Transport Across Membranes Flashcards
Describe the plasma membrane structure
The plasma membrane consists of phospholipids, proteins and carbohydrates.
The phospholipids have a hydrophobic end and a hydrophilic end which prevents it from being soluble in water but still allowing molecules to diffuse through
Describe the role of plasma membranes in cells
It controls the entry and exit of molecules which are crucial for cell function me survival like glucose and oxygen. It also plays a key role in cell communication and recognition.
What is the fluid mosaic model?
It’s the way of explaining the arrangement of molecules in the membrane. Phospholipid molecules form a continuous bi-layer. This layer is fluid because the phospholipids are constantly moving and protein molecules are dispersed through the layer like tiles in a mosaic.
What causes the phospholipids to arrange themselves into the ‘bi-layer’?
The “head” of the molecule is hydrophilic and the “tail” of the molecule is hydrophobic. This means the heads point outwards into the cell and on the outside of the cell.
Why won’t the bi-layer let water soluble molecules through?
The centre of the bi-layer is hydrophobic so it repels the water soluble molecules like ions which stops them from diffusing through.
How does the cell membrane allow for communication between other cells?
Cells that release chemicals can communicate due to receptor proteins on the bi-layer surface. When these receptor proteins bind with chemicals, it can activate it to perform a specific task ( insulin released by the pancreatic cells will tell liver cells to absorb glucose )
How are your cells recognised by your immune system etc?
Some proteins in the membrane have short chain carbohydrates attached to them. They are called glycoproteins and glycolipids. These let your white blood cells know that the cells are your own.
Why is having some cholesterol important in cell membranes?
Increases turgidity in cells which can prevent them from breaking up due to the cholesterol molecules fitting into the fluid membrane.
Describe the structure of a triglyceride
One glycerol molecule joined with three fatty acid molecules.
All fatty acid molecules have the same basic structure. Give the basic structure of a fatty acid
A carbon atom with a double bonded oxygen, an OH molecule and an R group ( hydrocarbon chain )
What is the difference between a saturated and unsaturated fatty acid molecule?
An unsaturated fatty acid has a double bond in the hydrocarbon chain which can cause the chain to kink.
How is a triglyceride formed?
They are formed from condensation reactions between a glycerol molecule and a fatty acid molecule ( 3 ) which forms an ester bond. The OH bond on the glycerol molecule is replaced by the oxygen atom from the fatty acid in the OH molecule which releases the water molecule.
How is a phospholipid molecule different to a triglyceride?
Instead of three fatty acid molecules it has two and a phosphate molecule.
Describe the emulsion test for lipids.
Add ethanol to the solution you want to test and shake for a minute. Then add the solution to water. In the presence of a lipid the solution will form a milky emulsion which will separate from the water. A higher number of lipids makes the emulsion more noticeably milky.
Describe the 4 main types of diffusion.
Diffusion: net movement of particles from high conc. to low conc. It is a passive process as it doesn’t require any energy.
Osmosis: movement of water molecules across a partially permeable membrane from an area of high conc. to low conc. Also a passive process.
Facilitated diffusion: net movement of particles from high conc. to low conc. Uses carrier proteins and channel proteins to aid diffusion of larger molecules and charged atoms through the plasma membrane. Passive process
Active transport : movement of molecules against a concentration gradient. Uses carrier proteins and co transporters which require ATP.
