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
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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
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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
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