Mitosis Flashcards
why do we need to replicate our cells?
o Growth
o Repair
o Reproduction (for unicellular organisms; mitosis is reproduction)
cells spend how long in mitosis
only about 10% of their life
G1
o Cellular growth
o Normal life (making proteins cellular respiration, etc)
o DNA is in the form of chromatin
o Cells spend 90% of their time her
S phase
o DNA synthesis
o Replicate the cell’s entire genome
o Cell will now have two copies of genetic info
o Only enter phase is they are going to reproduce
G2
o Prepare for mitosis
o Cell may spend a short time or a long time in GW
o Nothing really happens that can be seen under the microscope
M
o Mitosis
o Organize the replicated genome so that each daughter cell gets an identical genome to what the parent had in G2
Cancer
occurs when mitosis happens too often
G1 checkpoint
Determines if conditions are favorable for cell division and if the DNA is damaged
G2 checkpoint
checks for DNA damage
Metaphase checkpoint
determines if all chromosomes are attached to the spindle apparatus
contact inhibition
o Cells are prevented from replicating if they are in contact with other cells on all sides
o To become a tumor, a cell has to lose its contact inhibition
telomeres
o Limit the number of times in the life of a cell that it can undergo mitosis
How do we keep DNA organized?
- During interphase (G1, S, G2) the DNA is unwound (Chromatin) it winds up for mitosis
- DNA is wound around proteins and condensed into chromosomes
Chromosomes
- Humans have 46 chromosomes
- 23 pairs
- appear as a single strand
- when they have replicated, they have 2 strands joined at the center by a centromere
- in this state, each strand= chromatid
- one chromatid=1 chromosome
- two chromatids combined: 1 chromosome
chromatin
unwound DNA
chromosome
a unit of condensed DNA that replicates as one
chromatid
one of two “sisters”, a replicated chromosome
homologous pair
contain the same basic info, with slight differences
mitosis overview
- DNA is replicated in S phase
- DNA is organized into chromosomes and carefully arranged within the cell so that one copy of each homologous pair ends up at the far ends of the cell
- The cell can then split at the middle and each new cell will end up with a full genome
centrosome
a pole of spindle apparatus, contains centrioles
centriole
the anchors of the mitotic spindle determine direction of microtubules
kinetochore
proteins that attach sister chromatids to spindle
Prophase
- DNA condenses into chromosomes
- Nuclear envelope begins to disappear
- Spindle is beginning to form
- Nucleus is still intact
prometaphase
- Nuclear membrane has completely disappeared
- Spindle is fully formed
- Chromosomes attach to spindles
metaphase
chromosomes move to the middle of the cell (metaphase plate)
anaphase
sister chromatids separate and move to the poles
telophase
- A whole cell’s worth of DNA in each of the poles
- DNA begins to de-condense
- Nuclear envelope begins to re-form
cytokinesis
plasma membrane begins to pull in
two identical daughter cells
cells that don’t undergo mitosis
o Neurons (when you lose a neuron you can’t replace it) o All skeletal muscle cells (have thousands of nuclei; can’t decide which one to use) o Red blood cells (don’t have a nucleus)
how do viruses reproduce
o Do have a genome
o Manipulate the host cell that they live in to do their replication for them
steps for viral reproduction
- A virus cannot reproduce itself=no mitosis
- Viruses are composed of a genetic code (DNA or RNA) enveloped in an outer coat
- It must insert its genetic info into that of its host cell, and trigger the host cell to reproduce
- Needs a host cell to reproduce
- Many viruses trigger “out-of-control” mitosis
- The virus must be able to short-circuit the normal controls of mitosis
telomeres
sections of DNA on the end of the chromosomes that gets shorter each time the chromosome replicates
no more telomeres=no more replication
premature telomere shortening has been associated with disease and death
premature aging
