MCB L22

Question 1

State the use of glucose in the human body and why it can be used in this manner

Answer 1

Only fuel used by brain under non-starvation conditions

Glucose exists in a ring formation, therefore, less likely to modify proteins and affect their activity in a non-specific manner

Question 2

How does glucose enter the cell?

Answer 2

Insulin levels high after meal
Insulin binds to insulin receptors
Insulin receptors acitvated
Send electrical impulse to GLUT-4 protein (glucose transporter protein)
Transports glucose into the cell from outside the cell

Question 3

What is glycolysis (basics)?

Answer 3

Occurs in ALL prokaryotic and eukaryotic cells
10 reactions, in cytoplasm
Glucose converted into 2 molecules of pyruvate and 2 molecules of ATP
Also, glycolysis reduced NA+ to NADH
First step in anaerobic and aerobic respiration
2 consecutive stages

Question 4

Briefly describe stage 1 of glycolysis

Answer 4

Energy investment stage / energy input / trapping
1-5
Need 2 xATP
Glucose → 2x glyceraldehyde-3-phosphate

TRAPPING: trap glucose into cell, form molecule that can be readily cleaved into 2 x phosphorylated 3 carbon molecules

Question 5

Briefly describe stage 2 of glycolysis

Answer 5

Energy payoff phase / energy output / Generation
6-10
2x G3P → 2 x pyruvate
4x ATP produced

Question 6

Describe glycolysis step 1

Answer 6

Glucose phosphorylated into glucose-6-phosphate via ATP by hexokinase

Due to the phosphoryl group, glucose-6-phosphate cannot pass through extracellular membrane, locked / trapped in cell

Question 7

Describe glycolysis step 2

Answer 7

Phosphoglucose isomerase catalyses isomerisation of Glucose-6-phosphate into fructose-6-phosphate

isomerisation is a converstion of aldose to ketose

Important because only fructose-6-phosphate can be READILY cleaved into two 3-carbon molecule

Question 8

Describe glycolysis step 3

Answer 8

Phosphofructokinase phosphorylates fructose-6-phosphate into fructose-1,6-bisphosphate via ATP

IRREVERSIBLE under normal cellular conditions, COMMITED STEP (regulation point)

Question 9

Explain the difference between bisphosphate and diphosphate

Answer 9

Bisphosphate - 2 monophosphoryl groups are separated

Diphosphate - 2 phosphoryl groups connected by anhydride linkage (ADP)

Question 10

Describe glycolysis step 4

Answer 10

Fructose 1,6 - bisphosphate cleaved into 2 phosphorylated 3 carbon molecules by enzyme aldolase:

-G3P
-DHAP

DHAP not on direct pathway of glycolysis

Question 11

Describe glycolysis step 5

Answer 11

Isomerization of DHAP to G3P catalysed by TPI

This prevents phosphorylated 3 carbon molecule going to waste as it can now be used in glycolysis

Importance of this stage is shown by FPI deficiency, lower levels of DHAP isomerised to G3P. Therefore, less G3P, therefore, less pyruvate and ATP.

Can lead to:

-Haemolytic anaemia
-Neurodegeneration

Question 12

Describe glycolysis step 6

Answer 12

G3P oxidised + phosphorylated to 1,3 - bisphosphoglycerate

Catalysed by enzyme glyceraldehyde-3-phosphate dehydrogenase

1,3 - bisphosphoglycerate has high phosphoryl transfer potential, used to generate ATP in next step - it can be used to synthethise ATP from ADP and orthophosphate

Question 13

Describe glycolysis step 7

Answer 13

phosphoglycerate kinase catalyses transfer of phosphoryl group from 1,3 - bisphosphoglycerate to ADP to form ATP, and also forming 3-Glycerate phosphate

Question 14

Describe glycolysis step 8

Answer 14

3-glycerate phosphate mutase converts 3-glycerate phosphate to 2 glycerate phosphate by changing position of phosphoryl group

Question 15

State the function of mutase enzymes and give an examle

Answer 15

Mutase enzymes ctalayse the intramolecular shif of chemical groups

e.g. 3-glycerate phospate mutase

Question 16

Describe glycolysis step 9

Answer 16

Enolase catalyses the dehydration of 2-glycerate phosphate to phosphoenolpyruvate - (double bond induced)

Question 17

Describe glycolysis step 10

Answer 17

Pyruvate kinase catalyses the transfer of phosphoryl group from phosphenolpyruvate to ADP to form pyruvate and ATP

Importance of this step: Phosphoenolpyruvate is unstable due to phosphoryl group. Once phosphoryl group transferred to ADP, phosphoenolpyruvate can be converted to pyruvate (a stable ketone)

Question 18

State the overall net equation for glycolysis

Answer 18

Glucose + 2Pi + 2 ADP + NAD+ → 2 pyruvate + 2 NADH + 2H+ 4ATP + H20

Question 19

Which stages are involved in the Regulation of the glycolysis pathway and why?

Answer 19

Occurs at irrervsible steps, becuase the - delta G value is very high

Step 1

Step 3

Step 10

Question 20

Which enzymes are involved in the regulation of glycolysis?

Answer 20

Hexokinase
PFK (Phosphofructokinase) - Key Regulatory Enzyme
Pyruvate kinase

(ALL KINASES!)

Question 21

State how hexokinase is inhibited

Answer 21

Inhibited by its own product - glucose-6-phosphate - negative feedback

Question 22

State how PFK is inhibited, activated

Answer 22

Inhibited:

-ATP
-Citric

Stimulated:

-ADP, AMP
-Fructose 2, 6 - bisphosphate

Question 23

What type of enzyme is PFK?

Answer 23

Allosteric enzyme

Question 24

Describe how ATP inhibits PFK

Answer 24

ATP binds allosterically to enzyme PFK, to a region on PFK other than active site

When ATP is bound, PFK no longer shows Michaeles Menton Kinetics and therefore, rate of reaction slows down

Question 25

Descibe how pyruvate kinase is involved in the regulation of glycolysis

Answer 25

Pyruvate kinase inhibited by:

AcetylCoA
ATP
Fatty acids

Decreases rate of glycolysis when energy levels high (same as HEXOKINASE)

Activated by

Fructose 1,6 bisphosphate