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Cell Structure, Mitosis and Meiosis

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1 Cell Structure, Mitosis and Meiosis
Lecture 2 Cell Structure, Mitosis and Meiosis

2 Study Questions - Lecture 2
Describe the major components of a typical animal cell and their function(s). What is the cell cycle? At which stage is the genetic material replicated? What events take place at each phase? 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 mitosis. Describe how chromosomes are named on the basis of their centromere placement. What is meiosis? Describe the events that characterize each stage of meiosis. Contrast mitosis and meiosis. Explain why meiosis leads to significant genetic variation while mitosis does not.


4 Cells - “fundamental unit of life”
Prokaryotes -single celled -no nucleus -no organelles -DNA = single, circular molecule - e.g., bacteria Eukaryotes -single or multicellular -nucleus with nuclear membrane -DNA packaged into chromosomes -organelles present Biological Kingdoms: Monera, Protista, Fungi, Plantae, Animalia


6 Endoplasmic reticulum Microtubules (centriole) Chromatin/Chromosomes
Cellular Components Cell membrane Endoplasmic reticulum Ribosomes Golgi apparatus Lysosomes Mitochondria Microtubules (centriole) Nucleus (nucleolus) Chromatin/Chromosomes

7 Fluid-Mosaic Model of Membrane Structure - the thing
surrounding the internal components of the cell Bilayer (2 layers)- of proteins and lipids

8 Endoplasmic Reticulum-set of
interconnected membranes. 2 types. 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*

9 Golgi Apparatus After proteins and lipids are made by the Endoplasmic Reticulum they may be modified further and/or stored by the GA.

10 Lysosome - formed by GA, contain enzymes that break down
cellular debris and foreign substances brought into the cell

11 Mitochondria Aerobic respiration produces ATP Has own genome

12 Microtubule Cell shape, motion, and growth.

13 Microtubule- composed of tubulin.
Both cilia and flagella have the same Structure of microtubules: 9+2. Forms spindle during mitosis & meiosis

14 Nuclear Membrane or Envelope - two membranes which form
the nucleus, is porous. Allows RNA to leave nucleus.

15 Chromosome = DNA (deoxyribonucleic acid) + associated
proteins (mainly histones) = “packaged” DNA



18 Cell Cycle: replication of genetic material (=DNA) and nuclear
division (= mitosis + cytokinesis).

19 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

20 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

21 Interphase Not part of mitosis DNA is replicated chromosomes start to condense

22 Chromosome duplication

23 Prophase *Chromosomes coil and condense further. *Nucler membrane breaks down/ disappears. *Microtubules increase in number, spindle apparatus forms.

24 Metaphase *Nuclear membrane completely disappeared *Chromosomes move to equator of cell - begin to line up *Chromosomes attach to spindle via kinetochore

25 Centromeric Region

26 Anaphase *Movement of chromosomes via microtubules to opposite sides of the cell. One chromatid to one end the other Chromatid to the opposite end

27 Telophase *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.

28 Mitosis in a plant cell

29 Mitosis in an onion root

30 Chromosomes and Chromatids During Mitosis
Begin Interphase After Prophase Metaphase Anaphase telophase # of Chromosomes 4 8 Chromatids

31 Meiosis 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.

32 The human life cycle

33 Overview of meiosis: how meiosis reduces chromosome number

34 Independent Assortment

35 The stages of meiotic cell division: Meiosis I

36 Crossing-Over/Synapsis

37 A Tetrad from the Grasshopper

38 The stages of meiotic cell division: Meiosis I

39 The stages of meiotic cell division: Meiosis II

40 Oogenesis, 2n = 4

41 Spermatogenesis, 2n = 4

42 SEM of sea urchin sperm fertilizing egg

43 Chromosomes and Chromatids During Meiosis I
Begin Interphase After Prophase I Metaphase Anaphase Telophase # of Chromosomes 4 2 Chromatids 8

44 Chromosomes and Chromatids During Meiosis II
After Prophase II Metaphase II Anaphase Telophase # of Chromosomes 2 4 Chromatids

45 A comparison of mitosis and meiosis

46 A comparison of mitosis and meiosis: summary

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