Class notes 2 - DNA replication and mitosis Flashcards
What does 2n represent in mitosis?
a diploid or a cell with 46 chromosomes
What does n represent?
the number of different chromosomes as well as a haploid cell with 23 chromosomes (meiosis)
What does S phase stand for?
> synthesis phase
synthesis of DNA
DNA replication
What are the 5 steps in S phase? (see diagram)
1) DNA double helix prior to replication ( currently 46 DNA molecules in the nucleus).
2) via enzyme activity (not shown), the DNA helix is unwound and the double strands are separated. DNA polymerase attaches to both strands and begins the process of DNA replication. DNA polymerase moves upwards along the molecule.
3) DNA polymerase continues to move along each strand
4) DNA replication is completed and two new strands (called Daughter strands) are formed from the two original strands (called parent strands).
5) two complete and identical DNA molecules exist - hence the DNA has been replicated prior to cell division. there are now 46 replicated DNA molecules in each cell.
What are centromeres?
regions of DNA + protein that hold the replicated DNA molecules together.
What is chromatin?
a combination of DNA and protein.
what are two names for structual proteins?
Histone and scaffolding
what are structural proteins used for?
folding and condensing DNA
what happens in prophase?
> the DNA super coils/super condenses
what happens in Metaphase?
> replicated chromosomes line up single file (in random order) along the equator of the cell.
spindles have extended from centrioles to link up to centromere regions.
nuclear membrane has broken down.
what happens in anaphase?
> sister chromatids separate when spindles contract.
>chromatids migrate to opposite poles of the cell.
what is telophase?
> chromatids have fully migrated to opposit poles of the cell.
nuclear membranes begin to form and a dividing cell membrane begins to form.
this is also the beginning of Cytokinesis (actual cell division).
What happens in cytokinesis
> cytokinesis is now completed and the chromatids unwind back into their former chromatin state.
What are the phases of Mitosis?
>interphase >prophase >metaphase >anaphase >telophase >cytokinesis
