Midterm 2 Flashcards
What distinct compartments are part of the golgi complex?
- the cis face (CGN) of the Golgi faces the ER
- the trans face (TGN) is on the opposite side of the stack
- Medial cisternae are sacs between CGN and TGN
What are the functions of the cis Golgi network?
Functions to sort proteins for the ER or the next Golgi station
What are the functions of the trans Golgi Network?r
Functions in sorting proteins either to the membrane or various intracellular destinations
What happens in the medial cisternaie?
This is where processing takes place
What is the process of oligosaccharide glycosylation in the ER?
- biosynthesis of core oligosaccharide for N-linked glycosylation of certain asparagine residues
- initial processing of core oligosaccharide
- identification and removal of misfolded proteins
What is the process for oligosaccharide glycosylation in the CGN?
- attachment of N-acetylgalactosamine to serine or threonine
- first stem of phosphorylation of lysosomal proteins
What is the process for oligosaccharide glycosylation in the medial cisternae?
- removal of mannose
- second step of phosphorylation of lysosomal proteins
- attachment of N-acetylglucosamine
- addition of sialic acid
What is the process of oligosaccharide glycosylation in the TGN?
-attachment of surface to tyrosine
What is the general processing of an oligosaccharide (in terms of Golgi and ER)?
- First N-linked in the ER
- then goes through further processing in the Golgi Complex
Where are o-linked oligosaccharide abundant?
In the extra cellular matrix (ECM)
What does oligosaccharide coating a cell do to it?
it protects the cell
What are some known functions of glycosylation?
- participate in sorting in TGN
- protrusions from membrane can limit the approach of other macromolecules to the protein surface
- serve as recognition molecules in cell-cell interaction
- regulatory roles
What is the vesicular transport model?
Cargo is shuttled from the CGN to the TGN in vesicles (antegrade transport)
What is the cisternae maturation model?
Each cistern “matures” as it moves from the cis face to the trans face
What is the current model for movement of materials through the golgi complex?
Similar to cisternal maturation model but with vesicles retrograde where Golgi cisternae serve as primary anterograde carriers (combination of the the two)
What is the role of the COPII coated vesicles?
Move materials from the ER “forward” to the ERGIC and Golgi complex
What is the role of COPI coated vesicles?
Move materials from ERGIC and Golgi “backward” to ER, or from trans Golgi to cis Golgi cisternae
What is the role of Clathrin-coated vesicles?
Move materials from the TGN to endosomes, lysosomes and plant vacuoles
What does the KDEL sequence do?
Keeps the protein in the ER and it is not secreted out
What is a synaptic vesicles?
In neurons they store various neurotransmitters that are released at the synapse
What is the role of lysosomes?
-can hydrolysis virtually every type of biological macromolecule
What are lysosomal proteins tagged with in the cis-Golgi?
Phosphorylation mannose residues
What are tagged lysosomal enzymes recognized by?
By mannose 6-phosphate receptors which are bound by coat proteins
Where are mannose 6-phosphate residues added?
In the cis-Golgi
What is autophagy?
A pathway that allows cytotoxic proteins and organelles to be delivered to the lysosomal interior for degradation
How does autophagy occur?
- a double membrane structure envelops an organelle to produce a double-membrane sequestering vesicle called an autophagosome
- the autophagosome fuses with a lysosome, generating an autolysosome, in which both the inner membrane of the autophagosome and the enclosed contents are degraded
What is the docking stage?
A v-SNARE in the vesicle membrane interacts with the t-SNARES
What is exocytosis?
The discharge of a secretory vesicle or granule after fusion with plasma membrane
What is endocytosis?
Primarily a process by which the cell internalizes cell-surface receptors and bound extracellular ligands
What two categories can endocytosis be broken into?
- bulk-phase endocytosis (non specified)
- receptor-mediated endocytosis (specified)
What are AP2 adaptors and what is their role in endocytosis?
- adaptors on coated vesicle that face the cytosol
- AP2 adaptors engage cytoplasmic tails of specific receptors to select bound cargo molecules, and bind and recruit the clathrate molecules of the overlying lattice
- helps select cargo
What is Dynamin?
- a G protein required for the release of a clathrin-coated vesicle from the membrane where it forms
- acts as an enzyme that uses the energy from GTP to provide mechanical force
What occurs in G1?
- RNA and protein synthesis
- there is a restriction point that a cell needs to pass in order to enter S phase and continue through the cell cycle
What occurs in S phase?
- DNA synthesis doubles the amount of DNA in the cell
- RNA and protein are also synthesized
What occurs in G2 phase?
-RNA and protein synthesis continue
What are the phases of M phase?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
When does centrosome duplication occur?
-during S-phase
What occurs in Prophase?
- protein synthesis stops
- internal membrane systems that normally associate with microtubules disperse
- endocytosis and exocytosis stop
What occurs in Prometaphase?
- the definitive mitotic spindle is formed and chromosomes are moved by microtubules into the center of the cell
- a single kinetochore is attached to microtubules from both spindle poles
What occurs in Metaphase?
- chromosomes align at the metaphase plate
- chromatids are in a “tug-of-war” between two equally strong centrosomes
What are the three types of microtubules involved in mitosis?
- Kinetochore microtubules
- Astral microtubules
- Polar microtubules
Where are kinetochore microtubules connected?
-to the chromosomes
Where are astral microtubules located?
-project toward the cell cortex and interact with it thereby orienting the spindle of division
What do polar microtubules do?
-interact with microtubules from the opposite pole of the cell
What occurs in Anaphase?
-the two sister chromatids of each chromosome abruptly separate and move toward opposite poles
When is the spindle assembly checkpoint?
-at the metaphase/anaphase transition to check for misaligned chromosomes
What occurs in Telophase?
-the daughter cells return to interphase
What occurs in cytokinesis?
-the cytoplasm is partitioned into two cells
What the Ran-GAP?
- GTPase Activating Protein
- turns it off
What is Ran-GEF?
- Guanine-nucleotide Exchange Factor
- exchanges GDP for GTP
Explain the nuclear import cycle.
- Importin recognizes and binds to NLS (nuclear localization signal) on cargo protein in cytosol
- Importin and cargo protein go into nucleus
- Ran-GEF binds to complex and releases cargo protein
- Ran-GEF and Importin go out of nucleus
- Ran-GAP occurs and GTP is transferred to a GDP and Pi and releases Importin
- Importin is now free to recognize another NLS sequence
- Ran-GDP can diffuse into nucleus to go through GEF again
Explain the nuclear export sequence
- Exportin binds to Ran-GTP(GEF) and NES (nuclear export signal) of cargo protein
- transfers out of the nucleus
- GAP changes GTP to GDP and Ran releases the exportin and and cargo protein
- exportin and the cargo protein dissociate
- Ran-GDP is now able to diffuse into nucleus
- Exportin goes back into the nucleus to pick up more cargo
What are the microtubule motor proteins?
- kinesin
- dynein
What do MAPs (microtubule-associated proteins) do?
-generally increase the the stability of microtubules and promote their assembly
What are the roles of cytoplasmic dynein?
- position the spindle and move chromosomes during mitosis
- position the centrosome and golgi complex and moving organelles, vesicles and particles through cytoplasm
What are two MTOCs?
- centrosome
- basal body
What is a MTOC?
Any structure used by cells to nuclear and organize microtubules
What are centrosomes made of?
Gamma tubulin
What does the GTP cap do?
- adds stability to the microtubule
- GDP in beta tubulin causes a bend in the microtubule where when it stays as GTP and is not hydrolyzed it is straight
What is a catastrophe? (In regards to microtubules)
-GTP is hydrolyzed and the MT depolymerizes rapidly
What are two MAPs and what do they do?
- MAP2- promotes the formation of looser bundles in dendrites
- Tau- causes MTS to form tight bundles in axons
What are three actin polymerization regulating proteins?
- thymosin
- profilin
- cofilin
What does thymosin do?
- sequesters G-actin preventing polymerization’
- When it binds to G-actin then G-actin is unable to polymerize on the growing end
What is profilin?
- acts as an adenine exchange factor, promotes polymerization
- positive regulator
What is cofilin?
- binds ADP-actin and severs filaments
- can take off G-actin one by one
- can sever the filament
- negative regulator
What causes phagocytosis?
- actin is involved in phagocytosis
- actin binding protein networks exert a force
What is processivity?
-an enzyme’s ability to catalyze consecutive reactions without releasing its substrate
What are the steps of the contractile cycle?
- ATP binds to the cleft in the myosin head, releasing myosin from actin
- ATP hydrolysis to ADP+Pi causes weak binding to actin
- Pi release causes tight binding and power stroke backwards
- Actin is pulled backwards and ADP is released freeing the ATP binding cleft
- ATP binds to the cleft in the myosin head, releasing myosin
What are the components of the thin filament of sarcomeres?
- Actin
- Tropomyosin
- Troponin
How does calcium trigger contraction?
- motor neuron excitation signal
- signal transduction pathway leads to Ca2+ release from the ER
- Ca2+ binds to troponin causing conformation shift
- Troponin conformation shift moves tropomyosin out of place
- myosin binding site on actin is exposed
- when excitation signaling ceases, Ca2+ are pumped back into ER and muscle relaxes
