Intracellular compartments (Sept 19) Flashcards
What percentage of a cell volume is cytosol?
~50%
What percentage of a cell volume is cytosol?
~20%
The majority of cell membrane (by percentage, intra and extracellular) is taken up by _______, followed by ________, followed by ________.
Endoplasmic Reticulum
mitchondrial inner membrane
Golgi apparatus
There are some general trends in compartment size, why is it a bad idea to rely on any of these trends.
Because the cell will vary how much of each organelle it has based on its function and size.
What is the theory for the evolution of the nucleus?
That it began as an invagination of the cell membrane, which later closed off and stayed within the cell.
What is the theory for the evolution of the endoplasmic reticulum?
It developed out of the nuclear membrane. Indeed the extracellular nuclear membrane is continuous with the endoplasmic reticulum.
Describe the nuclear membrane.
It is has multiple nuclear pores, and is a fluid containing organ, like the endoplasmic reticulum. Indeed it is continuous with the endoplasmic reticulum.
What gives each organelle its unique activity?
The unique proteins it possesses.
How many proteins does the average Eukaryotic cell have within it?
How many different varieties?
~10^10
~10,000
Give to examples of organelles which maintain an electrochemical gradients across their bilayer.
ER: Ca2+
Mitochondria: H+
What are the three methods of protein trafficking within the cell?
- Vesicular transport
- Transmembrane transport
- Gated transport
Describe vesicular transport.
Vesicular transport is always between topologically equivalent areas.
ER has vesicular transport to?
Peroxisome and the Golgi.
Golgi has vesicular transport to?
ER, secretory vesicles, endosomes, early and late, cell exterior.
What is budding and fusing in vesicular transport?
budding: vesicle just beginning to leave a membrane surface.
fusing: A vesicle which is combining with a membrane surface.
Define transmembrane transport of proteins.
Movement through translocator channels across membranes. Moves into a topologically distinct department.
How does protein movement through a translocator channel differ from movement through a gated channel?
A protein must unwind and be fed through a translocator protein as a strand of amino acids, then it refolds on the other side. Gated channels can transport folded proteins through them.
Transmembrane transport normally moves proteins from within the ______, to within an ______ compartment.
Name three examples of transmembrane transport.
cytosol
intracellular
Cytosol–>mitochondria
Cytosol–>chloroplast
Cytosol–>ER
Has transmembrane transport been seen in the PM?
I don’t know… he doesn’t say. But the slides implied this isn’t known yet.
What are sorting signals?
They are areas of a protein which can be recognized and bound by specific receptors. Sorting signals essentially tell where to send the protein.
What are the two types of sorting signals?
Signal sequences: linear sequence of amino acids, generally at the Carboxyl or amino end of the protein.
Signal patches: little separated amino acid sequences which will line up once the protein has been folded, they will be recognized by receptors.
What is a signal patch or sequence analogous too?
An address on a postal letter.
Name three types of cells with no nucleus in animals.
Platelets
RBCs (accept in birds, reptiles)
Some cells in the lens of the eye
What cell type can have multiple nuclei in animals?
Skeletal muscle fibers.
What is the lumen between the two membranes of the nucleus?
Perinuclear space. It is continuous with the ER lumen.
What are nuclear lamina?
Intermediate fibers which form a matrix on the intra nuclear side of the nucleus.
Define Nucleoporins:
any protein which is a part of the nuclear pore complex.
How many nucleoporins are in each nuclear pore complex?
500-1000
Cytosolic fibrils:
Are repeating phenyl-alanine (F), and glycine (G). They reach out into the cytosolic place and are thought to bring in proteins via nuclear receptors (which will bind to their signal sequence).
How does the nuclear pore sit in the nuclear membrane?
The poor must be reacting with the hydrophillic head groups only, because the membrane curls around at the pore.
Can small molecules diffuse freely through nuclear pores?
What size must these molecules be?
yes if they are ~9 nM
Can large molecules freely diffuse into the nucleus?
No, they must be actively, selectively moved.
Define
nuclear-resident proteins:
Transcription Factor Proteins:
nuclear-resident proteins: These are proteins which are meant to reside in the nucleus, they must be transferred there from the cytosol were they were synthesized.
Transcription Factor Proteins: Enter the nucleus to bind DNA, change function.
Name three types of molecules that must be able to enter and exit the nucleus.
Nuclear-resident proteins. (in)
Transcription factors. (in)
mRNA (out
Where does a nuclear import signal send you to?
It sends you to the nucleus… without it the protein will not be able to enter.
______ where used to visualize protein transport into the nucleus.
Colloidal gold spheres
Why does protein tagging with colloidal gold spheres allow visualization of the protein?
Because gold will appear opaque on an electron microscope.
Nuclear import receptor.
There is a variety of nuclear import receptors. They bind proteins with distinct nuclear localization signals.
Nuclear import adaptor protein does what?
It binds to a protein with a unique signal sequence, and then binds to a nuclear import receptor.
G-proteins are a nickname for proteins which do what?
That bind and hydrolyze GTP. This gives them a switch like protein.
Do G proteins have GTPase activity?
Do they act as molecular switches?
Yes.
Yes.
What are downstream effector proteins?
They are proteins that result from the signal cascade caused by G proteins.
Generally, in what conformation must a G protein be in to interact with a downstream effector protein.
It must be bounded to GTP (not GDP, GTP). GTP GTP.
GAPs stands for?
GTPase-accelerating proteins
GEFs stands for?
Guanine nucleotide-Exchange Factors.
What do GAPs do?
Well since they are called GTPase accelerating proteins we can correctly assume they increase the rate at which GTP is hydrolyzed. GTP–>
What do GEFs do?
Guanine nucleotide-exchanger factors, enable the G protein to release GDP.
Are GAPs and GEFs specific for specific types of G proteins?
Yes. There is generally specificity in this system. With one type of G-protein having one type of GAP and GEF to help it catalyze.
Why is GAP necessary?
Because while G proteins are already hydrolytic enzymes (GTPases), the are GTPases with very low catalytic efficiencies. Therefor they need GAP.
What are the two main types of G-proteins?
Heterotrimeric G proteins
Monomeric G proteins
You stopped right before RAS. Make sure you cover RAS on your next series of slides.
DO IT!!!!!!!
