Ketone bodies Flashcards
Remember, when a patient has low glucose level, has diabetes or the insulin-receptor pathway is compromised, our cells can synthesize ketone bodies.
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What is the first step of ketogenesis liver?
two molecules of acetyl-CoA reacts together to form acetoacetyl-CoA by thiolase
What is the second step of ketogenesis liver?
acetoacetyl-CoA react with acetyl-CoA and water to form HMG-CoA via HMG-CoA synthase.
What is the third step of ketogenesis in the liver?
HMG-CoA releases one of its acetyl-CoA to form acetoacetate by HMG-CoA lyase.
Describe the two reactions in which acetoacetate generates two other ketone bodies.
- acetoacetate undergoes decarboxylation to form acetone by acetoacetate decarboxylase.
- acetoacetate is reduced into D-Bhydroxybutyrate by D-B-hydroxybutyrate dehydrogenase. This reaction is coupled with the oxidation of NADH and H+ into NAD+
Suppose our bodies need energy. How can we obtain energy from ketone bodies?
- D-B-hydroxybutyrate is oxidized into acetoacetate by D-B-hydroxybutyrate dehydrogenase. This reaction is coupled with the reduction of NAD+ into NADH and H+
- Acetoacetate reacts with succinyl-CoA to form acetoacetyl-CoA by B-ketoacyl-CoA transferase. (In this reaction the CoA is transferred onto acetoacetate and the succinyl is released)
- Acetoacyl-CoA reacts with coenzymeA to form two molecules of acetyl-CoA by thiolase.
Describe how fatty acid synthase is activated.
acetyl-CoA binds to the SH of KS and malonyl-CoA binds to the SH of ACP.
Describe what happens in the first step of the FA synthase complex.
Condensation reaction in which malonyl-CoA undergoes decaborxylation by binding to the acetyl group of acetyl-CoA (releasing CO2) and forming B-ketobutyryl-ACP
Describe what happens in the second step of the FA synthase complex.
Reduction reaction in which ACP transfer ketobutyryl onto KR to be reduced into hydroxybutyry. This reaction is coupled with the oxidation of NADPH and H+ into NADP+
Describe what happens in the third step of the FA synthase complex.
Dehydration reaction in which ACP trasnfers hydroxybutyryl onto DH to removes a water and form a double bond in the generated molecule, butenoyl.
Describe what happens in the fourth step of the FA synthase complex.
Reduction reaction in which ACP transfer butenoyl onto ER where the double bond is reduced into a single bond to form butyryl. This reaction is coupled with the oxidation of NADPH and H+ into NADP+.
Describe what happens in the fifth step of the FA synthase complex.
Transfer step in which ACP transfer the butyryl group onto KS
Where is NADPH obtained from to be used by fatty acid synthase?
- Pentose phosphate pathway
- malate is oxidized into pyruvate by malic enzyme (and CO2 - byproduct) which is coupled with the reduction of NADP+ into NADPH and H+
Explain the cycle involving acetyl-CoA, oxaloacetate, citrate, malate, and pyruvate. Make sure to detail which one requires ATP or NADH/NAD+.
- Acetyl-CoA reacts with oxaloacetate to form citrate (citrate synthase). This reaction release CoA-SH.
- Citrate is converted by into oxaloacetate by citrate lyase. This reaction requires ATP and CoA-SH.
- Oxaloacetate is reduced into malate by malate dehydrogenase. This reaction is coupled with the oxidation of NADH into NAD+
4a. Malte can be converted into oxaloacetate by malate dehydrogenase. This reaction is coupled with the reduction of NAD+ into NADH and H+
4b. malate can be oxidized into pyruvate by malic enzyme. This reaction is coupled with the reduction of NADP+ into NADPH and H+.
- Pyruvate is converted into oxaloacetate by pyruvate carboxylase. This reaction requires ATP and CO2.
Our bodies are only able to synthesize FAs up to a certain length, let’s say this length is C18. What would we need to do in order for our bodies to elongate a chain up to 20 carbons?
Obtain linoleate from our diet
