ap biology exam review (2002-2003) molecules and cells – 25%
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AP Biology Exam Review (2002-2003)
Molecules and Cells – 25%
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Chemistry of Life – 7% Water Organic molecules in organisms Free energy changes Enzymes
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Polar water molecule Polar
covalent bonds polarity
Polarity hydrogen bonding and various water properties
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Water properties Ex: How do the unique chemical and
physical properties of water make life on earth possible?
Cohesion: transpiration, blood Adhesion: transpiration Ideal solvent: xylem and phloem sap,
oceans, blood, hemolymph Density: maintaining marine life High specific heat: maintaining stability
(homeostasis)
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pH H2O + H2O H3O- + OH-
Water dissociation = H2O H+ + OH-
1/554 million water molecules dissociates in pure water.
pH = 7 when [H+] and [OH-] equal to 10-7
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Acids and Bases Acids: pH < 7Ex: stomach acid, increasing H+ gradient Bases: pH > 7 Neutral: pH=7Ex: blood, urine, body fluids
Buffers required to maintain neutrality. (homeostasis)
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Buffers H2CO3 + OH- HCO3
- + H2O HCO3
- + H+ H2CO3
Ex: Human red blood cellsCarbonic acid (H2CO3) and Bicarbonate
(HCO3-) buffers to maintain blood cell pH.
How can blood cell pH be raised or lowered?
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pH Make sure you
know the general pH of some biologically important aqueous solutions: blood, gastric guices, urine, seawater, etc.
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Dehydrationsynthesis Aka “condensation
reaction” To break up
polymers = hydrolysis
Hydrolytic enzymes (fungus, insect saliva) capable of hydrolyzing polymers.
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Organic molecules Macromolecules: carbohydrates, proteins,
lipids, nucleic acids, vitamins
Carbohydrates: energy storage (starch in plants, glycogen in animals); structural support (cellulose, chitin); energy (reactant in cellular respiration)
Ex: glucose, fructose, lactose (-ose) Human insulin and glucagon lowers and
raises blood glucose levels. (homeostasis)
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Storage vs. Structure
Starch, Glycogen Cellulose
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Organic molecules Proteins: structural support (microtubules,
microfilaments, intermediate filaments that make up muscle fibers), enzymes, regulatory proteins
Four folding levels: primary (peptide bonds between amino acids); secondary (hydrogen bonds); tertiary (R-group interactions); quaternary (multiple peptide interactions)
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Primary
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Alpha helices = hair fibers (keratin)
Beta-pleated sheets = silk
Secondary
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Tertiary Important
in the formation of active sites of enzymes
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Quaternary
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Protein denaturation Chaperonin, heat shock proteins
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Membrane proteins
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Organic molecules Lipids: membrane structure, long term
energy storage, brain insulation
Smooth endoplasmic reticulum product; stored in adipose tissue (made of fat cells)
Steroid rings: sex hormones, cholesterol (animals only)
Phospholipid: membrane
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Organic molecules Nucleic acids:
ATP, GTP, nucleotides
DNA remains within nucleus of eukaryotes.
Circular DNA in prokaryotes with plasmids
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Free energy changes Governed by two laws of
thermodynamics
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First law of thermodynamics Conservation of energy Ex: coupled reactions, nutrient
cycling
ATP ADP + P
GTPGDP + P
Coupled reactions happen in the electron transport chain.
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Second law of thermodynamics
Entropy Ex: 10% energy
loss in environment, proton gradient, diffusion, higher to lower concentration (countercurrent exchange), depolarization
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Exergonic vs. Endergonic reactions
What are some of these processes that occur in biological systems?
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Effects of enzymes
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Lock and key vs. induced fit model
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General enzyme characteristics Effective in small amounts Unchanged in a reaction (only substrate
changes) Doesn’t affect equilibrium in chemical
reaction (speeds up process in either direction)
Specific to act on substrate molecules Cofactors (inorganic metals) or coenzymes
(vitamins NAD and FAD) assist Inhibitors able to affect activity
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Competitiveinhibition
Example: oxygen binding to rubisco instead of carbon dioxide photorespiration
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Allosteric site Commonly called “regulatory site” Example: lac and trp operons
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Regulatory pathways Negative
feedback enables feedback mechanisms
Ex: body temperature regulation
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Trp operon in bacteria only
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Lac operon in bacteria only
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Enzymes Enzymes
denature with changes in temperature and pH.
Example showing Importance of homeostasis
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Protein receptors
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cAMP as secondary messenger Proteins and
receptors involved in signal amplification
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Cell to cell communication
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Signal transduction pathway
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Signal molecule