Fluid Mosaic Membranes (Cambridge (CIE) AS Biology): Flashcards
Exam code: 9700
1/280Still learning
Know0
Define the fluid mosaic model.
Was this flashcard helpful?
Cards in this collection (28)
Define the fluid mosaic model.
The fluid mosaic model describes a membrane as a phospholipid bilayer with proteins embedded in it, where the components are free to move ("fluid") and are scattered like tiles in a mosaic.
Why is the membrane described as "fluid" and a "mosaic"?
Fluid = the phospholipids and proteins can move within the layer.
Mosaic = the scattered proteins vary in shape and size, like tiles in a mosaic.
Describe the structure of a phospholipid.
It has a hydrophilic (water-loving) phosphate head.
It has two hydrophobic (water-hating) fatty acid tails.
Explain how hydrophilic and hydrophobic interactions cause a phospholipid bilayer to form.
The hydrophilic heads face outwards towards the water on each side of the membrane.
The hydrophobic tails point inwards, away from water, forming the centre of the bilayer.
Describe the arrangement of proteins in the fluid mosaic model.
Intrinsic (integral) proteins are embedded within or span the bilayer.
Extrinsic (peripheral) proteins sit on the surface of the bilayer.
The hydrophobic tails of phospholipids point , away from water.
The hydrophobic tails of phospholipids point inwards, away from water.
True or False?
A phospholipid bilayer forms because the fatty acid tails are attracted to water.
False.
The fatty acid tails are hydrophobic, so they are repelled by water and point inwards, away from it.
Describe the arrangement of cholesterol in the cell surface membrane.
Cholesterol molecules sit between the phospholipids in the bilayer, within the hydrophobic core.
Define glycolipid.
A glycolipid is a lipid with a carbohydrate chain attached, found on the outer surface of the membrane.
Define glycoprotein.
A glycoprotein is a protein with a carbohydrate chain attached, found on the outer surface of the membrane.
Describe the arrangement of glycolipids and glycoproteins in the membrane.
Their carbohydrate chains project outwards from the outer surface of the membrane, into the surrounding fluid.
What is the difference between intrinsic and extrinsic membrane proteins?
Intrinsic (integral) proteins are embedded in or span the bilayer.
Extrinsic (peripheral) proteins are found on the surface of the bilayer.
A carbohydrate chain attached to a protein forms a .
A carbohydrate chain attached to a protein forms a glycoprotein.
molecules sit between the phospholipids in the bilayer.
Cholesterol molecules sit between the phospholipids in the bilayer.
What is the role of phospholipids in the cell surface membrane?
They form the bilayer, which acts as a barrier to water-soluble substances.
This controls what enters and leaves the cell (permeability).
What is the role of cholesterol in the cell surface membrane?
It regulates membrane fluidity and gives the membrane stability.
It reduces permeability to small water-soluble molecules and ions.
Describe the roles of channel proteins and carrier proteins.
Channel proteins form water-filled pores for ions and polar molecules to pass through.
Carrier proteins change shape to move specific molecules across the membrane.
How do membrane proteins take part in cell signalling?
Some glycoproteins act as cell surface receptors.
They have a shape complementary to a specific signalling molecule (ligand), which binds to trigger a response.
How do glycoproteins and glycolipids allow cell recognition?
They act as cell surface antigens.
These allow cells to be recognised as "self" or "foreign".
proteins form water-filled pores that allow ions to cross the membrane.
Channel proteins form water-filled pores that allow ions to cross the membrane.
True or False?
Cholesterol makes the membrane more permeable to ions.
False.
Cholesterol reduces permeability to small ions and water-soluble molecules, and helps maintain membrane stability.
Define cell signalling.
Cell signalling is communication between cells using chemical signals (ligands) that produce a specific response in target cells.
Define ligand.
A ligand is a signalling molecule (e.g. a hormone) secreted by a cell that binds to a specific receptor on a target cell.
Outline the main stages of cell signalling.
1. A cell secretes a specific chemical (ligand).
2. The ligand is transported to a target cell (e.g. in the blood).
3. The ligand binds to a cell surface receptor on the target cell, triggering a specific response.
Define target cell.
A target cell is a cell with the complementary receptor for a specific ligand, allowing it to respond to that signal.
Why does a ligand only affect specific target cells?
The ligand only binds to receptors with a complementary shape.
Only target cells have these specific cell surface receptors.
A signalling molecule that binds to a cell surface receptor is called a .
A signalling molecule that binds to a cell surface receptor is called a ligand.
True or False?
Any cell in the body can respond to a particular ligand.
False.
Only target cells with the complementary receptor for that ligand can respond to it.
Sign up to unlock flashcards
or