BCH2022 Study Guide - Final Guide: Citric Acid Cycle, Ribose, Gluconeogenesis

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25 May 2018

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Overview

• Amount of energy, ATP depends which pathways dominate

• All pathways integrate

• What drives these pathways in one direction or another

• What are the irreversible reactions – most regulated

o Equilibrium reactions – less regulated

Exam Format

• Multiple choice questions

• Short answers

o Picture needed to annotate

o Equation need to finish

o Calculation

Citric Acid Cycle

• Which steps make NADH, FAD, GTP

Glycolysis

• Purpose: to make energy

• Do it when lots of glucose → stimulate insulin to remove glucose out of blood

system

Prioritize:

• What is the purpose of a pathway?

• What are the starting and ending molecules?

• Where is the pathway (in the cell, in a tissue, in an organ system)?

• How does the pathway connect to other pathways?

• What metabolic conditions turn the pathway on and off?

• What are the control points for regulating the pathway?

o Reactance, products and enzyme name of each regulatory step

o Additional regulatory molecules involved (vitamins, cofactors)

o Make sure you know how every step that makes or uses ATP

• What structural features are important for the function and interaction of

specific regulatory molecules in a pathway?

•

• What tissue is doing this – liver

• Liver is heart of metabolism

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• Inputs and outputs

• Glycolysis: all tissues

• Gluconeogenesis: rely on liver

to make glucose

• What amplifies these different

pathways

o What activates them

Pyruvate

• Explain why we make lactate

o Anaerobic respiration

o To make NAD+ to be made for glycolysis for pyruvate → energy

• Aerobic degradation to CO2 and H2O through TCA cycle

• Anaerobic reduction to lactate – bacteria and muscle

• Anaerobic fermentation to alcohol

o Glucose → lactate: glycolysis

o Lactate → lactate: Blood transport

• Allosteric reaction: either turn it up or

down

• Hormonal control

• Know enzymes involved

• Energy poor – need glucagon

• Glucose-6-phosphate has three

different directions

o Make glucose → pyruvate

o Make ribose sugars for

NADPH (for fatty acid

synthesis)

o Ribose backbone for nucleic

acids

• PFK-1: step 3 of glycolysis

o Activated by low energy molecules: ADP

etc

o Derived from hormonal control

• AMP: inactivates F26BP – gluconeogenesis

• Pyruvate kinase: step 10 of glycolysis

o Stimulated by AMP

• Pyruvate carboxylase: step 1 of gluconeogenesis

o Stimulated by acetyl-CoA

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Document Summary

Overview: amount of energy, atp depends which pathways dominate, all pathways integrate, what drives these pathways in one direction or another, what are the irreversible reactions most regulated, equilibrium reactions less regulated. Exam format: multiple choice questions, short answers, picture needed to annotate, equation need to finish, calculation. Citric acid cycle: which steps make nadh, fad, gtp. Glycolysis: purpose: to make energy, do it when lots of glucose stimulate insulin to remove glucose out of blood system. Inputs and outputs: glycolysis: all tissues, gluconeogenesis: rely on liver to make glucose, what amplifies these different pathways, what activates them. Phosphophenyl pyruvate (in mitochondria: nadh in cytosol. Ve g reactions: occur spontaneously: step 6 and 7 coupled. Regulation of glycogen synthesis: cascade of events phosphorylation of target proteins, know how this is operated, draw tables: what"s phosphorylated or dephosphorylated, kinase puts phosphates groups on.

Related Questions

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

1. C6H12O6 + 6O2 Ã 6CO2 + 6H2O Glucose is being _____ to _____ and oxygen is being _____ to _____. a. oxidized; carbon dioxide; reduced; water b. oxidized; water; reduced; carbon dioxide Incorrect c. reduced; water; oxidized; carbon dioxide d. reduced; carbon dioxide; oxidized; water

2. Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? a. the citric acid cycle Incorrect b. glycolysis c. the digestion of starch to glucose d. oxidative phosphorylation

3. Which of the following is a catabolic pathway? a. gluconeogenesis b. production of starch Incorrect c. glycolysis d. production of glycogen

4. Per molecule, the oxidation of a fatty acid results in _____ energy storage than the oxidation of glucose. a. the same b. less Incorrect c. more d. None of the above; fatty acids cannot be oxidized.

5. Of the eight reactions in the citric acid cycle, how many are oxidation-reduction reactions? a. one b. two c. three d. four e. five

6. The process of glycolysis transfers the energy in sugar molecules into the stored energy of activated carriers such as ATP and NADH. Which statement is true about glycolysis? a. Only eukaryotic organisms do glycolysis. b. The ten reactions of glycolysis are identical in all eukaryotic cells, but are different in prokaryotic cells due to their diverse metabolic strategies. Incorrect c. The ten reactions of glycolysis are identical in almost all living organisms on the planet. d. There are many ways to oxidize glucose and transfer energy into activated carriers; the diversity of organisms on the planet is reflected in the diversity of their mechanisms of glycolysis.

7. Referring to the sentence completed in #13 above, the purpose of the latter reaction (in active muscle cells) is to _____. a. accumulate lactic acid in the cell, which provides additional energy for the production of ATP Incorrect b. slow down glycolysis until oxygen becomes available again c. accelerate the Krebs cycle, which will restore the oxygen supply d. regenerate NAD+ so that glycolysis can continue in the absence of oxygen

8. What are the products of the citric acid cycle? a. carbon dioxide, NADH, FADH2 and GTP b. carbon dioxide, NAD+, FAD and GTP c. NADH, FADH2, and acetyl CoA Incorrect d. carbon dioxide and water

9. Which statement is true about enzymes? a. Enzymes catalyze chemical reactions because they make inherently endergonic reactions exergonic. b. Each enzyme in a cell can catalyze many different chemical reactions involving chemically different substrates. Incorrect c. Enzymes can only catalyze reactions in one direction. d. After catalyzing a reaction, an enzyme is permanently altered and can no longer bind substrate. e. None of the above is true. 1

10. âG measures the change in free energy in a system as it converts reactant (Y) into product (X). When [X] = [Y], âG is equal to _____. a. RT b. ÎGÂ° + RT c. ÎGÂ° d. ln [X]/[Y]

11. The âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. What conditions in the cell would lead to a âG for ATP hydrolysis of -11 kcal/mol? a. An increase in the ATP/ADP ratio b. An increase in anabolic activity in the cell c. Transport of ATP out of the compartment where the reaction is occurring Incorrect d. A decrease in the ATP/ADP ratio

12. In the first reaction of glycolysis, a phosphate transferred from ATP to a glucose molecule to produce glucose-6-phosphate and ADP. Under conditions existing in the cell, the free energy change for this reaction is -8.0 kcal/mole. Which of the following statements is true? Recall that the âGÂ° for the hydrolysis of ATP is -7.3 kcal/mol. a. Glucose concentrations in the cell are always low, making this reaction more favorable than would be expected. b. This reaction is less favorable than would be expected, given the âGÂ° of ATP hydrolysis. c. Glucose-6-P concentrations in the cell are very low relative to glucose concentrations, making the reaction more favorable than would be expected. d. The âGÂ° for the addition of a phosphate to glucose must be -0.7 kcal/mole.

13. Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S --> ES Keq for ES = 10 E + I> EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? a. When S is present in excess, no I molecules will bind to E. b. E binds I more tightly than S. c. The binding energy of the ES interaction is greater than that of the EI interaction. d. Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative.

BCH2022 Study Guide - Final Guide: Citric Acid Cycle, Ribose, Gluconeogenesis

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