BIO206H5 Lecture 4: BIO206_Lec4_Sept17

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31 Oct 2015
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Bio206 Lec 4 Sept 17
What are proteins and what do they do?
- evolved in intracellular communication
- act as receptors
- signalling
- enzymes
- motor protein
- transport
- gene regulation
- immune system antibodies
oprotects us from the surroundings
- storage
ostore nitrogen, carbon, components for long term survival of cells
Functions of protein are related to their unique structure and composition
- hundred of billions of different type of proteins are possible
- 3D structure and chemical reactivity contribute to defining protein functionality
- most complex macromolecule in living organisms
- proteins are linear, unbranched polymers of amino acids
-
Building blocks – amino acids
- 20 (21) differnet amino acids that make up all proteins
- Central Carbon (a carbon)
oAmino group
oCarboxyl group
oHydrogen
oSide chain (R group)
Determines what protein it will be
o4 different groups bonded to the tetrahedral Ca
all amino acids are stereo specific (meaning can
have both right and left hand forms)
D and L amino acids
- optical isomers (mirror images)
oidentical composition – 2 different 3D conformations
( like your 2 hands)
oL form used predominantly in cells
oEnzymes are stereospecific – can distinguish between D and L forms
amino acids
oLeft and right handed
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Condensation Reaction forms amino
acid
- uses peptide bonds
- R groups determines amino acids
The R (side) groups
Determine the nature of an amino acids;
reactivity and solubility
- Differs if R group is: nonpolar, polar uncharged, polar
charged
Amino acids Vary’s In:
- size and shape
- charge
- hydrogen bonding capacity
- chemical reactivity
- amino group and carboxyl group charge removed by
peptide bond formation
- only either side of the amino acid has a charge as the
peptide bond eliminates charges in the middle of the
amino acids
- Polar: dissolve in water
(hydrophilic)
- Non Polar: doesn’t dissolve in
water (hydrophobic)
- Aspartic acid and Glutamic acid
are net negative charge in normal
physiological environment
- Arginine, Lysine, Histidine are net
positive charge in normal
environment
Polar side groups
- 10 in total (5 are charged, 5 are uncharged)
Charged Groups
- acidic or basic ( + or – at physiological pH)
- simple –COO- or –NH3+ or more complex
- glutamic acid has one extra methyl group
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- histidine has a pKa of 6.5 therefore sometimes the compound will be positively
charged and sometimes it will be neutrally charged
Uncharged Groups
- OH (alcohol)
- Amide group (carbon double bond with O, with an nitrogen group)
- Hydrogen bonding
Nonpolar side groups
- R is a hydrocarbon or other uncharged group
- Hydrophobic
oLikes to associate with other hydrocarbons, lipids-not water
- Subgroups
oAliphatic linear – above
oAromatic (ring)
oOthers
- METHIONINE IS THE FIRST AMINO ACID ADDED BY THE RYBOSOME
(IT IS THE INITIATOR PROTIEN)
- these are
aliphatic
linear
- these are
aromatic
(ring)
- absorb UV
radiation due
to the rings
- Tryptophan,
phenylalanine, and tyrosine absorb UV radiation due to the ring structure
- Glycine does not have a cyro carbon and does not have D and L form (it is
reversible)
- Cysteine can bond with a disulphide bond as it can ionize
oCausing it to be very reactive
oCan exist as a polar amino acid or hydrophobic amino acid if it gets
ionized
Amino acid bonding with condensation reaction
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