Chapter 3: CELL PROCESSES

(across the cell membrane!)

Background Info…• Every living cell contains a liquid interior

(cytoplasm) and is surrounded by a liquid.

• The cell (plasma) membrane separates what is inside the cell from what is outside of the cellinside the cell from what is outside of the cell

• What is the MAJOR function of cell membrane?– regulate the movement of molecules from one side of

the membrane to the other.• In other words—control what gets in and what gets out!

Selectively permeable: • property of biological membranes which

allows some substances to pass more easily than others

Transport proteins:

• membrane proteins that transport

SPECIFIC molecules or ions across

biological membranes

GLUCOSE

Binding

TransportRecovery

Dissociation

Movement across the cell membrane can be:

1) PASSIVE

� cell does not have to spend

energy

� substance moves from where it

is MORE concentrated to where

it is LESS concentrated.it is LESS concentrated.

2) ACTIVE� cell “spends” energy to move a

substance from where it is LESS concentrated to where it is MORE concentrated (“UPHILL”)

Passive Transport: DIFFUSION

• movement of a substance from

where it is conc. to where it is less

conc. (“down a concentration

gradient”)gradient”)

– continues until equilibrium is reached

– occurs if cell membrane is

permeable to substance and if a

concentration difference exists.

– examples: oxygen (O2) and carbon

dioxide (CO2)

Passive Transport: OSMOSIS

• diffusion of WATER

across a selectively

permeable membrane;

water moves DOWN its

concentration gradient

• WATER moves from:

hypotonic side (low solute conc.)

to hypertonic side (high solute

conc.)

INSIDE

THE CELL

OUTSIDE

THE CELL

– the direction of water movement water

can be described/predicted based on if

the cell’s environment is:

• ISOTONIC: equal solute concentration compared to inside a cell

• HYPERTONIC: greater solute

concentration than inside a cellconcentration than inside a cell

• HYPOTONIC: lower solute concentration compared to inside a cell

WATER MOVES FROM

HYPO TO

HYPERTONIC!!!

In animal cells:

• in a HYPERTONIC environment,

water exits the cell;

cells shrivel and usually die

• in a HYPOTONIC environment,

water moves into cell,

causing it to swell and

possibly burst

Passive Transport: FACILITATED DIFFUSION

• diffusion of solutes across a membrane, with the help of transport proteins

(passive transport because it is movement (passive transport because it is movement down a concentration gradient; cell does not need to spend any energy)

• Examples:

-glucose

-amino acids

-some ions

ACTIVE TRANSPORT: energy-requiring process; molecules are moved across the cell membrane AGAINST their concentration gradient (“uphill”)

•protein “pumps” use energy

from ATP from ATP

Examples:

Na+; K+; H+;

Ca2+;

some sugars;

amino acids

ACTIVE TRANSPORT: ENDOCYTOSIS & EXOCYTOSIS

• transport of large molecules (e.g. proteinsand polysaccharides) into (“endo”) or out of (“exo”) the cell

ENDOCYTOSIS EXOCYTOSIS

*importing large

molecules by forming

vesicles out of the cell

membrane

**vesicle forms in a small **vesicle forms in a small

region of cell membrane

***used by cells to bring in

larger, extracellular

substances (e.g. proteins)

ENDOCYTOSIS EXOCYTOSIS

*exporting large

molecules by vesicles

fusing w / the cell

membrane

**vesicle buds from ER **vesicle buds from ER

or Golgi and migrates to

cell membrane

***used by cells to

export products (e.g.

cells in pancreas

secreting insulin)

3 types of Endocytosis:

1) Phagocytosis: solid particles (“cell eating”)

2) Pinocytosis: fluid droplets (“cell drinking”)

3) Receptor-Mediated Endocytosis: importing

of specific macromolecules by inward

budding of vesicles formed from COATED

PITS (e.g. cholesterol enters a cell this way)

Phagocytosis

Pinocytosis

Receptor-Mediated Endocytosis