Cell cycle and mitosis
- Created by: Jess
- Created on: 31-03-15 15:00
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- Cell cycle and mitosis
- Prokaryotes reproduce by binary fission, caused by environmental reproductive signal.
- Usually contain one circular, compacted and folded chromosome.
- Two important regions for replication
- Ori - Origin of replication
- Replication occurs through a "replication complex" of proteins
- After replication, the ori regions move towards opposite ends of the cell, aided by special proteins
- Pinching of the plasma membrane and synthesis of new cell wall materials result in separation of the two cells
- After replication, the ori regions move towards opposite ends of the cell, aided by special proteins
- Replication occurs through a "replication complex" of proteins
- Ter - Termination of replication
- Replication occurs through a "replication complex" of proteins
- After replication, the ori regions move towards opposite ends of the cell, aided by special proteins
- Pinching of the plasma membrane and synthesis of new cell wall materials result in separation of the two cells
- After replication, the ori regions move towards opposite ends of the cell, aided by special proteins
- Replication occurs through a "replication complex" of proteins
- Ori - Origin of replication
- Two important regions for replication
- Two important regions for replication
- Ori - Origin of replication
- Ter - Termination of replication
- Ori - Origin of replication
- Usually contain one circular, compacted and folded chromosome.
- Eukaryote reproduction is related to the needs of an entire organism rather than the single cell.
- Eukaryotes have many chromosomes thus DNA replication and segregation is far more intricate than that of prokaryotes
- The Cell Cycle: The period from one cell division to the next
- Interphase (G1>S>G2)
- G1: Chromosomes are single, unreplicated structures. Variable time period (Some cells enter a resting phase G0)
- S: DNA replicates and sister chromatids remain together
- G2: Cell prepares for mitosis E.g. producing spindle fibres
- Signals that trigger the transitions between the phases act through cyclin-dependant kinases (Cdk's)
- Cdk is activated by binding to cyclin; altering its shape, exposing its active site by phosphorylation
- E.g. Progress past the G1-S point is normally inhibited by retinoblastoma protein, but when phosphorylated by the G1-S cyclin-Cdk, RB becomes inactive and no longer blocks the cycle
- Cdk is activated by binding to cyclin; altering its shape, exposing its active site by phosphorylation
- MITOSIS and DNA structure
- Chromosomes condense to make separation easier
- DNA molecules normally associate with proteins (Histones) to form nucleosomes which are bound tightly to form chromatin
- Phases of mitosis
- PROPHASE: Chromatin condenses and chromatids become visible
- METAPHASE: Chromosomes line up at the midline
- ANAPHASE: Chromatids separate and move to opposite poles
- TELOPHASE: Nuclear envelope reform, spindle disappears and chromosomes become less compact.
- NB Chromatids become daughter CHROMOSOMES that have their own centromere as opposed to sharing one.
- Seperation of sister chromatids is controlled by cyclin- Cdk: it activates anaphase promoting complex.
- ANAPHASE: Chromatids separate and move to opposite poles
- Late in Prophase kinetochores form in the centromere region of each chromosome. Later the kinetochore microtubules attach to them and ensure that the chromatids will move to opposite poles.
- Kinetochores also contain motor proteins that alongside the shortening of the kinetochore microtubules cause the chromosome to move along the microtubules towards the poles
- METAPHASE: Chromosomes line up at the midline
- PROPHASE: Chromatin condenses and chromatids become visible
- Chromosomes condense to make separation easier
- Interphase (G1>S>G2)
- Prokaryotes reproduce by binary fission, caused by environmental reproductive signal.
- SPINDLE APPARATUS: Moves the sister chromatids apart. Made of microtubules and are controlled by centrosomes.
- Centrosomes identify the poles toward which the chromosomes move, formed by centrioles.
- Late in Prophase kinetochores form in the centromere region of each chromosome. Later the kinetochore microtubules attach to them and ensure that the chromatids will move to opposite poles.
- Kinetochores also contain motor proteins that alongside the shortening of the kinetochore microtubules cause the chromosome to move along the microtubules towards the poles
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