2.1.5 - Biological Membranes Flashcards
Phospholipid structure
A glycerol molecule
Two fatty acid tails (saturated and unsaturated)
Phosphate group
Properties of phospholipid
Phosphate group is polar —> hydrophilic
Fatty acid tails are non polar —> hydrophobic
(Amphipathic)
Why does soap dissolve the membrane easily
Membranes are made from lipids
What is selective permeability
When what goes in and out of the cell is regulated by only letting certain things in and out
Major molecules in cell membranes
Phospholipids
Proteins
Amphipathic
The molecule has dual nature (hydrophobic and hydrophilic)
What roles do proteins play in transport
Regulation
What kinds of cells have cell walls
Plant
Bacterial
Fungal
What are glycoproteins made from
Proteins
Sugars
Example of a glycoprotein
Antibodies - important in immune response
What are glycolipids made of
Fats
Sugars
Why can’t water pass through the phospholipids
The inside is non polar
How do proteins assist in transport
Allow big things and things that have a charge to move across the membrane
What is a plant cell wall made of
Cellulose
What is a bacteria cell wall made from
Peptidoglycan
What is a fungal cell wall made from
Chitin
Function of chlolesterol in cell membranes
Regulates fluidity of membrane by keeping phospholipids slightly apart or pulling them closer
Hydrophilic ends interact w/ heads and hydrophobic end interacts w/ tails; pulls them together
Prevent phospholipids from grouping together too closely and crytsallising
Function of glycoprotein in cell membrane
Cell adhesion - binding site for hormones and drugs
Cell signalling to coordinate activities of organisms
Antigens for the recognition of ‘self’
Acts as receptor
Function of glycolipid
Form cell markers/ antigens
Function of carbohydrates in cell membrane
Hydrophilic molecules that sit on the cell surface membrane and attracts water with dissolved solutes
Carrier protein
Changes shape to allow specific molecules in and out of the cell
Channel protein
These provide a hydrophilic channel that allows the passive movement of polar molecules down a concentration gradient
Water filled channel inside is lined with hydrophilic amino acids
Integral/ intrinsic proteins
Proteins that span the whole membrane
Either channel or carrier proteins
Protein receptor site
Acts as receptors to detect hormones and/or drugs
How do carrier proteins work
Molecule binds
Carrier protein changes shape
Releases molecules on the other side
When is diffusion rapid
Small
Non-polar molecules
Facilitated diffusion
Involves carrier and channel proteins within the cell membrane.
These help transport large, polar molecules e.g. glucose, across the membrane
Functions of a cell membrane
Can be a site of chemical reactions - contain enzymes
Cell signalling
Create conc. gradient
Has antigens so the immune system recognises it as ‘self’
Separates contents from outside - barrier (cell or organelles)
Regulates transport of molecules in/out of a cell or organelle
Seperates metabolic pathways
Factors affecting diffusion
Temperature Molecule size Conc. gradient Diffusion distance Surface area
Cell membrane permeability at higher temps
Phospholipids moving around so fluidity and permeability increases (more kinetic energy)
Cholesterol reduces the fluidity
The proteins could denature and the bilayer could be completely permeable
What does water dissolve
Polar solutes
What does ethanol dissolve
Membranes, disrupting cells which is why alcohols are used in antiseptic wipes
How do solvents affect permeability
Non polar or less polar solutes will disrupt membranes as the tails no longer orientate towards the middle. The membrane will become more fluid and more permeable
What happens if animal cells are put into pure water
Cell bursts open, it is cytolysed
What happens if animal cells are put in a solution with low water potential
Cell shrinks and appears wrinkled - it is crenated
What happens if a plant cell is put in pure water
Plant cell wall prevents bursting. Membrane pushes against cell wall - cell is turgid
What happens if a plant cell is put in a solution with very low water potential
Plasma membrane pulls away from the cell - it is plasmalysed
Water tendency
Measure of the tendency of water molecules to diffuse from one region to another
Measured in kPa
What is water potential affected by
The amount of solute it contains
The greater the amount of solute it contains, the lower or more negative the lower water potential
Osmosis
The passive movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane
Active transport
Movement of substances from low to high conc. across a cell membrane, using ATP and protein carriers (against a conc. gradient)
What do carrier proteins combine reversibly with
Specific solute molecules or ions. They also have a region that binds to and allows the hydrolysis of a molecule of ATP to release energy
Sodium potassium pump
Carrier proteins binds 3 Na+ ions and 1 ATP
ATP is hydrolysed to release energy and the carrier protein changes shape
Tonicity
How much solute is in the solution
Hypotonic
Less solute
Higher water potential
Hypertonic
More solute
Lower water potential
Highest water potential
0 kPa
Pure water - no solute dissolved
Endocytosis
Taking in large particles into the cell using vesicles and ATP
Csm invaginates when it comes into contact w/ substance
Enfolds membrane til it fuses –> forms vesicle
Vesicle pinches off and moves into cytoplasm to necessary organelle
Phagocytosis
Endocytosis carries out by phagocytic cells
Pinocytosis
Taking in liquid into the cell
Passive transport
Diffusion
Facilitated diffusion
Osmosis
Bulk transport
Movement of molecules through a membrane by the action of vesicles
Thickness of plasma membrane
7.5 nm
How factors affect the rate of diffusion
(Temp x SA x Conc. diff)/(diffusion distance x size of particle)
Receptor mediated endocytosis
Transports LDLs and viruses into the cell only
Requires ATP
Investigating cell membrane permeability
Cut 5 equally sized beetroots w/ a cork borer
Rinse and dry - to remove all pigment
Add beetroots to diff test tubes w/ 5cm^3 of water
Add each tt to a diff water bath w/ diff temp for same amount of time
Remove beetroot and using a pipette transfer remaining sol. to cuvette until 3/4 full
Use blue filter and measure abs
High abs, more pigment released, more permeable
Investigating water potential of plant cells
Prepare sucrose sol. of diff conc.
Use cork borer to get identically sized potato cylinders
Measure mass w/ mass balance
Place each cylinder is diff conc. solution for same amount of time
Calculate % change in mass
Plot conc. on x and % change on y to find when conc. was isotonic
Examples of model cells
Agar jelly
Visking tubing
Gelatine cubes
These have a similar cytoplasm to our cells
Investigating diffusion using model cells (conc.)
Prepare agar jelly / indicator and alkali (pink)
Prepare tt w/ diff conc. of acid
Cut equal sized cubes from agar jelly and place into tt
Use stopwatch and record time taken to go colourless
Higher conc. of acid = less time to go colourless
Repeat at least 3x and calculate mean
Why do we do repeats
Calculate mean
Reduce effect of random error
Precision
Having all your values close to EACH OTHER
Accuracy
Having all your values close to the TRUE VALUE
Why does facilitated diffusion not use ATP
Molecules have their own kinetic energy
Uses gradient
Which type of fatty acid tail contributes most to fluidity
Unsaturated
Intrinsic proteins
Channel proteins
Carrier proteins
Glycoproteins
Extrinsic proteins
Present in one side of bilayer
Hydrophilic R groups on outer surface
Can be present in either layer and some move between layers
Process of active transport
Molecule binds to receptor in channel of carrier protein
Binding of phosphate causes proteins to change shape - opening up to the inside
Molecule released to inside of cell
Phosphate released and recombines w/ ADP
Carrier protein returns to orig shape
Processes requiring ATP as an immediate source of energy
Active transport
Exocytosis
Endocytosis
