Chapter 1 - Cell Division

Chapter 1 - Cell Division - Cell division Cell division...

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Cell division Cell division - Reproduction is a key element of life - Requires 3 things: o 1) Replication of genetic material (2C-> 4C) o 2) Accurate segregation of genetic material o 3) Division of cytoplasm (organelles too) - Process needs to be controlled (how often, when it happens, etc. or become cancerous) - Responsive to environmental conditions Bacteria divide by binary fission - Prokaryotes have simple form of cell division - DNA duplication and segregation a concerted process (are coupled) - Lot less genetic material than eukaryotes o Usually single circular chromosome (as opposed to eukaryotes) - Replication begins at unique site o Origin of replication (attaches here first) o Bidirectional to unique site: terminus (can go in either direction all the way around the circular chromosome, meet halfway through at terminus) Prokaryotic Chromosome compaction - Chromosome larger than cell - Chromosome must be compacted, folded (so it will fit in the cell)
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o Complex with proteins (DNA has a negative charge, cannot compress against itself) o Supercoiled by topoisomerase - Problem for replication and segregation (unwind DNA, copy it, and wind it up again) - Chromosome is also attached to plasma membrane Binary fission - Segregation once thought to be passive o Now known to be an active process o Replicated DNA actively partitioned to different ends of cell o Requires specific sequences near origin (active process carried out by enzymes) - Growth of new membrane and a septum partitions of other cell contents o Septum forms at site of ring of FtsZ protein o FtsZ resembles microtubule protein tubulin involved in eukaryotic mitosis - Figure 10.1: Origin of replication, terminus, replication (bidirectional), segregation, FtsZ production, septum formation Eukaryotic chromosomes (check out figure 10.7) - Sister chromatids: 2 copies of the chromosome within the replicated chromosome - Homologue: same chromosome, different parent (each homologue is copied to create sister chromatids; same genes, different alleles)
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- Centromere: visible constriction in the middle of the chromosome (on the outside) o Short repeated DNA sequences - Kinetochore: proteins attached to centromere o Connect chromosomes to microtubules during mitosis - Cohesin: complex of proteins holding sister chromatids together Problems cells must solve - Chromosome compaction o Chromosomes are too long to fit into cell Means must always be folded (at any time, chromosomes are always compacted; even more so for separation) - Replication and chromosome separation occur at different times o Chromosomes are not “labeled” so they can’t tell the difference amongst the chromosomes o Means must keep chromatids of chromosomes attached until separation o Release of attachment is irreversible (key point in cellular division) Cleavage of cohesion Eukaryotic Chromosome compaction (figure 10.5) - Chromosomes are very long and must be condensed to fit within the nucleus o DNA is complexed with histone proteins o DNA are – charged, histones are + charged (allows for DNA to be compacted)
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This note was uploaded on 10/24/2011 for the course BIOL 111 taught by Professor Dr.zielinski during the Spring '08 term at Purdue.

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Chapter 1 - Cell Division - Cell division Cell division...

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