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Cell Metabolism > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

What is glycolysis?

Aerobic or anaerobic?

What are the 2 main concepts of glycolysis?

A

Glycolysis is the oxidation of glucose within the cytosol (cytoplasm) of individual cells, generating ATP and NADH

Glycolysis is central to metabolism. It is an anaerobic process and there are 10 reactions that make up the glycolysis pathway.

There are 2 main concepts: formation of high energy compounds using ATP, then the splitting of high energy compounds generating ATP.

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2
Q

Glycolysis part I: INVESTING ENERGY

Step 1

Reactants, products and what type of reaction?

A

Step 1 - Group transfer reaction
Glucose ————> glucose-6-phosphate
Catalysed by hexokinase
Uses atp ( atp —> adp via hydrolysis)

Irreversible reaction, commits cell to the following reactions of glycolysis as it traps glucose in the cell because of its negative charge (due to the phosphate group) its no longer complementary to glucose transporters

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3
Q

Glycolysis: INVESTING ENERGY

Step 2

Reactants, products and what type of reaction?

A

Step 2 - Isomerisation

Glucose-6-phosphate ——-> fructose-6-phosphate
Catalysed by phosphoglucose isomerase

Useful to generate fructose as it can be split into two equal halves when cleaved since it is symmetrical

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4
Q

Glycolysis: INVESTING ENERGY

Step 3

Reactants, products and what type of reaction?

A

Step 3 - Group transfer

Fructose-6-phosphate ——-> fructose-1,6-bisphosphate
Catalysed by phosphofructokinase
Uses atp (atp——>adp)

Product formed is still symmetrical
The regulation of phosphofructokinase (by negative feedback and other means) is a key control step for entry of sugars into the glycolysis pathway

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5
Q

Glycolyis: INVESTING ENERGY

Step 4

Reactants, products and what type of reaction?

A

Step 4 - Hydrolytic

Fructose-1,6-bisphosphate ———> glyceraldehyde-3-phosphate and dihydroxyacteone phosphate

Catalysed by the enzyme adolase

The fructose chain is split into two high energy compounds

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6
Q

Glycolysis: INVESTING ENERGY

Step 5

Reactants, products and what type of reaction?

Metabolic disease?

A

Step 5 - Isomerisation

Dihydroxyacetone phosphate ——-> glyceraldehyde-3-phosphate

Catalysed by TPI (triose phosphate isomerase)

By step 5 there’s now 2 molecules of glyceraldehyde-3-phosphate
Important for endocrinologists

Metabolic diseases: Deficiency in TPI is the only glycolytic enzymopathy that’s fatal, most sufferers die within 6 years of life.

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7
Q

Glycolysis: SPLIT COMPOUND TO GENERATE ATP

Step 6

Reactants, products and what type of reaction?

A

Step 6 - Redox and group transfer

2 x glyceraldehyde-3-phosphate ——-> 1,3-bisphosphoglycerate

Catalysed by glyceraldhyde dehydrogenase
Uses NAD+ (co-factor) + Pi——> NADH

NADH is generated at this stage which can later be used to generate more ATP within the mitochondria during oxidative phosphorylation

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8
Q

Glycolysis: SPLIT COMPOUNDS TO GENERATE ATP

Step 7

Reactants, products and what type of reaction?

A

Step 7 - Group transfer

1,3-bisphosphateglycerate ———> 3-phosphoglycerate

Catalysed by phosphoglycerate kinase
Generates ATP from ADP

kinases transfer phosphate groups to molecules, here the phosphate group is transferred to ADP

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9
Q

Glycolysis: SPLIT COMPOUNDS TO GENERATE ATP

Step 8

Reactants, products and what type of reaction?

A

Step 8 - Isomerisation

3-phosphoglycerate ———-> 2-phosphoglycerate

Catalysed by phosphoglycerate mutase

Shuffling of phosphate group from position 3 to 2 via addition and removal of phosphate groups

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10
Q

Glycolysis: SPLIT COMPOUND TO GENERATE ATP

Step 9

Reactants, products and what type of reaction?

A

Step 9 - Group removal/dehydration

2-phosphoglycerate ——-> phosphoenolpyruvate + h20

Catalysed by enolase

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11
Q

Glycolysis: SPLIT COMPOUNDS TO GENERATE ATP

Step 10

Reactants, products and what type of reaction?

A

Step 10 - Group transfer

Phosphoenolpyruvate ———-> pyruvate

Catalysed by pyruvate kinase

ADP —-> ATP ( phosphate group transferred to ADP)

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12
Q

Glycolysis net result (products formed)

A

The glycolysis cycle runs two times after step 5 as there are 2 molecules of glyceraldehyde-3-phosphate

Therefore products generated are:

  • 2 molecules of pyruvate
  • 2 molecules of ATP (4 are generated all together but two are used in the first stage, so net gain is 2)
  • 2 molecules NADH (can be used to generate ATP in ox phos)
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13
Q

3 fates of pyruvate

Fate 1: Alcoholic fermentation

A

Pyruvate ———> acetaldehyde

Catalysed by pyruvate decarboxylase (CO2 is produced)

Acetaldehyde ———> ethanol

Catalysed by alcohol dehydrogenase
NADH + H+ ——-> NAD+

Characteristic of yeasts
Occurs under anaerobic conditions

Alcohol fermentation serves to regenerate NAD+ allowing glycolysis to continue when oxygen is limited (I.e conditions in which the rate of NADH formation by glycolysis > rate of its oxidation by respiratory chain) NAD+ is needed for the dehydrogenation of gylceraldehyde-3-phosphate (first step in generating ATP)

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14
Q

3 fates of pyruvate

Fate 2: Generation of Lactate

A

Pyruvate ————-> Lactate
NAD+

Occurs under anaerobic conditions
Reversible reaction once sufficient lactate is produced
Mammalian muscle carries out this reaction during intense activity when oxygen is a limiting factor

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15
Q

3 fates of pyruvate

Fate 3: Acetyl coA generation

A

Pyruvate + HS-CoA ———-> acetyl coA + CO2

Catalysed by pyruvate dehydrogenase complex

This involves a series of reactions which takes place in the mitochondria

Acetyl coA formed is committed to entry into the TCA cycle

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16
Q

Acetyl CoA

A

The thioester bond in the Acetyl group is very high energy bond that is readily hydrolysed, allowing Acetyl CoA to donate the acetate (2C) to other molecules

-RNA ancestry suggests primeval origin

17
Q

Creatine phosphate as a buffer

A

Creatine phosphate ———> Creatine + ATP
ATP

Delta G (hydrolysis ATP) = -31 kJ/mole  and -43.1 kJ/mole (CP)
Reaction is energetically favourable

Muscles have a finite supply of ATP, the amount of ATP needed during exercise is only enough to sustain 1s of contraction

Creatine phosphate resources buffer demands for phosphate (there’s 25 mM Creatine phosphate in resting muscle vs 4 mM ATP)

Cell Metabolism (1 decks)

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