SBS017 Basic Biochemistry Dr. Jim Sullivan [email protected] Lecture 9 Enzymes: Basic principles.
Basic biochemistry 301
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Transcript of Basic biochemistry 301
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Biochemistry 301
Dr. Shabb
Rm. 2744 ECJRF
Wednesday, January 9, 2002
Water and Buffers
Friday, January 11, 2002
Amino Acids
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BMB 301 online
Biochemistry & Molecular Biology website
http://www.med.und.nodak.edu/bimd/biochem.html
click on “Biochemistry 301”
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Life and water
Life probably began in water
If life exists on another planet, it also probably requires water
It is a ubiquitous, innocuous solvent
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Water and cells
Most living cells are 60-90% water
The macromolecular components of cells assume shapes in response to water
www.smithsonianmag.si.edu
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Properties of water
Polarity
Hydrogen bonding potential
Specific heat, heat of vaporization
Nucleophilic
Ionization
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Water is a polar molecule
•Water has a dipole
moment
•“like dissolves like”
Fig. 2.1
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Water has hydrogen
bonding potential
H-bonds are non-covalent, weak interactions
H2O is both a Hydrogen donor and acceptor
One H2O can form up to four H-bonds
Figs. 2.3, 2.4
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The molecular structure
of water can
assume many forms
including…
“Ice-9”“Cat’s Cradle”
By
Kurt Vonnegut
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Water and H-bonds
High specific heat
Lots of heat is needed to break H-bonds and raise H2O temperature. Therefore, H2O is a good insulator.
High heat of vaporization
Lots of heat is needed to vaporize H2O. Therefore, sweat cools.
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Hydrophilicity
NaCl is an electrolyte
Anions and cations are solvated differently in H2O
Glucose is nonionic and hydrophilic
Figs. 2.6, 2.7
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hydrophobicity
Hydrophobic compounds and H2O don’t mix
Amphipathic molecules are part hydrophobic and part hydrophilic
Figs 2.8, 2.9
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Noncovalent
interactions in
biomolecules
Ionic
H-bond
van der Waals
Hydrophobic
Ionic>H-bond, hydrophobic>van der Waals
Fig. 2.13
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Water is nucleophilic
Water participates in many chemical reactions
it is electron rich
it is a weak nucleophile
it is present in high concentration
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Water weakly ionizes
Eq. 2.2
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pH is a measure of [H+]
in aqueous solutions
Basic pH > 7
neutral pH = 7
acidic pH < 7
Table 2.3, Fig. 2.16
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Weak acids and the acid
dissociation constant (Ka)
pKa = -log Ka
pKa is a measure of acid strength
The stronger the acid, the lower the pKa
Eq. 2.11
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pKa
can be related to pH
Henderson Hasselbach equation
Eq. 2.17
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pKa
and buffering capacity
One ionizable group can be titrated with one equivalent of strong base
the greatest buffering capacity of an ionizable group is at its pKa
Fig. 2.17
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pKa
and buffering capacity
Each ionizable group of a cpd has a unique pKa
buffered solutions resist changes in pH Fig. 2.19