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CELL REPRODUCTION
Chapter 8
Miss Colabelli
Biology CPA
CHROMOSOMES
•Rod shaped structures made of DNA and proteins
•Chromosomes are visible in cells undergoing
division
•Chromosomes are made by DNA coiling into tight
structures
•Consist of two identical halves
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
CHROMOSOME STRUCTURE
•Each chromosome is made of two “sister” chromatids
•Near center of the chromosome is the centromere
•Chromosomes are tightly coiled strings of DNA called
chromatin
CHROMOSOME NUMBERS
•There is a specific number of chromosomes in
each organism
• Ex: Humans have 46, chimpanzees have 48
•Humans have autosomes and sex chromosomes
•We have 2 sex chromosomes
• Either X or Y
•We also have 44 autosomes
• Which do not code for gender
CHROMOSOME NUMBERS
•Every cell of an organism produced by sexual
reproduction has two copies of each autosome
• One copy from mom and one copy from dad
•The two copies of each pair is called homologous
chromosomes
• Same size and shape
• Carry genes for the same traits
KARYOTYPE
•A karyotype is a picture of one set of chromosomes
• Shows you sex of organism
• Shows your any chromosomal disorders
CHROMOSOME NUMBERS
•A diploid cell contains 2 sets of
each chromosome
•Prefix di = 2
•Abbreviated as 2n
• n = number of chromosomes
•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 identical daughter cells
•Cell division is called binary fission
CELL DIVISION IN EUKARYOTES
•Eukaryotes
• Have a nucleus
• Have organelles
• Ex: Humans, plants
•Both nucleus and cytoplasm need to divide
•Process of making new cells is called mitosis
• Makes two identical daughter cells
•Complex reproduction
• Everything needs to be regulated!
•Much more complex process – about 18 hours!
CELL DIVISION AND REPRODUCTION
•Asexual Reproduction
• Produces identical offspring from a
single parent
• Used by many single-celled organisms
• Ex: bacteria
• Occurs very quickly
•Sexual Reproduction
• Produces genetically different
offspring from two parents
• Fusion of two parent cells
• Creates haploid gametes (sex cells)
THE CELL CYCLE
•A repeating set of events in
the life of a cell
•A cell splits to make 2
identical copies
•This occurs in 3 main stages
1. Interphase – growth
2. Mitosis – division of the
nucleus
3. Cytokinesis – Splitting of the
cytoplasm
INTERPHASE
•Cell growth
•Majority of cell’s life
span is spent in this
phase
•3 Part of Interphase:
•G1, S, G2
G1 PHASE
•Gap 1 Phase
•The cell is growing
to mature size
S PHASE
•S = synthesis of
DNA
•DNA is copied
so there is a set
for each new
cell
G2 PHASE
•Gap 2 Phase
•Cell grows again
•Replication of
organelles
•Cell prepares for
cell division
MITOSIS
Cell Division
MITOSIS
•The part of a cell’s life cycle when the cell’s
nucleus divides into 2 identical nuclei
•4 steps:
•Prophase
•Metaphase
•Anaphase
•Telophase
PROPHASE
•Shortening and tight coiling
of chromatin into
chromosomes
•Nucleus breaks down and
disappears
•Centrioles separate and
move to opposite poles of the
cell
• Centrosomes in plant cells
•Centrioles shoot off spindle
fibers
METAPHASE
• Spindle fibers are
connected to centromere
of chromosomes
• Spindle fibers move
chromosomes
• Chromosomes line up at
the equator of the cell
• Chromosomes are in the
MIDDLE
ANAPHASE
•Sister chromatids attach to
the short spindle fibers
•Chromatids of each
chromosome separate at the
centromere
• Chromosomes are pulled APART
•Spindle fibers shorten and
bring the sister chromatids
to opposite poles
• After chromatids separate, they are
called individual chromosomes
TELOPHASE
•Chromatids become chromatin
•Spindle fibers disassemble
•Nuclear envelope forms around each set
of chromatin
•Nucleolus reappears
CYTOKINESIS
Division on the cytoplasm
CYTOKINESIS
•Once mitosis has finished!
•Last stage of cell cycle
•Process is when the cytoplasm splits apart
CYTOKINESIS IN PLANT CELLS
•A cell plate forms between the two nuclei
•The cytoplasm divides
•A cell wall forms two daughter cells
CYTOKINESIS IN ANIMAL CELLS
•Cell membrane pinches in at equator
•Cleavage furrow
CELLS IN VARIOUS STAGES OF THE CELL
CYCLE
CONTROL OF CELL DIVISION
•Checkpoints (Regulatory Proteins)
• Repair enzymes fix any mutations
•G1 Checkpoint
• Proteins check to see if cell will be able to divide
• Check for cell size
•G2 Checkpoint
• DNA repair enzymes check results of DNA replication during S phase
•Mitosis checkpoint
• If all is correct, proteins will signal cell to exit mitosis
• Cell will renter interphase after cytokinesis and start process over again
•If a cell does not meet requirements for checkpoints, the cell
will be programmed to die
 Apoptosis is controlled cell death
Uncontrolled
Mitosis
is
cancer.
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
regulators that control mechanisms
•A mass of cancer cells is called a tumor
COMPARE/CONTRAST