Chapter 7 The Cell Cycle and Cell Division Key Concepts 7.2 Binary Fission and Mitosis 7.3 Cell Reproduction Control
Two types of Reproduction Asexual Reproduction Faster Creates genetically identical cells (clones) Common in nature Only 1 parent is involved Examples: binary fission in prokaryotes and mitosis in eukaryotes Sexual Reproduction Creates gametes (sex cells – sperm and egg cells) Product has genetic diversity 2 parents are involved Examples - meiosis
Basic Term - Chromosome Consist of DNA and protein 3 forms Chromatin – 1 long strand, wrapped around histones Chromatid – half of a chromosome Chromosome – full X, 2 sister chromatids held together by a centromere Contain specialized proteins called kinetochores Homologous Chromosomes – in pairs, similar in shape, size and information (1 from Mom and 1 from Dad) - TETRAD
Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 1)
Two kinds of Cells Diploid Cells Chromosomes are in pairs Abbreviated 2n Example – Somatic (body) cells, zygote Humans diploid # = 46 Haploid Cells Chromosomes are not in pairs Abbreviated 1n Example – Gametes/Sex Cells/Sperm/Egg/Spores Human haploid # = 23
Karyotype of Homo sapiens Mitotic (doubled) chromosomes taken from a white blood cell at metaphase 23 chromosome pairs, 46 total Stained with Giemsa stain to reveal differences in the DNA/protein associations. Banding distinctive to each chromosome What was the sex of this individual?
For any cell to divide Four events must occur for cell division: Reproductive signal—to initiate cell division Replication of DNA Segregation—distribution of the DNA into the two new cells Cytokinesis—division of the cytoplasm and separation of the two new cells
Concept 7.2 Both Binary Fission and Mitosis Produce Genetically Identical Cells In prokaryotes, cell division results in reproduction of the entire organism. The cell: Grows in size Replicates its DNA Separates the DNA and cytoplasm into two cells through binary fission
Cell Cycle 5 parts 1.G1 - growth 2.S – DNA Synthesis 3.G2 – prepare for mitosis 4.M – mitosis (PMAT) 5.C – Cytokinesis – division of the cytoplasm Interphase
3 parts – G1,S,G2 Nucleolus and Nuclear Membrane is Visible Longest phase of the cell cycle Chromatin is visible
Figure 7.5 The Phases of the Eukaryotic Cell Cycle (Part 2)
Prophase 1 st stage of mitosis Chromatin chromosomes Centrosome and spindle fibers are visible and start to organize and move to opposite poles Pair of centrioles Nuclear Membrane and Nucleolus disappear
Metaphase 2 nd stage of mitosis Chromosomes are lined up at the equator of the cell, connected to the spindle fibers by their centromere
Anaphase 3 rd phase in mitosis Chromosomes chromatids Spindle fibers pull the chromosomes apart and move them towards opposite poles
Telophase Last phase of mitosis Chromatids chromatin (less compact) Nuclear membrane and nucleolus return Overlaps with Cytokinesis
Cytokinesis After Interphase Division of the cytoplasm (cleavage furrow vs. cell plate) Each daughter cell contains an exact copy of DNA and are identical in every way
Concept 7.3 Cell Reproduction Is Under Precise Control The reproductive rates of most prokaryotes respond to environmental conditions. In eukaryotes, cell division is related to the needs of the entire organism. Cells divide in response to extracellular signals, like growth factors.
Concept 7.3 Cell Reproduction Is Under Precise Control Progression is tightly regulated— the G1-S transition is called R, the restriction point. Passing this point usually means the cell will proceed with the cell cycle and divide.
Concept 7.3 Cell Reproduction Is Under Precise Control Specific signals trigger the transition from one phase to another. Transitions also depend on activation of cyclin- dependent kinases (Cdk’s). A protein kinase is an enzyme that catalyzes phosphorylation from ATP to a protein. Phosphorylation changes the shape and function of a protein by changing its charges.
Concept 7.3 Cell Reproduction Is Under Precise Control Cdk is activated by binding to cyclin (by allosteric regulation); this alters its shape and exposes its active site. The G1-S cyclin-Cdk complex acts as a protein kinase and triggers transition from G1 to S. Other cyclin-Cdk’s act at different stages of the cell cycle, called cell cycle checkpoints.
Figure 7.10 Cyclins Are Transient in the Cell Cycle
Concept 7.3 Cell Reproduction Is Under Precise Control Example of G1-S cyclin-Cdk regulation: Progress past the restriction point in G1 depends on retinoblastoma protein (RB). RB normally inhibits the cell cycle, but when phosphorylated by G1-S cyclin-Cdk, RB becomes inactive and no longer blocks the cell cycle. RB + ATP RB-P + ADP Active – blocks cell cycle Inactive – allows cell cycle to go forward