BIOC 3560 Study Guide - Midterm Guide: Citric Acid Cycle, Protein Biosynthesis, Alanine

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24 Oct 2016

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Metabolism is the sum of chemical transformations. Oxidative (strips off e- and gives it to nad+) Anabolism: needs energy (uses atp) reductive (puts e- on using nadph) Types of pathways: (like yin/yang = the pathways must balance) Rates of biochemical pathways depend on the activities of enzymes that catalyze each step. Enzyme activity can be modified by many different mechanisms. Regulation at large energy drop: it is easier to control flow of water at waterfall = metabolism is essentially a flow of metabolites analogous to water flow. Every metabolic pathway has 1 or more enzyme-limited step. Rate limiting step: often exergonic and irreversible under cellular conditions (where you can control/regulate metabolism ) Enzymes catalyzing exergonic, rate-limiting steps are targets of: metabolic regulation. There are several big energy drops in glycolysis > where lots of metabolic control occurs. Atp pumped to make sure it is a favourable drop.

Related Questions

1. Consider all the pathways of carbohydrate metabolism discussed in biochemisty. List all the reactions that are:

a. unique to glycolysis (1)

b. unique to gluconeogenesis â give enzyme names (1)

c. shared between glycogen synthesis and glycogenolysis â give enzyme names (1)

2. Consider the enzyme hexokinase.

d. Hexokinase activity is regulated by glucose-6-phosphate by the process of _________________________. (1)

e. The liver isozyme of hexokinase, called glucokinase, is not susceptible to this type of regulation. Explain why this makes sense, considering the role of the

liver in maintaining the glucose balance for the organism. (2)

f. Glucokinase has a much higher Km for glucose than does hexokinase. How does this property help the liver act as a glucose storage organ? (2)

3. Lactate is a waste product in rapidly contracting muscle, but a fuel for resting muscle. Explain, with reference to the metabolic pathways through which lactate proceeds in each

case. (2)

g. When lactate is used as a fuel by muscle, how much ATP can the muscle obtain by complete oxidation of lactate? (1)

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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.

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BIOC 3560 Study Guide - Midterm Guide: Citric Acid Cycle, Protein Biosynthesis, Alanine

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