Unit 4.7 - Amino Acids, Peptides and Proteins (physicsandmathstutor)

Question 1

what is an α-amino acid

Answer 1

organic molecule containing a carboxylic acid group and amine group bonded to same carbon atom

Question 2

what is a carboxylic acid group

Answer 2

COOH

Question 3

what is an amine group

Answer 3

NH₂

Question 4

why are all amino acids chiral molecules

Answer 4

Carbon atom is bonded to 4 separate groups

Question 5

which amino acid does not contain a chiral carbon

Answer 5

glycine

Question 6

how are amino acids amphoteric

Answer 6

have basic amine group
have acidic carboxylic group

Question 7

what does amphoteric mean

Answer 7

have both acidic and basic properties

Question 8

what is a zwitterion

Answer 8

dipolar ion
has a POSITIVE charge in one part of the molecules and a NEGATIVE charge in another part

Question 9

what happens when an alkali is added to an amino acid zwitterion

Answer 9

NH₃⁺ donates hydrogen ion to OH⁻ ions of alkali = water
organic compound NO LONGER zwitterion (only contains negative charge)

Question 10

what happens when an acid is added to an amino acid zwitterion

Answer 10

COO⁻ accepts hydrogen ion from acid
organic compound NO LONGER zwitterion (only contains positive charge)

Question 11

why do amino acids have relatively high melting points

Answer 11

-zwitterion is usual form that amino acid exists in
∴ strong ionic attractions between neighboring zwitterions. large amount of energy needed to break ionic attractions

Question 12

explain solubility of amino acids in water

Answer 12

soluble because strong ionic attraction form between zwitterions and polar water molecules

Question 13

how does peptide bond form

Answer 13

during a concentration reaction between 2 amino acids.
a water molecule is lost

Question 14

what is difference between dipeptide and a polypeptide

Answer 14

dipeptide = 2 amino acids
polypeptide = >2 amino acids

Question 15

how do polypeptides lead to protein formation

Answer 15

when polypeptide chains become long, they can fold into proteins

Question 16

what does primary structure of protein involve

Answer 16

the sequence of amino acids which make up polypeptide chain

Question 17

what does secondary structure of protein involve

Answer 17

protein chain can form hydrogen bonds ∴ α-helix spiral
β-pleated sheet

Question 18

what does tertiary structure of protein involve

Answer 18

further folding = fibrous/globular
- ionic bonds
- hydrogen bonds
- disulphide bridges

Question 19

give 3 examples of how proteins are essential for living systems

Answer 19

• structural functions = nails, skin, collagen
• enzymes are proteins
• some hormones are proteins(insulin)