1. Cell Membranes - the basics Flashcards
What do membranes surround?
Cells are surrounded by membranes.
Eukaryotic cells, many of their organelles ate too.
What are cell-surface membranes?
They surround cells.
Barrier between the cell and its environment, controlling which substances enter and leave cell.
Partially permeable.
How do substances move across the cell-surface membrane?
Diffusion.
Osmosis.
Active transport.
What are cell-surface membranes sometimes called?
Plasma membranes.
What does it mean by membranes within the cells?
The membrane surrounding the organelles, dividing it up into different compartments.
Acts as a barrier between organelle and cytoplasm.
Partially permeable - control substances which enter and leave cell.
- Give an example of membranes within the cells?
Substances needed for respiration are kept together inside mitochondria by the membrane surrounding it.
- Give ANOTHER example of membranes within the cell?
RNA leaves nuclear via nuclear membrane (nuclear envelope).
DNA is too large to pass through partially permeable membrane, it remains in nucleus.
What 3 things do cell membranes consist of?
Lipids - mainly phospholipids.
Proteins.
Carbohydrates - attached to protein or lipid.
What happened in 1972?
The fluid mosaic model was suggested to descrive the arrangement of molecules in membrane.
What was the structure of the membrane like in the fluid mosaic model?
Phospholipids molecules form a continuous double layer called a bilayer.
Bilayer is fluid because phospholipids are constantly moving.
What is in the bilayer of a cell membrane?
Proteins scattered through bilayer like tiles in a mosaic.
Including channel and carrier proteins, which allow large molecules and ions to pass through membrane.
Cholesterol molecules also present here.
What is on the surface of the cell membrane?
Receptor proteins.
Allow the cell to detect chemicals released by other cells.
Chemical signals to the cell respond in some way.
EXAMPLE.
Give an example of a receptor molecules responding to a chemical signal?
Hormone insulin binds to receptor protein on liver cells, which tells cell to absorb glucose.
What do proteins do in the bilayer?
Some are able to move sideways through bilayer, while others are fixed in position.
Some proteins have carbohydrate attached to them - glycoproteins.
How thick is the bilayer?
Around 7nm thick.
