CP Biology Chapter 2The Chemistry of Life

Chemicals make up ALL matter – living and nonliving.• All life processes are chemical reactions.• Chemical signals between cells regulate

metabolism– enzymes, hormones

• Chemical signals in the environment– Attract a mate; attract pollinators– Scare away predators– Find food

Why is chemistry important in the study of biology?

ELEMENTS, ATOMS, AND MOLECULES

There are 92 naturally occurring elements–Only 4 make up most of the human body–CARBON–HYDROGEN (C H O N)- OXYGEN- NITROGEN

Elements of Living Cells

Major elements

Minor elements

Forming Compounds

Two or more elements combined in a fixed ratioIONIC BONDING

LE 2-3

Sodium Chlorine Sodium Chloride

Na

Metal, soft

Highly reactive

Cl

Gas

toxic

Salt

Crystal

Common, edible

Two or more elements in a FIXED RATIO

COMPOUNDS

Elements can combine to form compounds

Ions = charged particles

LE 2-7b

Na+

Cl-

NaCl is ionic - “crystal lattice” structure

Ionic Compound – “crystal lattice”

Attraction of opposite charges- ordered, fixed structure

Ionic Compouonds transfer electrons

Both atoms now have filled valence, but no longer

electrically neutral

Ionic – attraction of opposite charges• Ionic bonds dissociate in water

Covalent Bonding• Atoms SHARE valence electrons

– One bond = one shared pair (one from each atom)

Covalent bonds form “molecules

Double bond = two shared pairs (two from each atom)

Intramolecular v Intermolecular forces

CHEMICAL REACTIONS

Reactants Products•Chemical bonds break in reactants•atoms rearrange •New chemical bonds form•The number of atoms stays constant on

both sides of the equation Na+ + Cl- NaCl

2 H2 + O2 2 H2O

What is an isotope?Isotopes are atoms with the same atomic number but different masses

• different number of neutrons

• Behave the same way chemically!!

• Most elements have at least one isotope

Isotopes of Carbon

Isotopes of the same element have the same number of PROTONS and the same number of ELECTRONS.

- have the same chemical behaviors

Radioactive Isotopes

Have unstable nuclei

• Emit atomic particles as the “decay”

• Become a stable atom of a different element

Radioactive isotopes

• Also emit radiation• at a steady rate, called “half-life”

– Half-life: time for ½ of a sample to decay– Ex. Half-life of C-14 is 5700 years

• Can use radiation for many purposes

DATE FOSSILS

Carbon-14 and other isotopes • measure amount of C-14 present in a

fossil• compare to amount of present when it

died• tells us how old the fossil is

Carbon Dating FossilsC14 in

atmosphereC14 in carbon

dioxide

CO2 used by plants in

photosynthesis

Some C14 absorbed in

ocean

Some in animals after eating plants

When animals die, no more C14

taken in

Use as “tags” or “tracers”

• Same chemical properties as stable isotopes• Used the same in life processes• Can show how atoms and molecules are used in

living things– Carbon-14

• showed how plants make food from CO2

– Radioactive sulfur and phosphorus• showed how viruses enter cells

PET Scan - MEDICAL DIAGNOSIS

PET scan = Positron Emission Tomography• Radioisotope into blood collects in tissues• Amount of radiation shows organ function

- more active cells use more food and energy (ex. cancer cells)

- more active cells emit more radiation- ”hot spot”

Brain scan using radioisotope

A body scan showing areas of increased radiation (increased cell activity)

Increased radiation shows abnormal function

Thyroid scans – tumors?

A thyroid scan showing a “hot spot”

Scan showing increased uptake in thyroid gland

PET scans show functionCAT scans show structure

Radiation Therapy – treats cancer External therapy• beam of radiation aimed at tumor• from radioisotope, or from therapy X-ray

machine

Internal Therapy - Radioisotopes kill cancer cells

Tiny “seeds” put into tumor Injected into blood –

goes to specific organ

Uses in Industry• Nuclear energy• Sterilize surgery instruments• Kill bacteria in food• Long-life batteries