Biochemistry test 2

In which cellular compartment does the de novo synthesis of fatty acids (lipogenesis) primarily occur?

The cytosol

What is the immediate substrate for the de novo synthesis of fatty acids?

Acetyl-CoA

What is the primary end product of the fatty acid synthase system in humans?

Free palmitate

Which enzyme catalyzes the conversion of acetyl-CoA to malonyl-CoA?

Acetyl-CoA carboxylase

The conversion of acetyl-CoA to malonyl-CoA requires which vitamin as a cofactor?

Biotin

Name the two reductive steps in fatty acid synthesis that require NADPH as a cofactor.

Reduction of the 3-ketoacyl group and reduction of the 2,3-unsaturated acyl group

What molecule serves as the source of carbon dioxide for the carboxylation of acetyl-CoA?

Bicarbonate (HCO3−)

The fatty acid synthase complex in mammals exists as a dimer of two identical _____.

Polypeptide chains

In the fatty acid synthase complex, which protein contains pantothenic acid as 4'-phosphopantetheine?

Acyl carrier protein (ACP)

Which enzyme activity in the fatty acid synthase complex is responsible for liberating the final palmitate molecule?

Thioesterase

What are the two main pathways that provide NADPH for lipogenesis in the cytosol?

The pentose phosphate pathway and the malic enzyme reaction

Acetyl-CoA carboxylase is allosterically activated by _____.

Citrate

Which molecule acts as a feedback inhibitor of acetyl-CoA carboxylase?

Long-chain acyl-CoA (e.g., palmitoyl-CoA)

How does insulin affect the activity of acetyl-CoA carboxylase?

It promotes dephosphorylation, activating the enzyme

Glucagon and epinephrine inhibit lipogenesis by promoting the _____ of acetyl-CoA carboxylase.

Phosphorylation

In the presence of high AMP, which kinase phosphorylates and inactivates acetyl-CoA carboxylase?

AMP-activated protein kinase (AMPK)

Where does the elongation of existing fatty acid chains primarily occur?

The endoplasmic reticulum (microsomal system)

Fatty acids must be converted to an active intermediate before catabolism. What is this intermediate called?

Acyl-CoA

Which enzyme catalyzes the activation of a fatty acid to acyl-CoA, requiring ATP?

Acyl-CoA synthetase (thiokinase)

What is the primary site for β-oxidation of fatty acids?

Mitochondria

Which molecule transports long-chain acyl-CoA across the inner mitochondrial membrane?

Carnitine

Which enzyme is the gateway for fatty acid entry into mitochondria?

Carnitine palmitoyltransferase-I (CPT-I)

Which intermediate of lipogenesis inhibits CPT-I?

Malonyl-CoA

Each cycle of β-oxidation removes how many carbon atoms?

Two carbons (as acetyl-CoA)

Identify the four steps of β-oxidation.

Dehydrogenation (FAD), hydration, dehydrogenation (NAD+), thiolysis

What is the net ATP yield from complete oxidation of palmitate (C16)?

129 ATP

β-oxidation of odd-chain fatty acids produces acetyl-CoA and _____.

Propionyl-CoA

Why is propionyl-CoA glucogenic?

It is converted to succinyl-CoA

Where does oxidation of very-long-chain fatty acids begin?

Peroxisomes

Under what condition does the liver produce ketone bodies?

High fatty acid oxidation (starvation or diabetes)

Name the three ketone bodies.

Acetoacetate, D-3-hydroxybutyrate, acetone

Which enzyme is rate-limiting in ketogenesis?

HMG-CoA synthase

Ketone bodies are used by _____.

Extrahepatic tissues

Which enzyme required for ketone use is absent in liver?

Succinyl-CoA-acetoacetate CoA transferase (thiophorase)

High ketone bodies in blood is called _____.

Ketonemia

Δ9 desaturase produces what type of fatty acids?

Monounsaturated fatty acids

Why are linoleic and α-linolenic acids essential?

Humans cannot introduce double bonds beyond Δ9

Which C20 fatty acid is precursor for eicosanoids?

Arachidonic acid

Why is cyclooxygenase called a suicide enzyme?

It undergoes self-catalyzed destruction

How do NSAIDs reduce inflammation?

They inhibit COX and block prostaglandin synthesis

Leukotrienes are formed via which pathway?

Lipoxygenase pathway

Function of thromboxane A2?

Vasoconstriction and platelet aggregation

Function of prostacyclin (PGI2)?

Inhibits platelet aggregation

Common precursor of TAGs and phosphoglycerols?

Phosphatidate

Intestinal TAG synthesis starts from _____.

2-monoacylglycerol

Which phospholipid deficiency causes neonatal respiratory distress?

Dipalmitoyl lecithin

All sphingolipids derive from _____.

Ceramide

Ceramide is formed from serine and _____.

Palmitoyl-CoA

Tay-Sachs disease enzyme deficiency?

Hexosaminidase A

Gaucher disease accumulates _____.

Glucosylceramide

Four major plasma lipoproteins?

Chylomicrons, VLDL, LDL, HDL

Which transports dietary TAGs?

Chylomicrons

Which transports endogenous TAGs?

VLDL

Which mediates reverse cholesterol transport?

HDL

Main apoprotein of LDL?

Apo B-100

Cofactor for LPL?

Apo C-II

LPL is located in _____.

Blood capillaries

Chylomicron remnants are taken up via _____.

Apo E receptor

Which enzyme esterifies cholesterol in HDL?

LCAT

Rate-limiting enzyme of lipolysis?

Hormone-sensitive lipase (HSL)

Effect of insulin on HSL?

Inhibits via dephosphorylation

Brown fat uncoupling protein?

Thermogenin

Precursor of LDL?

VLDL

Deficiency causing fatty liver due to impaired VLDL?

Choline

High LDL leads to _____.

Atherosclerosis

Enzyme converting remnants to denser particles?

Hepatic lipase

SR-B1 function?

Uptake of cholesteryl esters from HDL

C2 donor in fatty acid synthesis?

Malonyl-CoA

Signal that inhibits fatty acid oxidation?

Malonyl-CoA

Excess liver fat condition?

Fatty liver (NAFLD)

What happens to CO2 in malonyl-CoA during synthesis?

It is released

Effect of fasting on lipolysis?

Increases lipolysis

Apolipoprotein unique to chylomicrons?

Apo B-48

FFA transport protein in blood?

Albumin

Fate of glycerol from adipose tissue?

Goes to liver

Acetoacetate converts to _____.

Acetone

Source of acetyl-CoA for lipogenesis?

Glycolysis

Cytosolic enzyme producing acetyl-CoA from citrate?

ATP-citrate lyase

α-linolenic acid belongs to which family?

Omega-3

EFA deficiency leads to accumulation of _____.

Mead acid

Enzyme converting arachidonate to PGH2?

Prostaglandin H synthase

Function of LTB4?

Chemotaxis

Ether phospholipids class?

Plasmalogens

Ceramide + phosphatidylcholine forms _____.

Sphingomyelin

Active sulfate donor?

PAPS

Niemann-Pick disease deficiency?

Sphingomyelinase

Krabbe disease deficiency?

β-galactosidase

Hormone regulating appetite and FA oxidation?

Leptin

Ketosis in cattle occurs when?

High glucose demand + low intake

Ethanol metabolism converts pyruvate to _____.

Lactate

Alcohol causes fatty liver because _____.

High NADH inhibits β-oxidation

LCAT activator?

Apo A-I

Function of carnitine translocase?

Exchange acylcarnitine/carnitine

Hypoglycin inhibits _____.

Acyl-CoA dehydrogenases

Refsum disease involves _____.

Phytanic acid

Zellweger syndrome lacks _____.

Peroxisomes

Thiolase function in β-oxidation?

Cleaves 3-ketoacyl-CoA

First step enzyme in TAG synthesis?

Glycerol-3-phosphate acyltransferase

Second messenger for lipolysis?

cAMP

Glucocorticoid effect on lipolysis?

Permissive effect