CHAPTER 2

The Chemistry of Living Things

Slide 2.1

“atom” means “can’t be cut” by Greeks 2500 years ago.

Atoms, the smallest functional unit of an element, consist of:

All Matter Consists of Elements Made of Atoms

Atoms are made of

• Protons: positive charge, in nucleus, are heavy, “p+”

• Neutrons: no charge, in nucleus, are heavy, “n0”

• Electrons: negative charge, outside nucleus “electron cloud”, very light (1/1840 of a proton or neutron), “e-”

Charges in an Atom

• The + charge on a proton is equal to the - charge on an electron.

• Atoms are neutral (have no overall charge)

• Therefore, the # of protons = # electrons in an atom.

Slide 2.2

Atomic number– determines the identity of the atom. – It tells us the number of protons in the atom. – It also tells us the number of electrons (b/c an atom is neutral in charge.)

– Ex: atomic number of carbon, C = 6– Question: how many protons? How many electrons? How many neutrons?

Isotopes

• The number of neutrons can vary from atom to atom in an element.

• Atoms of the same element w/different #s of neutrons are called ISOTOPES.

• In order to know how many neutrons in an atom you must be told.

• The mass number tells you how much mass the atom has. – Since p+ and n0 are the heavy parts, – mass # = # of p+’s + n0’s.

QUESTION: If the mass number of a carbon atom is 14,

• How many protons?• How many electrons?• How many neutrons?

• LET’S PRACTICE!– Whiteboard– Marker– Paper towel

Atomic Mass Units

• Atoms are weighed in a.m.u.• 1 a.m.u. is based on the mass of a Carbon-12

atom. – it has 6 p+ and 6 n0, – 1 a.m.u = 1/12 the mass of a carbon-12 atom.

IONS

• Electrons are in constant motion around the nucleus.

• e-s in the highest occupied level are called valence e-s.

• Some atoms lose or gain electrons in their valence level.

IONS

• When they do this, they get a charge.– If you lose an electron, the ion has a ___ charge– If you gain an electron, the ion has a ___ charge

ATOM v. ION

• ATOM – has no charge• ION- has a charge (b/c e-s have been lost OR

gained)

Slide 2.3.

BONDING: Atoms Combine to Form Molecules

• Atoms want a stable arrangement

• For most atoms this is 8 e-s in the valence level (for small guys, it’s 2 in the valence)

• There are 2 ways to get the e-’s you need.ShareGain/lose

Table 2.1Slide 2.4

Three Types of Chemical Bonds

Written NaCl NOT Na-Cl

Ionic Bonds

Elements of Living Organisms

Table 2.2Slide 2.5

Life Depends on Water• Water molecules are polar (they have slight

electrical charges, like little magnets)o Biological solvent-ex: K+ for muscle contractiono Hydrogen bonds make it expand when frozen

(animals in lakes can survive winter)oWater is liquid at body temperatureoWater can absorb and hold heat energyoWater helps regulate body temperature

Slide 2.6

Hydrogen bonds (dotted lines)

a.k.a. van der Waals forces

Oxygen slightly –ve charge

Hydrogen slightly +ve

Properties of Water (b/c of hydrogen bonding)

• Cohesion- attraction between molecules of the same substance. (water-water attraction)

Examples– Drops of water– Surface tension (Fig 2-8 p 41 of text)

Properties of Water (b/c of hydrogen bonding)

• Adhesion-attraction btwn molecules of different substances (water-other substance attraction)

Examples– Capillary action-water drawn up a tube– “Meniscus”= the curve shape water has when in a

tube

Water forms Important Mixtures

• Solutions

• when a substance dissolves in water• Ex: Salt-water.

• NaCl is pulled apart into IONS by the water.

Figure 2.8Slide 2.8

Water Keeps Ions in Solution

Water forms Important Mixtures(cont.)

• Suspensions

• Material does NOT dissolve, but separates into small pieces that remain floating

• Ex: blood w/red blood cells

ACIDS & BASES

• Water can form ions too!

• H2O H+ + OH-

• When by itself, water makes equal amounts of H+ + OH-

ACIDS & BASES (cont.)

• Some things cause water to release many H+ ions. These are acids.

• Some things cause water to release many OH- ions. These are bases.

• pH is a measure of the H+ concentration in a solution.

Figure 2.10Slide 2.10

The pH Scale

BUFFERS

(DON’T WRITE THIS) Remember homeostasis?

WRITE THIS:• All living things need to maintain a stable pH.– Humans need a pH between 6.5 & 7.5– Otherwise, chemical reactions get messed up.

• They do this through buffers: weak acids or bases that prevent sharp, sudden changes in pH– Ex: ______ for an upset stomach. It absorbs extra H+ ions.

(Section 3): Carbon “Organic” Compounds

• Why is carbon so special?• Carbon has 4 valence electrons, • Allows it to bond to many other things at

once.

• Pix of organic compounds important to living things

Carbon, the building block of living things:

• Is 18% of human body by weight

• Forms four covalent bonds

• Can form single or double bonds

• Can build micro- or macromolecules (big chains)

Slide 2.11

Section 3: Carbon (Organic) Compounds of Living Organisms

Figure 2.12Slide 2.12

Carbon Can Bond in Many Ways

Figure 2.14Slide 2.15

1: Carbohydrates MADE OF: C, H, O

FUNCTION: energy & structure

1. Sugars: short chains of

• Monosaccharides- 1 sugar ring

Ex: glucose, galactose

• Disaccharides-2 attached sugar rings

Ex: sucrose, fructose, lactose

2. Polysaccharides: thousands of monosaccharides joined in chains and branches

• Starch: made in plants; stores energy

• Glycogen: made in animals; stores energy

• Cellulose: undigestible polysaccharide made in plants for structural support

Slide 2.16

Types of Carbohydrates

Lipids: Insoluble in Water

TYPES OF LIPIDS• Triglycerides: energy storage molecules– Fatty acids: saturated and unsaturated

• Phospholipids: cell membranes

• Steroids: carbon-based ring structures– Cholesterol: used in making estrogen and

testosteroneSlide 2.17

2: LipidsMade of: C,H,(O)

Function: energy storage, waterproof coverings

Unsaturated triglyceride

Steroids (type of lipid)

• Made of: C,H, O, N

• Function: building materials, enzymes

• Structure• Made of monomers called amino acids

• The instructions for building proteins are in DNA

Slide 2.18

Proteins: Complex Structures Contructed of Amino Acids

Hemoglobin (4 protein strands held together)

Enzyme FunctionEnzymes:– are proteins– function as catalysts (something that speeds up

chem rxns)– facilitate chemical reactions

• Lower the activation energy (energy required to start a rxn.)

The function of an enzyme is dependent on:– temperature – pH – ion concentration– presence of inhibitors

Slide 2.19

Enzyme Action

Structure and Function of Nucleic Acids• Functions

– Store genetic information– Provide information used in making proteins

• Structure– Nucleotides consist of a phosphate group, a sugar,

and a nitrogenous base– DNA structure is a double helix: two associated

strands of nucleic acids– RNA is a single-stranded molecule

Slide 2.20

Structure of DNA and RNA• DNA: double-stranded– Sugar: deoxyribose– Nitrogenous bases: adenine, thymine, cytosine,

guanine– Pairing: adenine-thymine and cytosine-guanine

• RNA: single-stranded– Sugar: ribose– Nitrogenous bases: adenine, uracil, cytosine,

guanine– Pairing: adenine-uracil, cytosine-guanine

Slide 2.21.

DNA nucleotides

RNA structure

Figure 2.25Slide 2.22Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Structure and Function of Adenosine Triphosphate (ATP)