UNIT 1 BIOCHEMISTRY Part 1
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Transcript of UNIT 1 BIOCHEMISTRY Part 1
AP Biology 2007-2008
UNIT 1BIOCHEMISTRYPart 1
Hillis Textbook Chapter 2
Chemistry of Life
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Living and nonliving matter is composed of atoms.
Like charges repel; different charges attract.
Most atoms are neutral because the number of electrons equals the number of protons.
The number of protons identifies an element.•Number of protons = atomic number
•Atomic Mass or Weight= total number of protons and neutrons
Octet rule—atoms with at least two electron shells form stable molecules so they have eight electrons in their outermost
shells. Valence electrons are the outermost electrons.
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Element—pure substance that contains only one kind of atom
Living things are mostly composed of 6 elements:
Carbon (C) Hydrogen (H) Nitrogen (N)
Oxygen (O) Phosphorus (P) Sulfur (S)
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Behavior of electrons determines whether a chemical bond will form and what shape the bond will have.
Atoms with unfilled outer shells tend to undergo chemical
reactions to fill their outer shells.
They can attain stability by sharing electrons with other atoms or by losing
or gaining electrons.
The atoms are then bonded together into molecules.
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A chemical bond is an attractive force that links atoms together to form molecules. There are several kinds of chemical bonds.
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Ions are charged particle that form when an atom gains or loses one or more electrons.
Cations—positively charged ions
Anions—negatively charged ions
Ionic bonds result from the electrical attraction between ions with opposite charges.
The resulting molecules are called salts.
IONIC BONDS
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Ionic attractions are weak, so salts dissolve easily in water.
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Covalent bonds form when two atoms share pairs of electrons.
The atoms attain stability by having full outer shells.
Each atom contributes one member of the electron pair.
Carbon atoms have four electrons in the outer shell—they can form covalent bonds with four other atoms.
COVALENT BONDS
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Properties of molecules are influenced by characteristics of the covalent bonds:
Orientation—length, angle, and direction of bonds between any two elements are always the same.
Example: Methane always forms a tetrahedron.
Strength and stability—covalent bonds are very strong; it takes a lot of energy to break them.
Multiple bonds
Single—sharing 1 pair of electrons
Double—sharing 2 pairs of electrons
Triple—sharing 3 pairs of electrons
C C
N N
C H
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Attraction between the δ– end of one molecule and the δ+ hydrogen end of another molecule forms hydrogen bonds.
They form between water molecules. They are important in the structure of DNA and
proteins.
HYDROGEN BONDS
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Water molecules form multiple hydrogen bonds with each other—this contributes to high heat capacity.
A lot of heat is required to raise the temperature
of water—the heat energy breaks the hydrogen bonds.
In organisms, presence of water shields them
from fluctuations in environmental temperature.
WATER!
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Water has a high heat of vaporization—a lot of heat is required to change water from liquid to gaseous state. Thus, evaporation has a cooling effect on the environment.
• Sweating cools the body—as sweat evaporates from the skin, it transforms some of the adjacent body heat.
Hydrogen bonds also give water cohesive strength, or cohesion—water molecules resist coming apart when placed under tension.
• This permits narrow columns of water to move from roots to leaves of plants.
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Any polar molecule can interact with any other polar molecule through hydrogen bonds. WATER IS POLAR!
Hydrophilic (“water-loving”)—in aqueous solutions, polar molecules become separated and surrounded by water molecules
Nonpolar molecules are called hydrophobic (“water-hating”); the interactions between them are hydrophobic interactions.
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Why study Carbon? All of life is built on carbon Cells
~72% H2O ;) ~25% carbon compounds
carbohydrates lipids proteins nucleic acids
~3% salts Na, Cl, K…
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Chemistry of Life Organic chemistry is the study of
carbon compounds C atoms are versatile building blocks
bonding properties 4 stable covalent bonds
HHC
H
H
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Hydrocarbons Combinations of C & H
non-polar not soluble in H2O
hydrophobicstablevery little attraction
between molecules a gas at room temperature
methane(simplest HC)
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Hydrocarbons can grow
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Isomers Molecules with same molecular formula
but different structures (shapes) different chemical properties different biological functions
6 carbons
6 carbons
6 carbons
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Form affects function Structural differences create important
functional significance amino acid alanine
L-alanine used in proteins but not D-alanine
medicines L-version active but not D-version
sometimes withtragic results…
stereoisomersstereoisomers
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Form affects function Thalidomide
prescribed to pregnant women in 50s & 60s reduced morning sickness, but… stereoisomer caused severe birth defects
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Diversity of molecules
Substitute other atoms or groups around the carbon ethane vs. ethanol
H replaced by an hydroxyl group (–OH)
nonpolar vs. polar
gas vs. liquid
biological effects!
ethane (C2H6) ethanol (C2H5OH)
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Functional groups Parts of organic molecules that are
involved in chemical reactions give organic molecules distinctive
properties hydroxyl amino
carbonyl sulfhydryl
carboxyl phosphate
Affect reactivity makes hydrocarbons hydrophilic increase solubility in water
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Viva la difference! Basic structure of male & female
hormones is identical identical carbon skeleton attachment of different functional groups interact with different targets in the body
different effects
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Hydroxyl –OH
organic compounds with OH = alcohols names typically end in -ol
ethanol
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Carbonyl C=O
O double bonded to C if C=O at end molecule = aldehyde
if C=O in middle of molecule = ketone
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Carboxyl –COOH
C double bonded to O & single bonded to OH group compounds with COOH = acids
fatty acidsamino acids
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Amino -NH2
N attached to 2 H compounds with NH2 = amines
amino acids
NH2 acts as base
ammonia picks up H+ from solution
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Sulfhydryl –SH
S bonded to H compounds with SH = thiols SH groups stabilize the structure of proteins
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Phosphate –PO4
P bound to 4 O
connects to C through an O
lots of O = lots of negative chargehighly reactive
transfers energy between organic molecules ATP, GTP, etc.