Proteins

Question 1

Proteins

Answer 1

Proteins have a variety of functions within all living organisms.
They are very large molecules (polymers) made up of amino acids (monomers)

Question 2

General structures of an Amino Acids

Answer 2

• The R group is attached to central carbon
• Each R side chain has a different structure to it
• There are 20 different types of amino acid
• It is only the R group which differs in each case

Question 3

Formation of Polypeptides

Answer 3

Can be repeated many times with amino acids being added to produce polypeptide chains which may contain thousands of amino acids
Hydrolysis will break up a polypeptide and release the amino acids. This happens in digestion

Question 4

Primary structure

Answer 4

The sequence of amino acids held with peptide bonds

Question 5

Secondary structure

Answer 5

The folding of the polypeptide chain:
>coiled to form an alpha-helix
>folded to form beta-pleated sheets
-Held with hydrogen bonds

Question 6

Tertiary structure

Answer 6

This is the folding up of the alpha-helix to form a precise three-dimensional shape. Bonds may form between the R groups of the amino acids which find themselves close together. The shape is maintained by 4 types of bonds:

• hydrogen bonds
• ionic bonds
• disulphide bonds
• hydrophobic bonds

Question 7

Quaternary structure

Answer 7

This is two or more polypeptides held together e.g. insulin has 2 chains, haemoglobin and antibodies have 4
-Held with hydrogen bonds

Question 8

Fibrous proteins

Answer 8

-polypeptide chains don’t fold but remain as straight chains with several chains cross-linked (H bonds)
-secondary structure only - straight chains which can be linked by H bonds (quaternary structure)
-Insoluble
-Very stable and strong
Important for structures and strength e.g.
>tendons, skin - collagen
>hair, beaks, claws - keratin
>silk
>muscle contractile proteins

Question 9

Globular proteins

Answer 9

• polypeptide chain(s) are highly folded given compact 3D-shape
• tertiary structure and quaternary structure
• not very stable; tertiary structure easily disrupted (denatured)
• Important where precise shapes are required for molecular interactions e.g.
• enzymes
• transport proteins - haemoglobin
• hormones
• antibodies
• receptors
• plasma proteins

Question 10

Collagen

Answer 10

Fibrous protein found in skin and tendons. Provides strength and toughness
Made up of 3 polypeptide chains held with