2.3.1 Amino Acids & the Peptide Bond

Question 1

List the very important functions of proteins

Answer 1

1. Enzymes
2. Cell membrane components
3. Hormones (insulin and glucagon)
4. Transport proteins (hemoglobin and myoglobin)
5. Immunoproteins (antibodies)
6. Structural proteins (keratin, collagen)
7. Contractile proteins (actin and myosin)
8. Storage products (casein and ovalbumin)

Question 2

What makes the amino acids

Answer 2

A CH attached to an amino group (NH2) and to a carboxyl group (COOH) and to an R group

Question 3

What makes proteins different?

Answer 3

The R group attached to it

Question 4

How many different R groups occur in proteins?

Answer 4

20

Question 5

In order to form a peptide bond what must happen?

Answer 5

A hydroxyl (-OH) is lost from the carboxylic group of one amino acid and a hydrogen is lost form an amine group of another amino acid (condensation reaction)

Question 6

Define a dipeptide

Answer 6

molecule made up of two amino acids

Question 7

Define a polypeptide

Answer 7

molecule made up of many amino acids

Question 8

What is the primary structure of a protein?

Answer 8

The sequence of amino acids bonded by covalent peptide bonds; the DNA is responsible to determine the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence. Primary structure specific for each protein (one alteration of the sequence of amino acids can affect the whole shape and therefrore also the function)

Question 9

What is a secondary structure?

Answer 9

The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (a-helix or B- pleated sheet)

Question 10

What is the a-helix?

Answer 10

a helical structure formed by a polypeptide chain held in place by hydrogen bonds

Question 11

what is a B-pleated sheets

Answer 11

a loose sheet like structure formed by hydrogen bonding between parallel polypeptide chains

Question 12

How can the hydrogen bonds in a-helix and B-pleated sheet broken?

Answer 12

High temperatures and pH changes

Question 13

What are the additional bonds in tertiary structures?

Answer 13

1. Hydrogen (between R groups)
2. Disulphide (only between cysteine amino acids)
3. Ionic (between charged R groups)
4. Weak hydrophobic interactions (between non-polar R groups)

Question 14

What are Quaternary structures?

Answer 14

A structure in proteins that have more than one polypeptide chain working together as a functional macromolecule