Chapter 5 - Plasma Membranes Flashcards
What are the roles of membranes at the surface of cells?
- partially permeable barrier between cell and its surroundings
- allows for cell signalling
What are the roles of membranes within the cells?
- partially permeable membranes act as barriers between organelle and cytoplasm
- chemical reactions take place
- vesicles can be formed
- molecules can leave and enter (ie RNA leaving nucleus)
Describe how the phospholipid bilayer is arranged.
(1) phospholipid bilayer:
- phospholipids aligned with hydrophilic heads pointing outwards, hydrophobic tails facing inwards
What is the structure of cholesterol in the phospholipid bilayer, how is it binded and what is its function?
Cholesterol:
- lipid like molecule
- binds to hydrophobic tail of phospholipids
- packs phospholipids close together and decreases fluidity and makes them rigid
- at low temperatures, cholesterol prevents from packing closely and increases fluidity
What are the two types of proteins in the phospholipid bilayer?
intrinsic and extrinsic proteins
What is an intrinsic protein?
transmembrane (goes through both layers of phospholipid bilayer)
What are the two types of intrinsic proteins and how are they embedded into the membrane?
channel and carrier proteins
- have hydrophobic R groups on outer surface and bind to hydrophobic tails in phospholipid bilayer
What are two other carbohydrate based molecules in the membrane and what are their functions?
glycolipids:
- cell markers/ antigens
- recognised by immune system as self/ non self cells
glycoproteins:
- cell adhesion
- site where hormones can bind to
- act as receptors for cell signalling
What affects membrane structure and permeability?
(1) increasing temperature
- phospholipids have more KE therefore vibrate
- membrane becomes more fluid, loses its structure
- increases permeability
(2) solvents
- phospholipids dissolve in alcohol
- increases permeability
What substances can/ cant pass through the phospholipid bilayer?
- polar molecules, ions (charged molecules) cant pass straight through phospholipid bilayer (hydrophobic tails act as a barrier)
- lipid soluble molecules can pass straight through membrane through diffusion
Describe the procedure (including equipment) of how you could investigate membrane permeability.
method:
(1) cut 5 equal pieces of beetroot
(2) wash them thoroughly
(3) place each piece in 100 ml of distilled water each increasing by 10 degrees
(4) samples taken after 5 mins of the beetroot being soaked
(5) absorbance measured with a colorimeter
equipment:
- colorimeter (cuvettes)
- beetroot
PAG:
Why are the beetroot pieces washed under water?
to remove any surface pigment released by damaged cells
PAG:
Why were samples of the water containing beetroot taken after 5 mins of soaking?
to allow the mixture to equilibrate
PAG:
Why is the experiment repeated three times?
to increase reliability
PAG:
Why was the absorbance of the samples measured using a colorimeter with a blue filter?
because the pigment of the beetroot is red
PAG:
How does the amount of pigment affect the absorbance?
more pigment - absorbs the light therefore less light is transmitted
What is diffusion/ facilitated difusion?
The passive movement of particles from a region of high concentration to low concentration (down a concentration gradient)
How does facilitated diffusion differ from diffusion?
- facilitated diffusion requires the use of channel/ carrier proteins
- facilitated diffusion occurs when large molecules, polar molecules/ ions need to be transported
How are ions/ polar molecules transported through channel proteins?
channel proteins have a pore through which the molecules can diffuse through
How can large molecules travel through carrier proteins?
molecule attaches to carrier protein, it changes shape and allows molecule to pass through
What is active transport?
The active movement of particles from a low concentration to a high concentration (against concentration gradient)
How does active transport work through a plasma membrane?
- uses carrier protein
- molecule attaches to carrier protein
- ATP binds to protein and gets hydrolysed (breaks into ADP + P)
- P binds to carrier protein and changes its shape making pathway for molecule to pass through
- P released from carrier protein and binds with ADP to form ATP again
What are the two type of bulk transport (bulk transport)?
endocytosis and exocytosis
What are the two types of endocytosis and describe how it occurs?
phagocytosis (solids)
pinocytosis (liquids)
- membrane starts to bend inwards when molecule comes near it, gets engulfed by plasma membrane forming a vesicle
- vesicle is pinched off and moves into cytoplasm
Describe how exocytosis occurs.
- vesicles formed by Golgi apparatus move towards plasma membrane
- contents of the vesicle are released
What is osomosis?
The net movement of water particles through a partially permeable membrane from a region with a high water potential to a region with a low water potential
What will happen to an animal cell when put into a hypotonic, isotonic and hypertonic solution?
hypotonic - cytolysis (burst)
isotonic - remain the same as water is entering + leaving the cell at the same rate
hypertonic - crenate (shrivel)
What will happen to an plant cell when put into a hypotonic, isotonic and hypertonic solution?
hypotonic - turgid
isotonic - remains same as movement of water is equal rate
hypertonic - plasmolysed (shrivel)
What are the factors affecting diffusion?
(1) temperature - higher temp, faster rate of diffusion as particles have more KE and moving at faster rate
(2) difference in concentration - steeper the concentration gradient, faster the rate of diffusion
Describe the practical for investigating the factors affecting diffusion rates in modal cells.
- use dialysis tubing (similar to a membrane - partially permeable, doesn’t let large molecules pass through)
- fill it with a solution of molecules (glucose and starch)
- place in beaker of water
- do benedicts and iodine test
