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MCB-2 Block-3 Gems-4
Fatty Acids
23
Microbiology
Graduate
07/04/2011

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Term
Unsaturated Fatty Acids, general facts
Definition
Polyunsaturated have double bonds that are always 3 carbons apart(separated by methylene group)

Fatty acids only lengthened or shortened from COOH end

Mammals cannot insert new double bonds beyond c9-10

Unsaturated FAs, Double bonds must be modified before B-oxidation. Normal DBs in Cis form, oxidation requires isomerization to trans form.
Term
Mans essential fatty acids
Definition
Linoleic(18:9,12) gives rise to Arachidonic acid

a-liniolenic(18:9,12,15) acid gives rise to W-3 FAs.
Term
Generation of Cytosolic Acetyl CoA
(transport from mitochondria -> cytosol)
Definition
Acetyl-CoA + OAA -> Citrate(crosses membrane) + CoA-SH


In cytosol Citrate + CoA + ATP -> Acetyl CoA + OAA + ADP.

OAA + NADH -> Malate + Nad
Malate + NADP -> Pyruvate + NADPH + Co2.

Pyruvate goes back into mitochondria.
Term
Acetyl CoA carboxylase
Definition
Acetyl CoA + CO2 + ATP -> Malonyl CoA + ADP

Requires Biotin(Co2 carrier) covantly bound to lysine in schiff base.
Malonyl-CoA inhibits B-oxidaiton.

Inactivated by High malonyl-CoA
(Disintegration into monomers)

Phosphorylation -> Inactivates.
Term
Hormonal Control of acetyl CoA carboxylase
Definition
Insulin -> Dephosphorylationi of Acetyl-CoA carboxylase (activates)

Glucagon and Epi Inactivate. (cause FA and glucose mobilization)

Insulin -> protein phosphatase
Glucagon/Epi -> cAMP-protein kinase

Long term: prolonged fat-free diet or CHO-rich diets -> Change in gene expression
Term
Reactions in fatty acid synthesis
Definition

1. Acetyl-CoA binds to phosphopantetheine site (ACP) 2. Acetyl group -> Cysteine 3. Malonyl-CoA forms thioester with ACP 4. Malonyl CoA condenses with Acetyl CoA and CO2 group is released. Creates B-ketoacyl

Than reduction, Hydration, Reduction

NADPH both reductions

Term
Fatty Acid synthase control
Definition
Enzymes that increase in well fed-state

Acetyl-CoA carboxylase, ATP citrate lyase, G-6-P deh, Fatty acid synthase

Fatty acid synthase overexpressed in some breast/ovarian cancers, also a potential target in obesity
Term
Fatty acids to triglycerides
Definition
FA are first activated, and than esterified to form triacylglycerol(TAG)

Glycolysis is livers main source of C for glycerol.

Liver has glycerokinase, Fat cell does not.
Term
Linoleic Acid -> Arachidonic Acid
Definition
Activate Linoleic with CoASH
1 desaturation, 1 elongation, 1 more desaturation.

Elongations always add 2 carbons.
Term
Polyunsaturated FA's can be oxidized non-enzymically
Definition
At high O2 FAs are susceptible to auto-oxidation or peroxidation.

From ease of drawing away hydrogen from methylene group(between two double bonds)

Single O atom is inserted creating reactive aldehyde group.

If malon-dialdehyde the 2 aldehyde groups appear.
Can cross link protein(NH2 and SH groups) -> Lipofuscin accumulation.
Term
c-AMP and FA oxidation
Definition
c-AMP starts multiplicative cascade to start FA oxidation.

Lipid droplet unmasked by phoshporylation of perilipin

2nd TAG exposed to cleavage by intracellular Hormone-sensitive lipase.
(activated by Epineph/glucagon)

PKA phosphorylates HS-lipase and per
Term
Hormonal Control of Lipolysis
Definition
GLucocorticoids, Growth and thyroid hormone, facilitate lipolysis via induction of lipolytic proteins GLucocorticoids induce HS-lipase. Insulin inhibits HS-lipase via dephoshporylation
Term
Adipocyte breakdown of lipids
Definition
Adipose tissue releases unesterfied fatty acids and glycerol.

Albuin is a non-covalent carrier.

Glycerol travels to liver because adipocytes lack glycerokinase(glycerol to DHAP)
Term
FA transport into mitochondria for oxidation
Definition
FA -> Fatty acyl-CoA. (formation of acyl thioester energy rich compound)

ATP -> AMP drives thioester formation
Done by Fatty-acetyl-CoA Synthetases

Long chain Fa-CoA synthetase is outer membrane.

Medium and short chain in matrix.
Term
Carnitine(vit b20)
Definition
Required for transport of long chain FAs into matrix

Carnitine is made from lysine and methionine(3-CH3s) -> Trimetyllysine -> carnitine.

FA transfered from acyl-CoA to -OH on carnitine by carnitine-acyl-transferase and ester bond is formed.

In matrix FA rebinds CoA-SH and carnitine comes off
Term
B-Oxidation
Definition
Occurs in matrix of mitochondria. Oxidation by acyl-CoA deh -> FADH2 Hydration by Enoyl-CoA hydratase Oxidation by hydroxylcyl-CoA -> NADH deh Thiolysis by ketoacyl-CoA thiolase Yields Acetyl CoA
Term
Control of B-oxidation
Definition
Level of HS-lipase and Lipoprotien Lipase. (main suppliers of FFAs)

2nd malonyl-CoA: Inhibits carnitine-acyl transferase

Carnitine-acyl transferase I in liver increased expression in prolonged fast.
Term
Indirect allosteric regulation of B-oxidation
Definition
Carnitine-palmitoyl transferaesI: Inhibited by malonyl CoA.

B-oxidation itself has no direct inhibitors, just transport into mitochondria of Acetyl-CoA is regulated.
Term
Degradation of Very long(>24 C) FA
Definition
In peroxisomes, uses H202

E-FADH2 + O2 -> E-FAD + H2O2

Same process as mitochondrial B-oxidation, but first reaction catalyzed by H2O2

Zellwegers sydrome: functional peroisomes are absent, cant degrade VLFA-> deficicent plasmalogen.
Term
Refums Disease
Definition
Abberent α-oxidation of branched FAs(peroxisome)

When B-carbon bears -Ch3, the α-carbon cannot be oxidized, phytanic acid accumulates.

Normally α-carbon hydroxylated in O2-Vit C- Fe++ requiring reaction.

Deficient in refums(Phytanate hydroxylase)
Term
Oxidation of Odd-chain FAs
Definition
Propionyl-CoA is glucogenic precursor(odd numbered are keto and glucogenic)

1st: Carboxylation. Proprionyl CoA -> D-methymalonyl CoA.
Via propionyl CoA carboxylase, REquires biotin, CO2, ATP.

2nd racemerisation to L-methymalonyl CoA

3rd: Requires Cobalamin(Vit B12)
L-methylmalonyl CoA -> Succinyl CoA by methymalonyl CoA mutase.
Term
Medium-chain acty-CoA dehydrogenase deficnecy
Definition
Catalyzes first reaction in B-oxidation of medium chain FA

Lipid deposition and fatty liver.

Incorrectly diagnosed as Sudden infant death syndrome sometimes.

Low-fat diet and avoid fasting, usually detected during fasting hypoglycemia
Term
Carnitine(vit B20) deficiency
Definition
Common cause is Acyl-CoA deh deficiency accumulated Fatty acids form carnitine esters and are excreted in urine. LInked to hypoketotic hypoglycemia. Muscle cramps, weakness. Lipid droplets in muscle. Fatty degeneration of liver.
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