Human Anatomy and Physiology I Chapter 2 The Chemical Basis of Life Instructor: Mary Holman.

Human Anatomy and Physiology I

Chapter 2The 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

MajorElements in the Human Body

Oxygen Carbon

HydrogenNitrogenCalcium

Phosphorus

O CHNCaP

% body wt

65.018.5 9.5 3.3 1.5 1.0

Other Important ElementsIn the Human Body

Potassium K

Sulphur S

Sodium Na

Chlorine Cl

Magnesium Mg

Trace Elements

Iodine I Molybdenum MoFluorine F Chromium CrIron Fe Selenium SeCopper Cu Aluminum Al Silicone Si Boron B Vanadium V Tin SnZinc Zn Cobalt CoManganese Mn

Atomic StructureAtom • smallest portion of an element that retains

all the properties of the element• composed of subatomic particles:

• Proton – carries a single positive chargefound in the nucleus

• Neutron – carries no electrical chargefound in the nucleus

• Electron – very small particle that carries a single negative chargefound moving in varying energy

levels around the nucleus

Particle Charge Location

Electron

Proton

Neutron

--

+

none

In nucleus

In nucleus

Outside nucleus

Major Subatomic Particles

Fig. 2.3a

Hydrogen (H)

+

-

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 2.3b

Helium (He)

-

-

00+

+


Fig. 2.3c

Lithium (Li)

-

-

-

0

0++

00+


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 element12C 13C 14C

Periodic Table of the Elements

7Nitrogen

N14.0067

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

11p+

12n0

Sodium atom (Na) 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–).

17p+

18n0


Fig. 2.4a Two Atoms Forming An Ionic Bond

Fig. 2.4b

+ -11p+

12n0

Chloride ion (Cl-)Sodium ion (Na+)

(b) Bonded ions These oppositely charged particles attract electrically and join by an ionic bond.

Sodium chloride

17p+

18n0


Fig. 2.4b Bonded Ions

Important Ions in the Body

Na+

K+

Ca2+

Mg2+

Cl-

PO43-

NH4+

HCO3-

Covalent Bonds

• Formed when atoms share electrons

• Organic compounds contain many covalent bonds

Hydrogen atom +

H

Hydrogen molecule

H2

Hydrogen atom

H

+ + ++

- -

-

-


Fig. 2.5

=

A Covalent Bond creating a Molecule of Hydrogen


H

C

O

N

Fig. 2.6

Atomic # - 1 Atomic # - 8

Atomic # - 7 Atomic # - 6

Fig. 2.6a


HH

H2

Structural Formulasversus

Molecular Formulas

Fig. 2.6b


OO

O2

The Double Covalent Bond

O : : O . . . .. . . .

Fig. 2.6d


CO O

CO2

Carbon Dioxide

Fig. 2.6c


O

HH

H2O

Water - A Polar Molecule(+)

(-)

(+)

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

Slightly positive endsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 2.8a

O

H H

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

H

H

H

H

HH

H

H

O

O

O

O

O

Hydrogen bonds

(b)

Fig. 2.8b

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

Acids – electrolytes that dissociate to release hydrogen ions in water

HCl H+ + Cl-

Bases – 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

NaCl Na+ + Cl-

HCl + NaOH H2O + NaCl

Acid and Base Concentration

pH scale - indicates the concentration of hydrogen ions insolution Neutral pH 7;indicates equal concentrations of H+

and OH-

Acidic pH less than7; indicates a greater concentration of H+

Basic or alkaline pH greater than 7;indicates a greater concentration of OH-

OH– concentration increasesH+ concentration increases

AcidicH+

Relative Amountsof H+ (red)and OH– (blue)

BasicOH–

2.0gastricjuice

6.0corn

7.0Distilledwater

8.0Eggwhite

10.5milk ofmagnesia

11.5Householdammonia

pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Basic (alkaline)NeutralAcidic

3.0applejuice

4.2tomatojuice

5.3cabbage

6.6cow’smilk

7.4Humanblood

8.4Sodiumbiocarbonate


Pg. 68

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

Human Anatomy and Physiology I Chapter 2 The Chemical Basis of Life Instructor: Mary Holman.

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