Cell Membrane and Membrane Transport

Cell Membrane & Membrane transport

Cells· cells are the basic unit of life· 75 trillion in an adult human· vary greatly in size, shape, contents, and function

· 3 basic partscell membrane - encloses the cellsnucleus - houses genetic materials and controls

cellular activitiescytoplasm - fills out cell and houses organelles

A Composite Cell The Cell Membrane· a.k.a. plasma membrane· functions

a. maintains cell integrity (distinct inside and distinct outside)

b. controls passage of materials into and out of cell (selectively permeable - only certain substances can enter or leave)

· structurea. phospholipid bilayerb. cholesterol - helps stabilize membranec. proteins - channels, transporters, receptor for

hormones d. carbohydrates - cell markers

A. phospholipidA1 - hydrophilic headA2 - Hydrophobic tails

C, F, G. ProteinsD. CarbohydratesE. Cholesterol

Membrane Transport· interstitial fluid - extracellular fluid rich in nutrients· to maintain homeostasis cells must extract the exact amount of substances it needs at specific times· 2 ways

passive - does not require cellular energyactive - ATP needed to move substances across

membrane

Cell Membrane and Membrane Transport

Diffusion· passive process· characteristics

a. diffusion - molecules or ions move down their conc. gradient (high conc. to low conc.)

b. 3 requirements1. molecule/ion must be lipid soluble2. small enough to pass through membrane channels

(simple diffusion)3. or, assisted by a carrier molecule (facilitated

diffusion)· source of energy - kinetic energy of molecules· example - exchange of CO2 and O2 in the lungs· drawing -

· passive process· characteristics

facilitated diffusion - carrier proteins move molecules through a membrane from high to low conc.

limitations - # of carrier proteins in cell membranes

· energy - kinetic energy of molecules· example - movement of glucose through cell membrane· drawing -

Facilitated Diffusion

Osmosis· passive process· characteristics

osmosis - H2O moves from high to low conc. through a selectively permeable mem.· energy - kinetic energy of molecules· examples -

a. isotonic - conc. of H2O equal inside and out

b. hypertonic - conc. of H2O high inside cell

c. hypotonic - conc. of H2O high outside cell· drawing -

· active transport (requires ATP)· characteristics

carrier molecules move molecules or ions from regions of low conc. to regions of higher conc. (move up concentration gradient)· energy - cellular energy (ATP)· example - movement of ions, sugars, and amino acids through mem.· drawing -

Active Transport

endocytosis· active process (requires ATP)· characteristics

bringing materials into the cell· energy - cellular energy (ATP)· examples

pinocytosis (cell drinking) - mem. engulfs droplets of liquid from surroundings

phagocytosis (cell eating) - mem. engulfs solid particles from surroundings· drawing -

exocytosis· active process (requires ATP)· characteristics

vesicles fuse with mem. to expel substances from the cell· energy - cellular energy (ATP)· example - release of neurotransmitter from neurons· drawing -