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Intro to Biochemistry > 18 - Glycolysis > Flashcards

18 - Glycolysis Flashcards

1
Q

What is glycolysis in its simplest terms?

A

The breakdown of glucose-6-phosphate to pyruvate, along the way ATP is made from ADP and NAD+ is reduced to NADH

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2
Q

What two things are needed for glycolysis?

A

NAD+ and glucose

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3
Q

What is glycogenolysis?

A

The conversion of glycogen to glucose-1-phosphate

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4
Q

Whate is isomerization doing after glycogenolysis?

A

Isomerization occurs to convert glucose-1-phosphate to glucose-6-phosphate. Glucose-6-phosphate is the form of glucose that can undergo glycolysis

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5
Q

What is pyruvate converted to after glycolysis? What does this product do?

A

Acetyl CoA, enters the TCA cycle and makes CO2 byproduct.

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6
Q

What is the net reaction of glycolysis?

A

Glucose +2ADP + 2NAD+ + 2Pi = 2 pyruvate + 2 ATP + 2 NADH +2 H+ + 2 H20

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7
Q

What is phase 1 of glycolysis? (energy investment phase)

A

The energy investment phase where phosphorylation of glucose and conversion to 2 molecules of glyceraldehyde-3-phosphate occurs. 2 ATP are used in this reaction.

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8
Q

what is phase 2 of glycolysis? (ATP production phase)

A

Conversion of glyceraldehyde-3-phosphate to pyruvate and coupled formation of 4 ATP

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9
Q

What must be regenerated to keep glycolysis going? What three things might happen if regeneration does not occur?

A

NAD+ must be generated or else there are three possibilites:

REduction of pyruvate to lactate (anaerobic)

Reduction of pyruvate to ethanol (yeast)

Mitochondrial electon trransport chain/oxidative phosphorylation

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10
Q

List the five steps and intermediates in the investment phase of glycolysis (stage 1)

A
  1. Phosphorylation of glucose to glucose-6-phosphate
  2. Isomerization of glucose-6-phosphate to fructose-6-phosphate
  3. Second phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate
  4. Aldol cleavage of carbon backbone to form two trioses (glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
  5. Isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate
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11
Q

What are the 5 steps and intermediates in the iATP generating phase of glycolysis (stage 2)

A
  1. oxidation by dehydrogenase of glyceraldehyde-3-phosphate (NAD+ required) to glyceraldehyde-1,3-bisphosphate
  2. Substrate level phosphorylation of glycerate-1,3-bisphosphate to glycerate-3-phosphate (2 ATP produced)
  3. Isomerization of glucose-3-phosphate to glycerate-2-phosphate
  4. Dehydration of glycerate-2-phosphate to phosphoenolpyruvate
  5. Substrate level phosphorylation of phosphoenolpyruvate to produce 2 more ATP and a molecule of pyruvate
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12
Q

How does glucose enter cells?

A

Facilitated transport by GLUT transporters on cell surface. There are several isoforms of GLUT, it is tissue and cell type specific. Different isoforms are regulated differently.

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13
Q

Are GLUT transporters bidirectional?

A

Yes, in and out.

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14
Q

What happens after hexokinase has its way with glucose?

A

Glucose is phosphorylated to glucose-6-phosphate shortly after it enters the cell by hexokinase. This prevents it form leaving the cell because GLUT cannot transport glucose-6-phosphate . Therefore phosphorylation retains glucose

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15
Q

What two molecules are required in glucose phosphorylation by hexokinase? Which carbon is phosphorylated?

A

Mg2+ and ATP. The sixth carbon is phosphorylated, this is the one that sticks out of the 5 carbon ring.

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16
Q

Glucose and fructose are both what type of sugar?

A

Hexoses, becasue they are both 6 carbon sugars

17
Q

Describe the phosphorylation of glucose

A

Glucose nucleophilically attacks a phosphate group on ATP and takes it. Mg2+ acts as a stabilizer between the two phosphates, facilitating the nucleophilic attack of the phosphate

18
Q

What enzyme isomerizes glucose-6-phosphate to fructose-6-phosphate? What does it do?

A

phosphoglucose isomerase (PGI). Catalyzes reaction of converting hydrogen on C1 of glucose to CH2OH

19
Q

What enzyme catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate? What is important about this step? What directionality does this enzyme have and what two other materials are needed?

A

phosphofructokinase (PFK) with Mg2+. This is the rate-limiting step under many conditions. PFK catalyzes in one direction and requires ATP

20
Q

What is the rate limiting step in glycolysis?

A

The isomerization of fructose-6-phosphate to fructose-1,6-bisphosphate by PFK

21
Q

What enzyme is required for the cleavage of carbon backbone to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate? What are the shortened abbreviations for these two trioses?

A

Aldolase cleaves backbone of fructose-1,6-bisphosphate to form DHAP and GAP

22
Q

DHAP and GAP are interconverted by which enzyme?

A

Triose phosphate isomerase

23
Q

In the dehydrogenation and addition of inorganic phosphate (Pi = HPO4) of glyceraldehyde-3-phosphate (GAP) to 1,3-bisphosphoglycerate (1,3-BPG), what enzyme is involved? And what two other materials are needed? What is oxidized and what is reduced?

A

glyceraldehyde-3-phosphate dehydrogenase (GAPDH). NAD+ and a Pi are needed. GAP is oxidized and NAD+ is reduced

24
Q

What enzyme is used in the dephosphorylation of 1,3-bisphosphoglycerate to 3-phosphoglycerate (3PG) and the first generation of ATP?

A

Phosphoglycerate kinase (PGK), with the help of a magnesium ion.

25
Q

Steady state of PGK (phosphoglycerate kinase) action to produce first generation of ATP is influenced by what?

A

The concentration of ADP/ATP in the cell (ratio). When the cell has a lot of ATP, glycolysis slows down.

26
Q

What enzyme in glycolysis is an oxidoreductase?

A

GAPDH (glyceraldehyde-3-phosphate dehydrogenase

27
Q

What enzyme isomerizes 3-phosphoglycerate to 2-phosphoglycerate (2PG)?

A

Phosphoglycerate mutase (PGM)

28
Q

Which enzyme catalyzes generation of phosphoenolpyruvate (PEP) from 2-phosphoglycerate? What is a byproduct?

A

Enolase with the byproduct water

29
Q

What enzyme catalyzes the important step of the formation of pyruvate from phosphoenolpyruvate into pyruvate and 2 ATP? In what direction does this enzyme operate?

A

Pyruvate kinase (PK), only operates in one direction.

30
Q

NAD+ is generated in what?

A

Oxidative phosphorylation

31
Q

PK can only phosphate in one direction, is this the same story for PGK?

A

PGK (phosphoglycerate kinase) can phosphorylate and dephosphorylate

32
Q

What is the type of fermentation that makes lactate?

A

Homolactic fermentation

33
Q

Is there a change in oxidation state in anaerobic glycolysis? Why?

A

No, because NAD+ is reduced to NADH by GAPDH phosphorylating glyceraldehyde-3-phosphate to glycerate-1,3-phosphate, but then oxidated back to NAD+ by the conversion of pyruvate to lactate by lactate dehydrogenase (LDH) in homolactic fermentation

34
Q

Is lactate secreted by the cell? What is the consequence of this?

A

Yes, this causes acidification of cellular environment.

35
Q

What are the enzymes and intermediates involved in alcoholic fermentation under anaerobic conditions?

A

Pyruvate decarboxylase and alcohol dehydrogenase convert pyruvate in a two step mechanism to ethanol.

Pyruvate to acetaldehyde with pyruvate decarboxylase

Acetaldehyde to ethanol with alcohol dehydrogenase

Intro to Biochemistry (28 decks)

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