CP Biology Chapter 2 The 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 SodiumChlorine 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 CO 2 – 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 function CAT 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