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BIOLOGY 1A03 Lecture Notes - Spindle Apparatus, Sister Chromatids, Photographic Emulsion

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Joe Kim

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Chapter 11- The Cell cycle
Mitosis Cell division functions
-reproduction (uniceullular)
-growth, development, and tissue repair (multicellular)
M Phase and interphase:
-Interphase is nondividing phase
-Cells spend most of their time in Interphase
-interphase chromosomes not usually visible
Discovery of Cell Cycle
-researchers used radioactive isotopes to trace chromosomes (phosphorous and thymidine)
-use of isotopes known as autoradiography
-figured out there was an S phase (synthesis phase)
How long does S phase last? experiment
1.Feed radioactive thymidine to cells growing in culture. Only cells in synthesizing will have label
2. Wash extra thymidine out
3.Spread cells and expose to photographic emulsion
-S phase is about 8 hours long and there is a lagging gap between S phase and M phase
How does Mitosis Take Place?
-Eukaryotic chromosomes normally exist as extremely long, threadlike strands consisting of DNA
associated with globular proteins called histones
-DNA-protein material combined called chromatin
-Dna copies in a replicated chromosome is called chromatid. Chromatids from same chromosome called
sister chromatids
-chromatids joined by centromere
Cell cycle-Interphase
g1 phase: cell growth and duplication of organelles
S phase: DNA synthesis (chromosomes replicate)
g2 phase: cell growth and duplication of organelles continues to build the protein "machinery"
Why doe GAP phases exists?
-before mitosis occurs, the parent cell must be large enough size and must have required organelles, so
that daughter cells will operate normally
What is the G0 phase?
-the nondividing state
What are examples of cells in G0?
-nerve cells that are mature, and muscle cells
-Note that in other cells, such as liver cells, they can go back from G0 back into the cell cycle. This is
triggered by external cues (ex.growth factors released upon injury)
-visible in light microscope
-formation of mitotic spindle (spindle fibres pull chromosomes into daughter cells)
-centrosome: microtubule organizaing centre containing pair of centrioles
-spindle either move to opposite side or form on opposite sides
-nucleous dissapears and nuclear envelope fragments
--spindle fibres attached to chromosome
-kinetochore: each chromosome has two where spindle fibres attach (one on each side)
-chromosomes line up along a line called metaphase plate
-mitotic spindle formation compete
-sister chromatids pulled apart to create identical chromosomes
-kinetochore spindle fibres begin to shorten
-nuclear envelope begins to form around set of chromosomes .
-mitotic spindle fades away
Cleavage furrow: Fold in membrane of animal cell during cytokinesis due to actin filaments sliding
Cell plate: Line in between cells due to vessicles from golgi building up there
How do Chromosomes moves during Mitosis?
- the tubulin subunits of the kinetochore microtubules are depolymerized (lost) from the
kinetochore ends
- motor proteins, such as dynein attach and detach along the kinetochore microtubule’s length,
this results in chromosome movement
-protein in kinetecore catalyze the loss of tubulin subunits at the plus end , while motor proteins moves
towards the minus end.
-Use flourescent labels to make the metaphase chromosomes flurosce blue and microtubules yellow
2.Photobleach a section of microtubules
3. You will observe that microtubles shorten at kinetecore
Control of the Cell Cycle
Hetereokaryon: A cell that contains more than one nuclei
Do regulatory molecules control cell cycle phases?
a) 1. Fuse M phase cell with a cell of a different phase
2. chromosomes start to conduct M phase
b) 1. Inject M-phase cytoplasm and Interphase cytoplasm into a cell
2. Obeserve that the cell with M-phase cytoplasm will conduct M-phase
This driving factor is known as mitosis-promoting factor or MPF
MPF contains cyclin and Protein Kinase
Cyclins build up in concentration during interphase and peak during M phase
Protein kinase catalyzes ATP tranfser also known as cdk
-Protein kinase induces a conformational change
-Phosphatase reverses this
-Protease degrades protein
Cell Cycle-checkpoints
- under normal conditions, cell cycle checkpoints ensure that DNA replication (S phase of Interphase)
and mitosis take place only when conditions are favorable and the related processes are functioning
- checkpoints regulate the correct sequence of events in time and enforce synchrony of different
complex processes (ex. during spindle organization and chromosome contraction)
- involve rapid and reversible alterations, for example when functional groups change
(dephosphorylation and phosphorylation) or when proteins (cyclins) are broken down
G1 Checkpoint:
-Are the nutrients sufficient?
-are growth factors present?
-is sell size adequate?
-Is DNA undamaged?
G2 Checkpoint
-Is activated MPF present?
-Is chromosome replication successfully completed?
Metaphase checkpoint
Are all chromosomes attached to mitotic spindle?
*In cancer cells, cell cycle checkpoints fail!
know real world examples and how they look: google search!
Kinetochore microtubles: assist in movement of chromosomes
Nonkinetochore microtubles: -assist in elongating the entire cell during anaphase
-They form a cage-like newtork, which facilitates the activities of the cell cycle components