BIOL 310 - Ch 2 Lecture Notes

  • cell overview

    • prokaryotes: large circular chromosome & no organelles

    • eukaryotes: membrane bound organells, nucleus, mitochondria & chloroplasts

  • cells & DNA composition

    • prokaryotic: one circular chromosome packaged as nucleoid

      • extra-chromosomal DNA as plasmids; multiple copies of these dispersed around the cell

    • eukaryotic: two to many that are linear (diploid)

      • varies in size from small to larger

      • DNA packaged in histones

      • extra-chromosomal DNA in mitochondria & chloroplasts that are circular

    • eukaryotic genome

      • diploid with two to many chromosomes

      • genes & alleles (homo or heterozygous)

    • basic eukaryotic chromosome structure

      • each chromatid has two telomeres and one centromere

      • kinetochore on one chromosome where the spindle microtubules attach during metaphase & pull apart during anaphase

      • upper arm P; lower arm Q

    • chromosomes are classified by location of centromere

  • cellular replication

    • prokaryotes - binary fission

      • single chromosome and initial single origin of replication

      • once replicated, two copies with one single of origin that are pulled in opposite direction by poles situated at either end of the elongated cell

      • DNA segregates & fission of the cells occurs

    • eukaryotes - complex & slow, cell division by cell cycle

      • G1 - growth period

        • the cell can proceed forward or stay in G0 which is a nondividing phase

        • G1 / S checkpoint gives clearance to proceed to the S phase

      • S phase - synthesis phase

        • duplication of the genetic material

      • G2 - prepping the cell for mitosis

        • G2 / M checkpoint that corresponds to the correct molecular signals alerts process to continue

      • M - Mitosis

        • cell is divided to produce two genetically identical cells from one cycle

        • interphase - no activity

        • prophase - mitotic spindle forms & chromosomes condense

        • prometaphase - disintegration of nuclear membrane; spindle microtubules attach to chromatids

        • telophase - chromosomes lined up at spindle poles

        • anaphase - sister chromatids get pulled apart; genetic material located at the poles

        • metaphase - chromosomes line up on the metaphase plate

      • end result of mitosis: two daughter cell that are identical and diploid

  • Meiosis

    • gamete production which results in four daughter cells that an non-identical and haploid

    • there is one round of replication and two rounds of division

    • Middle Prophase I

      • chromosomes begin to condense and the spindle forms

    • Late Prophase I

      • homologous chromosomes pair up and formation of chiasmata occurs

      • crossing over takes place & the nuclear membrane breaks down

    • Metaphase I

      • homologous pair of chromosomes line up along the metaphase plate

    • Anaphase I

      • homologous chromosome separate and move towards opposite poles

    • Telophase I

      • chromosomes arrives at spindle poles

    • Prophase II

      • the chromosomes recondense within nuclear membrane

    • Metaphase II

      • individual chromosomes line up on the equatorial plate

      • more spindle fibers to pull apart individual chromatids apart

    • Anaphase II

      • sister chromatids separate and move towards opposite poles

    • Telophase II

      • four poles present

    • Cytokinesis

      • splits the cell into four daughter cells

  • Meiotic Recombination

    • reduction in chromosome number

    • crossing over occurs in prophase I

    • recombination and genetic diversity

    • synaptonemal complex - breaking & joining of chromosome to result in bivalent or tetrad chromatids

    • Mitosis - cohesin ring to keep sister chromatid together until the breakdown of cohesin during metaphase allows the sister chromatids to separate during anaphase

    • Meiosis - cohesin and protein shugoshin are present

      • shugoshin remains at the centromere during anaphase I to protect the sister chromatids from splitting

      • anaphase II degrades so cohesin breaks down to allow the chromatids to split

  • Meiosis in Male vs Female

    • male: produces large quantity of small mobile gametes

      • spermatids (1n)

    • female: produces few large stationary gametes

      • ovum (1n)

  • Plant reproduction

    • Meiosis → spores (undergo mitosis) → gametes (both male & female depending on genotype) → fuse by fertilization to form zygote

    • generation alternation: sporophyte to gametophyte

  • model organisms

    • typically small, simple, have a fast replication time, easy to keep, and easy to keep in large numbers