Exam 3 Flashcards
The difference between bright-field and fluorescence microscopy is…
That one views the light passing through the sample and the other actually looks at light emitted from the sample.
One drawback of electron microscopy is that it…
Cannot be used to view living cells
Your lab TA just gave you a culture dish in which he claims there are cells called fibroblasts attached to the bottom. You cannot see anything on the bottom and think the TA is putting one over on you. Which method of microscopy would you use to best and most easily visualize the unstained cells without killing them?
Phase contrast microscopy
Which type of microscopy requires coating the sample with a thin layer of a heavy metal and can produce three-dimensional images of small surface projections from cells?
Scanning electron microscopy (SEM)
Proteasomes act primarily on proteins that have been marked for destruction by the covalent attachment of which small protein?
Ubiquitin
Which of the following statements is NOT true about the differences between liver cells and kidney cells in the same organism?
They contain different genes
After an RNA molecule is transcribed from a eukaryotic gene, portions called ____________ are removed and the remaining ___________ are spliced together to produce an mRNA molecule with a continuous coding sequence.
Introns, exons
Which of the following modifications can be made to an RNA molecule in eucaryotic cells before the RNA molecule becomes a mature mRNA?
Splicing, addition of methylguanosine cap to 5’end, and polyadenylation
Use of this common reporter gene fused to your gene of interest (such as lamins) would allow you to see where the lamins are localized in a living cell and see how the lamin distribution changes during the cell cycle. What is this reporter gene called?
Green fluorescence protein (GFP)
You would like to eliminate or reduce the expression of the intermediate filament vimentin in certain mouse cells you are studying. Which of the following experimental approaches could you potentially use to reduce the gene expression?
Use RNA interference (RNAi) or make a knockout mouse
What is the benefit of phase contrast microscopy?
Ability to see living (or dead) cells without stains
What is the benefit of fluorescence microscopy?
Ability to label specific structures individually and compare fluorescence/distributions
What is the benefit of SEM?
Can see fine details of surfaces (3D)
What is the benefit of DIC?
Ability to see living (or dead) cells without stains and has slightly more 3D than phase contrast
What is the benefit of bright-field?
Can use stains to differentiate and see different cell structures
What is the benefit of TEM?
Better resolution, can see smaller structural details compared to light microscopy
When we say that the gene for a specific type of serotonin receptor is expressed in smooth muscle, what is meant by expressed?
The gene has been transcribed into mRNA
What does it mean to say that a gene is “turned off?”
No mRNA is being transcribed from that gene (it’s present but not expressed)
What would happen to the mRNA if the mRNA wasn’t polyadenylated?
It would likely be degraded more rapidly than if polyadenylated and may not be exported from the nucleus
What does phosphorylation do for RNA processing?
Phosphorylation of the tail of RNA polymerase II allows RNA-processing proteins to assemble there
What does capping do?
Modifies 5’ end of transcript (synthesized first) by addition of an atypical guanine bearing a methyl group after RNA polymerase II has produced some nucleotides
What is polyadenylation?
Provides a newly transcribed mRNA that’s trimmed and another enzyme adds a series of repeated A nucleotides
What is splicing?
Introns removed by spliceosome and exons stitched together with ligase
A major regulator of the cell cycle is a protein called cyclin. Cyclin levels gradually increase before mitosis, and then their levels suddenly drop when mitosis nears completion. Interestingly, mRNA levels for cyclin are constant throughout the cell cycle. What would you expect to be responsible for the rapid drop in cycling levels at the end of mitosis?
Increase in ubiquitin addition to cyclins
Antibodies can be membrane-bound or secreted, depending on whether a stretch of additional amino acids are present or not. What process do you think determines if these amino acids are present?
Alternative RNA splicing
You have identified a gene that is affected by an immune disorder. Describe two experiments you could do that would help you figure out what the gene does.
Three main approaches: See it (where it is localized?), block it (prevent it from functioning and see what happens) , and add it (either overexposes it or express it where it normally isn’t and see how it affects the cell). Specifically, use an antibody and add it to different tissue sections, add GFP and transfect it into cells, knockout mouse or use RNAi in cultured cells, transgenic mice
What cells would you expect to have a high density of cytoplasmic intermediate filaments?
Human skin epithelial cell or nerve cell but not amoeba or plant cell
Why is there an initial lag in the rate of formation of microtubules?
Due to nucleation of microtubules, the process of initially forming a microtubule from the tubulin subunits is slow (slower to build microtubule from scratch than adding tubulin dimers onto existing microtubules
Why does the curve of rate of formation of microtubules level out?
Since concentration of free tubulins begins to decrease, you get to an equilibrium point where the amount of tubulin being removed from microtubules is the same as the amount being added
If you were to measure the rate of formation of microtubules but add purified centrosomes, what part of the new graph would be dissimilar than the normal graph?
The beginning because it will nucleate faster so the curve will rise more quickly
How is cell function regulated?
Regulate activity/conformation of individual proteins by affecting its ability to bind to other molecules and altering levels of individual proteins *Both change in response to extracellular signals
How are proteins regulated?
Transcriptional control (rate), RNA processing control, mRNA transport and localization control (nuclear export), mRNA degradation control (rate), translation control (rate), protein degradation control (rate), and/or protein activity control (protein processing/transport)
Why does an increase in mRNA not necessarily equal an increase in protein?
There’s multiple steps to regulating protein levels
What are some experimental approaches to studying proteins/cells?
See it, block it, or add it
What is the see it approach?
Use microscopy and other methods (antibodies) to measure protein and mRNA expression to see where, in which cells, where within the cells it is expressed, does its location or expression change depending on signals coming in, or does modification of proteins change it
What is the block it approach?
“Knockout” mice or RNA interference or using inhibitors or dominant negative constructs
What is the add it approach?
Transgenic animals (new gene) or cell transfections with expression vectors
What is a benefit of cultured cells?
Easier to see and manipulate
What does growing cells in culture dishes require?
Salts, amino acids, vitamins, glucose, etc. (anything a normal cell needs to survive) and also requires growth factors found in the bloodstream
What is a primary cell culture?
Individual cells dissociated from tissue (some divide in culture, some do not)
What are immortalized cell lines?
Tumor cells like HeLa or manufactured cell lines that use tumor-promoting chemicals, genes, viruses, etc. that have continual cell division
What can you use to find where proteins are localized?
Light microscopy: Immunofluorescence (use labeled antibodies), labeled toxins, or directly tag (i.e. GFP)
What are some useful techniques to finding proteins in cells?
- ) Fluorescence microscopy
- ) Video and digital microscopy (follow in real time)
- ) Recombinant DNA techniques (i.e. express protein joined to GFP)
What are ways to get proteins into eukaryotic cells?
Transfection of DNA (get plasmid into cells using various methods such as Ca precipitation, lipids, electroporation), microinjection into cells, or recombinant viruses (replication deficient, infectious: express transgene)
The major types of intermediate filaments found in neurons are…
Neurofilaments
Keratins are NOT found in:
Bones
What regulates the formation and breakdown of keratin filaments?
Phosphorylation and dephosphorylation
Which of the following types of intermediate filaments are found in all animal cells?
Nuclear lamina
In most cells the minus ends of microtubules are stabilized by a structure called the _____________, which generally lies next to the nucleus.
Centrosome
A microtubule is said to have a polarity, with a plus end and a minus end, because:
The tubulin subunits are all lined up in the same direction, leaving α−tubulin exposed at one end of the microtubule and β-tubulin at the other.
What is dynamic instability?
The ability of a microtubule to switch back and forth between polymerization and depolymerization.
If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens to the microtubule?
The microtubule depolymerizes
What is a major function of intermediate filaments?
Prevent cells from breaking when under mechanical stretch
What are ways to manipulate gene expression?
Cell transfections or transgenic animals, “knockout” animal with null mutation, site directed mutagenesis (make constitutively active and dominant negative mutants), RNA interference to block or reduce gene expression
What do mutant keratin filaments do?
Cause skin disease because cells without intact filaments rupture and are weak because skin surface is about 85% keratin (mutations in basal layer)
What are functions of the cytoskeleton?
Structure and support, intracellular transport, contractility and motility, and spatial organization (i.e. cell polarity)
How are filaments composed and held together?
Formed spontaneously by subunit polymerization and held together by intermolecular forces (NOT covalent bonds)
What are some characteristics of intermediate filaments?
Only found in vertebrates, have high tensile strength, extensive lateral contacts give filament mechanical strength, and lack polarity
What are the two types of intermediate filaments and what types are within each?
Cytoplasmic: keratin in epithelial cells, vimentin and related in connective tissue, muscle, and glial cells, and neurofilaments in nerve cells; Nuclear: laming in all animal cells
In eukaryotic cells, the cell cortex is made of:
A network of actin filaments
Cilia and flagella bend as a result of…
Sliding of adjacent microtubules that are attached together
Dynein is to movement towards the cell center as _______ is to movement away from the cell center.
Kinesin
In the axons of neurons, vesicles and organelles are transported both towards and away from the cell body. This bi-directional movement is due to
Different motor proteins that move in opposite directions along the same microtubules.
The difference between cilia and flagella is
Cilia are not as long as flagella
In eukaryotic flagellum, the bending of microtubules is driven by:
The motor protein ciliary dynein
Addition of actin monomers to actin filaments is __________ at the __________ end.
Faster; plus
The concentration of actin monomers is high in the cytosol. What keeps these monomers from polymerizing totally into filaments?
The monomers are bound by proteins that prevent their polymerization
What are the steps to formation of microtubules?
Nucleation (slow initial formation that is enhanced at the centrosomes), elongation (rapid tubulin addition of existing microtubules), and steady state (reduced concentration of free tubulin limits further polymerization)
Which end of the microtubule is attached to the centrosome?
Minus
What is the difference between dynamic instability in microtubules and treadmilling in actin?
Dynamic instability is rapid growing and shrinkage in microtubules and treadmilling is when one end grows while the other shrinks and the filament seemingly moves
What are the three types of motor proteins?
Kinesin (plus end away from cell body), dynenin (minus end towards cell body), and myosin (on actin filaments)
What moves motor proteins and where do they move?
ATP hydrolysis; each type in one direction on microtubules that are of the same polarity
What is similar between actin and microtubules in their formation?
They both add more rapidly to the plus end that has ATP bound
What is actin polymerization limited by?
Nucleation and free actin concentration
What is the steady state?
Occurs at critical concentration and free monomer
Why is there preferential addition of G-actin at the plus ends?
Because critical concentration is lower at the plus ends versus minus ends
What happens if concentration of actin monomers is greater than the critical concentration? If concentration of monomers is lower than the critical concentration?
Monomers added; monomers lost
What happens if the free concentration is greater than the plus end critical concentration and lesser than the minus end critical concentration?
It’s at its steady state and tread milling occurs
How do cells control actin polymerization?
By blocking + or - ends or by nucleating filament formation
What are functions of actin filaments (F-actin)?
Cytokinesis, intracellular protein/organelle transport, muscle contractions, structural, and cell and growth cone motility
What is the contractile ring that separates 2 daughter cells during cytokinesis made of?
Actin and myosin II
Why do cells crawl?
To cross to the other side (cancer cells, neutrophils), immune response (neutrophils), wound healing (fibroblasts), and migration during development (neuron migration from proliferative zones and neuronal growth cone advance)
Crawling of mammalian cells, such as neurotrophils to the site of a bacterial infection, mainly involves what mechanism?
Protrusion of membrane in the direction of travel by actin polymerization
A key group of proteins that regulate the actin cytoskeleton is:
Rho protein family
Which actin-binding proteins would be most involved in the assembly and extension of lamellipodia?
Actin-related proteins (ARPs)
What do all types of myosins do?
Bind ATP and bind actin
At the leading edge of a crawling fibroblast is regularly extended a thin, sheet-like process known as a lamellipodia, which contains a dense meshwork of actin filaments. Where are the plus ends of actin filaments oriented in the leading edge of the lamellipodia?
Towards the plasma membrane
Muscle contraction is dependent upon
Actin and myosin
Which of the following changes takes place when a skeletal muscle contracts?
Sarcomeres become shorter
Calcium initiates muscle contraction by
Changing the conformation of troponin and tropomyosin so myosin can bind to actin
ATP hydrolysis in muscle is required for
Myosin conformation to change, releasing actin and cocking myosin head for next contraction
What contain actin and myosin?
A contractile bundle in a non muscle cell, a muscle cell sarcomere, and the contractile ring that carries out cytokinesis
What are phenomena required for cell motility?
Myosin-mediated contraction at the rear of the moving cell, integrin association with the extracellular environment, nucleation of new actin filaments, and polymerization on plus ends of actin filaments near leading edge
Explain why drugs that have opposite effects on actin filaments can have a similar effect on cell movements.
These drugs both stop cell movements because actin polymerization and depolymerization are both required for this process. As cells move forward, the growth of actin filaments by addition of monomers to the plus ends near the plasma membrane, helps push out the membrane. As this occurs, continuous depolymerization of actin filaments occurs at the minus ends away from the plasma membrane, freeing actin monomers to be added at the plasma membrane, allowing treadmilling to occur.
The extracellular matrix in mammalian tissues is derived from…
Proteins secreted from cells
What is the basal lamina?
A thin layer of extracellular matrix underlying an epithelium.
Osteocytes are bone cells. Collagen fibers and calcium salts are found in abundance between and among the osteocytes. The collagen and calcium salts are:
Part of the extracellular matrix
Cadherin is a(n)
Transmembrane cell adhesion protein
In the extracellular matrix of animal tissues, which of the following molecules allows the matrix to resist compression?
Proteoglycans
At desmosomes, cadherin molecules are connected to ________________.
Intermediate filaments
In animal connective tissues, tensile strength is chiefly provided by:
Collagen fibrils and fibers
Which type of protein in a fibroblast’s plasma membrane attaches to the extracellular matrix on the outside of the cell and (through adaptor molecules) to actin inside the cell?
Integrin
Which of the following statements about integrins are true?
- ) Integrins undergo extensive conformational changes on binding to molecules on either side of the plasma membrane.
- ) When an integrin binds to the extracellular matrix, it stretches into an extended, activated state to attach to molecules on the inside of the cell.
- ) Certain intracellular chemical signals can activate integrins from inside the cell, causing them to reach out and grab hold of extracellular structures.
- ) Integrins in fibroblasts can attach indirectly to collagen via fibronectin, an extracellular matrix protein
What is the process of neutrophil chemotaxis?
Peptides shed from bacteria activate receptor and receptor activation leads to activation of members of the Rho family
What does Cdc42 regulate?
Formation of filopodia
What does Rac regulate?
Formation of lamellipodia
What does Rho regulate?
Formation of stress fiber and focal contact
What do plants lack in the cytosol?
Intermediate filaments
What is the extracellular matrix?
Connective tissues and bone
Where is the extracellular matrix secreted from?
Fibroblasts and osteoblasts
What is the extracellular composed of?
Structural proteins like collagen and elastin, proteoglycans (polysaccharides linked to proteins), and adhesive proteins (fibronectin and laminin)
What is collagen?
A structural protein that is a major component of skin, cornea, tendons, cartilage, and bone that is the most abundant protein in the body
What are some collagen deficiencies?
Skurvy (loss of collagen fibrils) and collagen mutations that produce weak bones, loose joints, fragile skin, etc.
What are some cell-to-cell contact adhesion molecules?
Selectins (rolling leukocytes in blood vessels), cadherins, connexons (gap junctions), and immunoglobin superfamily
What are some cell-to-extracellular matrix adhesion molecules?
Integrins and proteoglycans
What is in the light region of the sarcomere?Dark region? Overlap region?
Actin; myosin; both
What happens to the sarcomere during muscle contraction?
It gets shorter so the actin regions on either side of the myosin get closer together and the actin regions become smaller (in that they overlap more with myosin so they become darker and there is less full actin)
What are the two main uses of ATP during contractions?
- ) Binding to myosin causes release from binding to actin filament and hydrolysis results in the cocking of the myosin head with subsequent actin binding and power stroke
- ) ATP hydrolysis required by Ca2+ pumps to remove Ca2+ from cytosol in order to stop contraction
What would happen if there were Ca2+ present intracellularly but no ATP?
Calcium would cause removal of tropomyosin block on myosin binding site of actin filament so myosin bound to actin can’t be released and muscles lock in place (can’t relax but can’t contract either and are in a state of rigor)
Our skin is somewhat pliable and soft to touch, yet very resilient to mechanical stress. List/describe the major proteins/components in skin that contribute to its toughness
keratins (intermediate filaments), adhesion molecules (cadherins for cell-cell, integrins for cell-basal lamina), linker proteins (crosslink intermed. filaments, connect keratins to adhesion proteins), collagen, and possibly proteoglycans
What is the most abundant protein found in tendons?
Collagen
What is the type of protein that directly connects muscle cells to tendons?
Integrins
With age comes an increase in facial wrinkles and a decrease in the thickness of lips. Therefore aged seekers of beauty can counteract those characteristics by increasing tissue volume around the eyes in order to smooth wrinkles or in the lips to make them fuller. Which of the following would be most effective to inject for these beauty-enhancing procedures?
Proteoglycans; proteoglycans have negative charges that attract positive ions and therefore absorb water (highly hydrophilic)
How do cells stick together?
Adhesion proteins (integrins and cadherins)
What does the combination of intermediate filaments connected to adhesion proteins do?
Gives cells strength and flexibility of cell layer
What is Duchenne Muscular Dystrophy caused by?
Caused by mutations to dystrophin which links ECM and actin cytoskeleton that leads to damage by mechanical stress
What are proteoglycans?
Proteins with attached polysaccharide chains that have charged sugars that absorb water and form gels which resist compression in joints
What are GAGs?
They make up proteoglycans and hyaluronan and influence signaling molecules and adhesion
What leads to ribosome docking on the ER?
Translation of ER signal sequence
What are transported through nuclear pores?
RNAs (mRNAs imported) and proteins (exported); small molecules diffuse, larger molecules actively transported
What do soluble proteins do and have in order to do this?
Translocate into ER during translation because they have an N-terminal ER signal sequence
What are signal sequences?
Necessary and sufficient for localization to ER
What does nuclear localization depend on?
Amino acid sequence
What is the function of the tight junction?
Seals neighboring cells in an epithelial sheet to prevent leakage of extracellular molecules between them and helps polarize cells
What is the function of the adherins junction?
Joins an actin bundle in one cell to a similar bundle in a neighboring cell
What is the function of the desmosome?
Joins intermediate filaments between neighboring cells
What is the function of the gap junction?
Forms channels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites, to pass from cell to cell
What is the function of the hemidesmosome?
Anchors intermediate filaments in cell to basal lamina
What are characteristics of inserting proteins into the ER?
Transmembrane proteins are inserted directly into the membrane, its the 1st stop for transmembrane, secreted, and lysosomal proteins
Why are all sugars attached to proteins found outside the cell and not on the cytoplasmic side of the plasma membrane?
Side of the membrane facing the cytosol always faces cytosol after every fusion and release (sugars exposed to lumens (organelle/vesicle lumen akin to extracellular space) and internal vesicle contents secreted outside cell
What happens to proteins in the ER?
Removal of signal peptide on soluble proteins, glycosolation, lipid anchor addition on some proteins, and proper folding of proteins
What are some characteristics of proper folding of proteins in the ER?
Assisted by chaperones, formation of disulfide bonds, abnormally folded proteins destroyed (functional but not present because it gets degraded before it makes it to the Golgi by quality control)
What happens to proteins in the golgi?
Proteolytic cleavage of pre-pro-proteins (signaling peptides), progressive enzymatic modification of sugars (aid proper folding, production of proteoglycans, resist proteolysis, and enable sorting), sorting of proteins (endosomes/lysosomes, secretory vesicle, and plasma membrane)
What type of secretion occurs with sorting of proteins in secretory vesicles?
Regulated secretion
What type of secretion occurs with sorting of proteins in the plasma membrane?
Constitutive secretion
Where do vesicles dock?
To specific location based on types of Rab and v-SNARE expressed
How do vesicles dock?
t-SNARE on target membrane binds to v-SNARE, holding vesicle close to target membrane so membranes can fuse
What are the mechanisms of protein sorting?
- ) Signal sequences to determine initial organelle location
- ) Sorting via vesicles from ER to final location
a. ) Selective uptake into vesicles (receptor-mediated, constitutive, and secretory protein aggregation)
b. ) Vesicles dock at specific locations
c. ) Indirect sorting via endosomes - ) Selective stabilization
What happens to material that has been through endocytosis (endocytosed material)?
Recycled back to membrane or degraded into lysosome
What is the process of receptor-mediated endocytosis?
Extracellular domain of receptor binds to ligand, intracellular domain binds to adaptin which binds to clathrin, and endocytosis by clathrin-induced vesicle formation occurs
Where are most membrane phospholipids and steroid hormones produced?
The smooth endoplasmic reticulum
Which organelle is essentially a small sac of digestive enzymes that functions in degrading worn-out organelles as well as macromolecules and particles taken into the cell by endocytosis?
Lysosome
Many proteins contain a sorting signal that determines whether the protein ends up in mitochondria, the endoplasmic reticulum or the cytosol. What is the sorting signal for proteins?
Part of the amino acid sequence of the protein.
If a translated protein has no signal peptide, where would you expect this protein to be found?
Cytosol
Where are most mitochondrial and chloroplast proteins made?
In the cell cytosol
What is true, in relation to the difference between protein entry into mitochondria versus the nucleus?
Proteins need to be unfolded in order to enter mitochondria, but nuclear proteins are translocated in their folded state.
What is true of ribosomes and the synthesis of proteins?
A common pool of ribosomes is used to synthesize both the proteins that stay in the cytosol and those that are destined for the ER.
What happens to proteins destined to enter the endoplasmic reticulum?
Begin to cross the membrane while still being synthesized.
How do proteins, like histones, that will reside in the nucleus cross?
Cross the nuclear membrane in a folded state after synthesis is completed in the cytosol.
How is the transfer of proteins from the cytosol to the endoplasmic reticulum different than the transfer of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus?
Proteins are transferred from ER to Golgi by way of vesicles not translocation across the membrane.
Which type of protein binds to improperly folded or improperly assembled proteins in the ER, holding them there until proper folding occurs?
Chaperone proteins
How are vesicles formed from Golgi membranes?
Clathrin proteins bind to each other and the membrane and this causes the membrane to curve and eventually form a vesicle.
Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels?
ER → Golgi → plasma membrane
Vesicles in cells will specifically bind to and dock onto the correct target organelle in cells. This specificity is due in part to certain proteins on the vesicles that help tether and dock the vesicles to the target. These proteins include what?
SNAREs and Rab proteins
What are a role for the oligosaccharides on glycosylated proteins? (there can be more than one correct answer)
They can protect the protein from degradation and hold it in the ER until it is properly folded, they can guide the protein to the appropriate organelle by serving as a transport signal for packaging the protein into appropriate transport vesicles, and when displayed on the cell surface, oligosaccharides form part of the cell’s protective carbohydrate layer.
How are lysosomal enzymes targeted to the lysosome?
Lysosomal enzymes get tagged with the sugar mannose 6-phosphate in the golgi, and then are sorted into specific vesicles by binding to the mannose 6-phosphate receptor.
Some proteins, such as nucleases, are sent to lysosomes after they are synthesized, and other proteins, such as cadherins are sent to the plasma membrane. Where does this sorting occur, so that cadherins and nucleases get packaged separately and sent to their proper locations?
Golgi apparatus
The uptake of large particles, such as cell debris and bacteria, by macrophages and neutrophils is called
Phagocytosis
What is NOT true of receptor-mediated endocytosis?
In receptor-mediated endocytosis, internalized vesicles fuse with lysosomes, which then mature into endosomes.
In what ways are the mechanisms of protein import into the nucleus, mitochondria, and ER all similar?
- ) All require binding of part of the protein (the signal sequence/localization signal) to some receptor so it can dock to organelle and be transported inside
- ) All involve active transport
- ) Initial translation of protein in cytosol, then imported
In what ways is protein import into the ER different from protein import into the nucleus?
Protein import into the ER requires the protein to be inserted as being translated (through a translocator), whereas import into the nucleus occurs after protein translation is complete, and the protein goes through a pore while in a fully folded conformation. (there are other minor differences as well that you don’t need to memorize)
You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein.
ER
You change the hydrophobic amino acids in an ER signal sequence into charged amino acids.
Cytosol
You move the N-terminal ER signal sequence to the C-terminal end of the protein.
Cytosol
You make a protein with signals for import into the nucleus and import into the ER.
ER
If a protein with 3 membrane-spanning sequences (one of which is before the signal peptidase cleavage site at the N terminus) and 3 non-membrane spanning regions where will the regions each be, respectively?
1st non-membrane region is in the ER lumen, 2nd is in the cytosol and 3rd is again in the lumen
What signal sequence would an Na+-glucose co-transporter have?
ER
What signal sequence would mitochondrial membrane proteins have?
Mitochondrial
What signal sequence would insulin have?
ER
What signal sequence would ribosomal proteins have?
None
What signal sequence would collagen have?
ER
What signal sequence would lamin have?
Nuclear localization signal
What signal sequence would cadherin have?
ER
What signal sequence would keratin have?
None
If the orientation of the Krt1 protein on the membrane of a Golgi-derived vesicle that will fuse with the plasma membrane is with the N-terminus inside the vesicle and the protein spanning the membrane, what is true of the protein during fusion?
When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space.
Hexosaminidase A (an enzyme normally located in lysosomes)?
- ER signal sequence
- ER→vesicle→Golgi→vesicle→endosome/lysosome
- Sugar addition (e.g., mannose-6-phosphate), cleavage of signal peptide, possibly others
What is the signal sequence, pathway, and modifications of insulin?
- ER signal sequence
- ER→vesicle→Golgi→vesicle→plasma membrane
- cleavage of signal peptide, form disulfide bonds, insulin also undergoes cleavage from
proinsulin. ..
Insulin is secreted, but Hexosaminidase A goes to lysosomes. The Na+-Glucose transporter ends up in the apical domain of intestinal epithelial cells, but Na+/K+ pump ends up in the basolateral domain. Describe two general mechanisms used by cells to sort the proteins (like those just mentioned) and get them to their correct locations.
- ) Sorted into vesicles by receptor-mediated process or selective aggregation or default constitutive pathway (so have secretory vesicle with insulin in it, for example, or all lysosomal enzymes packaged into another vesicle, other proteins may go constitutively to membrane)
- ) Vesicles dock/fuse at specific locations depending on what types of Rab and SNARE proteins present on vesicle.
- ) Other possibilities include transcytosis, etc.
After a chicken egg is fertilized, the growing embryo takes up yolk proteins via endocytosis. If you could label the yolk proteins with a fluorescent dye, what cellular compartments would you likely see the labeled proteins in, and in what order.
Would expect to possibly see fluorescence in vesicles taken up from membrane and then should go to endosome. From endosome may go to lysosome.
Ricin is one of the most toxic substances known: less than 2 mg injected into the bloodstream will kill an adult human. Ricin is produced by the castor bean plant as a 65 kd protein heterodimer composed of an A chain and a B chain. The B chain is a lectin that binds to carbohydrates on the cell surface. The A chain is an enzyme that modifies a highly conserved site in rRNA, leading to inhibition of translation. What is the most likely mechanism by which ricin enters the cell?a) The A chain binds to clathrin.
b) The A chain stimulates autophagy.
c) The B chain interacts with SNAREs.
d) The protein enters through pore complexes in the plasma membrane.
e) The protein is internalized by endocytosis.
e) The protein is internalized by endocytosis.
