Chemistry of Life

Chapter 2

PROPERTIES OF WATER 2.2

Key Concept

• Water’s unique properties allow life to exist on Earth.

Water

• Polar molecule – has slightly charged

regions

O

H H

_

+ +

Hydrogen Bonds

• Form between slightly positive hydrogen atoms and slightly negative oxygen atoms

Properties of Water

• Due to hydrogen bonds

Cohesive Behavior

– Cohesion • attraction of

molecules of a similar substance

– Adhesion • attraction of

molecules of different substances

Ability to Moderate Temperature

• Water resists changes in temperature

Expansion Upon Freezing

• Most (all?) substances are more dense when they are solid, but not water…

• Ice floats!!! – H-bonds form a crystal

Versatility as a Solvent

• Solvent – The dissolving agent

• Solute – The substance that is

dissolved

• Solution – A liquid that is a

homogenous mixture of substances

Water as a Solvent

• Polarity makes H2O a good solvent – Polar H2O molecules surround + and – ions

CARBON-BASED MOLECULES 2.3

Key Concept

• Carbon-based molecules are the foundation of life.

Carbon Atoms

• Can form bonds with up to 4 other atoms

Carbon-Based Molecules

• Have 3 general types of structures: – Straight chain

– Branched chain

– Ring

Subunits

• Many carbon-based molecules are made of many small subunits bonded together – subunit: monomer

– many monomers = a polymer

Macromolecules

• 4 main types found in living things: – carbohydrates

– lipids

– proteins

– nucleic acids

Carbohydrates

• Elements: – carbon

– hydrogen

– oxygen

– 1:2:1 ratio

• Building block: – monosaccharide

Carbohydrates

• Examples: – sugars

• monosaccharides

– starches, cellulose, glycogen • polysaccharides

Glucose

Carbohydrates

• Function: – energy reserve

– structure

Lipids

• Elements: – carbon (lots!)

– hydrogen (lots!)

Lipids

• Examples: – fats

– oils

– cholesterol

Lipids

• Function: – energy source

– make up cell membranes

– used to make hormones

Saturated vs. Unsaturated

• Saturated fatty acids: – all carbons are full,

lots of H-atoms – solid at room temp

• Unsaturated fatty

acids: – some double bonds

present – liquid at room temp

Proteins

• Elements: – carbon

– hydrogen

– nitrogen

– oxygen

– other

• Building block: – amino acid (20 different ones)

Proteins

• Functions: – antibodies

– muscle contraction

– enzymes

– hormones

– cell structure

Nucleic Acids

• Elements: – C, H, O, N, P

• Building block: – nucleotides

Nucleic Acids

• Examples: – DNA

• double stranded

• stores genetic info

– RNA • single stranded

• builds proteins

CHEMICAL REACTIONS 2.4

Key Concept

• Life depends on chemical reactions.

Chemical Reactions

• Bonds break and form during rxns

Bond Energy

• Energy is needed to start a rxn – activation energy

Exothermic Reactions

• Release more energy than they absorb

• Heat is released

Endothermic Reactions

• Absorb more energy than they release

• Heat is absorbed

ENZYMES 2.5

Key Concept

• Enzymes are catalysts for chemical reactions in living things.

Catalysts

• Enzymes are catalysts

• They lower the activation energy of a rxn – rxns are sped up

– increase rxn rate

Enzymes and Reactions

• Enzymes allow chemical rxns to occur

• Needed for almost all processes

• Most enzymes are proteins

Altering Enzymes

• Changing an enzyme changes its function

• Factors that can change an enzyme: – pH

– temperature

– concentration

STRUCTURE = FUNCTION