Membranes

the

cell

MEMBRANES & PROCESSES Robert Perry MALIBU HIGH SCHOOL

ALL CELLS HAVE AN EXTERNAL PLASMA MEMBRANE and all EUKARYOTES also have membrane-enclosed organelles

WHAT ARE THE 3 GENERAL FUNCTIONS OF ALL MEMBRANES ?

1- TO ENCLOSE AND PROTECT FROM THE ENVIRONMENT. 2- TO CONTROL THE PASSAGE OF SUBSTANCES IN AND OUT. 3- TO COMMUNICATE WITH THE EXTERNAL ENVIRONMENT.

DIFFUSION is the net movement of molecules from higher a region of______ concentration to a lowerregion of

THE FORCE OF THE MOLECULES “BOUNCING” AGAINST EACH OTHER IN A CONCENTRATED SOLUTION CAUSES THEM TO MOVE APART

SUPPOSE THE LOCKED ROOM WAS PACKED WITH PEOPLE. PEOPLE COULDN’T MOVE AROUND AND BUMPED INTO EACH OTHER AT EVERY TURN.

SUPPOSE WHAT WOULD HAPPEN IF SOMEBODY OPENED UP THE DOORS.

DIFFUSION !

( these people have no confusion about diffusion ! )

DIFFUSION occurs when a system is not at equilibrium.

A concentration gradient exists.

Dynamic equilibrium occurs when the movement of molecules is equal in all directions.

HIGH

LOW

Simple, inorganic, lipidsoluble molecules such as O2 , CO2, and H2O

(cytosol)

CONCLUSION: MOLECULES IN A SOLUTION DO NOT STOP MOVING, BUT AT EQUILIBRIUM THEIR MOVEMENT IS EQUAL IN ALL DIRECTIONS.

FACILITATED DIFFUSION

MOVES IONS AND MOLECULES THAT CANNOT DIFFUSE EASILY THROUGH WATER-FILLED TRANSPORT PROTEINS.

OSMOSIS diffusion of water semipermeable

v

through a membrane.

HYPOTONIC SOLUTION

HAS A LOW CONCENTRATION OF DISSOLVED SUBSTANCES COMPARITIVELY

ISOTONIC SOLUTION

HAS A THE SAME CONCENTRATION OF DISSOLVED SUBSTANCES COMPARITIVELY

HYPERTONIC SOLUTION

HAS A HIGH CONCENTRATION OF DISSOLVED SUBSTANCES COMPARITIVELY

OSMOSIS

Weight Change & NaCl Solutions 6

4

Wt. Change (g)

2

0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-2

-4

0.25 0.26 0.27 0.28 0.29 New % Salt Solutions for more precise data.

-6 % NaCl

OSMOSIS AND RED BLOOD CELLS:

Osmotic effects: plants vs. animals

Whole cell shrinks

Normal

Explodes

Cell interior shrinks

Flaccid

Turgid (normal)

ACTIVE TRANSPORT MOVEMENT OF MOLECULES AGAINST THE CONCENTRATION GRADIENT…AGAINST DIFFUSION…REQUIRES CELLULAR ENERGY IN THE FORM OF ATP

USES ENERGY

HOW DOES THE CELL TAKE IN & GET RID OF LARGE CHUNKS OF MATERIAL ?

food molecules or water molecules

membrane pinches together vacuole forms

digestion---->

release of secretions or wastes

vacuole reaches membrane

wastes or other molecules

SUMMARY: “FREE”

DIFFUSION

NO ENERGY USED

OSMOSIS SMALL STUFF: ATOMS and MOLECULES !

SUMMARY: “NOT FREE”

ACTIVE TRANSPORT

ENERGY IS USED

ENDOCYTOSIS EXOCYTOSIS

AGAINST CONCENTRATION GRADIENT

BIG STUFF: CHUNKS of FOOD, WATER or WASTES

THE END

The fluid mosaic model of MEMBRANES fluid molecules that easily move and flow. mosaic

made of different molecules put together in a pattern.

model

a scientific description or theory

OUTSIDE

FLUID MOSAIC MODEL

OUTER PROTEIN fat with sugar attached

INNER PROTEIN protein with sugar attached INSIDE

large channel protein

(leave room to add functions to this

THE PHOSPHOLIPID BILAYER THE FOUNDATION OF ALL MEMBRANES.

PHOSPHOLIPID

TRANSPORT PROTEINS (aka Channel Proteins) CARBOHYDRATE CHAINS

ACTIVELY TRANSPORT SUBSTANCES ACROSS MEMBRANE CELL INDENTITY AND RECOGNITION

OUTER PROTEINS

RECEIVE SIGNALS AND SEND TO CELL INTERIOR

INNER PROTEINS

ANCHOR POINTS FOR CYTOSKELETON

CHOLESTEROL

KEEPS PHOSPHOLIPID BILAYER FLUID

(add functions to your membrane diagram)