Membranes Flashcards
What do membranes do
-separate contents of cells from their environment
-separate different areas within cells (organelles) from each other. Some organelles are divided further by internal membranes.
-Site of some chemical reactions
-Site of cell signalling
-control what goes in and out of plant
What is compartmentalisation
The formation of separate membrane-bound areas in a cell.
Why is compartmentalisation important
Containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions, such as chemical gradients to be maintained, and protects vital cell components.
What’s the cell surface membrane also known as
The plasma membrane
What are membranes formed from
A phospholipid bilayer-The hydrophobic phosphate heads of the phospholipids form both the inner and outer surface of a membrane, sandwiching the fatty acid tails of the phospholipids to form a hydrophobic core inside the membrane.
What’s the difference between hydrophilic and hydrophobic
Something defined as hydrophilic is actually attracted to water, while something that is hydrophobic resists water.
What can the hydrophilic phosphate heads do
They can interact with water- cells normally exist in an aqueous environment, and the inside of cells and organelle are usually aqueous.
Describe the fluid mosaic model
Phospholipids are free to move within the layer relative to each other, giving the membrane flexibility, and because the proteins embedded in the bilayer vary in shape, size and position.
What’s an extrinsic protein
Or peripheral proteins, are present in one side of the bilayer. They normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins. They can be present in either layer and some move between layers.
What’s an intrinsic protein
A protein molecule spanning the phospholipid layer- 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’s a glycoprotein
A branching carbohydrate portion of a protein which acts as a recognition site for chemicals e.g. hormones
What’s a glycolipid (intrinsic)
Similar to glycoproteins. Lipids with attached carbohydrate(sugar) chains. The molecules are called cell markers or antigens and can be recognised by the cells of the immune system as self (of the organism) or non-self (of cells belonging to another organism)
What does cholesterol do in the membrane
Provides stability/flexibility
-Helps with the fluidity of the membrane
-packed between phosphate groups-prevents the movement of water-soluble chemicals across membrane.
What’s a channel protein (intrinsic)
Channel proteins provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes. They are held in position by interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the protein.
What are carrier proteins (intrinsic)
Have an important role in both passive transport (down a conc. gradient) and active transport (against a conc. gradient) into cells. This often involves the shape of the protein changing.
What are glycoproteins (intrinsic)
-They are embedded in the cell-surface membrane with attached carbohydrate(sugar) chains of varying lengths and shapes. Glycoproteins play a 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 the chemical binds to the receptor on glycoprotein, it elicits a response from the cell. This may cause a direct response or set off a cascade of events inside the cell.
How do some drugs work
By binding to cell receptors. For example, B blockers are used to reduce the response of the heart to stress.
What is cholesterol (extrinsic)
Lipid with a hydrophilic end and hydrophobic end. It regulates fluidity of membranes.
-positioned between the phospholipids, with the hydrophilic end interacting with the heads and the hydrophobic end interacting with the tails, pulling them together. In this way cholesterol adds stability to the membranes without making them too rigid.
Why is it called the fluid mosaic model
Fluid- phospholipids can move in each layer
Mosaic- protein molecules scattered within.
