Chapter 3

download report

Transcript Chapter 3

Chapter 2
The Chemical Level of Organization
Principles of Human Anatomy and Physiology, 11e
1
HOW MATTER IS ORGANIZED
• Chemical Elements
– substances that cannot be split into simpler
substances
– 112 elements
• O, C, H, N, Ca, and P make up 98.5% of total
body weight
– Trace elements are present in tiny amounts
• copper, tin, selenium & zinc
2
Structure of Atoms
• All elements = atoms of same type
• Subatomic particles
– Nucleus
• protons (p+)
• neutrons (n0)
– Electrons (e-) move about nucleus
in energy levels
– In neutral atom, # e- = # p+
• Atomic Number (Z)
– # protons in nucleus
– Identifies atom
3
ISOTOPES
• Atoms of an element w/ same # of protons but
different # of neutrons
• Isotopes
– Stable isotopes do not change nuclear structure
over time
– Radioactive isotopes
• Unstable  nuclei decay to form simpler & more
stable configuration
• Assessment of internal abnormalities
4
Ions & Molecules
• Ions form when an atom gives up or gains electrons
– (+) or (-) charge due to unequal # of p+ and e– Goal: atomic stability
• Molecule results from two or more atoms sharing electrons
– Ex: H2, N2, O2, CO2, H2O
5
Free Radicals
• Electrically charged atom/molecule w/ unpaired electron
• Unstable & highly reactive  chain reactions
• Can become stable
– giving up an electron
– taking an electron from another molecule
• Antioxidants inactivate oxygen-derived free radicals
• Ex: superoxide radical = oxygen w/ extra electron
– can induce tissue damage if chain rxn allowed to
propagate
6
Free Radicals & Your Health
• Possible sources: absorption of UV energy in
sunlight, x-rays, breakdown of harmful
substances, & normal metabolic reactions
• Cancer, diabetes, Alzheimer, atherosclerosis and
arthritis
• Dietary antioxidants: vitamins C and E, selenium
& beta-carotene (precursor to vitamin A)
7
CHEMICAL BONDS
• Forces of attraction holding atoms of compound
together
• Valence e- determine:
– type of bonding
– chemical stability
• 8 e- in outer shell = stable
• <8 e- in outer shell  gain/lose/share e• octet rule
8
Ionic Bonds
• Loss or gain of valence electron results in ion
formation
• Oppositely charged ions attracted to one another
– Cations
– Anions
• Electrolytes
• Ex: NaCl in Fig 2.4
9
Covalent Bonds
• Formed from sharing one, two, or three pairs of valence e– Strongest chemical bonds in the body
– Single, double, or triple covalent bonds
• Bond polarity
– Nonpolar covalent bond
• Equal sharing of electrons
– Polar covalent bond
• Unequal sharing of electrons
• Electronegativity difference
• N—H & C—O
10
Polar Covalent Bonds
• Unequal sharing of electrons between atoms
• Different centers of positive & negative charge
• In a water molecule, O attracts H electrons more strongly
– Oxygen has greater EN (indicated by negative delta sign)
– Overall polarity of molecule is in direction of oxygen
• See Fig 2.6
11
Hydrogen Bonds
• Special polar covalent bonds btwn H atom &
electronegative atom
– N…H or O…H
• Very weak intermolecular bonds
• Cohesive properties of water
• Occur between δ+ H of one H2O
& δ- O of another H2O (See Fig 2.7)
12
Chemical Reactions
• New bonds form and/or old bonds are broken
• Metabolism = sum of all chemical reactions in the body
• Law of conservation of mass
– Total mass of reactants equals total mass of products
13
Forms of Energy
• Energy = capacity to do work
– Kinetic energy = energy of motion
• Temperature
– Potential energy = energy stored by matter due to its
position
• Chemical energy
• Energy:
– Conserved in rxn
– May be converted
14
Energy Transfer
• Exergonic reaction
– bond broken has more energy than one formed
– extra energy is released
• usually as heat
• catabolism of food molecules
• Endergonic reaction
– requires energy be added to form a bond
• usually from a molecule of ATP
• EX: building proteins from amino acids
15
Energy Transfer in Chemical Reactions
• In living systems, ender- & exergonic reactions occur
together
• Coupled reactions essential to metabolism
– energy released from one reaction drives another
– Ex: glucose breakdown releases energy, which is used
to build ATP molecules
– Ex: ATP fuels transport across membranes, muscle
contraction & nerve impulses
16
Activation Energy
• Energy needed to break bonds & begin reaction (Fig 2.9)
• Increasing probability of collision
increases chance for reaction
• Increasing concentration & temperature are ways of
overcoming Ea, thus ↑ chances for collision
– more particles are in a given space
– particles move more rapidly
17
Factors Influencing Chemical Rxns
• Concentration
• Temperature
• Catalysts
– speed up chemical reactions by lowering amount of
energy needed to get reaction started (activation energy,
Ea)
– do not alter difference in potential energy between the
reactants & products
– orient colliding particles
– unchanged at end of reaction  often re-used many
times
– relevance??? Biological enzymes are catalysts!
18
Effectiveness of Catalysts
Difference in PE
19
Types of Chemical Reactions
• Synthesis
– > two atoms/ions/molecules combine to form new & larger
molecules
– anabolic reactions (bonds are formed)
A + B  AB
– generally endergonic
– Decomposition
– a molecule is broken down into smaller parts
– catabolic reactions (bonds are broken)
AB  A + B
– usually exergonic
20
Reversible Reactions
• Chemical reactions can be reversible
• Indicated by the 2 arrows pointing in opposite
directions between the reactants and the products
AB
A +
B
21
Water
• Most important & abundant inorganic compound in all living
systems
• Polarity makes it a good solvent  almost “universal” solvent
– Hydrophilic compounds
• Usually are polar
• Dissolve in water
– Hydrophobic compounds
• Usually nonpolar
• Do not dissolve in water
• Excellent medium for metabolic reactions of the body
23
Water as a Solvent
• Polar covalent bonds (hydrophilic vs. hydrophobic)
• Dissolves or suspends many substances
– Each water molecule interact w/ 4 or
more neighboring ions/molecules
– Hydration spheres
• Fig. 2.11 shows how water’s shape makes it such an
effective solvent.
24
Water in Chemical Reactions
• Hydrolysis: add’n of water breaks molecules apart
• Dehydration synthesis
– two simple molecules join together
– eliminate a molecule of water in process
• High heat capacity
– Resists changes in temperature  maintain body temp
– Due to hydrogen bonding
• High heat of vaporization
– amount of heat needed to change from liquid to gas
– evaporation of water from skin removes lots of heat 
why sweat cools you
25
Water as a Lubricant
• Major component of mucus & other lubricating fluids
– mucus in respiratory and digestive systems
– synovial fluid in joints
– serous fluids in chest and abdominal cavities
• organs slide past one another
• Found wherever friction needs to be reduced or eliminated
26
Inorganic Acids, Bases & Salts
• Dissociate into ions in water
– Acids: H+ + AHCl  H+ + Cl– Bases: OH- + cation
NaOH  Na+ + OH• Acid + base  salt & H20
– HCl + NaOH  NaCl + H2O
• Salts dissociate into cations & anions in water
– metal and nonmetal ions: NaCl + H2O  Na+ + Cl-
– not H+ or OH- !!
• Electrolytes
– important salts in body (Na, Cl, K)
– carry electric current (in nerve or muscle)
27
Acid-Base Balance & pH
• pH: measure of [H+] in moles/liter (M)
• pH scale: 0-14
– pH = 7  neutral  [H+] = [OH-]
– pH < 7  acidic  [H+] > [OH-]
– pH > 7  alkaline  [H+] < [OH-]
• A solution’s acidity or alkalinity is based on the pH
scale
• Biochemical reactions are very sensitive to even
small changes in pH
– pH of blood is 7.35 to 7.45
28
The Concept of pH
• pH is a logarithmic scale—it is NOT linear!
– Therefore—each unit in scale means 10-fold Δ in
[H+]
• Ex: a change of two pH units represents 100-fold diff in
[H+] 
– pH 1 contains 10-1 M H+ & pH 3 contains 10-3 M H+
– the diff in H+ ion concentration is 100—not 2!
• Ex: pH 8 vs. pH 11
– pH 8 = 10-8 M H+ & pH 11 = 10 -11 M H+
– pH 8 is 1000x more acidic than pH 11 (even tho both
are basic!)
29
Maintaining pH: Buffer Systems
• pH in body maintained fairly constant by buffer systems
• Buffers resist Δ in pH even when acid/base added
– consist of a weak acid & a weak base
– convert strong acids/bases into weak acids/bases
– Ex: carbonic acid-bicarbonate buffer system in blood
• HCO3- acts as weak base
• H2CO3 acts as weak acid
• H2CO3 ↔ H+ + HCO3• H2CO3  H+ + HCO3- (in presence of XS base)
• H2CO3  H+ + HCO3- (in presence of XS acid)
30
ORGANIC COMPOUNDS:
Carbon and Its Functional Groups
• Carbon forms bonds w/ itself
– Large complex molecules of varying shapes
• Most compounds do not dissolve easily in water
– useful for building body structures
• C compounds held together by covalent bonds
– 4 valence e-  forms 4 bonds
• Decompose easily
– good source of energy
• Functional groups have distinct chemical properties when
attached to organic molecule
31
Functional Groups
• Many different functional groups can attach to carbon skeleton
• Very large molecules = macromolecules
• Isomers have the same molecular formulas but different
structures (glucose & fructose are both C6H12O6)
• STRUCTURAL FORMULA OF
GLUCOSE (Fig 2.14)
C6H12O6 ISOMERS
32
Carbohydrates (CHO)
• Primary energy source in humans
– Include sugars, starches, glycogen, and cellulose
– Used to generate ATP
– Structural building blocks (DNA)
• Structurally, one H2O molecule/C atom
• Function as food reserves
– glycogen stored in liver & muscle
• Divided into three major groups based on size:
– Mono-/di-/polysaccharides
33
SUGARS: Monosaccharides
• Names of sugars generally end in “-ose”
• Monosaccharides
– 3-7 carbon atoms
– Monomers for building large CHO molecules in body
– Ex: glucose (a hexose) is main energy-supplying
compound in body
• Humans absorb only 3 simple sugars without further
digestion in small intestine
– glucose found in syrup or honey
– fructose found in fruit
– galactose found in dairy products
34
SUGARS: Disaccharides
• Formed from two monosacch. by dehydration synthesis
– glucose + fructose  sucrose (table sugar)
– glucose + glucose  maltose
– glucose + galactose  lactose (milk sugar)
• Can be split back into simple sugars by hydrolysis
• Figure 2.15
35
Polysaccharides
• Polymers of up to hundreds of monosaccharides
• Primary polysaccharide in humans = glycogen
– Stored in liver or skeletal muscles
– Hydrolyzed in response to ↓ blood sugar  glucose
released into blood (from liver only)
• Cellulose
– Plant polysaccharide
– Not digestible by humans  “fiber”
36
Lipids
• Contain carbon, hydrogen & oxygen
– Fewer oxygens than CHO (not 2:1 H:O ratio)
• Nonpolar covalent bonds
– Hydrophobic
– Insoluble in polar solvents such as water (plasma)
• Only very short-chain fatty acids dissolve in plasma
• Increase solubility by forming lipoproteins 
“cholesterol”
37
LIPIDS: Triacylglycerols (TAG)
• TAG (also called triglycerides) are what we call “fat”
• Most plentiful lipids in the body  provide protection,
insulation, and energy
• Found in fats and oils
– Fats = solid @ room temperature
– Oils = liquid @ room temperature
– Most concentrated form of energy
• 9 Calories/gram
• Proteins & carbs have only 4 Cal/gram!
– Unlimited storage capacity in body  adipose tissue
• ANY excess food energy is stored as fat
– All TAG contain glycerol backbone & three fatty acids
38
Saturation of Fatty Acids
• Determined by number of single or double covalent bonds
• Saturated FA contain single covalent bonds & maximum
possible # of H atoms
– Saturated fats = TAG w/ only saturated fatty acids
– Ex: lard, tallow
• Unsaturated FA lack some H atoms due to presence of > 1
double bond
– Monounsaturated fatty acids have one double bond
• olive oil, canola oil, & avocados (yum!!)
– Polyunsaturated fatty acids contain > 2 double bonds
• corn, safflower, soybean oils
– Double bonds form kink in structure of fatty acid
• fluid rather than solid
39
Clinical Application
• Essential fatty acids (EFA’s) are essential to human health
and cannot be made by the human body. They must be
obtained from foods or supplements.
– ω-3 fatty acids  anti-inflammatory
– ω-6 fatty acids  pro-inflammatory
• Not all inflammation is bad!
– Balance is important
– Conjugated fatty acids (CFA’s)  some implications for
weight loss…
• trans-fatty acids ↑ risk factors for CVD
40
Phospholipids
• Important membrane components
• Amphipathic
– polar head
• a phosphate group (PO4-3) & glycerol molecule
• forms hydrogen bonds with water
– 2 nonpolar fatty acid tails
• interact only with lipids
• hydrophobic
41
Steroids
• Four rings of carbon atoms
• Include
– cholesterol
• important component of cell membranes
• starting material for synthesizing other steroids
– sex hormones
– bile salts
– vitamin D
– cortisol
42
Other Lipids
• Eicosanoids include prostaglandins and leukotrienes.
– derived from 20-C fatty acids AA (ω-6) or EPA (ω-3)
– prostaglandins have wide variety of functions
• modify responses to hormones
• contribute to inflammatory response
• dilate airways
• regulate body temperature
• influence formation of blood clots
– leukotrienes = allergy & inflammatory responses
• PG & LT derived from EPA are biologically inactive
• Fatty acids; fat-soluble vitamins (D, E, K); and lipoproteins
43
Proteins
• Contain C, H, O, N & sometimes S
• 12-18% of body weight
• Functions:
– Give structure to body (primary role)
– Regulate processes
– Provide protection
– Help muscles contract
– Transport substances
– Enzymes
44
Proteins
• Constructed from combinations of 20 amino acids
– dipeptide formed from 2 amino acids joined by
peptide bond (covalent bond)
– polypeptide chains formed from 10 to 2000
amino acids
45
Amino Acid Structure
• Central carbon atom
• Amino terminus (NH2)
• Carboxyl terminus (COOH)
• Side chains (R groups) vary
between amino acids
– Amino acids identified by
side chain
46
Levels of Protein Structure
• Primary = sequence of amino acids
• Secondary = twisting & folding
– Alpha helices
– Beta pleated sheets
• Tertiary = 3-D shape of folded protein
– **Determines function**
– Disulfide bridges
– Hydrophobic domains in core of folded protein
• Quaternary = structure resulting from linkage of 2 polypeptides
• Shape influences its ability to recognize & bind other molecules
• Denaturation causes loss of characteristic shape and function
47
Bonds of Tertiary Structure
• Hydrophobic interaxn on
inside of folded protein
• Disulfide bridges stabilize
– covalent bond btwn S—H
groups of 2 cysteine a.a.
• H-bonds
• Loss of 3-D structure
(denaturation)  loss of
function
– Salts
– Heat
– Acid
48
Enzymes
• Biological catalysts
• Names generally end in “ase”
– Sucrose is digested by enzyme sucrase
• Properties:
– Highly specific in terms of substrate & reaction
– Highly efficient
– Highly regulated by variety of cellular controls
• Genes
• Active & inactive conformations
• Speed up chemical reactions by:
– Increasing frequency of collisions
– Lowering the activation energy
– Properly orienting colliding molecules (Figure 2.23)
49
Enzymes as Catalysts
Example:
• Normal body temperatures & concentrations are low
enough that rxns are effectively blocked by Ea barrier
– Lactose reacts very slowly w/ water to yield glc & gal
– Lactase (enzyme) orients lactose & water properly
– Thousands of lactose/water reactions may be catalyzed
by one lactase enzyme
– Without lactase, lactose remains undigested in intestines
• causes diarrhea and cramping  condition known as
lactose intolerance (NOT an allergy!!!)
51
Nucleic Acids: DNA and RNA
• Huge organic molecules containing C, H, O, N, P
• Deoxyribonucleic acid (DNA)
– genetic code inside each cell
– regulates most cellular activities
• Ribonucleic acid (RNA)
– relays instructions from genes in cell’s nucleus
– guides assembly of proteins by ribosomes
• Basic units of nucleic acids are nucleotides
– nitrogenous base
– pentose sugar
• deoxyribose
• ribose
– phosphate group (Figures 2.24a,b)
52
RNA Structure
• Differs from DNA
– single stranded
– ribose sugar not deoxyribose sugar
– uracil replaces thymine
• Three types of RNA
– messenger RNA
– ribosomal RNA
– transfer RNA
53
Adenosine Triphosphate (ATP)
• Energy currency of cells
• Generated from exergonic catabolic reactions
– Breakdown of fats, glucose
• Energy liberated upon hydrolysis
– ATP  ADP + Pi + energy
• Structure
– 3 PO4-3 groups
– adenine
– 5-carbon sugar (ribose)
54
Formation & Usage of ATP
• Hydrolysis of ATP (removal of terminal PO4-3 by ATPase)
– releases energy
– leaves ADP (adenosine diphosphate)
• Synthesis of ATP
– ATP synthase catalyzes add’n of terminal PO4-3 to ADP
– energy from 1 glc molecule generates up to 36 net
molecules of ATP
55