Module 2 Section 5 - Cell Membranes Flashcards
What do membranes control
Membranes control what passes through them
What are membranes at the surface of the cell
They are barriers between the cell and its environment
What does the membranes at the surface of cells control
Controls which substances enter and leave the cell
What is said about the permeability of membranes on the surface of the cell
They are partially permeable - they let some molecules through but others not
How would substances typically move across membranes at the surface of cells
Diffusion
Osmosis
Active transport
What do membranes on the surface of the cell allow
Recognition by other cells
Cell communication
What are membranes within cells
The membranes around organelle divide the cell into different compartments. Making functions more efficient.
What can membrane within cells form
Vesicles to transport substances between different areas of the cell
What do membranes within cells control
Which substances enter and leave the organelle, they are also partially permeable
Can you find membranes within organelles
Yes - these act as barriers between the membrane contents and the rest of the organelle
Membranes within cells can be the site of what
Site of chemical reactions
Cell membranes have a
Fluid mosaic structure
What are all membranes composed of
Lipids (mainly phospholipids), proteins and carbohydrates (usually attached to protein or lipids)
In 1972 what was suggested to describe the arrangement of molecules in the membrane
The fluid mosaic model
In the fluid mosaic model what forms a continuous double layer (bilayer)
Phospholipid molecules
Why is the phospholipid bilayer fluid
Because the phospholipids are always moving
What is present within the bilayer
Cholesterol
What is scattered throughout the bilayer
Protein molecules
What are glycoproteins
Some proteins that have a polysaccharide chain attached to it
What are glycolipids
lipids that also have a polysaccharide chain attached to it
What are the different components of the cell membrane
Phospholipid
Cholesterol
Proteins
Glycolipids
Glycoproteins
Phospholipid molecules have a
Head and tail
The Phospholipid head is
Hydrophilic - attracts water
The phospholipid tail is
Hydrophobic - repels water
How are the phospholipid molecules arranged
They automatically arrange themselves into a bilayer - head face out towards the water on either side of the membrane
The centre of the bilayer is
Hydrophobic meaning the membrane doesn’t allow water soluble substances through it
What does cholesterol give to a cell membrane
Gives the membrane stability
What is cholesterol
A type of lipid
Is cholesterol present in all membranes
Yes
Where does cholesterol fit in
Cholesterol molecules fit in between the phospholipids, they bind to the hydrophobic tails causing them to pack more closely meaning the membrane is less fluid and more rigid
What do proteins control in the cell
Proteins control what enters and exits the cell
Some protein form what in the membrane
channels in the membrane which allow small or charged particles through
Other proteins (carrier proteins) transport what
Molecules and ions across the membrane by active transport and facilitated diffusion
Proteins can acts as
Receptors for molecules in cell signalling, when a molecule binds to the protein a chemical reaction is triggered inside the cell
What do glycolipids and glycoproteins do for the cell
Act as receptors for messenger molecules
How do glycolipids and glycoproteins stabilise the cell
They form hydrogen bonds with surrounding water moelcules
Glycolipids and glycoproteins are sites where what bind
Drugs
Hormones
Antibodies
Glycolipids and glycoproteins are also what
Antigens
Cell signalling is..
How cells communicate with each other
How do cells communicate with each other
Messenger molecules
Describe the three steps a messenger molecule makes to communicate with other cells
-one cell releases a messenger molecule
-this molecule travels to another cell
-the messenger molecule is detected by the cell because it binds to a receptor on its cell membrane
What plays an important role in cell signalling
Cell membrane receptors
What act as receptors for messenger molecules
Proteins in the cell membranes (membrane-bound receptors)
What is specific about receptor proteins
Their shape
What can bind to the receptor proteins
Only messenger molecules with a complementary shape can bind to them
Different cells have different….
Types of receptors - they respond to different messenger molecules
What is a cell that responds to a particular messenger molecule called
Target cell
How do many drugs work
By binding to the receptors in cell membranes, they either trigger a response or block the receptor and prevent it from working
How can you investigate the permeability of a membrane
Beetroot cells contain a coloured pigment that leaks out - the higher the permeability the more pigment leaks out.
What affects the permeability of a membrane
Temperature
Solvent type
Solvent concentration
What happens to the permeability of a membrane if the temperature is below 0°c
-The phospholipid pack more closely due to not much energy and the membrane becomes rigid
-The channel and carrier proteins in the membrane deform increasing the permeability
-Ice crystals may form and pierce the membrane further increasing the permeability.
What happens to the permeability of a membrane if the temperature is between 0°c - 45°c
Phospholipids aren’t as packed because they can move around - the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy and this increases permeability
What happens to the permeability of a membrane if the temperature is above 45°c
The phospholipids start to melt and membrane becomes more permeable. The water inside the cell expands putting pressure on the membrane and channel and carrier proteins deform so they can’t control what enters and exits the cell which increases permeability.
What happens to the permeability of a membrane if you surround it in a solvent
A solvent such as ethanol increases membrane permeability of the cell membrane
Why does surrounding the cells in a solvent increase membrane permeability
This is because solvents dissolve the lipids in a cell membrane so the membrane loses its structure
What happens to the permeability of a membrane if you increase the concentration of the solvent
The permeability of the membrane will increase
