Pack 3 - Transport across cell Membrane Flashcards
Name the 5 basic components of the cell membrane.
- Phospholipids
- Cholesterol
- Proteins
- Glycoproteins
- Glycolipids
Describe the arrangement of phospholipids in the cell membranes and why it is like this.
- Hydrophilic heads point to outside the cell - attracted by water inside and outside the cell.
- Hydrophobic tails of both phospholipid layers point into the centre of the membrane - repelled by water.
What are the 3 functions of phospholipids in the cell
Membrane?
- To allow lipid soluble substances to enter and leave the cell.
- To prevent water soluble substances from entering and leaving the cell.
- To make the membranes flexible and self-sealing
Name the two types of protein in the cell membrane and their 6 functions.
Intrinsic (channel/carrier)
• transport water soluble substances across the membrane through channel proteins.
• allow active transport though carrier proteins.
Extrinsic (surface) proteins. • structural support • receptors, e.g. hormones • cell-surface receptors for identifying cells • help cells adhere and together
Name the 3 functions of cholesterol in the cell membrane.
- Reduce lateral movement of other molecules. (Strength)
- Make the membrane less fluid at higher temperatures
- Prevent leakage of water and dissolved ions from the cell (very hydrophobic).
Give 3 functions of glycolipids in the cell surface membrane.
- Recognition sites
- Help to maintain stability of the membrane
- Help cells attach to one another
Give a specific example of how glycolipids function on the cell surface membrane.
ABO blood system operates due to glycolipids acting as cell-surface receptors for specific chemicals.
Give 4 functions of glycoproteins in the cell surface membrane.
- Recognition sites
- Help cells attach to one another, forming tissues
- Allows cells to recognise one another (e.g. lymphocytes can recognise an organisms own cells)
- Cell-surface receptors for hormones and neurotransmitters
Give 4 reasons most molecules do not freely diffuse across the phospholipid bilayer.
- Not lipid soluble
- Too large
- Of the same charge as protein channels (repelled).
- Polar (cannot pass through phospholipid bilayer)
Why is the cell surface membrane described using the ‘fluid-mosaic’ model?
Fluid - individual phospholipid molecules move relative to one another, it is flexible/constantly changing shape.
What is the main difference between active and passive transport?
Active requires metabolic energy from ATP.
Passive does not (still requires kinetic energy molecules possess).
Define diffusion.
The NET movement of molecules or ion from a region of HIGHER concentration to a region of LOWER concentration until DYNAMIC equilibrium is reached.
Is facilitated diffusion a passive or active process?
Passive
What is required for facilitated diffusion to take place in the cell membranes (three things)?
- Carrier/channel proteins
- Difference in concentration gradient
- Kinetic energy of the molecules
Define facilitated diffusion.
Diffusion of specific molecules (down a concentration gradient) at specific points in the cell membrane (carrier/channel proteins).
Describe, using 4 points, how channel proteins work.
- Water-filled hydrophilic channels.
- Specific water-soluble ions.
- Only open in the presence of a specific ion.
- Ions bind causing it to change shape so that it remains closed on one side of the membrane but opens on the other.
Describe, using 2 points, how carrier proteins work.
- A molecule (e.g.glucose), specific the protein shape, binds to the protein.
- This causes the protein to change shape, so that the molecule is released on the other side of the membrane.
Define osmosis.
The passage of water from a region of HIGHER water potential (Ψ) to a region where it has a LOWER Ψ through a SELECTIVELY permeable membrane until dynamic equilibrium is established.
What is the Ψ of pure water?
0 kPa
If a red blood cell is placed in a solution with a HIGHER water potential than that of the cell, what will happen to the cell?
- Water will enter the cell.
* The cell will swell and eventually burst.
If a red blood cell is placed in a solution with a LOWER water potential than that of the cell, what will happen to the cell?
- Water will leave the cell.
* The cell will shrink/shrivel.
If a red blood cell is placed in an ISOTONIC solution, what will happen to the cell?
No change.
If a plant is placed in a solution with a HIGHER water potential than that of the cell, what will happen to the cell? What word(s) describes the condition of the cell?
- Water will enter the cell.
- Protoplast will swell
- The cell becomes TURGID
If a plant is placed in a solution with a LOWER water potential than that of the cell, what will happen to the cell? What word(s) describes the condition of the cell?
- Water will leave the cell.
- The protoplast shrinks
- This is called PLASMOLYSIS
