TCA cycle: Agbas Flashcards
L.O. Describe the overview of the citric acid cycle
in your answer include the basic AND the 3 stages that are found throughout the cycle (briefly
- helpful in metabolism (biochemical hub)
- oxidizing carbon fuels for harvesting high energy electrons
- amphibolic
- provides many other pathways with precursors for their reactions
- INSIDE the mitochondria
THREE stages:
- Degradation of energy nutrients
- Acetyl CoA pool
- Acetyl CoA entry into TCA
Define amphibolic
Catabolism and anabolism
What is the overall goal of the TCA?
To provide other pathways with high energy electrons that in turn will increase the amounts of ATP that is present
The TCA cycle involves the oxidation of 2-carbon units to produce
2CO2 molecules
1 GTP
High energy electrons in the form of NADH and FADH2
Describe acetate and the three ways (in detail) that acetyl CoA is able to be created
- lipids
- carbohydrates
- proteins
acetyl CoA is the activated form of acetate
- lipids: triacyl glycerol is transformed into fatty acids which undergo B-oxidation that creates acetyl CoA
- carbohydrates: Glucose is taken to pyruvate via oxidation which is then decarboxylated into 2 acetyl CoA
- proteins: broken down into amino acids which are then taken into acetyl CoA
Describe the three steps that are involved in taking pyruvate to acetyl CoA
- Decarboxylation removes one of the C atoms by giving off CO2, leaving 2 carbons left with a carbanion (this is catalyzed by the pyruvate dehydrogenase complex)
- Oxidation switches the C that has a negative charge to a carbocation, which serves as the binding site for acetyl CoA
- transfer acetyl group to Coenzyme A with the help of NAD+ to yield NADH
Describe the path of the pyruvate from the end of glycolysis to the entry into the TCA
Glycolysis yields the pyruvate in the cytosol of the cell and then the pyruvate that is destined for the TCA must enter the mitochondria via the mitochondrial pyruvate carrier
The pyruvate dehydrogenase complex catalyzes the decarboxylation of the pyruvate and then the CoA is added, creating the acetyl CoA who interacts with oxaloacetate to start the TCA
Describe the PDC in detail including
- Detailed description of the enzymes and what binds
- What cofactors are used (5 of them)
- The enzymes that are used to take the complex into its active form and then switch it to the inactive form
- There are 3 enzyme complexes
-E1: TPP, the site of phosphorylation and dephospho rylation
-E2: lipoic acid- the site where the CoA likes to hang out
-E3: NAD+ and FAD like to hang out here - TPP (thiamine pyrophosphate), lipoic acid, FAD, CoA, NAD+
- Pyruvate dehydrogenase kinase phosphorylates the TPP with the help of ATP and INACTIVATES the complex
Pyruvate dehydrogenase phosphatase removes the phosphate from the TPP and ACTIVATES the complex
What are the activators and inhibitors of the pyruvate dehydrogenase kinase?
Activators: acetyl CoA, NADH, ATP (remember, these are the products of the PDC reaction, so, if you have a lot of these hanging around, your complex needs to know that it needs to slow down its activity, therefore you will want the kinase to be activated that will INACTIVATE the complex via phosphorylation)
Inhibitors: Pyruvate, CoA, NAD+, ADP (these are what you need, or the reactants of the reaction that you want the complex to make shit with, so you will want the complex to be ACTIVE, which means you do not want the kinase to function, because she is gonna phosphorylate things and inactivate the complex)
What are the activators of the pyruvate dehydrogenase phosphatase?
Ca2+
Mg2+
What directly inhibits E2?
high acetyl CoA
If I have a bunch of ATP, will my phosphatases or kinases be working, and will my PDC be inactive or active?
With excess ATP, the kinases will be activated which will phosphorylate the complex, leading to inactivation
(and vice versa)
L.O. understand the mechanisms of the pyruvate dehydrogenase complex
Takes pyruvate to acetyl CoA with the use of 5 cofactors (TPP, lipoic acid, NAD, FADH, and CoA)
A kinase and a phosphatase are used in order to regulate the complex between its active and inactive states
The PDH is the LINK between glycolysis and the TCA
The overall goal is to take the pyruvate that is received from the glycolysis to make acetyl CoA for the TCA cycle.
OCCURS IN THE MITOCHONDRIA
Describe the first step of the TCA cycle including the intermediate that occurs within the interaction.
What kind of reaction is this?
Enzyme: citrate synthase
The acetyl CoA combines with a 4C oxaloacetate to form the intermediate, citryl CoA.
Citryl CoA reacts with water which takes the CoA away and forms citrate, a 6C molecule
*** oxaloacetate combines with the enzyme first and then the enzyme undergoes conformational changes to accept the acetyl CoA
condensation reaction
Describe the second step of the TCA cycle. 1. Oxaloacetate --> citrate 2. ??? Why is this reaction necessary What kind of reaction is this?
Aconitase isomerizes citrate into isocitrate via dehydration and hydration (basically it moves the -OH groups (isomerization)) with cis-aconitate being the intermediate (double bond)
It is able to bind to the citrate in the first place via the iron-sulfur cluster
THIS is important because the hydroxyl group is not in the proper location for oxidative decarboxylation (bc organic chemistry)
condensation reaction
