Proteins

Question 1

What are amino acids?

Answer 1

The basic monomer units which combine to make up the polymer polypeptides.

Question 2

What do polypeptides combine to form?

Answer 2

Polypeptides can be combined to form proteins.

Question 3

What is evidence for evolution?

Answer 3

The fact that the same 20 amino acids occur in all living organisms provides indirect evidence for evolution.

Question 4

Describe the structure of an amino acid.

Answer 4

• Central carbon atom attached to the 4 following grps:
• amino group (-NH2) - a basic group from which the amino part of the name amino acid is derived
• carboxyl group (-COOH) - an acidic group which gives the amino acid the acid part of its name
• hydrogen atom (H)
• R (side) group - a variety of different chemical groups. Each amino acid has a different R group.

Question 5

How do the 20 naturally occurring amino acids differ from each other?

Answer 5

• differ only in their R (side) group.

Question 6

Using amino acids, how can you form a dipeptide?

Answer 6

a condensation reaction (removal of H2O molecule)

The water is made by combining an -OH from the carboxyl group of one amino acid with an -H from the amino group of another amino acid.

The 2 amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.

Question 7

How can you break a peptide bond in a dipeptide molecule?

Answer 7

• using Hydrolysis (addition of water)
• to give its two constituent amino acids.

Question 8

What is polymerisation?

Answer 8

Amino acid monomers joining together through a series of condensation reactions, this process is called polymerisation.

Question 9

Describe the primary structure of an amino acid? *

Answer 9

• Polymerisation (series of condensation reactions joining together amino acid monomers)
• which leads to formation of a polypeptide.

Question 10

What are polypeptides?

Answer 10

Through a series of condensation reactions, many amino acid monomers can be joined together in a process called polymerisation.

The resulting chain of many hundreds of amino acids is called a polypeptide.

Question 11

Briefly describe the 4 structures in a protein.

Answer 11

• Primary structure is sequence/order of amino acids
• Secondary structure formed by hydrogen bonding (between amino
  acids) (a-helix/beta pleated sheet)
• Tertiary structure formed by interactions (between R groups)
• Quaternary structure contains >1 polypeptide chain OR formed by interactions/bonds between
  polypeptides

Question 12

What does the primary structure of a protein determine?

Answer 12

determines its ultimate shape and hence its function

Question 13

What can a change in just a single amino acid in the primary sequence lead to?

Answer 13

a change in the shape of the protein and may stop it carrying out its function.

In other words, a protein’s shape is very specific to its function.

Change its shape and it will function less well, or differently.

Question 14

What are the 2 basic types of proteins that determines it’s molecular shape called?

Answer 14

Globular proteins and

Fibrous proteins

It is the very different structure and shape of each of these types of proteins that enables them to carry out their functions.

Question 15

What type of functions do FIBROUS proteins have?

Give an example.

Answer 15

Fibrous proteins have STRUCTURAL functions.

e.g. Collagen

Question 16

What type of functions do GLOBULAR proteins have?

Give an example.

Answer 16

Globular proteins carry out METABOLIC functions.

E.g. enzymes and haemoglobin

Question 17

Describe the STRUCTURE of Fibrous Proteins.

Answer 17

Fibrous proteins form long chains which run parallel to one another. These chains are linked by cross-bridges and so form very stable molecules.

Question 18

Explain the structure of collagen.

Where is collagen found?

Answer 18

1°: unbranched polypeptide chain.

2°: the polypeptide chain is very tightly wound. Lots of the amino acid, glycine helps close packing.

3°: the chain is twisted into a second helix.

4°: made up of 3 such polypeptide chains wound together in the same way as individual fibres are wound together in a rope.

Collagen is found in tendons. Tendons join muscles to bones. When a muscle contracts the bone is pulled in the direction of the contraction.

Question 19

ESQ: Explain why the quaternary structure of collagen makes it a suitable molecule for a tendon.

(from the Kerboodle textbook)

Answer 19

The individual collagen polypeptide chains in the fibres are held together by bonds between amino acids of adjacent chains.