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?