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
