Chapter 4: Transport across cell membranes Flashcards
What is another name for the cell surface membrane?
The plasma membrane
What is the purpose of the plasma membrane?
to surround cells and organelles, to form a barrier between the cytoplasm and the environment.
Describe the basic structure of the cell surface membrane.
A bilayer of phospholipids.
What is the structure of a phospholipid?
a glyerol and phosphate group (molecule head) connected by an ester bond to two fatty acids (molecule tails)
How are the phospholipids arranged in the plasma membrane?
The hydrophilic phospholipid heads are attracted to the water, so point outside the membrane. the hydrophobic phospholipid tails repel water, so point inside the membrane.
What are the purposes of the phospholipids in the membrane?
allow lipid soluble substances to enter cell; prevent water soluble substance from entering/leaving cell; makes the membrane flexible and self-sealing.
What can be found embedded in the phospholipid membrane?
proteins, cholesterol, glycolipids and glycoproteins
What are the two ways proteins can be embedded in the plasma membrane?
on the surface, to provide mechanical support or span the whole bilayer, eg. protein channels and carrier proteins.
What is the purpose of proteins being in the phospholipid bilayer?
provides structural support; transporting water- soluble substances across the membrane; allow active transport; forms cell surface receptors; helps cells adhere together.
What is the purpose of cholesterol in the cell surface membrane?
reduce lateral movement of phospholipids; make membranes less fluid at high temps; prevent water leakage.
What are glycolipids?
they are carbohydrates covalently bonded with a lipid, the carbohydrate extends into the watery outside of the cell, to act as a receptor.
What is the purpose of glycolipids on the plasma membrane?
Act as recognition sites; help maintain the permeability of the membrane; help cells attach to each other to form tissues.
What are glycoproteins?
carbohydrates attached to the proteins on the cells surface membrane, as surface membranes for proteins.
What are glycoproteins function on the membrane?
act as recognition sites; help cells attach to each other; allows cells to recognise each other.
What is the optimum molecule to pass through the phospholipid bilayer?
a small, lipid-soluble and non-polar molecuels. (oxygen and CO2, small and nonpolar)
How are large lipid-soluble polar molecules transported across the cell surface membrane?
through facilitated diffusion or active transport.
What affects the permeability or the cell membrane?
Temperature and ethanol.
How does temperature affect the membranes permeability?
it increases the kinetic energy of the phospholipids making the membrane more fluid.
How does ethanol affect the membranes permeability?
it can dissolve phospholipids.
Why is the membrane a fluid-mosaic model?
fluid- the flexible molecules can move relative to each other. Mosaic- the embedded proteins forms a mosaic like pattern.
