Cell membrane Flashcards
What is the purpose of a cell membrane?
- As a physical barrier between the extracellular matrix and the intracellular molecules/organelles
- A selectively permeable membrane
- Ensures the necessary electrochemical gradient
- Communication between cells, adhesion, receiving signals, etc.
How do we ensure the continuity of the relationship between the outside and inner side of the cell membrane?
Integrin proteins that attach to the ECM and the cytoskeleton.
What is a property of the phospholipid that should be appreciated for consolidating the cell membrane?
It is amphipathic, meaning it has two opposing properties, hydrophilia (phosphate head) and hydrophobia (fatty acid tail)
What does cholesterol do?
Ensures the stableness of the system’s liquidity.
True or False?
No cell membranes are symmetrical
True, the cell membranes all have different numbers of peripheral proteins on their surfaces
A common example of this is the fact that the outer (extracellular) surface of the RBCs contains higher phosphatidylcholine and sphingomyelin while the inner surface (intracellular) of the membrane contains phosphatidylethanolamine and phoshphatidylserine
What layer does the glycolipid form?
The glycocalyx
What is the trilaminar display of the cell membrane?
Osmium tetroxide reacts with the glycocalyx and phosphate head to form a darker part that encloses the bright more hydrophobic part.
What are the 2 main differences between integral and peripheral proteins?
Integral proteins go through the whole protein – meaning they can only be extracted by detergent agents that destroy the cell membrane
Peripheral proteins go through only one side of the protein – meaning they can be extracted merely by using salt solutions
True or False
The glycocalyx layer of the trilaminar display looks clear!
False, it looks blurry.
What are glycoproteins for (in terms of intercellular communication)?
They make up a huge number of receptors responsible for adhesion, communication, and response towards signals.
What is the ‘lateral diffusion’ phenomenon for proteins? Give the experimental evidence for this!
When you trace the membrane proteins of a certain cell and then hybridize it with another cell, you would see these traces to be spread out around this hybrid cell
What are some factors that inhibit lateral diffusion of membrane proteins?
- Strong connections with the cytoskeleton
- Strong and tight epithelial junctions
- Lipid rafts
- Scaffolding proteins
Which membrane protein is especially not prone to lateral diffusion?
Enzymatic proteins since they are located at lipid rafts and have scaffolding proteins
What are the 4 functions of the scaffold proteins?
Assembly - acts as a place for assembling signaling proteins
Localization - localizes signaling proteins to certain areas
Feedback - activate or inhibits the reaction
Protection - protects signaling proteins from disturbing kinases
What is the difference between a channel and a carrier protein?
They both transfer particles in and out of the cell. The carrier protein however, changes in shape to accommodate hydrophobic molecules (it creates binding sites to help it go through cell membranes)
What are the 3 subtypes of endocytosis?
Phagocytosis, pinocytosis, and receptor-mediated endocytosis
What is the flow of phagocytosis?
It happens a lot in macrophages, they jolt out their pseudopods to engulf an antigen, they engulf them in phagosomes which then fuse with lysosomes.
What is the flow of pinocytosis?
Invagination of fluids into the cell, causing it to bud off into the cytoplasm of the cell in a pinocytic vesicle that either binds to the lysosome or experiences transcytosis which means that the vesicle travels all the way to the edge of the cell and releases its fluids.
Explain the flow of receptor mediated endocytosis!
Multiple ligands bind to a specific region of high-affinity receptors, this weight causes an invagination into the cell called coated pits.
The intracellular aspects of these coated pits contain clathrin that envelops the entire vesicle, hence the name coated vesicles. Endothelial cells have a similar mechanism, however instead of clathrin, they use caveolin
The cellular invagination then experiences uncoating and fusion to endosomes.
What are these clathrin’s functions?
They regulate vesicle size and scission
What molecule asides from clathrin is involved in vesicle scission?
Dynamins
What protein plays a big role in cellular trafficking?
Mostly Rab proteins, a small GTPase that binds guanine and related proteins
What are endosomes?
The fusion of lysosomes and vesicles that functions as a temporary digestive compartment.
What ensures an endosomes’ ability to work well?
Endosomes typically have proton pumps that ensure the acidity of the intraendosomal enviroment – resulting in higher hydrolytic activity.
