54 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.3 Cell Membranes And Transport) Flashcards
What is the model of cell membranes called?
The fluid-mosaic model of cell membranes
What is the cell membrane made up of?
The cell membrane is made up almost entirely of proteins and phospholipids.
What forms the basis of membrane structure?
Phospholipids are important components of cell-surface membranes and form the basis of membrane structure.
How are phospholipids arranged in the cell membrane?
Phospholipids can form bilayers, with one sheet of phospholipid molecules opposite another.
How is the hydrophilic heads of the inner layer of phospholipids arranged in the cell membrane?
The inner layer of phospholipids has its hydrophilic heads pointing in, towards the cell, and interacts with the water in the cytoplasm.
How is the hydrophilic heads of the outer layer of phospholipids arranged in the cell membrane?
The outer layer of phospholipids has its hydrophilic heads pointing outwards, interacting with the water surrounding the cell.
How is the hydrophilic tails of the phospholipid layers arranged in the cell membrane?
The hydrophobic tails of the two phospholipid layers point towards each other, to the centre of the membrane.
What molecules does the phospholipid component of the cell membrane allow to pass through?
The phospholipid component of a membrane allows lipid-soluble molecules across, but not water-soluble molecules.
What is the location of proteins in the cell membrane?
Proteins are scattered throughout the phospholipid bilayer of the membrane.
How many ways can proteins be embedded in the cell membrane?
There are two ways in which they are embedded.
What are the types of proteins embedded in the cell membrane?
- Extrinsic proteins
- Intrinsic proteins
Where are extrinsic proteins found in the cell membrane?
Extrinsic proteins are on either surface of the bilayer.
What are the functions of extrinsic proteins?
They provide structural support.
They form recognition sites, by identifying cells
They form receptor sites for hormone attachment.
Where are intrinsic proteins found in the cell membrane?
Intrinsic proteins extend across both layers of the phospholipid bilayer.
What are the functions of intrinsic proteins?
They include transport proteins.
These transport proteins use active or passive transport to move molecules and ions across the cell membrane.
What is the fluid-mosaic model?
The way in which the phospholipids and proteins are arranged in the membrane is called the fluid-mosaic model.
Who proposed the fluid-mosaic mode?
It was proposed by Singer and Nicolson in 1972.
What are the two parts of a phospholipid molecule?
- Phosphate head
- Fatty acid end made up of two fatty acid tails
Tell me about the phosphate head of a phospholipid molecule.
The phosphate head of a phospholipid molecule is polar (hydrophilic).
It interacts with other polar molecules, such as water.
Tell me about the fatty acid end of a phospholipid molecule.
The fatty acid end of a phospholipid comprises two fatty acid tails.
It is non-polar (hydrophobic).
It does not interact with water.
What are biological membranes made up of?
Biological membranes are phospholipid bilayers which contain protein molecules.
Do all biological membranes have the same properties? Why?
No.
Different fatty acids and proteins give the membranes different properties.
Fluid-mosaic model (Key-Term)
Model of the structure of biological membranes, in which proteins are studded through a phospholipid bilayer, as in a mosaic.
The movement of molecules within a layer of the bilayer is its fluidity.
Can protein hormones enter the cell? Why
No.
Protein hormones, such as insulin and adrenalin, are insoluble in lipids.
Hence they cannot diffuse through the phospholipid membrane into the cell.
How do protein hormones influence cell behaviour?
They bond to extrinsic protein receptor molecules, which influences the behaviour of cells.
What does this picture show?
Label its parts?
3D arrangement of molecules in a biological membrane
