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BIO 344 Exam 2
Terms in this set (107)
How do proteins get moved between the nucleus and cytosol
Nucleus- Gated transport
Mitochondria- trans membrane transport
ER- trans membrane transport then to vesicle transport to get to golgi
What are nuclear pore complexes (NPC)
Large structure that perforate the nuclear envelope and transports macromolecules bidirectionally in ER
What is a nuclear import receptor
initiates nuclear import, cytosolic proteins that bind the signal on the protein to be transported to the NPC then to cytsol
What molecule delivers energy to facilitate transport of large proteins into the nucleus
Describe the sub compartments of mitochondria and chloroplasts
Mito- inner and outer space with matrix in center.
Chloroplast- Thylakoid space and stroma in middle
What are protein translocators
mediate protein translocation across mitochondria
TOM- outer membrane
TIM- inner membrane
Why does it matter that the mitochondrial signal sequence for protein import forms an alpha helix? Describe the properties of this alpha helix
When folded as alpha helix, it is amphiphillic. One side alpha helix is polar, other side charged
Describe how proteins are imported into mitochondrial matrix
-Cross the membrane separately or both at once.
-Bind to their signal sequences
-TOM complex binds the signal sequence
-the interacting proteins strip off to prevent folding
What molecule provides energy for transport of proteins into the mitochondria
How do proteins get directed to the membrane space?
-Matrix space has to cross two different spaces at once
- has to have separate signaling sequence to be transferred to the inter membrane space
What is the difference between smooth ER and rough ER
Smooth- make phospholipid fatty acids, no ribosomes,
Rough- is rough, Yes ribosomes, where translation and synthesis of proteins occur
Where does protein synthesis start
Protein synthesis begins in the cytosol in free ribosomes
How does a protein get directed to the ER
The signal sequence binds to the Signal-Recognition Particle(SRP) which is possible due to the crystal structure of the SRP protein( accommodates many shapes, sizes and sequences)⇒ SRP binds to ribosome ⇒ribosome binds to ER during the protein synthesis block(ensures protein will not be released into cytosol)⇒ SRP-ribosome complex binds to SRP Receptor⇒ goes to protein translocator, SRP and SRP receptor are released ⇒The protein is then pulled by translocator across the membrane
What is the signal recognition particle and the SRP receptor do
- changes shape
-binds to ER
- recognizes signal squence
What happens to the signal sequence after a protein has passed into the ER
The signal sequence continues until it is blocked by a stop-signal sequence
How do transmembrane proteins end up in the ER membrane
ER signal sequences that have start and stop transfer signals
1. N-terminal signal sequence initiates translocation⇒an additional hydrophobic segment in the polypeptide chain stops the transfer process⇒ stop transfer signal enters translocator and anchors the protein in the membrane⇒conformation of translocator changes and discharges protein laterally into the lipid bilayer
2. Signal sequence is internal and not at N-terminal end⇒ SRP binds to internal signal sequence ⇒SRP brings the ribosome making protein to the ER (acts as a start-transfer signal) ⇒Protein translocation initiated and release from translocator, ⇒ Internal start signal sequence then stays in the lipid bilayer as a single membrane spanning alpha helix
3. Intrnal start transfer sequences can bind to the translocation apparatus via 2 methods which determines which part of the protein is moved from the ER to lumen. The resulting membrane protein can have the C or N-terminus on the luminal side.
What are start transfer and stop transfer signals
They are sequences of hydrophobic amino acids.
Start- amino acid that follows are transported across the membrane
Stop- transportation of amino acids that follow across the membrane
How are proteins that pass the membrane multiple times inserted into the ER membrane
Metabolite transporters contain internal signal sequences and snake through the TOM complex as a loop. It then binds to the chaperones in the intermembrane, which guide the proteins to the TIM 22 complex (it is specialized for insertion of multipass inner membrane proteins). TIM 22 inserts proteins using membrane potential but not mitochondrial Hsp70 or ATP.
How are proteins gylcosylated in the ER
Proteins are added to the asparagine amino acid on the N glycosolyated chain needed by an original precursor oligosaccharide which marks the protein. The original precursor is added to the asparagine amino acid in the form of englycosolation
(added to N glycoslated chain of asparagine amino acid, original precursor oligosaccharide added to asparginine amino acid)
What is the link between protein glycosylation and protein folding
Glycosylation checks for protein folding correctly.
What happens when a protein does not fold correctly
labeled with ubiquitin(label for destruction)
-exited from ER
Where are membrane lipids assembled
exclusively in the cytosolic layer of smooth ER
How do they end up in different organelles
SNARE proteins that guide vesicular transport
How come phospholipid exchange proteins are needed to transfer phospholipids from the ER to the mitochondria but these proteins are not needed to move phospholipids from the ER to the Golgi apparatus?
The phospholipids are made in the SER and is transferred needed a vesicle so we don't need it in the golgi but to get to the mitochondria it needs a protein.
Describe the endocytic and biosynthetic secretory pathways in the cell
Secretory pathway: to the ER and out
golgi- secretory vesicles
Endocytic: cell surface and in.
cell surface- early endosome- late endosome- lysosome
How is vesicular transport different from transmembrane transport
fuses with the vesicle and is transported to designated place. The transmembarne protein needs a protein.
Describe the different intracellular compartments involved in the secretory and endocytic pathways
Secretory pathways: ER to out- protein inside then exported- cytosol to ER to Golgi and out to exterior through signal mediated pathway.
or ER to golgi to late endosome to lysosome.
CARGO FROM INSDIE- secretory
CARGO FROM OUTSIDE-endocytic
What is a coated vesicle? Name 3 types. Describe the compartments each of the three types move between
-make the vesicle by bonding membrane
1. clathrin- cell membrane to early endosome
or gogli to late endosome
2. copI- golgi to ER or golgi to cell membrane
3. copII- ER to golgi
Describe the steps involved in the formation of clathrin coated vesicle
Clathrin protein forms a triskelion theme, assembled to form a cage that bends membrane
What is a dynamin and what does it do
pinches clathrin coated vesicle from the membrane
How come a fruit fly with a dynamin mutation ends up paralyzed
Dynamin mutation the vesicle is released from the membrane which causes a problem in the axon terminals
What is a SNARE protein? How does it lead a vesicle to the correct cellular address? How does it help the membrane of the vesicle and target compartment to fuse?
-ensure vesicle goes to correct target membrane and fuse vesicle membrane with membrane of target compartment
-V snare:vesicle membrane
T snare: target membrane
- brings them close and pushes H2O molecules out to allow fusing
How is the HIV fusion protein similar to a SNARE protein
One function is to make sure they are close enough for the membranes to fuse with one another. HIV protein is like a SNARE protein in that it brings the membrane close to fuse with target cell but does not latch on
How are proteins transported from the ER to the Golgi
through copII-coated transport vesicles
How are the correct proteins recruited into cargo vesicles
the use of cargo receptors
What is a vesicular tubular cluster
What type of proteins do you suspect to be retrieved from the Golgi back to the ER
Proteins that are recycled are receptor proteins.
What is the cis and trans face of the Golgi? Which side is closest to the ER? Where do proteins enter? Where do they exit?
Describe some of the functions of the Golgi apparatus
Where in the cell are the first polysaccharides added to proteins? Describe this polysaccharide?
-The original polysaccharide precursor
What two main types of polysaccharide are formed after modification in the Golgi? How are these 2 types different?
Why does a goblet cell in the small intestine have most of its Golgi on one side of the nucleus-polar distribution
Are the enzymes in the cis face of the Golgi identical to enzymes in the trans face?
No, different enzymatic reactions happening in different layers
What do lysosomes do?
How is the interior of the lysosome different from the cytosol
What kind of enzymes are present in the lysosome?
What label direct proteins from the Golgi to the lysosome
Describe 3 different pathways that lead to degradation in the lysosome
What is endocytosis?
up take of macromolecules
What is phagocytosis?
phagosome form and fuses with lysosome
What is autophagy
around organelle, fuse with lysosome
What is exocytosis?
What kind of protein coat is present on endocytic vesicles
Describe in detail how low density lipoprotein particles are taken up by the cell and how they provide cholesterol to the cell
How can a defect in the low density lipoprotein receptor lead to heart disease
Where do endoctosed materials go first?
What happens to the low density lipoprotein receptor after it is present in an endocytic vesicle
receptor picks it up with the LDL and is recycled back to the cell membrane
Can you predict what types of proteins would be recycled an what happens would be degraded
What is a multivescular body
moves stuff from the early endosome to late endosome
What is transcytosis and what do endosomes have to do with it
A receptor that combines antibody proteins that go to the early endosome proteins and go all the way across the cell
What are differences between and early and late endosomes
Early- have no hydrolyses and receptors from enodocytosis like LDL(gets recycled).
Late= does not recycle these and gets its hydrolyses from golgi, lower pH
What is the difference between a late endosome and a lysosome
Late endosome- receives material from early endosome and receives hydrolyses first from gogli
Why do recycling endosomes store important proteins. Describe the example of glucose transporters
Insulin, muscle and liver cells need this to take up glucose so the recycling endosome can fuse for a rapid signal
How come an intestinal epithelial cell has two distinct early endosomes
Two different types of proteins like a sodium glucose transporter so the early endosome will receive to different kinds of cargo.
Describe the 2 different pathways that deliver cell components to the cell exterior
-A substiuent pathway is always on.
-signal mediated secretion pathway turns on and off- insulin, mast cells
What are neurotransmitters delivered to the cell exterior via a regulated pathway
Neurotransmitters are released with an action potential so its a regulated pathway so it doesn't leave its neurotransmitters and communicates only with action potentials vis signal mediated secretion pathway- Ca imported in
What signal is required on the protein to deliver it to the cell surface via the constitutive pathway? What about diversion to the lysosome?
There is no signal required for constitutive pathway. Mannose 6 phosphate is needed for diversion of lysosome
What are mast cells?
What determines if histamines are released from cells?
What do histamines do
Signal mediate an immune response
What is a signaling pathway?
Why do cells have signaling pathways
To respond to changes in the environment
What is the difference between a cell surface and an intracellular receptor? How do the signals for these two types of receptors differ?
Describe 4 forms of intercellular signaling (cougars don't play silly ever)
1. contact dependent- cells have to be able to touch
2. paracrine: local
3. synaptic: neurotransmitter
4. endocrine: release into blood stream, throughout body-insulin
What is autocrine signaling? Why do cells use it when deciding to differentiate?
autocrine allows a group of cells but not a single cell to respond to a differentiation signal! Occurs when cell releases signal and presents receptor for signal
What is a hormone
What are gap junctions
allow signaling information to be passed from one cell to the next
What determines if a cell survives, divides, differentiates, or dies?
signal = survive, divide, differentiate
Does acetylcholine always cause the same changes in different cells? Describe some of the effects acetylcholine can cause in different cells
muscle cell- increase contraction
heart muscle cell- decrease contraction
salivary gland- increase secretion
Why must the lifetimes of signaling molecules be short?
Needs to be turned on or off otherwise it would be useless. Cannot be on all the time
What is nitric oxide? What role does it play in signaling pathways
acetylcholine causes release of nitric oxide receptors.
results in rapid relaxation of smooth muscle cell.
What are nuclear receptors
What types of ligands do they bind?
To steroid hormones via three domains:
1. steroid binding domain
2. DNA binding domain that recognize specific DNA sequences
3. transcription activation domain
Describe 3 domains of a nuclear receptor
1.Steroid binding domain
2. DNA binding
3. Tracsciption activation binding
Describe the 3 largest classes of cell-surface receptors. Give an example of each
1. ion channel linked receptors: acetylcholine receptor in skeletal muscle
2. G-protein linked receptor- changes happen inside cell- adrenaline
3. Enzyme linked receptor: 2 halves- insulin receptor
What are second messengers. Describe 3 types
What is a G protein linked receptor?
on the extracellular side, 3 subunits- Alpha beta gamma
Describe the structure of G-protein linked receptor
receptor on extracellular side, moves across plasma membrane
What is a G protein
binds to receptor when signaling molecule is present
Describe structure of G protein.
Inactive with 3 subunits- alpha, beta, gamma. when activated split into 2 parts- 1. alpha 2. beta and gamma
What happens to a G protein when it is activated
split into 2 parts- 1. alpha 2. beta and gamma
Give an example of a signal that binds to a G protein linked receptor
How is G protein decapitated?
hydrolysis in alpha subunit
How can the g protein linked receptor be deactivated when the signal remains present
Descrbe in detail how G proteins can change transcription patterns via cyclic AMP (cAMP).
g protein and receptor can activate a G protein which will signal GTP. cAMP bins to protein Kinase A, and then activates PKA once binded
What is kinase
phosporylates other proteins adding phosphate groups. may change shape
How is cAMP made
Describe in detail how G proteins activate Kinase C
What is a function of Ca2+ in the cell
How do cells keep Ca2+ concentrations low in cytosol
What are 2 differences between enzyme linked cell surface receptors and G protein linked cell surface receptors
Give an example of a signal that binds an enzyme linked receptor
receptor tyrosine kinase, as in fibroblast growth factor receptor (most enzyme-linked receptors are this kind)
What happens to an enzyme linked cell surface receptor when the correct signal docks?
It signals the signaling pathway
What is the Jak-STAT signaling pathway? What does Jak and what does STAT do?
Signaling pathway provides fast track to nucleus.
-Jak: enzyme linked receptor
-STAT: DNA binding protein
-can change transcription rapidly b/c they communicate directly with nucleus
Give an example of signal that activates the Jak-STAT pathway
Cytokine like interferon or erythropoetin
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