General properties of proteins

Question 1

What are amino acids?

Answer 1

The monomers from which proteins are made

Question 2

How are dipeptides formed?

Answer 2

The condensation of two amino acids

Question 3

How are polypeptides formed?

Answer 3

By the condensation of many amino acids

Question 4

What are the four stages of the structure in proteins?

Answer 4

• primary structure
• secondary structure
• tertiary structure
• quaternary structure

Question 5

Describe the primary structure of proteins

Answer 5

• many amino acids join together via a condensation reaction through a process known as polymerisation
• The resulting chain of many hundreds of amino acids is called a polypeptide
• polypeptide chains form the primary structure of the protein

Question 6

Describe the secondary structure of proteins

Answer 6

• carboxyl group from one amino acid bonds onto the amino group of the amino acids, forming peptide bonds and polypeptide
• the two groups form hydrogen bonds
• causing the polypeptide chain to be twisted into a S-D shape forming an alpha helix or folded into a beta pleated sheet

Question 7

Describe the tertiary structure of a protein

Answer 7

• alpha helices of secondary protein structure can be twisted and folded even more to give the protein a more specific and 3-D shape
• the structure is maintained by a number of different bonds:
  Disulfide bridges (strongest) , ionic bonds (strong but not as strong as disulfide bridges) and hydrogen bonds (weakest)

Question 8

Describe the quaternary structure of proteins

Answer 8

• many polypeptide chains bonding together
• large proteins often form complex molecules
• may be non-protein (prosthetic) groups associated with molecules

Question 9

Describe the structure and properties of fibrous proteins

Answer 9

Little or no tertiary structure
Long parallel polypeptide chains
Cross linkages at intervals forming long fibres or sheets
Usually insoluble
Many have structural roles
e.g. keratin in hair and the outer layer of skin, collagen (a connective tissue)

Question 10

Describe the structure and properties of globular proteins

Answer 10

Have complex tertiary and sometimes quaternary structures
Folded into spherical (globular) shapes
Usually soluble as hydrophobic side chains in centre of structure
roles in metabolic reactions
e.g. enzymes, haemoglobin in blood

Question 11

Is haemoglobin a fibrous or globular protein

Answer 11

Globular protein

Question 12

Is collagen a globular or fibrous protein?

Answer 12

Fibrous

Question 13

Describe the solubility of haemoglobin

Answer 13

Outward pointing hydrophilic side chains maintain solubility

Question 14

Describe the solubility of collagen

Answer 14

Usually insoluble

Question 15

Describe the prosthetic group of haemoglobin

Answer 15

• each polypeptide chain contains a haem group
• haem group is a prosthetic group
  i.e. an important permanent part of a protein molecule - not made up of amino acids
• when combined with 4 polypeptide chain it forms conjugated protein

Question 16

Describe the prosthetic group of collagen

Answer 16

Made up of three polypeptide bonds

Question 17

Describe the structure of haemoglobin including the number of chains and the way they are twisted

Answer 17

• made up of 4 polypeptide chains
• 2 identical alpha chains and 2 identical beta chains
• nearly spherical - hydrophilic side chains point inwards
• outward pointing hydrophilic side chains

Question 18

Describing the structure of collagen and the number of chains and the way they are twisted

Answer 18

• each of the three chains is a coil made up of 1000 amino acids
• H bonds form between chains giving strength
• made of 3 polypeptide chains, each in shape of a helix

Question 19

Describe the function of haemoglobin in the body including details about how its structure helps its function

Answer 19

• haem group has an iron ion at its centre
• the iron combines with oxygen at high oxygen concentrations
• and releases oxygen at low concentrations
• one haemoglobin molecule can carry 4 oxygen molecules
• colour is bright red when combined with oxygen/ purplish if not

Question 20

Describe the function of collagen in the body including details about how its structure helps its function

Answer 20

• walls of arteries prevents arteries bursting under high pressure
• tendons connect muscle to bones
• bones formed from collagen reinforced with other materials
  e.g. calcium phosphate to make them hard
• cartilage
• cosmetic treatment

Question 21

Describe the type of bonds in collagen which support the tertiary structure

Answer 21

Each collagen molecule forms covalent bonds called cross-links

Question 22

State what the major amino acid is in collagen and the reason for it

Answer 22

• Each polypeptide chain contains 1000 amino acids - every third amino acid is glycine (the smallest amoni acid)
• glycine allows the 3 polypeptides to lie closer together to form a tight coil (any other amino acids would be too big)