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

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

LE 2-7b

Na+

Cl-

NaCl is ionic - “crystal lattice” structure

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 present when it died• tells us how old the fossil is

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 in 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”

A thyroid scan showing a “hot spot”

Scan showing increased uptake in thyroid gland

A body scan showing areas of increased radiation

Increased radiation shows abnormal function

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 with Radioisotopes

1. Isotope injected into blood - Concentrates in diseased organ and radiation kills some cells 2. Radioactive “seeds” put directly into tumor- Radiation reaches cancer cells without going through healthy tissue

Radioisotopes kill cancer cells

Uses in Industry• Nuclear energy• Sterilize surgery instruments• Kill bacteria in food