Plasma Membranes! Flashcards
What is compartmentalisation?
The formation of separate membrane bound areas in a cell
What is a plasma membrane?
The cell surface membrane which separates the cell from its external environment
Which way do the hydrophilic heads face?
Outwards
Why do the hydrophobic tails remain inside the bilayer?
To create a hydrophobic core, membranes are usually located in aqueous environments
What is the fluid mosaic model?
Proteins occupy various layers within the membrane. Called the fluid mosaic model as the phospholipids are free to move within the layer relative to eachother, giving the membrane flexibility. Proteins in membrane vary in size shape and position
What is a glycoprotein?
Branching carbohydrate portion of a protein that acts as a recognition site for chemicals eg hormones
What is a glycolipid?
Acts as a recognition site eg for cholera toxins
Why is the role of cholesterol in the membrane?
For stability / flexibility
What is an extrinsic protein?
Protein molecule partly embedded in the membrane
What is an intrinsic protein?
Protein molecules spanning the phospholipid bilateral
What are the 2 types of intrinsic protein?
Channel proteins
Carrier proteins
How are intrinsic proteins adapted to function?
Embedded through both layers of membrane.
They have amino acids with hydrophobic R groups on their external surfaces, which interact with the hydrophobic core of the membrane keeping them in place.
What is the role of a channel protein?
Provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes. Held in position by interactions between hydrophobic core of the membrane and hydrophobic R groups on outside of the proteins.
What is the role of a carrier protein?
Involved in Passive transport down a concentration gradient and active transport into cells. This often involves the shape of the protein changing.
How are glycoproteins adapted to function?
Embedded in the cell surface membrane with attached carbohydrate chains of varying lengths and shapes. Glycoproteins Play a key role in cell adhesion ( when cells join together to form tight junctions in certain tissues) and as receptors for chemical signals
What is cell signalling?
When a chemical binds to a receptor or elicits a response from the cell. This may causes direct response or set off a cascade of events inside the cell.
Name some examples of cell signalling?
Receptors for neurotransmitters such as acetylcholine at a nerve cell synapse. The binding of neurotransmitters triggers or prevents an impulse at the next neurone.
Receptors for peptide hormones including insulin and glucagon, which affect the uptake and storage of glucose by cells.
What are glycolipids and what do they do?
They’re lipids with starches carbohydrate (sugar) chains. These are called cell markers or antigens which can be recognised by the cells of the immune system as self or non self.
What features to extrinsic proteins normally have?
Hydrophilic R groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins. Can be present in either layer and some can move between the layers.
What is the role of cholesterol within membranes?
Regulating the fluidity and stability of membranes.
How are cholesterol molecules positioned in the membrane?
Cholesterol molecules are positioned between phospholipids in the bilayer, with the hydrophilic end interacting with the heads and the hydrophobic end interacting with the tails pulling them together.
How does cholesterol prevent the membrane from becoming too solid?
By stopping the phospholipid molecules from grouping too closely and crystallising.
How does temperature affect plasma membranes?
As temperature increases the phospholipids will have more kinetic energy and will therefore move more. This makes a membrane more fluid and it will begin to lose its structure, if this temperature continues to increase, the cell will break down completely.
At higher temperatures the cell is more permeable to particles due to the increase in permeability.
At very high temperatures the carrier and channel proteins work denature, meaning the membrane permeability will be affected once again.
Why does water not disrupt cell membranes?
Charged phosphate heads (hydrophilic) interact with water keeping the membrane in tact. Non polar tails are oriented away from the water forming a bilayer with the hydrophobic core.
Why do organic / less polar molecules dissolve / disrupt the membrane?
Organic solvents can dissolve the membranes, therefore disrupting the cell.
Why are pure or strong alcohols toxic?
Because they can destroy the cells within the body.
How do alcoholic drinks affect the membranes?
Non polar alcohol molecules enter the cell membrane and the presence of these between the phospholipid disrupts the membrane. When disrupted, the membrane becomes more fluid and more permeable.
Many cells need intact membranes for specific functions eg nerve impulse transmission in nerve cells.
