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Chapter 2

BIO 110 Chapter Notes - Chapter 2: Deoxyribose, Amphiphile, Glycosidic Bond

Course Code
BIO 110

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Chapter 2 - The Chemistry and Energy of Life
Concept 2.1 - Atomic Structure is the Basis for Life’s Chemistry
Living and nonliving matter is composed of atoms
Nucleus - dense, positively charged part of an atom
Electrons - negatively charged particles w/ negligible mass
Protons - positively charged particles w/ mass of 1 dalton (Da)
Neutrons - no electrical charge w/ mass of 1 dalton (Da)
Opposite charge attract / like charges repel
Element - a pure substance that contains only one kind of atom
94 natural elements
Life is mostly made up of C, H, N, O, P, S
Physical and chemical properties depend on number of protons, neutrons, and electrons
Atomic number - the number of protons in an atom
Mass number - the total number of protons and neutrons in an atom
Isotopes - atoms with the same number of protons but differ in number of neutrons
Electrons determine how an atom will react
Bohr model - provides concept that an atom is largely empty space with a central
nucleus surrounded by electrons in orbits
Useful for describing behavior of atoms
The behaviors of electrons determine whether a chemical bond will form and
what shape the bond will have
Electron shells - orbits at various distances from the nucleus
The farther away an electron shell is from the nucleus, the more energy it has
(harder to escape positive charge of protons)
First shell - up to 2 electrons
Second shell - up to 8 electrons
Third shell 0 up to 18 electrons
Fourth and subsequent shells - up to 32 electrons
Electrons fill shells closest to nucleus before occupying shells farther away
Octet rule - states that an atom will lose, gain, or share electrons in order to
achieve a stable configuration of eight electrons in its outermost shell
Molecules - a chemical substance made up of two or more atoms
Concept 2.2 - Atoms Interact and Form Molecules
Chemical bond - an attractive force that links two atoms together in a molecule
Covalent bonds consist of shared pairs of electrons
Covalent bond - when two atoms share one or more pairs of electrons
Fills up outer shell for stable configuration
Four important aspects of covalent bonds:
Orientation - length and angle of bonds are the same; gives it its shape and
contributes to biological function

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Strength and Stability - very strong; takes a lot of energy to break; stable at
temperature that life exists
Multiple Covalent Bonds - single bond shares one pair of electrons; double bond
shares two pairs of electrons; triple bond shares three pairs of electrons
Unequal Sharing of Electrons - atoms don’t always share equally
Electronegativity - an atom’s affinity for electrons
More protons → more force to attract electrons
The closer the electrons to nucleus → greater electronegative pull
Electronegativity of 0.5 or less - nonpolar covalent
Polar covalent - when electrons are shared unequally
Hydrogen bonds may form within or between molecules with polar covalent bonds
Bonds between H and N, O, or F
A hydrogen bond is weaker than a covalent bond
Many hydrogen bonds together can have considerable strength
Important for determining and maintaining 3-D shape of DNA and proteins
Hydrogen bonding contributes to important properties of water
Hydrogen bond - the attraction between a positively charged hydrogen atom and
an electronegative atom of another molecule
Water is a universal solvent (liquid in which other molecules dissolve)
A water molecule can form an average of 3.4 hydrogen bonds
Important properties: heat capacity, cohesion, adhesion, surface tension
Water has a high heat capacity
Heat capacity - the amount of heat it takes to raise the temperature by one
Important for the large amounts of water in organisms
Water has a high heat of vaporization
Heat of vaporization - the heat required to change water from a liquid to a gas
Needs a lot of heat to break hydrogen bonds → heat must be absorbed by
Causes a cooling effect
Cohesion, Adhesion, and Surface Tension
Cohesion - the capacity of water molecules to resist coming apart when placed
under tension (sticks to itself)
Adhesion - the capacity of water molecules to resist coming apart from solid
surfaces when placed under tension (sticks to other surfaces)
Helps water move from roots to leaves of plants/trees
Surface tension - when water molecules at the surface are hydrogen-bonded to
the molecules below them → forms a film
Polar and nonpolar substances: Each interacts best with its own kind
Any polar molecules can interact with other polar molecule through hydrogen
Hydrophilic - water-loving, polar molecules
Hydrophobic - water-hating, nonpolar molecules (aggregate together in water)
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