Cellular Reproduction and the Cell Cycle

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Cellular Reproductionand the Cell Cycle
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What do all cells require to survive?

• A complete set of genetic instructions

produce required molecules direct life
processes

• Genetic instructions are coded in
• the DNA of cells

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Why do cells divide?
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Cell Cycle

• Activities of a cell from one cell
• division to the next

Why?
Cell grows, adding more cytoplasmic
constituents
Why?
DNA is replicated
cell divides into two identical daughter
cells
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Essential Features of Cell Division

• Transmit a complete copy of
• genetic information (DNA)

• Transmit materials necessary for
• cell to survive and use genetic
• information

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Two Fundamental Types of Cells (organisms)

• Prokaryotic
• Eukaryotic

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Prokaryotic Cell

• no nucleus genetic material
• (DNA) in cytoplasm

• no membrane-bound organelles

• cell division is called binary fission

• example bacteria

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Eukaryotic Cell

• membrane-bound organelles, including
• a nucleus

• genetic material (DNA) contained within
• the nucleus

• cell division of somatic cells called
• mitotic cell division

• examples fungi, protists, plants,
• animals

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During non-division phase of cell cycle

• DNA molecules in extended,
• uncondensed form chromatin

cell can only use DNA to produce molecules
when in extended state
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During division phase of cell cycle

• DNA molecules condense to form
• chromosomes prior to division

each chromosome is a single molecule of DNA
easier to sort and organize DNA into
daughter cells
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Prokaryotic Cell Cycle

• Prokaryotic chromosome a circular loop

• chromosome attaches to one point
• on plasma membrane

• chromosome is replicated
• replicated chromosome attached
• to plasma membrane at a different
• nearby point

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• cell elongates new plasma
• membrane is added between
• between chromosomes, pushing
• them towards opposite ends of cell

• plasma membrane grows inward
• at middle of cell

• parent cell is divided into two
• identical daughter cells

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What is Mitotic Cell Division?

• Division of somatic cells
• (non reproductive cells) in
• eukaryotic organisms

• A single cell divides into two
• identical daughter cells
• (cellular reproduction)

gt Maintains chromosome ploidy of cell
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Ploidy refers to the number of pairs of
chromosomes in cells

• haploid one copy of each
• chromosome
• designated as n

• diploid two copies ( pair) of each
• chromosome
• designated as 2n

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Each species has a characteristic number of
chromosomes Prokaryotes one
chromosome Crayfish 200 chromosomes Human
46 chromosomes gt 23 pairs of
chromosomes
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Diploid organisms receive one chromosome from
female parent ( maternal) and one
chromosome from male parent ( paternal)
A matched pair of maternal and paternal
chromosomes are called homologues
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• Prior to cell division
• chromosomes (DNA) are replicated
• (duplicated)

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Eukaryotic Cell Cycle

• 2 major phases
• Interphase (3 stages)
• DNA uncondensed ( chromatin)
• Mitotic cell division (4 stages)
• DNA condensed ( chromosomes)

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Interphase

• non-dividing state
• 3 stages

G1 cell grows in size organelles
replicated
S replication of DNA synthesis of proteins
associated with DNA
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G2 synthesis of proteins associated
with mitosis
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Mitotic Cell Division

• 2 major processes
• mitosis nuclear division
• gt preserves diploid number of
• chromosomes
• cytokinesis cytoplasmic division
• gt cell divides into two daughter cells

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Mitosis
4 phases
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Prophase

• 3 major events

i) chromosomes condense
ii) spindle fibers form
iii) chromosomes are captured by spindle
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Chromosomes Condense

• Recall that chromosomes were
• duplicated during interphase

• gt each chromosome consists of
• 2 sister chromatids attached to
• each other at the centromere

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Mitotic Spindle Forms

• spindle fibers are specialized
• microtubules

• spindle fibers radiate out from
• centrioles, forming the aster

• centrioles occur in pairs, and are
• duplicated during interphase

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• one pair of centrioles migrates to
• one pole of cell, the other pair
• migrates to opposite pole of cell

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Spindle Captures Chromosomes

• When spindle fibers are fully formed
• nuclear envelope disintegrates and
• nucleolus disappears

• Spindle fibers attach to chromosomes
• at the kinetochore, a structure located
• at the centromere

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• other spindle fibers do NOT attach
• to chromosomes, but retain free
• ends that overlap at cells equator
• gt free spindle fibers

• function of spindle fibers is to
• organize division of sister chromatids
• into daughter cells

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Anaphase

• sister chromatids separate

• spindle fibers attached to
• kinetochores shorten and pull
• chromatids poleward

• free spindle fibers lengthen and push
• poles of cell apart

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V-shaped chromatid
free spindle fibers
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Telophase

• spindle fibers disintegrate

• nuclear envelopes form around both
• groups of chromosomes

• chromosomes revert to their extended
• state

• nucleoli reappear

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Cytokinesis

• Animal cells
• microfilaments attached to plasma
• membrane form a ring around
• equator of cell
• ring contracts, like a drawstring,
• dividing the cytoplasm

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• Plant cells
• stiff cell wall makes pinching
• impossible
• Golgi complex buds off vesicles
• filled with carbohydrate
• vesicles line up at equator and
• fuse, producing a structure
• called the cell plate
• cell plate becomes new cell wall
• between the two cells

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Mitotic Cell Division
Functions

• Growth, maintenance, repair of body
• tissues

• Forms the basis of
• Asexual Reproduction