Unit 2 - Plasma membranes Flashcards
State 4 functions of plasma membranes
Options:
- recognition of other cells
- separates cell contents from the outside (barrier between cells and its environment)
- controls the passage of materials in and out
- allow cell communication
- phagocytosis
- cell to cell attachment
State 4 functions of membranes inside cells
Options:
- isolates DNA
- acts as an intracellular transport system
- compartmentalises reactions
- can be the site of chemical reactions
- ribosomes attach
- protection from lysosomes
- forms vesicles
Define compartmentalisation
The formation of separate membrane-bound areas
Why is compartmentalisation useful in cells?
- incompatible reactions occur within the cell
- isolates reactions making them more efficient
- allows reaction conditions to be maintained (e.g chemical gradients)
- protects cell components
Define partially permeable
A membrane that allows some substances to cross but not others
Define cell signalling
A complex system of intercellular communication
Define phospholipid bilayer
- arrangement of phospholipids found in cell membranes
- the hydrophilic phosphate heads form the inner and outer surface of a membrane ,
- sandwhiching the fatty acid tails to form a hydrophobic core
Why are membranes referred to as having a ‘fluid-mosaic structure’ ?
- the phospholipids are able to move freely relative to each other (fluid)
- the proteins embedded in the bilayer vary in shape, size, and position (mosaic)
Define glycoprotein
Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes
Define glycolipid
Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes
Define phospholipid
Modified triglycerides, where one fatty acid has been replaced with a phosphate group
What are channel proteins?
Membrane proteins that provide a hydrophilic channel through a membrane
What are receptor proteins?
Extrinstic glycopoteins that bind chemical signals, triggering a response by the cell
What are carrier proteins?
Membrane proteins that play a part in the transport of substances through a membrane
What is the approximate width of an animal cell plasma membrane?
7nm
What are the functions of cholesterol in cell surface membranes?
- regulates fluidity and adds stability to membranes
- prevents phospholipids from crystallising
What are the functions of phospholipids in cell surface membranes?
- forms basic structure
- acts as partially permeable barrier
- allows the passage of lipid soluble molecules
- prevents water soluble molecules from moving across
What are the functions of glycoproteins in cell surface membranes?
- receptors for chemical signals
- cell adhesion
- when chemical binds to the receptor, events inside the cell are set off
- binding sites for chemical e.g hormones
- Hydrogen bonds to water to stabilise membrane
What are the functions of glycolipids in cell surface membranes?
- act as antigens that can be recognised by the immune system
- form hydrogen bond with water molecules to stabilise membrane
What are the functions of carrier proteins in cell surface membranes?
- have an important role in both passive movement of polar molecules and ions down a concentration gradient
- this involves the shape of the protein changing
What are the functions of channel proteins in cell surface membranes?
-provide a hydrophillic channel that allows passive movement of polar molecules and ions down a concentration gradient
What are the functions of extrinsic proteins in cell surface membranes?
-can attach to the cytoskeleton
Define cell adhesion
The process by which cells make contacts with each other
Describe 2 ways in which cholesterol regulates membrane fluidity
- hydrophillic end of cholesterol interact with phosphate heads
- hydrophobic end of cholesterol interacts with fatty acid tails
- pulling the phospholipids together
- prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together
What 3 factors affect membrane structure?
Temperature
Solvents
Cholesterol
How does an increase in temperature affect cell membranes?
- increases membrane fluidity
- increases membrane permeability
- carrier and channel proteins are denatured at higher temperatures
- membrane loses its structure
Why does an increase in temperature increase membrane permeability?
- more temperature means phospholipids move more
- because they have a higher kinetic energy
- makes it easier for things to pass through
How do solvents affect cell membranes?
- membrane loses structure
- increases permeability
Why do solvents increase membrane permeability?
-solvents dissolve phospholipids
Give an example of a solvent that can dissolve phospholipids
Ethanol, Methanol etc.
Outline how the effect of temperature on membrane permeability can be investigated
- beetroot cells contain betalain
- when membranes are disrupted the red pigment is released
- pieces of equal size beetroot are placed in water and heated in waterbaths at different temperatures for the same amount of time
- the solutions are placed in a colorimeter
How can a colorimeter show the permeability of membranes?
- more permeable means more betalain leaks out
- more betalain means less light is absorbed by the detector
Outline how the effect of solvents on membrane permeability can be investigated
- beetroot cells contain betalain
- when membranes are disrupted the red pigment is released
- pieces of equal size beetroot are placed in different concentrations of a solvent for the same amount of time
- the solutions are placed in a colorimeter
Suggest 3 improvements of the design of the experiment
- cut pieces from same place in beetroot
- blot surface of beetroot before experiment
- use same volume of water
