Block 1 - Moving Parts (L8-10) Flashcards
Without energy/ATP, what happens to concentrations in the cell?
K decreases, Na increases, and the cell depolarizes
Compartments in the cell tend to me more (acidic/basic) than the cytoplasm.
acidic
What is the typical size of a lipid bilayer?
4-6 nm (5 nm)
Describe the interior (lumen) environment of the ER.
higher calcium concentration (serves as a calcium store), lower pH/more acidic
What kinds of proteins are formed in the rough ER?
integral membrane proteins, secreted proteins, lysosomal enzyme precursor proteins (they have to be made in a membrane, not free in the cytoplasm, and have to be kept track of instead of floating)
Describe the steps of targeting secretory proteins to the ER
- sequence emerges from the ribosome, and SRP binds to the end
- SRP takes the ribosome to the ER and binds SRP to the receptor
- SRP leaves, ribosome binds to Sec61, and the sequence enters the membrane channel
- finish translation, polypeptide translocates across the membrane
- polypeptide cleaved by signal peptidase and released into the ER lumen
Targeting proteins to the ER lumen and membrane allows for…
parts of the protein to be kept in a membrane vs. the lumen (such as integral membrane proteins)
What is the path of proteins after they leave the ER?
- vesicle packages from the ER move to the Golgi
- enter the cis Golgi network and then the cis face of the golgi
- Golgi modifies/sorts/packages the proteins
- vesicles exit the Golgi from the trans face then go through the Trans Golgi network
Who was Camillo Golgi?
discovered and described the Golgi tendon organ and Golgi apparatus, won a Nobel prize in 1906
What is the Golgi apparatus made of? What does it look like under electron microscopy?
a collection of membrane bound sacs called cistern, looks like a stack of pancakes
What are the cis and trans faces of the Golgi?
cis - toward the nucleus
trans - away from the nucleus
In general, what is the purpose of the golgi?
slow down the vesicles of protein, work on the proteins, and send them on to their destination
also sort and deliver lipids around the cell
What is glycosylation? What are O-linked vs. N-linked glycosylation?
adding sugars
O-linked: adding to a serine residue, in the golgi
N-linked: adding to a asparagine residue, at the ER
Where does synthesis of cholesterol and phospholipids occur?
the smooth ER
Glycosylation is a mechanism for modifying……
protein function
Describe the synthesis of phospholipids
- in the smooth ER, phospholipids are synthesized from cytosolic precursors on the cytosolic side of the bilayer
- they are translocated across the ER membrane by flippases, resulting in even growth of both halves of the phospholipid bilayer
What are Coat proteins?
they play a role in vesicle formation and movement
What role do microtubules play in protein transport?
carrier vesicles move along them to transport proteins from the cytoplasm of the vesicle, in the membrane of the vesicle, or membrane lipids themselves
When the carrier vesicle fuses with the plasma membrane it “turns inside out” so anything that was on the inside of the ER/vesicle is now on the outside of the cell membrane or outside the cell in general
Does protein orientation change from ER to golgi or Golgi to membrane?
ER to golgi it stays the same, but golgi/ER to membrane it is flipped
What do SNARE proteins do?
help the vesicles land where they are meant to go (grab onto proteins on the outside of vesicles and “pull them in”)
targeting and docking mechanism
If proteins are destined to have cytosolic receptors, where are they made?
If proteins are destined to have extracellular receptors, where are they made?
cytosolic - made toward the outside of the ER (the cytosol of the cell)
extracellular - made toward the lumen of the ER
What are secretory vesicles?
cargo for extracellular release, regulated secretion, and held in the cell until a signal causes the vesicle to fuse with the plasma membrane and release its contents
What are lysosomal vesicles?
cargo headed to lysosomes, including lysosomal enzymes (proteases) and lipid membrane components
What are exocytotic vesicles?
cargo for extracellular release, not necessarily regulated (constitutive secretion), and vesicles move continuously to fuse with plasma membrane and release contents
What are COPI and COPII vesicles used for?
COPI: vesicles headed back to the ER
COPII: vesicles headed from the ER to the golgi
Vesicles are routed to their destinations in many ways, but one is…
PIP proteins that define areas (like ZIP codes)
Secretory vesicles sometimes form at the…
trans face of the golgi
The secretory membrane system distributes ——— to the —– and ——-.
integral membrane proteins to the apical and basolateral plasma membranes
What are the 5 mechanisms of endocytosis? Which are selective
**phagocytosis
macropinocytosis
**clathrin-mediated endocytosis
caveolate-dependent uptake
nonclathrin/noncavaeolae-mediated endocytosis
What is phagocytosis? How does it work?
ingestion of large particles like bacteria, foreign bodies, and remnants of dead cells
Attachment depends on ability of cell to recognize the particle via…
- markers called “opsonins”
- antibodies that bind to bacteria
- complement proteins that tag infected or dying cells
After a particle is phagocytosed, what happens to it?
it fuses with a lysosome (forms a phagolysosome) which then degrades the particle using lysosomal enzymes
What is macropinocytosis?
ingestion of extracellular fluid, nonselective, and involves actin driven ruffles of the plasma membrane
What is caveolae-mediated endocytosis?
ingestion of extracellular substances (serum proteins, nutrients, etc.)
nonselective
involves caveolae (specialized regions of the plasma membrane)
What are caveolae?
- “little caves”
- micro domains of plasma membranes enriched with cholesterol
- stabilized by Caveolin
- flask shaped pits 50-100 nanometers in diameter
- distribution is varied (prevalent in endothelial cells and absent in neurons)
What is clathrin-mediated endocytosis?
- selective
- involves specialized regions of the plasma membrane called “coated pits”
- pits have a lattice of clathrin and adaptor proteins
- uptake of nutrients (iron, cholesterol)
- entry of ligand receptor complexes that may be concentrated into the pits
What proteins make up coated vesicles?
AP2, Cathrin, and Dynamin
What is nonclathrin/noncaveolae-mediated endocytosis?
- nonselective
- accounts for endocytosis that occurs when clathrin and Caveolin are disrupted or absent
- mechanism still uncertain
- may involve lipid rafts
- enables cholera toxin and shigella toxin entry
Which methods of endocytosis are selective?
phagocytosis and clathrin-mediated endocytosis
What are the 4 main components of the endocytosomal membrane system?
early endosomes
multivesicular bodies
late endosomes
lysosomes
How can endosomes be recycled?
early endosomes and multivesicular bodies can be directly recycled
early endosomes and late endosomes are indirectly recycled, so they are turned into a recycling endosome at the golgi before being exocytosed
As pH decreases ligand binding —– because…
decreases, because molecules break free into the lumen while the receptors stay in the vesicle membrane
Decrease in vesicle pH facilitates…
protein sorting in endosomal compartments
What is the cytoskeleton? What does it do for the cell?
an elaborate arrangement of protein fibers that serve functions such as…
- definition and maintenance of cell shape
- mechanical strength
- locomotion
- chromosome separation in mitosis and meiosis
- intracellular transport of vesicles and organelles
What are the three filaments that make up the cytoskeleton? What are their approximate sizes?
microfilaments (actin) - 6-8 nm
intermediate filaments - 10 nm
microtubules - 25 nm
What is the composition of microfilaments?
- strands of protein (actin monomers polymerize to form long, thin fibers)
What is the composition and function of intermediate filaments?
- neurofilaments, vimentin, keratins
- structural stability (provide a supporting framework within the cell)
What is the composition and function of microtubules?
- dimers of alpha tubulin and beta tubulin form 13 protofilaments that make a hollow cylinder
- influence cell structure and shape
- motility, organelle movement, cilia and flagella
- provide tracks for motor proteins
What is the function of microfilaments/actin?
- form a band just beneath the plasma membrane
- connect organelles to membranes
- influence cell motility and shape
- anchor membrane proteins to cytoplasmic proteins
- organization/function of microvilli
- anchor centrosomes at opposite poles of the cell during mitosis
- enable locomotion in cells such as leucocytes
- in skeletal muscle, actin interact with myosin to generate force
What are some types of intermediate filaments?
- keratins in epithelial cells
- nuclear laming form a meshwork that stabilizes the inner membrane of the nuclear envelope
- neurofilaments strengthen the long axons of neurons
- vimentins provide mechanical strength to muscle/other cells
What is a centriole vs a centrosome?
centriole:
- barrel shaped microtubule structure made of 9 microtubule triplets
centrosome:
- orthogonal (crosswise) arrangement of two centrioles
What are the roles of centrioles/centrosomes?
- microtubule organizing cente r
- cell motility
- organizing mitotic spindle during cell division
What does it mean that microtubules are dynamic?
- grow by polymerization of tubulin dimers at the “plus” end, which is away from the centrosome
- shrink with the release of tubulin dimers (depolymerization) at the “minus” end, which is toward the centrosome
What are cilia and flagella?
cilia - hair like structures that can beat in synchrony, sweep fluids across cells in the trachea and Fallopian tubes
flagella - whip-like structures that undulate to move cells
What are cilia and flagella composed of? What is the typical arrangement?
arrays of microtubules
typically 9 fused pairs on the outside with either 2, 4, or 0 unfused in the center
Protein “motors” move along…
microtubules
What are the two groups of microtubule motors, and what direction do they move in?
Kinesins - most move toward the plus end (away from centrosome)
Dyneins - move toward the minus end (toward centrosome)
What are the basic elements of neuronal sub cellular organization?
neurofilaments
microtubules
What are anterograde and retrograde movement?
anterograde:
- vesicles bud off of the golgi, move down the axon on microtubule tracks (toward the plus end)
retrograde:
- vesicles move along microtubule tracks (toward the minus end), back toward the golgi
Describe the polarity of axons and dendrites.
In axons, the plus end of microtubules point away from the soma, toward the synaptic terminal
In dendrites, polarity is more random
What is fast axonal transport?
- 100-400 mm/day
- motor proteins running on microtubule tracks
- anterograde movement: transport organelles that carry membrane proteins to the nerve terminal
- retrograde movement: transport vesicles containing neurotrophic factors back to the cell body
What is slow axonal transport?
- 1-4 mm/day
- mechanism still being studies
- delivery of cytosolic and cytoskeletal protein (microtubules, neurofilaments, and enzymes) to the nerve terminal
Do kinesin and dynein do retrograde or anterograde transport?
kinesin - anterograde transport
dynein - retrograde transport
Describe how motor proteins move.
- move unidirectionally
- stepwise
- series of conformational changes (mechanical cycle coupled to chemical cycle)
–ATP binding to motor
–hydrolysis of ATP
–release of ADP and Pi
–binding of new ATP
