Download The Plasma Membrane

The Plasma
Membrane
PREPARED BY
BAHAA KHUDER
TAMARA THAMIR
BAYDAA ABD ALILAH
ENAS AYAD
BAYAN HUMADI
TAIKA MOAFAK ATTASH
The Plasma
Membrane
BAHAA KHUDER
The Plasma Membrane

the fluid mosaic model (S.J Singer)

semi-permeable

fluid portion is a double layer of phospholipids, called the
phospholipid bilayer
The Plasma Membrane

Jobs of the cell membrane

Isolate the cytoplasm from the external
environment

Regulate the exchange of substances

Communicate with other cells

Identification
The Plasma
Membrane
TAMARA THAMIR
The Plasma Membrane

The Plasma Membrane is also called the Phospholipid bilayer

Phospholipids contain a hydrophilic head and a nonpolar
hydrophobic tail

Hydrogen bonds form between the phospholipid "heads" and
the watery environment inside and outside of the cell
Hydrophobic interactions force the "tails" to face inward
Phospholipids are not bonded to each other, which makes the
double layer fluid

Cholesterol embedded in the membrane makes it stronger and
less fluid
The Plasma
Membrane
TIAKA MOUFAK
Proteins embedded in membrane
serve different functions
1. Channel Proteins - form small openings for molecules to
difuse through
2. Carrier Proteins- binding site on protein surface "grabs"
certain molecules and pulls them into the cell
3. Receptor Proteins - molecular triggers that set off cell
responses (such as release of hormones or opening of channel
proteins)
4. Cell Recognition Proteins - ID tags, to idenitfy cells to the
body's immune system
5. Enzymatic Proteins - carry out metabolic reactions
The Plasma
Membrane
BAYDAA ABD ALILAH
Transport Across Membrane
The membrane is differentiallty permeable (also called
semipermeable ) - which means

Passive Transport

Simple Diffusion - water, oxygen and other molecules move
from areas of high concentration to areas of low
concentration, down a concentration gradient
Facilitation Diffusion - diffusion that is assisted by proteins
(channel or carrier proteins)

Osmosis - diffusion of water. Salt Sucks
Osmosis affects the turgidity of cells, different solution can
affect the cells internal water amounts

Contractiles Vacuoles are found in freshwater
microorganisms - they pump out excess water

Turgor pressure occurs in plants cells as their central
vacuoles fill with water.
The Plasma
Membrane
BAYAN HUMADI

Active Transport - involves moving molecules "uphill" against
the concentration gradient, which requires energy

Endocytosis - taking substances into the cell (pinocytosis for
water, phagocytosis for solids)
Exocytosis - pushing substances out of the cell, such as the
removal of waste
Sodium-Potassium Pump - pumps out 3 sodiums for ever 2
potassium's taken in against gradient

Demo - Starch in the baggie, iodine in the beaker. What
happens and why?
Observation of elodea cells in salt water. What happens and
why?
The Plasma
Membrane
ENAS AYAD
Modification of Cell Sufaces

Tight junctions are composed of protein fibers that seal
adjacent cells to prevent leakage, something which can
be useful in organs such as the bladder and the lining of
the digestive tract. Tight junctions literally fuse the cells
together forming a sheet of cells restricting molecules to
one side of the sheet or the other.

Tight junctions can also partition the cells in which they
are found. Certain membrane proteins can be restricted
to one side of the junction, as well, since the tight
junction prevents protein migration within the membrane.