Chapter 5 - Plasma Membranes Flashcards
Characteristics of cell surface membrane
Made up of phospholipids
That have hydrophilic heads and hydrophobic tails
That allow non polar molecules through and some small polar molecules ( water)
What is the fluid mosaic model
Idea that phospholipids are free to move like a fluid
The proteins embedded in the bilayer vary in shape size and position like tiles in a mosaic
What is the structure of glycoprotein
Protein with a branching carbohydrate portion of a protein which acts as a recognition site for chemicals
Structure of glycolipid
Carbohydrate chain attached to the membrane, not a protein recognition site
What is an intrinsic protein (examples)
Transmembrane proteins that are embedded through both layers of a membrane
Amino acids have hydrophobic r groups that interact with hydrophobic core
Channel protein
Carrier protein
Glycoprotein
Extrinsic proteins
Peripheral proteins that are only present on either side of the bilayer
Have hydrophilic r groups that interact with the polar heads
What is the role of cholesterol
Regulates the fluidity of the membrane
Adds stability - doesn’t let them touch and crystallise, pulls them together
How does temperature affect the membrane structure?
Phospholipids are always moving
Increases kinetic energy
Moves faster - loses structure - increases fluidity
Loss of structure increases permeability - easier for particles to cross
At high temperatures carrier and channel proteins will denature - involved in transport of proteins
How does solvents affect membrane structure
Organic substances that are less polar than water or non polar will dissolve membranes
Non polar alcohol can enter membrane and disrupt the structure of phospholipids - making the membrane more fluid and permeable
A practical to investigate the permeability of membranes
Beetroot
Put equal amounts of beetroot in tube and increase the water bath at intervals of ten - measure absorbance of each sample 5 minutes after temperature is reached
Using colorimeter with blue filter
Pigment is releases from cell
More pigment molecules absorb more light, light transmitted decreases
What is diffusion
The net movement of particles from a region of high concentration to a region of low concentration
Factors affecting the rate of diffusion
Temperature
- more kinetic energy - move at faster speeds
Concentration difference
- overall movement from high to low is larger
Practicals to find the rate of diffusion and surface area
Distance travelled / time
Volume filled / time
Factors that affect rate of diffusion across membranes
Surface area
- larger the area of a exchange surface
Thickness of membrane
- when particles move over a long distance, collisions are more likely, which will slow the rate of reaction
What is facilitated diffusion
Diffusion across a membrane through a protein channel
What is the rate of facilitated diffusion dependent on
Temperature Concentration gradient Surface area Cell membrane thickness Number of channel proteins present
Practical to investigate the factors affecting diffusion rates in model cells
Placed in different concentrations/ temperatures
Using dialysis tubing with pores
- water can pass through
- glucose can - use Benedict’s solution to test
- starch can’t - iodine test
What is active transport
The movement of molecules from a region of low concentration to a region of high concentration
Requires energy and carrier proteins - atp
How does active transport happen with Carrier proteins
- molecule binds to receptors on channel / carrier protein ( outside of cell)
- (inside of cell) atp binds to carrier protein and is hydrolysed into Adp and a phosphate
- when phosphate binds to carrier protein the protein changes shape, opening up to the inside of the cell
- molecule is released into the cell
- phosphate is released and recombined to adp to make atp
- Carrier protein returns
What is bulk transport
Another form of transport where large molecules or cells are moved into or out of a cell by enocytosis and exocytosis
Enzymes , hormones , bacteria
What is endocytosis
Bulk transport of material into cells
- phagocytosis - solids
- pinocytosis - liquids
- the cell surface membrane invaginate, bends inwards when it comes into contact with material
- membrane enfolds material until fuses and forms a vesicle
- vesicles pinches off and moves into the cytoplasm to transfer material
What is exocytosis
Vesicles formed by the Golgi apparatus moves towards and fuses with the cell surface membrane - contents of vesicles are released
- energy atp is required to move the vesicles along the cytoskeleton, changing the shape of cells to engulf and fusion of membrane
What is water potential
The pressure exerted by water molecules as they collide with a membrane or container
Pure water = 0 water potential
The more concentrated the more negative the water potential
What are the effects of osmosis on plants and animals cells
The increase of volume into a cell results in the increase in hydrostatic pressure
Cytolysis
Animal cells swell with water
- increases hydrostatic pressure
- the cell surface membrane can’t stretch to withstand the pressure
Crenation
Reduction in the volume of the cell
Shrivel
What do animal cells have to prevent cytolysis and crenation
Have control mechanisms - blood plasma
Makes sure they are surrounded by isotonic solutions
Why do plant cells have cell walls
They can’t control the water potential around them
Need strong cellulose walls
Turgid
Plant cells swell
Increased hydrostatic pressure pushes the membrane against the rigid walls
Plasmolysed
Plant cells shrivel
Reduction in volume of cytoplasm
Pulls the plasma membrane away from cell wall
What do channel proteins do
Hydrophilic channel
Allows passive movement of polar molecules and ions
Down a concentration gradient
Held in position by interactions between hydrophobic r groups on outside of protein and hydrophobic core of membrane
Carrier proteins
Passive and active transport
Involved changing of shape
Glycoproteins
Have receptors
That elicits response from the cell
Cell communication/signalling - responds to its environment
Cell adhesion - when cells join to form tight junctions in tissues
Insulin glucagon example for glycoproteins
Receptor for hormones insulin and glucagon
Affect uptake and storage of glucose by cells
Glycolipid
Cell markers/ antigens
Can be recognised by the immune system as self or non self
What can pass through a phospholipid bilayer
Non polar molécules - oxygen
Small Polar molecules - water / glucose
Only
Not ions
Partially permeable
Selectively permeable
Only allows certain types of molecules through but not all
Plasma membranes with protein channels that only allow specific substances to cross
