Why does a cell divide Cell cycle G
- Slides: 27
Why does a cell divide?
Cell cycle
• G 1 phase: Growth, cytokinesis finishes , protein synthesis, prepares to copy DNA • S phase: DNA copies itself • G 2: protein synthesis continues prepares to divide • M Mitosis Nucleus divides perfectly • Cytokinesis: cytoplasm divides sort of evenly
Unicellular organisms • Mitosis is reproduction • Nutrients, oxygen come in across the cell membrane. Waste products leave through the cell membrane. • The ability to maintain a chemical balance across the cell membrane is vital. • As the cell grows the volume increases faster than the surface area of the membrane. • When the cell can no longer maintain the traffic across the membrane. It signals the cell to divide.
Multicellular Organisms • If cells are limited to their size then in order to have large organisms they become multicellular. • Cells specialize into tissues each with a certain job. Nerves for communication and sensing, muscles for moving, digestive system for attaining food etc. • Each of these cells contain all the DNA but to specialize they turn off certain genes and turn on others.
How do cells divide? Mitosis and cytokinesis • • Mitosis How the nucleus divides exactly Uncoiled DNA copies itself (Chromatin threads) DNA coils up (Chromosomes) Centrioles go to each end of the cell Micro tubules attach to chromosomes Microtubules pull them apart Mitosis - You. Tube
Phases of mitosis • Prophase coil up • Metaphase line up • Anaphase separate • Telophase uncoil
Cytokinesis • Cytoplasm divides • At the end of telophase
Interphase cell does it’s work
Intephase Onion root tip White fish ovaries
Prophase cell prepares to divide Early prophase Late Prophase
Prophase • DNA • Centrioles coils up into Chromosomes migrate to the 2 poles • Aster starts to form • Nuclear • Chromosome envelopes disintegrates are doubled in chromatid pairs.
Prophase In allium root tip In white fish ovaries
Metaphase Chromosomes line up
Metaphase • Centrioles form a complete spindle • Microtubules attach to the kinetichores of the chromatid pairs • Chromatid Pairs line up across the equator. • Nuclear membrane is gone
Metaphase In allium root tip In white fish
Anaphase the chromotids separate
Anaphase • The micro tubules shorten and pull the chromatids apart. • The chromatids migrate to opposite ends of the cell • The micro tubules push the cell membrane make the cell longer
Anaphase In allium root tips In white fish ovaries
Telophase two new nuclei reform Early telophase Late telophase
Telophase • • • This is prophase backwards The nuclear envelope reforms. The chromosomes uncoil The aster disappears The cytoplasm starts to divide
Telophase In allium root tips In white fish ovaries
Cytokinesis cytoplasm divides
Animal cells make a cleavage furrow
Plant cells make a cell plate
Cytokinesis Allium root tip White fish ovaries
All the stages of mitosis in Allium root tips
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