Cellular Metabolism and Energy

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Questions and Answers

What is the primary function of energy released from the oxidation of food?

To catalyze chemical reactions

To synthesize ATP

To facilitate muscle movement and glandular secretion (correct)

To generate heat in the body

What is the term for the energy liberated from the oxidation of food?

Free energy of food oxidation (correct)

Energy of cellular respiration

Free energy of ATP hydrolysis

Energy of ATP synthesis

What is the approximate energy released per mole of ATP under standard conditions?

686k calories

7300 calories (correct)

12000 calories

5000 calories

What is the byproduct of the conversion of ATP to ADP?

Inorganic phosphate Signup and view all the answers

Where is ATP primarily located in the cell?

Cytoplasm and nucleoplasm Signup and view all the answers

What is the term for the energy-rich bonds in ATP?

High-energy bonds Signup and view all the answers

What is the purpose of coupled reactions in cellular metabolism?

To couple energy-releasing and energy-utilizing reactions Signup and view all the answers

What is the energy currency of the body?

ATP Signup and view all the answers

What is the primary role of glucose in carbohydrate metabolism?

Transporting carbohydrates to tissue cells Signup and view all the answers

What happens to fructose and galactose after absorption in the intestinal tract?

They are converted into glucose in the liver Signup and view all the answers

What is the final product of monosaccharides released from the liver?

Glucose and phosphate Signup and view all the answers

What percentage of monosaccharides circulating in the blood are normally glucose?

95% Signup and view all the answers

How does glucose transport through cell membranes?

Through facilitated diffusion Signup and view all the answers

What is the special mechanism used in some cells to transport glucose?

Active sodium glucose co-transport Signup and view all the answers

Why is facilitated diffusion necessary for glucose transport?

Because glucose is too large to pass through cell membranes Signup and view all the answers

What is the effect of insulin on glucose transport?

Makes glucose transport 10 times better Signup and view all the answers

What is the role of glucokinase and hexokinase in glucose metabolism?

To phosphorylate glucose Signup and view all the answers

What is the significance of glucose phosphatase in liver cells?

It reverses the phosphorylation reaction Signup and view all the answers

What is the approximate percentage of glycogen stored in liver cells?

5-8% Signup and view all the answers

What is the purpose of anaerobic release of energy through glycolysis?

To provide energy when oxygen is unavailable Signup and view all the answers

What is the limitation of anaerobic release of energy through glycolysis?

It is wasteful of glucose Signup and view all the answers

What is the location where the citric acid cycle occurs?

Matrix of mitochondria Signup and view all the answers

What is the result of the combination of acetyl-CoA and oxaloacetic acid in the citric acid cycle?

Formation of citric acid Signup and view all the answers

How many times is ATP formed during the citric acid cycle?

Once during ketoglutaric and succinic acid Signup and view all the answers

What is the role of phosphorylase in glycogenolysis?

Splitting away glucose molecules from glycogen Signup and view all the answers

What is the purpose of glycogenolysis?

To provide energy to the cell Signup and view all the answers

What is the result of the conversion of glucose-6-phosphate in glycogenesis?

Formation of glucose-1-phosphate Signup and view all the answers

What is the role of uridine diphosphate glucose in glycogenesis?

Converting glucose to glycogen Signup and view all the answers

What compounds can be converted into glucose or closely allied compounds and then converted into glycogen?

Lactic acid, glycerol, pyruvic acid, and some deaminated amino acids Signup and view all the answers

What is the form of phosphorylase under resting conditions?

Inactive Signup and view all the answers

What is necessary to occur to re-form glucose from glycogen?

Activation of phosphorylase Signup and view all the answers

What are two ways to activate phosphorylase?

Activation by epinephrine and glucagon Signup and view all the answers

What is the result of phosphorylase being in an inactive form?

Glycogen remains stored Signup and view all the answers

What is the purpose of activating phosphorylase?

To break down glycogen into glucose Signup and view all the answers

What is the normal blood glucose concentration in a person who has not eaten a meal within the past 3 to 4 hours?

90 mg/dl Signup and view all the answers

What is the maximum blood glucose concentration that can be reached after a meal containing large amounts of carbohydrates in a person without diabetes?

140 mg/dl Signup and view all the answers

Which hormones are intimately related to the regulation of blood glucose concentration?

Insulin and glucagon Signup and view all the answers

What is the primary function of the pancreatic hormones insulin and glucagon?

To regulate blood glucose levels Signup and view all the answers

What is the condition characterized by unregulated blood glucose levels?

Diabetes mellitus Signup and view all the answers

What is the main function of triglycerides in the body?

To provide energy for various metabolic processes Signup and view all the answers

What is the composition of chylomicrons?

9% phospholipids, 3% cholesterol, and 1% apolipoproteins Signup and view all the answers

What is the process by which triglycerides are broken down into monoglycerides and fatty acids?

Hydrolysis Signup and view all the answers

What is the fate of chylomicron triglycerides after they are hydrolyzed by lipoprotein lipase?

They are stored in adipose tissue Signup and view all the answers

What is the characteristic of stearic acid?

It has 18 carbon atoms and is fully saturated Signup and view all the answers

What is the characteristic of oleic acid?

It has 18 carbon atoms and one double bond Signup and view all the answers

What is the main function of adipose tissue in the body?

To store triglycerides until they are needed to provide energy elsewhere Signup and view all the answers

What happens to the fatty acid chains of triglycerides in adipose tissue when exposed to prolonged cold?

They become shorter or more unsaturated Signup and view all the answers

What is the percentage of the entire cell volume that triglycerides can occupy in fat cells?

80% to 95% Signup and view all the answers

What is the form of triglycerides inside fat cells?

Liquid Signup and view all the answers

What is the purpose of the hydrolysis of triglycerides in adipose tissue?

To transport free fatty acids to other tissues for energy production Signup and view all the answers

What is the role of albumin in the transport of free fatty acids in the blood?

To transport free fatty acids in combination with albumin Signup and view all the answers

What is the function of leptin and adiponectin, hormones secreted by adipose tissue?

To affect multiple body functions, including appetite and energy expenditure Signup and view all the answers

What is the primary location of fat storage in the body?

Adipose tissue and liver Signup and view all the answers

What is the term for the storage of triglycerides in adipose tissue?

Fat deposits Signup and view all the answers

What is the process by which triglycerides are broken down into fatty acids and glycerol in adipose tissue?

Hydrolysis Signup and view all the answers

What is the primary function of lipases in adipose tissue?

To catalyze the deposition of triglycerides from chylomicrons and lipoproteins Signup and view all the answers

What is the approximate rate of renewal of triglycerides in fat cells?

Once every 2 to 3 weeks Signup and view all the answers

What is the primary function of fat cells in supplementing fat synthesis?

Synthesizing fatty acids and triglycerides from carbohydrates Signup and view all the answers

What is the role of hormones in the activation of lipases in adipose tissue?

To activate the breakdown of triglycerides into fatty acids Signup and view all the answers

What is the dynamic state of storage fat in adipose tissue?

Dynamic, with rapid exchange of fatty acids Signup and view all the answers

What is the primary function of the liver in lipid metabolism?

To degrade fatty acids into small compounds that can be used for energy Signup and view all the answers

In which conditions are large quantities of triglycerides deposited in the liver?

During starvation, diabetes, and when fat is used for energy Signup and view all the answers

What determines the total amount of triglycerides in the liver?

The overall rate at which lipids are used for energy Signup and view all the answers

Where are triglycerides initially broken down into free fatty acids?

In the liver Signup and view all the answers

What is the source of the fatty acids that are redeposited as triglycerides in the liver?

Adipose tissue Signup and view all the answers

What is the primary function of the liver in lipid metabolism in relation to carbohydrates?

To synthesize triglycerides from carbohydrates Signup and view all the answers

What is the characteristic of liver triglycerides compared to those of adipose tissue?

They are more unsaturated Signup and view all the answers

In people with lipodystrophy, what happens to excess fat that cannot be stored in adipose tissue?

It is stored in the liver and other tissues Signup and view all the answers

What is the function of the dehydrogenase in liver cells?

To desaturate fatty acids Signup and view all the answers

What is the significance of the liver's ability to desaturate fatty acids?

It is functionally important to all tissues of the body Signup and view all the answers

What is the primary source of unsaturated fats in the body?

The liver Signup and view all the answers

What is the composition of liver cells in addition to triglycerides?

Phospholipids and cholesterol Signup and view all the answers

What is the primary function of the liver in regards to lipid storage?

To store excess fat that cannot be stored in adipose tissue Signup and view all the answers

What is unique about the liver's ability to desaturate fatty acids?

It can desaturate fatty acids more efficiently than adipose tissue Signup and view all the answers

In individuals with lipodystrophy, where does excess fat typically accumulate?

Liver and other tissues that normally store minimal amounts of lipids Signup and view all the answers

What is the significance of phospholipids and cholesterol in liver cells?

They are continuously synthesized by the liver Signup and view all the answers

What is the result of the liver's ability to desaturate fatty acids?

Liver triglycerides are more unsaturated than those in adipose tissue Signup and view all the answers

What is the enzyme responsible for desaturating fatty acids in the liver?

Dehydrogenase Signup and view all the answers

What is the percentage of caloric intake that fat forms in some Asian populations?

10% to 15% Signup and view all the answers

What is the first stage in using triglycerides for energy?

Hydrolysis of triglycerides into fatty acids and glycerol Signup and view all the answers

What is the form of glycerol after it enters the active tissue?

Glycerol-3-phosphate Signup and view all the answers

Which cells are exceptions to using fatty acids for energy?

Brain tissue and red blood cells Signup and view all the answers

Where must fatty acids be processed further before they can be used for energy?

Mitochondria Signup and view all the answers

What is the source of energy for many persons from the dietary intake of carbohydrates?

Triglycerides Signup and view all the answers

What is the transport form of fatty acids and glycerol in the blood?

Free form Signup and view all the answers

What is the main function of triglycerides in the body?

Energy storage Signup and view all the answers

Where does the degradation and oxidation of fatty acids occur?

In the mitochondria Signup and view all the answers

What is the byproduct of the degradation of fatty acids in the mitochondria?

Acetyl-Coenzyme A Signup and view all the answers

What is the purpose of carnitine in fatty acid metabolism?

To transport fatty acids into the mitochondria Signup and view all the answers

What is the process by which fatty acids are degraded in the mitochondria?

Beta-oxidation Signup and view all the answers

What is the first step in the use of fatty acids for energy production?

Transport into the mitochondria using carnitine Signup and view all the answers

What is the primary cause of obesity?

Ingestion of greater amounts of food than can be used by the body for energy Signup and view all the answers

What is the purpose of phospholipids in the body?

Structural purposes in cell membranes and intracellular membranes Signup and view all the answers

Where are phospholipids primarily synthesized in the body?

Liver cells Signup and view all the answers

What is necessary for the formation of lecithin?

Choline Signup and view all the answers

What is the role of intestinal epithelial cells in phospholipid synthesis?

Synthesis of phospholipids during lipid absorption from the gut Signup and view all the answers

What governs the rate of phospholipid formation?

The usual factors that control the overall rate of fat metabolism Signup and view all the answers

What is the result of triglyceride deposition in the liver?

Increased phospholipid formation Signup and view all the answers

What is the purpose of inositol in phospholipid synthesis?

Formation of cephalins Signup and view all the answers

Where are phospholipids transported in the body?

In lipoproteins Signup and view all the answers

What is the characteristic of phospholipids?

They are lipid-soluble Signup and view all the answers

What percentage of cholesterol in the lipoproteins of the plasma is in the form of cholesterol esters?

70% Signup and view all the answers

Where is the majority of endogenous cholesterol formed in the body?

Liver Signup and view all the answers

What is the basic structure of cholesterol synthesized from?

Multiple molecules of acetyl-CoA Signup and view all the answers

What is the term for the cholesterol absorbed from the gastrointestinal tract?

Exogenous cholesterol Signup and view all the answers

What is the function of cholesterol in the body?

Cell membrane structure Signup and view all the answers

What is the result of the modification of the sterol nucleus in cholesterol?

Formation of bile acids Signup and view all the answers

What is the characteristic of cholesterol?

Highly fat soluble Signup and view all the answers

What is the role of the liver in cholesterol formation?

It forms some of the endogenous cholesterol Signup and view all the answers

Study Notes

Metabolism

Foods provide energy to various physiological systems of the cell
Carbohydrates, fats, and proteins can be oxidized in cells to release energy
Energy is released in the form of heat, which can be burned with pure oxygen by fire
Energy is required for muscle function, glandular secretion, and other cellular functions

Free Energy

Energy liberated from the oxidation of food is called the Free energy of food oxidation (ΔG)
Measured in calories per mole of substance (e.g., 686k calories for the complete oxidation of 1 mole or 180g of substance)

Adenosine Triphosphate (ATP)

ATP is the "Energy Currency" of the body
Linked to energy-utilizing and energy-producing functions of the body
Can be gained and spent repeatedly
Produced by converting carbohydrates, proteins, and fats into ATP from adenosine diphosphate (ADP)
ATP is a labile chemical compound composed of adenine, ribose, and three phosphate radicals
High-energy bonds in ATP: 7300 calories per mole under standard conditions, 12000 calories under usual conditions (concentration and temperature)
ATP breakdown: ATP (12000 cals) → ADP (1200 cals) + PO3 (1000 cals); ADP (1200 cals) → AMP (2PO3) + 200 cals
Found in cytoplasm and nucleoplasm
Plays a crucial role in coupled reactions

Carbohydrate Metabolism

Glucose, fructose, and galactose are the three primary monosaccharides involved in carbohydrate metabolism.
After absorption in the intestinal tract, fructose and galactose are rapidly converted into glucose in the liver.
Glucose plays a crucial role in transporting carbohydrates to tissue cells.
Fructose and galactose are present in circulating blood, but they are eventually converted into glucose.

Glucose Conversion and Circulation

The liver contains glucose phosphatase, which degrades glucose-6-phosphate into glucose and phosphate.
As a result, the final product released from the liver is almost entirely glucose.
Approximately 95% of monosaccharides circulating in the blood are normally the final conversion of glucose.

Glucose Transport Through Cell Membranes

Glucose is transported through cell membranes into cellular cytoplasm.
The glucose molecule is too large to pass through cell membrane pores (180-100 A), but facilitated diffusion enables its transport.
Glucose binds to protein carrier molecules, allowing it to penetrate the cell membrane wall.
Glucose moves from areas of high concentration to areas of low concentration.
In special cells, glucose is absorbed through active sodium-glucose co-transport, which uses energy from active sodium transport to absorb glucose against a concentration gradient.

Insulin and Glucose Transport

Insulin increases facilitated diffusion of glucose, making it 10 times more efficient.
Without insulin, glucose relies on liver and brain cells for transport.

Phosphorylation of Glucose

Phosphorylation occurs due to glucokinase in the liver and hexokinase in other cells.
This process is irreversible except in liver cells, where glucose phosphatase can reverse the reaction.
Phosphorylation captures glucose in the cell by instantaneously binding with phosphate.
Glucose cannot diffuse back out of cells except in liver cells with phosphatase.

Glycogen Storage

Glycogen is a large polymer of glucose stored in liver and muscle cells.
Liver cells can store large amounts of glycogen (5%-8% of cell content).
Muscle cells store smaller amounts of glycogen (1-3% of cell content).
Glycogen precipitates in solid granules.

Anaerobic Release of Energy

When oxygen becomes unavailable, oxidative phosphorylation cannot occur.
Glycolysis releases energy into cells without requiring oxygen.
This process can be lifesaving for a few minutes but is wasteful of glucose.

Citric Acid Cycle

Also known as Tricarboxylic acid cycle
Acetyl portion of acetyl-CoA is degraded to CO2 and H2 atoms
Occurs in the matrix of mitochondria
Releases energy to form ATP, with all being oxidized
Acetyl combines with oxaloacetic to form citric acid, releasing CO2 and H2
ATP is only formed once during the conversion of ketoglutaric acid to succinic acid

Glycogenesis

Formation of glycogen from glucose
Glucose-6-phosphate is converted to glucose-1-phosphate, then to uridine diphosphate glucose, and finally to glycogen
Requires specific enzymes for conversion
Monosaccharides that can be converted to glucose can enter into the reactions
Smaller compounds like lactic acid, glycerol, pyruvic acid, and some deaminated amino acids can be converted to glucose or allied compounds and then to glycogen

Glycogenolysis

Breakdown of stored glycogen to re-form glucose in the cells
Glucose can then be used to provide energy
Glycogenolysis does not occur by reversal of the same chemical reactions that form glycogen
Each succeeding glucose molecule on each branch of the glycogen polymer is split away by phosphorylation, catalyzed by the enzyme phosphorylase

Phosphorylase and Glycogen

Phosphorylase is in an inactive form under resting conditions, allowing glycogen to remain stored.
Activation of phosphorylase is necessary to reform glucose from glycogen.
Activation of phosphorylase can occur through multiple mechanisms, including epinephrine and glucagon activation.

Blood Glucose Regulation

Normal blood glucose concentration in a person who has not eaten a meal within the past 3 to 4 hours is approximately 90 mg/dl.
After a meal containing large amounts of carbohydrates, blood glucose concentration rarely rises above 140 mg/dl in individuals without diabetes mellitus.
Regulation of blood glucose concentration is closely related to the pancreatic hormones insulin and glucagon.

Lipid Metabolism

Lipids are composed of triglycerides, phospholipids, and cholesterol.
Fatty acids are long-chain hydrocarbon organic acids and are a key component of lipid metabolism.

Triglycerides

Triglycerides are the main source of energy for various metabolic processes.
Triglycerides have a specific structure:
- Stearic acid: 18-carbon chain, fully saturated.
- Oleic acid: 18-carbon chain, one double bond.
- Palmitic acid: 16-carbon atoms, fully saturated.

Transportation of Triglycerides

Triglycerides are transported from the gastrointestinal tract through the lymphatic system in the form of chylomicrons.
Triglycerides are broken down into monoglycerides and fatty acids.
They are re-synthesized into droplets called chylomicrons in intestinal epithelial cells.
Chylomicrons consist of 9% phospholipids, 3% cholesterol, and 1% apolipoproteins.

Removal of Chylomicrons from Blood

After a large meal, chylomicron levels in plasma increase by 1-2% of total plasma, causing the plasma to appear turbid and sometimes yellow.
Within an hour, chylomicron levels decrease, and the plasma becomes clear.
Chylomicron triglycerides are hydrolyzed by lipoprotein lipase, and fat is stored in adipose tissue.
Capillaries of various tissues remove chylomicrons from the blood through the action of lipoprotein lipase.

Fat Transport and Storage

Free fatty acids are transported in the blood in combination with albumin
When fat stored in adipose tissue is needed for energy, it is transported from the adipose tissue to other tissues
Transport occurs through hydrolysis of triglycerides back into fatty acids and glycerol

Fat Deposits

Fat is stored in two major tissues: adipose tissue and liver
Adipose tissue is also known as fat deposits or tissue fat

Adipose Tissue

A major function of adipose tissue is to store triglycerides until they are needed for energy elsewhere in the body
Adipose tissue provides heat insulation and secretes hormones such as leptin and adiponectin, which affect appetite and energy expenditure

Fat Cells (Adipocytes)

Fat cells (adipocytes) are modified fibroblasts that store almost pure triglycerides (80-95% of cell volume)
Triglycerides inside fat cells are in a liquid form, which is necessary for hydrolysis and transport
When exposed to cold, fatty acid chains in fat cells become shorter or more unsaturated to decrease their melting point, ensuring the fat remains in a liquid state

Fat Cells and Fatty Acid Synthesis

Fat cells can synthesize small amounts of fatty acids and triglycerides from carbohydrates, supplementing liver synthesis.

Tissue Lipases and Fat Exchange

Large quantities of lipases are present in adipose tissue.
Lipases catalyze the deposition of cell triglycerides from chylomicrons and lipoproteins.
Hormone-activated lipases split triglycerides in fat cells, releasing free fatty acids.
Triglycerides in fat cells are renewed approximately every 2 to 3 weeks.
This rapid exchange of fatty acids means that stored fat is constantly changing, highlighting the dynamic state of storage fat.

Liver Lipid Metabolism

The liver's principal functions in lipid metabolism include degrading fatty acids into energy, synthesizing triglycerides from carbohydrates and proteins, and synthesizing other lipids like cholesterol and phospholipids from fatty acids.

Triglyceride Accumulation in the Liver

Large quantities of triglycerides accumulate in the liver during early stages of starvation, diabetes mellitus, and other conditions where fat is used for energy instead of carbohydrates.
In these conditions, triglycerides are mobilized from adipose tissue, transported as free fatty acids in the blood, and redeposited as triglycerides in the liver.
The liver is the site where the initial stages of fat degradation begin.

Regulation of Liver Triglycerides

The total amount of triglycerides in the liver is determined by the overall rate at which lipids are being used for energy under normal physiological conditions.

Liver Function in Lipid Storage

In obese individuals or those with lipodystrophy, the liver stores large amounts of lipids due to excess fat that cannot be stored in adipose tissue.
The liver accumulates lipids in addition to other tissues that normally store minimal amounts of lipids.
Liver cells contain triglycerides, phospholipids, and cholesterol, which are continually synthesized by the liver.
Liver cells are capable of desaturating fatty acids, making liver triglycerides more unsaturated than those in adipose tissue.
The liver's ability to desaturate fatty acids is crucial for all tissues, as many structural elements of cells contain unsaturated fats, and the liver is their primary source.
Desaturation of fatty acids is accomplished by a dehydrogenase in liver cells.

Liver Function in Lipid Storage

In obese individuals or those with lipodystrophy, the liver stores large amounts of lipids due to excess fat that cannot be stored in adipose tissue.
The liver accumulates lipids in addition to other tissues that normally store minimal amounts of lipids.
Liver cells contain triglycerides, phospholipids, and cholesterol, which are continually synthesized by the liver.
Liver cells are capable of desaturating fatty acids, making liver triglycerides more unsaturated than those in adipose tissue.
The liver's ability to desaturate fatty acids is crucial for all tissues, as many structural elements of cells contain unsaturated fats, and the liver is their primary source.
Desaturation of fatty acids is accomplished by a dehydrogenase in liver cells.

Fat Intake and Energy

Fat intake varies across cultures, ranging from 10-15% of caloric intake in some Asian populations to 35-50% in many Western populations.

Triglycerides and Energy

Triglycerides are used for energy, and many ingested carbohydrates are converted into triglycerides, stored, and used later as fatty acids for energy.

Hydrolysis of Triglycerides

Triglycerides are hydrolyzed into fatty acids and glycerol, which are then transported in the blood to active tissues for energy production.

Fatty Acids and Energy

Almost all cells (except brain tissue and red blood cells) can use fatty acids for energy.
Fatty acids must be processed further in the mitochondria before being used for energy.

Glycerol and Energy

Glycerol is converted into glycerol-3-phosphate in active tissues and enters the glycolytic pathway for glucose breakdown, producing energy.

Fatty Acid Transport and Degradation

Fatty acid degradation and oxidation occur exclusively in the mitochondria.
Carnitine is used as a carrier to transport fatty acids into the mitochondria.
Once inside the mitochondria, fatty acids separate from carnitine and undergo degradation and oxidation.

Beta-Oxidation of Fatty Acids

Fatty acid degradation in the mitochondria involves the progressive release of two-carbon segments.
These segments are released in the form of acetyl coenzyme A (acetyl-CoA).
The process of fatty acid degradation is known as beta-oxidation of fatty acids.

Phospholipids

Phospholipids consist of one or more fatty acid molecules and one phosphoric acid radical, and they usually contain a nitrogenous base.
They have similar physical properties despite variant chemical structures, being lipid soluble, transported in lipoproteins, and used throughout the body for structural purposes.

Formation of Phospholipids

Phospholipids are synthesized in essentially all cells of the body.
Certain cells have a special ability to form great quantities of phospholipids, with liver cells accounting for about 90% of phospholipid formation.
Intestinal epithelial cells also form substantial quantities of phospholipids during lipid absorption from the gut.

Regulation of Phospholipid Formation

The rate of phospholipid formation is influenced by the overall rate of fat metabolism.
When triglycerides are deposited in the liver, the rate of phospholipid formation increases.
Specific chemical substances are necessary for the formation of some phospholipids, such as choline for lecithin and inositol for cephalins.

Obesity

Obesity is caused by the ingestion of greater amounts of food than can be used by the body for energy.
Excess food, whether fats, carbohydrates, or proteins, is stored as fat.

Cholesterol Structure and Properties

Cholesterol is highly fat soluble and slightly soluble in water.
It can form esters with fatty acids, with about 70% of plasma lipoprotein cholesterol being in the form of cholesterol esters.

Absorption and Sources

Cholesterol is present in the normal diet and can be absorbed slowly from the gastrointestinal tract into the intestinal lymph.
There are two sources of cholesterol: exogenous (absorbed from the diet) and endogenous (formed in the body's cells).

Endogenous Cholesterol Formation

The liver forms essentially all the endogenous cholesterol that circulates in plasma lipoproteins.
All cells in the body form some cholesterol, as membranous structures partially consist of this substance.

Cholesterol Synthesis

The basic structure of cholesterol is a sterol nucleus synthesized from multiple molecules of acetyl-CoA.
The sterol nucleus can be modified to form cholesterol, cholic acid (bile acid precursor), and steroid hormones secreted by the adrenal cortex, ovaries, and testes.

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Description

This quiz covers the basics of cellular metabolism, including how cells obtain energy from food, coupled reactions, and the role of energy in various physiological functions.