Transcript BIO 169 METABOLISM AND ENERGETICS CHAPTER 25 created by Dr. C. Morgan TOPICS Introduction and Overview Carbohydrate Metabolism Lipid Metabolism Protein Metabolism Nucleic Acid Metabolism Metabolic Interactions Diet and Nutrition Bioenergetics Introduction and Overview.

BIO 169
METABOLISM AND
ENERGETICS
CHAPTER 25
created by Dr. C. Morgan
1
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
2
Introduction and Overview Objectives
Discuss the relationship between nutrients, the
digestive system, the cardiovascular system,
and cellular metabolism.
Review the storage of excess nutrients.
Review the definition of metabolism.
Discuss the metabolic functions within cells.
Discuss the roles of catabolism and anabolism.
3
Introduction
Metabolism is the sum of all chemical reactions taking
place in the body.
Chemical reactions occur within the cytosol and
organelles of cells and in the extracellular fluids.
Our interest is in the ability of a cell to extract from
nutrients sufficient chemical bond energy to produce
ATP, the energy currency for cellular work.
Additional high energy compounds are produced but
will not be discussed in any detail.
Oxygen, required for efficient nutrient use, is supplied
to the blood by the lungs.
The digestive system makes the nutrients available to
cells via the cardiovascular delivery system.
4
Introduction (cont)
Ideally, nutrient intake matches the metabolic demand of
cells.
If you take in more food than you need, it is stored in
adipose tissue for subsequent use.
Hormones, with some help from the nervous system, guide
cellular metabolic activities, the storage of reserves, and
the release of reserves from storage when they are
needed.
Nutrition is the absorption of nutrients from food.
The fate of the absorbed nutrients will be the focus of our
discussions.
5
Introduction (cont)
Metabolic activities occurring within cells is cellular
metabolism which performs several functions:
* recycles cellular components (metabolic turnover)
* provides energy for cell division and growth
*carries out specialized activities of differentiated cells
including secretion, contraction, nervous system
communication via action potentials
Catabolism is the breakdown of nutrients to harness energy
in the chemical bonds of new molecules, especially high
energy compounds such as ATP.
For efficiency, catabolism occurs in many small steps which
allows more released energy to be captured.
6
Introduction (cont)
ATP produced from catabolic reactions links catabolism to
anabolism, the building of new organic molecules needed
by the cell to carry out its activities.
New organic molecules are used for
* ongoing maintenance and repair
* growth
* production of cellular secretions
* building and storage of energy reserves.
Catabolism and anabolism depend on the availability of a
nutrient pool provided from digestion, absorption, and
distribution.
7
Introduction (cont)
Fig. 1
8
Introduction (cont)
Relationships--Metabolic turnover and ATP production
Fig. 2
9
Introduction (cont)
Overview of
nutrient use
in cellular
metabolism
Fig. 3
10
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
11
Carbohydrate Metabolism Objectives
Show the formula for glucose catabolism.
Discuss glycolysis.
Describe the production of ATP in mitochondria.
Show the energy yield of glycolysis and aerobic
cellular respiration.
Describe alternative catabolic pathways when
there is insufficient glucose available.
12
Carbohydrate Metabolism
From the nutrient pool cells first use the available
carbohydrates, then the lipids, and amino acids third.
Carbohydrate metabolism is mainly the story of glucose
catabolism – C6H12O6 + 6O2  6 CO2 + 6 H2O
There are two steps to the catabolism of glucose, glycolysis
which occurs in the cytosol and aerobic respiration which
occurs in the mitochondria.
The useful products of glycolysis are 2 pyruvic acid
molecules, 2 NADH, and 2 ATP for cellular use.
The pyruvic acids and NADHs move into the mitochondrion
for further processing which yields much more ATP.
13
Carbohydrate Metabolism (cont)
CYTOSOL
Fig. 4
14
Carbohydrate Metabolism (cont)
Needed for glycolysis are
*glucose molecules
*specific catalytic enzymes for each reaction
*ATP, ADP, and inorganic phosphate (Pi)
*NAD+ coenzyme carrier molecules that remove hydrogen
atoms during one of the reaction steps
The use of 2 ATPs prepares glucose for catabolism.
NAD+ becomes reduced and takes on a hydrogen atom and
one additional electron to become NADH.
NADH moves into the mitochondrion where it will donate its
electrons to the electron transport chain and H+ to solution.
15
Carbohydrate Metabolism (cont)
Reduction of NAD+
H+
proton
H+
oxidation of organic molecule
More than one hydrogen atom may be removed at a time.
NAD+ takes on 2 electrons, one proton, and leaves the other
proton in solution  NADH + H+
FADH takes on one complete hydrogen (in mitochondria)
16
Carbohydrate Metabolism (cont)
Phosphorylation of ADP occurs by two methods.
*Substrate-level phosphorylation is the transfer of a high
energy phosphate from a substrate molecule directly to ADP.
ATP is made by substrate-level phosphorylation during
glycolysis in the cytosol and in the TCA cycle which takes
place in the mitochondrial matrix
*Oxidative phosphorylation makes ATP using the electron
transport chain, oxygen, and chemiosmosis (a special
process occurring in the mitochondrion>90% of the ATP).
Review: oxidation is the loss of electrons from a molecule;
reduction is the gain of electrons by a molecule.
During coupled oxidation–reduction reactions, hydrogens
are also transferred to the carrier molecules.
17
Carbohydrate Metabolism (cont)
Recall that it is electrons that participate in chemical reactions.
Two types of carrier molecules, NADH and FADH2, that
deliver hydrogen atoms and their electrons to the electron
transport chain of the mitochondrion are important because
* for each NADH delivered, 3 ATPs are generated and
* for each FADH2 delivered, 2 ATPs are generated.
The CO2 that is given off as waste originates from the carbons
and oxygen in glucose.
The only thing actually harvested from glucose is the
energy from its chemical bonds and some hydrogens that
are temporarily used to create an electrochemical gradient in
the mitochondrion.
18
Carbohydrate Metabolism (cont)
The mitochondrion is a double
membrane organelle with an
inner compartment containing a
fluid called the matrix and an
outer intermembrane space
which also contains fluid.
The outer membrane has large
pores that allow ions, small
molecules, and carriers to cross.
Each pyruvic acid is
converted to an acetyl- A carrier protein contained in the
Co-A (2 carbons) and
inner membrane moves pyruvic
in the process
acid molecules into the matrix.
produces an NADH
and a CO2 as waste.
19
Carbohydrate Metabolism (cont)
TCA cycle completes the
catabolism of glucose.
(via GTP)
2 turns / glucose
Fig. 5
20
20
Carbohydrate Metabolism (cont)
NADH and
FADH2 donate
hydrogens and
electrons.
The mitochondrial
electron transport
system (ETS) is a
series of complex
molecules that
undergo coupled
oxidation-reduction
reactions.
Energy is used to move H+s into
the intermembrane space.
final
electron
acceptor
Fig. 6 a
21
Carbohydrate Metabolism (cont)
Aerobic respiration generates
most of the ATP
Fig. 6 b
22
Carbohydrate Metabolism (cont)
The donated electrons pass from one molecule to another
with the hydrogen protons pumped to the outer
compartment of the mitochondrion, creating an
electrochemical gradient.
As H+s pass back to the inner compartment through a
special membrane protein, ATPs are made.
Every 2 H+s passing back into the matrix provides enough
energy to produce one ATP by the special protein.
Oxygen is the last electron acceptor where it also
combines with the H+ to form metabolic water.
This is where you consume oxygen.
With insufficient oxygen, electron transport stops.
Total = 36 ATP from each glucose using glycolysis + ETS.
23
Carbohydrate Metabolism (cont)

24
Carbohydrate Metabolism (cont)
Glycogen,
triglycerides, and
proteins are
storage forms of
energy.
When there is
insufficient glucose,
triglyceride fragments
and amino acids are able
to enter glycolysis or the
TCA cycle at various
points to be catabolized.
Skeletal muscle and the
liver store glycogen.
25
Carbohydrate Metabolism (cont)
Overview
Glucose may be synthesized from
other starting materials in a
process called gluconeogenesis.
26
Carbohydrate Metabolism (cont)
Glycogenesis stores excess
glucose as glycogen in the
liver and skeletal muscle.
Glycogenolysis breaks
down glycogen stores to
yield glucose for
metabolism.
Note interconversions to
intermediates of glycolysis.
Fig. 8
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27
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
28
Lipid Metabolism Objectives
Discuss the mechanisms for lipid catabolism.
Describe the importance of lipids as energy reserves.
Discuss the synthesis of lipids.
Describe the transport and distribution of lipids.
Discuss the relationships of dietary fats and cholesterol
in health.
29
Lipid Metabolism
Lipolysis is catabolism of lipids and beta-oxidation is the
catabolism of fatty acids.
More energy is gained from the catabolism of a gram of
lipids than either carbohydrates or proteins.
Triglycerides represent most of the lipids stored in the body.
A triglyceride is catabolized into its component parts—a
glycerol molecule and three fatty acid chains.
The glycerol molecule enters the TCA cycle after it is
converted to pyruvic acid by enzymes in the cytosol.
30
Lipid Metabolism (cont)
Beta-oxidation is the
catabolism of fatty
acid chains.
Beta
oxidation
2 C fragments are
removed and
converted to acetylCoA molecules which
then enter the TCA
cycle.
ATP must be used in
the conversion but
reduced carriers are
formed.
Fig. 9
31
31
31
Lipid Metabolism (cont)
Lipids are the “best” energy stores because they provide
large amounts of ATP, are stored in compact droplets
contained in the cytosol, and are not degraded by water
soluble enzymes.
Oxygen is required since lipid catabolism occurs within the
mitochondrion by aerobic metabolism.
Because their catabolism requires more time, lipid reserves
are catabolized during times of rest (muscles) to save
valuable glycogen and glucose.
Skeletal muscles cycle between carbohydrate and lipid
metabolism depending on immediate demand.
32
Lipid Metabolism (cont)
Lipid synthesis (lipogenesis) involves the synthesis of
glycerol from intermediates of glycolysis and the synthesis
of fatty acid chains from acetyl-Co A fragments.
Not all fatty acids are able to be synthesized by cells.
Linoleic acid and linolenic acid molecules cannot be
synthesized so must be obtained from the diet.
Such a dietary requirement is an essential fatty acid.
These fatty acids which come from plant sources are
incorporated into cell membranes and are used to make
prostaglandins.
33
Lipid Metabolism (cont)
Lipid Synthesis – lipogenesis
Lipids may be
synthesized from most
nutrient fragments.
Fig. 10
34
34
Lipid Metabolism (cont)
All cells need lipids for their cell and organelle phospholipid
membranes and lipids are needed by some cells to build
steroid hormones.
Free fatty acids are able to diffuse into cells.
Because they are insoluble, lipids circulate as lipoproteins
which consist of large glycerides + cholesterol coated with
phospholipids and proteins.
The lipoprotein complexes, mostly made in the liver, are
water soluble and transported in the plasma.
The proteins on the outer surface are recognized by cell
receptors which determines cellular absorption of
particular lipids contained within lipoprotein
complexes.
35
Lipid Metabolism (cont)
Lipoproteins are grouped according to their size and relative
amount of lipid compared to protein.
Chylomicrons are the largest (0.03 – 0.05 m) with 95% of
their weight triglycerides.
Recall these are made by villi cells of the small intestine.
Very low-density lipoproteins (VLDLs) (0.025 – 0.075 m)
contain a large proportion of triglycerides and some
phospholipids + cholesterol that are delivered to peripheral
tissues.
Intermediate-density lipoproteins (IDLs) contain less
triglycerides and more phospholipids + cholesterol in
proportion to protein.
36
Lipid Metabolism (cont)
High-density lipoproteins (HDLs) (10 nm) contain about
equal proportions of lipid and protein with the lipids mostly
cholesterol and phospholipids (not triglycerides).
HDLs are moving materials from peripheral tissues back to
the liver for storage or excretion in the bile.
These lipids do not accumulate in vessels so sometimes
they are called the “good cholesterol”.
37
Lipid Metabolism (cont)
Lipid transport and utilization
Fig. 11 a
Capillaries that serve skeletal and cardiac muscle cells,
hepatocytes, and adipose cells have a lipoprotein lipase that
releases fatty acids and glycerides from chylomicrons.
Fatty acids and glycerides move into the interstitium.
38
38
Lipid Metabolism (cont)
Lipid transport
and utilization
move into cells
by endocytosis
Liver controls all other
lipoprotein distribution
Fig. 11 b
39
Lipid Metabolism (cont)
Dietary fats and cholesterol are the subjects of discussion.
Atherosclerosis (plaque buildup in arteries) is directly
related to elevated cholesterol levels in the blood.
Dietary cholesterol should be less than 300mg / day.
Only 20% of circulating cholesterol comes from dietary
sources and the rest comes from interconversions from
dietary saturated fats since excess lipids are made into
acetyl-Co As which are then made into cholesterol.
Thus, reducing overall fat intake, especially saturated fats,
helps reduce circulating cholesterol levels.
Genetic factors, age, and physical conditioning all affect
cholesterol levels.
40
Lipid Metabolism (cont)
If there is no family history of CAD, a blood cholesterol level
below 200 mg / dl is safe (no lifestyle changes needed).
A level >240 mg / dl requires major lifestyle changes.
A level > 350 mg / dl requires drug therapy.
Blood HDL levels may also be measured and the LDL level
calculated.
High total cholesterol plus elevated LDL (or low HDL) is
linked to the development of atherosclerosis.
The number of known risk factors for CAD along with blood
lipid levels determines the recommendations for lifestyle
changes or drug therapy.
41
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
42
Protein Metabolism Objectives
Recall the variety of proteins in the body.
Describe the events in amino acid catabolism.
Discuss why proteins are not quick energy sources.
Discuss protein synthesis.
43
Protein Metabolism
Your body contains more than 100,000 different proteins
assembled from 20 different amino acid monomers.
There is a constant turnover of cellular proteins that occurs by
enzymes present in the cytosol.
Mitochondria are able to make use of some amino acids in the
TCA cycle if carbohydrates and lipids are lacking.
Amino acids enter the TCA cycle at different points so the
number of reduced carriers generated varies.
The average ATP yield per gram of protein is comparable to
that for carbohydrates.
44
Protein Metabolism (cont)
The first step of amino acid catabolism is the removal of the
amino group (–NH2) which requires vitamin B6.
If the amino group is transferred to a keto acid molecule (a
double bonded oxygen on the middle carbon) to create a
new amino acid, the process is called transamination.
45
Protein Metabolism (cont)
The amino group may be removed by deamination
which also generates an ammonium ion or a toxic
ammonia molecule.
or NH3
46
Protein Metabolism (cont)
Most deamination occurs in the liver which is able to convert
the ammonia into nontoxic urea that is excreted in the urine.
Fig. 12 c
47
Protein Metabolism (cont)
The body is able to synthesize 10 amino acids.
There are 10 essential amino acids which must be obtained
in the diet of which 2 are nonessential amino acids that
may be synthesized but only in insufficient quantities.
Even though we do not generally use proteins as energy
sources, the diet must have a balance of proteins to supply
the amino acids needed for the synthesis of structural and
functional proteins.
In some third world nations, there are a number of protein
deficiency diseases linked to malnutrition.
Kwashiorkor and marasmus are two protein deficiency
diseases.
48
Protein Metabolism (cont)
The amino acids needed for protein synthesis are from
dietary sources, transamination reactions, and amination
reactions— the addition of an amino group to a short chain
carbon molecule.
Fig. 13
49
Protein Metabolism (cont)
Some genetic disorders arise because DNA does not code
for enzymes needed for amino acid metabolism.
Phenylketonuria (PKU) is a disorder where the enzyme to
convert phenylalanine to tyrosine is defective.
Tyrosine is needed to synthesize NE, E, dopamine, and
melanin.
Nervous system developmental problems will occur in infants
and young children if PKU goes undiagnosed.
When too much phenylalanine builds up in the blood, it
interferes with synthesis of other proteins.
50
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
51
Nucleic Acid Metabolism Objectives
Recall the forms of cellular nucleic acid molecules.
Discuss RNA catabolism and recycling.
Describe the synthesis of nucleic acids.
Summarize metabolic pathways.
52
Nucleic Acid Metabolism
DNA and RNAs represent the nucleic acids present in the
cell (polynucleotide = base+5Csugar+P).
The DNA is confined to the nucleus and is perpetual.
Three types of RNA, mRNA, tRNA, and rRNA are involved
in protein synthesis which occurs in the cytosol.
RNAs are continually recycled.
First, RNA polynucleotides are broken down into individual
nucleotides by appropriate enzymes.
Nucleotides may be further catabolized into sugars and
nitrogenous bases but more commonly they are simply
recycled into new macromolecules.
53
Nucleic Acid Metabolism
The only useful molecules from the catabolism of RNA are
the sugars which enter glycolysis and the nitrogenous
bases uracil and cytosine which may be converted to
acetyl-CoA.
The nitrogenous bases guanine and adenine cannot be
catabolized so are deaminated to form uric acid which is
excreted in the urine.
Normal plasma uric acid concentrations are 2.7 – 7.4 mg/dl.
Increases > 7.4 mg/dl cause body fluids to be saturated
with uric acid crystals which results in gout.
The buildup is usually linked to kidney function problems.
54
Nucleic Acid Metabolism
DNA synthesis occurs only prior to cell division.
RNA synthesis occurs continuously .
mRNA synthesis is controlled in part by hormones which
may permit, block, or change the amount of mRNA
synthesis.
mRNA molecules are degraded several minutes to a few
hours after they appear in the cytosol.
tRNA and rRNA molecules persist much longer—typically 5
days.
Specific enzymes catalyze all the reactions that synthesize
nucleic acid molecules.
55
Cellular Metabolism Summary
Fig. 14
56
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
57
Metabolic Interactions Objectives
Discuss the body locations where distinct metabolic
components are present based on the enzyme
composition of the cell.
Describe the absorptive state of the body.
Describe the postabsorptive state of the body.
Define obesity.
Discuss ketoacidosis and its link to diabetes.
58
Metabolic Interactions
The liver, adipose tissue, skeletal muscle, neural tissue, and
the remaining tissues of the body have distinctive metabolic
demands and interactions.
The liver, extremely important in metabolic regulation and
control, contains a huge diversity of metabolic enzymes.
Hepatocytes are able to catabolize and synthesize all
classes of macromolecules and can store glycogen.
The liver adjusts the level of circulating nutrients.
Adipose tissue, scattered throughout most of the body, stores
triglycerides which may be mobilized.
Skeletal muscle stores glycogen for its own use and muscle
proteins may be catabolized in extenuating circumstances.
59
Metabolic Interactions
Neural tissue must be supplied with glucose continuously in
order to maintain its function since it does not store energy
reserves.
Other peripheral tissues are able to metabolize a variety of
nutrients but do not store energy reserves.
During a daily routine, there are two patterns of metabolic
activities: the absorptive state and the postabsorptive
state.
The absorptive state follows the digestion and absorption of
nutrients from the intake of food.
If you eat three meals a day, you spend about 12 hours in
the absorptive state with insulin the main hormone since it
stimulates glucose movement into cells.
60
Metabolic Interactions (cont)
Absorptive State
Hormones
regulate
metabolism
(TABLE 1)
Fig. 15
61
Metabolic Interactions (cont)
During the absorptive state, liver hepatocytes adjust
circulating glucose and amino acid levels in blood arriving
via the hepatic portal circulation.
Insulin is the most important absorptive state hormone.
Insulin stimulates liver cells to take up glucose so the
blood level remains relatively stable (90 – 110 mg /
dl).
The liver uses what it needs and stores the rest as glycogen.
Amino acid levels range between 35 and 65 mg / dl.
The liver uses the absorbed amino acids for protein
synthesis.
Absorbed lipids move into the lymphatic circulation so are
62
Metabolic Interactions (cont)
Absorptive state (cont)
Adipose tissue removes fatty acids and glycerol for 4 to 6
hours after a meal high in fats.
Adipocytes also remove glucose and amino acids as
needed for synthetic activities.
Adipocytes will increase in size to accommodate the
the need for more storage space when intake > use.
Insulin stimulates all other tissues to absorb and use glucose.
Also when glucose levels are high, most tissues do not
absorb circulating lipids—leaving all of them for adipocytes.
Muscle cells store between 0.5 and 1% of their weight as
glycogen.
63
Metabolic Interactions (cont)
During the postabsorptive state
there is no nutrient absorption
occurring along the digestive
tract so cells adjust their
activities accordingly.
Metabolic reserves are
mobilized to meet cellular
needs.
Most reserves are
lipids stored as fat.
glucagon, epinephrine, and
glucocorticoid hormones
Fig. 16
64
Metabolic Interactions (cont)
Postabsorptive State
Fig. 17
65
Metabolic Interactions (cont)
Postabsorptive state (cont)
At a blood glucose of 80 mg / dl, liver cells turn to
glycogenolysis under the influence of glucagon and
epinephrine hormones.
The liver stores 75 – 100 g of glycogen which will maintain
blood glucose levels for about 4 hours at rest.
When the blood glucose level falls below 70 mg / dl, liver
cells begin to engage in gluconeogenesis under the
influence of glucocorticoids from the adrenal cortex.
During the postabsorptive state, liver cells will absorb fatty
acids and glycerol from the blood to provide energy.
Some molecules of acetyl-CoA generated by beta oxidation
are converted to ketone bodies used in peripheral tissues.
66
Metabolic Interactions (cont)
Postabsorptive state (cont)
Deamination and transamination of amino acids also takes
place in the liver with the generation of ketone bodies.
There are three types of ketone bodies, acetoacetate,
acetone, and betahydroxybutyrate.
These are acids that enter the general circulation.
Blood concentrations >30 mg / dl indicates ketonemia, an
indication of ketosis from lipid and amino acid metabolism.
If ketones appear in the urine it is called ketonuria.
Acetone may be evident in the breath of an individual in
uncontrolled diabetes mellitus if they are in a state of
diabetic ketoacidosis.
67
Metabolic Interactions (cont)
Postabsorptive state (cont)
Rising circulating levels of epinephrine, glucocorticoids, and
growth hormone stimulate adipocytes to mobilize their fat
reserves to the blood.
You have a 2 month supply with 50% in the hypodermis.
Skeletal muscle will use its stored glycogen reserves plus
fatty acids and ketone bodies that have been absorbed.
Other peripheral tissues will also eventually absorb fatty
acids and ketone bodies when glucose is exhausted.
Neural tissue relies on a continual glucose supply.
Only in advanced starvation will neural tissue utilize ketone
bodies and lactic acid (from muscle cells).
68
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
69
Diet and Nutrition Objectives
Describe the food groups and food pyramid.
Discuss nitrogen balance in the body.
Discuss the need for minerals.
Discuss the need for and types of vitamins.
Describe relationships between diet and disease.
Discuss some age related diet and nutrition
concerns.
70
Diet and Nutrition
Nutrition is the absorption of nutrients from food.
Normal cellular homeostasis depends on the delivery of
adequate nutrients, O2, and removal of wastes.
Your day-to-day nutritional requirements vary.
A balanced diet will contain all nutrients needed to
maintain homeostasis and sufficient water for fluid
balance.
An unbalanced diet will lead to malnutrition.
There are four to six basic food groups (depending on
your preferred groupings) from which daily food
selections should be made.
71
Diet and Nutrition (cont)
Food Pyramid
TABLE 2
Fig. 18
72
72
Diet and Nutrition (cont)
You need nitrogen for the synthesis of amino acids,
nitrogenous bases of nucleic acids, creatine in muscle
cells, and the porphyrin rings of hemoglobin, myoglobin,
and cytochromes (ETS).
To meet the need for nitrogen, you must have an adequate
dietary intake because you do not store nitrogen reserves.
You are in positive nitrogen balance if intake matches use
plus excretion in the urine and feces.
During starvation, nitrogen compounds are not catabolized
from cells until all other compounds are used.
73
Diet and Nutrition (cont)
Minerals are elements other than carbon, hydrogen, oxygen, or
nitrogen.
They are inorganic ions released as compounds dissociate.
Mineral ions are important for many reasons (TABLE 3):
*Sodium and chloride are osmotically important in the
maintenance of fluid homeostasis within compartments.
*Ions maintain the resting membrane potential in excitable cells.
*Ions conduct actions potentials in excitable cells.
*Ions release neurotransmitters.
*Ions act as cofactors for the many enzymatic reactions
(recall the clotting mechanism).
74
Diet and Nutrition (cont)
Ions (cont)
*Ions form part of the skeleton.
*Ions transport respiratory gases (HCO3–).
*Ions act as buffers.
Most vitamins are used as cofactors in enzyme reactions.
There are two vitamins groups, fat-soluble and watersoluble.
Vitamins A, D, E, and K are fat-soluble which means they
will be absorbed with other lipids (in micelles) along
the
digestive tract (see TABLE 4).
75
Diet and Nutrition (cont)
Inadequate intake of certain fat-soluble vitamins is
responsible for some disorders (recall rickets from a
vitamin D3 deficiency).
Excessive intake of vitamins may lead to hypervitaminosis
which may adversely affect liver functions.
Water-soluble vitamins include the B vitamins, niacin, and
vitamin C, all components of coenzymes (TABLE 5).
Niacin and vitamin B2 form part of the important carrier
compounds NAD and FAD that shuttle hydrogens and
electrons to the transport chain in mitochondria.
Several B vitamins are required for proper growth.
Water-soluble vitamins are not stored in any quantity.
76
Diet and Nutrition (cont)
You need 2000 – 2500 ml of water intake per day of which
about 48% comes from the solid foods.
Dietary problems in the U.S. center on an imbalance in the
diet.
Americans tend to eat too much of the wrong foods.
We eat too much fat which contributes to heart disease,
obesity, atherosclerosis, hypertension, and diabetes.
Two eating disorders involve inadequate nutrition.
Anorexia nervosa (self-induced starvation) and bulimia
(binging and induced vomiting) are most common among
adolescent females.
77
Diet and Nutrition (cont)
Nutritional requirements do not change with age but caloric
intake requirements do decrease by about 10% for each
decade past age 50.
There is an increased need for calcium in the diet for bone
homeostasis (and supplementary vitamin D3 for people
indoors most of the time).
Malnutrition is not uncommon in the elderly who lose their
desire to eat because food does not taste good any more
and shopping and food preparation are difficult.
Digestive activities also decline with age.
78
TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
79
Bioenergetics Objectives
Define bioenergetics and units of energy.
Discuss metabolic rate and its measurement.
Describe the concept of thermoregulation.
Present the mechanisms for heat transfer.
Discuss regulation of heat gain and loss.
Describe some individual variations with
respect to thermoregulation.
80
Bioenergetics
Energy is released as chemical bonds of nutrient
molecules are broken during catabolism.
The unit of measurement for this energy is the calorie.
One calorie is the amount of heat energy needed to raise
the temperature of 1 gram of water 1 degree
centigrade.
It is more practical to measure our food energy as packets
of 1000 calories, the kilocalorie (kc or C) which is the
Caloric value seen on food packaging labels.
Each Calorie will raise 1 kilogram of water 1 degree
centigrade.
Lipids have 9.46 C / gram; carbohydrates = 4.18 C / g;
proteins = 4.32 C / g.
81
Bioenergetics (cont)
The Caloric value of a gram of food can be measured by
placing a known quantity in a special chamber
(calorimeter) where it is oxidized by burning.
The calorimeter is surrounded by a known quantity of
water.
The temperature change in the water represents the
Caloric value of the food item.
Most foods are a mixture of carbohydrates, lipids, and
proteins.
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Bioenergetics (cont)
Your metabolic rate is your energy utilization in Calories /
selected unit (usually per hour).
Basal metabolic rate (BMR) is your resting utilization rate.
The average BMR is around 70 C / hr or 1680 C / day.
Daily requirements are determined by activity level and
individual metabolic differences.
Appetite is poorly understood.
Psychological and hormonal factors are important in appetite
regulation and control.
Leptin, a hormone released by adipocytes that are
synthesizing triglycerides, binds to neurons in emotional
centers that suppress appetite.
83
Bioenergetics (cont)
Energy released during metabolism that is not harnessed in
the chemical bonds of other compounds is released as
heat.
Since metabolism is only 40% efficient, it generates great
amounts of heat as a byproduct.
If body temperature is not maintained, serious problems will
arise.
Chemical reactions increase as temperature increases and
vice-versa; enzymes denature at temperatures above 40oC.
Thermoregulation is the homeostatic process that maintains
body temperature within acceptable limits.
84
Bioenergetics (cont)
85
85
Bioenergetics (cont)
You exchange heat with your surroundings by four
mechanisms: radiation, conduction, convection, and
evaporation.
*radiation is the loss of heat into the space around you (50%)
*conduction is heat transfer by contacting a surface that is at
a different temperature than your body (10% of loss)
*convection is movement of warm air away from your body
surface and its replacement by cooler air creating a current
(15% of loss)
*evaporation of water molecules from your body surface and
lungs removes heat (20% of loss)
Ideally, heat loss = metabolic heat generated or heat gained.
86
Bioenergetics (cont)
Thermoregulation is accomplished by the hypothalamic
heat-loss and heat-gain centers.
The heat-loss center output is via the parasympathetic n.s.
and the heat-gain center output is via the sympathetic n.s.
To promote heat-loss, output from the loss center causes
*dilation of peripheral blood vessels (inhibition of the
sympathetic output) which promotes heat loss by radiation
and convection
*stimulation of sweat glands to promote heat loss by
evaporation (not effective in high humidity conditions)
*an increase in rate and depth of ventilation
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Bioenergetics (cont)
Fig. 20
To restrict heat loss, heat gain
center causes peripheral vascular
constriction
heat conservation by
counter current exchange
in large vessels
88
Bioenergetics (cont)
To promote heat production, the heat-gain center causes
*shivering thermogenesis of skeletal muscles which may
increase heat generation up to 400%
*nonshivering thermogenesis which involves the
secretion of hormones that increase metabolic activity of
cells and nutrient conversions to support it.
The hormones most involved are epinephrine and thyroid
hormones via stimulation of hypothalamic TRHTSH.
89
Bioenergetics (cont)
Hypothermia is induced during open heart surgery in order
to decrease the metabolic demands of cardiac tissue.
Up to three hours of inactivity may be tolerated by an adult
heart when it is cooled to about 150C.
Individuals may become acclimatized to temperature
variations.
Surface to volume ratios affect heat loss.
Large individuals do not lose heat as efficiently as smaller
individuals.
Infants cannot shiver and their body temperature is less
stable than in adults.
Infants do have brown fat consisting of adipocytes in the
upper body that are innervated by sympathetic neurons
90
Bioenergetics (cont)
Sympathetic outflow increases metabolism in brown fat and
will generate heat proportionately.
Two people weighing the same will differ in thermal
responses.
If much of the weight is adipose tissue, they are well
insulated and have more difficulty with heat loss than an
individual with a large muscle mass.
The settings of hypothalamic temperature centers may also
vary throughout a 24 hour period among individuals.
Elevated body temperature is pyrexia and a fever is a
sustained body temperature above 37.20C.
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TOPICS
Introduction and Overview
Carbohydrate Metabolism
Lipid Metabolism
Protein Metabolism
Nucleic Acid Metabolism
Metabolic Interactions
Diet and Nutrition
Bioenergetics
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