physiology notes day 2: plasma membrane, passive & active transport

generalized body cell

plasma membrane (fluid mosaic model)

arrangement of molecules within the membrane that resembles a sea of fluid lipids that contain a mosaic of many different proteins

lipid bilayer

made up of phospholipids, cholesterol, and glycolipids

types of proteins present in membrane

integral and peripheral proteins

structure of the plasma membrane

functions of plasma membrane proteins

transporter

enzyme

cell surface receptor

cell surface identity marker

cell adhesion

attachment to the cytoskeleton

membrane permeability

how easily substances can pass through a cell membrane

selectively permeable

some substances can pass thru, others arent able to

homeostasis

exchange with the internal environment

crucial regulator of homeostasis

plasma membrane

determinants of transmembrane passage

size = small

hydrophilic-lipophilic balance (HLB) = lipidic

water-loving

hydrophilic (have difficulty passing through membrane)

fat/lipid-loving

lipophilic (easily passes through membrane)

processes for transmembrane passage

passive processes (

passive processes

no energy input required

down a concentration gradient (high to low concentration)

diffusion process

types diffusion processes

simple diffusion

facilitated diffusion (channel-mediated, carrier-mediated)

simple diffusion

solute diffuses from an area of high concentration to an area of low concentration

across lipid bilayer/plasma membrane

passive, down concentration gradient

small, lipidic moleucles

• fatty acids, steroids, fat-soluble vitamins

• respiratory gases

facilitated diffusion (carrier-mediated, channel-mediated)

the movement of substances from high concentration → low concentration through a membrane protein, without using energy (ATP).

channel-mediated facilitated diffusion

transport of ions (K+, Cl-, Na+, Ca++)

integral transmembrane proteins function as ion channels

passive, down a concentration gradient

the channel can have a gate; opens/closes in response to chemical or electrical changes inside/outside the cell

ex: diffusion of potassium ions through gated K+ channel

carrier-mediated facilitated diffusion

membrane carrier changes its shape

transport of larger, polar, charged molecules (glucose, amino acids, vitamins)

process

• molecule binds to specific transporter

• transporter undergoes a conformational change

• molecule released on other side of membrane

passive, down concentration gradient

glucose transporters (GLUTs)

characteristics: specificity, saturation, competition

active transport

cell uses energy (primarily from breakdown of ATP) to move substances across the membrane against a concentration gradient

goes from area of lower concentration to an area of higher concentration

breakdown of ATP

ATP → ADP + P, loss of phosphate group, provides energy

sodium potassium pump (salty banana)

active transport mechanism

contains transmembrane protein

Na+ / K+ / ATPase

pumps Na+ out of cells (against concentration gradient)

pumps K+ into the cells (against concentration gradient)

works to maintain an equilibrium

transmembrane protein

undergoes conformational changes

can bind (attach) & hydrolyse (break down) ATP → energy

sodium potassium pump must work non stop bc

• ion-gradients: action potentials in nerve cells

• tonicity in all cells

• drives secondary active transport (ex: pump glucose into all cells)

vesicles

small fluid-filled spherical sac, formed by budding off from a membrane

vesicular transport

material is moved into, or out, of cell wrapped in a membrane 

typically, involves the transport of very large molecules (proteins) & bacteria 

endocytosis

transport of material into a cell via a vesicle

3 types of endocytosis

phagocytosis, pinocytosis, RM endocytosis

phagocytosis

cell “eating”

only specialized cells=macrophages

membrane extends pseudopods and ingest a particulate

target bacteria & virusus

formation of a phagosome

phagosome fuses with lysosome → breakdown

Phagosome = holds it
Lysosome = digests it

psuedopods

temporary extension of a cell’s membrane and cytoplasm that help the cell surround engulf a particle during phagocytosis

particulate

small solid particle

phagosome

small membrane-bound sac inside a cell that contains the particle the cell has engulfed

lysosome

organelle containing enzymes that break down waste, particles, and damaged cell parts.

pinocytosis

cell “drinking”

all cells do this

invagination of the cell membrane, takes in surrounding fluids, including all solutes present

formation of pinosome

pinosome fuses with lysosome → breakdown

invagination

a cell membrane folds inward, creating a pocket or indentation.

pinosome

a small vesicle formed when a cell takes in extracellular fluid through pinocytosine

receptor mediated (RM) endocytosis

specific receptor on the cell binds with ligand

specific transport

invagination of the cell membrane to form vesicles

fusion with lysosomes, or avoid lysosomal trafficking

ex: LDL cholestrol levels

exocytosis

export from the cell, by fusion of the vesicle with the PM and expulsion of contents into ECF

transcytosis

combination of endocytosis and exocytosis

summary of plasma membrane transport mechanisms

• Passive (2)

  • Simple Diffusion

  • Facilitated Diffusion (2)

    • Channel-mediated 

    • Carrier-mediated 

• Active 

  • Primary active 

• Vesicular Transport 

  • Phagocytosis 

  • Pinocytosis 

  • Receptor-mediated endocytosis