BIOL 1000 Chapter Notes - Chapter 8: Cell Signaling, Protein Kinase, Cell Adhesion Molecule
29 Jun 2018
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CHAPTER 8: Cell Cycles
8.1 Cycle of Cell Growth & Division: An Overview
Mitotic cell division: DNA replication is followed by equal
separatation/segregation of replicated DNA molecules & their delivery to
daughter cells, ensuring that the 2 cell products have same genetic info as parent
cell. Mitosis: basis for growth & maintenance of body mass in multicellular
eukaryotes & reproduction in single-celled eukaryotes.
Chromosomes of eukaryotes are individual, linear DNA molecules w/
associated proteins. They get converted to a structure of 2 exact copies known as
sister chromatids in replication.
8.2 Cell Cycle in Prokaryotic Organisms
Prokaryotes go through cycle of binary fission involving coordinated
cytoplasmic growth, DNA replication & cell division produces 2 daughter
cells from parent cell.
Replication of bacterial chromosome consumes most time of cell cycle &
begins at single site (origin) through reactions catalyzed by enymes in middle of
cell. Once ori (origin of replication) is duplicated, the 2 origins move to the 2
ends of cell. Cytoplasm then divides through partition of cell wall material that
grows inward until cell is separated into 2 parts.
8.3 Mitosis & Eukaryotic Cell Cycle
Mitosis and interphase constitute cell cycle. Mieosis creates daughter nuclei that
are different b/c they have half the # of chromosomes as parent cell, but mitosis
creates exact copy. Interphase is from end of one mitosis to beginning of next,
has 3 stages:
1) G1 phase: cell carries out its function & sometimes grows. Varies in
length & determines cell division rate. If a cell stops deciding it instead enters a
G0 phase.
2) S phase: DNA replication & chromosome duplication occur. Cohesins
attach sister chromatid
3) G2 phase: brief gap in cell cycle during which cell growth continues &
cell gets prepared.
Mitosis has 5 stages:
1) Prophase: chromosomes condense into short rods & spindles begin to
form in cytoplasm.
2) Prometaphase: nuclear envelope breaks down, spindle enters former
nuclear area, & sister chromatids of each chromosome make connections to
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opposite spindle poles. Each chromatid has a kinetochore (at its centromere)
that attaches to spindle microtubules.
3) Metaphase: spindle is fully formed & the chromosomes moved by
spindle microtubules become aligned at metaphase plate determine’s
karyotype.
4) Anaphase: spindle separates sister chromatids & moves them to opposite
spindle poles. Chromosome segregation is complete.
5) Telophase: chromosomes de-condense & return to extended state typical
of interphase. New nuclear envelope forms around chromosomes.
Cytokinesis: division of cytoplasm completes cell division by producing 2
daughter cells, each containing daughter nucleus. In animal cells, proceeds by
furrowing (band of microfilaments just under plasma membrane contracts,
slowly separated cytoplasm into 2 parts). In plants, cell wall material is
deposited along the plane of former spindle midpoint & deposition continues
until a continuous new wall (cell plate) separates daughter cells.
8.4 Formation & Action of Mitotic Spindle
Animal cells: centrosome divides & 2 parts move apart, while
microtubules of spindles form between them. Plant cells: no centrosome, so
spindle microtubules form around nucleus.
In spindle, kinetochore microtubules run from poles to kinetochores of
chromosomes & nonkinetochore microtubules run from poles to a zone of
overlap at spindle midpoint without connecting to chromosomes.
During anaphase, kinetochores move along kinetochore microtubules,
pulling chromosomes to poles. Nonkinetochore microtubules slide over each
other, pushing poles farther apart.
8.5 Cell Cycle Regulation: controlled directly by complexes of cyclins &
cyclin-dependent protein kinase (Cdk). Cdk is activated only when combined w/
cyclin & then adds phosphate groups to target proteins, activating them.
Activated proteins trigger cell to progress to next cell cycle stage; each major
stage begins w/ activation of 1 or more cyclin-Cdk complexes & ends with
deactivation of complexes by breakdown of cyclins. 3 cyclins named after stage
@ which they activate Cdk: G1/S, S, and M cyclin degraded each time after
being used.
3 important internal controls create checkpoints to ensure that reactions of
one stage are complete before cycle proceeds to next stage: G1/S checkpoint
checks for damaged DNA, G2/M checkpoint checks for proper replication, &
mitotic spindle checkpoint (before metaphase checks for spindle
assembly/chromosome attachment).
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Document Summary
8. 1 cycle of cell growth & division: an overview. Mitotic cell division: dna replication is followed by equal separatation/segregation of replicated dna molecules & their delivery to daughter cells, ensuring that the 2 cell products have same genetic info as parent cell. Mitosis: basis for growth & maintenance of body mass in multicellular eukaryotes & reproduction in single-celled eukaryotes. Chromosomes of eukaryotes are individual, linear dna molecules w/ associated proteins. They get converted to a structure of 2 exact copies known as sister chromatids in replication. Prokaryotes go through cycle of binary fission involving coordinated cytoplasmic growth, dna replication & cell division produces 2 daughter cells from parent cell. Replication of bacterial chromosome consumes most time of cell cycle & begins at single site (origin) through reactions catalyzed by enymes in middle of cell. Once ori (origin of replication) is duplicated, the 2 origins move to the 2 ends of cell.
