CELLS - MEMBRANE TRANSPORT

Passive membrane transport

does not require the cell to expend

metabolic energy

Active membrane transport

Requires the cell to expend

metabolic energy, usually in the

form of ATP

● diffusion

● osmosis

● facilitated diffusion

Passive Membrane Transport includes:

● active transport

● secondary active transport

● endocytosis

● exocytosis

Active Membrane Transport includes:

Diffusion

the movements of solutes from an

area of higher solute concentration

to an area of lower solute

concentration , down a

concentration gradient

Solvent

substances dissolved

Solute

predominantly gas or liquid

diffuse down their concentration

gradients from a higher to lower

solute concentration until an

equilibrium is acheived

Concentration Gradient

difference in the concentration of a

solute and solvent between two

points, divided by the distance

between the two points

is said to be steeper while

concentration difference is large /

distance is small

Viscosity

is a measure of a fluids resistance

to flow

Lipid

soluble substances can diffuse

directly through the phospholipid

bilayer

Water

soluble substances, such as ions,

can diffuse across the cell

membrane only by passing through

cell membrane channels

Leak Channels

Gated Channels

2 classes of cell membrane channels:

Leak Channels

Constantly allows ions to pass

through

Gated Channels

Limit the movement of ions across

the membrane by opening and

closing

Osmosis

Diffusion of water (solvent) across

a selectively permeable membrane

from a region of higher water

concentration to lower water

concentration

Osmotic pressure

the pressure exerted by osmosis,

which is the force required to

prevent movement of water across

the cell membrane

Aquaporins

- also known as water channel

proteins that open and close to

adjust membrane permeability to

water

● isosmotic

● hyperosmotic

● hyposmotic

3 terms used to describe Osmotic

pressure of Solutions:

Isosmotic

solutions with the same

concentration of solute particles

have the same osmotic pressure

Hyperosmotic

One solution has a greater

concentration of solute particles,

and therfore a greater osmotic

pressure than another solution

Hyposmotic

the more dilute solution with the

lower osmotic pressure

Lysis

If the cell swells enough causing it

to rupture

Hypotonic

has a lower concentration of

solutes and a higher concentration

of water relative to the cytoplasm

of the cell. A cell is placed into a

solution and water moves into the

cell by osmosis, causing the cell to

swell.

Isotonic

Has the same solute concentrations

inside and outside the cell. A cell is

placed into a solution and neither

shrink or swells

Has the same solute concentrations

inside and outside the cell. A cell is

placed into a solution and neither

shrink or swells

Has a lower solute concentration

and higher water concentration

than the surrounding solution. A

cell is placed into a solution and

water moves out of the cell by

osmosis, causing the cell to shrink.

Tonicity

the condition in isotonic solution

wherein the shape of the cell

remains constant

Crenation

the condition in red blood cells

wherein the cell is shrinking

Mediated Transport

a membrane transport process by

which transport proetiens

mediate/assist the movement of

large, water-soluble molecules or

electrically charged molecules or

ions across the plasma membrane

● Facilitated diffusion

● Active Tansport

2 Mediated Transport Mechanisms:

Facilitated diffusion

A mediated transport that moves

substances into or out of the cells

from a higher to a lower

concentration, does not require

metabolic energy to transport

substances across the cell

membrane

Active Transport

a mediated transport process that

requires ATP, that moves

substances across the cell

membrane from regions of lower

concentration gradient to higher

concentration gradient AGAINST a

concentration gradient

Secondary Active Transport

Uses the energy provided by the

concentration gradient established

by the active transport of another

substance to transport other

substances.

- Involves the active transport of an

ion out of a cell establishing a

concentration gradient with a

higher concentration of ions outside the cell. No additional

energy is required.

Cotransport

The diffusing of substance moves

in the same direction as the initial

active transported substance

Countertransport

The diffusing of substance moves

in a direction opposite to that of the

initial active transported substance

Endocytosis

Process when material moves

through the plasma membrane and

into the cytoplasm by the

formation/ use of a vesicle

● Phagocytosis

● Pinocytosis

2 Types of Endocytosis:

Receptor Mediated Endocytosis

occurs when a specific substance

binds to the receptor molecule and

is transported into the cell

Phagocytosis

"cell eating", solid particles are

ingested and phagocytic vesicles

are formed encapsulating it, then

special enzymes break down whats

inside the vesicle

Pinocytosis

"cell-drinking", smaller vesicles

form and they contain molecules

dissolved in liquid, once collected,

they are brought inside the cell and

is processed/used

Exocytosis

Involves the use of membrane

bound sacs called secretory

vesicles that accumulate materials,

the vesicles move to the cell

membrane and fuse, ultimately

releasing the material from the cell

Selectively Permeable

allows only certain substances to

pass through it

Vesicle

a small membrane-bound sac