AP Biology Exam Review (2002-2003) Molecules and Cells – 25%

AP Biology Exam Review (2002-2003)

Molecules and Cells – 25%

Chemistry of Life – 7% Water Organic molecules in organisms Free energy changes Enzymes

Polar water molecule Polar

covalent bonds polarity

Polarity hydrogen bonding and various water properties

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)

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

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)

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?

pH Make sure you

know the general pH of some biologically important aqueous solutions: blood, gastric guices, urine, seawater, etc.

Dehydrationsynthesis Aka “condensation

reaction” To break up

polymers = hydrolysis

Hydrolytic enzymes (fungus, insect saliva) capable of hydrolyzing polymers.

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)

Storage vs. Structure

Starch, Glycogen Cellulose

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)

Primary

Alpha helices = hair fibers (keratin)

Beta-pleated sheets = silk

Secondary

Tertiary Important

in the formation of active sites of enzymes

Quaternary

Protein denaturation Chaperonin, heat shock proteins

Membrane proteins

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

Organic molecules Nucleic acids:

ATP, GTP, nucleotides

DNA remains within nucleus of eukaryotes.

Circular DNA in prokaryotes with plasmids

Free energy changes Governed by two laws of

thermodynamics

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.

Second law of thermodynamics

Entropy Ex: 10% energy

loss in environment, proton gradient, diffusion, higher to lower concentration (countercurrent exchange), depolarization

Exergonic vs. Endergonic reactions

What are some of these processes that occur in biological systems?

Effects of enzymes

Lock and key vs. induced fit model

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

Competitiveinhibition

Example: oxygen binding to rubisco instead of carbon dioxide photorespiration

Allosteric site Commonly called “regulatory site” Example: lac and trp operons

Regulatory pathways Negative

feedback enables feedback mechanisms

Ex: body temperature regulation

Trp operon in bacteria only

Lac operon in bacteria only

Enzymes Enzymes

denature with changes in temperature and pH.

Example showing Importance of homeostasis

Protein receptors

cAMP as secondary messenger Proteins and

receptors involved in signal amplification

Cell to cell communication

Signal transduction pathway

Signal molecule