Fatty Acid Synthesis Flashcards

Questions and Answers

Where does fatty acid synthesis occur and what type of process is it?

Anabolic process that occurs in the cytoplasm, primarily in the liver and adipose tissue.

What are the substrates for fatty acid synthesis?

Acetyl-CoA & ATP derived from glucose and NADPH from the pentose phosphate pathway.

What is the product of fatty acid synthesis?

Saturated palmitate (16:0), which can become unsaturated through elongation/desaturation.

How many ATPs are expended in order to produce a palmitate molecule from acetyl-CoA?

7 ATP Signup and view all the answers

What are the three parts of fatty acid synthesis?

Transport acetyl-CoA into the cytoplasm by citrate shuttle, activation of acetyl-CoA by acetyl-CoA carboxylase, synthesis of fatty acid by fatty acid synthase. Signup and view all the answers

Where does oxidative degradation of a fatty acid molecule begin?

The carboxyl end of the molecule. Signup and view all the answers

What is the function of fatty acid synthase?

Catalyzes the sequential addition of 2C units from acetyl-CoA to the carboxyl end of a growing fatty acid chain. Signup and view all the answers

During the course of fatty acid synthesis, the growing acyl group is transferred between which two molecules?

An acyl carrier protein and a cysteine side chain of the fatty acid synthase enzyme. Signup and view all the answers

What is the stoichiometry for the synthesis of palmitate from acetyl-CoA?

8 acetyl-CoA + 7 ATP + 14 NADPH --> palmitate + 14 NADP+ + 8 CoA + 6 H2O + 7 ADP. Signup and view all the answers

What is the 'committed' step of fatty acid synthesis and what enzyme catalyzes it?

Carboxylation reaction that forms malonyl-CoA from acetyl-CoA, catalyzed by acetyl-CoA carboxylase. Signup and view all the answers

What cofactor does acetyl-CoA carboxylase require for its activity?

A biotin cofactor. Signup and view all the answers

What does the citrate cleavage pathway provide for lipogenesis?

Acetyl-CoA and NADPH. Signup and view all the answers

What are the two roles of citrate in fatty acid synthesis?

It is cleaved by ATP citrate lyase to form acetyl-CoA and oxaloacetate and acts as an allosteric activator of acetyl-CoA carboxylase. Signup and view all the answers

What is the function of pyruvate carboxylase?

Converts pyruvate to oxaloacetate and produces NADPH. Signup and view all the answers

What characteristics do 'carboxylase' enzymes share?

ATP-dependent addition of a carboxylate group to a substrate with the help of a biotin cofactor. Signup and view all the answers

What is the difference between fatty acid synthase in mammals and bacteria?

In mammals, it is a single multifunctional protein; in bacteria, it is a complex of several proteins. Signup and view all the answers

Why is the condensation of the acetyl group to the malonyl group energetically favorable?

ATP generates a carboxybiotin intermediate, releasing CO2, which drives the reaction. Signup and view all the answers

What carbon atoms of palmitate are contributed by one acetyl-CoA used in fatty acid synthesis?

Carbons 15 and 16 at the omega-end of the fatty acid chain. Signup and view all the answers

What occurs during beta-oxidation of a fatty acid?

Two-carbon fragments are removed from the carboxyl end, forming a beta-keto acid. Signup and view all the answers

What reactions are performed in beta-oxidation and what molecules are used?

Oxidation by FAD, hydration by H2O, oxidation by NAD+, and thiolysis by Coenzyme A. Signup and view all the answers

Study Notes

Fatty Acid Synthesis Overview

Fatty acid synthesis is an anabolic process primarily occurring in the cytoplasm of liver and adipose tissue.
It involves transforming acetyl-CoA into fatty acids, primarily producing palmitate (16:0).

Substrates and Products

The main substrates for synthesis are acetyl-CoA, ATP, and NADPH derived from glucose metabolism.
The product of this synthesis is predominantly saturated palmitate.

Energy Requirement

To synthesize one molecule of palmitate from acetyl-CoA, 7 ATP are expended.

Steps of Fatty Acid Synthesis

The process involves:
- Transporting acetyl-CoA to the cytoplasm via the citrate shuttle.
- Activation of acetyl-CoA by acetyl-CoA carboxylase.
- Synthesis mediated by fatty acid synthase.

Oxidative Degradation

The degradation of fatty acids initiates at the carboxyl end of the molecule.

Fatty Acid Synthase Function

Fatty acid synthase is a dimeric enzyme that catalyzes the addition of 2-carbon units from acetyl-CoA to the fatty acid chain, functioning independently of ATP.

Acyl Group Transfer

During synthesis, the growing acyl group is transferred between an acyl carrier protein and a cysteine side chain on fatty acid synthase.

Stoichiometry of Palmitate Production

The synthesis reaction is:
- 8 acetyl-CoA + 7 ATP + 14 NADPH → palmitate + 14 NADP+ + 8 CoA + 6 H2O + 7 ADP.

Committed Step

The committed step involves the formation of malonyl-CoA from acetyl-CoA, mediated by acetyl-CoA carboxylase, requiring ATP and bicarbonate.

Acetyl-CoA Carboxylase Requirements

Activity of acetyl-CoA carboxylase necessitates a biotin cofactor.

Citrate Cleavage Pathway

The citrate cleavage pathway generates acetyl-CoA and NADPH for lipogenesis through cleavage of citrate transported into the cytosol from the TCA cycle.

Roles of Citrate in Synthesis

Citrate is cleaved into acetyl-CoA and oxaloacetate and acts as an allosteric activator of acetyl-CoA carboxylase.

Pyruvate Carboxylase Function

Pyruvate carboxylase converts pyruvate to oxaloacetate, replenishing what is lost during citrate transport and also producing NADPH.

Characteristics of Carboxylase Enzymes

Carboxylase enzymes generally utilize ATP for adding a carboxylate group to substrates, with biotin as a crucial cofactor.

Differences between Mammalian and Bacterial Fatty Acid Synthase

In mammals, fatty acid synthase is a single multifunctional protein, whereas in bacteria, it consists of a complex of several proteins.

Energetics of Acetyl and Malonyl Group Condensation

The condensation of acetyl and malonyl groups is energetically favorable due to the release of CO2, which contributes to the free energy of the reaction.

Contribution of Acetyl-CoA Carbons

The directly used acetyl-CoA provides the last two carbon atoms (15 and 16) of the palmitate fatty acid chain.

β-Oxidation Process

During β-oxidation, two-carbon fragments are enzymatically cleaved from the carboxyl end of the fatty acid, converting it into a β-keto acid through a series of oxidation, hydration, and thiolysis reactions.

Reactions and Molecules in β-Oxidation

Key reactions performed include oxidation by FAD, hydration with H2O, oxidation by NAD+, and thiolysis by Coenzyme A.

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Description

Test your knowledge on fatty acid synthesis with these flashcards. Learn about the anatomical process and identify the key substrates involved in fatty acid production. Ideal for students of biochemistry and metabolism.