Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biological Chemistry 1A > Metabolism 3: Glycolysis > Flashcards

Metabolism 3: Glycolysis Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What is glycolysis?

A

The sequence of reactions that metabolises glucose to pyruvate with the accompanying production of energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the overall products of glycolysis?

A

Glycolysis converts glucose into two three carbon units and two molecules of adenosine triphosphate (ATP)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where is glucose metabolised in humans?

A

In cytosol in the cytoplasm - enters by a specific transporter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the two classifications of monosaccharide?

A

Aldoses and ketoses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does glucose interconvert between alpha and beta forms?

A

By mutorotation
The reversible ring opening of each anomer to the open chain aldehyde form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why is beta pyranose more common than alpha pyranose?

A

Because large groups prefer to be as spaced out as possible
In beta pyranose, the -OH groups are in the cis form, and point as far away as possible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the most common sugar consumed in our diets?

A

Sucrose
A disaccharide made up of a 6-membered ring of glucose and a 5-membered ring of fructose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is sucrose broken down in the body?

A

Salivary glands in the mouth release salivary amylase which partially hydrolyses sucrose in the mouth
In the stomach, acid further hydrolyses
The majority of sugar digestion occurs in the small intestine catalysed by membrane-bound sucrase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the first step of glycolysis?

A

Phosphorylation of glucose by ATP to give glucose-6-phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Which enzyme catalyses step 1 of glycolysis?

A

Hexokinase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the two parts to step 1 of glycolysis?

A

Attachment of glucose to hexokinase
Hydrolysis of ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where does equilibrium lie in step 1 of glycolysis?

A

In favour of the products because the overall free energy is negative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What condition is important for the first part of step 1 of glycolysis, and why?

A

Glucose must bind to hexokinase in a water-free environment to prevent ATP hydrolysis from occuring at this stage in the reaction
Ensures that glucose acts as the nucleophile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does glucose act as a nucleophile in step 1 of glycolysis?

A

Aspartic acid residues in hexokinase act as a base to deprotonate the -OH group on carbon-6 of glucose
Allows O- to act as a nucleophile
Nucleophilic attack occurs on the terminal phosphate of ATP
New covalent bond forms, phosphorylating glucose and forming a molecule of ADP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Which bond breaks to form ADP in step 1 of glycolysis?

A

The phosphoanhydride bond between beta and gamma phosphates in ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is an amino acid residue?

A

An amino acid that has been incorporated into a protein with its free amino acids and carboxyl groups replaced by linkages to neighbouring residues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How does glucose bind to hexokinase in step 1 of glycolysis?

A

Via induced-fit mechanism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the role of Mg2+ ions in step 1 of glycolysis?

A

Mg2+ is a cofactor
Mg2+ binds to ATP to form MgATP - stabilises ATP by reducing electrostatic repulsion by partially neutralising the negative charges on the oxygens in the phosphate groups

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the second step of glycolysis?

A

Conversion of glucose-6-phosphate to fructose-6-phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Which enzyme catalyses step 2 of glycolysis?

A

PhosphoGlucose Isomerase (PGI)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe how step 2 of glycolysis occurs.

A

1) Pyranose ring opens via the breaking of the hemiacetal bond to form an open chain
2) Isomerisation occurs in a mechanism of proton transfer catalysed by acid-base chemistry using active site amino acid residues
3) The carbonyl on carbon-1 of glucose is protonated, converting the aldehyde group into a hydroxy group
4) Hydroxyl group on carbon-2 of glucose is deprotonated, forming an enediol intermediate
5) A proton is then transferred to carbon-2, enabling the rearrangement into the ketose form
6) Hemiketal bond forms, allowing the ring structure of fructose-6-phosphate to form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the three amino acid residues involved in step 2 of glycolysis?

A

Glutamic acid (Glu)
Lysine (Lys)
Histidine (His)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is a hemiacetal bond?

A

The bond between the -OH group and the aldehyde group in glucose
This bond is why the sugar ring is closed
Breaking this ring leads to formation of the open-chain form of the molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is a hemiketal bond?

A

The bond between the -OH group and the ketone group in glucose
This bond must be formed at the end of step 2 of glycolysis to form a closed ring ketose structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Is there a cofactor involved in step 2 of glycolysis?

A

No
Active site residues on the surface of PhosphoGlucose Isomerase catalyse the reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the third step of glycolysis?

A

The phosphorylation of fructose-6-phosphate to form fructose-1,6-bisphosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Which enzyme catalyses step 3 of glycolysis?

A

Phosphofructokinase (PFK)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Is there a cofactor involved in step 3 of glycolysis?

A

Yes
Mg2+ is the cofactor, it helps to stabilise ATP by partially neutralising the negative charges on the O- in ATP

29
Q

How does fructose-6-phosphate act as a nucleophile in step 3 of glycolysis?

A

Similar to step 1 of glycolysis
Amino acid residues in the active site of phosphofructokinase act as base
Deprotonates -OH on carbon-1 of fructose-6-phosphate
Allows O- to act as an efficient nucleophile to attack the terminal phosphate on ATP

30
Q

What are the products of step 3 of glycolysis?

A

Fructose-1,6-bisphosphate
ADP
H+

31
Q

What is allosteric regulation?

A

The regulation of a protein by binding an effector molecule at a site other than the enzyme’s active site (the allosteric site)

32
Q

How does allosteric regulation occur in step 3 of glycolysis?

A

When ATP binds to the allosteric site, it causes a conformational change
Causing the shape of the active site to change
So it is no longer complementary to fructose-6-phosphate
Slowing down the reaction to control the production of ATP

33
Q

What is the fourth step of glycolysis?

A

The cleavage of fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) via aldolase

34
Q

Which enzyme catalyses step 4 of glycolysis?

A

Aldolase
Works by facilitating the formation of a Schiff base

35
Q

How is the Schiff base formed in step 4 of glycolysis?

A

Lysine residues in aldolase’s active site react with the carbonyl group on fructose-1,6-bisphosphate, forming imines (Schiff bases)

36
Q

Name the mechanism of step 4 of glycolysis and describe it.

A

Retro-aldol reaction
1) Formation of Schiff base between lysine residue and carbonyl group on fructose-1,6-bisphosphate
2) C-C bond breaks between C3 and C4, cleaving the molecule in two
3) Forms glyceraldehyde-3-phosphate (GAP) and an enamine intermediate
4) Enamine is hydrolysed, releasing dihydroxyacetone phosphate (DHAP)

37
Q

What is the fifth step of glycolysis?

A

The conversion of DHAP into GAP

38
Q

Which enzyme catalyses step 5 of glycolysis?

A

Triose Phosphate Isomerase (TIM or TPI)

39
Q

Why is the fifth step of glycolysis necessary?

A

Only glyceraldehyde-3-phosphate (GAP) can be further metabolised in glycolysis
Dihydroxyacetone phosphate (DHAP) cannot therefore must be converted into GAP

40
Q

Which amino acid residues are present in the active site of the enzyme in step 5 of glycolysis?

A

Histidine and glutamic acid
Both are involved in the mechanism

41
Q

How does the enzyme in step 5 of glycolysis work?

A

TIM closes around dihydroxyacetone phosphate (DHAP)
Aligns the amino acid residues perfectly with the molecule to allow the reactions to occur efficiently
After the reaction, the amino acid residues are regenerated so can be reused again in more reactions

42
Q

What are the benefits of the enzyme involved in step 5 of glycolysis?

A

1) Accelerates reaction by a factor of 10^8 compared to a simple base-catalysed reaction
2) Suppresses undesired side reaction: decomposition of the enediol intermediate into methyl glyoxal - which is energetically favourable so would occur without TIM

43
Q

What is NAD?

A

Nicotinamide adenine dinucleotide
A coenzyme dinucleotide involved in redox reactions carrying electrons from one reaction to another

44
Q

How many reactions are there in glycolysis overall?

A

10 reactions

45
Q

How many stages are there to glycolysis?

A

Three stages

46
Q

How many reactions involve the energy investment of ATP?

A

2 reactions

47
Q

How many reactions involve paying back energy investment in the form of NADH and ATP?

A

3 reactions

48
Q

Describe the free energy change of the conversion of glucose into pyruvate.

A

The free energy change is negative
Means the reaction is spontaneous under the given conditions

49
Q

What are the three regulatory enzymes involved in glycolysis?

A

1) Hexokinase (step 1)
2) Phosphofructokinase (step 3)
3) Pyruvate kinase (step 10)

50
Q

What is the role of the regulatory enzymes in glycolysis?

A

To control the rate of glycolysis
And prevent hypoglycemia/hyperglycemia

51
Q

What is insulin?

A

A hormone produced by the beta-cells in the islets of Langerhans in the pancreas
In response to high blood glucose levels

52
Q

What are the three pathways that pyruvate can enter after glycolysis?

A

1) Production of acetaldehyde and then ethanol (in yeast and bacteria)
2) Production of lactate (in anaerobic conditions)
3) Production of acetyl CoA (in aerobic conditions) to then undergo further oxidation

53
Q

Describe how pyruvate is converted into lactate in anaerobic conditions.

A

Catalysed by lactate dehydrogenase
Lactate is produced under anaerobic conditions e.g. in muscles during intense exercise

54
Q

Give the overall equation for the production of lactate in anaerobic conditions from glucose.

A

Glucose + 2Pi + 2ADP –> 2Lactate + 2ATP + 2H2O + 2H+

55
Q

How is lactate converted into glucose in the liver?

A

Gluconeogenesis

56
Q

What is gluconeogenesis?

A

Glucose synthesis from alternative substrates
E.g. pyruvate
During times of starvation

57
Q

How are gluconeogenesis and glycolysis linked?

A

By the Cori cycle
Via the bloodstream

58
Q

Describe how pyruvate is converted into ethanol in humans.

A

First pyruvate is converted into acetaldehyde via pyruvate decarboxylase
Then acetaldehyde is converted into ethanol via alcohol dehydrogenase

59
Q

How is ethanol catabolysed by the digestive system?

A

Ethanol –> Acetaldehyde
Acetaldehyde –> Acetic acid
Acetic acid –> Acetyl CoA

60
Q

Describe how ethanol is produced in yeast.

A

1) Decarboxylation reaction catalysed by pyruvate decarboxylase, requiring a coenzyme derived from vitamin B1
2) Reduction reaction catalysed by alcohol dehydrogenase and is zinc-dependent

61
Q

Why is fermentation commercially significant?

A

Fermentation accounts for 80% of world ethanol production worldwide
20% of ethanol is produced synthetically from ethene

62
Q

What are four problems with fuel from waste biomass?

A

1) Large amounts of biomass required - needing large reaction vessels
2) Production time scale is long: it takes 48 hours to produce 9% ethanol in water
3) Separation costs of ethanol from media is high
4) Large amounts of waste are produced

63
Q

What is gasohol?

A

A fuel mixture of gasoline and ethanol
Ethanol can be produced from waste plant material and used in gasohol manufacture

64
Q

How are micro-organisms important in the chemical industry?

A

For fine chemical and pharmaceutical production
E.g. production of citric acid for food use

65
Q

Give an example of large-scale pharmaceutical production.

A

Synthesis of penicillin by penicillium chrysogenum
Usually by fermentation

66
Q

Describe how pyruvate is further metabolised in aerobic conditions.

A

Pyruvate is converted into acetyl CoA
Enters the Krebs cycle which can be used to release a large amount of energy

67
Q

Where does the Krebs cycle occur?

A

Inside mitochondria

68
Q

Where does glycolysis occur?

A

In the cytosol in cytoplasm

Biological Chemistry 1A (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions