OLI AP Unit 3 Module 6 membrane transport

2 categories of passage of substances through cell membrane

passive

active

passive transport

cell does not need ATP but needs a driving force

active transport

cell must use ATP

passive passage driving force

usually kinetic energy in form of a concentration gradient

2 main types of passive processes across cell membranes

diffusion and facilitated diffusion

osmosis and tonicity

passive process across vessel membranes

filtration

diffusion relies on

kinetic energy and a concentration gradient

kinetic energy is affected by

temperature

size of molecules

magnitude/steepness of gradient

medium the molecules are in

as kinetic energy increases

rate of diffusion increases

diffusion

movement of molecules from an area of high concentration to an area of lower concentration

types of diffusion of molecules across a cell membrane

simple

facilitated

simple diffusion

no aid from a protein

very small or lipid soluble molecules

oxygen, carbon dioxide, lipids

facilitated diffusion

channel or carrier protein is used

molecules which have a lower concentration inside cell than outside

glucose

nonpolar molecules ability to cross plasma membrane

easily cross because they interact favorably with nonpolar lipids

hydrophobic

small polar molecules ability to cross plasma membrane

can pass through small temporary holes in membrane

large polar molecules ability to cross plasma membrane

difficulty crossing

ionic compounds ability to cross plasma membrane

difficulty crossing

interact unfavorably with lipids

types of channels for facilitated diffusion

always open

gated

for specific molecules

facilitated diffusion

process of moving impermeable molecules across.a membrane down their concentration gradient using channels or pores

no input of additional energy

water flows with a net movement toward

the region that has a higher concentration of solutes

osmosis

movement of water across a semipermeable membrane in response to an imbalance of solute

osmotic pressure

pressure created by water moving to the area with the greater number of solutes

aquaporins

protein membrane channels that water passes through

3 types of solutions for concentrations of solutes outside the cell relative to inside cell

isotonic

hypertonic

hypotonic

isotonic

solutes and water are equally concentrated in and out of cell

0.9% NaCl

5% dextrose

many medical preparations are isotonic to our cells

hypotonic solution

low solute concentration and high water concentration compared to cell

distilled water

cell will gain water

hypertonic solution

high solute concentration and low water concentration compared to cell

salty or sugary solutions

water flows out of cell

human cells have an internal solute concentration of approximately

1%

filtration

passive

uses a pressure gradient

non-specific

capillary exchange

nephrons to filter blood from urine

hydrostatic pressure

force that pushes molecules for filtration

countered by osmotic pressure

active transport

cell uses ATP

molecule is moved against concentration gradient

large molecule is moved

3 main types of active processes

primary active transport or solute pumps

endocytosis

exocytosis

primary active transport

move ions from low concentration to high concentration

needs ATP, a membrane protein transporter, and enzymes

example of active transport pump

Na/K+ pump keeps Na+ concentrations higher out of cell and K+ concentrations higher in cell

secondary active transport

relies on energy from electrochemical gradients

set up by primary active transport

proteintransporters

transport molecules

cotransport/symport

molecules move in same direction

countertransport/antiport

molecules are moved in opposite directions

SGLT1

Na+/glucose transport protein

endocytosis

material is engulfed within an infolding of plasma membrane then brought into cell within a cytoplasmic vesicle

steps of endocytosis

1. particle makes a dimple in cell membrane

2. pit deepens, invaginates further, and pinches off to form a vesicle in cytoplasm

3. vesicle fuses with lysosome to break down solid contents

4. resulting molecules are released to cytoplasm

forms of endocytosis

phagocytosis

pinocytosis

phagocytosis

uptake of large solid particles

pinocytosis

uptake of fluid and any small molecules dissolved within it

receptor-mediated endocytosis

cells recognizing specific particles and engulfing them in a more targeted way

how does receptor-mediated endocytosis work

particle binds to a membrane protein receptor on cell surface which induces endocytosis

exocytosis

an internal vesicle fuses with plasma membrane and releases contents to outside

balance of exocytosis and endocytosis

preserves plasma membrane size

keeps cell size constant

importance of endocytosis and exocytosis

immunity