BCHM 316 Lecture Notes - Lecture 7: Acetyl-Coa, Pyruvate Dehydrogenase, Citric Acid Cycle

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10 Feb 2018

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So after glycolysis pyruvate dehydrogenase catalyzes the conversion of pyruvate to acetyl coa. In this conversion, there is a loss of co2! Glycolysis in the cytosol but the conversion of pyruvate to acetyl coa occurs in the mitochondria. The outer membrane: is freely permeable to small molecules and ions. The inner membrane: is impermeable to most small molecules and ions, including h+ Cristae are folds that help form the matrix. Atp, adp, inorganic phosphate, mg2+, ca2+, k+ Coash + nad+ pyruvate co2, acetyl-coa + nadh (removes energy) The pyruvate dehydrogenase complex has three subunits (e1 + e2 +e3) The acetyl group is transferred to the coa enzyme. Note the negative delta free energy, this is an exergonic process. This reaction involves 5 coenzymes: tpp, lipoic acid, coenzyme a, flavin adenine dinucleotide and nicotinamide adenine dinucleotide. The function of tpp is to decarboxylate pyruvate! So to remove a carboxyl group from pyruvate and yield a hydroxyethyl tpp carbanion.

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Carbohydrates are broken down into glucose monomer and dimers. Glucose is converted to pyruvate and then to acetyl CoA. Acetyl CoA enters the citric acid cycle and is broken down to CO2 and in the process produces NADH & FADH2, which is utilized in the generation of ATP via the electron transport chain. Why does the cell go through this elaborate pathway to convert glucose to carbon dioxide and water and in the process generate ATP? Why not use a simpler and shorter mechanism to breakdown glucose?

1. Integrated metabolism

A. A molecule of glucose that you eat can eventually be transformed into part of a fatty acid that you store. Circle the pathways/cycles below that are part of this overall flow of carbon atoms. Cross out any that are not.

Gluconeogenesis, beta-oxidation, citric acid cycle, glycolysis, urea cycle, fatty acid synthesis

B. Trace the metabolic path of this glucose molecule through the enzymes it encounters along the way to being made into fat. Write all the enzymes in the list below into the proper places in the figure below. If the enzyme is not used, write its name in a ânot used" column. If it is used, write the enzyme in the order that the carbon atoms from glucose encounter the enzymes.

Pyruvate dehydrogenase, fumarase, aldolase, lactate dehydrogenase, pyruvate kinase, acetyl CoA carboxylase, fatty acid synthase, hexokinase, carnitine acyltransferase, ATP synthase

B. What is the minimum number of glucose molecules that would be necessary to be the carbon source for synthesis of a 16-carbon fatty acid through this pathway?

C. How many net glucose can be made from one molecule of a 16-carbon fatty acid?

2. Describe each cycle/transport system (compounds, compartments, tissues) and explain its purpose:

A. citrate transport system

B. Cori cycle

C. glucose/alanine cycle

Explain the logic of these pathway regulations:

A. Phosphofructokinase, not hexokinase, is the main regulation site of glycolysis.

B. SuccinylCoA inhibits the entry of acetyl CoA into the citric acid cycle.

C. NADH inhibits pyruvate dehydrogenase.

D. Citrate inhibits the citric acid cycle and activates acetyl-CoA carboxylase.

E. Insulin leads to activation of glycogen synthase.

ochrereindeer904

35. During the complete catabolism of glucose, CO2 is released during ____ (note: Krebs cycle = citric acid cycle)
A. glycolysis only
B. Krebs cycle only
C. Krebs cycle and oxidation of pyruvate
D. oxidation of pyruvate only
E. Krebs cycle, glycolysis and oxidation of pyruvate

36. A reaction center, a primary electron acceptor and many chlorophyll molecules are all components of a/an _________ .
A. fluorescence center
B. photosystem
C. electron transport chain
D. carbon-fixation unit
E. electromagnetic spectrum

37. Which of the following generates the most reducing power?
A. anabolism of isoleucine
B. Calvin cycle
C. glycolysis
D. citric acid cycle
E. Hobbes reactions

38. After completion of the citric acid cycle (Krebs cycle), most of the usable energy from the original glucose molecule is in the form of _____.

A. acetyl CoA
B. ATP
C. NADH
D. CO2
E. FADH2

39. The light reactions of photosynthesis occur in:
A. all membranes of the chloroplast
B. the stroma
C. the matrix
D. the tonoplast membrane
E. thylakoid membranes

40. When chloroplasts are illuminated with white light, chlorophyll primarily absorbs:
A. photons of all wavelengths
B. green light only
C. red light only
D. blue light only
E. red and blue light

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BCHM 316 Lecture Notes - Lecture 7: Acetyl-Coa, Pyruvate Dehydrogenase, Citric Acid Cycle

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