CP Biology Chapter 2 The Chemistry of Life
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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
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