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THE PROCESS OF SCIENCE

– What is science?– The word science is derived from a Latin verb

meaning “to know.”

Discovery Science

• Science seeks natural • As a formal process of

Hypothesis-Driven Science

• Science seeks natural causes for natural phenomena.

– This limits the scope of science to the study of structures and processes that we can observe and measure.

• As a formal process of inquiry, consists of a series of steps.

– The key element of the scientific method is hypothesis-driven science.

Hypothesis-Driven Science– As a formal process of inquiry, the scientific method

consists of a series of steps.• The key element of the scientific method is

hypothesis-driven science.

Revise and repeat

Observation Question Hypothesis Prediction Experiment

Revise and repeat

Observation: Question:What’s wrong

Prediction:If I replace the Experiment:

I replace theHypothesis:

Th fl hli ht’

Hypothesis-Driven Science

My flashlightdoesn’t work.

What’s wrongwith my

flashlight?

If I replace thebatteries, theflashlight will

work.

I replace thebatteries with

new ones.

Experimentsupports

hypothesis;make additional

predictionsand test them.

The flashlight’sbatteriesare dead.

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Theories in Science– What is a scientific theory, and how is it different

from a hypothesis?• A theory is much broader in scope than a

hypothesis.• Theories only become widely accepted in science if

they are supported by an accumulation of extensivethey are supported by an accumulation of extensive and varied evidence.

Chemistry of Life– Matter is anything that occupies space and has mass.– Matter is found on the Earth in three physical states:

• Solid • Liquid• Gas

Atoms

ProtonsNeutronsElectrons

Nucleus222

– Each element consists of one kind of atom.• An atom is the smallest unit of matter that still retains the

properties of an element.

NucleusElectrons

Cloud of negativecharge (2 electrons)

2

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– Matter is composed of chemical elements.• Elements are substances that cannot be broken down

into other substances.

Chemistry of Life

Change the number of PROTONS in the nucleus and you change the ELEMENT

– Elements differ in the number of subatomic particles in their atoms.

• The number of protons, the atomic number, determines which element it is.

• An atom’s mass number is the sum of the number of protons and neutrons.

• Mass is a measure of the amount of matter in an object.

Chemistry of Life

j

Periodic Table of the Elements

Atomic number = number of protons within the nucleus

Other nonmetals Halogens Noble gases Other metals

Rare earth metals Transition metals Alkali earth metals Alkali metals

SyntheticGasLiquidSolid

Legend

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Chemistry of Life

Carbon (C): 18.5%

Calcium (Ca): 1.5%

Oxygen (O):65.0%

Phosphorus (P): 1.0%Potassium (K): 0.4%Sulfur (S): 0 3%

– Twenty-five elements are essential to life.– Four elements make up about 96% of the weight of

the human body:• Oxygen• Carbon

Hydrogen (H):9.5%

Nitrogen (N):3.3%

Trace elements: less than 0.01%Boron (B) Manganese (Mn)

Magnesium (Mg): 0.1%

Sulfur (S): 0.3%Sodium (Na): 0.2%Chlorine (Cl): 0.2%

Cobalt (Co)Chromium (Cr)

Iron (Fe)Iodine (I)Fluorine (F)Copper (Cu) Silicon (Si)

Zinc (Zn)Vanadium (V)Tin (Sn)

Molybdenum (Mo)Selenium (Se)

• Hydrogen• Nitrogen

First electron shell(can hold 2 electrons)

Outer electron shell(can hold 8 electrons)

Electron

Chemical Properties of Atoms– Electrons determine how an atom behaves when it encounters

other atoms.

Hydrogen (H)Atomic number = 1

Carbon (C)Atomic number = 6

Nitrogen (N)Atomic number = 7

Oxygen (O)Atomic number = 8

© 2010 Pearson Education, Inc.

Covalent Bonds– A covalent bond forms when two atoms share one or

more pairs of outer-shell electrons.– Atoms held together by covalent bonds form a

molecule.

Name(molecular formula)

Electron configuration Structural formula Space-filling model Ball-and-stick model

Hydrogen gas (H2)

Oxygen gas (O2)

Methane (CH4)

Single bond(a pair of shared electrons)

Double bond(two pairs of shared electrons)

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Ionic Bonds– When an atom loses or gains electrons, it becomes

electrically charged.• Charged atoms are called ions.• Ionic bonds are formed between oppositely charged ions.

Outer shellhas 1 electron

Outer shell

The outer electron is strippedfrom sodium and completesthe chlorine atom’s outer shell

Completeouter shells

Outer shellhas 7 electrons

NaSodium atom

ClChlorine atom

The attractionbetween theions—an ionicbond—holdsthem together

Na+Sodium ion

Cl−Chlorine ion

Sodium chloride (NaCl)

Hydrogen Bonds– Water is a compound in which the electrons in its

covalent bonds are shared unequally.• This causes water to be a polar molecule, one with opposite

charges on opposite ends.

(slightly +) (slightly +)

H H

O

(slightly –)

Hydrogen bonding• Weak bonds formed

between hydrogen and another atom – Surface tension of water

• Important as pintramolecular bonds, giving shape to proteins and other biomolecules

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WATER AND LIFE– Life on Earth began in water and evolved there for 3

billion years.• Modern life remains tied to water.• Your cells are composed of 70%–95% water.

Properties of Water• Numerous properties due to the hydrogen bonding

Properties of Water

Microscopic tubes

Evaporation fromthe leaves

– Water molecules stick together as a result of hydrogen bonding.

• This is called cohesion.

Cohesion due tohydrogen bondsbetween watermolecules

SEM

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– Heat and temperature are related, but different.• Heat is the amount of energy associated with the movement of

the atoms and molecules in a body of matter.• Temperature measures the intensity of heat.

– Water can absorb and store large amounts of heat while only changing a few degrees in temperature.

Properties of Water

– Water can moderate temperatures.

– Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid.

• Hydrogen bonds give water an unusually high surface tension.

Properties of Water

*solution

*solvent *solute *aqueous solution

Water is the solvent of life

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Basicsolution

Oven cleaner

Householdbleach

Human bloodPure water

Household ammonia

Milk of magnesia

Seawater

7

8

9

10

11

12

13

14

Incr

easi

ngly

bas

ic(lo

wer

H+

conc

entr

atio

n)

Neutral[H+] = [OH–]

Acids, Bases and pH

Neutralsolution

Acidicsolution

Grapefruit juice,soft drinkLemon juice,gastric juice

Tomato juice

Urine

pH scale0

1

2

3

4

5

6

Incr

easi

ngly

aci

dic

(gre

ater

H+

conc

entr

atio

n)

Carbon and Organic Chemistry

– Carbon is a versatile atom.– Carbon forms large, complex, and diverse molecules

necessary for life’s functions.– Organic compounds are carbon-based molecules.

Structuralformula

Ball-and-stickmodel

Space-fillingmodel

• Variations in Carbon skeletons Carbon skeletons vary in length

Carbon skeletons may be unbranched or branched

Carbon and Organic Chemistry

Carbon skeletons may have double bonds,which can vary in location

Carbon skeletons may be arranged in rings

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– Larger hydrocarbons form fuels for engines.– Hydrocarbons of fat molecules fuel our bodies.

Hydrocarbons

• The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton

– These atoms are called functional groups– Some common functional groups include:

Carbon and Organic Chemistry

Hydroxyl group Carbonyl group Amino group Carboxyl group

Found in alcoholsand sugars Found in sugars Found in amino acids

and urea in urine (fromprotein breakdown)

Found in amino acids,fatty acids, and somevitamins

Macromolecules– On a molecular scale, many of life’s molecules are

gigantic, earning the name macromolecules.– Three categories of macromolecules are

• Carbohydrates• Proteins• Nucleic acids

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*most macromolecules are polymerspolymermonomer

The making and breaking of polymers:Dehydration reaction: Hydrolysis:

Macromolecules

• Carbohydrates include

Carbohydrates

– Small sugar molecules in soft drinks• Monosaccharides & Disaccharides

– Long starch molecules in pasta and potatoes• PolysaccharidesPolysaccharides

• Monosaccharides are simple sugars

Monosaccharides

– Glucose, found in sports drinks

– Fructose, found in fruit

H t i• Honey contains both glucose and fructose

Glucose Fructose

Isomers

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• In aqueous solutions, monosaccharides form rings

Monosaccharides

(a) Linear and ringstructures

(b) Abbreviated ringstructure

• A disaccharide is a double sugar

Disaccharides

• Disaccharides are joined by the process of dehydration synthesis

Glucose Glucose

Maltose

• The most common disaccharide is sucrose, common table sugar

– It consists of a glucose linked to a fructose

– Sucrose is extracted from sugar cane and the

Disaccharides

from sugar cane and the roots of sugar beets

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Polysaccharides

(a) Starch

Starch granules inpotato tuber cells

Glucosemonomer

– They are long chains of sugar units– They are polymers of monosaccharides

(a) Starch

(b) Glycogen

GlycogenGranulesIn muscletissue

(c) Cellulose

Cellulose molecules

Cellulose fibril ina plant cell wall

• Most animals cannot derive nutrition from fiber– How do grazing animals survive

on a diet of cellulose?

Polysaccharides

Proteins• Proteins perform most of the tasks the body

needs to function– They are the most elaborate of life’s molecules

MAJOR TYPES OF PROTEINSStructural Proteins Storage Proteins Contractile Proteins Transport Proteins Enzymes

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• All proteins are constructed from a common set of 20 kinds of amino acids

The Monomers: Amino Acids

Aminogroup

Carboxylgroup

Sidegroup

Carboxylgroup

Aminogroup

Sidegroup

Sidegroup

Amino acid Amino acid

• Cells link amino acids together by dehydration synthesis

Proteins as Polymers

– The resulting bond between them is called a peptide

Dehydrationsynthesis

Sidegroup

Sidegroup

Peptide bond

called a peptide bond

• Primary structure

Th ifi

1 510 15

20253035

4045

5055

6065

70

– The arrangement of amino acids makes each protein different

Protein Structure

– The specific sequence of amino acids in a protein

75 80 85

9095

100

105110 115

120125

129

Amino acid

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• A slight change in the primary structure of a protein affects its ability to function– The substitution of one amino acid for another in

hemoglobin causes sickle-cell disease

1 2 3 6 7. . . 146

Protein Structure

(a) Normal red blood cell Normal hemoglobin

1 34 5

6

(b) Sickled red blood cell Sickle-cell hemoglobin

2 314 5

6 7. . . 146

• Proteins have four levels of structure

Hydrogen bond

Pleated sheet

Amino acidPolypeptide(single subunit)

Protein Structure

(a) Primary structure

Hydrogen bond

Alpha helix

(b) Secondary structure

(c) Tertiary structure

Completeprotein,with fourpolypeptidesubunits

(d) Quaternary structure