Transcript Human Anatomy and Physiology I

Human Anatomy and Physiology I
Chapter 2
The Chemical Basis of Life
Instructor: Mary Holman
• Matter
• Elements
– Can’t be broken down into simpler
substances
– 97 natural elements, >100 known
– Organized into a Periodic Table
Major
Elements in the Human Body
% body wt
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
O
C
H
N
Ca
P
65.0
18.5
9.5
3.3
1.5
1.0
Other Important Elements
In the Human Body
Potassium K
Sulphur
S
Sodium
Na
Chlorine Cl
Magnesium Mg
Trace Elements
Iodine
I
Fluorine
F
Iron
Fe
Copper
Cu
Silicone
Si
Vanadium V
Zinc
Zn
Manganese Mn
Molybdenum
Chromium
Selenium
Aluminum
Boron
Tin
Cobalt
Mo
Cr
Se
Al
B
Sn
Co
Atomic Structure
Atom
• smallest portion of an element that retains
all the properties of the element
• composed of subatomic particles:
• Proton – carries a single positive charge
found in the nucleus
• Neutron – carries no electrical charge
found in the nucleus
• Electron – very small particle that
carries a single negative charge
found moving in varying energy levels
around the nucleus
Major Subatomic Particles
Particle
Charge
Location
Electron
--
Outside nucleus
Proton
+
In nucleus
Neutron
none
In nucleus
Fig. 2.3a
-
+
Hydrogen (H)
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Fig. 2.3b
+
0
0
+
Helium (He)
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Fig. 2.3c
+ 0
+
0 0
0
+
-
Lithium (Li)
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Atomic number - equal to the
number of protons or electrons in an
atom
Atomic mass - equal to the average
total number of neutrons plus protons
Isotopes - atoms with differing
numbers of neutrons in atoms of the
same element
12C 13C 14C
Periodic Table of the Elements
7
Nitrogen
N
14.0067
Periodic Table Appendix D - Pg 931
Bonding of Atoms
• Bonds form when atoms combine with other atoms
through interactions between their electrons
• Electrons of an atom occupy regions of space called
electron shells which circle the nucleus
• For atoms with atomic numbers of 18 or less, the
following rules apply:
• The first shell can hold up to 2 electrons
• The second shell can hold up to 8 electrons
• The third shell can hold up to 8 electrons
Valence Number
Number of electrons in outer shell or
energy orbital of an element
These electrons participate in
bonding with atoms of other
elements
Shifting of valence electrons occurs
in bonding with other atoms
There are two types of bonds that
hold atoms together in a
molecule:
Ionic bond
Covalent bond
Valence # determines which kind of
bond an atom is likely to make
Bonding of Atoms: Ions
Ion
• An atom that gains or loses electrons to become stable
• An electrically charged atom
Cation
• Positively charged ion
• Formed when an atom
loses electrons
Anion
• Negatively charged ion
• Formed when an atom
gains electrons
Ionic Bonds
• An attraction between a cation
and an anion
• Formed when one atom gives up
one or more electrons to another atom
Fig. 2.4a
Two Atoms Forming An Ionic Bond
Fig. 2.4a
11p+
12n0
Sodium atom (Na)
17p+
18n0
Chlorine atom (Cl)
(a) Separate atoms
If a sodium atom loses an electron to a chlorine atom, the sodium
atom becomes a sodium ion (Na+), and the chlorine atom becomes
a chloride ion (Cl–).
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Bonded Ions
Fig. 2.4b
Fig. 2.4b
+
11p+
12n0
17p+
18n0
Sodium ion (Na+)
-
Chloride ion (Cl-)
Sodium chloride
(b) Bonded ions
These oppositely charged particles attract electrically and join by
an ionic bond.
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Important Ions in the Body
Na+
K+
Ca2+
Mg2+
ClPO43NH4+
HCO3-
Covalent Bonds
• Formed when atoms share
electrons
• Organic compounds contain
many covalent bonds
A Covalent Bond creating a Molecule of Hydrogen
Fig. 2.5
H
H
-
-
H2
-
+
+
+
+
-
Hydrogen atom
+
Hydrogen atom
=
Hydrogen molecule
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Fig. 2.6
H
Atomic # - 1
N
Atomic # - 7
O
Atomic # - 8
C
Atomic # - 6
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Fig. 2.6a
Structural Formulas
versus
Molecular Formulas
H
H
H2
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The Double Covalent Bond
Fig. 2.6b
O
.. ..
.O. : : O
..
O
O2
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Carbon Dioxide
Fig. 2.6d
O
C
O
CO2
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Water - A Polar Molecule
Fig. 2.6c
(+)
(+)
H
H
O
(-)
H2O
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Fig. 2.8a
Bonding of Atoms:
Polar Molecules
Polar Molecules
• Molecule with a slightly negative end and a slightly positive end
• Results when electrons are not shared equally in covalent bonds
• Water is an important polar molecule
Slightly negative end
O
H
H
Slightly positive ends
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Fig. 2.8b
Hydrogen Bonds
Hydrogen Bonds
• A weak attraction between the positive end of one polar molecule and
the negative end of another polar molecule
• Formed between water molecules
• Important for protein and nucleic acid structure
H
H
O
H
O
H
O
H
O
H
H
O
(b)
Hydrogen bonds
H
H
H
Molecular Formulas
Depict the elements present
and the number of each atom
present in the molecule
H2
H2O
C6H12O6
Acids, Bases, and Salts
Electrolytes – substances that release ions in water
NaCl  Na+ + ClAcids – electrolytes that dissociate to release hydrogen ions
in water
HCl  H+ + ClBases – substances that release ions that can combine with
hydrogen ions
NaOH
Na+ + OH-
Salts – electrolytes formed by the reaction between an acid and a
base
HCl + NaOH
H2O + NaCl
Acid and Base Concentration
pH scale - indicates the
Relative Amounts
concentration of hydrogen ions in
of H+ (red)
and OH– (blue)
solution
8.4
Neutral pH 7;
7.4
Acidic
6.6
Sodium
H
cow’s Human biocarbonate
5.3
blood
4.2
indicates equal
milk
cabbage
3.0
11.5
tomato
10.5
2.0
apple juice
Household
+
milk of
gastric juice
concentrations of H
ammonia
8.0
magnesia
juice
7.0
Egg
6.0
Distilled white
Basic
and OHcorn
water
OH
3
4
5
6
7
8
9
10
11
12
13
14
Acidic pH less than pH 0Acidic 1 2H concentration
increases
OH concentration increases
Neutral
Basic (alkaline)
7; indicates a greater
concentration of H+
Pg. 68
+
–
+
–
Basic or alkaline pH greater than 7;
indicates a greater concentration of OHCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Buffers
A buffer solution is one that maintains a
constant pH upon the addition of either
acid or base.
It consists of a weak acid and a weak
base. It can “sponge up” excess H+ if
added to a solution, or it can release H+
if the H+ concentration drops.
Inorganic Compounds
• Generally
do not contain C*
• Usually smaller than organic molecules
• Usually dissociate in water, forming ions
• Water, oxygen, carbon dioxide, and
inorganic salts
* exceptions: CO, CO2, HCO3
Important Inorganic Compounds
Water (H2O)
• Most abundant compound in living material
• Two-thirds of the weight of an adult human
• Major component of all body fluids
• Medium for most metabolic reactions
• Important role in transporting chemicals in the body
• Absorbs and transports heat
Oxygen (O2)
• Used by organelles to release energy from
nutrients in order to drive cell’s metabolic activities
• Necessary for survival
Important Inorganic Compounds
Carbon dioxide (CO2)
• Waste product released during metabolic reactions
• Must be removed from the body
Inorganic salts
• Abundant in body fluids
• Sources of necessary ions (Na+, Cl-, K+, Ca2+, etc.)
• Play important roles in metabolism
Organic Compounds
• Contain C and H
• Usually larger than inorganic
molecules
• Dissolve in water or organic liquids
• Carbohydrates, lipids, proteins,
nucleic acids, and adenosine
triphosphate