DNA Replication, Meiosis And Mitosis Flashcards
(25 cards)
What is the purpose of DNA replication?
To duplicate the code it carries. The code can then be passed to daughter cells.
Step one of DNA replication.
DNA helicase (enzyme) unwinds and separates the double strand by breaking the weak H bonds. Each half of the parent molecule is used as a template.
Step two of DNA replication.
The enzyme primase attaches a short sequence of RNA, known as a primer, to show DNA polymerase where to start adding nucleotides.
Step three of DNA replication.
Complementary nucleotides are added by the enzyme DNA polymerase. Synthesis of the new daughter strand is in a 5’ to 3’ direction.
Step four of DNA replication.
The result is the production of two identical DNA molecules that are each made of one parent strand and one daughter strand. Therefore it is semi-conservative.
Step five of DNA replication.
In eukaryotic organisms, two sister chromatids are now ready for cell division. In prokaryotes, two circular chromosomes are now ready for binary fission.
Mitosis
nuclear division occurring in the somatic cells that maintains the parental diploid number of chromosomes in the daughter cells; for bodily growth and asexual reproduction.
Meiosis
cell division concerned with the production of gametes in sexually reproducing organisms. Involving one cycle of DNA replication and two rounds of cell division, results in the production of four haploid daughter cells from each original diploid cell.
What is the cell cycle?
A continuous but ordered sequence of events in the life of a cell from when it was formed from a parent cell until its own division.
What is interphase?
prior to any cell division, a doubling of the genetic material needs to take place.
Prophase in mitosis
- Chromatin threads condense to form chromosomes.
- Nuclear membrane disintegrates and nucleus disappears.
- Miotic spindle begins to form and is completed by the end of prophase. Spindle fibres attach to each chromosome at its centromere.
- The two centrosomes (each containing two centrioles) move toward opposite poles of the cell.
Metaphase in mitosis
- Chromosomes move to centre of cell and line up along the equator.
- Centromeres of the chromosome are aligned on equator.
- The centrioles are located at opposite poles of the cell.
Anaphase in mitosis
- Spindle micro tubules shorten and pull on the centromere: sister chromatids separate.
- Spindle microtubules pull sister chromatids to opposite poles of the cell.
- At end of phase, each pole has a complete identical set of maternal and paternal chromosomes.
- Sister chromatids now referred to as chromosomes.
Telophase in mitosis
- Chromosomes decondense to form chromatin; can no longer be seen under microscope.
- Two new nuclear membranes form, one for each new daughter cell.
- Nucleoli reappear and spindle apparatus disappears.
- Cell elongates to become ready for cytokinesis.
Prophase I
Chromosomes condense, nucleus disappears, spindle forms.
Synapse
The process when homologous chromosomes lie side by side. The chromosomes are now called bivalent.
Chiasma/Chiasmata- the point at which the homologous arms contact.
Metaphase I
Nuclear envelope degrades, chromosomes line up at the middle.
Anaphase I
Maternal and paternal chromosomes moved to opposite pole. Separation is called disjunction.
Telophase I
Spindle breaks down, cell starts to divide, nuclear envelope forms around 2 new nuclei.
End of meiosis I
Cytokinesis occurs, meiosis I is complete.
Prophase II
Spindle forms at right angles to the first one.
Metaphase II
Chromosomes move to equator.
Anaphase II
Chromatids separate and move to poles.
Telophase II
Spindle fibres disappear, chromosomes decondense, nuclear envelope and nucleoli form.
