Glycolysis and metabolism Flashcards
What is a metabolite?
- An intermediate or product of metabolism
- usually small molecules
What is the function of metabolites?
- fuel
- structure
- signalling
- regulatory effects on enzymes
- defence
- interactions with other organisms
How are metabolites linked?
Between metabolic reactions
What are metabolic reactions?
The life-sustaining enzyme-catalysed reactions that allow organisms to grow, reproduce, respond to changes in the environment and maintain structure
What is a metabolic pathway?
a sequence of chemical reactions undergone by a compound or class of compounds in a living organism (the product of one enzyme acts as the substrate for the next enzyme)
Is glucose taken in from the environment or synthesised in the body?
Glucose can be absorbed through the diet or created in the body by gluconeogenesis
What is typically thought of as the universal energy provider?
Glycolysis
How to you convert glycogen to glucose?
Glycogenolysis
How do you convert glucose to Glycogen?
Glycogenesis
How do you convert glucose to pyruvate?
Glycolysis
How do you convert pyruvate to glucose?
Gluconeogenesis
How do you convert pyruvate to lactate or ethanol?
Fermentation by anaerobic respiration
What do you convert pyruvate to ATP?
TCA cycle and electron transport chain
Where does glycolysis occur?
cytoplasm
What are the two phases of glycolysis?
ATP consumption and ATP production
In glycolysis what does one glucose molecule get converted to using ATP?
1 x glucose-6-phosphate
What is the net production from glycolysis per molecule of glucose?
2x ATP
2x NADH
2x Pyruvate
What is anaerobic metabolism?
Incomplete oxidation of glucose to lactate and hence less energy is produced
What is aerobic metabolism?
Aerobic respiration allows for the complete oxidation of glucose and produces more ATP
What are the stages of glycolysis? (in general)
1 x glucose —> 1 x glucose-6-phosphate (-ATP)
1 x glucose-6-phosphate —> 1x fructose-6-phosphate (-ATP)
1x fructose-6-phosphate—> EITHER 2x dihydroxyactetone phosphate OR 2x glyceraldehyde-3-phosphate
2x glyceraldehyde-3-phosphate —> 2x 1,3-diphosphoglycerate (2NAD+–> 2NADH)
2x1,3-diphosphoglyverate—> 2x 3-phosphoglycerate (2ADP–>2ATP)
2x 3-phosphoglycerate —> 2x 2-phosphoglycerate
2x 2-phosphoglycerate —> 2x phosphoenolpyruvate
2x phosphoenolpyruvate —> 2x pyruvate (2ADP –> 2ATP)
How is glucose imported into mammalian cells?
Sodium monosaccharide co-transport system using SGLTs
Sodium independent facilitated diffusion using GLUT transporters
What is Hexokinase?
Enzyme used in the first step of glycolysis to phosphorylate glucose at the 6th carbon creating glucose-6-phosphate
What is the purpose of glucose phosphorylation?
Traps glucose in cells preventing the molecule leaving through GLUT2
Destabilises glucose so further metabolic reactions can be carried out.
What is the importance of cleavage from a 6C molecule to a 3C molecule?
Allows for the production of 2 molecules of pyruvate.
What can fructose-1,6-bisphosphate be converted to?
Either:
Glyceraldehyde-3-phosphate (G3P)
OR
Dihydroxyacetone phosphate (DHAP)
What is important about DHAP?
It cannot be converted into 1,3-Bisphosphoglycert directly and therefore must be converted to G3P in an extra stage before glycolysis continues.
How does the sodium monosaccharide co-transport system work?
- energy requiring process
- transports glucose against conc gradient
- the transport of glucose is coupled to sodium which moves down conc-gradient
How does sodium-independent facilitated diffusion work when transporting glucose?
-mediated by a group of 14 glucose transporter isoforms (GLUT1-GLUT14)
- transport protein has a binding site for glucose outside the cell
- glucose binds to the binding site
- The binding causes the protein to change shape exposing glucose to the inside of the cell
- glucose passes into the cell and the protein returns to original shape
What is needed to transfer glucose to glucose-6-phosphate?
- ATP (gets converted to ADP and H+)
- Mg2+
- Hexokinase
What is the role of the divalent metal ion (Mg2+) in the first step of glycolysis?
forms a complex with ATP to activate the ATP into losing a phosphate group
What is the conformation of hexokinase?
2 lobes
What happens to hexokinase when glucose binds?
- large conformational change
- two lobes move closer to each other when glucose binds
- the cleft between the lobes closes and glucose is surrounded by the protein
- only the hydroxyl group on the 6 carbon of glucose is available for reaction.
Why is the conformational change of the hexokinase lobes important?
Environment around glucose is non-polar
Hydrophobic space allows ATP to diffuse to glucose
Ensures phosphorylation of glucose and not ATP hydrolysis
What are the ways in which pyruvate is metabolised?
Transamination
Aerobic respiration
Anaerobic fermentation
What does transamination of pyruvate produce?
forms alanine to be used in gluconeogenesis
What does aerobic respiration of pyruvate produce?
Generates Acetyl CoA to be used in the TCA cycle
What does the fermentation of pyruvate produce in humans?
Generates lactate
What does the fermentation of pyruvate produce in yeast?
Generates ethanol
What enzyme catalyses the reaction between glucose and glucose-6-phosphate? (step 1)
Hexokinase (HK)
What enzyme catalyses the reaction between Glucose-6-phosphate and fructose-6-phosphate? (step 2)
Phosphoglucose isomerase
What enzyme catalyses the reaction between fructose-6-phosphate and fructose-1,6-bisphosphate? (step 3)
Phosphofructokinase (PFK)
What enzyme catalyses the reaction between fructose-1,6-bisphosphate and G3P/DHAP? (step 4)
Aldolase
What enzyme catalyses the reaction between DHAP and G3P? (step 5)
Triose phosphate isomerase
What enzyme catalyses the reaction between G3P and 1,3-bisphosphoglycerate? (step 6)
G3P dehydrogenase
What enzyme catalyses the reaction between 1,3-bisphosphoglycerate and 3-phosphoglycerate? (step 7)
Phosphoglycerate Kinase (PG-kinase)
What enzyme catalyses the reaction between 3-phosphoglycerate and 2-phosphoglyverate? (step 8)
Phosphoglycerate mutase
What enzyme catalyses the reaction between 2-phosphoglycerate and phosphoenolpyruvate? (step 9)
Enolase
What enzyme catalyses the reaction between phosphoenolpyruvate and pyruvate? (step 10)
Pyruvate kinase (PK)
