chapter 2 cellular reproduction © john wiley & sons, inc

Chapter 2Cellular Reproduction

© John Wiley & Sons, Inc.

Chapter Outline

Cells and ChromosomesMitosisMeiosisLife Cycles of Some Model Genetic

Organisms


Cells and Chromosomes

In both prokaryotic and eukaryotic cells, the genetic

material is organized into chromosomes.


Eukaryotic: 23, non-circular, linear

Prokaryotic: 1, circular

Viruses: 1, DNA circular; 1, RNA linear

The Cellular EnvironmentCytoplasm / cytosol / Nucleus/ …the inside of a

cell….. Plasma membrane….the outside of the cell…

Water ( 70-80 %)

Hydrophilic and Hydrophobic Molecules; Amphiphatic

Carbohydrates (Glucose and Glycogen)

Lipids (Cholesterol, phospholipids and fatty acids)© John Wiley & Sons, Inc.

The Cellular Environment

Proteins (amino acids to polypeptide), including enzymes

Ribonucleoproteins, including RNAse as an enzyme

Membrane—made of lipids and proteins

Cell Wall: cellulose [murein-(sugars and amino acid)-in bacteria)


Animal and Plant Cells


Organelles:

Ribosome:is cell organelles that consist of RNA and proteins. They are responsible for assembling the proteins of the cell.

Mitochondria: is the cell's power producers. They convert energy into forms that are usableBy the cell.

Golgi:is responsible for manufacturing, warehousing, and shipping certain cellular products.

Lysosome:is a membranous sacs of enzymes. These enzymes are typically hydrolytic and can digest cellular macromolecules.

Endoplasmic Reticulum: is a network of tubules and flattened sacs that serve a variety of functions in the cell. The rough endoplasmic reticulum manufactures membranes and secretory proteins. The smooth ER has a wide range of functions including carbohydrate and lipid synthesis.

Plasma membrane: is a thin semi-permeable membrane that surrounds the cytoplasm of a cell, enclosing its contents. Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell, while keeping other substances out.

Cilia and flagella:are protrusions from some cells that aid in cellular locomotion. They are formed from specialized groupings of microtubules called basal bodies.

Nucleus:is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction.

Nucleolus contains nucleolar organizers which are parts of chromosomes with the genes for ribosome synthesis on them

Nuclear envelope:is a double membrane that contains the nucleus. These membranes separates the contents of the nucleus from the cytoplasm.

Nuclear pore: is a protein complex that helps to maintain the shape of the nucleus and assists in regulating the flow of molecules into and out of the nucleus.

Microtubules:are hollow rods, functioning primarily to help support and shape the cell as well as regulate cell cycle and division.

Microfilaments:or actin filaments are solid rods and are active in muscle contraction. They are particularly prevalent in muscle cells.

Cell wall:Outer covering of most cells that protects the bacterial cell and gives it shape.

Pilus:is a protein tube structure. It transfers genes from one bacteria to other bacteria.

Chloroplast:is the organelle where photosynthesis occurs in photosynthetic eukaryotes.

The organelle is surrounded by a double membrane.

Vacuole:structure in a plant cell that provides support and participates in a variety of cellular functions including storage, detoxification, protection, and growth.

Centriole: is found in animal cells and help to organize the assembly of microtubules during cell division.



No Organelles:

Chromosomes Double-stranded DNA with

associated proteins and sometimes RNA

Prokaryotic cells contain one circular chromosome plus smaller plasmids ( ?)

Most eukaryotic cells contain several large linear chromosomes plus a circular mitochondrial DNA


Vocabulary for ChromosomesDiploid: cells with 2 copies of each chromosomesHaploid: cells with one copy of each chromosomesSomatic cells: any cells of an organism, diploid and go

under mitosis.Germ line: reproductive cells that give rise to gametesGametes: specialized cells (sperm and ova)Centromere: point of interaction of each chromosomes;

region of chromosomes required for its movement.


Cell Division in Prokaryotes:Fission

A mother cell divides to produce two daughter cells.

The mother cell’s chromosome is duplicated prior to fission.

Each daughter cell receives one copy of the chromosome and more or less the rest of the content.

Clone—a population of genetically identical cells.

Colony—a visible mass of cells (1 to 250 cells).


http://mitosissection2.tumblr.com/

Division time?Phases1- lag 2- log3- stationary4- death

Cell Division in Eukaryotes:Inter (I) Phase and Mitosis (M) Phase


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30 min to

Cells, the basic units of all living things, are enclosed by membranes.

Chromosomes, the cellular structures that carry the genes, are composed of DNA and protein.

In eukaryotes, chromosomes are contained within a membrane-bounded nucleus; in prokaryotes they are not.

Eukaryotic cells possess complex systems of internal membranes as well as membranous organelles such as mitochondria, chloroplasts, and the endoplasmic reticulum.


Haploid eukaryotic cells possess one copy of each chromosome; diploid cells possess two copies.

Prokaryotic cells divide by fission (binary)

Eukaryotic cells divide by mitosis and meiosis.

Eukaryotic chromosomes duplicate when a cell’s DNA is synthesized; this event is characteristic of the S phase of the cell cycle.


MitosisWhen eukaryotic cells divide, they distribute their genetic material

equally and exactly to their offspring.


Inter-phase: Chromatin---Heterochromatin

---Eurochromatin

M-phase: Chromosomes

Mitosis in Animal Cells


mechanical force?

Centrosomes, Microtubules, and Centrioles.


Microtubule organizing centers (MTOCs)

Centrosome duplicates (S phase)

Centrosomes move to opposite sides of nucleusduring prophase.

Mitotic spindle assembles (microtubules=MT)

Spindle MTs make contact with chromosomes---centromere

(sequence repeated DNA sequence=heterochromatin=CEN sequences)

---kinetochore(protein-like containing structure)

Cytokinesis inAnimal and Plant Cells


Cleavage furrow associated with the contractile ring (Actin and Myosin)

As a cell enters mitosis, its duplicated chromosomes condense into rod-shaped bodies (prophase).

As mitosis progresses, the chromosomes migrate to the equatorial plane of the cell (metaphase).

Later in mitosis, the centromere that holds the sister chromatids of a duplicated chromosome together splits, and the sisters chromatids separate (or disjoin) from each other (anaphase)


As mitosis comes to an end, the chromosomes decondense and a nuclear membrane reforms around them (telophase).

Each daughter cell produced by mitosis and cytokinesis has the same set of chromosomes; thus, daughter cells are genetically identical.


Meiosis

Sexual reproduction involves a mechanism that reduces the number of chromosomes by

half.


Homologues


Xx or Xy

Comparison ofMitosis and Meiosis


Reduction

Non-reduction

Prophase I: Leptonema

Chromosomes condense

Each chromosome has two sister chromatids


Prophase I: Zygonema

Synapsis (pairing) of homologous chromosomes

Synaptonemal complex


The Synaptonemal Complex


Function ?Structural...

Prophase I: Pachynema

Chromosomes condense further

Bivalent of chromosomesTetrad of chromatids

Crossing over occurs (exchange material)


Prophase I: Diplonema

Paired chromosomes separate slightly but are in contact as chiasmata


Chiasmata


Prophase I: DiakinesisNuclear envelope fragments

Spindle fibers (MT) attach to kinetochores

Chromosomes move to central plane in pairs


Metaphase I

Paired chromosomes are oriented toward opposite poles

Terminalization: chiasmata move toward telomeres

Why? Spo11-double-strand DNA breaker


Anaphase I

Chromosome disjunction (separation of paired chromosomes)

Separated homologues move toward opposite poles


Telophase I

Chromosomes reach the poles; nuclei forms

Spindle apparatus is disassembled

Daughter cells separated by membranes

Chromosomes decondense

Each chromosome still has two sister chromatids


Prophase II

Chromosomes condense

Chromosomes attach to a new spindle apparatus

Sister chromatids are attached to spindle fibers from opposite poles


Metaphase II

Chromosomes align at equatorial plane


Anaphase II

Centromeres split

Chromatid disjunction—sister chromatids move toward opposite poles


Telophase II

Separated chromatids gather at poles; daughter nuclei form

Each chromatid is now called a chromosome

Each daughter nucleus contains a haploid set of chromosomes


Cytokinesis


Daughter cells are NOT genetically identical

Maternal and paternal homologues synapse, then disjoin independently.

Homologous chromosomes exchange material by crossing over


Diploid eukaryotic cells form haploid cells by meiosis, a process involving one round of chromosome duplication followed by two cell divisions (meiosis I and meiosis II).

During meiosis I, homologous chromosomes pair (synapse), exchange material (cross over), and separate (disjoin) from each other.

During meiosis II, chromatids disjoin from each other.



Human 23 3,200 20 to 25,000

Life Cycle ofSaccharomyces cerevisiae

(yeast).


Spermatogenesis and Oogenesis in Mammals



Arabidopsis thaliana, plant

In yeast, haploid cells with opposite mating types fuse

to form a diploid zygote, which then undergoes meiosis

to produce four haploid cells

Meiosis in the reproductive organs of Arabidopsis

produces microspores and megaspores, which

subsequently develop into male and female

gametophytes


The double fertilization that occurs during

Arabidopsis reproduction creates a diploid

zygote, which develops into an embryo, and a

triploid endosperm, which develops into

nutritive tissue in the seed

In mice and other mammals, one cell from

female meiosis becomes the egg, whereas all

four cells from male meiosis become sperm


chapter 2 cellular reproduction © john wiley & sons, inc

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