week 7 Flashcards by Mary Wilson

metabolically irreversible and regulated steps in glycolysis

#1 (hexokinase)	
#3 (phosphofructokinase)	
#10 (pyruvate kinase)

How well did you know this?

Not at all

Perfectly

Gluconeogenesis irreversible step enzymes

Phosphatase enzymes
Pyruvate kinase-Pyruvate carboxylase /
PEP carboxykinase

Phosphofructokinase - Fructose-1,6-Bisphosphatase

Hexokinase - Glucose-6-Phosphatase

How well did you know this?

Not at all

Perfectly

location of gluconeogenesis

cytoplasm of liver and kidney cells

How well did you know this?

Not at all

Perfectly

why is CO2 used in the first step of gluconeogenesis

to increase the entropy of the reaction and drive it forward

How well did you know this?

Not at all

Perfectly

inorganic phosphate

How well did you know this?

Not at all

Perfectly

pyruvate carboxylase

converts pyruvate to oxaloacetate. phosphorylates CO2 and adds it to pyruvate

How well did you know this?

Not at all

Perfectly

PEP Carboxykinase

Conversion of oxaloacetate to PEP

GTP is hydrolyzed to provide energy and donates a phosphoryl group

How well did you know this?

Not at all

Perfectly

Fructose-1,6-bisphosphatase

Hydrolysis of F-1,6-BP to F-6-P

How well did you know this?

Not at all

Perfectly

Fructose-1,6-bisphosphatase regulation

Allosteric regulation:
citrate stimulates (**Why this?!)
fructose-2,6-bisphosphate inhibits
AMP inhibits (doesnt have enough energy to make glucose for the body)

How well did you know this?

Not at all

Perfectly

Glucose-6-Phosphatase

Conversion of Glucose-6-P to Glucose

occurs in the ER of liver cells

How well did you know this?

Not at all

Perfectly

Why does glucose conversion occur in the ER

ER vesicles filled with glucose diffuse to the plasma membrane, fuse with it and open, releasing glucose into the bloodstream.

How well did you know this?

Not at all

Perfectly

Lactate Recycling

cori cycle

pyruvate is reduced to lactate. Lactate is then returned to the liver, where it can be reoxidized to pyruvate by liver LDH. Liver provides glucose to muscle for exercise and then reprocesses lactate into new glucose

How well did you know this?

Not at all

Perfectly

Regulation of Gluconeogenesis

Inhibited by glycolysis

Important steps are regulated

How well did you know this?

Not at all

Perfectly

Undernourished person consuming alcohol leads to…

hypoglycemia

How well did you know this?

Not at all

Perfectly

How can alcohol cause hypoglycemia

Ethanol inhibits liver gluconeogenesis since the liver cannot metabolize the excess reducing equivalents (NADH) made by oxidizing ethanol. This blocks conversion of lactate to glucose, promotes conversion of alanine to lactate, can even create mild lactic acidosis

How well did you know this?

Not at all

Perfectly

Glycogen

animal storage of glucose) is a long polymer of glucose – long chains connected by a-(1–>4) bonds, and branches connected by a-(1–>6) bonds

How well did you know this?

Not at all

Perfectly

Starch

is the plant form of glucose storage

How well did you know this?

Not at all

Perfectly

How is glycogen and starch catabolized?

Amylase is an endoglycosidase. It cleaves dietary amylopectin or glycogen to maltose, maltotriose and other small oligosaccharides. It is active on either side of a branch point, but activity is reduced near the branch points

How well did you know this?

Not at all

Perfectly

Is tissue glycogen different from dietary glycogen?

Yes. Tissue glycogen’s breakdown is carefully controlled.

How well did you know this?

Not at all

Perfectly

Metabolism of tissue glycogen

Glycogen phosphorylase cleaves glucose from the nonreducing ends of glycogen molecules
This is a phosphorolysis

How well did you know this?

Not at all

Perfectly

How Is Glycogen Synthesized?

Glucose units are activated for transfer by formation of sugar nucleotides

UDP-glucose pyrophosphorylase

driven by pyrophosphate hydrolysis.
The reaction is a phosphoanhydride exchange, with a phosphoryl oxygen of glucose-1-P attacking the a-phosphorus of UTP to form UDP-glucose and pyrophosphate.

Glycogenin

a protein that forms the core of a glycogen particle

Glycogen synthase

transfers glucosyl units from UDP-glucose to C-4 hydroxyl at a nonreducing end of a glycogen strand

How Is Glycogen Metabolism Controlled

A highly regulated process, involving reciprocal control of glycogen phosphorylase and glycogen synthase.Both enzymes are regulated by covalent modification - phosphorylation

Glycogen phosphorylase regulation

allosterically activated by AMP and inhibited by ATP, glucose-6-P and caffeine

glycogen synthase regulation

is stimulated by glucose-6-P

Glucagon and epinephrine (hormone regulation)

stimulate glycogen breakdown - opposite effect of insulin

insulin (hormone regulation)

stimulates glycogen synthesis and inhibits glycogen breakdown

Pentose Phosphate Pathway (PPP)

Provides NADPH for biosynthesis Produces Ribose-5-P Two oxidative processes followed by five non-oxidative steps

PPP location

Operates mostly in cytoplasm of liver and adipose cells | NADPH is used in cytosol for fatty acid synthesis

Oxidative steps of PPP

1. Glucose-6-P Dehydrogenase (G6PD)* Irreversible 1st step - highly regulated! 2. Gluconolactonase Uncatalyzed reaction happens too 3. 6-Phosphogluconate Dehydrogenase An oxidative decarboxylation (in that order!)

Non-oxidative steps

Makes a bunch of different types of sugars through 4 types of reactions

Variation on the PPP depends on..

what product is needed at the moment. Such as ribose-5-P, NADPH, or ATP

Central metabolism

glycolysis and TCA cycle

reciprocal regulation of metabolic pathway enzymes

``` Allosteric regulation of enzymes (modulated) Covalent modification (de)phosphorylation ```

metabolic processes in the cytoplasms

fatty acid synthesis, glycolysis, most gluconeogenesis rxns, pentose phosphate pathway

metabolic processes in the mitochondria

TCA cycle, oxidative phosphorylation, fatty acid breakdown

during glycolysis, 1 glucose gets converted into...

2 pyruvate molecules

Pyruvate can be further metabolized to

Lactate or ethanol (anaerobic) Acetyl CoA (aerobic)

Net ATP of glycolysis

2 ATP. | 2 ATPs used, 4 ATPs made

2 stages of glycolysis

hexose and triode stage

3 metabolically irreversible steps of glycolysis

1. Hexokinase 2. Phosphofructokinase 3. Pyruvate Kinase

Hexokinase

phosphorylates glucose to generate glucose-6-phosphate (G6P)

Isozyme

multiple forms of an enzyme

Phosphofructokinase-1 (PFK-1)

Catalyzes transfer of a phosphoryl group from ATP to F6P to form fructose 1,6-bisphosphate (F1,6BP)

phosphofructokinase-2 (PFK-2)

synthesizes fructose 2,6-bisphosphate (F2,6BP)

Regulation of Phosphofructokinase-1

inhibited by high levels of citrate, ATP, and F2,6BP | activated by AMP

Pyruvate Kinase (PK)

converts phosphoenolpyruvate (PEP) into pyruvate

Metabolism of Pyruvate to Ethanol (yeast - anaerobic)

Two reactions required: (1) Pyruvate decarboxylase (2) Alcohol dehydrogenase

The Pasteur Effect

the slowing of glycolysis in the presence of oxygen (This is due to the fact that more ATP is produced under aerobic conditions than under anaerobic conditions, therefore less glucose is consumed aerobically )

Reduction of Pyruvate to Lactate (muscles - anaerobic)

Muscle lactate dehydrogenase converts pyruvate to lactate | This reaction regenerates NAD+ for use by GAPDH in glycolysis