Download Cellular Metabolism

Cellular Metabolism
1.
Free Energy
a.
Free energy is energy available for doing work
i. Cells release free energy in exergonic reactions
ii. Endergonic reactions require energy to occur
2.
The Role of Enzymes
a.
Enzymes are catalysts that encourage exergonic reactions to occur
i. Activation energy - energy required to start a reaction
1.
Enzyme reduces activation energy of a reaction
ii. Cofactors - may be metallic ions
iii. Coenzymes - small organic molecules - many are what we call vitamins
b.
Enzyme action
i. Associates with substrate in a very specific way.
ii. Enzyme-substrate complex
1.
Stresses chemical bond in substrate - less energy required to complete
reaction
iii. Enzymes are highly specific to a particular substrate
1.
3.
succinic dehydrogenase only works on succinic acid
Chemical energy transfer by ATP
a.
ATP - adenosine triphosphate
i. Two very high energy bonds
ii. Energy is released by hydrolysis of bonds - used in coupled reactions to cause an
endergonic reaction to occur.
4.
1.
ATP is the energy coupling agent
2.
ATP doesn't last long
Overview of respiration
a.
ATP is the common denominator of energy in cells
i. How do you get the energy from food to ATP?
ii. Redox reactions
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Cellular Metabolism
1.
Transfer of electrons from one compound to another
2.
Electron donor = e- + electron acceptor + energy
3.
Fire - wood is electron donor, oxygen is electron acceptor - lots of
energy released in flames
4.
b.
Can have different final electron acceptors
Two kinds of energy metabolism
i. Aerobes - final electron acceptor is oxygen
ii. Anaerobes - final electron acceptor is some other molecule
c.
Cellular respiration - the oxidation of fuel molecules with molecular oxygen as the final
electron acceptor
i. Overview - Figure 4-10
ii. Glycolysis - happens in cytoplasm
1.
2.
Glucose is split into two 3-carbon sugars
a.
Start with Fructose 1,6 diphosphate
b.
Series of other intermediates
c.
ATP formed
d.
NAD- is reduced to NADH
Step-by-step the glucose molecule is pulled apart and the energy in its
bonds is turned into energy in the bonds of ATP
3.
End point is pyruvic acid
iii. Krebs Cycle - named for Hans Krebs who discovered it
1.
Pyruvate is oxidized to acetyl coenzyme A
a.
Actually the coenzyme A carries the acetyl group
b.
Drops it into the Krebs Cycle
c.
Cycles until acetyl group is completely oxidized to carbon
dioxide
d.
Produce more ATP's and NADH's and FADH2
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Cellular Metabolism
iv. Electron transport chain - Where do the reduced compounds go
1.
NADH and FADH2
2.
Down the electron transport chain - remember, these compounds carry
electrons
3.
Oxydative phosphorylation
a.
Complex chain of enzymes and transfers inside of
mitochondria
i. Electrons are passed from compound to compound in
the mitochondrion
ii. Build up of hydrogen ion in mitochondrion
1.
Produces ATP - method is unclear
2.
Electron is eventually attached to oxygen
a.
b.
Forms water
Lots of ATP produced
v. Comparison of ATP and NAD production in Glycolysis and Krebs cycle plus
oxidative phosphorylation
d.
1.
Total Glycolysis + Krebs Cycle + OP
2.
Glucose + 2 ATP + 36 ADP +36P+6 O2 Æ 6 CO2 + 2 ADP + 36 ATP + 6 H2O
3.
Glycolysis alone
4.
Glucose + 2ADP +2P +2NAD+ Æ 2 pyruvics + 2NADH + 2 ATP
Anaerobic Glycolysis
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Cellular Metabolism
i. What if there is no oxygen to be a final electron acceptor?
1.
What if you are an anaerobe?
2.
You can only do glycolysis
3.
You are at a severe energy disadvantage
4.
You can use an organic compound as a final energy acceptor
a.
Use the extra electrons to reduce pyruvic to lactic acid
i. Done in animals
b.
Release 1 carbon as carbon dioxide and reduce what is left to
ethanol
i. Done in yeasts - alcoholic fermentation
5.
Anaerobic glycolysis is 1/18th as efficient as complete oxidation of
glucose
a.
If you live in an environment with no oxygen, this is what you
are stuck with - anaerobic bacteria
b.
6.
Some extreme parasites
What about normal animals?
a.
They are forced into situations where oxygen is limiting
i. Diving - seals and whales
ii. Humans under heavy exertion
b.
Do anaerobic glycolysis as produce lactic acid
i. Incur an oxygen debt - lactic acid must be oxidized
eventually
ii. Feel the burn - that is the lactic acid building up in
your muscles as you exercise
iii. Gasping for breath - you are repaying the oxygen
debt that you incurred
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