Fatty Acid Metabolism Overview

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Questions and Answers

What is the primary role of malonyl CoA in fatty acid metabolism?

To inhibit carnitine acyl transferase I, thus blocking beta-oxidation. (correct)

To act as a precursor for the synthesis of palmitate.

To activate fatty acid synthase for fatty acid synthesis.

To promote the transport of fatty acids into the mitochondria for beta-oxidation.

Which of the following best describes the regulation of fatty acid synthesis and degradation?

They are independently regulated, with no direct influence on each other.

They are both upregulated by high levels of glucagon and epinephrine.

They are reciprocally regulated, meaning they are not typically active at the same time. (correct)

They are simultaneously active to maintain a constant energy supply.

Where does the desaturation of fatty acids predominantly occur?

In the mitochondrial intermembrane space, acting on free fatty acids.

In the mitochondrial matrix, using acetyl CoA as a substrate.

In the cytoplasm, using malonyl CoA as a substrate.

In the smooth endoplasmic reticulum, acting on fatty acids in phospholipids. (correct)

Which of the following is NOT a precursor for the biosynthesis of triacylglycerols (TG)?

Acetyl CoA. Signup and view all the answers

What is the primary donor of two-carbon units in the fatty acid elongation system?

Acetyl CoA. Signup and view all the answers

What is the primary reducing agent used in fatty acid synthesis?

NADPH Signup and view all the answers

Which molecule provides the two-carbon units for fatty acid chain elongation?

Malonyl CoA Signup and view all the answers

In which cellular compartment does fatty acid synthesis primarily occur?

Cytosol Signup and view all the answers

What is the role of Acyl Carrier Protein (ACP) in fatty acid synthesis?

It carries the growing fatty acid chain Signup and view all the answers

What prosthetic group is essential for the activity of acetyl CoA carboxylase?

Biotin Signup and view all the answers

At which carbon chain length does the fatty acid synthase complex typically cease elongation?

C16 Signup and view all the answers

In the fatty acid synthase complex, what type of linkage is formed with KS and ACP?

Thioester linkage Signup and view all the answers

Which of these locations is the least active site for fatty acid synthesis?

Skeletal Muscle Signup and view all the answers

Which enzyme catalyzes the transfer of the acetyl group from acetyl-CoA to the -SH of phosphopantetheine?

Acetyl-CoA-ACP transacetylase (AT) Signup and view all the answers

What molecule is released when malonyl-CoA is formed from acetyl-CoA?

CO2 Signup and view all the answers

In fatty acid synthesis, what role does NADPH primarily serve?

An electron donor for reduction reactions Signup and view all the answers

Which enzyme is responsible for the dehydration step in fatty acid synthesis?

β-D-hydroxyacyl dehydratase (HD) Signup and view all the answers

What type of isomer is generated by the β-ketoacyl ACP reductase?

D isomer Signup and view all the answers

What is the total number of NADPH molecules required to synthesize one molecule of palmitate?

14 Signup and view all the answers

Before condensation with malonyl-CoA, to which part of the β-ketoacyl-ACP synthase (KS) is the butyryl group transferred?

The Cys-SH of β-ketoacyl ACP synthase (KS) Signup and view all the answers

In vertebrates, how many separate polypeptides constitute the fatty acid synthase complex?

One large polypeptide with two domains Signup and view all the answers

What is NOT the main source of acetyl CoA for fatty acid synthesis?

Beta-oxidation of fatty acids Signup and view all the answers

How many cycles of condensation, dehydration and reduction are required to synthesize a 16-carbon fatty acid like palmitic acid?

7 Signup and view all the answers

How is acetyl CoA transported from the mitochondria into the cytosol for fatty acid synthesis?

As a molecule of citrate Signup and view all the answers

What provides the reducing power for fatty acid synthesis?

NADPH Signup and view all the answers

Which of the following reactions directly produces NADPH for fatty acid synthesis?

Oxidation of malate to pyruvate Signup and view all the answers

Which enzyme's activity determines the rate limiting step of fatty acid synthesis?

Acetyl CoA carboxylase Signup and view all the answers

Which of these is a negative feedback regulator of fatty acid biosynthesis?

Palmitoyl CoA Signup and view all the answers

What is the effect of citrate on fatty acid synthesis?

Allosterically activates acetyl CoA carboxylase and Precursor of cytosolic acetyl CoA, Increasing F.A. synthesis Signup and view all the answers

Where does the synthesis of phospholipids primarily occur?

Smooth endoplasmic reticulum Signup and view all the answers

Which of the following is NOT involved in the synthesis of triglycerides?

Red blood cells Signup and view all the answers

What is the parent compound of sphingolipids?

Ceramide Signup and view all the answers

What is the first step in the biosynthesis of sphingolipids?

Condensation of palmitoyl CoA and serine Signup and view all the answers

What is the role of phospholipases in the degradation of phospholipids?

Hydrolyze esters in phosphoglycerides Signup and view all the answers

What happens to ceramide after it is cleaved by ceramidase?

It breaks down into sphingosine and free fatty acid Signup and view all the answers

How are polar lipids transferred to specific cell membranes after their synthesis?

In vesicles by the Golgi apparatus Signup and view all the answers

What activates one of the OH groups in the biosynthesis of phospholipids?

Nucleotide (CDP) Signup and view all the answers

Where is glycerol 3-phosphate primarily synthesized?

In liver and adipocytes Signup and view all the answers

Which type of enzyme is responsible for the synthesis of phosphatidic acid?

Acyl CoA synthetase Signup and view all the answers

What is the parent compound of triglycerides (TG) and phospholipids?

Glycerol 3-phosphate Signup and view all the answers

What condition is necessary for glucose to enter adipocytes for TG synthesis?

Insulin dependence Signup and view all the answers

Which hormone does NOT play a role in regulating triglyceride metabolism?

Thyroid hormones Signup and view all the answers

What happens to excess carbohydrates or proteins in terms of energy storage?

They are stored as triglycerides. Signup and view all the answers

Which is NOT a step in the biosynthesis of membrane phospholipids?

Formation of cyclic structures Signup and view all the answers

What is the fate of triglycerides in the liver?

They are packed with cholesterol and exported. Signup and view all the answers

Study Notes

Lipid Metabolism

Dietary lipids are metabolized
Fatty acids and ketone bodies undergo β-oxidation
Fatty acids, triacylglycerols, and phospholipids are synthesized
Cholesterol and steroids, as well as plasma lipoproteins, are synthesized

Lipid Biosynthesis

Endergonic and reductive reactions utilize ATP and NADPH
Fatty acid synthesis is not the reversal of degradation, utilizing different enzymes
Synthesis occurs in the cytosol, while degradation happens in the mitochondrial matrix
Intermediates are covalently linked to the -SH group of ACP and CoA
Fatty acid elongation happens through the sequential addition of 2-carbon units
Reductant in fatty acid synthesis is NADPH
Elongation typically ends at C16, with further elongation or double bond insertion handled by other enzymatic systems
A large portion of body fatty acids comes from dietary carbohydrates and proteins

Formation of Malonyl-CoA

This process is catalyzed by acetyl CoA carboxylase, which has three domains
It involves the addition of a CO2 group to Acetyl-CoA, utilizing ATP
The enzyme biotin is involved

Acetyl CoA Carboxylase Enzyme

The enzyme consists of multiple components
Biotin carboxylase is a component
Transcarboxylase is a component
Other components are involved

Biosynthesis of Fatty Acids

The process involves a series of steps
Condensation is a crucial step
Carbon units are added one by one, using a fatty acid synthase complex

Fatty Acid Synthase Complex of E. coli

The complex consists of seven polypeptides
Functionally distinct components
Roles in the process
Acetyl-CoA to fatty acids

The F.A Synthase Growth

The fatty acid chain lengthens as malonyl CoA donates 2-carbon units
Palmitate synthesis (16-carbon fatty acid) results from seven steps of condensation, reduction, and dehydration
The process consumes 7 malonyl CoA molecules, 14 NADPH, and 7 ATPs, yielding palmitate

Source of Acetyl CoA

Pyruvate breakdown in mitochondria is the main source
Amino acid catabolism, along with fatty acid β-oxidation (to a lesser extent), contribute
Acetate is shuttled out of mitochondria as citrate, as the mitochondrial membrane is not permeable to acetate

Source of NADPH

Oxidation of malate to pyruvate generates NADPH
Pentose phosphate pathway also produces NADPH
The electron-donating NADPH is crucial for fatty acid synthesis

Regulation of F.A Synthesis and Degradation

Acetyl-CoA carboxylase is the rate-limiting step in the synthesis pathway
Palmitoyl-CoA inhibits biosynthesis
Citrate is an allosteric activator for acetyl-CoA carboxylase
Regulation takes place at multiple levels, coordinating synthesis and degradation
Hormone-mediated regulation exists
Dietary changes can influence the expression levels of the enzymes involved involved in the biosynthesis processes

Fatty Acid Synthase of Different Organisms

Bacterial and plant fatty acid synthesis utilizes distinct proteins performing different activities
In yeast, 7 activities are split across two different polypeptides
Vertebrates utilize a single large polypeptide to execute all 7 enzymatic activities

Biosynthesis of Triacylglycerols (TG)

Fatty acids are ingested or synthesized and directed to storage or membrane incorporation
The pathways for TG synthesis are dependent on the body's needs (e.g., rapid growth)
Excess carbohydrates are stored as fats
TG and phospholipid synthesis share similar precursors
TG synthesis is primarily in the liver and adipocytes

Glycerol 3-Phosphate Synthesis

Liver and adipocytes produce glycerol 3-phosphate from glucose during glycolysis (as an intermediary metabolite)

Phosphatidic Acid

A trace amount is found in the body
A crucial intermediate in phospholipid and TG biosynthesis

Biosynthesis of Membrane Phospholipids

Building blocks for membrane production
Synthesis involves joining glycerol/sphingosine with fatty acids, and adding polar head groups, with changes in head groups to produce different phospholipids
Two major synthesis pathways for phospholipids based on the strategy are used to attach head groups
The pathways involve attaching "activated" head groups onto the backbone with specific enzymes

Degradation of Phospholipids

Phospholipases, present in various tissues and pancreatic juices, hydrolyze the phosphodiester bonds of phosphoglycerides

Degradation of Sphingomyelin

Sphingomyelinase removes phosphorylcholine from the sphingolipid backbone, leaving ceramide
Ceramidase then cleaves ceramide into sphingosine and a fatty acid

Biosynthesis of Sphingolipids

Synthesis involves creating a sphinganine backbone via a 18-carbon chain
Fatty acyl CoA attaches to the sphinganine backbone
Sphingolipids are crucial for cellular function

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Description

Test your knowledge on key aspects of fatty acid metabolism, including the roles of malonyl CoA, acetyl CoA carboxylase, and the fatty acid synthase complex. This quiz covers synthesis, degradation, and the cellular processes involved in fatty acid metabolism. Perfect for students in biochemistry or related fields!