Download Option B2 Proteins

OPTION B: Human Biochemistry
B2: Proteins
Objectives
B.2.1 Draw the general formula of 2-amino acids
B.2.2 Describe the characteristic properties of 2amino acids.
B.2.3 Describe the condensation reaction of 2-amino
acids to form polypeptides
B.2.4 Describe and explain the primary, secondary,
tertiary structure of proteins.
B.2.5 Explain how proteins can be analysed by
chromatography and electrophoresis.
B.2.6 List the major functions of proteins in the
body.
Jan 3, 2010




Natural polymers made by amino acids.
Proteins important to humans are made
of
20 α-amino acids (in data booklet)
Essential amino acids: amino acids our
body cannot synthesize (10)
Complete protein: a protein made of
essential amino acids, e.g. casein (milk,
eggs, soybeans)
Human Biochemistry
Jan 3, 2010
3
Human Biochemistry
Jan 3, 2010
4
Human Biochemistry
Jan 3, 2010
5
Human Biochemistry
Jan 3, 2010
6
Human Biochemistry
Jan 3, 2010
7
>At isoelectric point
>identical ionizations
>only zwitterion
>H3N+-CHR-COO- form
>no net charge
H++ H2N-CHR-COO-← H3N+-CHR-COO- → H3N+-CHR-COOH + OH>At high pH
>Extra OH- reacts with H+
>[H+] drops
>Equilibrium shifts to the left
>At low pH
>Extra H+ reacts with OH>[OH- ] drops
>Equilibrium shifts to the right
>H2N-CHR-COO- form
>negative charge
>H3N+-CHR-COOH form
>positive charge
Human Biochemistry
Jan 3, 2010
8
H3N+-CHR-COO- + H+→ H3N+-CHR-COOH + H2O
>when H+ is added
>equilibrium shifts to right
>[H+] drops
>pH remains the same
>buffer action
>when OH- is added
>equilibrium shifts to left
>[OH-] drops
>pH remains the same
H2O + H2N-CHR-COO-← OH- + H3N+-CHR-COO-
>buffer action
Human Biochemistry
Jan 3, 2010
9
Human Biochemistry
Jan 3, 2010
10
Acid
Right
Amino
Left
Human Biochemistry
Jan 3, 2010
11
Primary structure
>sequence of amino acids
>characteristic of protein function
Secondary structure
>folding of polypeptide chain
>by Hydrogen bonds
α-helix: between atoms of the same chain, e.g. hair,
wool
pleated sheet: between parallel chains, e.g. silk
random coil: no repeating pattern
Tertiary structure
>3D shape of secondary structure
> several types of interaction
Quaternary structure
>3D shape of tertiary structures of different
polypeptide chains
Human Biochemistry
Jan 3, 2010
12
Human Biochemistry
Jan 3, 2010
13
Tertiary structure
Myoglobin
Human Biochemistry
Jan 3, 2010
14
Quaternary structure
Haemoglobin
Human Biochemistry
Jan 3, 2010
15
Human Biochemistry
Jan 3, 2010
16
Human Biochemistry
Jan 3, 2010
17






Structural (collagen, keratin)
Catalysts (enzymes)
Hormones (insulin)
Antibodies (interferons)
Transport (haemoglobin)
Energy (from muscles)
Human Biochemistry
Jan 3, 2010
18
Human Biochemistry
Jan 3, 2010
19
Rf =
distance traveled by compound
distance traveled by solvent
Rf is specific for each amino acid
Human Biochemistry
Jan 3, 2010
20
>At isoelectric point (pH of buffer)
>identical ionizations
>only zwitterion
>H3N+-CHR-COO- form
>no net charge
>not affected by electric field
H++ H2N-CHR-COO-← H3N+-CHR-COO- → H3N+-CHR-COOH + OH-
Different amino acids have different isoelectric points
Human Biochemistry
Jan 3, 2010
21
Electrophoresis
(constant pH)
Human Biochemistry
Jan 3, 2010
22
Human Biochemistry
Jan 3, 2010
23