EEB 100 Lecture Notes - Lecture 1: Phosphofructokinase 2, Phosphofructokinase, Glucokinase

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12 Feb 2022

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UCLA

Department

Ecology and Evolutionary Biology

Course

EEB 100

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Document Summary

Regulated steps of glycolysis: hexokinase, pfk, pyruvate kinase. Also, steps that need to be bypassed to make glucose. Glycolysis and gluconeogenesis share many enzymes but different enzymes at points of regulation. Regulate the 2 to ensure they don"t run at the same time (futile cycles) Not regulated by energy charge since g6p isn"t committed to a catabolic pathway. Can"t regulate by energy charge since provides substrates for both u-type and r-type pathways. Isozymes: catalyze the same reaction but different kinetic properties, regulation, tissue expression. Hexokinase (all tissues), non-specific, low km, inhibited by g6p. G6p trapped in the cell, product inhibition when enough glucose for energy. Glucose present, hexokinase phosphorylates it unless inhibited by g6p. Glucokinase (liver), specific (glucose), high km, not inhibited by g6p. Maintain blood glucose: [blood glucose], by storing, release later. High blood glucose: store as glycogen (continuously phosphorylates glucose) Glucose, insulin: insulin activates genes to make more hexokinase & glucokinase (glucagon opposite, inhibits)

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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Why does ATP allosterically inhibit the hexokinase enzyme (firststep in glycolysis) instead of inhibiting the pyruvate kinaseenzyme (last step in glycolysis)?

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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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EEB 100 Lecture Notes - Lecture 1: Phosphofructokinase 2, Phosphofructokinase, Glucokinase

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