Cell Membranes & movement Flashcards
(30 cards)
the cell surface membrane
a plasma membrane which surrounds cells and forms the boundary between the cell cytoplasm and the environment
what are the functions of the cell-surface membrane?
forms a barrier between two environments
allows different conditions to be established and maintained
controls the movement of substances between environments - partially permeable
What is a phospholipid?
made of a hydrophilic phosphate head and a hydrophobic hydrocarbon tails forming a bilayer
what is the function of a bilayer?
allows lipid-soluble substances to enter and leave the cell,
prevents water-soluble substances entering and leaving the cell,
makes the membrane flexible and self-sealing which provides structure
What do enzymes do embedded in the cell-surface membrane?
Speed up reactions in the cell and meditate a response
Plasma membrane
all membranes around and within cells cells have the same basic structure
What do extrinsic proteins embedded in the phospholipid do?
Serve as receptor molecules eg: for hormones
What do intrinsic proteins do?
Some act as carriers to transport water soluble material across the membrane
What is the overall function of proteins?
Provide structural support
Act as channels - allow active transport
From cell membrane receptors
What is the role of cholesterol in the cell-surface membrane?
Add strength
Maintain fluidity and integrity
Prevents loss of water as hydrophobic
Pulls the fatty acids tails close together preventing lateral movement and therefore increasing stability
What is the role of glycolipids in the cell-surface membrane?
Act as recognition sites
Maintains stability of the membrane
Helps cells attach to one another & form tissues
What is the role of glycoproteins in the cell-surface membrane?
Act as recognition sites - receptors
Aids the formation of tissues
What does the carb chain do?
Combines with lipids to form larger molecules
What does the hydrophilic channel do?
Allows facilitated diffusion to occur - highly selective
What is the pore for?
Get, store and distribute resources
Capture, absorb and filter liquids
Why are some molecules not able to diffuse across the cell-surface membrane?
As they are not soluble in lipids so can’t pass through the phospholipid bilayer, they are also too large to pass through the channels or have the same charge (or are polar so are repelled by the non-polar hydrophobic tails) as the charge on the protein channel so are repelled
Why is the cell-surface membrane referred to as a fluid mosaic model?
Fluid because the phospholipid molecules can move relative to one another and mosaic because the proteins in the bilayer vary in shape, size and pattern
what is the ease at which the proteins move dependent on?
The number of phospholipids with unsaturated fatty acids
What are protein carriers?
Proteins responsible for moving substances across the plasma membrane
Define simple diffusion?
The passive net movement of molecules from an area of high concentration to an area of lower concentration.
What are the factors that increase the rate of diffusion?
Larger surface area
Thinner absorbing surface
Increased temperature
Steep concentration gradient
Define facilitated diffusion?
The passive net movement of molecules from an area of high concentration to an area of lower concentration with the aid of a protein carrier
What is a protein channel?
Water filled membrane bound hydrophilic channel across the width of the membrane allowing specific water-soluble ions to pass through
What is a carrier protein?
A large molecule binds to the protein causing a change in shape of the protein so the molecule is able to be released into the membrane on the opposite side, the protein then reverts back to its original shape
