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UNIT 1: INTRODUCING BIOLOGY Chapter 2: Chemistry of life

UNIT 1: INTRODUCING BIOLOGY

Chapter 2: Chemistry of Life

I. Atoms, Ions, and Molecules (2.1)

A. Living things consist of

atoms of different elements

1. An atom is the smallest basic unit of matter

2. An element is one type of atom

3. An atom has a nucleus and electrons

a. The nucleus has protons and neutrons

b. Electrons are in energy levels outside the

nucleus

4. A compound is made of atoms of different

elements bonded together

a. Water (H20)

b. Carbon dioxide (CO2)

c. Many other carbon-based

compounds in living things.

B. Ions form when atoms gain or lose electrons

1. An ion is an atom that has gained or lost

one or more electrons

a. Positive ions -lost electron(s)

b. Negative ions -gain electron(s)

2. Ionic bonds form between oppositely

charged ions

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1. A covalent bond forms when atoms share a pair

of electrons

a. Multiple covalent bonds

b. Diatomic molecules

2. A molecule is two or more atoms held together

by covalent bonds

II. Properties of Water

A. Life depends on hydrogen bonds in water

1. Water is a polar molecule

a. Polar molecules have slightly

charged regions

b. Nonpolar molecules do not have charged

regions

c. Hydrogen bonds form between slightly positive

hydrogen atoms and slightly negative atoms.

2. Hydrogen bonds are responsible for three

important properties of water.

a. High specific heat

b. Cohesion- attraction between

molecules of the same substance

(because of hydrogen bonds, water is

very cohesive)

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c. Adhesion- attraction between different

substances. Adhesion between water and other

charged or polar substances very important force.

(responsible for capillary action)

B. Many compounds dissolve in water

1. A solution is formed when

one substance dissolves in

another

a. A solution is a

homogeneous mixture

b. Solvents dissolve other substances

c. Solutes dissolve in a solvent

2. “Like dissolves like”

a. Polar solvents dissolve polar solutes

b. Nonpolar solvents dissolve nonpolar

solutes

c. Polar substances and nonpolar

substances generally remain separate

C. Some compounds form acids and bases

1. An acid releases a hydrogen ion when it

dissolves in water

a. High H+ concentration

b. pH less than 7

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2. A base removes hydrogen ions from a solution

a. low H+ concentration

b. pH greater than 7

3. A neutral solution has a pH of 7

III. Carbon-Based Molecules (2.3)

A. Carbon atoms have unique bonding

properties

1. Carbon forms covalent bonds with up

to four other atoms, including other

carbon atoms.

2. Carbon-based molecules have three general

types of structures

a. Straight chain

b. Branched chain

c. Ring

B. Many carbon based molecules are made of

many small subunits bonded together

1. Monomers are the individual

subunits

2. Polymers are made of many

monomers

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B. Four main types of carbon-based molecules are

found in living things.

1. Carbohydrates are made of carbon,

hydrogen, and oxygen

a. Carbohydrates include

sugars and starches

b.Monosaccharides are

simple (single) sugars

c. Disaccharides are

double sugars

c. Polysaccharides include starches, cellulose,

and glycogen

d. Carbohydrates can be

broken down to provide

energy for cells

e. Some carbohydrates

are part of cell

structure

Fig. 5-6

(b) Glycogen: an animal polysaccharide

Starch

Glycogen Amylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria Glycogen granules

0.5 µm

1 µm

Fig. 5-8

Glucose monomer

Cellulose molecules

Microfibril

Cellulose microfibrils in a plant cell wall

0.5 µm

10 µm

Cell walls Fig. 5-10

The structure of the chitin monomer.

(a)

(b)

(c)

Chitin forms the exoskeleton of arthropods.

Chitin is used to make a strong and flexible surgical thread.

2. Lipids are nonpolar molecules that include fats,

oils, and cholesterol

a. Many contain carbon chains called fatty

acids

b. Fats and oils contain fatty acids bonded to

glycerol.

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Fig. 5-11

Fatty acid (palmitic acid)

Glycerol

(a) Dehydration reaction in the synthesis of a fat

Ester linkage

(b) Fat molecule (triacylglycerol)

Fig. 5-11b

(b)

Fat molecule (triacylglycerol)

Ester linkage c. Lipids have several different functions

1). Broken down as a source of energy

2). Make up cell membranes

3). Used to make hormones

d. Fats and oils have different types of fatty acids

1). Saturated fatty acids

2). Unsaturated fatty acids

Fig. 5-12a

(a)

Saturated fat

Structural formula of a saturated fat molecule

Stearic acid, a saturated fatty acid

Fig. 5-12b

(b)

Unsaturated fat

Structural formula

of an unsaturated

fat molecule

Oleic acid, an unsaturated fatty acid

cis double

bond causes

bending

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Fig. 5-12

Structural formula of a

saturated fat

molecule

Stearic acid, a

saturated fatty

acid

(a) Saturated fat

Structural formula of an unsaturated fat molecule

Oleic acid, an

unsaturated

fatty acid

(b) Unsaturated fat

cis double bond causes bending

e. Phospholipids make up all cell membranes

1). Polar phosphate “head”

2). Nonpolar fatty acid

“tails”

Fig. 5-13

(b)

Space-filling model (a)

(c)

Structural formula Phospholipid symbol

Fatty acids

Hydrophilic head

Hydrophobic tails

Choline

Phosphate

Glycerol

Hy

dro

ph

ob

ic t

ails

H

yd

rop

hilic

head

Fig. 5-14

Hydrophilic head

Hydrophobic tail

WATER

WATER

3. Proteins are polymers of amino acid monomers

a. Twenty different

amino acids are used

to build proteins in

organisms

b. Amino acids differ in side groups, or

R groups

c. Amino acids are linked by peptide

bonds

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Fig. 5-21a

Amino acid

subunits

+H3N

Amino end

25

20

15

10

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1

Primary Structure

Fig. 5-21b

Amino acid

subunits

+H3N

Amino end

Carboxyl end 125

120

115

110

105

100

95

90 85

80

75

20

25

15

10

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1 Fig. 5-19a

A ribbon model of lysozyme (a)

Groove

Fig. 5-21f

Polypeptide backbone

Hydrophobic interactions and van der Waals interactions

Disulfide bridge

Ionic bond

Hydrogen bond

d. Proteins differ in the number and order of amino

acids

1). Amino acids interact to give a protein its

shape

2). Incorrect amino acids change a proteins

structure and function

Protein Types

• Enzymes

• Contractile

• Defensive

• Hormonal

• Receptor

• Sensory

• Storage

• Structural

• Transport

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4. Nucleic acids are polymers of monomers called

nucleotides

a. Nucleotides are made of

sugar, phosphate group, and a

nitrogen base.

Nucleotide: Monomer of Nucleic Acids b. DNA stores genetic information

c. RNA builds proteins

Fig. 5-UN2 Fig. 5-UN2a Fig. 5-UN2b

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IV. Chemical Reactions (2.4)

A. Bonds break and form during chemical

reactions.

1. Reactants are changed during a

chemical reaction

2. Products are made by a chemical

reactions.

C6H12O6 + O2 CO2 + H2O reactants products

Cellular Respiration Photosynthesis

CO2 + H2O C6H12O6 + O2

B. Bond energy is the amount of energy that

breaks a bond

1. Energy is added To break bonds

2. Energy is released when bonds form

C. A reaction is at equilibrium when reactants and

products form at the same rate.

CO2 + H2O H2CO3

D. Chemical reactions release or absorb energy

1. Activation energy is the amount of energy

that needs to be absorbed to start a

chemical reaction.

2. Exothermic reactions release more energy than

they absorb.

a. Reactants have higher bond energy than

products

b. Excess energy is released by the reaction

3. Endothermic reactions absorb more energy

than they release.

a. Reactants have lower bond energy than

products

a. Energy is absorbed by the reaction to

make up the difference.

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V. Enzymes (2.5)

A. A catalysts lowers activation energy

1. Catalysts are substances that speed

up chemical reactions

a. Decrease activation energy

b. Increase reaction rate

B. Enzymes allow chemical reactions to occur

under tightly controlled conditions.

1. Enzymes are catalysts

in living things

a. Enzymes are

needed for almost all

processes

b. Most enzymes are

proteins

C. Disruptions in homeostasis can prevent

enzymes from functioning.

1. Enzymes function best in a small range of

conditions

2. Changes in temperature and pH can

break hydrogen bonds.

3. An enzyme’s function depends on its

structure

D. An enzyme’s structure allows only certain

reactants to bind to the enzyme

1. Substrates

2. Active Site

E. The lock-and-key model helps illustrate how

enzymes function

1. Substrates brought together

2. bonds in substrates weakened