Prokaryotic Cell Reproduction
 Binary Fission:* asexual cell division to produce a new organism
o No nuclei to divide, Copy the single circular chromosome
o Copies move to ends of cell as it elongates
o Plasma membrane grows to divide cell in half
Eukaryotic Cell Reproduction
All about Chromosomes
 Chromatin:* DNA & histone protein; uncoiled & not visible
o Histone: primary protein, acts as a spool.
 Chromosomes: One long strand of DNA wrapped around histones
o Visible during division
o Sister Chromatid:* Exact copy of one chromosome, still attached
o Centromere:* attaches 2 chromatids
o Homologous Chromosomes:* chromosomes that are copies of each other
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Non-sister chromatids are not exact copies, one from each homologous chromosome
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Carry the same gene in the same place but each may carry different versions

One from each parent
Cell Division*
 Reproduction of cells, cells come from preexisting cells
 Used to grow (new cells), to repair (damaged cells) & to replace (dead cells)
 Cell Cycle: two broad stages
o Interphase:* cell growth & organelle and chromosome duplication
o Mitotic (M) Phase:

Mitosis:* division of the cell, creates an exact copy of each cell

Cytokinesis:* division of the cytoplasm
Interphase*
 G1 (Gap Phase 1): Cell grows to full size
o Go: cells exit the cycle after G1, active but no longer divide (nervous system cells)
 S (synthesis):* DNA replication occurs when signaled
o DNA is chromatin, not visible, Each chromosome doubled, called sister chromatids
 G2: Cell prepares for division
Mitosis: creates two genetically exact daughter cells
 Prophase*
o Chromatin condenses forming visible chromosomes (sister chromatids) joined at the centromere
o Nucleoli disappear
o Spindles appear in the centrosomes and move to ends of cell

Centrosomes:* cloud of cytoplasmic material that contain centrioles
▫
Centrioles:* pair of 9+2 microtubules in animal cells, involved in cell division. Actual function is unknown
Spindle:* football shaped structure of microtubules that guide chromosomes
 Prometaphase (new – usually associated with prophase)
o Nuclear envelope disappears, spindles attach to the kinetochore (centromere region) on the sister chromatids
 Metaphase*
o Spindle fully formed, chromosome line up along metaphase plate with the kinetochores facing opposite poles
 Anaphase*
o Centromeres split and move to opposite poles. Cell begins to elongate
o Sister chromatid is now a daughter chromosome.
 Telophase*
o Nucleoli and nuclear envelope appear, cell continues to elongate
o Chromosomes and spindles disappear
Cytokinesis*
 Division of cytoplasm, cytoskeleton essential, occurs with telophase
o Plant: uses to vesicles which fuse together to form the cell plate
o Animal: cleavage furrow uses microfilaments to pinch the cell in half
Control of the Cell Cycle
 Some very specialized cells never divide (nervous system cells)
 Anchorage dependence: contact with a solid surface to divide
 Density-dependent Inhibition: cell stop dividing when they touch each other
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

Size & Nutrients: large enough to divide & plenty of energy
Growth Factors:* proteins that stimulate cells to divide
o PDGF (platelet derived growth factor): injury brings platelets for clotting, PDGF secreted, nearby cells divide
 Control Signals
o G1–S transition: restriction point, continues if all basic conditions are met

Non-dividing cells never pass this, enter G0
o G2–M phase transition:

MPF (maturation promoting factor), appears during late Interphase

Master switch: activates other proteins (kinase) that cause the parts of division to occur. Examples: chromatin
condenses, nuclear membrane disappears, destroys Cyclin

Made of 2 parts: Cdc2: constant amount of the protein kinase, Cyclin: proteins involved in the cell cycle, amount
changes (cycles), activates cdc2
Cancer*
 Abnormal cell division, mutations of genes (DNA) controlling cell cycle
 Characteristics
o Odd chromosome numbers & metabolism
o Ignore density–dependent inhibition
o Surface proteins change, lose anchorage
o Immortal with nutrients (HeLa since 1951)
 Transformation: change normal cell to cancerous. Can be biological, physical, chemical, or genetic
 Tumor: mass of dividing cells. Either benign (noncancerous) or malignant (cancerous)
Meiosis:* division to produce gametes
 Creates 4 genetically unique, haploid cells that become gametes
o n = haploid:* one copy of each unique chromosome; humans = 23

Gametes:* sex chromosomes (eggs & sperms)

Females = XX
and
Males = XY
o 2n = diploid:* two copies of each unique chromosome; humans = 46
o Somatic cells:* any cell in the body other then the gametes

Autosomes:* other 22 pairs of chromosomes
 Divides 2 times – IPMATiPMAT
 Interphase – identical to mitosis
 Prophase I:
o Chromosomes & spindle appear, nucleolus & nuclear envelope disappear
o Synapsis: homologous chromosomes pair up
o Tetrads:* paired homologs each with 4 chromatids (2 chromosomes)
o Crossing-over:* exchange of chromosome parts in non-sister chromatids = variability
o Chiasma:* the point where chromatids are crossed
 Metaphase I: Tetrads line up (paired/synapsed homologous chromosomes)
 Anaphase I: Tetrads separate creating haploid genomes
 Telophase I: Chromosomes & spindle disappear, nucleolus & nuclear envelope appear, cytokinesis (maybe)
 Interkinesis: pause no DNA replication
 Prophase II:
o Chromosomes and spindle appear, nucleolus and nuclear envelope disappear
o No synapsis or crossing over, haploid not diploid
 Metaphase II: Chromosomes line up
 Anaphase II: Sister chromatids separate
 Telophase II and cytokinesis:
o 2 divisions = end up with 4 genetically unique cells
o Human Sperm = 4, Human Egg = only 1
 Ultimate Results
o Number of chromosomes is cut in half from 2n to n
o Crossing-over mixes up alleles of genes on chromosomes
o Each of the four gametes is genetically unique