Cell Bio 406 Lecture 5
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Cell Bio 406 Lecture 5
Cellular Biology 406
Channels and Gating
What makes the bilayer impermeable to polar, hydrophillic, and large molecules?
The interior hydrophobic layer
How are membrane transport proteins separated?
channels and carriers, depending on the mode of transportation.
What do ion channels do?
catalyze the rapid and selective transport of ions down their electrochemical gradient
What carries proteins?
transporters and pumps.
Why do transporters and pumps require energy?
They transport against the electrochemical gradient.
Which is faster? channels or carriers?
what mediates permeation of a channel protein?
Where do channels allow permeation?
Which membrane transport protein uses passive transport?
What is the process by which channel proteins open and close in response to stimuli?
What are the types of gating?
How are carrier proteins subdivided?
transporters and pumps
How are transporters further divided?
How do transporters work?
couple with energy stores in electrochemical membrane gradients to facilitate movement
How to pumps work?
Use ATP hydrolysis to drive energetically less favorable substrate accumulation
What type of transport requires energy?
What does primary active transport use?
How does secondary active transport work?
electrochemical potential difference
What is negative resting membrane potential?
inside the cell is slightly more negative than outside
what changes the membrane potential?
ion movement across the membrane
What is membrane potential?
a voltage difference
What is used to generate signals in electrically excitable cells?
how long for a movement of ions through an ion channel?
Are large or small changes in concentration necessary for a change in membrane potential?
What are action potentials?
electrical signals that depend on several types of ion channels.
What do action potentials do?
enable rapid communication between cells.
What are key elements of action potentials?
How is membrane depolarization mediated?
by the flow of Na+ ions into the cell through voltage dependent Na+ channels.
How is repolarization controlled?
transport of K+ ions through several different types of K+ channels.
What does an alteration of action potentials signal?
a predisposition for arrhythmias or epilepsy.
What is membrane targeting of proteins?
cells localizing proteins to specific organelles and membranes.
What is the entry point into the secretory pathway?
How are proteins localized to organelles?
targeting/sorting signals (amino acid sequences in polypeptide)
Where are proteins folded into correct three-dimensional structures?
What are the two basic targeting pathways?
post-translational and co-translational
What is the targeting/sorting signal called?
What happens to a polypeptide if there is no protein tag?
It remains in the cytoplasm.
How does the secretory pathway work?
By small vesicles that bud off the membrane of the source organelle and fuse with the membrane of the distention organelle, releasing the enclosed protein within.
Where do signa'/sorting sequences target nascent secretory membrane proteins to and why?
ER for translocation
What happens to secretory proteins?
they translocate completely
What happens to transmembrane proteins?
They are integrated into the ER membrane
What does the ER do?
Fold and modify proteins
How does the ER fold and modify proteins?
enzymes and chaperones
How does translocation into the cytoplasm occur?
SRP binds to the new sequence as it emerges from the ribosome and docks it to the ER membrane
What is required to translocate SRP bound ribosome/RNA into the ER?
What are the steps to targeting of secretory proteins?
1. Signal sequence translated at 5' end of mRNA.
2. Sequence recognized by SRP and translation halted.
3. SRP recognizes docking protein and brings ribosome to rough ER and signal sequence is inserted.
4. SRP is released.
5. Preotein synthesis restarts and polypeptide chain is pulled through membrane. Signal sequence is cleaved off.
6. Protein in lumen of RER. Ribosome is recycled.
What assists in folding of newly translocated proteins?
What are examples of chaperones?
Hsp-70 and Hsp-90
What is BiP?
Where is BiP located?
In the ER lumen
How do chaperones often function?
What happens to terminally misfolded proteins?
They are targeted for degradation
What degrades misfolded proteins?
What tells the proteosome to degrade misfolded protein?
what is UPR?
unfolded protein response activates ATF6 an d Xbp1.
UPR inhibits protein synthesis.
Triggers cell protective and cell death responses.
What does rough er do?
What does smooth er do?
steriod synthesis and drug detox
What is sarcoplasmic reticulum for?
calcium storage and release
Where is sarcoplasmic reticulum?
in contractile cells
When does the composition of the ER change?
in response to the needs of the cell
How does the composition of the ER change?
Reticulons (proteins in ER that change its curvature) form tubules
What do TOM and TIM do for the mitochondrial matrix?
associate physically and the protein being imported passes directly from one to the other.
What provides energy for import into the mitochondria?
Hsp70 (ATPase chaperone)
When do proteins fold?
before they are imported into the peroxisomes
What is a peroxisome involved in?
catabolism of fatty acids and other metabolic pathways
Where are peroxisomal signal sequences recognized?
in the cytosol
Where are peroxisomal signal sequences targeted?
To a translocation channel
How many pathways are there for a peroxisomal protein?
What is endocytosis?
bringing in of material from outside cell
What are the three types of endocytosis?
what is exocytosis?
discharge of material from vesicles at the cell surface to outside
What is the exocytic pathway?
ER and golgi
What is the endocytic pathway?
early and late endosomes
What happens in vesicle-mediated transport?
a membrane bound vesicle buds from one compartment and fuses with another
Transport to plasma membrane can be ____ or ______ in the exocytic pathway.
constitutive or regulated
What is important in processing endocytosed material?
low pH and degradative enzymes in endosomes
What is the endocytic pathway for?
used to internalize nutrients and regulate the cell surface expression of proteins
What happens to endocytosed macromolecules
they are recycles or degraded
What is the pH of each endosome/lysosome
6.5- early endosome
pH of organelle0 late endosome
What is phagocytosis?
engulfing a solid particle by a phagocyte or a protist to form an internal phagosome
what is pinocytosis?
small particles are brought into the cell forming an invagination (liquids)
what is receptor mediated endocytosis?
clathrin-mediated or caveolin-mediated
What are the steps to vesicle-mediated transport?
What are Rab proteins?
small GTPases that localize to particular organelles.
What happens to receptors?
some are recycles to the cell surface. Others are degraded in lysosomes.
sorting of proteins using endo/exocytic pathways leads to..