Fragen, die nicht in der Vorlesung vorkamen Flashcards
Avery, McLeod, McCarthy führten 1944 Experiment durch. Wie wurde da
bewiesen dass DNA die Erbsubstanz ist?
Paper 1944: Explanation of Griffith`s work- DNA is genetic material
Vorher: Griffith führte ein Experiment mit lethalen S-strain und harmlosen R-strain Pneumococcen durch:
Injektion der Maus mit:
- S-strain -> tot
- R-strain -> lebt
- S-strain durch Hitze abgetötet -> lebt
- S-strain durch Hitze abgetötet + lebende R-strain -> tot
einige Jahre später: Beweis von Avery und Co, dass DNA die Erbsubstanz ist
S-strain: zellfreie Fraktionen verschiedener Moleküle getestet ob diese den R-strain transformieren
- RNA -> nein
- DNA -> ja
- Protein -> nein
- Lipide-> nein
- Kohlenhydrate-> nein
Beweis, dass DNA die Erbsubstanz ist
Base pairing can only work between antiparallel chains that have opposite polarities. But what does polarity mean?
a) The polarity commonly refers to the orientation of its sugar-phosphate backbone. The way in which the nucleotide subunits are linked together gives a DNA strand its chemical polarity. If we imagine that each nucleotide has a knob (phosphate) and a hole, each chain, formed by interlocking knobs with holes, will have all of its subunits lined up in the same orientation. Moreover, the two ends of the chain can be easily distinguished, as one will have a hole (3’hydroxyl) and the other a knob (5’ phosphate). This polarity in a DNA chain is indicated by referring to one end as the 3’ end and the other as the 5’ end. This convention is based on the details of the chemical linkage between the nucleotide subunits.
b) Polarität: Die beiden Ende der DNA sind chemisch unterschiedlich->
- 3 Ende: freie 3 Hydroxylgruppe -> an C3 Atom der Ribose
- 5 Ende: 5Phosphatgruppe -> an C5 Atom der Ribose
Nukleotide sind kovalent durch Phosphodiestergruppen durch die 3Hydroxylgruppe des einen Zuckers mit der 5Phosphatgruppe des nächsten Zuckers miteinander verbunden. -> Das gibt dem Polynukleotidstrang seine Polarität.
This is part of the yeat genome. The light red bars represent genes. Why are they not all on one strand?
a) Die Polymerase kann in beide Richtungen lesen, bzw. es kann die Transkriptionsrichtung ändern.
b) Hohe Dichte an Genen, daher kodieren die beiden Stränge für verschiedene Gene.
Definite centromere, centrosom, centriole and telomere!
Centromere- Constricted region of a mitotic chromosome that holds sister chromatids together, also the site on the DNA where the kinetochore forms and then captures microtubules from the mitotic spindle.
centrosom- (cell centre) Centrally located organelle of animal cells that is the primary microtubule-organizing center and separates to form the two spindle poles during mitosis. In most animal cells it contains a pair of centrioles.
centriole- Short cylindrical array of microtublules, usually found in pairs at the centre of a centrosome in animal cells.
telomere- Structure at the ends of linear chromosomes, associated with a characteristic DNA sequence that is replicated in a special way. Counteracts the tendency of the chromosome otherwise to shorten with each round of replication.
Kinetochore - eine spezielle, platten- oder halbkugelförmige Struktur ausProteinenund DNA-Abschnitten, die dem Zentromer seitlich aufsitzt und in Kernteilungsvorgängenals Ansatzstelle für die Fasern desSpindelapparatesdient. Nachdem die Spindelfasern (Mikrotubuli) an dem Kinetochor angedockt haben, beginnt ein Proteinkomplex die Bindung der Schwesterchromatiden zu lösen. Nachdem die Schwesterchromatiden nicht mehr aneinander haften, werden sie während der frühen Anaphase über die Mikrotubuli zu den Polen des Spindelapparates gezogen.
Do we really need nucleoli?
Nucleolus nur bei Vertebraten für die Entwicklung wirklich notwenig. The maternal nucleolus is essential for early embryonic development in mammals. With fertilization, the paternal and maternal contributions to the zygote are not equal. The oocyte and spermatozoon are equipped with complementary arsenals of cellular structures and molecules necessary for the creation of a developmentally competent embryo. The nucleolus is exclusively of maternal origin. The maternal nucleolus is not necessary for oocyte maturation; however, it is necessary for the formation of pronuclear nucleoli after fertilization or parthenogenetic activation and is essential for further embryonic development. In addition, the nucleolus in the embryo produced by somatic cell nuclear transfer originates from the oocyte, demonstrating that the maternal nucleolus supports successful embryonic development.
Is there chromatin-remodeling during mitosis?
a) During mitosis, at least some of the chromatin-remodeling complexes are inactivated, which may help mitotic chromosomes maintain their tightly packed structure.
b) Während der Mitose sind einige Chromatin-Remodeling Komplexe inaktiviert damit die mitotischen Chromosome ihre dicht bepackte Struktur behalten.
