Lecture 3 Flashcards
true or false; acetyl CoA can be used to synthesize fatty acid if there is a surplus of glucose
true
where is acetyl CoA usually resynthesized
liver, adipose tissue, mammary tissue
What is acetyl CoA converted when there is a surplus of glucose
maloyl CoA
What reaction occurs so that acetyl CoA will be converted to malonyl CoA
Biotin dependent CO2 fixation reaction
What is the enzyme for the biotin dependent CO2 fixation reaction
acetyl CoA carboxylase
- biotin is a caofactor
where do biosynthetic reaction occur
cytosol
What are the two ways in which acetyl CoA can be formed
B oxidation
decarboxylation of pyruvate in the mitochondria
How is acetyl CoA transported to the cytoplasm
via the formation of citrate
What does acetyl CoA carboxylase consist of
biotin carboxylase
bitoin carrier protein
carboxyl transferase
What does biotin catalyze
the transfer of the bicarbonate group to biotin
- the activated CO2 is now covalently bound to biotin, itself bound to its carrier protein via a lysine residue
- the carboxylated biotin transfers the carboxyl group to acetyl-CoA in the carboxyl transferase reaction
true or false; Malonyl CoA strongly inhibits the carnitine acyl transferase on the inner mitochondrial membrane
true
what is the significance of malonyl CoA from inhibiting carnitine acyl transferase
stops futile cycling of the newly made fatty acids being broken down by B-oxidation
What is fatty acid synthase
- is a complex involving multiple subunits surrounding a hollow chamber
- its purpose is to catalyze the addition of 2C to hydrocarbon chain forming fatty acids
What happens in stage 1 of fatty acid synthase
- ) acetyl group transferred from acetyl CoA to ACP
- thioester bond is formed to a PHOSPHOPANTETHEINE cofactor bound to the protein - ) acetyl group then passed to B keto-acyl-S-ACP sythase; where it is linked via a thioester bond to cysteine- SH group
- ) malonyl CoA is attached to another ACP molecule and the acetyl and malonyl groups are condensed to form acetoacetyl-ACP with loss of CO2
What happens during stage 2 in fatty acid synthase
acetoacetyl-ACP now undergoes three reactions:
reduction
dehydration
another reduction
which convert it to buytryl ACP
reducing power used is NADPH
What does the central core of the fatty acid synthase comprise of
the ACP forming swinging arm to move the growing fatty acyl chain between each of the enzyme subunits
what happens during the elongation step ; stage 3
butyryl ACP can now react with another malonyl ACP to form a 6C B ketoacyl ACP —> hexoyl-ACP
5 further cycles will generate palmitoyl ACP from which the Palmitoyl group is transferred to Co-ASH
Where does the elongation of fatty acids longer than 16 carbons occur
mitochondria and ER
- uses acyl-CoA, malonyl CoA, NADPH
What controls fatty acid synthesis
largely under hormonal control
- insulin stimulates fatty acid synthesis by stimulating glucose entry into the cells and activating pyruvate dehydrogenase
What inhibits acetyl CoA carboxylase
is inhibited by long chain fatty acyl CoAs and synthesis also slows if NADPH is limiting
What are the two isoforms of acetyl CoA carboxylase
ACC1
ACC2
Where is ACC1 present
in liver and adipose tissue
Where is ACC2
isoform found in cardiac and skeletal muscle
How are triacylglycerides resythesized
glycerol 3 phosphate accepts acyl chains from acyl CoAs using transferase
What is diacylglycerol 3 phosphate
aka phosphatidic acid
intermediate in fat as well as phospholipid biosynthesis
What can ceramides (sphingolipids) react with
- ) choline to yield sphingomyelin
- ) sugars to yield cerebrosides
- ) sugars and sialic acid to yield gangliosides
What are used in the biosynthesis of phosphoacylglycerol
phosphatidyl serine
phosphatidylethanolamine
