Mitosis Flashcards
Somatic cells contain __ chromosomes and __ pairs
46 chromosomes, 23 pairs
What is a zygote
A fertilized egg. 1 cell.
Somatic cell proliferation consists of which 3 main divisions and what subdivisions?
- Interphase (cell growth and DNA rep)
- G1, G0, G2. and S phase - Mitosis (nuclear division)
- Phophase, pro metaphase, metaphase, anaphase, telophase - Cytokinesis (cytoplasm division)
What occurs during interphase G1
- The cell grows in size.
- Most non-dividing cells are stuck in G0, which is a branch off G1.
- Prior to proceeding to S phase, the cell is checked at the G1 checkpoint. In order to pass the checkpoint, the size, protein reserves and DNA must meet requirements for the cell to enter S phase.
What occurs during G1 checkpoint?
Prior to proceeding to S phase, the cell must be checked to ensure that the size, protein reserves, and DNA passes.
If protein reserves are no adequate, the cell is halted. May enter G0 until it builds up more protein levels.
If DNA is damaged, p53 halts the cell cycle and recruits enzymes to repair the DNA. If DNA cannot be repaired, p53 can trigger apoptosis.
Transition from G1 into S phase is regulated by cell-signaling molecules called
cyclins and cyclin dependent kinases.
What occurs during the S phase
- Centrosome replication occurs (which are comprised of 2 centrioles) and are surrounded by a mass of proteins (PCM).
- DNA semi-conservative replication occurs using:
- DNA helices at the origin of replication
- ssDNA binding proteins to keep the strands separated
- RNA primase to lay down RNA primers so DNA pol can add nucleotides to the 3’ end.
- Extra RNA primase is needed for the lagging strand, but not the leading strand.
- RNA primer is removed and then replaced with DNA by DNA pol. Sealed by ligase.
Centrosomes are comprised of 2
Centrioles
Why are telomeres necessary?
Since there are primers at the end of the lagging strands, when they are removed by exonuclease, they cannot be replaced since they have a free 5’ end and not a free 3’ end.
Therefore, the parent strand has a 3’ overhang.
Telomeres consist of a repeating sequence of
6 nucleotides. Get shorter with each DNA replication/ When they get too short, the cell becomes inactive (senescent) and dies.
Senescent
Inactive cell
Which cells have telomerase, an enzyme that can extend telomeres?
Stem cells, egg cells, sperm cells, and cancer cells.
What occurs during G2?
The cell grows in size. Prior to proceeding to mitosis, the cell is checked at the G2 checkpoint. Size and DNA replication must meet requirements for cell to enter mitosis. Regulated by cyclin and cyclin dependent proteins.
What is the purpose of the G2 checkpoint?
To ensure that the cell is large enough and that DNA replication was successful. If the cell is too small or DNA was inaccurately replicated, it will not move forward.
Regulated by cyclin and cyclin dependent proteins.
What occurs during prophase
Chromatin condenses into chromosomes. Chromosomes consist of 2 sister chromatids (dsDNA pairs), a centromere (where the sister chromatids are linked) and telomeres
Spindle fibers (composed of microtubules AKA tubules) emerge from centroSOME. Centrosomes move to opposite ends of poles.
Chromatids are made up of
dsDNA each
Centromere
Connects sister chromatids together
What occurs during prometaphase
The nuclear envelope breaks down, nucleolus disappears, and kinetochores appear at the centromeres so that the mitotic spindle can attach.
What occurs during metaphase
Chromosomes line up along metaphase phase with help from spindle fibers attached to centrosomes.
Prior to proceeding to anaphase, there is a metaphase checkpoint that makes sure all sister chromatids are correctly attached to the spindle fibers.
What occurs during anaphase
Sister chromatids separate from the force of the spindle fibers into 2 identical chromosomes and are pulled to opposite ends of the cell.
What occurs during telophase?
Chromosomes are now at opposite poles and they begin to decondense. Nuclear envelope begins to form and so does nucleolus. Mitotic spindles disintegrates.
What occurs during cytokinesis?
Begins in either anaphase or telophase and finishes shortly after telophase.
Actin-myosin ring inside the cell membrane forms a cleavage furrow due to contraction. Divides the cell into 2 with its own dsDNA, nucleus, cytoplasm, and organelles.
