BCH 261 Lecture Notes - Lecture 5: Lactose Permease, Enolase, Dna Replication
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30 Nov 2020
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Lecture 5 - Proteins
1) Catalysis
a) enolase (in the glycolytic pathway)
b) DNA polymerase (in DNA replication)
2) Transport:
a) hemoglobin (transports O2 in the blood)
b) lactose permease (transports lactose across the cell membrane)
3) Structure:
a) collagen (connective tissue)
b) keratin (hair, nails, feathers, horns)
4) Motion:
a) myosin (muscle tissue)
b) actin (muscle tissue, cell motility)
Enantiomers
In fischer projections, left and right
side are going towards you so look
which side has the heavier atom
If right is heavier, D
If left is heavier, L
Cells predominantly L-enantiomer
Ionization of Amino Acids
● If high pH, H+ is released
○ Becomes negatively charged
○ Deprotonated
○ At acidic pH, the carboxyl group is protonated and the amino acid is in the
cationic form
● At neutral pH, the carboxyl group is deprotonated but the amino group is protonated. The
net charge is zero; such ions are called Zwitterions
● If low pH, H+ is acquired
○ Becomes positively charged
○ Protonated
○ At alkaline pH, the amino group is neutral –NH2 and the amino acid is in the
anionic form
When amino acids are joined into a polypeptide, only some of the chemical groups remain
ionizable
● Termini of polypeptide
● R-groups of any residue
○ His, Lys, Arg, Asp, Glu
Peptide Functions
● Hormones and pheromones:
○ insulin (think sugar)
○ oxytocin (think childbirth)
○ sex-peptide (think fruit fly mating)
● Neuropeptides
○ substance P (pain mediator)
● Antibiotics:
○ polymyxin B (for Gram - bacteria)
○ bacitracin (for Gram + bacteria)
● Protection, e.g. toxins
○ amanitin (mushrooms)
○ conotoxin (cone snails)
○ chlorotoxin (scorpions)
Insulin
Average MW of Peptides
● Average MW of AA is 138 Da
● In biology use: 128 Da (smaller AA predominate in cells)
● In proteins, average MW for residues: 128 - 18 (MW H2O) = 110 Da
● Therefore the #residues in a protein = MW protein / 110
● Or the MW of a protein = number of residues X 110 Da
Prosthetic Groups
● A prosthetic group is a tightly bound, specific non-polypeptide unit required for the
biological function of some proteins
● Covalent prosthetic groups:
○ Lipoproteins: proteins modified with a lipid