Lecture 15 - Membranes Flashcards
Bacteriophages Attacking a Bacteria:
1- BP recognizes specific proteins and binds
to a cell through its tail fibers
2- Sheath contracts, injecting the viral DNA
into the cell through the spikes on the
bottom of the structure
3- the viral DNA inserts itself into the
bacterial genome and highjacks the cellular
machinery to make more viral proteins and
DNA which assembles into more BPs
4- Will cause the cell membrane to rupture
(killing the cell)
Virus Life Cycle: Lysogenic life cycle
1- Envelope has glycoproteins on it that
recognize and bind to specific plasma
membrane receptors on the cell
2-Virus undergoes endocytosis and enters
the cytosol
3- Virus fuses with the endosome and this
releases the capsid
4- the RNA is translated by host cell
machinery, the RNA is replicated by a viral
specific RNA pol.
5- Capsid proteins are made on free ribosomes in the cytosol and the glycoproteins that are going to insert into the plasma membrane are made on the ER and moved through the endomembrane system
6- Capsid forms around RNA, moves towards the plasma membrane, interacts with the viral glycoproteins are undergoes exocytosis
Functions of Biological Membranes
1) Define cell boundary
2) Define enclose compartments
3) Control movement of material into and out
of cell / organelles
4) Allow response to external stimuli
5) Enable interactions between cells
6) Provide scaffold for biochemical activities
the trilaminar structure is a ______ _______
lipid bilayer
The lipid bilayer is made up of
phospholipids
Proteins are embedded in or associated with the
phospholipid
bilayer
components are mobile
Fluid
diverse ‘particles’ like proteins, carbohydrates, and cholesterol penetrate the lipid layer; Components can interact
Mosaic
phospholipids consist of a
glycerol backbone bound by:
– Two non-polar fatty acyl
molecules (“fatty acid chains”)
– A polar head group linked by a phosphate residue
Phosphatidyl….
ethanolamine
choline
serine
inositol
Phospholipids are amphipathic
– Hydrophilic - attracted to / binds water
– Hydrophobic - repelled by water
Lipid molecules, like phospholipids,
spontaneously aggregate to bury their
hydrophobic tails in the interior and expose
their hydrophilic heads to water.
A molecule will always be in a conformation
in which it is the most
stable
Micelles are
usually formed by fatty acids with only
one hydrophobic chain
Synthesis occurs in
pre-existing membrane
Synthesis occurs in a multistep process at the interface of the
cytosol and outer endoplasmic reticulum membrane
ER membrane contains all the
molecular machinery (enzymes) for synthesis and distribution
Three classes of membrane proteins
INTEGRAL
PERIPHERAL
LIPID-ANCHORED
INTEGRAL membrane proteins span
the lipid bilayer
PERIPHERAL membrane
proteins associate with the
surfaces of the lipid bilayer
LIPID-ANCHORED proteins attach to a
lipid in the bilayer
Different integral (transmembrane)
proteins have different functions
For instance:
1) Transport of nutrients and ions.
2) Cell-cell communication (gap
junction)
3) Attachment
Lipids move easily, laterally within
leaflet
Lipids movement between leaflets is
difficult and slow
