2. living organisms can be divided into two large groups
the prokaryotes and eukaryote:
3.
4. The eukaryotic cell is subdivided by membranes:
-On the outside, it is enclosed by a plasma membrane.
- Inside the cell, Additional membranes divide the internal
space into compartments.
6. -Proteins usually account for the largest proportion, at 1/2.
-By contrast, CHO, which are only found on the side facing
away from the cytoplasm, make up only a few percent.
-The ratio between the proteins and lipids depend on function:
-myelin, the insulating material in nerve cells, three-quarters
of which consists of lipids.
-the inner mitochondrial membrane is characterized by a very
low lipids and a particularly high of proteins.
7. MEMBERANE LIPIDS
-Phospholipids are predominant in membrane lipids in
comparison with glycolipids and cholesterol (with the
exception of inner mitochondrial membranes).
-Triacylglycerols (neutral fats) are not found in membranes.
- Glycolipids (a ganglioside is shown here) are mainly found
on the outside of the plasma membrane.
9. Saturated fatty acids have straight tails, whereas unsaturated
fatty acids, which generally exist in the cis form in membranes,
make kinked tails
Amphipathic
the two
regions of the
molecule
have
incompatible
solubilities
10. phospholipids organize themselves into a form that
thermodynamically serves the solubility requirements
of both regions.
A micelle Bilayers
11. Protein
- Membrane phospholipids act as
a solvent for membrane proteins.
- proteins can be amphipathic:
hydrophilic regions protruding
at the inside and outside faces of
the membrane
connected by a hydrophobic
region traversing the
hydrophobic core of the bilayer.
-some protein bounded with lipid
formed lipoprotein or CHO and
formed glycoprotein.
12. Extensive nonpolar regions within a transmembrane protein
can create a pore through the membrane.
-b sheets in the protein secondary structure form a
cylinder called a b-barrel
-b-barrel interior is polar and allows water and small
polar molecules to pass through the membrane
14. FLUID- because individual phospholipids and proteins can
move side-to-side within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered
protein molecules when the membrane is viewed from
above.
Cellular membranes are fluid mosaics of lipids and
proteins
Lateral movement occurs
107 times per second.
Flip-flopping across the
membrane is rare.
15. Membrane structure results in selective
permeability
A cell must exchange materials with its surroundings, a
process controlled by the plasma membrane
Plasma membranes are selectively permeable, regulating
the cell’s molecular traffic.
Selective permeability of the membrane can provid by
channel, ion pump, substrate, specific receptor signals
(hormones).
Transport system
- Small molecules by diffusion (simple, facilatied, active)
- Transport of large molecules by endocytosis or exocytosis.
16. Diffusion
passive Active
-Aganist electrochemical gradient.
- Away from thermodynamic
equilibrium
- energy required supplied by ATP,
electron cain transport or light.
-with electrochemical gradient.
- Spontaneous toward equilibrium
- No energy required.
Simple facilitated
Osmosis
17. The Permeability of the Lipid Bilayer (polarity,
particle size and charges)
Hydrophobic (nonpolar)
molecules, such as
hydrocarbons, can dissolve
in the lipid bilayer and pass
through the membrane
rapidly
Polar molecules, such as
sugars, do not cross the
membrane easily
Simple Diffusion
O2 or H2O diffusing into a cell and CO2
diffusing out
18. The rate limiting factors in this case are:
-molecular size
-Shape
-charge
-its concentration on both side of the memberane
-solubility of the solute
- thermal agitation of that specific molecule, by the concentration
gradient across the membrane, and by the solubility of that solute
Polar charge denisity
19. Facilitated Diffusion: Passive Transport Aided by
Proteins
Channel proteins: have a polar interior allowing specific
polar molecules or ions to pass through.
Aquaporins Ion channels Gated channels
Na, K, Ca
liganted gated Voltage gated
20. Carrier proteins (transporter):
- Some specific solutes diffuse down electrochemical gradients
across membranes more rapidly than might be expected.
- Protein bind to molecules and change shape to shuttle them
across the membrane.
-A transport protein is specific for the substance it moves.
-Glucose or amino acids moving from blood into a cell.
Types:
Facilitated transport—passive (uniport)
Active transport—requires energy (The carrier protein in
this system act as pump to mentain electrochemical gradient
in this biological system) e.g. The sodium-potassium pump is
one type of active transport system
21. Carrier proteins used in active transport include:
- -uniporters – move one molecule at a time
- -symporters – move two molecules in the same
direction
- -antiporters – move two molecules in opposite
directions
22. -the carrier protein exists in two principal conformations.
-In the “pong” state, it is exposed to high concentrations of
solute, and molecules of the solute bind to specific sites on the
carrier protein.
- Transport occurs when a conformational change exposes
the carrier to a lower concentration of solute (“ping” state).
explains facilitated diffusion “Ping-Pong” mechanism
23. - This process is completely reversible, and net flux
across the membrane depends:
- (1) The concentration gradient across the membrane.
- (2) The amount of carrier available (this is a key control
step).
- (3) The rapidity of the solute-carrier interaction.
- (4) The rapidity of the conformational change for both the
loaded.
NB: Hormones regulate facilitated diffusion by changing the
number of transporters available.
- Insulin increases glucose transport in fat and muscle and
enhances amino acid transport in liver and other tissues.
- glucocorticoid hormones is to enhance transport of amino
acids into liver, where the amino acids then serve as a
substrate for gluconeogenesis.
26. Bulk transport across the plasma membrane occurs
by exocytosis and endocytosis
- Large molecules, such as polysaccharides and proteins,
polynucleotides cross the membrane in bulk via vesicles
-Bulk transport requires energy.
-Endocytosis is a reversal of exocytosis, involving different
proteins.
Endocytosis requires
(1) energy, usually from the hydrolysis of ATP;
(2) Ca2+ in extracellular fluid; and
(3) contractile elements in the cell (probably the
microfilament system)
27. Endocytosis
It involved attachement the substrate to cell memberane
invagination of the memberane to engulf the substance
as finally migration the particle to the cell
There are three types of endocytosis
◦ Phagocytosis (“cellular eating”):
occurs only in macrophages and granulocytes.
Phagocytosis involves the ingestion of large particles
such as viruses, bacteria, cells, or debris.
◦ Pinocytosis (“cellular drinking”)
28. Fluid-phase pinocytosis is a nonselective process in
which the uptake of a solute by formation of small vesicles
is simply proportionate to its concentration in the
surrounding extracellular fluid eg fibrolasts
absorptive pinocytosis, is a receptor-mediated
selective process primarily responsible for the uptake of
macromolecules for which. there are a finite number of
binding sites on the plasma memberane. the system limit
uptake of fluid or soluble unbound macromolecules, and
only specific molecules are enter the cell by high rate. As an
example, the low-density lipoprotein (LDL)
30. - Most cells release macromolecules to the exterior by
exocytosis.
- This process is also involved in membrane remodeling.
- The signal for exocytosis is often a hormone which, when it
binds to a cell-surface receptor, induces a local and transient
change in Ca2+ concentration.
Exodcytosis
31. molecules released by exocytosis fall into three
categories:
(1) They can attach to the cell surface and become
peripheral proteins, eg, antigens.
(2) They can become part of the extracellular matrix, eg,
collagen and glycosaminoglycans.
(3) They can enter extracellular fluid and signal other cells.
Insulin, parathyroid hormone, and the catecholamines
Exodcytosis
33. Functions of Plasma Membrane
It mechanically holds the cell organs togetter.
Regulate transport in & out of cell (selectively permeable)
Allow cell recognition
Provide anchoring sites for filaments of cytoskeleton
Provide a binding site for enzymes
Interlocking surfaces bind cells together (junctions)
Plasma membrane formed closed component around the cellular
protoplasm to separate cell from other.
Memberanes estabilished different component within the cells to prevent
the interferences between opposite process
- selective permeability acts as a barrier creating a gradiant between inside
and outsides the cells
