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Define Metabolism?

All the chemical reactions in a living cell


What is the C and N component that is usually added to anabolic pathways?

CO2 and NH4


What is Intermediary metabolism?

Synthesis & degradation of small molecules


Define a linear pathway? Give an example.

Enzyme catalyzed steps where the product of one rxn is the substrate for the next rxn.

Ex: Glycolysis


Define a cyclic pathway. Give an example

Enzyme catalyzed steps that form a closed loop; indicating the intermediates are regenerated with every cycle.

Ex: citric acid cycle


Define Spiral metabolic pathway. Give an example

Enzyme catalyzed steps that use the same set of enzymes repeatedly for lengthening or shortening.

Ex: Fatty-acid synthesis


Why do metabolic pathways proceed in steps?

1. Allows release of energy in manageable
2. Control points for metabolism
3. Reaction specificity for enzymes


What is the Flux of a metabolic pathway regulated by?

1. Supply of substrates
2. Removal of products
3. Activity of enzymes


What is negative feedback? What are the 2 advantages to this system of regulation?

Negative feedback is a system of regulation where the product of a pathway can inhibit the enzyme of an early step.

1. This is a self restoring form of regulation; when the products are low, the pathway will start up again
2. Early step is inhibited; Metabolic intermediates don’t get created needlessly


What is Positive feedback? What is the advantage of this form of regulation?

When a metabolite early in the pathway activates an enzyme downstream in the pathway.

Different enzymes can be activated; one enzyme coming alive makes the one downstream come alive


What are the 4 major ways that metabolism is controlled?

1. Controlling concentration of enzyme
2. Controlling activity of enzyme
- control substrate/product concentration
- allosteric inhibition/activation
- covalent modification; phosphorylation/dephosphorylation
3. Compartmentation
-Physical; a membrane border
4. Signal transduction; hormones/gfs required


Phosphorylation can be activating or deactivating; explain how it affects a) catabolic pathways b) anabolic pathways

a) catabolic pathways: Adding P = activating, de P = deactivating

b) anabolic pathways: de P = deactivating, Adding P = activating


Give 2 examples of compartmentation.

1. Citric acid cycle and electron transport chain in Mitochondria

2. Glycolysis and Glycogenesis in Cytosol


What are the 3 advantages of compartmentation?

1. Metabolites can exist in totally separate pools
2. Opposing metabolic pathways can take place at the same time
3. Can create high local concentration of enzymes w/o them affecting other parts of the cell


Are metabolic pathways at equilibrium? If not, what are they?

Metabolic pathways are in steady state; reactants are “steadily” replaced as reactants are steadily “removed”


Why is glucose a good fuel?

1. Releases alot of energy when oxidized; very exergonic

2. Can be efficiently stored


Under anaerobic conditions, how is NAD+ regenerated?

By fermentation: pyruvate is reduced to ethanol or lactate


What is the principle source of ATP in anaerobic organisms?

Glycolysis (can’t use electron transport chain)


How is glycolysis regulated by insulin?

1. Insulin binds to receptors on the cell
2. Causes vesicles containing GLUT4 to fuse with the cell membrane
3. GLUT4/hexose transporter allows speedy import of Glucose into the cell, in the absence of insulin, GLUT4 is not triggered to fuse with cell memebrane


How is hexokinase inhibited?

It’s inhibited by negative feedback; by it’s product glucose 6-phosphate


What inhibits phosphofructokinase I?

ATP allosterically inhibits it, AMP activates it


What product from the citric acid cycle inhibits phosphofructokinase I?



Is phosphorylated or dephosphorylated kinase more active?

Dephosphorylated kinase is more active


Where do galactose, fructose and mannose enter glycolysis?

Galactose: Converted to Glucose 6-phosphate

Fructose: G3P

Mannose: fructose 6-phosphate


What is the Warburg effect?

When tumours obtain ATP by using glycolysis and then fermentation to breakdown glucose to lactate even in the presence of oxygen


What are all the precursors to gluconeogenesis?

Pyruvate, lactate, amino acids, glycerol


What 2 enzymes of glucogenesis arn’t found in the cytosol?

Glucose 6 phosphotase (in ER)

Pyruvate carboxylase (in mitochondria)


How is pyruvate carboxylase regulated?

Activated by Acetyl CoA
Deactivated by high concentration of Glucose


How is phosphoenolpyruvate carboxykinase regulated?

Through gene expression only


How is fructose 1,6-bisphosphotase regulated?

Activated by Citrate

Deactivated by AMP