MCB L22 Flashcards
State the use of glucose in the human body and why it can be used in this manner
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
How does glucose enter the cell?
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
What is glycolysis (basics)?
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
Briefly describe stage 1 of glycolysis
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
Briefly describe stage 2 of glycolysis
Energy payoff phase / energy output / Generation
6-10
2x G3P → 2 x pyruvate
4x ATP produced
Describe glycolysis step 1
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
Describe glycolysis step 2
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
Describe glycolysis step 3
Phosphofructokinase phosphorylates fructose-6-phosphate into fructose-1,6-bisphosphate via ATP
IRREVERSIBLE under normal cellular conditions, COMMITED STEP (regulation point)
Explain the difference between bisphosphate and diphosphate
Bisphosphate - 2 monophosphoryl groups are separated
Diphosphate - 2 phosphoryl groups connected by anhydride linkage (ADP)
Describe glycolysis step 4
Fructose 1,6 - bisphosphate cleaved into 2 phosphorylated 3 carbon molecules by enzyme aldolase:
-G3P
-DHAP
DHAP not on direct pathway of glycolysis
Describe glycolysis step 5
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
Describe glycolysis step 6
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
Describe glycolysis step 7
phosphoglycerate kinase catalyses transfer of phosphoryl group from 1,3 - bisphosphoglycerate to ADP to form ATP, and also forming 3-Glycerate phosphate
Describe glycolysis step 8
3-glycerate phosphate mutase converts 3-glycerate phosphate to 2 glycerate phosphate by changing position of phosphoryl group
State the function of mutase enzymes and give an examle
Mutase enzymes ctalayse the intramolecular shif of chemical groups
e.g. 3-glycerate phospate mutase
Describe glycolysis step 9
Enolase catalyses the dehydration of 2-glycerate phosphate to phosphoenolpyruvate - (double bond induced)
Describe glycolysis step 10
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)
State the overall net equation for glycolysis
Glucose + 2Pi + 2 ADP + NAD+ → 2 pyruvate + 2 NADH + 2H+ 4ATP + H20
Which stages are involved in the Regulation of the glycolysis pathway and why?
Occurs at irrervsible steps, becuase the - delta G value is very high
Step 1
Step 3
Step 10
Which enzymes are involved in the regulation of glycolysis?
Hexokinase
PFK (Phosphofructokinase) - Key Regulatory Enzyme
Pyruvate kinase
(ALL KINASES!)
State how hexokinase is inhibited
Inhibited by its own product - glucose-6-phosphate - negative feedback
State how PFK is inhibited, activated
Inhibited:
-ATP
-Citric
Stimulated:
-ADP, AMP
-Fructose 2, 6 - bisphosphate
What type of enzyme is PFK?
Allosteric enzyme
Describe how ATP inhibits PFK
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
Descibe how pyruvate kinase is involved in the regulation of glycolysis
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
