Ch 3 The Cellular Level of Organization

three main parts of a cell

plasma membrane, cytoplasm, nucleus

describe the structure of the lipid layer

structural framework of plasma membrane where polar phosphate (hydrophilic) groups face extracellular and intracellular fluids and nonpolar fatty (hydrophobic) acid molecules are in interior of bilayer

structure of membrane proteins

hydrophobic (non-polar) amino acids interacting with the lipid core and hydrophilic (polar) amino acids exposed to aqueous environments on either the inside or outside of the cell; integral (embedded or spanning the membrane) or peripheral (loosely attached to the surface)

function of membrane proteins

transport (channels, pumps, and carriers), enzymatic activity, signal transduction (receiving external signals), cell-cell recognition, intercellular joining, and anchorage to the cytoskeleton and extracellular matrix

selective permeability

some substance can cross the membrane more readily than others

types of molecules that can diffuse through the lipid bilayer

nonpolar, uncharged molecules such as oxygen, carbon dioxide, and steroids and slightly permeable to small uncharged polar molecules such as water and urea

concentration gradient

the difference in chemical concentration from one area to another

electrical gradient

the difference in charge from one area to another

electrochemical gradient

the difference in both concentration and charge from one area to another

passive transport

does not require cell to provide energy for transport; kinetic energy causes movement

active transport

substances move uphill or against their chemical and/or electrical gradient; requires cell to provide energy for transport (usually energy stored in ATP)

diffusion

substances move down chemical gradients and/or electrical gradients until equilibrium is reached; a type of passive transport

factors that affect the rate of diffusion

steepness of the concentration gradient, temperature, mass of the diffusing substance, surface area, and diffusion distance

simple diffusion

does not use transport proteins; gases like oxygen, carbon dioxide, and nitrogen, lipids like fatty acids, steroids, and fat soluble vitamins (A, D, E, and K), and small unchanged polar molecules such as water and small alcohols

channel-mediated facilitated diffusion

substances pass through channels created integrated membrane proteins; most channels are ion channels and some channels will randomly open while others are gated or plugged

carrier-mediated facilitated diffusion

a carrier membrane protein transports substance across plasma membrane; cell homeostatic mechanisms control amount of substance transported by controlling number of carrier protein; substances include: glucose, fructose, and galactose, vitamins

osmosis

diffusion of water across plasma membrane; water diffuses from area of high concentration to area of low concentration

hypertonic solution

a solution with a higher solute concentration

hypotonic solution

a solution with a lower solute concentration

isotonic solution

has the same solute concentration

State the direction of water movement when a cell is placed in a hypotonic solution.

water moves into cell; cell swells and may burst

State the direction of water movement when a cell is placed in a hypertonic solution.

water moves out of cell; cell shrivels

State the direction of water movement when a cell is placed in an isotonic solution.

no net water movement of water into or out of cell

sources of energy used for active transport

ATP + water → ADP + P + energy (hydrolysis)

primary active transport

hydrolysis of ATP provides the energy for active transport; shape of carrier protein or pump changes to allow substance to be transported across the plasma membrane

secondary active transport

the energy for active transport is obtained from the diffusion of a substance ( mainly diffusion of NA+)

transport in vesicles

substances cross plasma membrane in vesicles and ATP supplies the energy for transport

endocytosis

vesicles transport substances from the outside of the cell to the inside of the cell

exocytosis

vesicles transport substances from the inside of the cell to the outside of the cell

cytoplasm

everything inside the cell membrane except the nucleus, including organelles

cytosol

the jelly-like, watery matrix filling a cell, containing water, ions, proteins, and nutrients

structure of the nucleus

double-membrane organelle containing nuclear pores, chromatin, and a nucleolus

function of the nucleus

ontrols cell activities by storing DNA and regulating gene expression

transcription

copies DNA into messenger RNA (mRNA); happening in the nucleus

translation

decodes mRNA into a chain of amino acids; occurring at ribosomes in the cytoplasm

cell cycle

a period during which a cell grows and divides into two genetically identical cells; begins when a cell is produced by cell division and ends when the cell divides

parts of the cell cycle

interphase where the cell conducts its normal metabolic activity and mitotic phase where the nucleus divides and the cytoplasm divides

cytokinesis

the division of cytoplasm

somatic cell

(normal cells) any cell in the body except a germ cell (reproductive cell)

reproductive cell

haploid cell—such as a sperm or egg—used in reproduction to combine with another gamete and form a new organism; gametes have 23 chromosomes

Describe the purpose of somatic cell division and state where it occurs.

o produce two identical daughter cells for growth, repair, and replacement of tissues, and it occurs in all body cells except reproductive cells

chromosome number in somatic cells

46 chromosomes

chromosome number in reproductive cells

23 chromosomes

Describe the purpose of reproductive cell division and state where it occurs.

to produce haploid gametes (sperm or eggs) for reproduction, and it occurs in the testes of males and the ovaries of females