Amino Acids And Proteins

Question 1

Describe the general structure of an amino acid

Answer 1

CHIRAL CARBON with 4 distinct groups:

• H
• NH2 at N terminal
• COOH at C terminal
• R group (different for each AA)

Question 2

Which sterioisomer is naturally found in amino acids and why?

Answer 2

• TRANS (L-form)

- Cannot be superimposed

Question 3

What does the solubility of a protein depend on?

Answer 3

• POLARITY

- Ability to form hydrogen bonds with water molecules

Question 4

Define AMPHIPATHIC and explain how amphipathic molecules behave in aqueous solution

Answer 4

• Amphipathic molecules have both POLAR AND NON-POLAR regions
• In aqueous solution hydrophobic non polar regions cluster together and hydrophilic polar molecules interact with water
• FORMATION OF A MICELLE

Question 5

Give 5 examples of the roles of proteins in the body

Answer 5

• Biological catalysts (e.g. Enzymes)
• Structural support (e.g. Collagen)
• Ion channels (e.g. Na+ channels in plasma membrane)
• Transporters (e.g. Haemoglobin)
• Receptors (e.g. Hormones, neurotransmitters)

Question 6

Explain how an amino acid can be ionised

Answer 6

• ZWITTERION
• When placed in acidic solution -NH2 —> -NH3+
• When placed in alkali solution -COOH —> -COO-

Question 7

Describe how amino acids can be classified

Answer 7

• Classified according to chemical properties of R groups

- Non polar, Polar (uncharged) and Polar (charged)

Question 8

Describe the features of a NON-POLAR amino acid

Answer 8

• HYDROPHOBIC
• Overall charge = 0
• Can be aliphatic or aromatic

Question 9

Give 5 examples of non-polar amino acids

Answer 9

• Glycine
• Leucine
• Phenylalanine
• Tryptophan
• Valine

Question 10

What is the difference between ALIPHATIC and AROMATIC?

Answer 10

• ALIPHATIC molecules consist of long chain/branched hydrocarbons
• AROMATIC molecules contain a benzene ring

Question 11

How can some molecules be polar but have no overall charge?

Answer 11

• Contain polar groups that can interact with water

- Big bulky side chains

Question 12

Give 5 examples of POLAR, UNCHARGED amino acids

Answer 12

• Serine
• Asparagine
• Tyrosine
• Threonine
• Cysteine

Question 13

Give 5 examples of POLAR, CHARGED amino acids and state their overall charge

Answer 13

• Lysine (+ve)
• Histindine (+ve)
• Arginine (+ve)
• Aspartate (-ve)
• Glutamate (-ve)

Question 14

Explain how the pH of a solution will affect the structure of the amino acid

Answer 14

• pH > pKa then amino acid group will be DE-PROTONATED

- pH

Question 15

Describe the formation of a peptide bond

Answer 15

CONDENSATION REACTION of -COOH group on one amino acid and -NH2 group on another amino acid

Question 16

What are the properties of a peptide bond?

Answer 16

• Rigid
• Planar
• COVALENT

Question 17

Define the ISOELECTRIC POINT (pI) of a protein

Answer 17

pH at which the protein has NO OVERALL NET CHARGE

Question 18

How could you predict the overall net charge of a protein at physiological pH (7)?

Answer 18

• pH > pI protein will be DE-PROTONATED so will be -ve charged (ACIDIC)
• pH

Question 19

Name 4 types of intermolecular forces commonly found in biological molecules

Answer 19

• Hydrogen bonding
• Ionic bonding
• Van der Waals forces
• Hydrophobic interactions
• (Disulphide bonds - between cysteine residues)

Question 20

What is meant by a CONJUGATED PROTEIN?

Answer 20

Contains COVALENTLY LINKED chemical components in addition to amino acids e.g. Haem groups in haemoglobin, lipids in lipoproteins