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45 Cards in this Set

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MIcrosatellite instability (variations in length) can lead to predisposition for what type of disease? What phase of the cell cycle to these errors in replication occur in?
Microsatellite instability can predispose to cancer. These result from errors in replication, which occur during S-phase.
What special repair of the replication errors that occur in the cell cycle S phase, happen in what subsequent phase?
Repair of replication errors occurs during G2 (specifically mismatch repair).
What are the 5 phases of the cell cycle? Which phase do inactive cells live most of their lives in? Which phase do active cells spend the most time in?
The five phases are G0, G1, S, G2, and M. Inactive cells spend most of their life cycles in G0 (e.g. neurons). Active cells spend most of their life cycles in G1 (e.g. intestinal epithelial cells).
DNA repair of what error can take place in the G1 phase of the cell cycle? Which method of repair is employed?
Thymine dimer repair occurs in this phase via excision endonuclease activity.
DNA repair of what error can take place in the S phase of the cell cycle? Which method of repair is employed?
Proofreading action of DNA polymerase III (prokaryotes) and DNA polymerase D and A (eukaryotes) removes incorrect bases with a 3' to 5' exonuclease activity.
DNA repair of what error can take place in the G2 phase of the cell cycle? Which method of repair is employed?
DNA mismatch base repair occurs here via hMLH1 and hMSH2 gene activity.
How does methylation of certain sequences of DNA affect the transcription of those regions?
Methylation of DNA (particularly CG sequences) are typically associated with silencing certain gene regions.
Name some of the most important genes associated with maintaining fidelity of replicating DNA, and whose loss of function is associated with the development of cancer.
G0 phase: XP (thymine dimer- bulky lesion-repair)

G1 phase (check point): Rb, TP53

S phase: DNA polymerase proofreading during DNA synthesis

G2 phase: MLH1, MSH2 (mismatch repair)
What type of RNA polymerase is confined to the Nucleolus of the cell?
The nucleolus is the structure of the cell that is required for ribosomal synthesis. While all RNA polymerases are located in the nucleus, only RNA Polymerase I is restricted to the nucleolus, because it is involved in the synthesis of 28S, 18S, and 5.8S rRNAs, which are employed for ribosome synthesis.
Are DNA polymerases located in the Nucleus or Nucleolus?
DNA Polymerases are largely restricted to the nucleus, but not to the nucleolus, because it participates in DNA replication, rather than ribosome synthesis.
What is the function of RNA Polymerase II? Where is it found?
RNA polymerase II is the primary polymerase that transcribes DNA to RNA. It is found all around the nucleus.
What are the jobs of RNA Polymerase III?
RNA Polymerase III synthesizes tRNA, but also rRNAs and other small RNAs found in the cytosol and nucleus.
Which form of chromatin is loosely packed and transcriptionally acitve? Is this the form that DNA takes during mitosis?
Euchromatin is seen as the loosely packed, "open", transcriptionally active form of chromatin. During mitosis Euchromatin becomes condensed to form Heterochromatin, in which the nucleic acid wraps tightly around histones.
Compare and contrast Heterochromatin to Euchromatin.
Heterochromatin:
Transcriptionally inactive, methylated, deacetylated histones, dark-staining on electronmicroscopy

Euchromatin:
Transcriptionally active, unmethylated DNA, acetylated histones, light-staining on electron microscopy
What type of DNA damage is base excision repair used for?
Base excision repair recognizes and repairs individual bases damages by chemical modifiction (e.g. deamination of cytosine to uracil)
What is Photolyase and what is its job? What other cellular mechanisms perform the same function?
Photolyase is an enzyme that mediates the direct repair of ultraviolet (UV) radiation-induced pyrimidine dimers by breaking the abnormal covalent bonds between the adjacent pyrimidines. Global genomic nucleotide excision repair and Transcription-coupled nucleotid excision repair perform similar functions.
Xeroderma pigmentosum is due to defects in what type of cellular repair mechanism?
Deficiencies in nucleotide excision repair proteins lead to the development of Xeroderma pigmentosum.
What are Connexons? What is purpose do they serve?
Connexons are tightly packed tubular protein subunits that form patterns to create a hexagonal lattice-work, which forms hydrophilic channels connecting the cytoplasm of adjacent cells. Connexons are responsible for making Gap Junctions. These junctions permit direct passage of ions and small molecule between cell to conduct electrical impulses.
Where are Sealing strands found?
Sealing strands are found in tight junctions.
Where are tonofilaments found?
Tonofilaments are found in desmosomes and hemidesmosomes.
Where is Type IV collagen most commonly found?
Type IV collagen is found in the basal lamina of basement membranes.
What is the purpose of Gap Junctions? Describe the subunits that make up gap junctions.
Gap Junctions are important for signaling between adjacent cells. Gap junctions form when Connexon proteins create a pore between adjacent cells. A hexagonal lattice of connexon allows ions and small molecule to pass between cells.
Rank the rate of passage of the following substances through the cell membrane from fastest to slowest: gases, urea, glycerol, glucose, sodium.
Gases > Urea > Glycerol > Glucose > Na+
Describe the three factors that affect membrane permeability to molecules.
1) The physical dimensions of a molecule

2) The lipid solubility of the molecule

3) The valence or charge of a molecule
SRP (signal recognition peptide) is important for what cell function?
The SRP binds to the N-terminal amino acid signal during initial synthesis of proteins destined for the plasma membrane or the organelles of the endocytic or exocytic pahtways. SRP binding to the newly synthesized N-terminal signal sequence arrests synthesis on free ribosomes to provide time for the complex to bind to an SRP receptor on the RER. Subsequently the SRP is released, which allows protein synthesis to continue simultaneously with proper insertion into the RER membrane or RER lumen.
What is the terminal residue that targets soluble enzymes for delivery to lysosomes?
This is a terminal Mannose-6-phosphate residue.
What is the job of DNA Topoisomerase vs. DNA Helicase?
DNA Topoisommerase relieves the tension onf the DNA upstream and downstream of the replication fork by cutting the DNA allowing it to unravel, and resealing the nick. DNA Helicase uses ATP energy to unwind the dsDNA at the replication fork.
Describe the signs and symptoms associated with Pemphigus Vulgaris. What is the characteristic sign that will be positive and distinguish it from Bullous Pemphigoid? What is the treatment?
Pemphigus Vulgaris is seen mostly in elderly patients. Lesions usually begin in the oral mucosa and can also be found on the scalp, face, neck, and trunk. Acanthosis with intraepidermal blisters and a positive Nikolsky sign (pressure to skin separates epidermis) separate this condition from Bullous pemphigoid. The treatment is glucocorticoids and immuno suppressants as this is an autoimmune disease in which antibodies attack desmoglein in Desmosomes.
What is the key pathology of Pemphigus Vulgaris?
IgG antibodies attacking desmoglein. Desmoglein is the transmembrane cadherin that forms the intercellular linlkages at Desmosomes. Desmosomes provide the strangest attachments between neighboring cells.
Sealing strands are part of what type of cell-cell junction? What is the purpose of these types of junctions?
The Zonula Occludens, also known as a tight junction is connected through sealing strands. Tight junctions extend completely around the apical borders of epithelial cell and serve to seal the intercellular clefts from contact with the outside environment.
Describe Desmosomes and their special associated Tonofilaments.
Desmosomes, also known as the macula adherens, have disk-shaped appositions of plaques in adjjacent cells anchored by Tonofilaments that radiate into the interior of each opposing cell.
Which cell to cell junction consists of a hexagonal lattice of tubular protein subunits? What type of protein are the subunits made out of? What is the special purpose of these junctions?
These types of cell to cell junctions are known as Gap junctions and the consist of a hexagonal lattice of tubular protein subunits of Connexin proteins that allow communication of ions between cells.
What cell to cell connection is used to attach squamous epithelial cells to basement membranes?
Hemidesmosomes.
Which cell to cell connection is found only on the apical borders of epithelial cells?
Tight junctions (zonula occludens) are found only on the apical borders of epithelial cell, and seal off the intercellular gaps of the cells from the outside environment. Any time a question requires you to determine which junction type prevents interactions of tissue with the outside environment, think of tight junctions.
What are Hamerhead Ribozymes? how do they work? What disease of the nervous system are they being studied to treat?
Hammerhead rybozymes catalyze the sequence-specific cleavage of RNA phosphodiesterase bonds of mature RNA, due to the secondary structure they form. Synthetic RNAs containing sequences complementary to the mutant SOD1 mRNA (implicated in ALS) and squences necessary to form the hammerhead catalytic structure are being studied as a possible therapy for ALS.
Which motor proteins are directed towards the (+) end of microtubles, i.e. those ends that are located towards the outside of the cell and are used in anterograde transport?
Kinesins are (+) directed motor proteins.
Which proteins are responsible for retrograde/ (-)-end directed movement on microtubules in cells? Which direction do Myosins move in?
Dyneins are (-)-directed microtubule proteins. Myosins are all (+) directed microfliament proteins.
Deficient actin would prevent normal formation of what structural proteins inside of cells?
Deficient actin would prevent normal microfilament formation or function.
What are intermediate filaments?
Intermediate filaments serve primarily a structural role within cells. They have different proteins attached to them, depending on the cell tissue type.
What is Actin and what structural components of the cell does it make up?
Actin makes up the monomeric units that comprise cytoskeletal structural microfilaments.
What are Myosins and what structural components of the cell does it make up?
Myosins are microfilament proteins that are directed toward the (+) end of the filament.
What is Tubulin and what structural components of the cell does it make up?
Tubulin makes up the monomeric units that comprise microtubules (necessary for movement of cargo through the cell).
What are Kinesins and what structural components of the cell does it make up?
Kinesins are motor proteins that move cargo toward the (+) end of the microtubule (anterograde).
What are Dyneins and what structural components of the cell does it make up?
Dyneins are motor proteins that move cargo toward the (-) end of the microtubule (retrograde).
What organelle in the Enterocyte is responsible for creating chylomicrons? What does it absorb first before it can do this?
Enterocytes have the ability to pick up Mixed Micelles from the gut lumen for repackaging in the Smooth Endoplasmic Reticulum as chylomicrons.