Cell Membranes Flashcards
What is the role of the plasma membrane?
Partially permeable membrane between:
the cell and its environment
Organelles and the cytoplasm
. Site of chemical reactions
. site of cell signalling
Describe what the fluid mosaic model consists of
Its made up of a:
.Phospholipid bilayer
. Cholesterol
.Glycolipids and glycoproteins
.Proteins
Whats the difference between extrinsic and intrinsic proteins?
Extrinsic- Partially Held on the surface of the membrane
Intrinsic - embedded embedded in the membrane
What is the job of the phospholipid bilayer
It forms a barrier that limits movement of some substances in and out of the organelles so its partially permeable
, Small, fat soluble substances dissolve in the bilayer and diffuse across.
Water - soluble molecules and ions cannot easily cross over.
What does Cholesterol do In the fluid mosaic model.
It fits between the tails of the phospholipid molecules. It inhibits the movement of phospholipids, Reducing fluidity of membrane, it makes it less permeable to water and ions.
increases the mechanical strength and stability of membranes
What does the fluid mosaic model help explain?
What does the fluid mosaic model help explain?
Passive and active movement between cells and their surroundings
Cell-to-cell interactions
Cell signalling
Why is it described as mosaic?
The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above
What is the function of glycolipids and glycoproteins ?
contain carbohydrate chains that exist on the surface (, which enables them to act as receptor molecules
bind with certain substances at the cell’s surface
What are the three type of receptors?
Signalling receptors for hormones and neurotransmitters
Receptors involved in endocytosis
Receptors involved in cell adhesion and stabilisation. ( as the carbohydrate part can form hydrogen bonds with water molecules surrounding the cell
What do Transport proteins in membranes do?
ransport proteins create hydrophilic channels to allow ions and polar molecules to travel through the membrane.
What two types of transport proteins?
- Channel protein
- Carrier proteins (Carrier proteins change shape to transport a substance across the membrane)
Whats special about transport proteins?
Specific to a particular ion / molecule.
What affect does temperature have on membrane permeability?
As temp increases the fluidity of lipids in the membrane, this makes the cell membrane less effective to stopping polar molecules.
At too high temperatures the proteins in the membrane also denature, this disrupts the membrane structure so it no longer forms and effective barrier.
What affect does organic solvents have on membrane permeability?
They dissolve the the lipids in the membrane causing it to loose its structure.
Define diffusion.
The net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration.
How does steeper concentration gradient affect diffusion?
A greater difference in concentration means that more molecules will pass over so a greater rate of diffusion
What affect does temperature have on rate of diffusion?
As you increase the temp the particles have more kinetic energy so this means they will diffuse at a faster rate.
What affect does Surface area have on rate of diffusion?
The greater the surface area across the greater the number of molecules that can cross at one moment so increased rate of diffusion.
What if you have large molecules or Ions /polar molecules
Large molecules diffuse more slowly as they require more energy to move.
Non polar molecules diffuse directly as they are soluble in the phospholipid bilayer.
What if you have large molecules or Ions /polar molecules
Large molecules diffuse more slowly as they require more energy to move.
Non polar molecules diffuse directly as they are soluble in the phospholipid bilayer.
What type of substances require Facilitated diffusion?
Large polar molecules such as glucose and amino acids.
Ions such as sodium and Cl-
What are the two proteins that help in facilitated diffusion?
Channel and Carrier proteins
Whats the difference between channel and carrier proteins?
Channel are water filled they allow charged substances to diffuse through.
