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Copy of Cell Membranes

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sadie skiles

on 5 November 2013

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Transcript of Copy of Cell Membranes

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The plasma membrane is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell.
Function
1. Protects the cell

2. Controls what enters and exits the cell
selectively permeable – it will allow some things to pass through, while blocking other things

3. Homeostasis
The Plasma Membrane
lipid bilayer: two sheets of lipids making up a single membrane
embedded with proteins and strenthened with cholesterol

phospholipids are in a shape like a head and a tail
Heads like water (hydrophilic), face out
Tails do not like water (hydrophobic), face in
include transporters, channels, receptors, enzymes, structural membrane-anchoring proteins and proteins responsible for cell adhesion
Transport across the membrane
Movement of particles from an area of high concentration to an area of low concentration

Caused by Brownian motion (movement of particles because of the movement of their atoms)

Continues until an equilibrium is reached
No energy is needed to move particles
Simple diffusion:
Passive, spontaneous, no energy use
Substance passes through the hydrophobic core with out aid
Only small hydrophobic molecules can do this
CO2, O2, ethanol

Facilitated diffusion:
Passive, spontaneous, no energy use
Cross with the aid of transport proteins

Channel proteins: tunnels particles “fall” through
Carrier proteins: bind specific molecules, then deposit the molecules across the membrane
Structure
Carrier proteins : embedded proteins change shape to open and close passages
Endocytosis: taking something into the cell.
Exocytosis: expelling something from the cell.
Passive diffusion of water across a selectively permeable membrane
physical process without input of energy
semipermeable membrane separating two solutions of different concentrations permeable to the solvent, but not the solute
Occurs until water is balanced on both sides of the membrane.
Isotonic solutions – the same dissolved solute.
Hypotonic solutions – less dissolved solute
Hypertonic solutions – more dissolved solute.
http://www.nclark.net/osmosisPocus.gif
Diffusion
Active transport
Energy is needed to move particles
Passive transport
Membrane proteins
Lipid bilayer
Includes diffusion and osmosis
All cells acquire the molecules and ions they need from their surrounding extracellular fluid
unceasing traffic of molecules and ions
goes in and out of the cell through its plasma membrane
Permanently attached to the biological membrane
Determine what particles can pass through
Act as markers that are recognized by chemicals and molecules from the inside and the outside of the cell
Specific membrane proteins recognize a substance needed
Allows it access to cross the membrane
otherwise would not:
membrane is impermeable to the substance
moved in the wrong direction of the concentration gradient
Bulk flow
Factors Affecting Diffusion Rate?
Steepness of concentration gradient
Steeper gradient, faster diffusion
Molecular size
Smaller molecules, faster diffusion
Temperature
Higher temperature, faster diffusion
Vesicles are used to transport large particles across the membrane, requires energy
Exocytosis:Cytoplasmic vesicle merges with the membrane and releases its contents
Endocytosis:membrane sinks inward, pinches off and forms a vesicle
Biological membranes are composed mainly of lipids and proteins
lipid bilayer with proteins scattered throughout
some cholesterol in the middle

Fluid mosaic model: membranes are two-dimensional fluids
both lipids and proteins are constantly in motion
Transport proteins: regulate the transport of polar molecules and ions through the membrane

Channel proteins: are pores or channels lined with certain amino acids that allow certain molecules and ions to pass through

Carrier proteins: have binding sites that grab certain molecules then changes shape and moves the molecule across the membrane

Receptor proteins: trigger cellular responces when hormones or nutrients in the extracellular fluid bind to them, trigger cellular changes like increasing metabolism, cell division, movement, secretion of hormone

Recognition proteins: serve as identification tags, are often glycoproteins, have a branched carbohydrate attached to the protein (glyco = carbohydrate) Allow cells to recognize other cells, protect your cells from your bodies immune system
Osmosis
Osmotic Pressure
Class Vote:
Water, a polar molecule, can cross the plasma membrane?:

1. Freely passes between the layers with no energy input
2. Not at all
3. Only with the help of a carrier protein and energy spent
4. Only with the help of a carrier protein to pass into a lower concentration

Raise 1, 2,3, or 4 fingers to answer
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