mitosis & cytokinesis. why do eukaryotic cells divide by mitosis? growth & repair for...
TRANSCRIPT
Mitosis & Cytokinesis
Why do Eukaryotic cells divide by Mitosis?
Growth & Repair for multicelled organisms
Reproduction of single celled organisms
AmobeaReproducing
Cells dividing by Mitosis…….
• Identical to original cell
• Same chromosome #
• Identical chromosome makeup
Skin
What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many
genes, regulatory elements and other nucleotide sequences.
What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many
genes, regulatory elements and other nucleotide sequences.
What are chromosomes?A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many
genes, regulatory elements and other nucleotide sequences.
Sister Chromatids
So where is DNA located?
In the Nucleus
In the Chromosomes
Cell division requires coordinated division of chromosomes (mitosis) …..
…… and division of the cytoplasm (cytokinesis).
From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle.
In multicellular organisms like us, progress through the cell cycle is carefully regulated.
Stages of Mitotic Cell Division
• Interphase - intermission• Prophase - 1st• Metaphase - middle• Anaphase - apart• Telophase – far or seperate
Interphase
• “Intermission”
• Normal metabolic activities
• Major state • DNA = chromatin
Late Interphase
• Prepares for mitosis• DNA doubles = Sister chromatids• Centrioles double in animals
Prophase• Nuclear membrane
disappears• Doubled DNA =
condensed• “chromosomes”
visible• Spindle fibers
Metaphase
• Chromosomes line up mid- cell
• Facing inward
Anaphase• Chromosomes move to
opposite poles at Centrioles in animals
• Spindle apparatus in plants
Telophase• Cells divide• Cell plate or
membranes form• Nucleus reappears
Cytokinesis: cell’s cytoplasm divides & splits apart
Plant versus Animal Mitosis
Plant:• Cell wall from cell plate in telophase• Spindles
Animal:• No cell wall membrane during cytokinesis• Centrioles
In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells
Cleave furrow in a dividing frog cell.
Animal Telophase
Interphase
The Plant Cell Wall Forces Cytokinesis to Play by Different Rules
Plant AnaphaseInterphase
Spindle & spindle fibers: Pull apart the sister chromatids
Spindle fibers
Returns to Interphase
• “Intermission”• Normal metabolic activities• Major state • DNA = chromatin
DNA and Its Faithful Replication – The Knit of Identity
Because DNA stores genetic information and is faithfully replicated, information is passed largely unaltered from cell-to-cell, generation-to- generation.
Proteins and Their Production – The Primary Reason for DNA
Cell Division DemandsCoordination of DNA Replication, Mitosis and Cytokinesis
DNA Replication – Simple in Principle, Complicated in Practice
DNA is Packaged into Chromosomes
DNA in the cell is virtually always associated with proteins.
The packaging is impressive – 2 meters of human DNA fit into a sphere about 0.000005 meters in diameter.
chromatin
duplicatedchromosome
The Link Between DNA Replication and Chromosome Duplication
DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell
95% of the time, chromosomes are like this.
(chromatin)
Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.
A Karyotype is an Arranged Picture of Chromosomes At Their Most Condensed State
A normal human karyotype
Boy or girl?
Note that almost all chromosomes come in homologous pairs.
From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle
In multicellular organisms like us, progress through the cell cycle is carefully regulated.
The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes
Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions.
interphase prophase metaphase
Mitosis Precisely and Evenly Divides Duplicated Chromosomes
Cytokinesis is the process of cell division and it is distinct and separable from mitosis.
Mitosis in Action
Blue shows DNA, green shows spindle fibers.
Cancerous cells……...
1.Divide too many times
2.Divide into more than two cells!
• Masses of cells =
• “tumors”
• benign
• malignant
Cancer Is One Outcome of A Runaway Cell Cycle
Licentious division - prostate cancer cells during division.