Lecture 5 - Membrane structure, function, composition (proteins) Flashcards
what kind of errors can happen during protein synthesis?
misfolding, damage, short-lived proteins
what is a protease
an enzyme that breaks down protein by hydrolyzing their peptide bonds
What proteins need for proteasome to degrade them?
Ubiquitin chain
what is proteasome?
cylinder protein machine that degrades other proteins in the eukaryotic cell located in the nucleus and cytosol
The concentration of a protein in a cell depends on the rates at which the mRNA and protein are _______ and _____.
synthesized and degraded
Protein degradation in the cytosol and nucleus occurs inside large protein complexes called ______.
proteasome
Proteins that enter to proteasome have been marked by ______, a small protein
tag, which is ______ bond
ubiquitin and covalently bonded
what is Proteolysis
the breakdown of proteins by proteasomes
how do you see specific protein?
western blot and you have to know the protein you are looking for
most abundant lipid in cell membrane
phospholipids, which has hydrophilic head and hydrophobic tail
what is amphipathic?
having both hydrophobic and hydrophilic regions in a molecule
what other lipids are amphipathic?
sterol and glycolipid
hydrophobic molecules tend to do what in water?
come together to form a fat droplet
why do hydrophobic molecules avoid water?
primarily because it is uncharged and unpolarized
describe the function of the cell membrane
- Serve as boundary and permeability barriers for molecules to specific compartments
- Regulate transport of molecules and ions.
- Provide platforms/surface area (e.g., ER, thylakoid membranes)
- Serves as sites of signaling for cellular communication (e.g., detect and transmit electrical and chemical signals)
- Enable capacity for cell movement and expansion
why do bilayers form the ball?
as a sheet it is energetically unfavored because of the exposed hydrophobic tails, when it is enclosed then it is energetically favored
does an unsaturated hydrocarbon tail have a kink?
yes
what happens to free edges in the cell membrane?
it is quickly resolved
the ____ the hydrocarbon tail, the more movement is allowed
shorter because there is less Van der Waal forces
what kind of movement happens to the lipid bilayer?
flexion, rotation, and lateral diffusion
the _____ unsaturated the hydrocarbon tail, the more movement is allowed
more
cholesterol are classified as?
sterol
phospholipids form bilayers only in _____ solvents 1
polar
where are new phospholipids formed?
in the cytosolic surface of the ER to the cytosolic half of the bilayer
how does the inner layer of the bilayer have new phospholipids?
outer lipids are transferred by scramblase to the inner layer, a transporter protein
what is scramblase?
a phospholipid translocator that flips phospholipids for symmetrical growth of the bilayer
most cell membranes are asymmetric, why?
occurs in the golgi, where specific phospholipd translocators (flippase) selectively remove phospholipids from the non-cytosolic side to cytosolic side.
flippase is an enzyme
ATP dependent and new membrane is still from the ER
what is flippase?
An enzyme that catalyzes the transfer of extracellular phospholipids to the cytosolic monolayer of the bilayer, needs ATP
How does cholesterol affect the membrane?
can stiffen bilayer, make it less flexible, and less permeable
what is the cytosol
The gel-like fluid that is mostly water
All membranes have distinct
surfaces with varying composition
of …..
phospholipids, glycolipids and
proteins.
what is it called when the membrane of the golgi breaks of?
A tranport vesicle
the cytosolic face always faces the cytosol, even when fusing with the p
where are the glycolipids found?
Mainly in the plasma membrane and are on the noncytosolic side
no flippase happens
sugar groups (from golgi) face extracellular space and is trapped in this monolayer
what are the three main membrane lipid molecules?
phospholipids, sterols, and glycolipids
the two monolayers of a cell membrane have diff. lipid compositions. (T/F)
True
this provides different functions of the two faces of the membrane
does choloeterol have a fatty acid tail?
No
it has a hydrocarbon tail but isnt fatty acid
New membrane phospholipids are synthesized by enzymes bound to the —– side of the —– membrane.
cystolic and the ER
polypeptide chains often cross the bilayer as ……
an alpha helix
what are different ways proteins associate with the membrane?
- transmembrane (embedded within)
- monolayer association (embedded on 1 side by alpha helix)
- lipid-linked (covalently attached lipid molecule)
- protein attached (noncovalent attached with other proteins)
what do plasma membrane proteins do?
- transport molecules and ions
- act as anchors
- detect signals for cell comm.
- act as enzymes
what is a peripheral membrane protein?
indirectly attached to the membrane
“protein attached”
how is the alpha helix oriented in the membrane?
hydrophobic section of the amino acid is embedded to the hydrophobic section of the membrane, although backbone is hydrophilic
formed by hydrogen bonding the backbones and the hydrophobic side chains
what is a beta barrel?
made from beta sheet rolled into cylinder. outside of barrel is hydrophobic and inside barrel is hydrophilic
example would be Porin Proteins in mitochondrial and bacterial outer membranes
how is a hydrophilic pore made?
From alpha helices(many) so its like cylinders that sit circular and form an aqueous pore for transport
what do you use to destroy the lipid bilayer?
use detergent, which disrupts hydrophobic associations
glycoprotein = ?
glycosylated protein
Explain the carbohydrate layer of the plasma membrane
sugars attached on the outside of the embedded proteins of the membrane form slippery surface
protects against mechanical forces and lubricate
covalently attached
how can proteins move in the membrane?
membrane is fluid so they can move by lateral diffusion
how can lateral mobility be restriced?
- tethered by protein-protein intertaction (inside)
- tethered to ECM molcules (outside)
- tethered to another cell cortex inside cell
- diffusion barriers
define glycocalyx
the carbohydrate layer of the membrane
