Module 2.5 Biological Membranes Flashcards
What are the functions of membranes within the cell
They compartmentalise the cell (substances needed for respiration are inside the mitochondria)
They act as a barrier (only certain things can leave, for example mRNA from the nucleus)
They also act of a site for chemical reactions
Also there are membranes within the cell (organelles)
Can form vesicles for transport
What is the function of membranes out of the cell
Partially permeable
Allow recognition by other cells
Can you draw the plasma membrane
Can water soluble molecules pass through the phospholipid bilayer
No, because the centre of the bilayer is hydrophobic. So water soluble cannot pass through.
But fat soluble ones can
Describe what a phospholipid looks like
Hydrophilic head
Hydrophobic tail
Hydrophobic tails face each other whereas the hydrophilic tails point outside towards the water.
What the structure and role of cholesterol
Structure- has a flattened shape, allows it fit through bilayer. It is part hydrophobic and part hydrophilic
Function- stabiles the membrane, they control the fluidity. Bind phospholipids more closely to make the membrane more rigid and less fluid
What two kinds of proteins are in the cell surface membrane
Extrinsic
Intrinsic
What is the role of a carrier and channel proteins
Can transport charged molecules across the bilayer.
Carrier proteins can change shape.
The proteins can be used for specific ions, like a sodium channel
What is the role of glycoproteins and lipids
Can help stabilise the membrane by forming hydrogen bonds with water molecules
glycoprotein: Cell communication
glycolipid: Cell recognition
Can you draw two molecules of water
What two things can affect a membrane permeability
Solvents
Temperature
What does a solvent do in the plasma membrane
It dissolves the lipids
So plasma membrane loses structure
Makes membrane more fluid
What would happen to the plasma membrane under 0 degree C
Phospholipids packed closely together
Membrane is rigid
Not that much movement
Channel proteins denature
Ice crystals form which pierce membrane when it thaws
Membrane more fluid
What happens when the temperature is between 0 and 45 degree C
Kinetic energy increases
Phospholipids vibrate more
Membrane is partially permeable
What happens to the membranes permeability above 45 degree C
more kinetic energy so more vibrations
bilayer melts
Membrane becomes more permeable
Proteins denature
How do cells communicate with each other
Through cell signalling
What would happen if cells could not communicate
Functions in the body would not work properly
Could cause diseases like diabetes, cancer
Cell division would not occur
It would be very bad
Explain how cells surface membranes contribute to cell signalling
So a signal is released
Glycoproteins/lipids act as receptors
The receptor is specific to the signal(messenger molecule)
The shape of the receptor and the signal are complimentary
The binding of signal and receptor causes a change in the target cell
Cell surface membrane allows entry of some signal molecules
Which component becomes more fluid as temperature increases
Phospholipids bilayer
What component of the cell surface membrane becomes denatured when temperature increases
Proteins (channel, carrier)
Why is the fluid mosaic model called the fluid mosaic model
Fluid- because the phospholipids bilayer keeps moving
Mosaic- proteins are dotted around
The student concluded that yeast cells are killed between 50 °C and 70 °C.
Suggest one way in which the student could have improved the accuracy of this experiment
and one way in which he could have improved the reliability
Exam question
Accuracy
Take temperatures between intermediate temperatures (50 to 70 degree C)
Reliability
Take more readings at each temp
Give two examples as hormones as messenger molecules
FSH
Glucagon
Explain how glycoproteins can act as receptors
Help with communication between cells
Cell recognition/identification
Work together to trigger a résponse
Define diffusion
Net movement of particles down a concentration gradient
Facilitated diffusion requires a protein channel
What factors affect diffusion
- Temperature (particles vibrate more)
- Surface area to volume ratio
- Concentration gradient
- distance (thinner the membrane, more diffusion)
Define active transport
Movement of particles from an area of low concentration to a high font
- against concentration gradient
- using energy involving protein carriers
Define bulk transport
Active transport of large molecules
What is endocytosis
-molecule enters cell
-membrane engulfs thing
Examples: phagocytosis, pinocytosis
What is exocytosis
- Exit cell
- fuses with cell membrane
- released
Define osmosis
- Net movement of water down a water potential gradient
- through partially permeable membrane
What happens to an animal and plant cell in a hypertonic solution
Animal- water will leave animal cell through osmosis. The cell will then shrivel up
Plant- water will leave plant through osmosis, the cell will become plasmolysed, plasma membrane detaches from cell wall
What will happen to a plant and animal cell in a hypotonic solution
Animal cells- water will move Into cell by osmosis, the cell will burst
Plant cells- water will move into cell by osmosis, the cell will become turgid. Plasma membrane will push against cell wall.
