Download Chapter 8 Your Body`s Metabolism

Your Body’s Metabolism
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Metabolism

Sum of all chemical reactions in the body’s cells
• Generation of energy from carbohydrates, proteins, and
fats
- Anaerobically
- Aerobically
• Production of biological compounds
- Nonessential amino acids
- Intermediate substances needed for metabolism
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Metabolism



Never stops
Adapts to individual needs and the environment
Has several metabolic pathways
• Glycolysis
• TCA cycle
• Electron transport chain
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Overview of Energy Metabolism
Figure 8.1
Metabolism in the Cell

Chemical reactions involved in energy production

Different cells perform different functions

Each cell’s structure in similar
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Metabolism Takes Place within Cells
Figure 8.2
Cell Structure

Cell construction is similar for all cells

Outside of cell
• Plasma membrane
- Holds in the cell contents

Inside of cell
• Includes several special internal structures: organelles
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Internal Cell Structure

Organelles
• Mitochondrion
- “Powerhouse of the cell”
- Aerobic metabolism
• Ribosomes
- Help manufacture proteins
• Smooth endoplasmic reticulum
- Produces lipids

Cytosol
• Fluid portion of cell
• Anaerobic metabolism
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Liver

Is the most metabolically active organ in the body

First organ to metabolize, store, and distribute nutrients
after absorption

Proteins, carbohydrates, and fats are absorbed as:
• Amino acids
• Monosaccharides
• Glycerol and fatty acids
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Liver

Proteins, carbohydrates, and fats are in the liver converted
to
• Usable forms of energy
• Storage forms
- Glycogen
- Triglycerides
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The Metabolic Fate of Food
Figure 8.3
Metabolic Pathways

A sequence of reactions that convert compounds from one
form to another in the production of energy

Different nutrients follow different pathways

All pathways eventually converge into a pathway called the
TCA cycle
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Anabolic and Catabolic Reactions
Figure 8.4
Enzymes and Hormones

Enzymes allow chemical reactions of metabolism to occur
at rates sufficient to maintain normal body function

Coenzymes assist enzymes

Hormones regulate anabolic and catabolic reactions
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Quick Review

Metabolism is the sum of all metabolic processes that occur
in the cells

Mitochondria is the site of most of the metabolic reactions

Metabolic processes follows specific pathways
• Anabolic which use energy to build new substances
• Catabolic which produce energy by breaking down
molecules

Enzymes and coenzymes catalyze reactions

Hormones regulate reactions
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Energy Drinks: Can They Alter Metabolism?

Main ingredient is caffeine
• Promotes lipolysis
• Overall excess can cause negative health effects
- Elevated heart rate and blood pressure
- Anxiety
Limit
caffeine
- Diminished ability to concentrate
intake to no
- Insomnia
more than
300
milligrams
per day
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Energy Drinks: Can They Alter Metabolism?

Mixing energy drinks with alcohol doubles
• Risk of injury
• Need for medical attention
• Driving with intoxicated drivers
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How Does the Body Fuel Metabolism?
Transforms
compounds to
Builds new adenosine
compounds triphosphate
(ATP)
Disassembles
macronutrients
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Adenosine Triphosphate (ATP)

A high-energy molecule composed of adenine, ribose, and
three phosphate molecules
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Part of Figure 8.5
Adenosine Triphosphate (ATP)

Only source of energy used directly by the cell

Energy is stored in the bonds that connect the phosphate
groups

The body must continually produce ATP to provide a
constant supply of energy
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ATP to ADP (Adenosine Diphosphate)
Figure 8.5
Creating ATP from ADP and Creatine
Phosphate

Regenerating ATP from ADP requires inorganic phosphate

Sources
• Inorganic phosphate produced from initial breakdown of
ATP
• Inorganic phosphate in creatine phosphate
(a.k.a. phosphocreatine or PCr)

Process requires energy
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Creatine Phosphate

High-energy compound in muscle cells

Creatine combine plus inorganic phosphate

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Creatine Phosphate

Creatine monohydrate – a supplement sold in stores
• Marketed to athletes to maximize PCr stores
• Research
- Increased performance of short-duration,
high-intensity activities
- Side effects
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Anaerobic and Aerobic Metabolism

Anaerobic metabolism
• Produces more ATP per minute
• Limited in use, provides only 1–1.5 minutes of maximal
activity
• Involved in high-intensity, short-duration activities, e.g.,
sprinting, heavy weight lifting
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Anaerobic and Aerobic Metabolism

Aerobic metabolism
• Produces less ATP per minute
• Is able to produce ATP indefinitely
• Involved in low-intensity, long-duration activities
When demand for ATP is greater than the rate of
metabolism the activity slows down
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Quick Review

ATP – energy the body uses to fuel all metabolic reactions

ATP is not stored
• Formed from ADP and inorganic phosphate
- Creatine phosphate can donate inorganic phosphate
• Produced during anaerobic metabolism
• Produced during aerobic metabolism
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Carbohydrates to Energy

Carbohydrate metabolism is the backbone of energy
production

Glucose
• Important energy source for the brain and red blood cells
• Generates energy anaerobically and aerobically
• Transforms to energy via four metabolic pathways
- Glycolysis
- Intermediate reaction pyruvate to acetyl CoA
- Tricarboxylic acid (TCA) cycle
- Electron transport chain
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Glycolysis





Breakdown of glucose
First step in forming ATP from glucose
Takes place in the cytosol of the cell
Ten-step catabolic process
One six-molecule glucose process to two three-carbon
molecules of pyruvate and two molecules of ATP
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Glycolysis

The other monosaccharides can also be used to produce
ATP
• Fructose enters glycolysis after going through seven
metabolic steps
• Galactose enters after going through four metabolic steps
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Glycolysis Summary

Ten-step process that produces
• Two molecules of ATP
• Two molecules of pyruvate
• Two energized coenzyme molecules
• Two hydrogen ions that are transported to the electron
transport chain
• Two water molecules
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The Fate of Pyruvate
Figure 8.7
The Cori Cycle
Figure 8.8
Quick Review

Glycolysis
• Process by which carbohydrates provide energy to the
cell
• Backbone of metabolism
• One glucose molecule yields
- Two hydrogen ions
- Two pyruvate
- Two ATP
- Two water molecules
- Two energized coenzymes

Pyruvate
• Reduce to lactate during anaerobic metabolism
• Converted to acetyl CoA during aerobic metabolism
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Fats to Energy

Dietary fat (triglycerides) yields six times more energy

Triglycerides
• Glycerol backbone
• Three fatty acids
• Stored in adipose tissue

Glycerol and fatty acids can be used for fuel

Glycerol produces little energy
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Triglycerides

Hydrolyzed to fatty acids and glycerol during lipolysis
• Reaction catalyzed by an enzyme in the adipose tissue
- Glucagon during times of fasting or starvation
- Epinephrine or cortisol when under stress

Once in the blood stream, they travel to the tissues and
enter the metabolic pathway
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Fatty Acids and Glycerol

Glycerol
• Glucogenic – can be transformed to glucose

Fatty acids
• Ketogenic – can be transformed to ketone bodies
• Ketones are the backup fuel for brain and nerve function
when glucose is limited
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Glycerol

In the liver
• Converted to glucose through gluconeogenesis
• Enters glycolysis to produce ATP and pyruvate
• Path entered depends on body’s need for glucose

Brains and nerves prefer to use glucose for fuel

Red blood cells can only use glucose for fuel

When the diet is low in carbohydrates glucose must come
from other sources
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Quick Review

Both the glycerol and fatty acid portions of triglycerides
provide energy

Fatty acids are the more concentrated sources of energy and
are ketogenic, nonglucose forming

Glycerol is glucogenic forming glucose through
gluconeogenesis
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How Does Protein Provide Energy?

Amino acids
• Primary use/most important function is building protein
• If the amino acid is not used to build protein the amine
group must be removed through deamination
• Excess can be used for energy production, converted to
glucose, or stored as fat
• Used, in a limited extent, for energy in diets low in
kilocalories and/or carbohydrate
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Ketogenic verses Glucogenic Amino Acids

Ketogenic amino acids
• Leucine
• Lysine

Both ketogenic and glucogenic amino acids
• Isoleucine
• Tryptophan
• Phenylalanine
• Tyrosine

Glucogenic amino acids
• The fourteen other amino acids
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Glucogenic and Ketogenic Amino Acid Metabolism
Acetyl CoA cannot be used to make glucose
Figure 8.10
Amino Acids to Glucose

Glucogenic amino acids
• Major source of blood glucose when the diet is lacking in
carbohydrate
• Can come from food
• Can come from the breakdown of muscle
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Quick Review

Amino acids can
• Be used to produce energy
• Be used to produce glucose
• Convert to fatty acids and can be stored as triglycerides

Must be deaminated to be used for energy

Once deaminated can be transformed into:
• Pyruvate
• Acetyle CoA
• TCA cycle compounds

Glucogenic amino acids can be converted to glucose
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Where Do the Macronutrients Come
Together?

Acetyl CoA
• “Gateway” molecule for aerobic metabolism
• Carbohydrates, proteins, and fat all eventual converted to
acetyl CoA
• Alcohol also converted to acetyl CoA
• Macronutrients enter the TCA cycle as acetyl CoA
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The Tricarboxylic Acid (TCA) Cycle

Gathers electrons from the carbons in the energy nutrients

Transfers stored energy to two coenzyme hydrogen ion
carriers to be released in the electron transport chain

One molecule of acetyl CoA enters the TCA cycle at a time
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The TCA Cycle
Figure 8.11
The Tricarboxylic Acid Cycle

Each cycle produces
• Two carbons that are lost to CO2
• Eight hydrogen atoms and their electrons
• Small amount of energy as GTP

Provides the starting material for creating nonessential
amino acids through transamination
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Transamination

The transfer of an amino group from one amino acid to an
alpha-keto acid to form a new nonessential amino acid

Carbon skeleton for nonessential amino acids come from
• Pyruvate from glycolysis
• Alpha-ketoglutarate from the TCA cycle
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Transamination
Figure 8.12
The Electron Transport Chain

Final stage of metabolism when electrons are transferred
from one complex to another, resulting in the formation of
ATP and water

Generates 90% of the ATP used by the body for energy,
growth, and maintenance

Takes place in the inner mitochondrial membrane of the
cell
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The Electron Transport Chain
Figure 8.13
The Electron Transport Chain

Flavoproteins
• Protein complexes that transfer the electrons through the
electron transport chain
• Contain B vitamin riboflavin
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The Electron Transport Chain

Cytochromes
• Protein complexes that move electrons down the electron
transport chain
• Contain iron and copper
• Iron deficiency can slow down this metabolic process
Though vitamins and minerals do not provide energy, they
are essential for energy production
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Overview of Energy Metabolism
Figure 8.14
Quick Review

Acetyl CoA is the gateway molecule for all energy
nutrients

Acetyl CoA combines with oxaloacetate to form citrate in
the first step of the TCA cycle

The TCA cycle produces
• Two energized coenzymes
• Two molecules of CO2
• Small amount of energy as GTP

Electrons from hydrogen atoms in coenzymes enter the
electron transport chain

Protons are used to form ATP during the electron transport
chain
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What Happens if You Eat Too Much or
Too Little

Metabolism adjusts
• Anabolic reactions store excess kilocalories as glycogen
and adipose tissue
• Catabolic reactions use glycogen, adipose tissue, and
proteins for energy
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Metabolism Adapts during Feasting or Fasting
Figure 8.15
If You Don’t Eat Enough

With continued fasting
• Ketone bodies from fatty acids used as an alternative fuel
source
• Ketogenesis peaks three days into fasting or limited
carbohydrate intake

Ketoacidosis, often seen in type 1 diabetics, can result from
a build-up of excess ketone bodies in the blood and cause
• Impaired heart activity
• Coma
• Death
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Quick Review

Ingestion of excess kilocalories
• Anabolic metabolism
• Excess energy from carbohydrates, proteins, fats, and
alcohol are converted to fat and stored

Fasting or starvation
• Catabolic metabolism
• Fat is broken down to fatty acids
• Glycerol and amino acids maintain blood glucose
• Lack of glucose leads to formation of ketone bodies for
energy
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How Does the Body Metabolize Alcohol?

Alcohol
• Contains 7 kilocalories per gram
• Absorbed directly through the stomach mucosa and
intestinal lining
• Metabolized by the liver, about half an ounce per 1.5
hours
• Excess stored as fat in the adipose tissue and liver
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The Metabolism of Alcohol
Figure 8.17
Quick Review

Alcohol is absorbed and metabolized in the liver by two
enzyme systems
• ADH – most efficient
• MEOS
- Used when intake is high
- Also used for drugs

Alcohol is also metabolized in the brain

Excess energy from alcohol is converted to fatty acids and
stored as triglycerides
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What Are Inborn Errors of Metabolism?

Genetic conditions in which an individual lacks an enzyme
that controls a specific metabolic pathway

Results in the buildup of toxins

Cannot be cured

Can be controlled through diet
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Quick Review

Inborn errors of metabolism are the result of a defective
gene

Treatment includes strict dietary regimen to control
symptoms while providing adequate nutrition
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