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Chapter 27: Nutrition and
Metabolism
Dr. Kim Wilson
Overview of Nutrition

Nutrition refers to the food (nutrients) we eat
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Malnutrition: a deficiency in the consumption of food,
vitamins, and minerals
Categories of nutrients
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Macronutrients: nutrients that the body needs in large amounts
(bulk nutrients)
 Macromolecules such as carbohydrates, fats (lipids), proteins
 Water
 Macrominerals: minerals needed in large quantity (e.g.,
sodium, chloride, calcium)
Micronutrients: nutrients needed in very small amounts
 Vitamins
 Microminerals (trace elements): minerals needed only in very
small quantities (e.g., iron, iodine, zinc)
Balance of nutrients is required for good health
Food Pyramid – Balanced
Nutrition
Metabolism
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Def: the use of nutrients
through many chemical
processes
Catabolism breaks food
down into smaller molecular
compounds and releases two
forms of energy: heat and
chemical
Anabolism: a synthesis
process
Both processes take place
inside cells continuously and
concurrently
Functions of Metabolism
To release and use energy from foods
 To synthesize one substance from another
 To prepare waste products for excretion
 Vitamins and minerals are "keys" to releasing
energy
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ATP and Metabolism
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Chemical energy released by catabolism must be transferred to
adenosine triphosphate (ATP), which supplies energy toward the
reactions of all cells
Carbohydrates

Complex carbohydrates
 Polysaccharides: starches; found in
vegetables and grains; glycogen is
found in meat
 Cellulose: a component of most
plant tissue; passes through the
system without being broken down
 Disaccharides: found in refined
sugar; must be broken down before
they can be absorbed
 Monosaccharides: found in fruits;
move directly into the internal
environment without being
processed directly
 Glucose: carbohydrate most
useful to the human cell; can be
converted from other
monosaccharides (Figure 27-4)
Conversion of
Monosaccharides

Fructose and
galactose are
converted to
glucose by liver
cells.
Carbohydrate Metabolism

Human cells catabolize most of the carbohydrate
absorbed and anabolize a small portion of it

How?
 3 steps:
1. Glycolysis
2. Citric Acid Cycle (Kreb's Cycle)
3. Electron Transport Chain/Oxidative
Phosphorylation
Glycolysis

Glycolysis: the first process of carbohydrate catabolism;
consists of a series of chemical reactions (Figure 27-5)
 The pathway for the catabolism of glucose that leads to
pyruvate
 What?
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Glucose (a six carbon sugar) is split into two molecules of a
three-carbon sugar
Where?
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Occurs in the cytoplasm of all human cells
An anaerobic process: the only process that provides cells
with energy under conditions of inadequate oxygen
 Breaks down chemical bonds in glucose molecules and
releases approximately 5% of the energy stored in them
 Prepares glucose for the second step in catabolism—the
citric acid cycle
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Glycolysis
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Stage 1 -- Consumes 2 ATP/glucose
 glucose is phosphorylated,
converted to fructose, and then
fructose is phosphorylated
 produces 2 molecules of
triosphosphate/glucoseGlyceraldehyde-3-Phosphate
Stage 2 - Produces 4 ATP/glucose
 Gly-3-P is oxidized by NAD+ and
phosphorylated with Pi producing
1,3-bisphosphoglycerate and
NADH
 Phosphates are transferred to ADP
producing ATP in two different
steps
 Final product is (2 Pyruvate + 2
ATP + NADH)
What happens after glycolysis?
Citric Acid Cycle (Kreb’s Cycle)
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NADH must be oxidized to NAD+ --> Final steps depend
upon whether O2 is available
Aerobic conditions (Citric Acid Cycle)
 Pyruvate transported to mitochondrion
 Pyruvate Dehydrogenase-decarboxylates pyruvate and
oxidizes forming Acetyl-CoA, CO2, and NADH <== X 2
for each glucose
 Krebs Cycle oxidizes Acetyl-CoA producing 2 CO2, 3
NADH, FADH2, and GTP <== X 2 for each glucose
 NADH and FADH2 have high potential energy and yield
many ATP during
Catabolism of
Glucose
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Anaerobic
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Glycolysis
1 glucose (6 carbon atoms)  2
pyruvic acid (3 carbon atoms)
Aerobic
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Citric Acid Cycle
Pyruvate used to make acetyl CoA
Each turn of the cycle oxidizes 1
pyruvate, so it takes 2 turns to
completely oxidize 1 glucose.
Two turns produce 8 NADH, 2
FADH2, and 2 ATP.
NADH and FADH2 are then
oxidatively phosphorylated,
resulting in 28 more ATP.
The 3 stages together produce 30
to 38 ATP.
Electron Transport System
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Electron transport system
 Where? Mitochondria cristae (folds)
 What? High-energy electrons (along with their protons)
removed during the citric acid cycle enter a chain of electron
acceptor molecules embedded in the inner membrane of the
mitochondria
 As electrons move down the chain, they release small bursts of
energy to pump protons between the inner and outer
membrane of the mitochondrion
 As each molecule first picks up and then gives off electrons, it
becomes reduced and then oxidized and the energy is given up
(oxidative phosphorylation)
 Energy is released during these oxidation-reduction reactions
to produce ATP
 Protons move down their concentration gradient, across the
inner membrane, driving ATP synthase
Electron Transport Chain
At the top of the cascade the electrons are
still high energy electrons but at the bottom
or end of the process their energy has been
released. These "low energy" electrons are
recombined with the hydrogen ions together
with oxygen from respiration to make water.
 Most of the ATP, 34 of the 36 or 38
produced, is produced by the electron
transport system.
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In an indirect mechanism called a
proton pump, the energy is used to
pump protons or hydrogen ions
across a membrane and as these
ions move back along the gradient
produced their energy is used to
make ATP.
Oxidative Phosphorylation

Oxidative phosphorylation: the joining of a phosphate group to
adenosine diphosphate to form ATP by the action of ATP synthase
Energy Release from Glucose
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Energy is
released mostly
as heat
Some
transferred to
usable form –
ATP
Heart and liver
cells can shuttle
electrons more
efficiently and
canb synthesize
more ATP (up to
36)
Cori Cycle
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Def: circular pathway in which
lactic acid produced by
anaerobic respiration in
skeletal muscles is carried to
liver cells
In the liver lactic acid is
converted back to glucose
and stored as liver glycogen
or returned to the bloodstream
Bloodstream = where the
glucose may be taken up by
muscle cells and used for
respiration or stored as
muscle glycogen
Glycogenesis
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Glycogenesis: a series of chemical reactions in which glucose molecules are
joined to form a strand of glucose beads
Occurs when the blood glucose level increases above the midpoint of its
normal range
Glycogenolysis
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The reversal of
glycogenesis (glucose is
converted into something
else to use for energy)
It means different things in
different cells.
Ex. Gluconeogenesis: the
formation of new glucose,
which occurs chiefly in the
liver
 Liver cells form glucose
from tissue proteins and
fats.
Insulin and Glucose
Metabolism
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Control of glucose
metabolism: hormonal and
neural devices maintain
homeostasis of blood glucose
concentration
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Insulin: secreted by beta cells to
decrease blood glucose level
Glucagon increases the blood
glucose level by increasing the
activity of the enzyme
phosphorylase
Incretins: GI hormones that, in
the presence of glucose in the
gut, stimulate insulin release
from the pancreas, thereby
decreasing blood glucose levels
(e.g., GLP-1, GIP)
Hormones and Their Effects
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Hormones that cause the blood glucose level to rise are called
hyperglycemic
Insulin is hypoglycemic because it causes the blood glucose
level to decrease
Epinephrine: hormone secreted in times of stress; increases
phosphorylase activity
Adrenocorticotropic hormone stimulates the adrenal cortex
to increase its secretion of glucocorticoids
Glucocorticoids accelerate gluconeogenesis
Growth hormone increases blood glucose level by shifting
from carbohydrate to fat catabolism
Thyroid-stimulating hormone has complex effects on
metabolism
Lipids
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Dietary sources of lipids
 Triglycerides: the most common lipids; composed of a
glycerol subunit attached to three fatty acids
 Phospholipids: an important lipid found in all foods
 Cholesterol: an important lipid found only in animal
foods
 Dietary fats
 Saturated fats contain fatty acid chains with no double
bonds
 Unsaturated fats contain fatty acid chains with some
double bonds
Lipids
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Transport of lipids: transported in blood as chylomicrons,
lipoproteins, and fatty acids
 In the absorptive state, many chylomicrons are present in the
blood
 Postabsorptive state: 95% of lipids are in the form of
lipoproteins
 Lipoproteins consist of lipids and protein and are formed in
the liver
 Blood contains three types of lipoproteins: very low
density, low density, and high density
 Fatty acids are transported from the cells of one tissue to
the cells of another in the form of free fatty acids
Cholesterol and Heart Disease
Lipid Metabolism
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Lipid metabolism
 Lipid catabolism:
triglycerides are hydrolyzed
to yield fatty acids and
glycerol
 Glycerol is converted to
glyceraldehyde-3phosphate, which enters
the glycolysis pathway
 Fatty acids are broken
down by beta-oxidation and
catabolized through the
citric acid cycle
Proteins

Sources of proteins
Proteins are assembled from a pool of 20
different amino acids
 The body synthesizes amino acids from other
compounds in the body
 Only about half the necessary types of amino
acids can be produced by the body; the rest are
supplied through diet; found in both meat and
vegetables
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Protein Metabolism
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Anabolism is primary and catabolism is
secondary
Protein anabolism: process by which proteins
are synthesized by ribosomes of the cells
 Protein catabolism: deamination takes place in
the liver cells and forms an ammonia molecule,
which is converted to urea and excreted in urine,
and a keto acid molecule, which is oxidized or
converted to glucose or fat
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Protein and Nitrogen Balance
Protein balance: the rate of protein anabolism
balances the rate of protein catabolism
 Nitrogen balance: the amount of nitrogen taken
in equals the nitrogen in protein catabolic waste
 Two kinds of protein or nitrogen imbalance
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 Negative
nitrogen balance: protein catabolism
exceeds protein anabolism; more tissue proteins are
catabolized than are replaced by protein synthesis
 Positive nitrogen balance: protein anabolism
exceeds protein catabolism
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Control of protein metabolism: achieved by
hormones
Vitamins
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Vitamins: organic molecules necessary for
normal metabolism; many attach to enzymes
and help them work or have other important
biochemical roles
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The body does not make most necessary
vitamins; they must be obtained through diet
 The
body stores fat-soluble vitamins but not watersoluble vitamins
Role of Vitamin E
Antioxidant
properties
 Reduces and
neutralizes free
radicals
 Protective effect
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Minerals
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Minerals: inorganic elements or salts found in
the earth (Table 27-4)
Attach to enzymes and help them work and
function in chemical reactions
 Essential to the fluid/ion balance of the internal
fluid environment
 Involved in many processes in the body, such as
muscle contraction, nerve function, hardening of
bone
 Too large or too small an amount of some
minerals may be harmful
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Calcium Intake in Women
Iron Intake
Metabolic Rate
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Def: the amount of energy released by catabolism
Metabolic rates are expressed in two ways
 Number of kilocalories of heat energy expended per hour or day
 As normal or as a percentage above or below normal
Basal metabolic rate: the rate of energy expended under basal conditions
 Factors: size, body composition, sex, age, thyroid hormone, body
temperature, drugs
Healthy Body Compositions
Basal Metabolism
Total Metabolic Rate
Total metabolic rate: amount of energy used
in a given time
 Main determinants
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 Factor
1: basal metabolic rate
 Factor 2: energy used to do skeletal muscle work
 Factor 3: thermic effect of foods
Energy Balance and Weight
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The body maintains a state of
energy balance
The body maintains a weight when
the total calories in the food
ingested equals the total metabolic
rate
 Body weight increases when
energy input exceeds energy
output
 Body weight decreases when
energy output exceeds energy
input
 In starvation, the carbohydrates
are used first, then fats, then
proteins
Mechanism for Regulating Food
Intake
Hypothalamus plays a part in food intake
 Feeding centers in the hypothalamus exert
primary control over appetite
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Appetite center
 Cluster
of neurons in the lateral hypothalamus that, if
stimulated, increases appetite
 Orexigenic effects: factors that trigger appetite
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Satiety center
 Group
of neurons in the ventral medial nucleus of the
hypothalamus that, if stimulated, decreases appetite
 Anorexigenic effects: factors that suppress appetite
(anorexia is loss of appetite)