4.7 - Amino acids, peptides and proteins

Question 1

What are amino acids

Answer 1

Contain both NH2 (amine) and COOH (acid) group

       H
       |   R   -   C   -   COOH
      |
       NH2

Question 2

What are alpha amino acids

Answer 2

Alpha amino acids are those with a NH2 and COOH group attached to the same carbon, they are found and used in nature

Glycine
H
|
H - C - COOH
|
NH2

Alanine
H
|
CH3- C - COOH
|
NH2

All alpha amino acids apart from glycine form optical isomers from their chiral centre

Question 3

What are the trends of melting points and solubility in amino acids

Answer 3

Amino acids have a higher boiling point and solubility than expected, they can form ZWITTER IONS so have increased ionic character

This occurs at around 1 isoelectric point
When H+ is added and pH decreases (acidic)

     H          C 
    |           || H -  C    -      C 
   |            |
  NH3+    OH 

When OH- is added and pH increases (basic)

       H           O 
       |           || H  -    C      -     C
       |            |
     NH2        O-

Question 4

What are dipeptides

Answer 4

Dipepetides are two amino acids joined together by a condensation reaction forming amide linkages
- if amino acids are different there are two different potential dipeptide structures

eg. Glycine and cysteine
COOHCH2NH2 + COOHCHNH2CH2SH > NH2CH2C=O-NHCH(CH2SH)COOH + H2O

Question 5

What are polypeptides and proteins

Answer 5

• when multiple amino acids join together they form peptide chains
• large chains are proteins

Proteins have a wide range of jobs in the body
Including muscles and enzymes

Question 6

Why are some of the functions of proteins

Answer 6

• brewing: yeast + amylase/ glucose to breakdown plants
• biological washing powder
• cheese - renin/renet

Question 7

What are the three protein structures

Answer 7

1. Primary
   - the order of amino acids within a chain
2. Secondary
   - the shape of chains, caused by hydrogen (protein folding)
3. Tertiary
   - the arrangement of chains relative to each other
   Alpha helix and beta pleated sheets

Held together by hydrogen bonds and sulphur bridges