Haemoglobin

Answer 14

• globular
• Prosthetic = haem group ferrous Iron (Fe2+)
• contain 4 polypeptide chains (2 Alpha and 2 Beta each with haem)
• Arranged in pairs - forming subunits in Proteins
• Picks up oxygen from capillaries. Reversible reaction: oxyhemoglobin
  -Only hydrogen and ionic. No sulfide bonds/bridges.

Question 15

Describe Collagen

Answer 15

-Fibrous\
- Insoluble
- no Prosthetic
- 3 polypeptides of amino acids (1000 amino acids long each)
- Strands bundle together to form fibrils.
- Hydrogen bonds
- Form covalent bonds with neighbouring collagen forming cross links.
- Many fibrils form collagen fibres
- Found outside of blood vessels, preventing wall of arteries bursting\
- Bones - made from collagen reinforced with other materials e.g., calcium phosphate to make them hard.
- Cartilage and connective tissue
-Cosmetic treatment.