BIOL 1000 Lecture Notes - Lecture 10: Trimethoprim, Hemoglobin, Sarcomere

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Published on 31 Jan 2013
Lecture 10
Energy and Enzymes
Mainly in Chapter 4
Free Energy (ΔG) – portion of a systems energy available to do work
o Takes entropy and enthalpy into account
o ΔG = Enthalpy + Entropy
o Enthalpy Heat or radiation transfer (H)
ΔH – Change of enthalpy
Enthalpy of Products Enthalpy of reactants (HPROD - HREACT)
If ΔH < 0 – Exothermic, favoured reaction (should go that way)
If ΔH > 0 – Endothermic, non-favoured reaction (shouldn’t go that way, requires
energy input [usually in form of heat])
o Entropy Randomness is favoured over order (S)
i.e. More free molecules in a system
Favoured state is the state with more free molecules
2 TNT 15 Product Molecules
Therefore the 15 product molecules favoured because 15 > 2
Releases lots of energy
ΔS = SProd - SReact
o Exergonic reactions release heat energy (ΔG < 0)
o Endergonic take in heat energy (ΔG > 0)
See sheet for diagrams
NB: Opposite reactions of endergonic vs. exergonic have the same magnitude,
different sign (Like Newton’s Third...)
o Endergonic reactiona usually coupled to exergonic reactions
Metabolic Pathways
Catabolic breaks down complex molecules
Anabolic build up complex molecules
Enzymes are catalysts that reduce the value of activation energy (energy needed to start a
Enzymes bring molecules in a specific position that will change them up by making them react
with certain AA’s and leave differently
Work best at certain conditions
o Pepsin is a low pH because it’s in the stomach
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o Need things like heat, pH
If not perfect, the protein’s shape is changed
o Cofactors needed sometimes too
Fe, Mg (inorganic materials)
These stabalize molecules, transfer electrons
Iron for example does this in the ETC
Organic factors are called “coenzymes”
Help as donors of something (redox etc.)
Example of this would Folic Acids that donate methyl
Haemoglobin needs Fe as a cofactor (carries O2 in the blood)
Enzymes in the ETC need this too
Active Site
Numbers on things like “GLU 35” mean what number in the primary sequence
NB : DNA and RNA have tertiary structures
The “Enzyme Intermediate” (EI) state is unstable
The glycosidic bond (α-Form) has been hydrolyzed
Lowering Activation Energy
Localizing reactants (two molecules must be put together perfectly [like two people being PUT
shoulder to shoulder])
o Enzymes localize and orient reactants to be in the perfect state
Move e-, H+ or both
o Take protons off of certain areas so that water or anything else can more easily access
where it needs to be accessed (leaves less to randomness)
Bond Stress
o Bending molecules so that electrons are easier to break
Enzymes in Extreme Conditions
Enzymes that can survive and work optimally at extreme conditions
o T. Aq. In 72oC
o It’s DNA Polymerase in Polymerase Chain Reaction (PCR) is used for forensics, disease
identification where DNA Replication (in the lab) is done at high temperatures
High temps used to make much more DNA than is available at that time
o DNA Polymerase is called “TAQ Polymerase”
o PCR (Basics!)
Heat to denature DNA (95oC)
Prime DNA to prepare the DNA Polymerase (60oC)
Replicate DNA (72oC)
Repeats 30 times!
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If one starts with 1 DNA molecule, they end up with 230 = Approx 109
Note, in reality about 40 template molecules are required for this to
The rate of reaction how fast a product is made
o Rate = # Products Made / # Enzyme Molecules / Time = Velocity (V)
Saturation level is when the rate of reaction is at its maximum VMAX
o All enzymes are complexed with substrate, cannot do much more
o As more substrate added, more product is made until VMAX attained, where a plateau
o AT ½ VMAX Substrate [] is called KM (the Michaelis Menton Constant)
This is a characteristic for all enzyme substrate pairs
Different for all enzymes (indicates efficiency)
Lower KM = Higher Efficiency because this means it can reach it’s VMAX earlier!
Alcohol Aldehyde (via Alcohol Dehydrogenase) ADH
o Different people have different booze control because of the KM value for their personal
Aldehyde Acetate (Aldehyde Dehydrogenase)
Disulfiram Irreversible deactivates ALDH
o This makes you build up aldehyde quickly so it makes you have hangover symptoms
Competitive Inhibition
o Inhibitor and substrate compete for active site
o Suicide inhibitors become irreversibly changed (can be overcome) [Covalent Bond]
o KM increases with the competitive inhibitors
o Viagara
High cGMP leads to reduction of Ca2+
cGMP phosphodiesterase increased Ca2+ Vascular Muscle Contraction
Pharm companies looked for PDE (phosphodiesterase) inhibitors to lessen
constriction and blood pressure
Viagara was designed to do this
In Males, it inhbited PDE in penile vascular muscle increased blood
o Isoforms/Isozymes enzymes perform same catalytic function but usually made from
different genes and thus significantly different primary sequences of amino acids
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