Topic 2 - plasma membranes Flashcards
What is a phospholipid
A lipid molecule combined with a phosphate group
it has a fatty tail and a phosphate head
Where are phospholipids found
In plasma cell membranes
How does the phosphate head in phospholipids attach to the lipid
The phosphate head binds to the glycerol in the lipid
What are the two fatty acids in phospholipids
A saturated fatty acid (single carbon bond)
an unsaturated fatty acid (carbon double bond)
the unsaturated acid is bent slightly
What are the main properties of a phospholipid
Hydrophilic phosphate head (attracts water)
Hydrophobic fatty tail (repels water)
What are plasma membranes
The plasma membrane (aka cell membranes) is a selective barrier that surrounds all cells
what is the purpose of the plasma membrane
It is selectively permeable (controls what enters and exits a cell)
It separates the substance inside and outside the cell
it allows cell signaling (contains receptors)
What is the phospholipid bilayer
A thin polar 2 layer cell membrane which makes up plasma membranes - made from phospholipids
It separates extracellular and intracellular fluids
How are phospholipids arranged in the phospholipid bilayer
The hydrophilic phosphate heads point outwards
the hydrophobic fatty tails point inwards towards each other
What does amphipathic mean / amphipathic molecule
‘dual nature’
A molecule with an arrangement of a positive / negative charge and an uncharged area
Why do phospholipid bilayers form
When the phospholipids are in water (specifically plasma in humans) The hydrophilic head will point outwards to the water, and the neutral hydrophobic tails will face each other
What is the charge of the phosphate head in phospholipids
negative
What is the charge of the fatty tail in phospholipids
neutral
How is the plasma membrane adapted to deal with changing temperatures
When compressed by a low temperature the unsaturated fatty tails ‘elbow’ the adjacent phospholipids saturated fatty acid.
This creates more room between phospholipids, helping to maintain fluidity preventing the cells from freezing / rupturing
Why is having more saturated fatty acids ( c-c) in phospholipids bad for cold environments
When compressed saturated fatty acids press in to each other making a fairly dense rigid membrane
This reduces fluidity, which could cause the cell to rupture
If these were unsaturated fatty acids, the membrane would be less rigid
Are there more or less saturated fatty acids in organisms living in high temperatures
More saturated fatty acids (c-c)
What is the fluid mosaic model
A model that shows the structure of a plasma membrane
What can be found in plasma membranes
Phospholipids
Proteins (several types)
Cholesterol
What is the purpose of Cholesterol in plasma membranes
Maintains fluidity by preventing fatty acid chains sticking together
Reduces membrane permeability to small water soluble molecules (e.g prevents ions leaking in /out)
What is the purpose glycolipids + glycoproteins do in plasmas membranes
Cell recognition / signaling
Facilitating immune response
They provide energy to the cell
What is the purpose of carrier proteins in plasma membrane
Protein carriers / carrier proteins
Proteins with specific binding sites that allow for selective transport in and out of plasma membranes
What is the purpose of protein channels in plasma membrane
Channels that allow multiple specific molecules to flow freely through them into a cell
What are integral (intrinsic) proteins
Proteins that are embeded in the phospholipid bilayer, such as protein channels or carrier proteins
Proteins that span the whole layer of the plasma membrane
What are peripheral (extrinsic) proteins
Proteins that are entirely utside the membrane
They function of as receptors and are often connected to glycolipids / glycoproteins
What is cell signalling
The process of cellular communication in the body
This can be thrrough hormones
WHAt is a cells cytoskeleton
A network of microtubules and filiments that make up a cells structure / shape
It helps organise the cell
How are most integral proteins are embedded in the bilayer
They have a hydrophobic side that anchors them to the membrane
How are extrinsic proteins bonded to the membrane
They are bonded weakly through intermolecular forces such as ionic bonds
What is diffusion
The net overall movement of particles from a high to low concentration that continues passively until equillibrium is reached
What is simple diffusion
The passive net movemnet of molecules from a high concentration to a lower concentration
What molecules move through simple (passive) diffusion
Small hydrophobic molecules
Gasses
Small non-polar molecules
What is facillitated diffusion
The process of spontaneous passive movement across a biological membrane via the aid of channel proteins (from an area of high concentration to an area of low concentration)
Carrier proteins that DO NOT need ATP are rarely used in fascilliated diffusion
What molecules move through facillitated diffusion
Large polar molecules and ions
What factor limits only Facilliated diffusion
The number of channel proteins
If the channel proteins are saturated the rate of diffusion is limited
What factors effect the rate of diffusion and osmosis
Concetration / water potential gradient - The steeper the gradient the faster the rate
Surface area : volume ratio - The larger the raio the fater the rate
Diffusion distance - The shorter the distance the faster the rate
Temperature
What is active transport
The movemnt of molecules from against a concentration gradient using ATP and carrier proteins
What molecules are moved by active transport
Ions and polar molecules
Is equillibrium ever reached in active transport
No, active transport can continue until no molecules are left to be transferred
What can stop active trasnport (affecting ATP)
If metabollic reactions slow down not enough atp will be produced stopping active transport
What is Osmosis
The net movement of water from a region of high water potential to a region of low water potential through a partially permeable membrane
no proteins are required
What molecules are transported through osmosis
water molecules ONLY
As a liqiuid
What is bulk transport
A cellular process where large amounts of material are moved in or out of a cell
What is exocytosis
The bulk transport of materials out of a cell
The golgi aparatus packages cell contents in secretory vesicles
The vesicle fuses with the plasma membrane
The contents of the vesicle are expelled
What is endocytosis
The bulk transport of materials into a cell
The cell engulfs the materials / molecules
The plasma membrane invaginates t form a vessicle
The vessicle containing the materials moves to the golgi aparatus
What is invagination
The process of forming a cavity / pocket
What happens to plasma membranes and their fluidity below 0C
The phospholipids become packed together and fluidity decreases
Ice crystals can form, fracturing the membrane and increasing fluidity
What happens to plasma membranes and their fluidity between 0 and 45C
The phospholipids can move
The membrane is semi-permeable
The higher the temperature the more gaps between the membrane = greater fluidity
What happens to plasma membranes and their fluidity above 45C
The phospholipids gain too much energy and move away from each other
Water pressure from inside the cell can cause lysis
Fluidity increases rapidly until the cell bursts
How does the permeability of plasma membranes change with fluidity + temperature
As fluidity increases permeability increases
Therefore as temperature increases permeability increases
How is water transported into a cell
It moves via osmosis
The water moves across the phospholipid bilayer or through channel proteins called aquaporins
Why does permeability increase when fluidity increases
When fluidity increases there are larger gaps between phospholipids
This makes it easier for molecules to diffuse across the membrane
