What is Biology ? by m1Z60682


									          Lecture 2
Cell Structure, Mitosis and Meiosis
Study Questions - Lecture 2

1) Describe the major components of a typical animal cell and their
2) What is the cell cycle? At which stage is the genetic material replicated?
   What events take place at each phase?
3) Discuss the concepts of homologous chromosomes, diploidy, and haploidy.
   What characteristics are shared between two chromosomes considered to
   be homologous?
4) What is mitosis? Describe the events that characterize each stage of
5) Describe how chromosomes are named on the basis of their centromere
6) What is meiosis? Describe the events that characterize each stage of
7) Contrast mitosis and meiosis. Explain why meiosis leads to significant
   genetic variation while mitosis does not.
     Cells - “fundamental unit of life”

  Prokaryotes                    Eukaryotes
  -single celled                 -single or multicellular
  -no nucleus                    -nucleus with nuclear
  -no organelles                    membrane
  -DNA = single, circular        -DNA packaged into
     molecule                       chromosomes
  - e.g., bacteria               -organelles present

Biological Kingdoms: Monera, Protista, Fungi, Plantae, Animalia
Cellular Components
     Cell membrane
 Endoplasmic reticulum
    Golgi apparatus
 Microtubules (centriole)
  Nucleus (nucleolus)
Fluid-Mosaic Model of Membrane Structure - the thing
surrounding the internal components of the cell

  Bilayer (2 layers)- of proteins and lipids
Endoplasmic Reticulum-set of
interconnected membranes. 2

Rough ER (studded with
Ribosomes) - involved in
production and modification
of proteins

Smooth ER- (no ribosomes) -
involved in production of
lipids, detoxification of molecules,
and calcium storage in muscle cells

*Ribosomes formed in nucleolus*
Golgi Apparatus
After proteins and
lipids are made by the
Endoplasmic Reticulum
they may be modified
further and/or stored
 by the GA.
Lysosome - formed by GA, contain enzymes that break down
cellular debris and foreign substances brought into the cell
Aerobic respiration produces ATP
Has own genome
Cell shape, motion,
and growth.
Microtubule- composed of tubulin.
Both cilia and flagella have the same
Structure of microtubules: 9+2.
Forms spindle during mitosis & meiosis
Nuclear Membrane or Envelope - two membranes which form
the nucleus, is porous. Allows RNA to leave nucleus.
Chromosome = DNA (deoxyribonucleic acid) + associated
proteins (mainly histones) = “packaged” DNA
Cell Cycle: replication of genetic material (=DNA) and nuclear
division (= mitosis + cytokinesis).
       Cell Cycle: Interphase
• Before mitosis
• Time of high metabolic activity
• DNA replicated and synthesized
• Three phases: G1, S, and G2
• G1(gap 1)- longest stage of cell cycle, RNA,
  protein sysnthesis
• S (synthesis)- DNA replicated , 2 chromatids per
  chromosome, chromatids genetically identical
• G2(gap 2)- RNA synthesis, not well understood
           Cell Cycle: Mitosis
• Process of cell division(nuclear division) which
  produces daughter cells genetically identical to the
  parent cell
• Four Phases (P-M-A-T): prophase, metaphase,
  anaphase, and telophase.
• Upon completion of the phases of mitosis (nuclear
  division) the cell “officially” divides into two by a
  process called cytokinesis - division of cytoplasm
Not part of mitosis
DNA is replicated
chromosomes start to condense
Chromosome duplication
*Chromosomes coil and condense further.
*Nucler membrane breaks down/ disappears.
*Microtubules increase in number, spindle apparatus
*Nuclear membrane completely disappeared
*Chromosomes move to equator of cell - begin to line up
*Chromosomes attach to spindle via kinetochore
Centromeric Region
*Movement of chromosomes via microtubules
to opposite sides of the cell. One chromatid to one end the other
Chromatid to the opposite end
*Genetically identical info at each pole
*Spindle fibers disappear
*Chromosomes uncoil
*Nuclear envelope reforms around

Cytokinesis - is separate from mitosis,
= pinching of cell/divison of cytoplasm.

Mitosis + Cytokinesis result in two
identical daughter cells.
Mitosis in a plant cell
Mitosis in an onion root
      Chromosomes and Chromatids
            During Mitosis
                Begin         After       After      After      After       After
              Interphase   Interphase   Prophase   Metaphase   Anaphase   telophase

    # of
                 4            4            4          4           8          4

    # of
                 4            8            8          8           8          4
• Cell division which results in halpoid “sex” cells
  (i.e., egg and sperm)
• One replication of the genetic material (DNA)
  during interphase, but two nuclear divisions
  (meiosis I and meiosis II).
• Results in haploid (N) cells (= gametes in animals)
  from an initial diploid (2N) cell
• Very similar to mitosis except that the cells
  produced are not genetically identical.
The human life cycle
Overview of meiosis: how meiosis reduces chromosome number
Independent Assortment
The stages of meiotic cell division: Meiosis I
A Tetrad from the Grasshopper
The stages of meiotic cell division: Meiosis I
The stages of meiotic cell division: Meiosis II
Oogenesis, 2n = 4
Spermatogenesis, 2n = 4
SEM of sea urchin sperm fertilizing egg
      Chromosomes and Chromatids
           During Meiosis I
                Begin         After       After      After      After       After
              Interphase   Interphase   Prophase   Metaphase   Anaphase   Telophase
                                            I          I          I           I

    # of
                 4            4            4          4           4          2

    # of
                 4            8            8          8           8          4
Chromosomes and Chromatids
     During Meiosis II
                 After      After      After       After
               Prophase   Metaphase   Anaphase   Telophase
                  II          II         II          II

     # of
                  2          2           4          2

     # of
                  4          4           4          2
A comparison of mitosis and meiosis
A comparison of mitosis and meiosis: summary

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