Module 2: Biological membranes Flashcards
What is a membrane?
a structure that separates the contents of the cell from their environment and also separates the organelles within cells
What is the name given to the formation of separate membrane bound areas in a cell
compartmentalisation
What is the name of the membrane that surrounds cells and organelles and how permeable is it?
What is its width?
the plasma membrane
its partially permeable
7nm
What are the components of the plasma membrane?
the phospholipid bilayer
intrinsic proteins
extrinsic proteins
glycoproteins and glycolipids
cholesterol molecules
Describe the structure of the phospholipid bilayer
is made up of phospholipids that have polar hydrophilic phosphate heads and non polar hydrophobic fatty acid tails
Describe the structure of an intrinsic protein and give the names of an intrinsic protein
they have an amino acid containing a hydrophobic R group on their surface which interact with the hydrophobic core keeping the proteins in place
-channel protein
What does a channel protein do
What does a carrier protein do
it provides a hydrophilic pathway that allows polar molecules to cross the membrane
plays an important role in passive and active transport by changing its shape
What does the bilayer do
it allows the membrane to be selectively permeable by preventing large/charged molecules from directly diffusing across
What is the role of glycoproteins
What is an antigen?
they play a role in cell adhesion and cell signalling by acting as receptors/antigens
a molecule on the cell surface that triggers an immune response
What is the role of glycolipids
3 points
they can be used as antigens and they also help maintain stability and facilitate cell recognition
Describe the structure and function of an extrinsic protein and name one
they contain amino acids that have hydrophilic R groups on their outer surface that interact with polar heads
-they are involved in molecule transport
-carrier protein
What are the main functions of the plasma membrane?
7
-keeps cell components inside the cell
-controls movement of substances in/out of the cell
-isolates organelles from the rest of the cytoplasm which allows cellular processes to occur separately
-acts as a site for biochemical reactions
-allows a cell to change shape
-contains receptors for other molecules (hormones)
-enables adjacent molecules to stick together
What is the name given to the plasma membrane model and why?
the fluid mosaic model
because the membrane is fluid and the arrangement of phospholipids and proteins creates a mosaic pattern
What is the role of cholesterol
it regulates membrane fluidity and adds stability
What are the different transport systems that happen across membranes
simple diffusion an facilitated diffusion
osmosis
active transport
endo and exocytosis
What is diffusion
the passive net movement of small , non polar , lipid soluble molecules from an area of high to low concentration (down their concentration gradient)
How is facilitated diffusion different to simple diffusion
it requires a transport molecule and a membrane
What is osmosis
the passive diffusion of water molecules from an area of low solute concentration to an area of high solute concentration across a partially permeable membrane
What is active transport
the net movement of molecules across a partially permeable membrane from an area of low to higher concentration against its concentration gradient
What does active transport require
ATP
What does exo/endocytosis do and how do they differ
they transport large particles by enclosing them in vesicles made from the plasma membrane
exo-out of the cell
endo-into the cell
What is a solvent and what is the main solvent used by biological organisms
its a liquid that dissolves other substances
water
What is meant by water potential
What units is it measured in
the tendency of water molecules to move
kiloPascals (kPa)
What is the water potential of pure water and if solute is added to a solution does this make the water potential less or more negative?
0kPa
more negative , water potential cant be greater than 0
Do water molecules move from less negative to more negative or vice versa?
they always move from a less negative solution to a more negative solution
What is meant by osmotic concentration and is it affected by insoluble molecules
the volume of dissolved solutes in a solution
no
Is solute potential always negative or always positive?
Is pressure potential always negative or always positive?
s-always neg
p-always pos
What does it mean if a solution is isotonic to the cell
the solution has the same osmotic conc./water potential as the cell so there is no net movement
What does it mean if a solution is hypertonic to the cell
the solution has a higher osmotic concentration than the cell so there is net movement out of the cell
What does it mean if a solution is hypotonic to the cell
the solution has a lower osmotic concentration than the cell so there is net movement into the cell
In animal cells , what is the effect of net movement in and out of the cell?
What effect do they have on plant cells?
What does plasmolysis and turgid mean?
in- causes the cell to lyse (burst)
out-causes it to shrink
in-makes the cell turgid and the vacuole becomes too full
out-causes plasmolysis and vacuole shrinks
plasmolysis-cell membrane pulled away from the cell wall
turgid-membrane pushed right up against cell wall
What factors affect the rate of diffusion? 3
concentration gradient
membrane thickness
surface area of membrane
When does active transport need to be used? 2
When does bulk transport have to be used?
when cells need to move substances quickly
when they need to move substances against their concentration gradient
when extremely large/large quantities of substances need to be transported across the membrane
What 2 factors affect membrane permeability and structure?
temperature and solvents
What happens to the plasma membrane when the temperature is increased?
the phospholipids have more kinetic energy so move more which makes the membrane more fluid
HOWEVER if temperature continues to increase the membrane loses its structure and becomes more permeable
carrier and channel proteins also denature at high temperatures
Why does a high temperature cause the membrane to lose its structure?
because the phospholipids gain more and more kinetic energy meaning they collide with each other with great force , causing gaps to emerge in the bilayer and eventually breaking down the molecules due to the collisions
What effect does a solvent have on membrane structure and permeability
they dissolve the membranes
non polar molecules such as alcohol molecules can enter the cell membrane and stay between the phospholipids disrupting the membrane which makes it more permeable
