Cell Membrane Flashcards
The cell membrane can be described as a _____ _______ model”
fluid mosaic
Why is the cell membrane called a fluid mosaic model?
it has fluid with a mosaic of proteins
Describe the phospholipid bilayer
phosphate head, lipid tail
Define amphipathic
a molecule that’s hydrophobic and hydrophilic
Define semi-permeable
allows only some materials through
_____ __________ _______ can dissolve in the lipid bilayer
Small nonpolar molecules
Give an example of small nonpolar molecules
hydrocarbons
_____ ______ _________ do not
cross the membrane easily
large polar molecules
Give an example of large polar molecules
sugars
What is a freeze-fracture?
a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer
How does the cell membrane maintain fluidity?
The phospholipids constantly trade places from side to side. Every once in a while they will trade with a phospholipid from the other layer.
High temperatures cause ____ movement, lower temperatures cause ____.
more; less
Describe cholesterol
a steroid hormone found in membranes to help maintain fluidity
Where are integral proteins located?
they go through the whole membrane
Where are peripheral proteins located?
they sit on the outside of the membrane (inside of the cell).
Cell membrane proteins do what six main things?
- Transport materials in and out
- Act as Enzymes
- Pass signals
- Identify other cells
- connect to other cells
- attach the cytoskeleton to the ECM fibers
How to carbohydrates aide cell recognition
Carbohydrates can bond to the lipids (glycolipids) or more often proteins (glycoproteins) in the membrane by protruding from the membrane.
Define passive transport
requires no energy
Define simple diffusion
molecules move from an area of higher concentration to lower concentration
In simple diffusion, molecules move ____ their concentration gradient
down
Simple diffusion occurs until occurs until what happens?
equilibrium is reached
Define osmosis
diffusion of water molecules thru a selectively permeable membrane
Osmosis moves molecules from ____ to ____ water concentration
high; low
the force exerted by osmosis is called _______ _________
osmotic pressure
Define hypertonic solution
more dissolved material in solution than in the cell
What happens into a cell in a hypertonic solution?
water flows out of the cell and the cell shrivels up
Define hypotonic solution
more dissolved material in the cell than in the solution
What happens to a cell in a hypotonic solution?
water flows into the cell and increases osmotic pressure. the cell may burst
Define isotonic solution
same amount of dissolved material in the solution and cell
What happens to a cell in a isotonic solution?
equilibrium is reached
Animal cels prefer which type of solution?
isotonic
Plant cells prefer which type of solution?
hypotonic
Define osmoregulation
control of water balance
Why don’t cells burst?
-cells in organisms don’t usually come into contact with pure water -plant cells have cell walls that keep the cell from expanding -some cells use pumps
Describe facilitated diffusion
diffusion with the assistance of integral transport proteins (Still Passive transport)
What do channel proteins do?
allow certain materials to flow in and out (down their concentration gradient.)
What is a aquaporin?
channel protein that only lets water in
What are ion channels
also called gated channels, open and close in response to a chemical or electrical stimulus
What do carrier porteins do?
change shape to escort certain material in and out of the cell
Define active transport
Proteins act as pumps to move material from low to high concentration
The proteins that act as pumps in active transport are called what?
electrogenic pumps
Active transport requires _______
energy
What does the Sodium-Potassium pump do?
pumps sodium out and potassium in. (low to high concentration)
What does a electrochemical gradient do?
moves the ions across the membrane like an electric current to do work
How does a electrochemical gradient work?
Pumps create a build up of ions on either side of the membrane, which creates an electric charge. The charge causes an electrochemical gradient
Define cotransport
electrochemical gradient used to move other molecules across the membrane
Define endocytosis
a vesicle formed to take materials into the cell
Define exocytosis
a vesicle putting materials out of the cell
What are the 3 types of endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor mediated endocytosis
Describe phagocytosis
engulfing solid particles
Describe pinocytosis
engulfing liquid substances (extracellular fluid)
Describe receptor mediated endocytosis
particles called ligands bind to receptors, which signals the engulfing of the particles.
What is the difference between channel proteins and carrier proteins?
Solutes diffuse through the pore of channel proteins, whereas carrier proteins bind solutes on one side of membrane and release it on the other side. Also, carrier proteins have very slow transport rates.
How is membrane fluidity influenced by membrane composition?
Membranes must be fluid to work properly. Saturated fats (ex: butter) make it “stiff” because they are solid at room temperature. Unsaturated fats (oil) helps it “bend” which helps the cell work better - liquid at room temperature
How does cholesterol resist changes in membrane fluidity with temperature change?
Cholesterol at moderate temperature reduces membrane fluidity by reducing phospholipid movement, but at low temperatures, it hinders solidification by disrupting the regular packing of phospholipids.
Define tonicity
ability of a solution to cause a cell to gain or lose water
Define turgid
buildup of water in a cell that makes the cell swollen.
If a plant cell is flaccid, it is in a __ environment
isotonic
If a plant cell is turgid, it is in a __ environment
hyptonic
What can speed up the process of osmosis?
the presence of aquaporin.
Active transport uses energy to move solutes __ their gradients
against
Explain how large molecules are transported across a cell membrane.
Through a process called endocytosis, in which molecules enter cells within vesicles that pinch inward from the plasma membrane.
