B L3 Flashcards
What are 4 major ways in which glucose can be utilised?
- synthesis of structural polymers (extracellular matrix and cell wall polysaccharides)
- Storage (in the form of starch, glycogen, sucrose)
- Oxidation via pentose phosphate pathway/hexose shunt (to produce ribose - 5 - phosphate – which is used in nucleotides)
- oxidation via glycolysis (to give pyruvate)
Define the following:
- Glycolysis
- Gluconeogenesis
- Glycogenesis
- Glycogenolysis
- Pentose phosphate pathway
Which of the glucose transporters are insulin sensitive? where are they present?
GLUT 4
In the muscle and adipose tissue
What are the different glucose transporters? and where are they present?
GLUT 1- Endothelial and RBCs
GLUT 2 - pancreas and liver
GLUT 3 - brain
GLUT 4- adipose tissue and muscle cells
GLUT 5- intestines and kidney
What glucose transporter is present in the brain? Why?
GLUT 3
What glucose transporters are presnt in the pancreas and the liver? why?
GLUT 2
– take up large amounts of glucose for storage as glycogen in the liver not sure why in pancreas
What are the 5 imp types of reactions that occur in glycolysis?
- Phosphoryl transfer (Transfer of phosphate grp from ATP to an intermediate or from an intermediate to ADP)
- Phosphoryl shift (A phosphoryl group is transferred from an oxygen atom to another within a molecule by a mutase)
- Isomerisation ( conversion of a ketose into an aldose or vice-versa by an isomerase)
- Aldol cleavage (
- Dehydration ( Removal of water by a dehydratase)
What are the products of the net reaction of glycolysis?
2 ATP and 2 NADH molecules + 2 pyruvate
What are the two stages of glycolysis?
The Investment stage
The payoff stage
What is uptaken and what is produced in the two stages of glycolysis
The Investment stage:
– 2 ATP molecules are hydrolysed to give ADP
The payoff stage:
– 4 ATP molecules are produced
– 2 NADH molecules produced from the reduction of 2 NAD+ molecules
Draw a diagram of the Investment phase of glycolysis and label the priming/irreversible reactions. Also mention which reactions are spontaneous and which ones aren’t.
What is the reaction that links the Investment and the payoff phase in glycolysis?
Glyceraldehyde 3- Phosphate (G3P) + Dihydroxyacetone Phosphate (DHAP) — Triose Phosphate isomerase —>
2 Glyceraldehyde 3- Phosphate
In this step DHAP is converted to G3P – they are interchangeable molecules
Which step in glycolysis commits glucose to staying in the cell?
The first step:
Glucose — hexokinase –> Glucose -6- Phosphate
Which step in glycolysis commits glucose to undergoing glycolysis?
The third step:
Fructose -6- phosphate – Phosphofructokinase-1(PKF-1) –> Fructose 1,6 bisphosphate
What regulates hexokinase activity?
Hexokinase is subject to product inhibition by glucose 6-phosphate.
G-6-P inhibits hexokinase activity in all cells except liver cells (as liver stores large amounts of glucose thus theres unlimited uptake)
What regulates Phosphofructokinase-1 activity?
It is regulated by ATP mainly
If there’s high ATP it will inactivate this enzyme as no more ATP production is needed. As metabolic needs of the cell are being met thus no more Energy needed
Draw out and label the pay-off pathway of glycolysis
What is the function of kinases?
Kinases are enzymes that transfer PO4 grps btwn ATP and various substrates (either to or from)
What metals does pyruvate kinase require for its activity?
Divalent metals like Mg 2+ or Mn 2+
Write down the summary equation for glycolysis.
ggggg
What is used and made in glycolysis reaction?
Used:
- 2 ATP
- 1 glucose
- 2 NAD +
Made:
- 4 ATP
- 2 NADH (must be redoxidised for to NAD for glycolysis to continue)
- 2 Pyruvate
What enzyme cleaves glucose from glycogen and starch? What molecule does this give?
Glycogen phosphorylase
Glucose-1-phosphate
What are the following hydrolysed into?
Lactose
Sucrose
Lactose - glucose + galactose
Sucrose - glucose + fructose
When do most of the sugars feed into glycolysis?
During the investment phase
What are the fates of pyruvate?
Hypoxic/anaerobic conditions:
- 2 pyruvate —> 2 ethanol + 2 CO2 (by alcohol dehydrogenase)
(happens in fermentation process in yeast) - 2 Pyruvate —> 2 lactate (by lactate dehydrogenase)
(happens in muscle cells during exercise when there is high metabolic activity and not enough O2 to meet demands)
Aerobic conditions
- 2 Pyruvate —> 2 Acetyl CoA (by pyruvate dehydrogenase)
Proceeds into the citric acid cycle
Differentiate btwn fast and slow twitch muscle fibres
Fast twitch:
- white fibres
- short bursts of energy
- Muscle of domestic birds and sprinters
- nearly devoid of mitochondria
- almost all energy generated by anaerobic glycolysis
—-> Anaerobic glycolysis produces less ATP but produces it 100x faster than oxidative phosph. (2 ATP per glucose)
Slow twitch:
- red fibres
- contract slow and steadily
- Muscle of migratory birds and marathon runners
- high number of mitochondria (gives it the red colour)
- almost all energy by oxidative phosphorylation
—–> Oxidative phosph is much slower than anaerobic glycolysis but produces more ATP (32 ATP per glucose)
Regeneration of NAD from NADH - when is it done? how? Write down the equations
- NADH (from glycolysis) needs to be regenerated into NAD in anaerobic conditions in order for ATP production to occur via the glycolytic pathway.
ALCOHOL FERMENTATION:
- done by plant tissues, invertebrates and yeast regenerate NAD thru alcohol fermentation:
Pyruvate —-> Acetaldehyde (release of CO2 and enzyme is pyruvate decarboxylase)
Acetaldehyde —–> ethanol (by alcohol dehydrogenase) (oxidation of NADH to NAD)
HOMOLACTIC FERMENTATION:
In muscle cells – pyruvate is reduced to lactic acid
Pyruvate —–> Lactate (by lactate dehydrogenase) (NADH gets oxidised to NAD)
What is the role of 2, 3 diphosphoglycerate (a by-product of glycolysis) in RBCs ? When would its conc increase?
It decreases deoxyhaemoglobin’s affinity for O2 thus allowing it do perfuse into tissues more
The concentrations increase in the RBC at higher altitudes and in anemia thus promoting the release of O2 into the tissues
Tumor cells and their affect on glycolysis
Tumor cells grow really rapidly more than angiogenesis (production of capillaries) can keep up with.
This results increased levels of anaerobic metabolism
Tumor cells increased expression of LDH (lactate dehydrogenase – converts pyruvate into lactate and vice-versa)
What are the 3 main enzymes responsible in regulating glycolysis?
- Hexokinase
- Phosphofructokinase - 1
- Pyruvate kinase
What is glycolysis and gluconeogenesis? Where do they mainly occur?
Glycolysis - conversion of glucose to pyruvate
–> Occurs mainly in the muscle and brain
Gluconeogenesis - Synthesis of glucose from pyruvate, amino acids and other noncarbs
–> Occurs mainly in the liver
What are the 3 steps in gluconeogenesis that are different from glycolysis - what are the enzymes used? and What are the intermediates?
Which one of the following cannot escape from the selectively permeable inner mitochondrial membrane?
- Malate
- Oxaloacetate
- Pyruvate
- Phosphoenolpyruvate (PEP)
Oxaloacetate
Oxaloacetate can either be used within the mitochondria for the TCA cycle
or
Can be converted into malate or PEP to allow transport to cytosol for gluconeogenesis
What is produced and used in gluconeogenesis?
Does it produce ATP?
When is it used?
Uses:
2 Pyruvate
4 ATP
2 NADH + 2 H+
2 GTP
4 H2O
Produces:
1 Glucose
4 ADP
2 NAD+
2 GDP
6 Pi
No ATP produced but 4 ATP consumed thus very high energy consuming reaction
Thus this reaction is only performed when necessary.
Glucose is the only source of energy/ATP used by the brain, nervous system and RBCs. Thus this process allows the generation of glucose when energy stores are depleted during:
– Starvation
– Overnight fasting
– Exercise
Which of the following dont use glucose as their only energy source?
- Brain
- Muscles
- Nervous system
- RBCs
Muscles
Which of the following cant be used to synthesise glucose in animals? How is this different in plants, yeast and many bacteria?
- pyruvate
- amino acids
- lactate
- oxaloacetate
- glycerol
- fatty acids
Fatty acids (product of their degradation is Acetyl-coA which cant be converted into oxaloacetate)
Sugars (pyruvate, oxaloacetate and lactate) and amino acids along with glycerol can be used to synthesise glucose
Plants, yeast and many bacteria can use Fatty acids to synthesise glucose.
Cori cycle
L-lactate produced in the muscles under anaerobic conditions like during vigorous exercise (glucose —> pyruvate thru glycolysis and pyruvate converted to lactate under anaerobic conditions)
The lactate is transported to the liver where it undergoes gluconeogenesis and is converted back to glucose.
The glucose is then transported back to the muscle via the bloodstream where it can be used for energy production
This process requires a lot of energy and is thus conducted in the liver as the liver metabolises fats for energy and not in the muscles to prevent further expenditure of energy.
Where does the pentose phosphate pathway occur? another name? What are the main products?
In the cytosol
Hexose monophosphate shunt
NADPH and Ribose-5-phosphate
What happens to the 5-C sugars that arent needed for synthesis of nucleotides? What cells does this happen often in?
they are shunted back and and recycled to the mainstream of glycolysis and are converted back into Fructose-6-phosphate and Glyceraldehyde-3-phosphate
Happens often in RBCs as they dont need to divide as often thus limited need for synthesis of DNA and RNA
Draw the Pentose phosphate/Hexose monophosphate shunt pathway
Wat happens in the non-oxidative phase of the pentose phosphate pathway?
Glucose - 6 - phosphate is regenerated from Ribose - 5- phosphate
Happens in cells that need more NADPH than R-5-P (nucleotides)
Like in the liver and adipose tissue cells
What determines whether G-6-P will continue with the glycolysis pathway or go into the pentose phosphate pathway?
The concentration of NADPH in the cell
If there’s a high conc. of NADPH then glycolysis will occur and the pentose shunt pathway will be inhibited.
What does G-6-P dehydrogenase deficiency result in?
Impairs the ability of an erythrocyte to form NADPH
This results in haemolytic anemia
