VT 105
Comparative Anatomy and Physiology
Chemistry and Metabolism
CHEMICAL LEVEL OF ORGANIZATION
element – building block of matter; cannot be split into a simpler substance by
ordinary chemical means
chemical symbol – 1 or 2 letters representing an element
C = carbon
H = hydrogen
O = oxygen
N = nitrogen
Na = sodium
K = potassium
Cl = chloride
Ca = calcium
P = phosphorus
Mg = magnesium
atom – smallest unit of an element
nucleus – dense core of an atom
protons – positively charged particles
neutrons – uncharged particles
electrons – negatively charged particles that surround nucleus
electron shells – regions where electrons are usually found
# of protons = # of electrons (electrically neutral)
molecule – 2 or more atoms held together by chemical bonds
CHEMICAL BONDS – forces that hold atoms of a molecule together; depends on the
arrangement of electrons
valence shell – outer, reactive electron shell
usually 8 electrons in the valence shell is most stable; allows prediction
of reactivity
(in some small atoms the valance shell has only 2 electrons)
Ionic Bonds – one atom loses valence electrons to another; molecule is held
together by attraction of opposite charges
ion – charged particles
anion – gains electrons (negatively charged)
cation – loses electrons (positively charged)
ionic compounds break into ions when dissolved in water
Covalent Bonds – atoms share valence electrons; most common bonds in body
single bond (share 1 pair of electrons) – hydrogen molecule
double bond (share 2 pairs of electrons) – oxygen molecule
nonpolar covalent bond – electrons shared equally
polar covalent bond – unequal electron sharing; produces partial electrical
charges on the atoms sharing electrons
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Hydrogen Bonds – weak bonds between hydrogen atoms (partial positive charge)
and neighboring atoms with partial negative charges (eg. O or N)
too weak to form molecules - form attractions between molecules or parts
of molecules
CHEMICAL REACTIONS – foundation of all life processes
Metabolism – sum of all chemical reactions occurring in body
reactants – starting substances
products – ending substances
Types of Reactions
anabolic reactions (synthesis) – smaller reactants combine to form larger
products; requires energy input
catabolic reactions (decomposition) – larger reactants broken down into
smaller products; releases energy
Energy of Chemical Reactions
activation energy – energy investment needed to start a reaction
makes valence electrons unstable so they can react
kinetic energy - energy of motion
(at body temperature atoms are always in motion)
factors affecting reaction rate:
concentration of reactants
temperature – higher temperature = more kinetic energy
enzymes – biological catalysts
molecules that lower activation energy by binding reactants
and orienting them so their valence electrons can react
chemical energy – stored energy in chemical bonds; cannot be created or
destroyed, but can be converted into other forms (other chemical
bonds, mechanical energy, heat)
INORGANIC MOLECULES – found in environment and are usually structurally
simple
Water – most important inorganic molecule
biological solvent – dissolves biological molecules so they can react with
each other
(solvent + solutes = solution)
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water is a polar covalent molecule
hydrophilic (water-loving) – dissolves easily in water
charged particles (ions and polar covalent molecules)
electrolytes – ions can conduct electrical currents
hydrophobic (water-fearing) – dissolve poorly in water
uncharged particles (nonpolar covalent molecules)
water participates in metabolic reactions
hydrolysis reaction – using water to break down larger molecules
dehydration synthesis – joining 2 smaller molecules by removing a
molecule of water
Acids, Bases, and Salts – ionic compounds
acids – dissolve to form hydrogen ions [H+] (proton donors)
bases – dissolve to form anions that can bind H+ (proton acceptors)
salts – dissolve to form other anions and cations
pH – measurement of a solution’s acidity or alkalinity(basicity)
pH scale
pH 7 = neutral
lower pH = more acidic = more hydrogen ions
higher pH = more basic = fewer hydrogen ions
buffers – chemicals that stabilize pH of a solution by accepting or
donating H+ when needed
cells only function properly within a narrow pH range
ORGANIC MOLECULES – produced by living cells
contain carbon and hydrogen (+ oxygen, nitrogen, phosphorus, other elements)
joined almost entirely by covalent bonds
may be very large and structurally complex
carbon skeleton – chain of carbon atoms; each can form 4 covalent bonds
functional groups – other atoms in specific arrangements attached to carbon
skeleton; confer characteristic chemical properties
CLASSES OF ORGANIC MOLECULES
CARBOHYDRATES - sugars, starches, glycogen, cellulose
primarily an energy source in the body
general chemical formula – 1 carbon:2 hydrogen:1 oxygen
types of carbohydrates:
monosaccharides – simple sugars; 3-7 carbons
glucose – main carbohydrate in blood
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disaccharides – 2 monosaccharides joined by dehydration
synthesis (eg. lactose – milk sugar)
polysaccharides – 10s to 100s of monosaccharides
glycogen – carbohydrate storage in animals
starch – carbohydrate storage in plants
cellulose – structural carbohydrate in plants
LIPIDS – fats and oils, phospholipids, steroids, fatty acids, triglycerides
contain carbon, hydrogen, less oxygen than carbohydrates
mainly hydrophobic molecules
types of lipids:
fatty acids – carbon/hydrogen chains with carboxyl group
can be catabolized for energy
saturated fatty acids – only single covalent bonds between
carbon atoms (straight chains)
unsaturated fatty acids – at least 1 double covalent bond
between carbon atoms (bent chains)
triglycerides (fat) – energy storage, insulation
glycerol – 3-carbon backbone + 3 fatty acids
phospholipids – main component of cell membranes
glycerol + 2 fatty acids – nonpolar tail (hydrophobic)
polar head (hydrophilic)
amphipathic – has polar and nonpolar regions
steroids – cholesterol, sex hormones, cortisol
have 4 carbon rings
PROTEINS – major structural and functional molecules of body
contain carbon, hydrogen, oxygen, and nitrogen (some sulfur)
amino acids – 20 different building blocks of proteins
central carbon with one H
amino group (-NH2)
carboxyl group (-COOH)
R group – unique group for each different amino acid
peptide bond – dehydration reaction links amino acids
peptide – chain of amino acids
(2) dipeptide, (3) tripeptide, (>10) polypeptide
proteins – 1 or more polypeptide chains, may be very structurally
complex; function is related to shape
primary structure – chain of amino acids
secondary structure – repeated twisting or folding due to hydrogen
bonds – alpha helix, beta pleated sheet
tertiary structure – 3-D twisting due to hydrophilic and
hydrophobic interactions, and disulfide bridges
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quaternary structure – some proteins are composed of more than
1 polypeptide chain held together like tertiary structures
enzymes – 100s of protein catalysts (end in –ase)
function depends on structure
very specific – only catalyze specific reactions
substrate – reactant molecule(s) enzyme acts on
active site – site that binds specific substrate(s)
very efficient – may increase reaction rate millions of times
enzyme is not altered or used up
enzyme regulation
enzyme concentration
inorganic cofactors (eg. Ca)
organic coenzymes (eg. vitamins)
denatured enzyme – loses its functional structure
pH, temperature
NUCLEIC ACIDS – DNA, RNA
control heredity and cell function through protein synthesis
composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus
nucleotides – building blocks of nucleic acids
5-carbon sugar
DNA – deoxyribose
RNA – ribose
phosphate group
nitrogenous base (5 types)
adenine (A) – DNA and RNA
guanine (G) – DNA and RNA
cytosine (C) – DNA and RNA
thymine (T) – DNA only
uracil (U) – RNA only
nucleic acid strands have backbones of sugars and phosphates joined by
dehydration reactions
RNA is single-stranded
DNA is a double-stranded helix held together by hydrogen bonds between
nitrogenous bases of adjacent strands
ATP (adenosine triphosphate) – stores energy released by catabolic reactions
nucleotide – adenosine monophosphate
phosphorylation (addition of high energy phosphates by specific enzymes)
ADP (adenosine diphosphate) – 1 high-energy phosphate bond
ATP – 2 high-energy phosphate bonds
breaking the high-energy bonds releases energy to use in anabolic reactions
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METABOLIC PATHWAYS
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 act as coenzymes
minerals – ions (eg. Na+, K+, Ca+2) needed for many functions
cofactors for enzymes
maintain water balance
participate in physiological processes
USES OF NUTRIENTS
Energy Production - catabolism
Uses of Energy From Food
heat production (60%)
active transport – moving molecules in and out of cells
movement of body, organs, cells, or within cells
anabolism (energy stored in ATP until needed)
Building Blocks for Anabolism
Examples of Anabolic Reactions
body repairs and maintenance
growth and reproduction
synthesis of secretions
storage – nutrients not needed immediately are stored
glycogen – carbohydrate stores in muscle and liver
triglycerides – lipid stores mainly in adipose tissue
CARBOHYDRATE METABOLISM
SOURCES OF CARBOHYDRATES – glucose
diet – starches, cellulose, sugars
catabolized in digestive tract to monosccharides and absorbed into blood
glycogen stores
hydrolysis reactions break down to form glucose
converting lipids, lactic acid, and some amino acids to glucose
GLUCOSE CATABOLISM – breaking down glucose to make energy (ATP)
4 Steps of Glucose Catabolism
1) glycolysis
1 (6C) glucose ----> 2 (3C) pyruvates
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activation energy is required – 2 ATP used
net gain (per glucose)
2 ATP
2 NAD+ coenzymes form 2 NADH
anaerobic respiration (no O2 present) pyruvic acid converted to lactic acid
aerobic respiration (O2 is present) pyruvate enters mitochondria where the
the following processes break it down further using oxygen
2) Formation of Acetyl-CoA
2 (3C) pyruvates + 2 coenzyme A -----> 2 (2C) acetyl CoA
net gain (per glucose)
2 CO2
2 NADH
3) Kreb’s cycle – 2 acetyl CoA enter cycle and are broken down
net gain (per glucose)
4 CO2
2 ATP
6 NADH
2 FAD coenzymes form 2 FADH2
4) Electron Transport System
NADH and FADH2 (from previous steps) are oxidized
H are removed and transferred to oxygen molecules
energy released is used to form ATP molecules
net gain (per glucose)
34 ATP
6 H2O
SUMMARY OF GLUCOSE CATABOLISM
C6H12O6 + 6 O2 ---------> 6 CO2 + 6 H2O + 38 ATP
glucose is oxidized (H and its electrons removed) to form CO2
oxygen is reduced (H and its electrons added) to form water
Other organic molecules with lots of H bonds can be oxidized in the mitochondria
to form ATP molecules.
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LIPID METABOLISM
SOURCES OF LIPIDS
diet – fats, oils, cholesterol
catabolized in digestive tract and absorbed into blood as
lipoproteins – lipid droplets surrounded by proteins
(lipids are hydrophobic – don’t dissolve well)
conversion of excess carbohydrates or amino acids to lipids
conversion of one type of lipid (triglyceride stores) to another
(essential fatty acids – cells cannot synthesize, must obtain from diet)
LIPID CATABOLISM – breaking down lipids for energy
lipolysis – triglycerides hydrolyzed to form glycerol and 3 fatty acids
glycerol converted to acetyl-CoA, which enters Kreb’s cycle
fatty acids converted to acetyl-CoA or ketones
lipids provide more ATP than glucose (more H to remove)
excess lipids are converted to triglycerides (fat) and stored
PROTEIN METABOLISM
SOURCES OF AMINO ACIDS
diet – protein from meat and other animal tissues, certain plant tissues
(eg. seeds, grains), bacteria in digestive tract
catabolized in digestive tract and absorbed into blood as amino acids
conversion of carbohydrates or lipids to amino acids
conversion of one amino acid to another
break down of protein in body tissues (especially muscles) – last resort
(essential amino acids – cells cannot synthesize enough, must obtain from diet)
AMINO ACID CATABOLISM – breaking down amino acids for energy
deamination – amino group (NH2) removed from amino acids
produces nitrogenous wastes
ammonia (toxic) liver converts to less toxic molecules
urea in mammals
uric acid in birds and reptiles
following deamination molecules enter the Kreb’s cycle at various points
AMINO ACID ANABOLISM – the main use of amino acids in the body is formation
of structural and functional proteins of the body
the instructions for making these proteins are found on the cell’s DNA
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METABOLIC FUNCTIONS OF TISSUES
Liver – main regulator of nutrient content in blood
stores glycogen
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
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
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