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ChemicalBasis of Life

2.1-2.2August 7, 2012

AgendaGeneral

HousekeepingReview Chapter 2

2.1

Research Paper

2.2

Assignments

Overview Process

Review• Are the ribs superficial to the lungs? How do

you know?• In which cavity is the thymus located?

• Locate the nine abdominopelvic regions onyourself and list some of the organs found ineach

– Use four strips of tape to mark yourself

Chapter 2:Chemical Basis of Life• 2.1 Introduction

• 2.2 Structure of Matter

• 2.3 Chemical Constituents of Cells

The Big Idea• Chemistry and Homeostasis

– Maintaining the proper assortment andquantity of thousands of different chemicalsin your body, and monitoring the interactionsof these chemicals with one another, are twoimportant aspects of homeostasis

2.1 Introduction• Objectives

– Explain how the study of living materialdepends on the study of chemistry

What is Chemistry?• The study of anatomy and physiology begins with

an understanding of chemistry

• Chemistry is the branch of science that considersthe composition of matter and how thiscomposition changes

• Body structures and functions are a result ofchemical changes within cells

2.2 Structure of Matter• Objectives

– Discuss how atomic structure determines how atomsinteract

– Describe the relationships between atoms andmolecules

– Explain how molecular and structural formulassymbolize the compositions of the compounds

– Describe three types of chemical reactions– Define pH

Elements & Atoms• Matter is anything that has mass and takes up space• All forms of matter are composed of chemical elements

which are substances that cannot be split into simplersubstances by ordinary chemical means

• Elements are given letter abbreviations called chemicalsymbols

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• Major Elements constitute about 96% of thebody’s mass

– O, C, H, N

• Lesser Elements contribute about 3.6% of thebody’s mass

– Ca, P, K, S, Na, Cl, Mg, Fe

• Trace elements are elements in our bodies,present in tiny amounts and account for theremaining 0.4% of the body’s mass

– Several trace elements have importantfunctions in the body

Atomic Structure• Units of matter of all chemical elements are

called atoms.• An element is a quantity of matter composed

of atoms of the same type.

• Atoms contain three types of subatomicparticles

• Electrons (e-) are very small and light (mass about1/2000th that of proton or neutron), oftenrepresented as orbiting around the nucleus

• In reality, they are found in a “cloud” of probabilitysurrounding the nucleus

• Protons (p+) and neutrons (n0) form the nucleusof an atom

– Protons are large, positively-charged particles

•The number of protons in the nucleus(called the atomic number) determines theelement

• Neutrons are the second largest particle thatmake-up the nucleus of atoms

– Unlike protons, neutrons have no charge

– They do add mass, however, and determine thevariety, or “isotope” of a certain element

•Isotopes are atoms of an element that havedifferent numbers of neutrons

•Carbon-12 vs. Carbon-14, which has 2 extraneutrons in nucleus

• Mass is measured as a dalton (atomicmass unit)

• Certain numbers are used to describedifferent properties of elements

- Atomic number is the number ofprotons in an atom

- Mass number is the sum of protonsand neutrons in an atom

- Atomic mass (atomic weight) is theaverage mass of all naturally occurringisotopes

Elements in the Human Body Ions• Atoms that have given up or gained an electron in

their outer electron shell (also called the valenceshell)

– Written with its chemical symbol and (+) or (–)

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Molecules• Molecules are formed when

atoms share electrons• Written as a molecular formula showing the

number of atoms of each element (H2O)

• The oxygen gas in the atmosphere we breathis really not oxygen the atom, but a pair ofoxygen atoms linked together into an oxygenmolecule (O2)

Compounds• A substance that contains atoms of two or

more different elements

– Most of the atoms in the body are joinedinto compounds

•H2O

•NaCl

•O2 is not a compound. Why?

• The atoms of a molecule are held together by forcesof attraction called chemical bonds

• The likelihood that an atom will form a chemicalbond with another atom depends on the number ofelectrons in its outermost or valence shell

• Atoms will interact in ways that produce a chemicallystable arrangement of eight valence electrons in eachatom (Octet Rule)

Ionic Bonds• Ions form when an atom loses or gains a valence

electron• Positively and negatively charged ions are attracted to

one another• Cations are positively charged ions that have given up

one or more electrons (they are electron donors)• Anions are negatively charged ions that have picked

up one or more electrons that another atom has lost(they are electron acceptors)

• Ionic compounds that break apart into positive andnegative ions in solution are called electrolytes

Covalent Bonds• Formed by the atoms of molecules sharing one,

two, or three pairs of their valence electrons

• Covalent bonds are the strongest chemical bonds

• Single, double, or triple covalent bonds are formedby sharing one, two, or three pairs of electrons,respectively

• Covalent bonds may be nonpolar or polar

• In a nonpolar covalent bond, atoms share theelectrons equally

– Nonpolar covalent bonds are the mostcommon types of covalent bonds

• Polar covalent bonds are formed by the unequalsharing of electrons between atoms

• Polar covalent bonds are extremely importantbecause the all-important water molecule makesuse of this bond

• In water, oxygen attracts the hydrogen electronsmore strongly, making oxygen slightlyelectronegative as indicated by the negativeGreek delta sign

Hydrogen Bonds• Are weak interactions (approximately 5% as strong

as covalent bonds) between hydrogen andadjacent electronegative atoms like oxygen orsulfur

• Result from attraction of oppositely charged partsof molecules—they should not be confused withcovalent bonding to hydrogen which involvesactual sharing of electrons

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Chemical Reactions• Chemical reactions occur when electrons in the

valence shell are shared or transferred

– Old bonds are broken in the reactants and newbonds are formed in the product(s)

• Metabolism is the “sum of all the chemical reactionsin the body”

• Law of Conservation of Mass

– The total mass of reactants equals the total massof the products

Catalysts• Factors that cause a collision (and a chemical reaction

to take place) include the temperature and theconcentration of the reactants, and the presence orabsence of a catalyst

• Catalysts are chemical compounds that speed upchemical reactions by lowering the activation energyneeded for a reaction to occur

• Catalysts are neither consumed nor produced in thereaction– They are used over-and-over again, often several

million times per second

Types of Chemical Reactions• Synthesis Reactions• Anabolism- A + B ➙ AB- Two or more atoms, ions, or molecules

combining to form a new, larger molecule- Usually endergonic because they absorb more

energy than they release

N2 + 3H2 2NH3

• Decomposition Reactions

• Catabolism

- AB ➙ A + B

- Large molecule breaks down into smaller atoms,ions, or molecules

- Usually exergonic because they release moreenergy than they absorb

2H2O2 2H2O + O2

• Exchange Reactions

- AB + CD ➙ AD + CB

- The ions in both compounds have“switched” partners

HCl + NaHCO3 H2CO3 +NaCl

• Reversible Reactions

- AB ↔ A + B

- Products can revert back to the originalreactants

- Some reactions are only reversible underspecial conditions

- Many reversible reactions in the body requirespecific enzymes to guide the reaction inopposite directions

Inorganic Acids, Bases, & Salts• An acid is a substance that dissociates into H+ and

is considered a proton donor• A base is a substance that dissociates into OH-

and removes H+ from a solution (protonacceptor)

• Salts, when dissolved in water, dissociates intocations and anions, neither of which is H+ or OH-

• Acids and bases react with one another to formsalts

pH• pH = –log[H+]

– Concentration of H+ in moles/L

• It is a scale that runs from 0 to 14

• The pH scale is a logarithmic scale, not a linear scale– Because of the “negative” in the formula, the lower the

number, the higher the H+ concentration ([H+])• Because it is logarithmic, a change of two or three pH

units represents a change in the [H+] of 100 or 1000– A solution with pH=1 is 100 times more concentrated

in H+ ions than a solution with a pH=3– A solution with pH=11 contains 1000 times less H+

ions than a solution with a pH=8

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• pH < 7 is acidic ([H+] > [OH-])

• pH > 7 is alkaline ([H+] < [OH-])

• A salt (like KCl) is neutral

Clinical Connections• Harmful and Beneficial Effects of Radiation

– Some radioactive isotopes release radiation that can breakapart molecules, producing tissue damage and/or causingdifferent types of cancer• Radon-222, produced during the break down or uranium,

may seep out of the soil and accumulate in buildings. It hasbeen linked to cases of lung cancer

– Other radioisotopes can be used as tracers to follow themovement of certain substances through the body

• Thallium-201 is used to monitor blood flow through theheart during exercise stress tests

Assignments• Finish Chapter 1 Review WS

• Begin Chapter 2 Review WS• Read Section 2.3

• Choose five pieces of technology used inscience and brainstorms improvements youwould like to see made to it

• Terminology Quiz next class (1.6 & 1.7)