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Cell Growth and Reproduction
• Cell Theory: – All cells come from pre-existing cells
• Cell Division:– Cells produced from one cell (parent cell)– Result is two or more identical cells– Repairs worn-out tissue (ex: skin) – Allows organisms to grow and change
• Ivy to wrap around a trellis
Cell Growth and Reproduction
• Chromatin: long strands of DNA wrapped around proteins– Chromosomes exist as chromatin for most of
cell’s lifetime– Spaghetti noodles
• Chromosomes carry genetic information that is copied and passed on to new cells– Like wound spaghetti
Cell Growth and Reproduction
• Before cell division, chromosome is in spaghetti-like CHROMATIN state
• As cell division begins, chromosomes take on a new tightly packed shape
Cell Growth and Reproduction
• Cell Cycle: Sequence of growth and division of the cell.
• Majority of cell’s life is spent during INTERPHASE or the cell’s growth period
Cell Growth and Reproduction
• INTERPHASE:– Longest phase: Growth Phase– Cell grows in size– Carries on metabolism– Chromosomes are duplicated to prepare for
division
• 3 Stages:
Cell Growth and Reproduction
• INTERPHASE:– 3 Stages:
• Cell grows, protein production is high• Cell copies its chromosomes• Centrioles replicate and cell prepares for division
Cell Growth and Reproduction
• After INTERPHASE, cell enters period of division, also called MITOSIS
• Mitosis: period of cell division– Forms two daughter cells with complete set of
chromosomes
Mitosis
Cell Growth and Reproduction
• MITOSIS:– As cell gets to the maximum size, it begins to
undergo MITOSIS (cell division)
– FOUR PHASES:• Prophase• Metaphase• Anaphase• Telophase
Cell Growth and Reproduction
• 1st Phase of Mitosis: PROPHASE– Long stringy chromatin coils up into visible
chromosomes
Spindle fibers
Disappearing nuclear envelope
Doubled chromosome
Cell Growth and Reproduction
• 1st Phase of Mitosis: PROPHASE– Each duplicated chromosome is made of two
halves called SISTER CHROMATIDS
Sister chromatids
Cell Growth and Reproduction
• 1st Phase of Mitosis: PROPHASE– Towards end of Prophase, nucleus begins to
disappear as nuclear envelope and nucleolus disintegrate
– Centrioles begin to migrate to opposite ends of cells
Cell Growth and Reproduction
• 1st Phase of Mitosis: PROPHASE– Sister chromatids held together by
CENTROMERE• Located just outside of nucleus• Plays role in chromatid separation
Centromere
Cell Growth and Reproduction
• 1st Phase of Mitosis: PROPHASE– As pairs of CENTRIOLES move to opposite
ends of cell, the SPINDLE forms between them• SPINDLE: football-shaped, cage-like structure• Separates sister chromatids during Mitosis
Spindle
Cell Growth and Reproduction
• PROPHASE: Let’s break it down– Chromosomes coil up– Sister Chromatids form– Nucleolus and Nuclear Envelope disintegrates– Centrioles migrate to opposite ends– Spindles form between Centrioles
Cell Growth and Reproduction
• 2nd Phase of Mitosis: METAPHASE– Doubled chromosomes attach to spindle fibers
by centromeres– Chromosomes pulled up by spindle fibers and
begin to line up on equator of spindles
Cell Growth and Reproduction
• 2nd Phase of Mitosis: METAPHASE– One sister chromatid’s spindle fiber extends to
one pole while other spindle fiber extends to opposite pole
Cell Growth and Reproduction
• 2nd Phase of Mitosis: METAPHASE– What is the importance?
• This arrangement of the chromatids ensures that each new cell receives identical and complete set of chromosomes (DNA)
Cell Growth and Reproduction
• 3rd Phase of Mitosis: ANAPHASE– Beginning of sister chromatid separation– Centromeres split– Chromosomes separate from each other– Shortening of spindle fibers pull apart
chromatids to opposite poles
Cell Growth and Reproduction
• 4th Phase of Mitosis: TELOPHASE– Begins once chromatids reach opposite poles– Chromosomes begin to to unwind– Spindle breaks down
Cell Growth and Reproduction
• 4th Phase of Mitosis: TELOPHASE– Nucleolus and nuclear envelope reappears around
new set of chromosomes– Double membrane forms between two new nuclei– Two daughter cells formed
Cell Growth and Reproduction
• Cytokinesis:– After Telophase, cell’s cytoplasm divides– Animal Cells: At end of Telophase, plasma
membrane pinches off forming two separate cells.
– Plant Cells: Cell plate laid across cell’s equator—there is no pinching off. Cell membrane forms around each cell and new cell walls form on each side of cell plate