PowerPoint Presentation on Primary Protein Structure

1. Primary Structure – the sequence of amino acids
PROTEIN STRUCTURE

2. PRIMARY STRUCTURE
 Sequence of amino acids in protein linked by
covalent amide (peptide) bonds

3. CONDENSATION AMINO ACIDS: AMIDES OR
PEPTIDE BONDS
O O O
H2N C + H2N C + H2N C Amino acids condense
HC OH CH OH
CH2 OH
to form amides – or
CH3 alanine glycine glutamine CH2
H2C peptide bonds
Peptide or amide bond C
H2N O
O
+ O Protein chain made up
H3N C H O
HC N C of amino acids
H HC N C - covalently bonded by
CH3 CH O
CH3
CH2
amide bonds
H2C
C
H2N O

4. SEQUENCE MATTERS
 Functioning proteins have
O O
O
unique primary structure –
H2N C + H2N C + H2N C
sequence of amino acids
HC OH CH2 OH CH OH
CH3 alanine glycine glutamine CH2
in the chain
H2C
 This primary sequence
Peptide or amide bond C determines how the
H2N O
O protein folds into 3-D
O
H3N
+
C H O shape required for protein
HC N C
H HC N C -
function
CH3 CH O
CH3  Sequence has a free
N-terminal amino acid CH2 C-terminal amino acid
H2C amino end (N-terminal
alanine (free amino end) glutamine (free carboxyl end)
C
amino acid)
H2N O
 Sequence has free
carboxyl end (C-terminal
amino acid

5. SEQUENCE MATTERS
O O O
H2N C + + H2N  When 3 amino acids
H2N C C
HC OH CH2 OH CH OH reacted together, 6
CH3 alanine glycine glutamine CH2 possible different
H2C
tripeptides result
C
H2N O
Possible sequences
 Sequence of amino acids
in proteins determined by
ala-gly-gln
sequence of nucleotides
ala-gln-gly on m-RNA, which is
gly-ala-gln transcribed from DNA
gly-gln-ala
gln-ala-gly
gln-gly-ala

6. Vasopressin (antidiuretic
hormone
• 9 amino acid polypeptide
forms cyclic structure
• N terminal amino acid:
glycine
• No C terminal amino acid
(due to ring structure)
• Conserves body fluids
, reduces loss of water in
urine
• Leads to constriction of
blood vessels, increase in
blood pressure
POLYPEPTIDE HORMONES

7. Oxytocin
• 9 amino acid polypeptide with
cyclic structure
• N-terminal amino acid: glycine
• No C-terminal amino acid
• Well studied effects:
• Stimulates milk production
• Stimulates muscle contraction
for birth
• Promotes maternal behavior
• Possible association with
development of human
bonding an interpersonal
relationships
• Compare structure to
vasopressin: 2 amino acids
different – very different
physiological effects!
POLYPEPTIDE HORMONES

8. Lysozyme
• Enzyme breaks down
bacterial cell walls
• Found in egg
whites, human tears
• Single polypeptide chain
of 129 amino acids
• N-terminal amino acid is
lysine
• C-terminal amino acid is
leucine
Disulfide bonds considered
to be part of tertiary
structure.
PROTEIN PRIMARY STRUCTURE