Dr. Mhawi 2 Cell Membranes Flashcards
What does the plasma membrane consist of?
–Consists of a bilayer of phospholipids within which protein and cholesterol molecules are embedded
- Plane of phospholipids within which membrane proteins are able to move laterally
- Movement of proteins within the membrane is highly controlled (not free movement)
True or False: Transmission electron microscopy (TEM) is required to explore the details of the plasma membrane.
True
Describe this image
When viewed with TEM plasma membrane and intracellular membranes appear as two electron-dense lines (leaflets) separated by an electron-lucent (non-staining) layer
Describe the function of lipid rafts?
- Called lipid rafts
- Exist in different functional classes
- Contain high concentration of cholesterol, glycosphingolipids and
membrane-associated proteins
- Lipid rafts are involved in signal transduction, T lymphocyte activation, and HIV virus entry into CD 4 T lymphocytes
- Rafts are less fluid than the surrounding none raft membrane
- Due to the high concentration of cholesterol
- Rafts can be mobilized to different regions of the membrane following stimulation
What are the two main types of membrane proteins
Integral proteins and Peripheral proteins
Integral proteins:
-Transmembrane proteins that pass through
the lipid bilayer (single pass or multiple pass)
- Partially lipid-anchored proteins:
Located outside lipid bilayer, on extracellular or
cytoplasmic surface
Peripheral proteins:
Located outside lipid bilayer (i.e., cytoplasmic or
extracellular sides)
______ for ions, amino acids, sugars
_______for diffusion of ions and small molecules
_______ to detect and transduce chemical signals
•e.g., receptor to hormones
_______ proteins: anchor cytoskeleton to extracellular matrix
•e.g., family of integrins
______ such as ATPases, disaccharidases and sipeptidaes
________ such as junctional proteins
Pumps
Channels
Receptor
Linker
Ezymes
Structural
Explain this image.
- Integrins are transmembrane linker proteins
(consist of α and β subunits; dimer)
- Responsible for specific interactions between cell
cytoskeleton (actin filaments) and the extracellular matrix
(collagen fibers)
What is this image?
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TEM of freeze-fractured plasma membrane. Arrows point to aggregated transmembrane proteins. V, vesicle.
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Why do some membrane proteins form in clusters?
-Fluidity of the membrane enables clusters of some membrane proteins to assemble at certain sites within the membranes to form specialized structures
Explain how membrane proteins are confined to specific domains in a continuous plasma membrane
–e.g., in epithelial cells of the GIT or kidney tubules specific plasma membrane enzymes and transport proteins are confined to the apical surface of the cells (red)
–Others, functionally different proteins, are confined to the basal and lateral surfaces (green)
•The confinement of the proteins to their domains is maintained by tight junctions made by another plasma membrane proteins
True or False: Plasma membrane contains about 70% of the cellular cholesterol
False: 90%
______ amount of cholesterol decrease membrane fluidity
______ amount of cholesterol increases membrane fluidity
______ of the optimal range for membrane fluidity influences many biological lfunctions
Greater
Lesser
Alteration
____ is the outer leaflet of the plasma membrane is covered with fuzzy layer of branched carbohydrates chains attached either to lipid and form glycolipids or to protein and forms glycoproteins
Glycocalyx
What are the 4 functions of the glycocalyx?
- attachment of some cells (e.g. fibroblasts)
- cell recognition
cells of transplanted tissue/organ may be rejected due to the recognition of foreign integral membrane glycoproteins
- enzymes
- receptor sites for hormones
Describe the image
Glycocalyx
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Function of Plasma Membrane Domains
What are the 3 types of membrane transport?
Simple diffusion
Membrane transport porteins
Vesicular transport
How do carrier proteins work?
- Transfer small water-soluble molecules
- Highly selective (transporting only one type of
molecule)
- Carrier may undergo conformational changes to carry out their job.
- some require energy (active transport, e.g. Na+/K+ pumps and H+ pump)
- Some do not require energy (passive transport, e.g. glucose transporters)
How do channel proteins work?
•Transfer ions and small water-soluble molecules via hydrophilic channels through the plasma
membrane
•Channel proteins are regulated:
–In neurons by membrane potentials (voltage-gated ion channels)
–In skeletal muscles by neurotransmitters of the neuromuscular junction (ligand-gated ion channels)
–In the inner ear by mechanical stress (stress-activated ion channels)
How do clathrin coated vesicles work?
Upper panel: Series of electron micrographs illustrating the process of the uptake of low density lipoprotein (LDL) by a clathrin coated vesicle. The process is initiated when LDL molecules (red) are recognized by receptors located in the plasma membrane (yellow). At this site the plasma membrane (black line) is indented toward the cytoplasm and the indentation is coated with clathrin molecules (blue) to form a clathrin coated pit (stage 1). Clathrin coated pit progresses into a deep invagination (stage 2) that eventually gives rise to a clathrin coated vesicle (stage 3). This vesicle is still connected to the plasma membrane by a neck (stage 3). Dynamin (green scissors in stage 3) is an enzyme that pinches off and suspends the vesicle free in the cytoplasm(stage 4). Later, the free vesicle with its content is directed to the lysosome to breakdown the LDL (stage is not shown). Lower panel: comparable series of interpretive diagrams.
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How do coatomer coated vesicles work?
cover made of proteins that play a role in protein transport between rER and Golgi network
–Anterograde transport
- Vesicles move from rER to Golgi
- Vesicles are coated with COP II
–Retrograde transport
- Vesicles move from Golgi to rER
- Vesicles are coated with COP I
How do caveolin coated vesicles work?
Cross section of a capillary. Arrows point to caveolin-coated vesicles scattered throughout the tiny cytoplasm of the endothelial cells that make the wall of the capillary. The vesicles are engaged in the transportation of molecules into and out of the capillary lumen.
_______ – substances enter the cell
_______ – substances exit the cell
_______ – substances enter the cell from one side and exit from the other side
ENDOCYTOSIS
EXOCYTOSIS
TRANSCYTOSIS (plasma cell from mothers breast)
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