Cell Membranes Flashcards
state three functions of the membrane at the surface of cells
•they are a barrier between the cell and it’s environment, they partially permeable, they control which substances enter and leave the cell, they let some molecules through but not others, substances can move across plasma membrane by diffusion, osmosis or active transport
•allow recognition by other cells
•allow cell communication
describe three functions of membranes within the cell
•membranes around organelles divide the cells into different compartments, act as barrier between the organelle and cytoplasm
•membranes within cells can be the sites of chemical reactions
•they can form vesicles to transport substances between different areas of the cell
give three molecules that are present in animal cell membrane
proteins
lipids
carbohydrates
what is the fluid Mosaic structure?
fluid mosaic model describes the arrangement of molecules in the membrane
explain why the plasma membrane can be described as having a fluid mosaic structure
•in the model, phospholipid molecules form a continuous double layer
•this bilayer is fluid because the phospholipid molecules are constantly moving
• cholesterol molecules are present within the bilayer
• protein molecules are scattered through the bilayer like tiles in a mosaic
• some proteins have a polysaccharide (carbohydrate) chain attached to them, these are glycoproteins
• some lipids have a polysaccharide chain attached to them, these are glycolipids
what is the structure of a phospholipid molecule
they have a head and a tail
describe the head and tail of a phospholipid molecule
head is hydrophilic, it attracts water
tail is hydrophobic, it tells water
•molecules automatically arrange themselves in a bilayer, head faces put towards the water on either side of the membrane
Describe the centre of the fluid mosaic model
The centre of the bilayer is hydrologic, so membrane doesn’t allow water soluble substances through it and acts as a barrier to dissolved substances
( fat soluble substances can dissolve in the bilayer and pass directly through the membrane)
what type of molecule is cholesterol?
Cholesterol is a type of lipid
what does cholesterol molecule do to the membrane?
Cholesterol gives the membrane stability
How does cholesterol molecules give the membrane stability?
cholesterol molecules fit between the phospholipids, they bind to the hydrophobic tails of the phospholipids,
Causing them to pack more closely together, which makes the membrane less fluid and more rigid
what does protein do for the membrane
protein controls what enters and leaves the cell
what are the three types of proteins in membrane
•some proteins form channels in the membrane, these allow small or charged particles through
•some proteins are carrier proteins, they transport molecules and ions across the membrane by active transport and facilitated diffusion
•some proteins act as receptors for molecules in cell signalling, when a molecule binds to the protein a chemical reaction is triggered inside the cell
what do glycolipids and glycoproteins do for the membrane
Glycolipids and glycoproteins act as receptors for messenger molecules
different functions of Glycolipids and glycoproteins in the membrane
Glycolipids and glycoproteins stabilise the membrane by forming hydrogen bonds with surrounding water molecules
• sites where drug, hormones and antibodies bind
• act as receptors for cell signalling
