Cell Membrane and Membrane Transport
Cells
Cell Membrane
& Membrane transport
A Composite Cell
· 3 basic parts
cell membrane - encloses the cells
nucleus - houses genetic materials and controls
cellular activities
cytoplasm - fills out cell and houses organelles
· cells are the basic unit of life
· 75 trillion in an adult human
· vary greatly in size, shape, contents, and function
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)
· structure
a. phospholipid bilayer
b. cholesterol - helps stabilize membrane
c. proteins - channels, transporters, receptor for
hormones
d. carbohydrates - cell markers
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 energy
active - ATP needed to move substances across
membrane
A. phospholipid
A1 - hydrophilic head
A2 - Hydrophobic tails
C, F, G. Proteins
D. Carbohydrates
E. Cholesterol
Cell Membrane and Membrane Transport
· passive process
· characteristics
Diffusion
a. diffusion - molecules or ions move down their conc.
gradient (high conc. to low conc.)
b. 3 requirements
1. molecule/ion must be lipid soluble
2. 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
· 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 -
Osmosis
Active Transport
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
· 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 -
· drawing -
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 -