TheLifeCycleofCells. Cell Growth A cell is limited by its cell size The larger the cell the harder...
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Transcript of TheLifeCycleofCells. Cell Growth A cell is limited by its cell size The larger the cell the harder...
Cell Growth
• A cell is limited by its cell size
• The larger the cell the harder it is to move through tissue and get nutrients
• In order to stay alive and not grow continuously, the cell will divide
Reasons why to divide
• DNA– Genetic information stored– Found in the nucleus of the cell– DNA would not be able to keep up with demand of
the cell
• Transport– Rate decreases as the cell size increases– Takes too long for nutrients and wastes to move in
and out of cell
Surface Area to Volume• Surface Area
– Area on outside of cell where reactions can occur
– As a cell increases, the surface area decreases
Chromosomes
• Made up of our DNA
• Holds genetic information
• Tight coils or rod like structures
• Organisms have a specific amount of chromosomes.– Humans have 46 chromosomes of DNA in
every somatic cell
Chromosome Structure• Histones are proteins that DNA wraps around
to make the chromosome shape
• Chromosomes are made of two sister chromatids– Identical to each other
Chromosomes• Centromeres are in the center of a chromosome
• Chromosomes are tightly coiled strings of DNA called chromatin
• Chromatin is the string-like form of DNA
Chromosome Numbers
• There is a specific number of chromosomes in each organism
• Humans autosomes and sex chromosomes
• We have 2 sex chromosomes– Either X or Y
• We also have 22 autosomes – Which do not code for gender
Diploid/Haploid
• A diploid cell contains 2 sets of each chromosome– Prefix di = 2
• A haploid cell contains only 1 set of each chromosome– Half of the total number– Usually sex cells
Cell Division in Prokaryotes• Prokaryotes
– No nucleus– No organelles– Ex: Bacteria
• Reproduction is VERY fast– Copy DNA– Split into two cells
• Cell division is called binary fission
Eukaryotic Cell Reproduction
• Eukaryotes– Have a nucleus– Have organelles– Ex: Humans, plants
• Complex reproduction – Everything needs to be controlled!
• Much longer process – about 18 hours!
Cell Reproduction• A cell splits to make 2
identical copies
• If asexual reproduction– Only 1 cell involved
• This occurs in 3 main stages1. Interphase – Growth
2.Mitosis – Splitting of the cell
3.Cytokinesis – Splitting of the cytoplasm
Interphase• Cell growth
• 90% of cell’s life is spent in interphase.
• 3 Part of Interphase: –G1, S, G2
S Phase• Takes place when
cells are too big
• S = Synthesis of DNA
• DNA is replicated so there is a set for each new cell
G2 Phase
• Cell growth again
• Replication of organelles
• Last stage of interphase
• Cell prepares for cell division
•cell is not dividing
• cell is growing, performing respiration, producing, photosynthesizing, doing whatever functions it is supposed to do
•At some point, the cell can’t diffuse fast enough and that signals the end of interphase
•At the very end of interphase, the chromatin makes an exact copy of itself in a process called DNA replication.
How is DNA copied?
• Each cell has an protein called helicase– Enzyme the unwinds the DNA making 2
identical strands– http://www.youtube.com/watch?v=zdDkiRw1P
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Mitosis• The part of a cell’s life cycle when the cell divides it nuclear contents into 2 nuclei which are identical
•Mitosis consists of 4 steps:
•Prophase
•Metaphase
•Anaphase
•Telophase
• all sub-cellular organelles disappear
• centrioles separate and move to opposite poles
• chromatin become chromosomes
• centrioles shoot off spindle fibers (short and long)
• centromere splits
•sister chromatids attach to the short spindle fibers
•short spindle fibers shorten and bring the sister chromatids to opposite poles.
• chromatids become chromatin (one at each pole)• spindle disappears• subcellular organelles reappear
Cytokinesis• Once mitosis has finished!
• Last stage of cellular reproduction
• This process is when the cytoplasm splits apart
• There are now 2 identical cells
Control of Cell Division
• G1 Checkpoint– Enzymes will kick in if cell is large enough and
conditions are favorable to reproduce
• G2 Checkpoint– DNA repair enzymes will fix any mutations, if
checkpoint is passed mitosis will occur
• Mitosis checkpoint – if all is correct, the 2 daughter cells will enter G1 phase and start over again
When Control is Lost
• Enzyme proteins are not functioning properly causing cell to reproduce out of control
• Could cause cancer• Cancer cells do not respond to body’s
signals that control mechanisms