Metabolism part 1 Flashcards
What is metabolism?
The complete set of catabolic (exergonic) and anabolic (endergonic) reactions that occur within living cells
Where is energy in ATP stored?
In the phosphoanhydride bonds
How do we obtain energy?
Through the oxidation of organic molecules (food)
What is the difference between NAD and NADP?
NADP has a phosphate
The molecules pick up energy in the form of 2 high energy electrons and a proton - hydride ion
What is glycolysis and when does it occur?
Obtaining energy from glucose
Consists of 10 steps
Occurs in both aerobic and anaerobic conditions
What is step 1 of glycolysis?
Glucose is trapped in the cell and it is phosphorylated by hexokinase which adds a phosphate from ATP hydrolysis. This forms glucose 6 phosphate which cant leave the cell
What is step 2 of glycolysis?
Glucose 6 phosphate undergoes isomerisation to form fructose 6 phosphate
What is step 3 of glycolysis?
The fructose 6 phosphate is phosphorylated to form Fructose 1,6 bisphosphate catalysed by PFK
What is step 4 and 5 of glycolysis?
Aldolase splits the F 1,6 BP into G-3-P and DHAP but DHAP is not on the glycolysis pathway but is an isomer of G-3-P so is converted to it
What is the importance of converting from glucose to fructose?
It would have split into 2 x isomers (2 and 4C molecules instead)
What is step 6 of glycolysis?
Enzyme 1 binds to the G-3-P and catalyses its oxidation
NAD+ accepts the electrons and is reduced
The enzyme is displaced by Pi to create a high energy sugar phosphate (1,3- bisphosphoglycerate)
What is step 7 of glycolysis?
The intermediate binds to enzyme 2 which catalyses the transfer of Pi to ADP
thus creating ATP and generating a carboxylic acid 3-phosphoglycerate
What is step 8 of glycolysis?
3- phosphoglycerate is converted to its isomer 2 - phosphoglycerate
What is step 9 and 10 of glycolysis?
2- phosphoglycerate loses a molecule of water becoming phosphoenolpyruvate (PEP) which is unstable so donates a phosphate group to ADP forming ATP and PEP is converted to pyruvate.
Where does lactate come from?
In anaerobic cells glycolysis is the principle source of ATP
NAD must be regenerated to enable glycolysis to continue
When no O2 can act as the final electron acceptor NADH passes electrons to pyruvate to form lactate
How is PFK regulated?
Regulatory molecules bind to the allosteric site to either increase or decrease the affinity of PFK for F-6-P
Activated by - AMP, F 2,6 BP
Inhibited by - ATP, decrease in pH and citrate
What is gluconeogenesis?
Occurs in the liver and is the formation of glucose from non carbohydrate precursors e.g. lactate, glucogenic amino acids
Why is gluconeogenesis not the reverse of glycolysis?
It would be energetically unfavourable
What is step 1 of gluconeogenesis?
The mitochondria converts pyruvate to oxaloacetate by pyruvate carboxylase which adds CO2 as it has a biotin prosthetic group
What is step 2 of gluconeogenesis?
Oxaloacetate is converted to malate which can leave the mitochondria (very impermeable) it is then converted back to oxaloacetate in the cytosol by NADH. This is then converted into PEP
What is step 3 of gluconeogenesis?
The reverse of glycolysis occurs and fructose 1-6 bisphosphate forms it is then converted to fructose 6 phosphate which is isomerised to form glucose 6 phosphate which is then converted to glucose
How is glycolysis and gluconeogenesis regulated?
Glycolysis generates ATP so AMP activates glycolysis and inhibits gluconeogenesis
What is the Cori cycle?
During heavy exercise - high glycolytic flux in the muscles- lactate can enter the blood and then enter the liver where it undergoes gluconeogenesis converting it back to glucose
Outline the entry into the TCA cycle
Pyruvate moves into the mitochondria where pyruvate dehydrogenase complex converts it to acetyl co A
It does this by decarboxylating it, then it is oxidised by NADH, co enzyme A is added forming acetyl co A
