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Cell Cycle & DivisionCell Cycle & Division
Biology I
Cell DivisionCell Division Cell Division: • All cells are derived from
preexisting cells (Cell Theory)
• Cell division is the process by which cells produce new cells
• Cell division differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)
• Cells grow in number, not in size.
Reasons for Cell Division:
• Cell growth • Repair & replacement of
damaged cell parts • Reproduction of the species
How often do cells divide?•Some cells must be repaired often such as cells lining the intestines, white blood cells, skin cells with a short lifespan. •Other cells DO NOT divide at all after birth such as muscle, nerve cells, brain cells, female egg cells.
Chromosomes & Their Chromosomes & Their StructureStructure
• The plans for making cells are coded in their DNA.
• DNA, deoxyribose nucleic acid, is a long thin molecule that stores genetic information.
• DNA is organized into molecules called chromosomes.
Chromosomes & Their Chromosomes & Their StructureStructure
• Chromosomes are made of protein & a long, single, tightly- coiled DNA molecule visible only when the cell divides.
• When a cell is NOT dividing the chromosome (DNA) is less visible & is called chromatin.
Chromosomes & Their Chromosomes & Their StructureStructure
• Centromeres hold duplicated chromosomes together until they are separated in cell division.
• When DNA makes copies of itself before cell division, each half of the chromosomes is called a sister chromatid. – Each sister chromatid contains identical genetic
information.
Chromosomes & Their Chromosomes & Their StructureStructure
Chromosome NumbersChromosome Numbers • Humans somatic or body cells
have 23 pairs of chromosomes or 46 chromosomes (diploid or 2n number)
• The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location)
• Human reproductive cells or gametes (sperms & eggs) have one set or 23 chromosomes (haploid or n number)
• Every organism has a specific chromosome number
Organism Chromosome Number (2n)
Human 46
Fruit fly 8
Lettuce 14
Goldfish 94
Types of ReproductionTypes of Reproduction• Asexual Reproduction
– Reproduction of cells involving only ONE parent.
– The organism will make a copy of itself. Produces identical offspring.
– Types: • Binary Fission (bacteria) • Mitosis (most
eukaryotic cells)• Vegetative propagation• Budding
Binary FissionBinary Fission
Vegetative PropagationVegetative Propagation
• Form of asexual reproduction in plants.
• Part of the plant detaches from the parent plant to form their own organism.
• Genetically identical to parent.
BuddingBudding
• A form of asexual reproduction in the plant in which a new organism develops from an outgrowth of the parent.
• Genetically identical to the parent plant.
Types of ReproductionTypes of Reproduction
• Sexual Reproduction– Reproduction that involves TWO parents– Produces offspring that are genetically diverse.– Happens in the sex cells (sperm and egg) which
are called gametes.
Cell CycleCell Cycle
Mitosis-prophase-metaphase-anaphase-telophase
G1 G2
Sphase
interphase
Cell CycleCell Cycle
• The cell cycle includes 3 main parts: interphase, mitosis, and cytokinesis. – Mitosis = nuclear division– Cytokinesis = division of the cytoplasm
InterphaseInterphase
• The longest stage of the cell cycle.
• Called the resting stage because the cell isn’t dividing.
• Consists of 3 stages: – G1: cell growth– S (synthesis): DNA synthesis– G2: prepare for cell division
InterphaseInterphase1. G1. G11 (gap) phase: (gap) phase: Main growth stage
Cell increases in size
Cell makes organelles
2. S phase:2. S phase: Copying of all of DNA’s instructions (DNA Replication)
DNA in the form of chromatin (not visible)
3. G3. G22 (gap) phase: (gap) phase: Preparation time for mitosis/meiosis (cell division)
Cell continues growing
Needed proteins produced
ProphaseProphase• Longest phase of mitosisLongest phase of mitosis
• Nucleolus disappears
• Chromatin condenses into chromosomeschromosomes, consisting of two sister chromatidssister chromatids.
• CentriolesCentrioles move apart (not found in plants).
• Spindle fibers Spindle fibers form and attach from centriolescentrioles to centromeres. centromeres.
• Nuclear membrane disappears.
ProphaseProphase
late prophaselate prophaseearly prophaseearly prophase
centrioles
spindle fibers
centromere
nuclear envelopedisappearing
asterfibers
Prophase Prophase
• Animal Cell • Plant Cell
MetaphaseMetaphase
• Shortest phase of mitosis
• ChromosomesChromosomes line up across the middle of cell middle of cell (center of cell – equator of cell).
• The centromere of each chromosome attaches to spindle fibers.
MetaphaseMetaphase
metaphase plate
centrioles
spindle fibers
asterfibers
MetaphaseMetaphase
• Animal Cell • Plant Cell
AnaphaseAnaphase• Sister chromatids Sister chromatids separate and move apart.• After separation, chromatidschromatids are now considered
chromosomeschromosomes.
• During this phase, the cell contains twice the normal number of chromosomeschromosomes.
• Cell begins to elongateelongate.
• At the end, there are equal numbers
of chromosomeschromosomes at the poles.
AnaphaseAnaphase
No longer sister chromatidssister chromatids, now chromosomeschromosomes
centriolesspindle fibers
asterfibers
AnaphaseAnaphase
• Animal Cell • Plant Cell
TelophaseTelophase
• Nuclear membrane reappears.• Nucleolus reforms. • ChromosomesChromosomes uncoil and appear as chromatin
again.• In the end, two genetically identical nuclei are
present.• Cytokinesis begins.
TelophaseTelophase
cleavage furrow (cytokinesis)
nuclear membrane reforming nucleolus reappears
TelophaseTelophase
• Animal Cell • Plant Cell
CytokinesisCytokinesis• Division of the cytoplasm of
the cell and its organelles into two new daughter cells.
• Cytokinesis differs between plants and animals:– Animals: a cleavage furrow
forms to make the circular shape.
– Plants: a cell plate forms where new cell wall will be to make the rectangular shape.
cell platecell plate
CytokinesisCytokinesis• Animal Cell: cleavage
furrow• Plant Cell: cell plate
2 daughter cells identical to original
Parent cell
Chromosomes are copied and double in number
Chromosomes now split
Question:Question:
• A cell containing 20 chromosomes at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes chromosomes eacheach?
Answer:Answer:
• 20 chromosomes20 chromosomes
Question:Question:
• A cell containing 4040 chromatidschromatids at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes eachchromosomes each?
Answer:Answer:
• 20 chromosomes20 chromosomes
• Cancer is Uncontrolled Mitosis:
• Mitosis must be controlled, otherwise growth will occur without limit (cancer)
• Control is by special proteins produced by oncogenes
CANCER
