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YEAR 2 HUMAN BIOCHEMISTRY > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Glycolysis is the central pathway for what?

A

Carbohydrate metabolism

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2
Q

What are 3 examples of organisms that use glycolysis

A

Mammals, bacteria and plants

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3
Q

Is glycolysis an anaerobic or aerobic process?

A

It is an anaerobic process

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4
Q

How many phases are involved in glycolysis

A

There are 2 phases in glycolysis

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5
Q

How many carbons does glucose have?

A

Glucose has 6 carbons (C6)

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6
Q

Glycolysis involves the breakdown of glucose (C6) into what? And what is the result of this?

A

Breakdown of glucose into 2 molecules of pyruvate
Results in a net production of 2 ATP molecules

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7
Q

How many carbons does a Pyruvate molecule have?

A

3 carbons

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8
Q

Where does glycolysis occur in mammalian cells?

A

Glycolysis occurs in the cytosol of mammalian cells

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9
Q

How many reactions does glycolysis consist of?

A

Consists of 10 reactions

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10
Q

Describe what is involved in phase 1 of glycolysis

A
  • Converts glucose to two glyceraldehyde 3-phosphate molecules
  • energy requiring phase (catabolic, or energy investment)
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11
Q

Describe what is involved in phase 2 of glycolysis

A
  • Generates two pyruvate molecules
  • Energy producing phase (anabolic, or energy payoff)
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12
Q

What are the 4 products of glycolysis?

A

•2x Pyruvate
•4x ATP
•2x NADH
•2x H2O

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13
Q

What are the 3 irreversible reactions in the glycolysis pathway?

A

•Hexokinase
•Phosphofructokinase
•Pyruvate kinase

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14
Q

What happens in reaction 1 of glycolysis?

A

Reaction 1 = Hexokinase
- Glucose is irreversibly phosphorylated into Glucose-6-phosphate
- Powered by the hydrolysis of ATP

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15
Q

What is the transfer of a phosphate group from ATP onto another molecule called? And why is it important?

A
  • Transfer of a phosphate group from ATP onto another molecule is called a phosphoryl transfer
  • Important to trap Glucose inside the cells
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16
Q

What are the names in order of reactions 1-10 in glycolysis

A

1= Hexokinase
2= Phosphoglucose isomerase
3= Phosphofructokinase
4=Aldolase
5= Triose phosphate isomerase
6= Glyceraldehyde 3-phosphate dehydrogenase
7= Phosphoglycerate kinase
8= Phosphoglyceromutase
9= Enolase
10= Pyruvate kinase

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17
Q

What is involved in reaction 2 of ** glycolysis **

A
  • isomerisationof glucose-6-phosphateto fructose-6-phosphate​
  • the reaction is the conversion of analdosesugar intoaketosesugar
  • reaction 2 = Phosphoglucose isomerase

Aldose = Aldehyde group
Ketose = Ketone group

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18
Q

What is involved in reaction 3 of glycolysis?

A
  • Reaction 3= Phosphofructokinase
  • Fructose-6-phosphate isphosphorylatedagain to generatefructose-1,6-bisphosphate​
  • This is the second phosphoryl transfer reaction of glycolysis
19
Q

What 2 things is Phosphofructokinase described as?

A

Phosphofructokinase is an isoenzyme and allosteric

20
Q

Describe the term allosteric

A
  • Enzymes that have an additional binding site for effector molecules other than the active site
    -ATP is an allosteric effector​
  • high levels inhibit the enzyme, low levels activate
21
Q

Isoenzymesare a combination of what subunits?

A
  • M4, M3, M2L2, ML3, L4
22
Q

What does phosphofructokinase exit as?

A
  • Exists as a tetramer
    -The tetramer is composed of L and M subunits​
23
Q

What are muscles and the liver rich in?

A

Muscles are rich in M4; the liver is rich in L4​

24
Q

What is involved in reaction 4 of glycolysis?

A
  • Fructose-1,6-bisphosphate iscleavedinto two 3-carbonfragments​
  1. Dihydroxyacetonephosphate – aketose​
  2. Glyceraldehyde 3-phosphate – an aldose
25
Q

What is involved in reaction 5 of glycolysis?

A
  • reaction 5= Triose phosphate isomerase
  • The subsequent reaction uses only glyceraldehyde 3-phosphate​
  • Dihydroxyacetonephosphate (DHAP) is converted toglyceraldehyde-3-phosphate
  • When glyceraldehyde 3-phosphate is used, the equilibrium isrestored by conversion of DHAP to glyceraldehyde 3-phosphate​
    ​
26
Q

Summarise phase 1 of glycolysis

A
  • Phase 1= involves reactions 1 to 5
  • Catabolic, energy investment phase
  • 2 molecules of ATP have beenused
  • Glucoseis converted to two molecules of glyceraldehyde3-phosphate
    -The key intermediate in this series of reactionsis fructose-1,6-bisphosphate. The enzyme thatcatalyses this reaction, phosphofructokinase, issubject toallostericcontrol
27
Q

What is involved in reaction 6 of glycolysis?

A
  • Reaction 6= Glyceraldehyde 3-phosphate dehydrogenase
  • The first reaction that begins the conversion to pyruvate
  • involvesthe oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.​
  • This reaction involves addition of an inorganic phosphate group(Pi).​
    -NAD+is reduced to NADH
28
Q

What is involved in reaction 7 of glycolysis?

A
  • Reaction 7=Phosphoglycerate kinase
  • 1,3-bisphosphoglycerate is converted to 3-phosphoglyceratebyPhosphoglyceratekinase.​
    -This step involves another reaction in which ATP is produced
  • ATP is produced by phosphorylation ofADP​
    -1,3-bisphosphoglycerate transfers a phosphate group to ADP.
  • known assubstrate-levelphosphorylation​
  • Reaction is catalysed byphosphoglyceratekinase and “paysoff” the ATP debt created by the priming reactions in the firstphase.
29
Q

What is involved in reaction 8 of glycolysis?

A
  • Reaction 8= Phosphoglyceromutase
  • The next step involves the isomerization of 3-phosphoglycerateto 2-phosphoglycerate​
  • A “mutase” catalyses migration of a functional group within asubstrate.
30
Q

What is involved in reaction 9 of glycolysis?

A
  • Reaction 9= Enolase
  • Enolase = Phosphopyruvate hydratase
  • 2-phosphoglycerate loses one molecule of water,producingPhosphenolpyruvate​
  • Enolasecatalyses the reaction and requires a Mg2+cofactor​
31
Q

What are the 3 isoenzymes involved in reaction 9 of glycolysis and give key features of all 3

A
  1. αα or non-neuronal enolase (NNE)
    - Found in a variety of tissues, including liver, brain, kidney, spleen, adipose
    -Present at some level in all normal human cells
  2. ββ or muscle-specific enolase (MSE)
    - this enzyme is largely restricted to muscle
    -where it is present at very high levels
  3. γγ or neuron-specific enolase (NSE):
    - Expressed at very high levels in neurons and neural tissues
    - can account for as much as 3% of total soluble protein
    - expressed at much lower levels in most mammalian cells.
32
Q

What is involved in reaction 10 of glycolysis?

A
  • Reaction 10= pyruvate kinase
  • Phosphoenolpyruvatecontains a high energy bond
  • Transfers its phosphate group toADP, producing ATP and pyruvate.
  • Another example ofsubstratelevel phosphorylation​
  • Reaction is catalyzed by pyruvate kinase
33
Q

Summarise phase 2 of glycolysis

A
  • Phase = Reactions 6-10
  • Anabolic
  • energy producing phase
  • Two molecules of pyruvate areproduced for each molecule of glucose that entered thepathway.
  • These reactions involve the production of 2 molecules ofNADH, and the net production of 2 ATP for each molecule ofglucose.
34
Q

What are the metabolic fates of NADH and pyruvate in mammals after being produced by glycolysis?

A
  • NADHcan be recycled via aerobic or anaerobicpathways:​
  • In aerobic conditions (O2is available), NADH is re-oxidized in the electron transport pathway, makingATP in oxidative phosphorylation.
  • 3 molecules of ATPcan be made from one molecule of NADH.​
  • In anaerobic conditions (O2is not available), NADH isre-oxidized bylactate dehydrogenase(LDH) whichprovides NAD+for more glycolysis.
35
Q

Under anaerobic conditions: eg. Actively contracting muscle. What is the most important pathway for the regeneration of NADH+ ?

A

The most important pathway for the regeneration ofNAD+is reduction of pyruvate to lactate.

36
Q

What is the goal of aerobic metabolism of pyruvate?

A
  • Goal is to get pyruvate into the citric acid cycle
    -where the products of glucose can becompletely oxidised, leading to the productionof many ATP molecules.​

2 steps required to achieve this:​
Convert pyruvate into acetyl-CoA​
Put the acetyl CoA into the citricacid cycle.

37
Q

What part of the cell contains the enzymes that perform glycolysis?

A

Cytosol

38
Q

Complete the following:

In the glycolytic pathway, one molecule of the 6-carbon compound, ———- is converted into 2 molecules of the 3-carbon compound, ————-.

A
  1. glucose
  2. Pyruvate
39
Q

Before glycolysis can occur, glucose must be trapped inside the cell. Explain how this is achieved

A

Glucose is phosphorylated to glucose 6-phosphate by hexokinase.

40
Q

Name two glycolytic reactions that involve phosphoryl transfers.

A

Hexokinase and phosphofructokinase

41
Q

Name one glycolytic reaction that is an example of substrate level phosphorylation.

A

The one catalysed by phosphoglycerate kinase or pyruvate kinase

42
Q

Glyceraldehyde 3-phosphate is oxidised during glycolysis. Choose the option below which best explains what happens to the hydrogen atom and the electron that are removed during oxidation.

a. They reduce NAD+
b. They oxidise NAD+
c. They are transferred to ATP
d. They are eliminated as methane

A

a. They reduce NAD+

43
Q

Glycolysis is a pathway which occurs:

a. Eukaryotic cells only
b. Prokaryotic cells only
c. Most muscle cells
d. Virtually all cells

A

d. Virtually all cells

44
Q

If 1NADH yields 3ATP molecules by oxidative phosphorylation, how many ATP molecules are made from one molecule of glucose undergoing glycolysis?

A

8

YEAR 2 HUMAN BIOCHEMISTRY (12 decks)

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