cell division and genetics – mechanisms for a knit of identity and thread of distinction
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Cell Division and Genetics – Mechanisms for a Knit of Identity and Thread of Distinction. DNA and Its Faithful Replication – The Knit of Identity. - PowerPoint PPT PresentationTRANSCRIPT
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Cell Division and Genetics – Mechanisms for a Knit of Identity and Thread of Distinction
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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.
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Proteins and Their Production – The Primary Reason for DNA
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Cell Division DemandsCoordination of DNA Replication, Mitosis and Cytokinesis
What’s so important about cell division (3 reasons)?
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Cell division requires coordinated division of chromosomes (mitosis) …..
…… and division of the cytoplasm (cytokinesis).
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DNA Replication – Simple in Principle, Complicated in Practice
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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
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The Link Between DNA Replication and Chromosome Duplication
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DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell
95% of the time, chromosomes are like this.
Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.
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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.
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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.
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The Cell CycleEvents that occur in the life of a cell.Includes 3 major stages:1. Interphase 2. Mitosis3. Cytokinesis
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1. Interphase (Cell is not dividing)
G1 Phase – carries out basic functions & performs specialized activities.duration is extremely variablecontains restriction checkpoint ~ cell “decides” to:divideenter a quiescent phase (G0)
die
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1. Interphase (Cell is not dividing)G0 Phase – cell maintains
specialized characteristics, but does not divide
Ex. neurons & muscle cells
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1. Interphase (Cell is not dividing)S Phase – cell replicates
chromosomes & synthesizes proteinsanimal cells replicate centrioles as well
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1. Interphase (Cell is not dividing)G2 Phase - cell synthesizes
additional proteins (ex. tubulin) & assembles/stores
membrane material
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2. Mitosis (M phase) – Equal distribution of replicated genetic material. Four steps:
Prophase Metaphase Anaphase Telophase
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2. Mitosis – Prophase replicated chromosomes condense centrosomes separate & migrate
toward opposite sides of cell
mitotic spindle forms (microtubules grow out from centrosomes)
nucleolus and
envelope disappear
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2. Mitosis – Late Prophase (prometaphase)
nuclear membrane breaks down spindle fibers
attach to centromeres of chromosomes
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2. Mitosis – Metaphase chromosomes
are lined up single-file along equator of mitotic spindle
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2. Mitosis – Anaphase Centromeres part,
sister chromatids (now called chromosomes)
separate chromosomes
move toward opposite poles
?
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2. Mitosis – Telophase mitotic spindle
breaks down chromosomes
decondense nuclear
membranes reform around two nuclei
nucleoli reappear
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3. Cytokinesis Distribution of cytoplasm to
daughter cells begins during anaphase or
telophase differs in animal & plant cells
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3. Cytokinesis in animal cells Cleavage furrow (slight indentation)
forms around equator of cell Actin & myosin
microfilaments act like a drawstring to pinch the cell in two
Usually an equal division
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In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells
Cleave furrow in a dividing frog cell.
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Review of the M-phase
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Cancer Is One Outcome of A Runaway Cell Cycle
Licentious division - prostate cancer cells during division.