Chapter 2 Chemical Basis of Life Atoms and molecules Types of molecular bonds Acids/bases Macromolecules

Levels of Organization 1-5

Atoms Atoms - composed of subatomic particles: Proton – carries a single positive charge Neutron – carries no electrical charge Electron – carries a single negative charge Neutron (n0) Proton (p+) Electron (e–) Nucleus Central part of atom Composed of protons and neutrons Electrons move around the nucleus Nucleus

Atoms Electrically neutral, positive protons equals negative electrons Neutron (n0) Electrically neutral, positive protons equals negative electrons Proton (p+) Electron (e–) Nucleus

Atoms Isotopes- vary in the number of neutrons May be stable or unstable Unstable isotopes emit atomic radiation (energy or pieces of themselves)

Clinical Applications Radioactive Isotopes commonly used iodine-131 for thyroid function thallium-201 for heart function gallium-67 and cobalt-60 for cancer others assess kidney functions, measure hormone levels and bone density changes

Molecules Two or more atoms combine Molecular formula tells you what’s in it Ex: H2O, two hydrogen atoms and one oxygen atom

How do the two (or more) atoms bond together? Based on the number of electrons in regions of space called electron shells First shell= 2 Second = 8 Third = 8 Can have many more shells

Electron shells Lower shells are filled first If the outermost shell is full, the atom is stable - - - + + + + - + + - - Hydrogen (H) Helium (He) Lithium (Li)

Types of bonds Ionic bonds: form when atom or molecules lose or gain electrons and form ions. Ions of opposite charges attract. Covalent bonds: electrons are shared, these are strong bonds Hydrogen Bonds: Hydrogen bonds form between molecules or portions of large molecules.

Ionic bonds Formed when electrons are transferred from one atom to another Ions Cation Anion

Covalent bond Formed when atoms share electrons H H H2 - - - + + + + - Hydrogen atom + Hydrogen atom Hydrogen molecule

Covalent bond Electrons can spend more time in one atom than others Creates a polar molecule Slightly negative ends Slightly positive ends

Hydrogen bonds Weak attraction between positive end of one polar molecule and negative end of another polar molecule Ex: water H O Hydrogen bonds

Chemical reactions NaCl ’ Na+ + Cl- Reactant Products Occur when chemical bonds form or break among atoms or molecules NaCl ’ Na+ + Cl- Reactant Products

Acids and Bases Acids- dissociate to release hydrogen ions in water Bases- release ions that can combine with hydrogen ions HCl  H+ + Cl- NaOH  Na+ + OH-

pH scale How many hydrogen ions are in solution

Changes in pH and Buffers Blood pH Normal blood pH is 7.35 – 7.45 Alkalosis occurs when blood pH rises to 7.5 – 7.8 Acidosis occurs when blood pH drops to 7.0 – 7.3 Homeostatic mechanisms help regulate pH Buffers are chemicals which act to resist pH changes Human body has several buffer systems

Macromolecules Large molecules Every living thing on Earth has the following macromolecules: Carbohydrates, Lipids, Proteins, Nucleic Acids

Carbohydrates Major source of energy Simple sugars link to form large sugars Glucose (monosaccharide) Glucose Fructose Sucrose (disaccharide) Cellulose (polysaccharide)

Lipids Fats, hormones, cell membrane Store energy, hormone precursors, cellular membrane component

Proteins Involved in virtually all cell functions Proteins have very complex shapes, which allows them to carry out specific functions Our DNA codes for proteins in the flow of genetic information

Nucleic Acids Genetic information molecule (mainly DNA) - encodes, transmits genetic information Made up of nucleotides = phosphate, sugar, base - bases = adenine (A), thymine (T), guanine (G), cytosine (C)