Citric Acid Cycle BIOC192 - Lecture 30 ✔️
what complex of the electron transport chain is succinate dehydrogenase a part of? -what is the function of this complex?
-complex II -oxidise FADH2 back to FAD (where the FAD is reduced by the citric acid cycle when succinate is converted into fumarate via the enzyme succinate dehydrogenase)
PQ: what does a reduced coenzyme indicate?
A: captured energy
PQ: what is substrate level phosphorylation?
A: direct use of energy from a substrate molecule conversion into a product to drive the synthesis of ATP (or equivalent) (where this will occur via the phosphorylation of ADP/GDP to ATP/GTP and remember in the first 2 that occurred during glycolysis, the P was coming from cleaving the phosphate off of the previous molecule HOWEVER the 3rd substrate level phosphorylation that occurs in the citric acid cycle, the P does not have to come from the substrate)
PQ: what is the conversion of succinate to fumarate to malate to oxaloacetate similar to?
A: steps 1, 2 and 3 of the beta oxidation of fatty acids
what is the energy of GTP equivalent to?
ATP
why is the succinate dehydrogenase (SDH) located in the inner mitochondrial membrane?
due to the fact that the enzyme is shared between the citric acid cycle and the electron transport chain
where does the citric acid cycle occur?
mitochondrial matrix
lecture 30 readings:
-Chapter 13, pages 217 - 222 in your textbook OR -Chapter 19 in Biochemistry by M.K. Campbell 9th edition.
lecture 30 objectives:
-describe how the products of glycolysis and β-oxidation feed into the citric acid cycle. -describe the key reactions in the citric acid cycle and how energy is conserved/captured in the citric acid cycle. -describe the how the citric acid cycle may be inhibited and the consequences of inhibition on energy metabolism. ( You do not need to learn the citric acid cycle. A diagram showing all the substrates and enzymes in order will be provided in the exam. This diagram is available to view on Blackboard.)
why does sodium fluoroacetate stop the citric acid cycle from working? [DIAGRAM on slide)
-fluoroacetate gets metabolised into fluoroacetly CoA (which is similar to the acetyl CoA) -therefore the citrate synthase produces fluorocitrate (similar to citrate) -in the next step, fluorocitrate binds to and inhibits aconitase (competitive inhibitor that causes the inactivation of the enzyme WHERE the conversion of citrate to isocitrate is not able occur) -this stops the subsequent citric acid cycle steps from occur, resulting in death
what is the location of the succinate dehydrogenase (SDH) enzyme? -what coenzyme does the succinate dehydrogenase (SDH) interact with?
-in the inner mitochondrial membrane -FAD
what are the stages of the citric acid cycle? (2) -what is captured in both these steps?
-release of carbon (as CO2) -regeneration of the starting molecule -energy
citric acid cycle summary: release of carbon
-two carbons removed -energy conserved as NADH -a four C molecule has been regenerated (succinyl-CoA) (the rest of the cycle is concerned with regenerating oxaloacetate and capturing some energy)
what is significant about FAD in terms of its association with enzyme succinate dehydrogenase?
flavin coenzymes or flavoproteins are tightly bound to the proteins or enzymes with which they interact
what is the location of the electron transport chain?
in the inner mitochondrial membrane
what is the citric acid cycle also known as?
krebs cycle
what is the poison that is found in 1080?
sodium fluoroacetate (used to target possums)
what occurs to the 2 carbon molecules entering the citric acid cycle as acetyl CoA?
they exit as 2CO2 (therefore the food molecules have been completely oxidised)
true or false, targeting the citric acid cycle is a method of killing?
true (fluoroacetate is produced by certain plants to kill the herbivores eating the plant)
lecture 30 objective based self assessment:
• Where in the cell does the citric acid cycle occur? • Carbon enters the citric acid cycle (CAC) in the form of acetyl-CoA, where does this acetyl-CoA come from? • What are the two major parts of the CAC? • How is energy captured in the CAC? • The first key reaction in the cycle is a condensation reaction, what is the product of this reaction and where does the energy for this reaction come from? • What key events happen in an oxidative decarboxylation? • The conversion of succinyl CoA to succinate enables a substrate level phosphorylation. Describe what happens in a substrate level phosphorylation. • The conversion of succinate to oxaloacetate is very similar to the reactions in which pathway? • What is the overall CAC reaction? • How does sodium fluroacetate inhibit the CAC? i.e., after ingestion, what compound is it converted to and what component of the CAC does this inhibit?
