Proteins

Question 1

What is the structure of an amino acid

Answer 1

• an amino acid consists of a carboxyl group which is OH+O+C A hydroxide, an oxygen, joined to a carbon
• a amine group which consists of H+H+N, 2 Hydrogens joined to a nitrogen
• and another carbon with 1 hydrogen and a variable R group which has 21 different possibilities

Question 2

Describe the formation of a peptide bond

Answer 2

1- the hydrogen from the amine group of the first amino acid is cleaved by and enzyme
2- the hydroxide of the carboxyl group of the second amino acid is cleaved by another enzyme
3- a different enzyme catalysts the forming of a peptide bond between the carbon on the carboxyl group of the second amino acid and the nitrogen of the amine group of the fist amino acid

Question 3

Why is the forming of a peptide bond called a condensation reaction

Answer 3

• because the hydroxide and the hydrogen that were cleaved from the amino acids bond to make water

Question 4

Define primary structure of a protein and name the bonds involved

Answer 4

• the primary structure is the sequence of amino acids joined by peptide bonds

Question 5

Define the secondary structure of a protein and name the bonds involved

Answer 5

• this is the regular shape taken up by parts of a polypeptide chain eg alpha helix, beta pleated sheet
• the bonds involved are hydrogen bonds between DELTA NEGATIVE CO on one amino acid and DELTA POSITIVE NH on another

Question 6

Define tertiary structure of a protein and name the bonds involved

Answer 6

• this is the overall 3D shape of a protein
• this is formed by:
  •hydrogen bonds between polar R groups
  •ionic bonds between oppositely charged R groups
  •(covalent) di-sulphide bridge between 2 cysteines
  •hydrophobic interaction between hydrophobic R groups

Question 7

Define quaternary structure and name the bonds involved

Answer 7

• The arrangement of two or more polypeptide chains that associate together to form a protein molecule
• bonds involved are hydrogen, ionic, di-sulphide bridge, hydrophobic

Question 8

What is a conjugated protein

Answer 8

• this is the protein that contains regular polypeptide chain(s) that bond to a prosthetic group
• eg quite a lot of enzymes

Question 9

What is a globular protein

Answer 9

• compact, water soluble, usually spherical in shape
  -a variety of amino acids
• usually have hydrophilic R groups on their exterior so that they can interact with water
• mainly metabolic roles
  -examples are
  •hormones such as insulin (needs a specific shape)
  •enzymes
  •haemoglobin

Question 10

What are fibrous proteins

Answer 10

• formed from long insoluble molecules (hydrophobic R groups)
• high proportion of the same amino acid, very linear structure
• they are strong, they have structural roles eg
  •keratin, found in nails and hair, made with high proportion of cysteine which makes lots of disulphide bridges
  •elastin, found in elastic fibres in the blood vessels, and in alveoli
  • collagen, connective tissue found in the skin, tendons, 3 proteins structures wound about each other, flexible, high tensile strength,