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28 Cards in this Set
- Front
- Back
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What is the purpose of the cell cycle? |
To copy the genome and partition the copies equally between the daughter cells To enable a multicellular organism to grow to dult size to maintain the total cell number of an adult organism to replace lost or damaged cells |
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How so prokaryotes divide? |
binary fission |
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Method of binary fission |
DNA attatched to cytoplasmic membrane Cell enlarges and DNA duplicates Septum forms Cells divide in two, DNA partitioned into each cell Cells seperated |
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What are the two pathways that must be coordinated in the cell cycle |
Replication of DNA and cytokinesis |
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What happens in the replication of DNA? |
Circular chromsome of prokaryotes has one origin of replication from which two replication forks form This creates two identical copies of the circular chromosome |
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How is the timing of cytokinesis and replication co-ordinated? |
DNA replication must be initiated before completion of the previous round as it takes much longer |
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What happens in cytokinesis? |
First a ring of protien (FtsZ) is formed on the inner surface of the cytoplasmic membrane at the future division site FtsZ us distributed randomly throughout the cytoplasm of the cell and will contract to form two new ells |
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What are the additional complications of the eukaryotic cell cycle? |
Genome is composed of multiple linear chromosomes Multicellularity Numerous organelles Cell cycle varies from organism to organism and at different times in organisms life |
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What does the eukaryotic cell cycle consist of? |
G1 S G2 M |
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What happens in the G1 phase? |
growth phase- there is doubling of the mass of organelles and protein and synthesis of enzymes needed for DNA synthesis |
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What happens in the S phase? |
DNA synthesis- At the end of the S phase each chromosome consists of a pair of identical sister chromatids The sister chromatids must not be allwed to seperate from each other so they are bound together by cohesin |
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What would happen if sister chromatids drifted apart? |
Bipolar attatchment to the mitotic spindle would be difficult to achieve |
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What happens in the G2 phase? |
Preperation for mitosis- marked by two events: Chromosome condensation- condensin encircles loops of DNA and compreses the sister chromatids to give a compact structure Formation of mitotic spindle- Nuclear membrane is broken down so the spindle has access to the chromosomes. The klesin subunit of cohesin is cleaved by protease meaning spindle can pull the chromosomes apart |
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what happens in cytokinesis in prokaryotes |
Once the sister chromatids have reahed the opposite poles of the cell the nuclear membrane begins to reform and the cytoplasm is divided into two by a contractile ring of filaments composed of actin and myosin II |
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What is the difference between cytokinesis in animals and plants? |
In animals the contractile ring divides the cytoplasm from the outside in whereas in plants the contractile ring does not form. Instead a new cell wall is constructed by the phagmoplast between the daughter cell nuclei so cytoplasm is partitioned from the inside out |
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What are the variations of the cell cycle? |
Timing Early embyronic cells- divison without growth so cells get smaller wheras somatic cells maintain size Nuclear envelope dynamics- unicelular= closed mitosis and multicellular= open mitosis Polarity- some cells divide assymetrically |
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What is the difference between open and closed mitosis? |
open= nuclear membrane breaks down and then reforms closed= nuclear membrane remains intact throughout |
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How do stem cells replicate differently? |
Stem cells are attached to niche cells which blocks their differentiation but allows cell division One daughter cell is released and is free to differentiate whereas the other remains attatched and is a stem cell |
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What is anchorage dependence? |
displayed by many animal cells in whch cells must be attatched to a substratum in order to divide |
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What is density dependent inhibition? |
this is where cells stop dividing once they contact each other |
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What are the cell cycle control systems? |
Cell cycle engine Co-ordination Checkpoints |
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What is the cell cycle engine? |
phases of the cell cycle are driven by the action of protein kinase levels of kinase remain constant kinase activates the phases of the cycle but only when it is bound to cyclin |
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Why are cyclins key to regulating the cell cycle? |
they undergo cycles of synthesis and degredation so their levels fall and rise There are different cyclin dependent protein kinases and cyclin, each pair activation a different phase of the cell cycle |
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What is meant that the cell cycle is co-ordinated? |
phases must occur in the proper order and once per cycle |
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What checkpoints are there in the cell cycle? |
Restriction point in G1- instructs cell to divide G2/M- checks is DNA synthesis is complete Spindle checkpoint- checks is each chromosome is attatched to spindle DNA damage checkpoint-operates throughout cycle and stops cycle while damage is repaired |
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What is the consequence of a DNA damage checkpoint? |
cycle keeps going despite DNA damage so mutations accumulate which leads to cancer |
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What happens if the spindle checkpoint fails? |
There is unequal segregation of chromosomes which causes human aneuploidies |
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What happens to the cell cycle in cancers? |
siganls that start and stop the cycle are ignored checkpoints no longer operate cells do not communicate with eachother |
