Cell Membrane Flashcards
Plasma Membrane model in 1935 by J.R. Danielli and H. Davson, proteins also part included
Sandwich Model
Plasma Membrane model in 1950 by J.D. Robertson
Unit Membrane Model
Plasma Membrane model in 1972 by S.J. Singer and G.L. Nicolson
Fluid Mosaic Model
made of Phospholipids
Plasma Membrane
Red Blood Cells analyzed
Enough for Phospholipid bilayer
Polar heads face out and Nonpolar tails face in
Does not explain why some
nonlipids are permeable
Gorter and Grendel
2 layers of globular proteins with phospholipid inside to make a layer and then join 2 layers together to make a channel for molecules to pass
Sandwich Model
Outer layer of protein with phospholipid bilayer inside, believed all cells same composition, does not explain how some molecules pass through or the use of proteins with nonpolar parts, used transmission electron microscopy
Unit Membrane Model
Phospholipid bilayer with proteins partially or fully imbedded, electron micrographs of freeze-fractured membrane
Fluid Mosaic Model
Structure of the Plasma Membrane
Phospholipid bilayer
Hydrophilic head
Hydrophobic tails
Transmembrane / Intrinsic / Integral
Peripheral / Extrinsic
the plasma membrane is the consistency of olive oil at body temperature, due to unsaturated phospholipids.
Fluid
cells differ in the amount of _________
unsaturated to saturated fatty acid tails
at body temperature it lessens fluidity by restraining the movement of phospholipids, at colder temperatures it adds fluidity by not allowing phospholipids to pack close together
Cholesterol affects fluidity
membrane proteins form a collage that differs on either side of the membrane and from cell to cell (greater than 50 types of proteins), proteins span the membrane with hydrophilic portions facing out and hydrophobic portions facing in. Provides the functions of the membrane
Mosaic
Proteins of the Plasma Membrane Provide 6 Membrane Functions
1) Transport Proteins
2) Receptor Proteins
3) Enzymatic Proteins
4) Cell Recognition Proteins
5) Attachment Proteins
6) Intercellular Junction Proteins
How do materials move into and out of the cell?
Materials must move in and out of the cell through the plasma membrane.
Some materials move between the phospholipids.
Some materials move through the proteins.
three types of passive transport?
Diffusion
Facilitated Diffusion
Osmosis
Molecules can move directly through the phospholipids of the plasma membrane
Diffusion
Materials that pass through the plasma membrane by diffusion
Gases (oxygen, carbon dioxide)
Water molecules (rate slow due to polarity)
Lipids (steroid hormones)
Lipid soluble molecules (hydrocarbons, alcohols, some vitamins)
Small noncharged molecules (NH3)
the net movement of molecules from a high concentration to a low concentration until equally distributed.
Diffusion
Diffusion rate factors
temperature, pressure, state of matter, size of concentration gradient, and surface area of membrane.
substances diffuse through membranes without work by the cell or atp usage
passive transport
Molecules can move through the plasma membrane with the aid of transport proteins
Facilitated Diffusion
is the net movement of molecules from a high concentration to a low concentration with the aid of channel or carrier proteins.
Facilitated Diffusion
How do molecules move through the plasma membrane by facilitated diffusion?
Channel and Carrier proteins
Water Molecules can move directly through the phospholipids of the plasma membrane
Osmosis
is the diffusion of water through a semipermeable membrane. Water molecules bound to solutes cannot pass due to size, only unbound molecules. Free water molecules collide, bump into the membrane, and pass through.
Osmosis
water travels from an area of higher concentration to an area of lower water concentration
Osmosis
Movement _____ when osmotic pressure equals hydrostatic pressure
stops
refers to the total solute concentration of the solution outside the cell.
Tonicity
What are the three types of tonicity
Isotonic
Hypotonic
Hypertonic
prevents bursting of plasma membrane
cell wall
is normally bathed in a very hypotonic solution. It takes in water until the cell is full.
plant cell
A plant cell placed in a ____________ solution loses water. Ultimately outward flow stops when the cytosol concentration matches that of the solution.
hypertonic
use osmosis in hypotonic soil to maintain rigidity
Plants
the pressure of water molecules against the cell wall. The cell swelling stops when the expanding membrane hits the cell wall.
Turgor Pressure
when a plant wilts (sags) in a hypertonic environment, since the water in the cells diffuses out and turgor pressure is lost
Plasmolysis
three types of Active transport
1) Active Transport
2) Exocytosis
3) Endocytosis
types of Endocytosis
Phagocytosis
Pinocytosis
Receptor-Mediated endocytosis
ATP energy is required to move the molecules through
Active transport
Molecules move from areas of low concentration to areas of high concentration with the aid of ATP energy.
Requires protein carriers called Pumps
Active Transport
occurs when active transport of a solute indirectly drives transport of other substances
Cotransport
Plants commonly use the gradient of __________ generated by ___________ to drive active transport of nutrients into the cell
hydrogen ions, proton pumps
Importance of Active Transport
Bring in essential molecules: ions, amino acids, glucose, nucleotides
Rid cell of unwanted molecules
Maintain internal conditions different from the environment
Regulate the volume of cells by controlling osmotic potential
Control cellular pH
Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium-Potassium pump and Proton pumps)
Movement of large molecules bound in vesicles out of the cell with the aid of ATP energy (i.e. cell wall materials). Vesicle fuses with the plasma membrane to eject macromolecules.
Exocytosis
example molecules that uses exocytosis
Proteins, polysaccharides, polynucleotides, whole cells, hormones, mucus, neurotransmitters, waste
Movement of large molecules into the cell by engulfing them in vesicles, using ATP energy.
Endocytosis
“Cellular Eating” – engulfing large molecules, whole cells, bacteria
Phagocytosis
examples of cells that do phagocytosis
Ex. Unicellular organisms engulfing food particles.
“Cellular Drinking” – engulfing liquids and small molecules dissolved in liquids; unspecific what enters.
Pinocytosis
Types of Cell Junctions in animal cells
Tight Junctions
Desmosomes
Gap Junctions
Types of Cell Junctions in plant cells
Plasmodesmata
Channels between the cell walls of plant cells that are lined with the plasma membranes of adjacent cells and smooth ER runs through
Plasmodesmata
Allows for the exchange of cytosol between adjacent cells; moving water, small solutes, sugar, and amino acids.
Plasmodesmata
parts of the plant that uses Plasmodesmata
Xylem and Phloem in Plants
It is a quantitative description of the free energy states of water.
Water Potential
The concepts of free energy and water potential are derived from the
second law of thermodynamics
is based on the ability of water to do work
Water Potential
Forces that act on any molecule which affect its ability or potential to do work:
pressure
concentration
electrical
gravity
Pressure + Concentration + Electrical + Gravity =
Chemical Potential
greek symbol for Water Potential
ΨW, is the letter ‘psi’ (pronounced ‘sigh’)
not simplified Definition of Ψw
ΨW = ΨP + ΨS + ΨM + ΨE + ΨG
meanings of
ΨP
ΨS
ΨM
ΨE
ΨG
ΨP = pressure potential
ΨS = osmotic or solute potential
Ψm = membrane potential
ΨE = electrical potential
- ignore because water is uncharged
ΨG = gravitational potential
- ignore because gravity is not a large force for small trees
Simplified Definition of Ψw
Ψw = ΨP + ΨS + ΨM
- represents the pressure in addition to atmospheric pressure
pressure potential
represents the effect of dissolved solutes on water potential;
osmotic or solute potential
addition of solutes will always ______ the water potential
lower
represents the effect of other membranes in the cell on water potential
membrane potential
Water Potential of Plant Tissue
has _____ components and is always ____
Water Potential of Plant Tissue has three components and is always negative
Water Potential of Plant Tissue three components
Pressure Potential (+)
Osmotic or Solute Potential (-)
Membrane Potential (-)
Pure water water potential
Ψw = 0
pressure that keeps cell membrane pressed against cell wall
Membrane potential
water potential
soil>roots
true
water potential moves from greater water potential to lesser water potential
true
allow ions, small solutes, and water to pass in facilitated diffusion
Channel Proteins
move glucose and amino acids in facilitated diffusion
Carrier Proteins
Facilitated diffusion is rate limited, by
the number of proteins channels/carriers present in the membrane.
The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries
draws fluid back in
Osmotic pressure
forces fluid out of the capillary
The pressure exerted by a fluid at equilibrium at any point of time due to the force of gravity
hydrostatic pressure
