CAS BI 105 Lecture Notes - Lecture 14: Spindle Apparatus, Cellular Respiration, Telomere

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Cell Cycle: Mitosis and Meiosis
Cellular Replication
Why do we need to replicate our cells?
Growth
Repair
Reproduction (for unicellular organisms - mitosis is reproduction
Cells do not replicate all the time, it is one small part of a cell’s life
Mitosis = Reproduction for bacteria
Reproduction of the genome, then the
cell splits into two
^parent cell splits into two daughter
cells
*cells spend only 10% of their lifespan
in Mitosis
Phases:
G1 -
*G = gap
Cellular growth
Normal life
(making proteins, getting rid of waste, cellular respiration)
DNA is in the form of chromatin
Cells spend most of their life in this stage
S -
DNA synthesis phase
The cell replicates its entire genome
At the end of the process, you will have 2x the amount of DNA that was present in G1
Enters this stage in anticipation of reproducing
G2 -
*G = gap
Preparation for mitosis
The cells may be replicating proteins or organelles in prep for mitosis to begin
The amount of time in this phase can vary
Mitosis -
Organize the replicated genome so that each daughter cell gets an identical genome to what the
parent had in G1
Cancer = too much mitosis (cells are reproduced too frequently)
Controlling Mitosis
Cell Cycle controls genes
Stops cells at certain points in the cell cycle until it is appropriate to proceed
CHECKPOINT 1: G1: determines if conditions are favorable for cell division OR if the DNA is
damaged
CHECKPOINT 2: G2: checks for DNA damage
CHECKPOINT 3: Metaphase: determines if all the chromosomes are attached to the spindle
apparatus
*if these checkpoints are not functioning properly, then the cell cycle can go awry
Contact Inhibition
Cells are prevented from replicating if they are in contact with other cells on all sides
Telomeres
Limit the number of times in the life of a cell that it can undergo mitosis
Each cell can only undergo mitosis about 50 times
The amount of telomere can run out
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Mitosis
When we replicate our cells we want to make an exact copy of the cell
DNA Replication
DNA holds the blueprint for every molecule within a cell
The eukaryotic cell has a lot of DNA to replicated and keep track of
Mitosis is only successful if every gene gets into daughter cells
Keeping DNA Organized
During interphase (G1, S, G2) the DNA is unwound (chromatin) and is wound up for mitosis
^this DNA is wound around proteins and condensed into chromosomes
Chromosome - a discreet body of DNA
Chroma - color
Some/Soma - body
Chromatin - DNA
Chromosome - bodies of DNA organized by color
*humans have 46 TOTAL chromosomes/23 DIFFERENT chromosomes organized into pairs
1 from mother, 1 from father
Contain the same basic info with slight differences
*Homologous Pair = a pair of attached chromosomes
Appear as a single strand
When they have replicated, they have 2 strands joined at the center by a centromere
Centromere - DNA that is hidden beneath the kinetochore proteins
^in this state, each strand = a chromatid
I = 1 chromosome with 1 chromatid
II = 1 chromosome that is REPLICATED with 2 chromatids
CHROMA-
Chromatin - unwound DNA
Chromosome - a unit of condensed DNA that replicates as one
^can have 1 or 2 sister chromatids
Chromatid - one of two “sister”, a replicated chromosome
Chroma - color (G)
Cytoskeleton - system of protein within the cell that helps move organelles around
The cell builds a spindle of microtubules and attaches the chromosomes to it
CENTRO-
Centrosome - a pole of spindle apparatus’ that contain centrioles
Centriole - the anchors of the mitotic spindle that determine the direction of the microtubules
Kinetochore - proteins that attached sister chromatids to the spindle
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 split at the middle and each new cell will end up with a full genome
Mitosis -
Prophase
DNA condenses into chromosomes
Nuclear envelope begins to disappear BUT nucleus still intact
Spindle is beginning to form
If something affects the spindle, then mitosis will be stopped in this stage
Pro-metaphase
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