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Chromosome Formation
Histone Proteins- Help maintain shape of the chromosome
Chromosomes-ROD Shaped structure made of DNA and Protein
Homologous Chromosomes- Humans have 46 chromosomes
23 homologous pairs
AUTOSOMES
SEX CHROMOSOMES
Humans have 2
Male XY
Female XX
Humans Have 44 Autosomes
Honeybee (female) – 32
2n Chromosomes
Adder’s Tongue Fern - 1262 Common Frog - 26
Cat - 38 Maize - 20Human - 46
Does more chromosomes mean a bigger or more complicated organism?
Chromosome number does not determine complexity of organism
DIPLOID CELLS VS. HAPLOID CELLS
Diploid 2N= Contains both
autosomes in a homologous pair
Human Body Cells are Diploid
Contain 46 chromosomes and 23 pairs
Haploid 1N= Contains 1 autosome of
homologous pair
Human sex cells are Haploid
Egg and Sperm Cell
Contain 23 Chromosomes and no pairs
Prokaryotes vs. EukaryotesCharacteristicsProkaryotes
Single celled organisms
No membrane bound nucleus or organelles
Simple and smaller
Have a cell wall
Few chromosomes
Eukaryotes Make up multicellular
organisms Have membrane bound
organelles and nucleus Complex and Larger
Many chromosomes
DNA located in the nucleus
Chromosomes coil and condense before cell division
Prokaryotic Cell DivisionProkaryotic Cell Division
• Binary fissionBinary fission• Division of prokaryotic cell into two offspring cellsDivision of prokaryotic cell into two offspring cells
Cell Division in EukaryotesCell Division in Eukaryotes
Cell Division occurs in two stagesCell Division occurs in two stages
Mitosis/MeiosisMitosis/Meiosis Division of the nucleusDivision of the nucleus Four stages (Prophase, Metaphase, Anaphase, Four stages (Prophase, Metaphase, Anaphase,
Telophase)Telophase)
CytokinesisCytokinesis Division of the cytoplasmDivision of the cytoplasm
Prokaryotic vs Eukaryotic Cell Division
Prokaryotes DNA is circular and attached to
the plasma membrane DNA does not wrap around
proteins to form chromosomes before cell division
Binary Fission(most cells) Cell membrane will develop
between the two copies of DNA Cell Doubles in size Cell membrane pinches off Cell Wall forms around new
cell membrane
Eukaryotes
Chromosomes coil and condense before cell division
Consists of 2 Divisions1)Division of the nucleus Mitosis – body
cells(Diploid Cells) Meiosis- sex cells
(Haploid cells)2) Division of the
Cytoplasm Cytokinesis
What is the same in Euk and Prok cell division? Create new cells Genetically identical DNA is copied before cell division Cytoplasm will divide
CELL CYCLE-CELL CYCLE- Repeating set of Repeating set of events in the life of the cellevents in the life of the cell
Interphase-Interphase-longest stage in the cell cyclelongest stage in the cell cycle
G1 – Cell growth (cell grows to a mature size)G1 – Cell growth (cell grows to a mature size)
S – DNA is copied (double the amount of S – DNA is copied (double the amount of DNA)DNA)
G2 – Growth and preparation for cell divisionG2 – Growth and preparation for cell division
G0-Cells that do not divide will remain in G0 G0-Cells that do not divide will remain in G0 (occurs at the end of G1)(occurs at the end of G1)
Cell divisionCell division
Mitosis/Meiosis – Nucleus dividesMitosis/Meiosis – Nucleus divides
Cytokinesis – Division of the cytoplasmCytokinesis – Division of the cytoplasm
What triggers the cell to leave on phase What triggers the cell to leave on phase and move to the next?and move to the next?
Checkpoints = traffic signalCheckpoints = traffic signal Proteins regulate the processProteins regulate the process
Three main checkpointsThree main checkpoints G1 checkpoint(end of G1)G1 checkpoint(end of G1) G2 checkpoint (during G2)G2 checkpoint (during G2) Mitosis checkpoint (toward Mitosis checkpoint (toward
the end of mitosis)the end of mitosis)
Control of Cell Division
G1 checkpoint-Cell Growth CheckpointG1 checkpoint-Cell Growth Checkpoint Checks to see if the cell is healthy and has reached a Checks to see if the cell is healthy and has reached a
mature sizemature size Will determine if the cell will divideWill determine if the cell will divide
G2 checkpoint-DNA synthesis checkpointG2 checkpoint-DNA synthesis checkpoint DNA repair enzymes check the results of DNA replicationDNA repair enzymes check the results of DNA replication
Mitosis checkpoint-Mitosis checkpoint- If cell passes this checkpoint, the cell will exit Mitosis and If cell passes this checkpoint, the cell will exit Mitosis and
move into G1 of interphasemove into G1 of interphase
What happens if there is a mutation in one of these proteins?What happens if there is a mutation in one of these proteins?
Organelle ReviewOrganelle Review
CentrosomesCentrosomes Contain two centriolesContain two centrioles Made of microtubulesMade of microtubules Acts as anchors in cell divisionActs as anchors in cell division
Plants centosomes do not contain centriolesPlants centosomes do not contain centrioles
Mitotic Spindle fibers-Two Main typesMitotic Spindle fibers-Two Main types Kinetochore Fibers-Kinetochore Fibers- Attach from centriole to Attach from centriole to
centromere of chromosomes and assists in centromere of chromosomes and assists in movement of chromosomesmovement of chromosomes
Polar FibersPolar Fibers – Extend from pole to pole and – Extend from pole to pole and keep the shape of the cell during cell divisionkeep the shape of the cell during cell division
Organelle Review
Nuclear envelopeNuclear envelope•Double Phospholipid bilayer Double Phospholipid bilayer
surrounding nucleussurrounding nucleus•Surrounds the DNASurrounds the DNA
NucleolusNucleolus•Dense area where DNA is Dense area where DNA is
concentrated in the nucleusconcentrated in the nucleus•Ribosomes (rRNA) is synthesizedRibosomes (rRNA) is synthesized
MITOSIS Division of the nucleus Forms two identical daughter cells Four phases
Where does it occur? Somatic Cells (Body cells)
Why does it occur?Why does it occur?• Asexual reproductionAsexual reproduction• Growth and developmentGrowth and development• To replace old cells or dying cellsTo replace old cells or dying cells
ProphaseProphase
• Chromatin coils and condenses Chromatin coils and condenses into chromosomesinto chromosomes
• Nucleolus and nuclear Nucleolus and nuclear membrane break down and membrane break down and disappeardisappear
• Centrosomes appear and move Centrosomes appear and move to opposite ends of the cellto opposite ends of the cell
• Spindle Fibers appear: Spindle Fibers appear: Kinetochore fibers extend from Kinetochore fibers extend from kinetochore of each chromatid kinetochore of each chromatid to centrosome.to centrosome.
Metaphase
Metaphase = MiddleMetaphase = Middle Kinetochore fibers Kinetochore fibers
move chromosomes move chromosomes to center of the cellto center of the cell
All chromosomes All chromosomes line up in a single file line up in a single file lineline
46 chromosomes 46 chromosomes lined up in the lined up in the middle (Humans)middle (Humans)
AnaphaseAnaphase
AnaphaseAnaphase• Chromosomes separate at Chromosomes separate at
the centromere and the centromere and chromatids move to opposite chromatids move to opposite polespoles
• Chromatids are now Chromatids are now considered individual considered individual chromosomeschromosomes
TelophaseTelophase• Chromosomes are on opposite Chromosomes are on opposite
sides of the cellsides of the cell• Centrioles disappear and Centrioles disappear and
Spindle fibers disassemble and Spindle fibers disassemble and disappeardisappear
• Chromosomes unwind into less Chromosomes unwind into less tightly coiled chromatin tightly coiled chromatin
• Nuclear envelope forms around Nuclear envelope forms around each set of chromosomeseach set of chromosomes
• Nucleolus forms in each of the Nucleolus forms in each of the newly forming cellsnewly forming cells
Animation
CYTOKINESISCytokinesis-the division of the Cytokinesis-the division of the
cytoplasmcytoplasm
Animal cells:Animal cells:
Pinching inward of the cell membrane Pinching inward of the cell membrane occurs.occurs.
Called Cleavage furrowCalled Cleavage furrow
In plantsIn plants cell plate formationcell plate formation
Mitosis vs. MeiosisMitosis vs. Meiosis
Where do they occur?Where do they occur? Mitosis – in the body cellsMitosis – in the body cells Meiosis – in the germ cellsMeiosis – in the germ cells
Why does it occur?Why does it occur? MitosisMitosis
• Asexual reproductionAsexual reproduction• Growth and developmentGrowth and development• To replace old cellsTo replace old cells
MeiosisMeiosis• Formation of gametes (egg and sperm cells) Formation of gametes (egg and sperm cells)
that will be used in sexual reproductionthat will be used in sexual reproduction
MeiosisMeiosis
Also known as reduction divisionAlso known as reduction division Occurs in germ cells found in the ovaries and testesOccurs in germ cells found in the ovaries and testes Produces sex cells which are haploidProduces sex cells which are haploid Occurs in two phasesOccurs in two phases
Meiosis IMeiosis I• Reduces the number of chromosomes from diploid Reduces the number of chromosomes from diploid
to haploidto haploid Meiosis IIMeiosis II
• Produces four haploid daughter cellsProduces four haploid daughter cells
Meiosis IMeiosis IProphase IProphase I
DNA coils tightly into chromosomesDNA coils tightly into chromosomes Spindle fibers and centrosomes Spindle fibers and centrosomes
appearappear Nucleolus and nuclear envelope Nucleolus and nuclear envelope
disassembledisassemble Synapsis =Pairing of homologous Synapsis =Pairing of homologous
chromosomeschromosomes Tetrad =Pair of homologous Tetrad =Pair of homologous
chromosomes twisted around each chromosomes twisted around each other other
Crossing over may occurCrossing over may occur Genetic recombinationGenetic recombination
Meiosis IMeiosis I Metaphase IMetaphase I
• Tetrads line up along midlineTetrads line up along midline• Independent assortment occursIndependent assortment occurs
Anaphase IAnaphase I• Homologous chromosome pairs(Tetrads) are separated and Homologous chromosome pairs(Tetrads) are separated and
move to opposite poles (Independent assortment occurs)move to opposite poles (Independent assortment occurs)
Telophase ITelophase I• Chromosomes reach opposite ends of cellChromosomes reach opposite ends of cell• Spindle Fibers disappearSpindle Fibers disappear• In some cells the nuclear envelope will reappearIn some cells the nuclear envelope will reappear• Cytokinesis beginsCytokinesis begins
Meiosis IIMeiosis II
Prophase IIProphase II Spindle fibers form and attach to the centromere of the Spindle fibers form and attach to the centromere of the
double stranded chromosomes. (Nuclear envelope double stranded chromosomes. (Nuclear envelope will disappear if it was created)will disappear if it was created)
Metaphase IIMetaphase II Double stranded chromosomes are moved to the Double stranded chromosomes are moved to the
midline of the dividing cellmidline of the dividing cellAnaphase IIAnaphase II
Chromatids separate and move toward opposite polesChromatids separate and move toward opposite polesTelophase IITelophase II
Nuclear membrane forms and nucleolus reappears, Nuclear membrane forms and nucleolus reappears, spindle fibers and centrosomes disappear, chromatin spindle fibers and centrosomes disappear, chromatin uncoils into chromosomesuncoils into chromosomes
Cytokinesis II
Division of the cytoplasm occurs Division of the cytoplasm occurs resulting in four new cellsresulting in four new cells
Each cell contains half the original Each cell contains half the original amount of chromosomes amount of chromosomes
Development of Gametes in Development of Gametes in AnimalsAnimals
SpermatogenesisSpermatogenesis produces Sperm or produces Sperm or
SpermatozoaSpermatozoa produces fourproduces four
OogenesisOogenesis Cytoplasm is divided unequallyCytoplasm is divided unequally Produces one mature egg cell or OvaProduces one mature egg cell or Ova Polar bodies are the three other products of meiosis Polar bodies are the three other products of meiosis
and they will eventually degenerate.and they will eventually degenerate.