cellular basis of inheritance
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Cellular Basis of Inheritance. Chapter 9. Cells come from other cells. Repair Growth Reproduction Asexual Reproduction Sexual Reproduction. Sexual Reproduction. Genetic Material comes from 2 parents. Asexual Reproduction. Genetic Material comes from 1 parent Budding Cloning - PowerPoint PPT PresentationTRANSCRIPT
Cellular Basis of InheritanceChapter 9
Cells come from other cells• Repair• Growth• Reproduction
– Asexual Reproduction – Sexual Reproduction
Sexual Reproduction• Genetic Material comes from 2 parents
Asexual Reproduction• Genetic Material comes from 1 parent
– Budding– Cloning– Fragmentation– Sporulation
Binary Fission (Prokaryotes way of Asexual Reproduction)• Cell division in prokaryotes produce 2
identical daughter cells
The Cell Cycle• Sequence of growth
and division of a cell• Interphase = period
of growth• Mitosis = period of
nuclear division• Cytokinesis = period
of cell division
Cell Cycle Movie
Limits on Cell Size• Diffusion – becomes slow and
inefficient as the cell becomes larger• Surface Area/Volume Ratio – as a cell
increases, its volume increases faster than its surface area
• DNA content – if a cell doesn’t have enough DNA to program its metabolism, it cannot survive
Chromosome Structure• Chromatin -
Uncondensed form• Genetic material
spends most of its time as chromatin
• During prophase, the chromatin material coils up and condenses to become a chromosome (coiled form of DNA)
Chromosome Structure
• Chromosomes -condensed rod shaped structures made of coiled DNA, (only seen in mitosis phase)
Chromosome StructureThe DNA wraps around a histone core to form
bead like structures known as nucleosomes• This occurs during prophase• Histones – proteins that help DNA coil
Chromosome Structure• The nucleosomes
coil even more • The coils become
the chromosome
• From smallest to most coiled is the following – Double helix– DNA and histone protein– Coil– Super coil– Chromosomes
Centromere• Each half of a replicated
chromosome is called a chromatid
• Sister chromatids: The 2 identical halves of the double structure are sister chromatid; exact copies of each other
• Centromere: site where sister chromatids are adjoined
Chromosome or chromatid?
• 1 chromosome• 1 chromatid
• 1 chromosome (doubled)• 2 chromatids (sisterchromatids)
Replication
Mitosis and MeiosisHow and Why Cells Divide
Onion root
Interphase• G1 phase= Growth
phase• S phase = synthesis
phase – make copy of DNA
• G2 phase – Growth and cell maintenance for preparation of division occurs: - for example copying
organelles
Interphase
• Gene replication occurs
• Cell maintenance occurs:– make ATP– excrete wastes– make proteins– produce new
organelles
Prophase
• Chromatin coils up into visible chromosomes
Prophase
• Centrioles begin to migrate to opposite sides of the cell
• Nucleus begins to dissappear as nuclear envelope and nucleolus disintegrate
Prophase
• Spindle fibers – form between centrioles
- And attach to chromosomes
Metaphase
• Chromosomes line up at the center of the cell
(along the equator) • (shortest phase)
Anaphase
• Chromatids split and one is pulled to each of the poles; centromere first
• Each chromatid is identical
• One copy of each chromosome goes to each side (pole)
Telophase• Final phase of mitosis• Chromatids reach opposite ends
of the cell• Opposite events of prophase:
– chromosomes unwind into chromatin
– spindle breaks down– nuclear envelope forms around
2 new sets of chromosomes (to create 2 new nuclei)
– nucleolus forms in each nucleus• Cytokinesis begins (before
telophase is finished)
End of Mitosis• Nuclei go back into interphase• Cytokinesis begins
Cytokinesis• Animal Cells:
– Form Cleavage Furrow – membrane pinches off and
half of the cell contents go to each new daughter cell
• Plant Cells:– forms Cell Plate – because plants have a rigid
cell wall, the plasma membrane does not pinch in; a cell plate forms across the equator
When do cells divide?• Growth of a multicellular organism - due to increase in # of cells, not
size of cells!– Living things grow by producing more cells, not cells getting bigger same
size now as baby, size or organism depends on number of cells– Cell division enables multicellular organisims to grow and develop from a
single fertilized egg – one single cell can divide to form a multicellular human
– Cells can grow a little bit ex fat cells don’t divide once reach puberty –but can grow much larger
• - even if not growing in size still produce new cells to replace old• Cell division even when fully grown to renew and repair cells or replace
old that die of wear and tear or accidents ex bone marrow supplys new blood cells
• *Red blood cells only live 120 days 2.5 million new must be made/second?, but must be controlled growth (or cancer)
• * Cells that line the digestive system organs – go through entire cell cycle in 6 hours