2B Cell Membranes Flashcards
Give 5 roles of a membrane
- Partially permeable barrier
- Has binding sites
- Confers antigenic properties to the cell
- Site of certain reaction
- Compartmentalises different cell reactions in organelles
What is the main constituent of the cell membrane?
Phospholipids
What is the structure of phospholipids like?
It is similar to the structure of other lipids
What is the role of phospholipids in the cell membrane?
- Allow lipid soluble substances to enter + leave the cell
- Prevents water soluble substances from moving
How do phospholipids affect the structure of the membrane?
It makes the membrane flexible and self-sealing
What is the model called to describe the arrangement of the phospholipids in the membrane?
Fluid mosaic model
What is cholesterol?
A fatty substance
What role does cholesterol have in a cell membrane?
- It is hydrophobic - therefore it pulls the tails together
- This adds strength + rigidity to the membrane
What reduces the movement of other molecules in the membrane?
Cholesterol
Why is the structure of membrane called a fluid mosaic model?
- Phospholipids bilayer has proteins embedded in it
- Phospholipids can move freely through the bilayer
What is a glycolipid?
A carbohydrate bound to a lipid
What is a glycolipid like?
The lipid portion is embedded in phospholipid bilayer
Carb portion extends outside cell
What is the role of a glycolipid?
Act as recognition + binding sites
What are the two types of protein in the membrane?
- Intrinsic proteins
- Extrinsic proteins
What is an intrinsic protein?
Span the membrane and act as channel + carrier proteins
What are intrinsic proteins made of?
Protein only
What are extrinsic proteins?
On the surface of the membrane (internal or external)
Act as receptors/enzymes
What are extrinsic proteins made of?
Many have carbohydrates attached, forming a glycoprotein
What is diffusion?
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
What sort of molecules can diffuse across the membrane?
Small, non-polar molecules i.e. oxygen and CO2
Is diffusion passive?
Yes - no energy is required for this process
Is facilitated diffusion passive?
Yes
Where does the energy for facilitated diffusion come from?
The process relies on the kinetic energy of diffusion molecules
Does facilitated diffusion occur up of down a conc. gradient?
down
How does facilitated diffusion occur?
- Through transmembrane channels + carriers
- It has to happen at these specific points
What are protein channels?
Water filled hydrophilic channels
Protein channels are selective, what does this mean for the tendencies of the channel?
The channel will remain closed unless the specific ion is present
What do protein channels let through?
Specific water soluble ions
How does a carrier protein work?
Molecule binds to protein, which causes it to change shape + is then released
What energy do carrier proteins use for the required process?
Only use the kinetic energy of the molecules
Do molecules have to be specific to the carrier protein?
Yes they only let certain molecules through
What is osmosis?
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
What water potential does pure water have?
0
What is water potential measured in?
Units of pressure - kPa
What are the units for water potential?
Psi