Glycolysis Flashcards Preview

BB1702 Biochemistry: Structure and Function > Glycolysis > Flashcards

Flashcards in Glycolysis Deck (34)
Loading flashcards...
1

Define Glycolysis

"The sequence of reactions that metabolises one molecule of glucose to two molecules of pyruvate with the net production of two molecules of ATP"

2

What molecules are formed in glycolysis, starting from glucose and ending at pyruvate?

  1. Glucose
  2. Glucose 6-phosphate
  3. Fructose 6-phosphate
  4. Fructose 1,6-bisphotphate
  5. Glyceraldehyde 3-phosphate (and dihydroxyacetone phosphate)
  6. 1,3-Bisphosphoglycerate
  7. 3-Phosphoglycerate
  8. 2-Phosphoglycerate
  9. Phosphoenolpyruvate
  10. Pyruvate

3

Fill in the missing molecules:

4

Fill in the missing enzymes:

5

What are the types of reactions that the enyzmes in glycolysis carry out?

  1. Phosphoryl transfer
  2. Isomerisation
  3. Phosphoryl transfer
  4. Aldol Cleavage
  5. Isomerisation
  6. Phosphorylation couples to oxidation
  7. Phosphoryl transfer
  8. Phosphoryl shift
  9. Dehydration
  10. Phosphoryl transfer

6

Stage one begins with the conversion of glucose into ________ ___________, which consists of three steps: phosphorylations, isomerisation, and another phosphorylation. It is completed with the cleavage of the ________ ___________ into two three-carbon fragments: _________ __________ and ________________ _________.

Stage one begins with the conversion of glucose into fructose 1,6-bisphosphate, which consists of three steps: phosphorylations, isomerisation, and another phosphorylation. It is completed with the cleavage of the fructose 1,6-bisphosphate into two three-carbon fragments: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.

7

Glucose enters cells through specific transport proteins and has one principal fate: it is ___________ by ATP to form ______ __________. This step is notable for two reasons: (1) _______ _________ cannot pass through the membrane because it is not a substrate for the glucose transporters, and (2) the addition of the _________ group acts to destabilize glucose, thus facilitating its further metabolism. The transfer of the _________ group from ATP to the hydroxyl group on carbon __ of glucose is catalyzed by __________.

Glucose enters cells through specific transport proteins and has one principal fate: it is phosphorylated by ATP to form glucose 6-phosphateThis step is notable for two reasons: (1) glucose 6-phosphate cannot pass through the membrane because it is not a substrate for the glucose transporters, and (2) the addition of the phosphoryl group acts to destabilize glucose, thus facilitating its further metabolism. The transfer of the phosphoryl group from ATP to the hydroxyl group on carbon 6 of glucose is catalyzed by hexokinase.

8

What is the equation for the formation of acetyl CoA from pyruvate?

Pyruvate + NAD+ + CoA → acetyl CoA + CO2 + NADH + H

9

What is the function of a kinase?

Kinases are enzymes that catalyze the transfer of a phosphoryl group from ATP to an acceptor.

10

The isomerization of glucose 6-phosphate to fructose 6-phosphate is a conversion of an ______ into a ______.

The isomerization of glucose 6-phosphate to fructose 6-phosphate is a conversion of an aldose into a ketose.

11

Glyceraldehyde 3-phosphate is on the direct pathway of glycolysis, whereas _____________ ________ is not. Unless a means exists to convert _____________ ________ into glyceraldehyde 3-phosphate, a three carbon
fragment useful for generating ATP will be lost. These compounds are isomers that can be readily interconverted: _____________ ________ is a ketose, whereas glyceraldehyde 3-phosphate is an _____. The isomerization of these three-carbon phosphorylated sugars is catalyzed by ______ _________ __________.

Glyceraldehyde 3-phosphate is on the direct pathway of glycolysis, whereas dihydroxyacetone phosphate is not. Unless a means exists to convert dihydroxyacetone phosphate into glyceraldehyde 3-phosphate, a three carbon fragment useful for generating ATP will be lost. These compounds are isomers that can be readily interconverted: dihydroxyacetone phosphate is a ketose, whereas glyceraldehyde 3-phosphate is an aldose. The isomerization of these three-carbon phosphorylated sugars is catalyzed by triose phosphate isomerase.

12

What is the overall reaction for the conversion of glucose into pyruvate?

Glucose + 2Pi + 2 ADP + 2 NAD→ 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2

13

What are the three main products that can be formed from pyruvate?

  1. Ethanol
  2. Lactate
  3. Acetyl CoA

14

_______is formed from pyruvate in a variety of microorganisms in a process called ______ ____ fermentation. The reaction also takes place in the cells of higher organisms when the amount of oxygen is limiting, as in ______ cells during intense activity. The reduction of pyruvate by NADH to form ______ is catalysed by ______ _____________.

Lactate is formed from pyruvate in a variety of microorganisms in a process called lactic acid fermentation. The reaction also takes place in the cells of higher organisms when the amount of oxygen is limiting, as in muscle cells during intense activity. The reduction of pyruvate by NADH to form lacate is catalysed by lactate dehydrogenase.

15

What is the purpose of the gluconeogenic pathway?

To convert pyruvate into glucose

16

What are the main noncarbohydrate precursors for gluconeogenesis?

Lactate, amino acids, and glycerol

17

Gluconeogenesis in the _____ and ______ helps to maintain the glucose level in the _____ so that the brain and muscle can extract sufficient glucose from it to meet their metabolic demands.

Gluconeogenesis in the liver and kidney helps to maintain the glucose level in the blood so that the brain and muscle can extract sufficient glucose from it to meet their metabolic demands.

18

In glycolysis the following reaction occurs:

 

How is this bypassed in gluconeogenesis?

19

In glycolysis the following reaction occurs:

 

How is this bypassed in gluconeogenesis?

20

In glycolysis the following reaction occurs:

 

How is this bypassed in gluconeogenesis?

21

In gluconeogenesis, oxaloacetate is transported from a mitochondrion in the form of ______: oxaloacetate is reduced to malate inside the mitochondrion by an NADH-linked ______ ____________.

In gluconeogenesis, oxaloacetate is transported from a mitochondrion in the form of malate: oxaloacetate is reduced to malate inside the mitochondrion by an NADH-linked malate dehydrogenase.

22

To keep glucose inside the cell, the generation of free glucose is controlled in two ways. 

  1. The enzyme responsible for the conversion of glucose 6-phosphate into glucose, _______-__-___________, is regulated.
  2. The enzyme is present only in tissues whose metabolic duty is to maintain _____-_______ homeostasis i.e. the _____ and ______.

To keep glucose inside the cell, the generation of free glucose is controlled in two ways. 

  1. The enzyme responsible for the conversion of glucose 6-phosphate into glucose, glucose 6-phosphatase, is regulated.
  2. The enzyme is present only in tissues whose metabolic duty is to maintain blood-glucose homeostasis i.e. the liver and kidney

23

The glycolytic pathway has a dual role; it degrades ________ to generate ATP and it provides building blocks for synthetic reactions, such as the formation of _____ ______.

The glycolytic pathway has a dual role; it degrades glucose to generate ATP and it provides building blocks for synthetic reactions, such as the formation of fatty acids.

24

Reactions catalysed by what enzymes are virtually irreversible in glycolysis? [3]

Reactions catalysed by:

  • Hexokinase
  • phosphofructokinase
  • pyruvate kinase

25

 Phosphofructokinase is the most important control site in the mammalian glycolytic pathway. High levels of ___ allosterically inhibit the enzyme. ___ binds to a specific _________ site that is distinct from the catalytic site. The binding of ___ _______ the enzyme’s affinity for fructose 6-phosphate. Thus, a ____ concentration of ___ converts the hyperbolic binding curve of  fructose 6-phosphate into a sigmoidal one. AMP reverses the inhibitory action of ___, and so the activity of the enzyme _________ when the ATP/AMP ratio is lowered. In other words, glycolysis is _________ as the energy charge falls. A _______ in pH also inhibits phosphofructokinase activity by augmenting the inhibitory effect of ___. The pH might fall when muscle is functioning anaerobically, producing excessive quantities of _____ ____. The inhibitory effect protects the muscle from _______ that would result from the accumulation of too much acid.
 

 Phosphofructokinase is the most important control site in the mammalian glycolytic pathway. High levels of ATP allosterically inhibit the enzyme. ATP binds to a specific regulatory site that is distinct from the catalytic site. The binding of ATP lowers the enzyme’s affinity for fructose 6-phosphate. Thus, a high concentration of ATP converts the hyperbolic binding curve of  fructose 6-phosphate into a sigmoidal one. AMP reverses the inhibitory action of ATP, and so the activity of the enzyme increases when the ATP/AMP ratio is lowered. In other words, glycolysis is stimulated as the energy charge falls. A decrease in pH also inhibits phosphofructokinase activity by augmenting the inhibitory effect of ATP. The pH might fall when muscle is functioning anaerobically, producing excessive quantities of lactic acid. The inhibitory effect protects the muscle from damage that would result from the accumulation of too much acid.
 

26

 Hexokinase, the enzyme catalyzing the _____ step of glycolysis, is inhibited by its product, ________-__-_________. _____ concentrations of this molecule signal that the cell no longer requires _______ for energy or for the synthesis of glycogen, a storage form of _______, and the _______will be left in the blood.

 Hexokinase, the enzyme catalyzing the first step of glycolysis, is inhibited by its product, glucose 6-phosphate. High concentrations of this molecule signal that the cell no longer requires glucose for energy or for the synthesis of glycogen, a storage form of glucose, and the glucose will be left in the blood.

27

The inhibition of phosphofuctokinase leads to the inhibition of what other enzyme?

Hexokinase

28

Why is phosphofructokinase rather than hexokinase the pacemaker of glycolysis? 

In muscle, glucose 6-phosphate can also be converted into glycogen. The first irreversible reaction unique to the glycolytic pathway, the committed step, is the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate. Thus, it is highly appropriate for phosphofructokinase to be the primary control site in glycolysis. 

29

Define allosteric control

The regulation of a protein by binding an effector molecule at a site other than the protein's active site. The site the effector binds to is termed the allosteric site.

30

 Pyruvate kinase, the enzyme catalyzing the _____ irreversible step in glycolysis, controls the _______ from this pathway. This final step yields ATP and ________, a central metabolic intermediate that can be ________ further or used as a building block. ATP allosterically ________ pyruvate kinase to slow glycolysis when the energy charge is ____. Finally, alanine also allosterically _______ pyruvate kinase—in this case, to signal that building blocks are abundant. When the pace of glycolysis _________, fructose 1,6-bisphosphate, the product of the preceding irreversible step in glycolysis, activates the ______ to enable it to keep pace with the oncoming high flux of intermediates. 

 Pyruvate kinase, the enzyme catalyzing the third irreversible step in glycolysis, controls the outflow from this pathway. This final step yields ATP and pyruvate, a central metabolic intermediate that can be oxidized further or used as a building block. ATP allosterically inhibits pyruvate kinase to slow glycolysis when the energy charge is high. Finally, alanine also allosterically inhibits pyruvate kinase—in this case, to signal that building blocks are abundant. When the pace of glycolysis increases, fructose 1,6-bisphosphate, the product of the preceding irreversible step in glycolysis, activates the kinase to enable it to keep pace with the oncoming high flux of intermediates.