Biology 233
Human Anatomy and Physiology
Chapter 25 Lecture Outline
METABOLISM – all of the chemical reactions in the body
enzymes – organic catalysts (proteins) that regulate rate of reactions
NUTRIENTS – molecules required to maintain normal metabolism
absorbed from diet or synthesized in cells
major nutrients – carbohydrates, lipids, proteins
vitamins – needed in small quantities to form various substrates or coenzymes
minerals – ions needed for many functions
maintain osmotic balance
cofactors for enzymes
participate in physiological processes
USES OF NUTRIENTS
Energy Production
catabolism (decomposition reactions) – breaking down large molecules
into smaller ones
exergonic reactions – release energy as bonds break
Uses of Energy From Food
heat production (60%)
active transport
movement – microtubules, muscles
anabolism
Building Blocks
anabolism (synthesis reactions) – combining smaller molecules to form
more complex ones
endergonic reactions – require energy input to form bonds
Examples of Anabolic Reactions
structural maintenance
growth and division
synthesis of secretions
storage – nutrients not needed immediately are stored for
future use
Storage Molecules:
glycogen – carbohydrate stores in muscle and liver
triglycerides – lipid stores mainly in adipose tissue
COUPLING OF CATABOLISM AND ANABOLISM IN THE BODY
ATP (adenosine triphosphate) – energy currency of body
ATP has 2 high-energy phosphate bonds
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phosphate bonds are formed using energy from catabolic reactions
and broken to release energy for anabolic reactions
ADP – one high energy phosphate removed
(AMP – both high energy phosphates removed)
ENERGY TRANSFER
Oxidation-Reduction Reactions
oxidation – removal of electrons (with H)
(catabolism – exergonic)
reduction – addition of electrons (with H)
(anabolism – endergonic)
Oxidation and Reduction Coupling (redox reactions)
H and electrons are removed from one molecule and added to another
molecules (eg. glucose) with many hydrogen atoms can be oxidized to
release energy
coenzymes – intermediary molecules that accept or donate H and electrons
NAD+(oxidized) / NADH + H+ (reduced)
FAD (oxidized) / FADH2 (reduced)
in aerobic respiration the final electron acceptor is oxygen
O2 + 2H2 -------> 2H2O (oxygen is reduced)
ATP SYNTHESIS
phosphorylation – addition of phosphate groups to a molecule
substrate level phosphorylation – energy from breaking a chemical bond is used to
phosphorylate ADP
(eg. ADP + creatine phosphate -----> ATP + creatine)
oxidative phosphorylation – energy from oxidation of organic molecules in
mitochondria (aerobic respiration) is used to add phosphate to ADP
(sequence of reactions requiring coenzymes and oxygen)
CARBOHYDRATE METABOLISM
SOURCES OF CARBOHYDRATES
monosaccharides absorbed from diet
most monosaccharides are converted to glucose in the body
glycogenolysis – breaking down glycogen stores to form glucose
occurs in liver (and skeletal muscle)
gluconeogenesis – forming new glucose from non-carbohydrates
occurs when glycogen stores are depleted
cells convert lipids, lactic acid, and some amino acids to glucose
USES OF GLUCOSE
ATP synthesis – main source of cellular ATP
glycogenesis – excess glucose stored as glycogen in liver and skeletal muscle
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lipogenesis – converted to lipids
amino acid synthesis – converted to amino acids
GLUCOSE CATABOLISM
breaking down glucose to make ATP
4 Steps of Glucose Catabolism
1) glycolysis – anaerobic respiration (no oxygen used)
occurs in cytoplasm
(6C) glucose ----> 2 (3C) pyruvic acids
activation energy is required – 2 ATP used
produces 4 ATP
net gain (per glucose)
2 ATP (substrate-level phosphorylation)
2 NAD+ reduced to 2 NADH
(in the absence of O2 pyruvic acid is converted to lactic acid)
2) Formation of Acetyl-CoA
2 pyruvic acids are converted to 2 acetyl-CoA
occurs in mitochondrial matrix
2 (3C) pyruvic acid + 2 coenzyme A -----> 2 (2C) acetyl CoA
net gain (per glucose)
2 CO2
2 NADH
3) Citric Acid Cycle (TCA cycle, Kreb’s cycle)
2 acetyl CoA enter cycle and are broken down
occurs in mitochondrial matrix
in one cycle:
1 (2C) acetyl CoA + (4C) molecule -----> (6C) citric acid
citric acid is oxidized (4 H2 removed by coenzymes)
and decarboxylated (2 CO2 removed)
net gain (per glucose)
4 CO2
2 ATP (substrate-level phosphorylation)
6 NADH, 2 FADH2
4) Electron Transport System
occurs on mitochondrial cristae (inner membrane)
chain of redox reactions involving membrane proteins
NADH and FADH2 (from previous steps) are oxidized
membrane proteins are reduced in sequence
energy released powers proton pumps – H+ pumped
into intermembranous space
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H channels (ATP synthase) use energy from H+ gradient to
phosphorylate ADP (oxidative phosphorylation)
(form 3 ATP / NADH and 2ATP / FADH2)
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oxygen is the final electron (and H+) acceptor (forms H2O)
net gain (per glucose)
32-34 ATP
6 H2O
SUMMARY OF GLUCOSE CATABOLISM
C6H12O6 + 6 O2 ---------> 6 CO2 + 6 H2O + 36-38 ATP
glucose is oxidized to form CO2
oxygen is reduced to form water
LIPID METABOLISM
SOURCES OF LIPIDS
monoglycerides, fatty acids, steroids absorbed from diet in chylomicrons
lipogenesis – synthesis of lipids from carbohydrates, amino acids, or other lipids
(essential fatty acids – cells cannot synthesize, must obtain from diet)
USES OF LIPIDS
structural – plasma membranes, myelin sheath
functional & regulatory – lipoproteins for lipid transport, steroid hormones
ATP synthesis – converted to substrates for citric acid cycle
gluconeogenesis, amino acid synthesis
triglycerides – excess nutrients stored in adipocytes and broken down as needed
LIPID TRANSPORT – hydrophobic; combine with transport proteins to dissolve
in body fluids
Lipoproteins – shell of proteins surrounding lipids to make soluble in body fluids
chylomicrons
transport lipids from intestinal cells to lymph, then to blood
rapidly removed from blood by liver, adipocytes, skeletal and
cardiac muscles
Liver packs lipids for transport to various cells;
VLDLs (very low-density lipoproteins)
transport triglycerides produced by liver to adipocytes and other
cells
used for energy or stored in adipocytes
LDLs (low-density lipoproteins)
transport cholesterol to cells
used in membranes, steroid hormones, bile salts
excess forms arterial plaques (bad cholesterol)
HDLs (high-density lipoproteins)
transport excess cholesterol from cells to liver for removal
(good cholesterol)
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LIPID CATABOLISM
lipolysis – triglycerides split into glycerol and fatty acids
glycerol converted to pyruvic acid ---> acetyl-CoA ---> citric acid cycle
fatty acids converted to acetyl-CoA ---> citric acid cycle
lipids provide more ATP than glucose (more H to remove)
PROTEIN METABOLISM
SOURCES OF AMINO ACIDS
amino acids absorbed from diet
synthesized from carbohydrates, lipids, or other amino acids
(essential amino acids – cells cannot synthesize enough, must obtain from diet)
USES OF AMINO ACIDS
protein synthesis (gene expression)
structural proteins – collagen, keratin
regulatory proteins – hormones, enzymes, neurotransmitters
functional proteins – hemoglobin, antibodies
ATP synthesis – enter citric acid cycle at various points
gluconeogenesis, lipogenesis
(Protein synthesis is the main use of amino acids. The body uses carbohydrates
and lipids for energy first, when possible, to conserve body proteins)
PROTEIN CATABOLISM
deamination – amino group (NH2) removed from amino acids
occurs in liver
produces nitrogenous wastes
ammonia (toxic) converted to
urea (relatively harmless) – excreted in urine
following deamination
enter citric acid cycle - oxidized for ATP
gluconeogenesis
lipogenesis
METABOLIC INTERACTIONS
METABOLIC FUNCTIONS OF TISSUES
Liver – main regulator of nutrient content in blood
breaks down or synthesizes carbohydrates, lipids, and amino acids as
needed by cells
breaks down, stores, detoxifies, or excretes wastes and toxins
Adipose tissues – store or release lipids, as needed
Skeletal muscles – store glycogen as an energy source
contain many proteins – can be used as an energy source during periods
of stress or starvation
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Neural tissues – rely primarily on glucose for energy
no energy stores – need a constant supply of glucose
Other tissues – can use glucose, fatty acids, amino acids, and other organic
molecules for energy
endocrine system regulates their choice of nutrients
ABSORPTIVE STATE – following a meal, when nutrients are being absorbed
glucose taken into cells (insulin) – used for energy and stored as glycogen
or triglycerides
amino acids used for protein synthesis
lipids used for synthesis and stored as triglycerides
POSTABSORPTIVE STATE – between meals, when no absorption is occurring
blood glucose level maintained by glycogenolysis or gluconeogenesis
glucose sparing – most cells use lipids and amino acids for energy
ketone bodies – acids formed by catabolizing lipids or proteins
cells can use in citric acid cycle to produce ATP
high levels (starvation) cause low blood pH (ketoacidosis)
METABOLISM AND THERMOREGULATION
(thermoregulation – regulation of body temperature)
body metabolism is about 40% efficient
60% of energy released by reactions is lost as heat
body temperature is proportional to metabolic rate
core temperature – temperature of deep tissues
normal is 98.6o F (37o C)
hyperthermia – high core temperature
fever – sustained temperature >99oF
hypothermia – low core temperature
hypothalamus regulates body temperature
thermoreceptors in skin, mucous membranes and hypothalamus
Regulatory Mechanisms:
venoconstriction/venodilation in skin
cellular metabolism – ANS, thyroid hormones
shivering (skeletal muscle tone increases)
sweat glands - ANS
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