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

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.

CELLS

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

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

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 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*

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

Mitochondria Aerobic respiration produces ATP Has own genome

Microtubule 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

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

Chromosome duplication

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

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

Centromeric Region

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

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.

Mitosis in a plant cell

Mitosis in an onion root

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

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.

The human life cycle

Overview of meiosis: how meiosis reduces chromosome number

Independent Assortment

The stages of meiotic cell division: Meiosis I

Crossing-Over/Synapsis

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 Interphase After Prophase I Metaphase Anaphase Telophase # of Chromosomes 4 2 Chromatids 8

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

A comparison of mitosis and meiosis

A comparison of mitosis and meiosis: summary