Please enable JavaScript.
Coggle requires JavaScript to display documents.
CELL MEMBRANES AND TRANSPORT - Coggle Diagram
CELL MEMBRANES AND TRANSPORT
All matter entering cells passes through the plasma membrane
The
plasma membrane is the barrier
through which all matter entering cells should pass.
It is also called the
cell surface membrane.
It has the following functions:
To give the cell structure.
To allow substance to exit and enter the cell.
Cell-cell recognition and cell-cell signalling.
The plasma membrane mainly consists of phospholipid molecules arranged in a bilayer
Hydrophilic heads
of phospholipid molecule face outwards and the
hydrophobic tails
face inwards.
Forms,
Hydrophobic, Non-polar region in the middle of the bilayer,
preventing charged ions and polar molecules from passing through.
The plasma membrane also contains proteins
Intrinsic proteins -
lie across both layers of the membrane (carrier protein)
Extrinsic protein -
Either in one layer of the membrane or on the surface of the membrane. (glycoprotein)
Glycoproteins
Are proteins with carbohydrate chain attached
Both involve cell-cell recognition
Glycolipid
Lipids with carbohydrate chain attached
Membranes also contain
cholesterol, helps increase the rigidity of the membrane.
Temperature increase = kinetic energy = moves at faster rate
, causes the membrane to become more fluid and therefore more permeable.
The plasma membrane in the fluid mosiac model by Singer and Nicolson
Fluid = all parts of the membrane can
more relative to each other.
Mosaic =
proteins are dotted throughout the membrane
like mosiac tiles .
Diffusion is the net movement of molecule or ions down a concentration gradient
Net movement of molecules or ions from an
area of high concentration to an area of low concentration
Occurs from phospholipid bilayer and is the r
esult of random movement of molecules.
Only
lipid-soluable molecules which are non-polar and uncharged
can pass through the phospholipid bilayer
Proteins are not involved. As the movement is down the concentration gradient,
chemical energy, ATP is not needed
Molecules which can diffuse through the phospholipid bilayer
Oxygen
Carbon dioxide
Facilitated diffusion requires membrane proteins
Large, water -soluble, polar molecules and charged ions
pass through the plasma membrane
by facilitated diffusion.
Examples: Of a molecule that moves across the membrane by facilitated diffusion is
glucose
Facilitated diffusion
involves the
molecule or ion passing through a carrier protein or a hydrophilic pore within a channel protein.
Polar molecules and ions cannot pass through the hydrophobic core of the bilayer.
Movement from an area of
high concentration to
an area or l
ow concentration
, does
not require ATP.
- Cotransport
In which two substances are simultaneously transported across the membrane by a carrier protein.
Example: Uptake of glucose with Na+ into the epithelial cells of the ileum by sodium glucose transport proteins.
- A number of factors increase the rate of diffusion
:
Increasing concentration gradient
Increasing solubility of lipids
Increasing temperature
In facilitated diffusion, as the
concentration difference between the inside and outside of the cell increases
so does the rate of facilitated diffusion.
At a
very high concentration differences
the rate of
facilitated diffusion reaches a maximum level and levels off.
This is
due to carrier proteins or channel proteins
in the plasma membrane
becoming saturated (constantly full).
Meaning that
increasing in the concentration difference
between the inside and outside now
does not further increase the rate of diffusion.
Active transport is the movement of molecules or ions up a concentration gradient.
Active transport is the movement against the concentration gradient
, from low to high concentration,
ATP is required
An example of active transport
Transport of mineral ions such as nitrates into the root hair of plant cells.
Carrier protein
in the plasma membrane is
used as a pump.
Active transport can be stopped with
metabolic poisons such as
cyanide.
Cyanide stops ATP from being produced
. As active transport requires ATP,
no active transport will occur
Large molecule can be released from cells by exocytosis (**material passing out from the cell, EXit)
**
A
vesicle fuses with the plasma membrane
and the
molecule in the vesicle is released to the outside of the cell.
Example of this is:
A
modified protein being
formed in the Golgi Apparatus and
released by exocytosis.
Exocytosis requires requires ATP, and is important in secretory cells
Large substances can be taken into the cell by endocytosis (
Material passing into the cell ENter)
In endocytosis the plasma membrane folds around the molecule and engulfs it.
The substance is then trapped in a vesicle or vacuole within the cell. Endocytosis can be divided into 2 categories:
Phagocytosis
:
Endocytosis of large, solid substances, (e.g - white blood cells ingesting bacteria)
Pinocytosis:
Endocytosis of smaller substances, such as fluids
Water moves across the plasma membrane
Movement of water molecules from a higher water potential to a lower water potential across across a partially permeable membrane
Water potential is the potential energy of water relative to pure water.
Partially permeable membrane is important in osmosis as it ensures the solute does not also diffuse and counteract the effects of osmosis
*Water potential = solute potential + pressure potential
The solute potential is
generated by the solutes dissolved in water.
The pressure potential is the
pressure generated by the cytoplasm pushing on the cell wall in cells that have one
. As the cell wall is rigid and inelastic it resists this pressure.
Pure water has a water potential of 0kPa.
This is the
highest possible water potential,
so all solutions have a negative water potential.
Osmosis can sometimes be described as movement from a more negative to a less negative water potential.
During osmosis the
solution with the highest water potential is known as the hypotonic solution
, while the
solution with the lower potential is hypertonic.
Osmosis will continue until both solutions have the same water potential
. The two solutions will then become
isotonic
. At this point water will still move but there will be no net water movement ( water potential will remain the same.
Plant cells in hypersonic solution will lose water and become flaccid and plasmolyse.
Plasmolysis is where the cytoplasm shrinks and becomes away from the cell wall. This will cause the plant to wilt. If a plant is placed in hypersonic, they will water, swell and become turgid.
Animal cells placed in hypersonic solution will lose water and become shrivelled.
Blood cells become crenated.
If an animal cell is placed in hypersonic solution, it will gain water, swell and then burst.