3. Eukaryotes & the plasma membrane Flashcards
what is the endomembrane system
the specialised membranes inside the cell
describe plant cell walls
composed of cellulose fibres embedded in a polysaccharide matrix- this consists mainly of hemicellulose and pectin
how large are nuclear pores in the double nuclear membrane
100nm in diameter
where is hemicellulose and pectin found
in the polysaccharide matrix in the cell wall
what is chromatin
DNA and histone proteins
where are ribosomes manufactured
in the nucleolus
list 4 functions of the plasma membrane
- separates cell contents from its external environment
- controls the entry of nutrients and exit of waste products
- maintains electrolyte balance in the cell
- acts as a sensor to external signals
membrane lipids are ampiphatic. What does this mean?
have both hydrophobic and hydrophilic parts
what are the three main types of lipids in membranes
- phospholipids
- cholesterol
- glycolipids
describe the structure of a phospholipid
polar hyrohpillic head
two hydrophobic carbon tails
what does cholesterol do
increases membrane stability
true or false:
lipid molecules can exchange places with adjacent lipid molecules
true
what type of molecule in cholesterol
steroid
what does cholesterol do at warm temperatures
at warm temperatures cholesterol restrains movement of phospholipids and provides stability
how can you observe membrane proteins
using free fracture electron microscopy
what are the functions of membrane proteins
- transport proteins= sodium/potassium pump
- receptor sites e.g. for a hormone
- cell junctions e.g. tight junctions
what causes cystic fibrosis
causes by a defective chloride ion channel resulting in viscous mucus build up
what is a glycocalyx
a network of polysaccharides that project from cellular surfaces
why are membrane carbohydrates important
involved in cell to cell recognition
what is pinocytosis
cells infold part of the plasma membrane to take up extracellular fluid in small. vesicles
what is phagocytosis
uptake of insoluble material, in protozoa it is a form of feeding
what is receptor mediated endocytosis
involves the binding of macromolecules to specific cell surface receptors- this triggers endocytosis
what is the role of Clathrin
endocytosed macromolecules are coated with a bristle like protein called clathrin
Clathrin polymerises around the vesicle forming a cage like structure.
how does exocytosis occur
vesicles fuse with the plasma membrane expelling the contents into the surrounding medium
