Energy Transformation 2
- Photosynthesis is endergonic and anabolic.
- Cellular respiration is exergonic and catabolic.
- Cellular respiration is converting free energy in CH bonds into ATP.
- Potential energy in food has lots of CH bonds, is conserve energy by changing
to a form that cells can use (ATP).
Cellular Respiration (what we should know for exam):
- Where is it found in cell?
- What glycolysis does it do?
- How does free energy change in relative amounts?
- Does it require oxygen?
- Where is the carbon? Starting with glucose we have 6 carbons.
- Compare with photosynthesis (photosynthetic electron transport).
- Splitting of glucose, beginning of cellular respiration.
- Almost every living organism has
- Cytosolic pathway, don’t need specialized membrane, just need enzymes
floating around in cytosol.
- Nothing particularly eukaryotic about cellular respiration.
- Only the location is different in eukaryotes as opposed to in bacteria for
- Two molecules of pyruvate is the product of glycolysis, extract energy from
glucose to reduce NAD to NADH (oxidation).
- What has more free energy, a molecule of glucose or two molecules of
pyruvate? A molecule of glucose.
- Initial consumption of ATP (energy investment stage) and then get two ATP
out and two NADH from one glucose molecule.
- Energy coupling: first reaction, glucose and hexokinase come together with
phosphate, gives positive delta G, endergonic. Couple this endergonic
reaction with exergonic reaction. Exergonic reaction powers overall reaction.
- Hydrolysis of ATP is the exergonic reaction in energy coupling. Water
removes phosphate. - Energy coupling happens all over metabolic pathways.
- Kinetically it’s not a very fast reaction although it’s very spontaneous.
- Hexokinase can bind glucose or ATP; water cannot get into active site. Not
really hydrolysis of ATP, more break down of ATP.
- Energy in terminal phosphate is conserved and transferred immediately to
- Want phosphorylate glucose because: makes the glucose more reactive, more
readily wanting to break down, more free energy. Also, it stops it from
leaving the cell (phosphate is negative, glucose is positive).
- Substrate-level phosphorylation: second reaction in glycolysis. Enzyme used
is pyruvate kinase, catalyzes removal of phosphate from PEP, generates ATP.
Phosphoryl transfer potential, when they can generate ATP through
substrate level phospholrylation. Mitochondria: Where rest of cellular respiration occurs
- Chloroplasts have 3 membranes, mitochondria only have 2.
- Pyruvate in cytosol, if charged you have to transport it, won’t just leak
- Mitochondrial matrix is where it wants to go.
- Lots of CH bonds in pyruvate.
- Decarboxylation occurs and it takes carbon dioxide from pyruvate. No free
energy in this part of molecule so get rid of it.
- Dehydrogenase: group of enzymes which catalyze the oxidation and
reduction of NAD NADP, etc.
- Gives 2 NADH, want to make acetyl group more reactive, coenzyme A helps
with this. Acetyl CoA is the result of this reaction.
- Pyruvate dehydrogenase complex is where these enzymes for this part of
cellular respiration are located.
- Citric Acid cycle pulls remaining electrons from CH bonds to get ATP, this
occurs still in the matrix.
- 1 glucose gives two acetyl CoA, watch how many carbons in cycle.
- Oxaloacetate is substrate of citris acid cycles, 4 carbon compound.
- 2 carbon from actetyl CoA giving 6 carbon molecule citrate in first step of
- All carbon gets lost in this cycle. Remaining two carbon lost here.
- Free energy trapped in citrate. Then oxidizing citrate to reduce NAD, we get
NADH, ADP and FADH2. - Oxidative phosphorylation (in matrix): goal is to get energy in electron
carriers and convert to ATP. Electron carriers are the FADH, NADH and ADP
generated in citric acid cycle.
- Complex 1 drives oxidation of NADH, mobile carri