Lippincott's Biochemistry Chapter 16 - Fatty Acid, Triacylglycerol, and Ketone Body Metabolism

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Questions and Answers

What role does insulin play in the activity of Acetyl CoA carboxylase (ACC)?

Insulin dephosphorylates ACC, activating it. (correct)

Insulin stimulates the degradation of ACC.

Insulin phosphorylates ACC, making it inactive.

Insulin has no effect on the activity of ACC.

Which factor is responsible for upregulating ACC synthesis in the long-term?

High-carbohydrate diet (correct)

Prolonged low-calorie diet

Increased aerobic exercise

Increased intake of dietary fats

Which transcription factor is associated with the upregulation of ACC by carbohydrate intake?

AMP-activated protein kinase (AMPK)

Fatty acid synthase (FAS) regulator

Carbohydrate response element-binding protein (ChREBP) (correct)

Sterol regulatory element-binding protein-1c (SREBP-1c)

How does Metformin affect ACC activity in the context of type 2 diabetes treatment?

It inhibits ACC activity via AMPK activation. Signup and view all the answers

What is the effect of a high-fat, low-carbohydrate diet on ACC synthesis?

It decreases ACC synthesis. Signup and view all the answers

What is the primary role of Citrate in relation to ACC activity?

Citrate activates ACC allosterically. Signup and view all the answers

What distinguishes short-term regulation of ACC from long-term regulation?

Short-term regulation involves hormonal changes, while long-term focuses on dietary patterns. Signup and view all the answers

What is the consequence of ACC inactivation due to increased AMPK activity?

Decreased fatty acid synthesis Signup and view all the answers

Which fatty acid configuration is typically found on carbon 1 of a triacylglycerol?

Saturated fatty acid Signup and view all the answers

What is the role of glycerol 3-phosphate in triacylglycerol synthesis?

It serves as the initial acceptor of fatty acids. Signup and view all the answers

Which pathway primarily produces glycerol 3-phosphate in the liver?

Glycolysis Signup and view all the answers

What is the primary energy reserve of the body stored in adipocytes?

Triacylglycerols Signup and view all the answers

How does the presence of unsaturated fatty acids affect the melting temperature (Tm) of lipids?

It decreases the Tm. Signup and view all the answers

What distinguishes brown adipocytes from white adipocytes in terms of TAG function?

Brown adipocytes utilize TAG for thermal energy through nonshivering thermogenesis. Signup and view all the answers

Which of the following is NOT a method for producing glycerol 3-phosphate?

Direct hydrolysis of triacylglycerols Signup and view all the answers

Which statement correctly describes the solubility of triacylglycerols (TAG)?

TAG are only slightly soluble in water. Signup and view all the answers

What is a significant metabolic fate of dihydroxyacetone phosphate (DHAP) in the context of lipid synthesis?

It is a precursor for glycerol 3-phosphate. Signup and view all the answers

What part of the fatty acid synthesis process is regulated by ACC?

Rate-limiting step of fatty acid synthesis Signup and view all the answers

Which molecule is primarily responsible for the covalent regulation of acetyl CoA carboxylase?

AMP Signup and view all the answers

Which molecule is a negative regulator of ACC activity?

Palmitoyl CoA Signup and view all the answers

What is the role of NADPH in the fatty acid synthesis mechanism described?

It is used in reductions to form saturated acyl groups. Signup and view all the answers

What role does biotin play in the function of ACC?

It acts as a cofactor for carboxylation Signup and view all the answers

How does citrate affect the activity of ACC?

It activates ACC through allosteric mechanisms Signup and view all the answers

What is the primary function of biotin in metabolic processes?

It serves as a coenzyme for carboxylation reactions. Signup and view all the answers

How does citrate affect the activity of acetyl CoA carboxylase?

It induces changes in enzyme conformation leading to activation. Signup and view all the answers

In what way does AMPK regulate ACC?

By phosphorylating and inactivating ACC Signup and view all the answers

In the context of fatty acid synthesis, what differentiates short-term regulation from long-term regulation?

Short-term regulation includes covalent modifications, while long-term regulation affects gene expression. Signup and view all the answers

What type of regulation is primarily discussed in relation to ACC activity?

Short-term reversible regulation Signup and view all the answers

Which of the following statements about ACC is true?

ACC is regulated by both allosteric and covalent modifications. Signup and view all the answers

What does the phosphorylation of ACC by AMPK indicate about the cellular energy state?

Energy levels are low. Signup and view all the answers

Which hormone counteracts the activity of ACC?

Glucagon Signup and view all the answers

ACC is suggested to exist in what form when inactive?

Dimeric structure Signup and view all the answers

What is the primary function of acetyl CoA carboxylase in fatty acid synthesis?

Converts acetyl CoA to malonyl CoA Signup and view all the answers

In the regulation of fatty acid synthesis, which factor has a stimulating effect on acetyl CoA carboxylase activity?

Increased citrate levels Signup and view all the answers

Which of the following best describes the role of biotin in metabolism?

Functions as a cofactor for carboxylases Signup and view all the answers

What impact does an increase in citrate levels have on enzyme activity related to fatty acid synthesis?

It activates acetyl CoA carboxylase Signup and view all the answers

Which of the following scenarios exemplifies short-term regulation in fatty acid metabolism?

Immediate hormonal responses to meal intake Signup and view all the answers

What is the predominant type of fatty acids found in human physiology?

Monounsaturated and saturated fatty acids Signup and view all the answers

Why does the introduction of a cis double bond in fatty acids affect their physical properties?

It results in a decrease in melting temperature Signup and view all the answers

What impact does increasing chain length have on the melting temperature (Tm) of fatty acids?

It increases Tm Signup and view all the answers

Which configuration is most commonly found in human fatty acids that contain double bonds?

Cis configuration Signup and view all the answers

How does the presence of double bonds in fatty acids contribute to membrane fluidity?

It maintains a fluid nature of membrane lipids Signup and view all the answers

What intermediate is produced from the oxidative conversion of malate aside from NADPH?

Carbon dioxide Signup and view all the answers

Which of the following correctly describes the source of cytosolic NADH used in the reduction of oxaloacetate to malate?

Glycolysis Signup and view all the answers

What is the primary two-carbon donor used in the elongation of palmitate in the smooth endoplasmic reticulum?

Malonyl CoA Signup and view all the answers

What characteristic differentiates the elongation capabilities of the brain from other tissues in fatty acid synthesis?

It has enhanced ability to produce very-long-chain fatty acids. Signup and view all the answers

Which pathway is primarily cited as a source of NADPH in addition to the oxidative conversion of malate?

Pentose phosphate pathway Signup and view all the answers

What dietary change leads to an increase in the synthesis of acetyl CoA carboxylase (ACC)?

A diet high in carbohydrate and low in fat Signup and view all the answers

Which transcription factor is involved in the upregulation of ACC by insulin?

SREBP-1c Signup and view all the answers

What is the effect of prolonged consumption of excess calories on ACC activity?

It increases ACC expression and fatty acid synthesis. Signup and view all the answers

How does Metformin influence the activity of ACC in the context of type 2 diabetes treatment?

Through activation of AMPK, inhibiting ACC activity Signup and view all the answers

What dietary condition is associated with a decrease in ACC synthesis?

Low-calorie, high-fat, low-carbohydrate diet Signup and view all the answers

In the metabolic process, what effect does an increase in AMP kinase (AMPK) activity have on ACC?

It inhibits ACC and fatty acid synthase expression. Signup and view all the answers

What is the primary outcome of elevated levels of insulin in the metabolic pathway involving ACC?

Promotion of ACC activity and fatty acid synthesis Signup and view all the answers

What is the main metabolic effect of the decarboxylation during fatty acid synthesis?

It drives the reaction by providing free energy. Signup and view all the answers

Which process involves covalent and allosteric regulation of acetyl CoA carboxylase?

AMPK activity Signup and view all the answers

What role do NADPH-dependent reductions play in the context of fatty acid synthesis?

They convert the 3-ketoacyl group to saturated acyl groups. Signup and view all the answers

What is the primary consequence of acetyl CoA carboxylation by acetyl CoA carboxylase?

Conversion of acetyl CoA to malonyl CoA. Signup and view all the answers

Which component is essential for the acyl carrier protein domain's function?

Phosphopantetheine Signup and view all the answers

Which molecule primarily indicates a high energy state in the context of fatty acid metabolism?

Citrate Signup and view all the answers

What does the presence of a dehydration step achieve in the fatty acid synthesis pathway?

It generates a more compact structure. Signup and view all the answers

What impact does an increase in malonyl CoA concentration have on fatty acid synthesis?

It inhibits fatty acid elongation processes. Signup and view all the answers

How does the reduction of the 3-ketoacyl group influence fatty acid synthesis?

It transforms the structure to a more saturated form. Signup and view all the answers

What is the primary product formed after the reduction of the keto group in the fatty acid synthesis process?

An alcohol group Signup and view all the answers

Which enzyme is responsible for removing a molecule of water during the synthesis of palmitate?

3-Hydroxyacyl-ACP dehydrase Signup and view all the answers

During palmitate synthesis, which domain is primarily involved in reducing the double bond formed between carbons 2 and 3?

Enoyl-ACP reductase Signup and view all the answers

What is the significance of acetyl coenzyme A (CoA) in the synthesis of fatty acids like palmitate?

It acts as a carbon donor in the synthesis process. Signup and view all the answers

What type of chain is produced at the end of the initial synthesis stages, following the steps outlined in the fatty acid synthesis pathway?

Butyryl-ACP Signup and view all the answers

What modification occurs during the synthesis of palmitate that involves changing the oxidation state of carbon atoms?

Reduction of a keto group to an alcohol Signup and view all the answers

In the described synthesis pathway, which step comes immediately after the formation of a trans double bond between carbons 2 and 3?

Reduction of the double bond Signup and view all the answers

What is released during the condensation of the butyryl unit and malonyl group in the fatty acid synthesis process?

Carbon dioxide Signup and view all the answers

What role does NADPH play in the fatty acid synthesis mechanism described?

It acts as a reducing agent in biosynthetic reactions. Signup and view all the answers

Which of the following substances is generated as a result of repeated cycles of the fatty acid synthesis steps?

Palmitate Signup and view all the answers

What is the maximum length of the fatty acid chain produced before termination of the synthesis process?

16 carbons Signup and view all the answers

What characteristic is associated with the acyl carrier protein (ACP) domain in the fatty acid synthesis process?

It serves as a temporary attachment for growing fatty acid chains. Signup and view all the answers

How many NADPH molecules are required for the synthesis of one palmitate?

14 NADPH Signup and view all the answers

What process underscores the rate-limiting nature of the ACC reaction in fatty acid synthesis?

Incorporation of acetyl CoA Signup and view all the answers

What is the product formed after the reduction, dehydration, and subsequent reduction steps starting from the carbonyl group at carbon 3?

Hexanoyl-ACP Signup and view all the answers

What is the final product released after the cleavage of the thioester bond by palmitoyl thioesterase?

Palmitate Signup and view all the answers

What is the fate of the two carbons in palmitic acid that are not derived from malonyl CoA?

They are found at the methyl end. Signup and view all the answers

Which pathway is primarily responsible for providing NADPH during fatty acid synthesis?

Pentose phosphate pathway Signup and view all the answers

What initiates the cycle of reactions in fatty acid synthesis with butyryl unit transfer?

Transfer of the butyryl unit from the ACP Signup and view all the answers

During fatty acid chain elongation, what type of group is attached to the ACP?

Malonyl group Signup and view all the answers

Match the following types of fatty acids with their characteristics:

Saturated = No double bonds Monounsaturated = One double bond Polyunsaturated = Multiple double bonds Trans = Double bonds in trans configuration Signup and view all the answers

Match the following configurations of fatty acids with their effects on melting temperature:

Long-chain saturated = Higher melting temperature Short-chain saturated = Lower melting temperature Cis unsaturated = Lower melting temperature Trans unsaturated = Higher melting temperature Signup and view all the answers

Match the following terms with their descriptions:

FFA = Free fatty acids transported with albumin TAG = Triacylglycerol, storage form of fats Cholesteryl esters = Ester of cholesterol and fatty acids Phospholipids = Major components of cell membranes Signup and view all the answers

Match the following types of fatty acids with their configurations:

Cis configuration = Bends or kinks at double bonds Trans configuration = Linear structure Omega-3 fatty acids = First double bond at the third carbon Omega-6 fatty acids = First double bond at the sixth carbon Signup and view all the answers

Match the following characteristics of fatty acids with their implications:

Presence of cis double bonds = Increases membrane fluidity Saturated fatty acids = Higher melting temperatures Polyunsaturated fatty acids = More fluid and less stable Long-chain fatty acids = Higher melting temperatures due to length Signup and view all the answers

Match the following essential fatty acids with their characteristics or precursors:

a-Linolenic acid = Precursor of omega-3 fatty acids Arachidonic acid = Precursor of prostaglandins Lignoceric acid = Very long-chain fatty acid Linoleic acid = Precursor of arachidonic acid Signup and view all the answers

Match the following fatty acid chain lengths with their classifications:

C4 to C6 = Short-chain fatty acids C14 to C20 = Long-chain fatty acids C6 to C12 = Medium-chain fatty acids C22 and above = Very long-chain fatty acids Signup and view all the answers

Match the following fatty acids with their respective carbon configurations:

a-Linolenic acid = $18:3(9,12,15)$ Arachidonic acid = $20:4(5,8,11,14)$ Lignoceric acid = $24:0$ Neivonic acid = $24:1(15)$ Signup and view all the answers

Match the following steps in fatty acid synthesis with their descriptions:

Acetyl CoA transfer = First step in fatty acid synthesis NADPH usage = Reductive process in synthesis ATP involvement = Energy input in fatty acid chain elongation Cytosolic production = Location of fatty acid synthesis in cells Signup and view all the answers

Match the following conditions with their associated impacts on essential fatty acids:

Deficiency of Linoleic acid = Arachidonic acid becomes essential Excess carbohydrates = Can be converted to fatty acids Inadequate dietary fats = Results in dry, scaly dermatitis Increased consumption of TAG = Supplies fatty acids for synthesis Signup and view all the answers

Study Notes

Fatty Acid, Triacylglycerol, and Ketone Body Metabolism

Fatty acids exist free in the body or as esters in molecules like triacylglycerols (TAG).
Free fatty acids (FFA) are transported on serum albumin in the bloodstream, mainly from adipose tissue to other tissues, particularly muscle and liver, during fasting.
FFA are oxidized by tissues to generate energy and in liver, serve as precursors for ketone body synthesis.
FFA constitute a structural component of membranes (phospholipids and glycolipids).
Esterified fatty acids (TAG) stored mainly in white adipose tissue (WAT) form the body's major energy reserve.
Metabolic alterations in fatty acid pathways are associated with obesity and diabetes.

Fatty Acid Structure

Fatty acids consist of a hydrophobic hydrocarbon chain attached to a terminal carboxyl group (-COOH).
At physiological pH, the carboxyl group ionizes to -COO⁻.
The hydrophobic portion dominates in long-chain fatty acids (LCFAs), making them insoluble in water.
LCFAs, for transport, require proteins.

Fatty Acid Saturation

Fatty acid chains can contain no double bonds (saturated) or one or more double bonds (unsaturated).
Nearly always, unsaturated fatty acids exist in the cis configuration. This results in a kink in the fatty acid chain.

Essential Fatty Acids

Linoleic acid (ω-6) and α-linolenic acid (ω-3) are essential fatty acids. Meaning humans cannot synthesise these and require them from their diet.
These are important for growth, development, and are precursors to other biologically active molecules.

Fatty Acid De Novo Synthesis

Excess carbohydrates and proteins can be converted into fatty acids.
This process primarily occurs in the liver and lactating mammary glands.
Acetyl-CoA, a product of glucose or amino acid metabolism, donates carbons to elongate fatty acid chains.
The process is endergonic and requires ATP and NADPH.
Acetyl CoA from mitochondria must be transported into the cytosol to initiate this process.
Citrate, a product of the citric acid cycle, is transported out of the mitochondria into the cytosol, then converted to acetyl-CoA.
Acetyl CoA carboxylase (ACC) is the rate-limiting enzyme in the process. This enzyme catalyzes the carboxylation of acetyl-CoA to malonyl-CoA.
ACC is regulated by allosteric effectors (citrate promotes, palmitoyl-CoA represses) and covalent modification (phosphorylation).
The process takes place in the cytosol and uses fatty acid synthase (FAS) as a multifunctional enzyme for the subsequent reactions.

Triacylglycerol (TAG) Storage and Function

TAGs are composed of a glycerol molecule attached to three fatty acids.
TAGs are insoluble in water and are stored in the form of lipid droplets in adipocytes, forming the main body's energy reserve.
TAG is a highly reduced and anhydrous form of fuel storage.

Glycerol 3-Phosphate Synthesis

Glycerol 3-phosphate is a crucial intermediate in TAG synthesis, serving as the initial acceptor of fatty acids.
Glycerol 3-phosphate is formed either from glucose or from free glycerol (in the liver).

Fat Mobilization and Fatty Acid Oxidation

Mobilization of stored TAG in adipose tissue (lipolysis) involves the hydrolysis of TAG, releasing free fatty acids and glycerol.
Hormone-sensitive lipase (HSL) is a key enzyme in this process, responding to hormonal signals like epinephrine promoting lipolysis.
Free fatty acids are transported in the blood bound to albumin to reach target organs for utilization or to the liver for oxidation.

Ketone Body Synthesis

The liver can produce ketone bodies (acetoacetate, 3-hydroxybutyrate, and acetone) from acetyl-CoA when the supply of glucose is limited.
They act as alternative fuel sources for organs like the brain and heart during prolonged fasting or starvation or in cases like diabetes.
Increased levels of ketone bodies in blood are characteristic of starvation or untreated diabetes.
The process called ketogenesis occurs in liver mitochondria.
Fatty acids are oxidized in the liver to form ketone bodies.

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Description

Explore the fundamental aspects of fatty acid, triacylglycerol, and ketone body metabolism. This quiz covers key concepts including free fatty acid transport, energy generation, and their roles in metabolic disorders. Test your knowledge on the structure and functions of fatty acids in the body.