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Lecture 8

BIO 1140 Lecture Notes - Lecture 8: Oxidative Phosphorylation, Intermembrane Space, Prokaryote

Course Code
BIO 1140
Doug Johnson

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Cell Bio Lecture 8
1. Contrast and compare the structure and function of a G protein-coupled receptor and a
receptor for a lipid-soluble signal (such as a steroid hormone)
- One receptor is found on the membrane and one is found inside the cell. One is found
on the membrane because it is activated by water-soluble signals, the lipid soluble signals
can enter the cell. They both have the structural feature of a ligand-binding site. The G
protein-coupled receptor has 7 transmembrane domains that hold it in the membrane. In
the case of the G protein-coupled receptor it is located within the membrane and then
activates pathways within the cell. Lipid-soluble receptors have a DNA binding domain is
a structural feature that allows it to regulate gene transcription. G protein coupled
receptor has a G protein-binding domain on the cytosolic side of the membrane.
2. Relate the structure of ATP to its function as the energy currency of the cell
- There are 3 phosphate groups on ATP, phosphate group carries a negative charge as does
the rest of the molecule, so when you split that phosphate group off the rest of the
molecule, the energy that would go in to making that negative-negative bond is released
as usable energy. When you go from one molecule of ATP to 2 molecules (ADP and Pi)
you increase entropy, which increases energy. Phosphate as an independent molecule is
more stable because the electrons can distribute evenly whereas when it is bound to ADP
it is less stable because the electrons cannot distribute as evenly. So, when the phosphates
lyses from the ATP it becomes more stable and releases energy.
Glycolysis contd…
- Fate of pyruvate depends on Oxygen availability
- In absence of Oxygen, NAD+ is regenerated.
Glucose => 2 Pyruvate => Pyruvate oxidation => citric acid cycle => Oxidative
No Oxygen
Glucose =>Fermentation => lactate or ethanol => 2 ATP
Lactate when using working very hard for short period of time. Lactic acid accumulates
and causes fatigue. (Makes dairy products)
Alcoholic fermentation. Pyruvate is decarboxylated (One carbonated is removed to give
CO2) and acetaldehyde. Then using NADH forms ethyl alcohol. (Yeast uses it in absence
of oxygen, makes beer and alcohol, gives bread as well, CO2 causes yeast to rise, alcohol
is burned off when it bakes)
Goldfish use alcohol fermentation. Can survive without oxygen for hours or days by
using the alcoholic fermentation pathway. Goldfish skeletal method uses the alcoholic
fermentation pathway. When they’re anoxic, muscle breaks down glucose to generate
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pyruvate, enters alcoholic fermentation pathway, ethanol leaves through gills. This is
useful because they don’t generate lactic acid and so they don’t get tired.
In absence of O2, fermentation is essential to…
a) Generate energy through the production of lactate or ethanol.
b) Avoid the accumulation of pyruvate
c) Regenerate NAD+ so that glycolysis can continue
d) Avoid the accumulation of H+ (generated when NAD+ is reduced)
e) All of the above explain why fermentation is essential in the absence of O2
Regulation of Glycolysis
- Feedback regulation
- Goal is maintenance of cellular [ATP];[AMP]
Allosteric regulation of key enzymes
Allosteric regulators – Activators; inhibitors
If ATP levels fall/AMP levels rise, pathways are ramped up to increase ATP production
and vice verse.
3 Key enzymes in the glycolytic enzymes to maintain this [ATP]:[AMP] levels.
1. Phosphofructokinase – regulated by the substrates and products of this pathway.
AMP acts as a stimulator of phosphofructokinase, when AMP levels are high it
stimulates phosphofructokinase to ramp up glycolysis. Citrate and ATP are
phosphofructokinase inhibitors; they act to slow down glycolysis when their
levels are high. Regulation occurs allosterically – allosteric regulators bind to the
enzyme, by doing so they change its conformation either increasing or decreasing
activity of the enzyme. Ex. ATP acts as a allosteric inhibitor, it binds to an
allosteric site of phosphofructokinase and in doing so would reduce
phosphofructokinase activity, whereas AMP would act as a allosteric regulator
bind to a different site of phosphofructokinase and ramp up its activity.
Gluconeogenic pathways is when the cell has enough energy so instead of
oxidizing glucose it stores glucose to be used in the future when its needed.
Pyruvate enters the mitochondrion
- Porin (large channels in the membrane), pyruvate-H+ cotransports (specialized
transporter, brings pyruvate into mitochondrial matrix)
Remainder of aerobic respiration occurs in the mitochondrion
The Mitochondrion – powerhouse of the cell
Structure-function relationships
- Outer membrane contains porins
- Inner membrane – High fluidity, permeability barrier, highly folded, 75% protein
(pyruvate transporter, electron transport chain, ATP synthase)
- Matrix contains enzymes of pyruvate oxidation, citric acid cycle
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