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Cell Reproduction and Division
How do cells get here?
Cell Cycle
Figure 17.1
Cell cycle
• The events that happen to a cell from when it is created to when it divides again.
• Interphase: growth and cell living– G1: cell mass increases
– S: DNA set is doubled
– G2: components for division are made
• some cells like neurons never leave interphase.
Human Life Cycle
Chromosome map
A physical location exists for all genetic traits on a chromosome
Cell ReproductionResults
Mitosis: all cells, 2 cells with same number of chromosomes
Meiosis: only in gonads 4 cells are produced with a single set of
23 chromosomes
What would cloning be?
Making an exact copy: cloning
When cells divide
• When a cell divides each new cell receives DNA (instructions) and cytoplasmic machinery to start its own operation.
– DNA: contains genes that code for proteins, which in turn serve as structural materials and enzymes. They give the body its appearance.
Mitosis and Meiosis
• Mitosis: used for growth of multicellular organisms
• Meiosis: is used only in germ cells for the production of gametes.
Chromosomes
• A complex of DNA and protein
• Prior to division a copy is made and the two are held together at the centromere
• The loose form in the nucleus is the chromatin
Chromosome Numbers
• Chromosomes come in pairs, one from each parent
• Chromosome pairs carry the same information and are called homologous chromosomes
• n= haploid #, is the number of chromosome types
• 2n=diploid number, all cells have 2 sets of chromosomes
Mitosis
• Prophase: chromosomes condense• Metaphase: chromosomes line up• Anaphase: chromosomes begin to divide• Telophase: a new nucleus forms
• Endpoint: 2 cells with half the cell mass but the same number of chromosomes, the cells are clones
Mitosis figure
Meiosis
• Occurs in testes called spermatogenesis
• Occurs in ovaries called oogenesis
• Anaphase to telophase 1 results in haploid cells
• Anaphase 2 to telophase 2 results in 4 haploid cells
Genetic variation is the result of
• Crossing over that occurs during prophase I
• Anaphase I- chromosomes separate randomly into haploid cells.
• Of all the genetically diverse gametes produced, chance determines which will meet.
Information
• During each division information must be moved from the mother cell to the daughter cells.
• This info is held in the form of DNA
• This info is due to the unique sequence of the DNA
• One slight change in your DNA may be handed down to all the generations that follow.
The Why of Genetic variation
Genetic Variation
• What gives variety to a sperm?
• What gives variety to an oocite?
• Why is it almost impossible for two people to be exactly alike?
• Why can people say “all whites look alike” “she looks just like her mother” “he looks like a Frenchman”
DNA structure
Information flow in a cell.
• Replication- DNApolymerase creates a copy of DNA from an old copy. Semiconservative replication
• Transcription- RNApolymerase creates an RNA copy of a DNA gene template
• Translation- Ribosomes convert the RNA gene template into a protein
• The Central Dogma
Protein Synthesis: Transcription
• Process:– DNA for a gene unwinds– RNA polymerase assists in copying base sequence in
RNA nucleotides– Primary transcript made, includes introns and exons– Introns edited out– Messenger RNA strand produced
Genetic Code• Codon: sequence of three RNA bases, code for
amino acids• Duplicate codons: all but one amino acid
(methionine) have more than one codon• DNA grammar:
– Start: AUG (methionine), begin all genes– Stop: UAA, UAG, UGA, one ends each gene
Three Steps of Translation
Figure 17.8
Regulation of Cell Reproduction
• Internal control mechanism– Regulate cell cycle: cyclins
• Outside Influences– Can modify cell cycle: platelet-derived growth
factor
Environmental Factors Influencing Cell Differentiation
• Differentiation in early development:– After 8-cell stage, cells exposed to different
environments inside versus outside the ball– To date embryonic cloning: can occur at 8-cell stage
• Differentiation in later development:– Two factors:
• Developmental history of earlier cells
• Local environment
• Even clones may not be exactly alike
• Examples?