CAS BI 105 Lecture Notes - Lecture 14: Spindle Apparatus, Cellular Respiration, Telomere
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
find more resources at oneclass.com
find more resources at oneclass.com