the cell membrane
Post on 24-Feb-2016
34 Views
Preview:
DESCRIPTION
TRANSCRIPT
The Cell MembraneMs. NapolitanoHonors Biology
12/10 – Do Now Please get your clickers! Turn in your webquest if you did not
hand it in last class. Think about the following question:
Why are cells small?
The Cell Membrane Selectively permeable – allows some
substances to cross more easily than others 8 nm thick Fluid mosaic model
Fluid structure of phospholipids with a mosaic of various proteins embedded in it
Cholesterol maintains fluidity – acts as a temperature buffer less fluid as temp increases (restricts
movement) More fluid as temp decreases (maintains space)
The Structure of the Cell Membrane
Membrane Proteins Different types of cells contain different
types of membrane proteins
Integral proteins – embedded into the hydrophobic core of the lipid bilayer Can go all the way through the membrane
Peripheral proteins – on the surface of the membrane
Types of Membrane Proteins Transport
Channel/carrier proteins allow polar molecules & ions to pass through hydrophobic layer
Channel & carrier proteins are substance specific Enzymatic Signal Transduction (chemical messages)
Receptor proteins transmit information from outside of the cell to inside of the cell
Cell Recognition ID tags – glycolipids or glycoproteins
Intercellular Joining Join together adjacent cells
Cell Support Attach to cytoskeleton or extracellular matrix for stability
What type of membrane protein is this?
1 2
0%0%
1. Integral2. Peripheral
A cell that has been frozen will have a more fluid membrane than a cell at room temperature.
1 2
0%0%
1. True2. False
What would happen to a cell that lacks cholesterol in the membrane?
1 2 3 4
0% 0%0%0%
1. It would not be able to transport materials into/out of the cell
2. The membrane would change drastically with temperature
3. It would not be able to use enzymes effectively
4. Chemical messages would not be able to get into the cell
What is the function of membrane carbohydrates?
1 2 3 4
0% 0%0%0%
1. Transport2. Signal
transduction3. Cell recognition4. Intercellular
joining
Passive Transport Passive Transport – movement across the cell
membrane that does not require energy Diffusion – movement of particles from an area of
high concentration to an area of low concentration until an equilibrium is reached Said to go with/down its concentration gradient
Concentration gradient – the difference in the concentration of a substance across a space
Equilibrium – concentration of a substance is equal throughout a space
Doesn’t stop moving
OsmosisOsmosis – the diffusion of free water
across a selectively permeable membrane
Water diffuses across the cell membrane from a region of low solute concentration
to that of a higher solute concentration until it reaches equilibrium
Really cool video!http://www.youtube.com/watch?v=EsJ73x4ycp0
Osmoregulation in Cells without Cell Walls
Osmoregulation – control of water balance Tonicity – ability of a solution to cause a cell to
gain/lose water Isotonic solution – no net movement of water
across the cell membrane Hypertonic solution – more free water inside the
cell Cell loses water to environment and shrivels
Hypotonic solution – less free water inside the cell Water will enter the cell and swell (and maybe lyse) Some cells have a contractile vacuole to pump water
out of the cell
Animal Cells
Osmoregulation of Cells with Cell Walls
Plant cells are healthiest in a hypotonic solution, osmotic pressure keeps cell walls turgid (very firm)
Plant cells are flaccid (limp) in an isotonic solution
In a hypertonic solution, the cell membrane will shrink and pull away from the cell wall Called plasmolysis (wilting)
Plant Cell
U – Tube (not YouTube!)
Which of the following can readily diffuse across a lipid bilayer?
1 2 3 4
0% 0%0%0%
1. Glucose2. Oxygen3. Carbon dioxide4. Both 2 & 3
If you immerse a living cell in a hypotonic solution, water will…
1 2 3
0% 0%0%
1. Diffuse into the cell
2. Diffuse out of the cell
3. Show no net movement
Plant 1 is in better shape than plant 2 because the cells of plant 1 are…
1 2 3 4
0% 0%0%0%
1. Turgid2. Flaccid3. Undergoing
plasmolysis4. The same as
plant 2Plant 1Plant 2
The image below is a U-Tube with a semi-permeable membrane. How will water flow?
1 2 3
0% 0%0%
1. It won’t2. Left to right 3. Right to left
12/ 16 Do Now: Get Your Clicker! Compare/Contrast Active & Passive
Transport Compare/Contrast Diffusion & Osmosis
Facilitated Diffusion Facilitated diffusion: passive transport aided
by proteins Channel proteins – hydrophilic passageways
Some always open for diffusion Rate of movement is determined by concentration
gradient (+) charged ions more likely to diffuse into the cell (-) charged ions more likely to diffuse out of the cell Some ion channels have gates and can be opened
by: Stretching of the cell membrane Change in electrical charge Binding of specific molecules
Voltage Gated ChannelsNerve cells transmit electrical signals by
opening a series of Na+ gated channels1. Channel is closed2. Area changes voltage3. Channel opens briefly4. Na+ flood into cell – voltage changes5. Channel closes and electrical signal passes
on to the next voltage channel
Chemically (Ligand) Gated Channels Nerve cells send out a neurotransmitter called
acetylcholine (ACh) to nearby muscle cells to signal muscles to contract1. ACh binds to ACh receptor proteins2. Receptor gate opens for a microsecond to allow
Na+ in3. Na+ sets off muscle contraction
Facilitated Diffusion Carrier Proteins1. Specific substance
binds to carrier protein2. Protein changes shape
and transports substances across cell membrane
3. Molecule is released into the cell, and carrier protein returns to its original shape
Which image best represents facilitated diffusion?
1 2 3 4
87%
0%0%
13%
1. 12. 23. 34. 4
1 2
3
4
____are transported by a particular carrier or pass through a particular channel.
1 2 3 4 5
13%
20%
0%
40%
27%
1. All water soluble ions or molecules
2. Certain water soluble molecules or ions
3. All insoluble molecules or ions
4. Certain insoluble ions or molecules
5. Only the smallest molecules or ions
Active TransportActive Transport – uses energy to move
solutes against the concentration gradient
Carrier proteins act as “pumps” powered by ATP
Examples: Sodium Potassium Pump Proton Pump Cotransport
Sodium Potassium Pump Pumps 3 Na+ out of the cell and 2 K+ into the cell Actively transports both ions against their
concentration gradient, powered by ATP Prevents Na+ from accumulating in the cell Steps:
1. 3 Na+ and a P (from ATP) bind to inside protein pump
2. Pump changes shape transporting 3 Na+ across membrane and out
3. 2 K+ bind to pump and are transported across membrane
4. 2 K+ and P are released inside of cell
Sodium Potassium Pump
The sodium-potassium pump passes
1 2 3 4
87%
0%7%7%
1. More Na+ out than K+ in
2. K+ out and Na+ in on a one-for-one basis
3. Na+ out and K+ in on a one-for-one basis
4. K+ and Na+ in the same direction
Proton PumpActively transports protons (H+) through
the internal membranes of mitochondria and chloroplasts
Cotransport (Coupled Transport) Cotransport – an ATP-powered pump that
transports a specific solute Can indirectly drive the active transport of
several other solutes Ex: as proton pumps pump H+ out, H+ diffuse back into the cell pulling sucrose molecules into the cell with it
By a mechanism called cotransport
1 2 3 4 5
7%
47%
0%
27%
20%
1. sugar moves down (with) its concentration gradient while sodium moves up (against) its concentration gradient
2. sodium moves outward against is concentration gradient while sugar moves inward down its concentration gradient
3. sugar and sodium move inward down their concentration gradient
4. sodium moves inward down its concentration gradient while sugar moves inward up its concentration gradient
5. sodium and sugar move outward against their concentration gradient
Bulk Transport Substances that are too large to be transported by
carrier proteins Exocytosis (export)
Secretion of macromolecules by fusion of vesicles with membranes, releasing the contents outside of the cell
Endocytosis (import) Cell membrane engulfs particles and pinches off to
form vesicles inside the cell. Vesicle may fuse with lysosomes or other organelles
3 Types: Phagocytosis – engulf another organism Pinocytosis – engulf fluid Receptor-mediated - specific
Exocytosis (top)/Endocytosis (bottom)
A cell engaged in phagocytosis must be
1 2 3 4 5
80%
0%
20%
0%0%
1. engulfing a live organism
2. acquiring a liquid 3. engulfing a dead
organism4. transporting bulk
dissolved nutrients
5. transporting bulk solid material
Substances transported by facilitated diffusion
1 2 3 4 5
87%
0% 0%
13%
0%
1. move passively through specific channels from an area of greater concentration to one of lower concentration
2. are limited to solvents3. must have movements coupled to
those of other substances4. may flow to a region of higher
concentration by the expenditure of energy
5. are restricted to only one direction through the membrane
A contractile vacuole is an organelle that pumps excess water out of many freshwater protozoan cells. A freshwater protozoan was placed in solution A and observed to form contractile vacuoles at a rate of 11 per minute. The same protozoan was then placed in solution B and observed to form contractile vacuoles at a rate of 4 per minute. Based on this information, which of the following statements is correct?
1 2 3 4 5
40%
7% 7%
0%
47%
1. Solution A is hyperosmotic to solution B.
2. Solutions A and B are isosmotic.
3. Solution B is hyperosmotic to solution A.
4. Solutions A and B are isosmotic to the protozoan cell.
5. Both a and b
The methods of membrane transport that don't require protein channels or carriers are
1 2 3 4 5
13%
0%
87%
0%0%
1. osmosis 2. Diffusion3. Phagocytosis4. Exocytosis5. all of the above
top related