Molecular biology chapter 9
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Molecular biology chapter 9 - Marcador
Molecular biology chapter 9 - Detalles
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| What is a chromosome? | A discrete unit of the genome carrying many genes. Each consists of a very long molecule of duplex DNA and an approximately equal mass of proteins. It is visible as a morphological entity only during cell division. |
| What is a nucleoid? | The structure in a prokaryotic cell that contains the genome. The DNA is bound to proteins and is not enclosed by a membrane. |
| What is the chromatin? | The state of nuclear DNA and its associated proteins during the interphase (between mitoses) of the eukaryotic cell cycle. |
| What is the packing ration? | The ratio of the length of DNA to the unit length of the fiber containing it. |
| What is a capsid? | The external protein coat of a virus particle. |
| What limits the length of DNA that is incorporated into viruses? | Limited by the structure of the headshell. |
| What is the state of the Nucleic acids in the virus head shells? | Extremely condensed. |
| What is icosahedral symmetry? | A structure with 60 rotational symmetries (such as a soccer ball). |
| How do filamentous RNA viruses assemble? | Condense the RNA genome as they assemble the headshell around it. |
| What is a nucleation center? | A duplex hairpin in TMV (tobacco mosaic virus) in which assembly of coat protein with RNA is initiated. |
| How do spherical DNA viruses assemble? | Insert the DNA into a preassembled protein shell. |
| What is terminase? | An enzyme that cleaves multimers of a viral genome and then uses hydrolysis of ATP to provide the energy to translocate the DNA into an empty viral capsid starting with the cleaved end. |
| What are the properties of the bacterial nucleoid? | The bacterial nucleoid is ~80% DNA by mass and can be unfolded by agents that act on RNA or protein. -The nucleoid has ~400 independent negatively supercoiled domains. |
| What does the bacterial genome consist of | The bacterial genome consists of a large number of loops of duplex DNA, each of which forms an independent structural domain. |
| Properties of interphase DNA in eukaryotes? | DNA of interphase chromatin is negatively supercoiled into independent domains of ~85 kb. |
| Properties of the metaphase chromosomes? | Metaphase chromosomes have a protein scaffold to which the loops of supercoiled DNA are attached. |
| What is MARs and SARS? | DNA is attached to the nuclear matrix at specific sequences called MARs or SARs. The MARs are A-T-rich but do not have any specific consensus sequence. |
| What is chromosome scaffold? | A proteinaceous structure in the shape of a sister chromatid pair, generated when chromosomes are depleted of histones. |
| What are the two types of chromatins? | Euchromatin and Heterochromatin |
| When can we see individual chromosomes? | Individual chromosomes can be seen only during mitosis. |
| What is euchromatin? | During interphase, the general mass of chromatin is in the form of euchromatin, which is slightly less tightly packed than mitotic chromosomes. |
| What is heterochromatin? | Tightly packed form of DNA (condensed) Regions of heterochromatin remain densely packed throughout interphase. |
| What is a chromocenter? | An aggregate of heterochromatin from different chromosomes. |
| Where does chromosomes sit in the nucleus? | Chromosomes occupy chromosome territories in the nucleus and are not entangled with each other. |
| What are G-bands? | Certain staining techniques cause the chromosomes to have the appearance of a series of striations, which are called G-bands. |
| What’s the difference between bands and interbands? | The bands are lower in GC content than the interbands. |
| Where in chromosomes bands are genes concentrated the most? | Genes are concentrated in the G-C-rich interbands. |
| What are chromomeres? | Densely staining granules visible in chromosomes under certain conditions, especially early in meiosis, when a chromosome may appear to consist of a series of chromomeres. |
| What are lampbrush chromosomes? | A lampbrush chromosome is a meiotic bivalent in which the two pairs of sister chromatids are held together at chiasmata. |
| How does sites of gene expression on lampbrush chromosomes look like? | Sites of gene expression on lampbrush chromosomes show loops that are extended from the chromosomal axis. |
| What is polytene chromosomes? | Giant chromosomes found in larvae of certain dipterans. They are the largest and most cytogenetically useful. have a series of bands that can be used as a cytological map. |
| What is in situ hybridization? | Hybridization performed by denaturing the DNA of cells squashed on a microscope slide so that reaction is possible with an added single-stranded RNA or DNA; the added preparation is radioactively labeled and its hybridization is followed by autoradiography. |
| What’s the relationship between polytene chromosomes and in situ hybridization? | Individual bands containing particular genes can be identified by in situ hybridization. |
| What are puffs? | Bands that are sites of gene expression on polytene chromosomes expand to give “puffs.” |
| How is eukaryotic chromosomes held on the mitosis spindle? | A eukaryotic chromosome is held on the mitotic spindle by the attachment of microtubules to the kinetochore that forms in its centromeric region. |
| What is the microtubule organizing center (MTOC) ? | A region from which microtubules emanate. In animal cells the centrosome is the major microtubule organizing center. |
| What is a centromere? | A constricted region of a chromosome that includes the site of attachment (the kinetochore) to the mitotic or meiotic spindle. It consists of unique DNA sequences and proteins not found anywhere else in the chromosome. |
| What is acentric fragment ? | A fragment of a chromosome (generated by breakage) that lacks a centromere and is lost at cell division. |
| How are centromeres characterized? | Centromeres are characterized by a centromere-specific histone H3 variant, and often have heterochromatin that is rich in satellite DNA sequences. |
| What is satellite DNA? | Consists of a very large arrays of tendemly repeating, non coding DNA Is the main component of functional centromeres and form the main structural constitute of heterochromatin. |
| What makes the centromeres different in higher eukaryotic chromosomes? | Centromeres in higher eukaryotic chromosomes contain large amounts of repetitive DNA and unique histone variants. |
| What are telomeres? | A region of repetitive nucleotide sequences at each end of a chromosome. A typical telomere has a simple repeating structure with a G-T-rich strand that extends beyond the C-A-rich strand. |
| Why are telomeres important? | The telomere is required for the stability of the chromosome end. Telomeres Seal the Chromosome Ends and Function in Meiotic Chromosome Pairing |
| What does telomeres consist of? | A telomere consists of a simple repeat where a G-rich strand at the 3ʹ terminus typically has a sequence of (T/A)1–4 G>2. |
| What happens in the reaction catalyzed by the protein TRF2 in the telomeres? | The protein TRF2 catalyzes a reaction in which the 3′ repeating unit of the G+T-rich strand forms a loop by displacing its homolog in an upstream region of the telomere. |
| How can we visualize the telomeres cluster? | (FISH) fluorescence in situ hybridization |
| What is telomerase? | A Ribonucleoprotein Enzyme that adds as pieces dependent telomere repeat sequence to the 3’ end of telomeres. |
| How does telomerase work? | Telomerase uses the 3′–OH of the G+T telomeric strand to prime synthesis of tandem TTGGGG repeats. The RNA component of telomerase has a sequence that pairs with the C+A-rich repeats. One of the protein subunits is a reverse transcriptase that uses the RNA as template to synthesis the G+T-rich sequence. -Telomerase positions itself by base pairing between the RNA template and the protruding single-stranded DNA primer. |
| Where is telomerase expressed? | Telomerase is expressed in actively dividing cells and is not expressed in quiescent cells. |
| What happens if telomeres are lost? | Loss of telomeres results in senescence. |
| How senescence is escaped? | Escape from senescence can occur if telomerase is reactivated, or via unequal homologous recombination to restore telomeres. |
| What is the result of Telomerase mutations? | Mutation in telomerase causes telomeres to shorten in each cell division. |
| Can crossing over happen in telomeres? | Crossing-over in telomeric regions is usually suppressed by mismatch-repair systems, but can occur when they are mutated. |