bio 156 chapter 2 powerpoint
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BIO 156
Chapter 2
Atoms and Subatomic Particles
•Atoms are the fundamental unit of all matter.
•Atoms contain electrons, protons, and neutrons.
Elements are pure substance that contains only one type of atom.
•92 naturally occurring elements are known
•only about 20 are found in organisms
•Four elements in this group: carbon, oxygen, hydrogen, and nitrogen (remember: COHN) comprise 98% of the atoms of all living things
Isotopes are alternative forms of atoms, differing only in the number of neutrons additional neutrons makes some atoms a bit unstable.
•To achieve a more stable state, many isotopes release tiny energetic particles from their nuclei.
•These emissions are known as radiation
•Radioactive isotopes are called radionuclides
The Making of a Molecule
Atoms combine to form molecules.
•Compound: a substance made up of two or more atoms
•Molecule: the smallest particle of a compound that still retains the properties of that compound.
Atoms bond to form more stable configurations.
There are two types of bonds that form between atoms:
1. Ionic 2. Covalent
Electrons are responsible for creating the bonds that hold atoms together
Ionic bonds are electrostatic attractions between two oppositely charged particles.
Ionic bonds form between two atoms when one loses an electron and the other gains an electron
This reaction creates two charged particles, known as ions
Covalent bonds are formed by the sharing of electrons between atoms
Covalent Bonds Simplified
Covalent Bonds Simplified
Polar covalent bonds occur any time there is an unequal sharing of electrons by two atoms
A polar covalent bond’s atoms bear a slight charge—either positive or negative
Chemical compounds fall into two broad groups: organic and inorganic.
Organic compounds contain molecules that are made primarily of carbon atoms.
Inorganic compounds are compounds that are not organic
Water, Acids, Bases, and Buffers
Water is vital to life for many reasons.
•Water is a major component of all cells and organisms
•Water serves as a solvent, a transport medium, and a lubricant.
•Water participates in many chemical reactions.
•Water helps regulate body temperature.
Acids are substances that add hydrogen ions to solution; bases remove them.
•Acidity is measured on the pH scale
•A solution with a pH less than 7 is acidic.
•A solution with a pH greater than 7 is basic.
•On the pH scale, a change in one pH unit represents a tenfold change in acidity
•Most biochemical reactions occur at pH values between 6 and 8.
Homeostasis is ensured in part by buffers, molecules that help maintain pH within a narrow range.
•Buffers help maintain a constant pH by removing hydrogen ions from solution when levels increase.
•Buffers give back the hydrogen ions when levels fall.
Overview of Other Biologically Important Molecules
1. Carbohydrates
2. Lipids
3. Amino acids and proteins
4. Nucleic acids (DNA)
End of Chapter 2
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