Cellular Reproduction Cellular Reproduction

Chapter 9Chapter 9

Limits of Cell Growth: The larger the cell, the more difficult it is for materials to enter and leave it.

Rates of Cell Growth: E. coli can double its volume in = 30 minutes. In one day, a single cell would grow into a 14 kg mass of bacteria. In 3 days = mass of the earth

Controls on Cell Growth: cells of the heart and nervous system rarely grow. Cells of the skin and digestive tract grow and divide rapidly throughout Life; old, worn out, and damaged cells. Cells will grow until they come into contact with each other.

Uncontrolled Cell Growth: Cancer cells grow out of control until they have used up all of their nutrients

Chromosomes:Chromosomes: Made up of chromatin (DNA and Made up of chromatin (DNA and

protein) protein) Total length of DNA is = 10,000 x length of the Total length of DNA is = 10,000 x length of the

chromosome. chromosome.

In 1973, Don and Ada Olins and Christopher In 1973, Don and Ada Olins and Christopher Woodcock discovered the chromosome’s DNA Woodcock discovered the chromosome’s DNA was coiled around special proteins called was coiled around special proteins called histones.histones.

DNA and histone molecules form beadlike DNA and histone molecules form beadlike

structures called structures called nucleosomes.nucleosomes. Nucleosomes form a thick fiber, shortened by a Nucleosomes form a thick fiber, shortened by a

system of loops and coils.system of loops and coils.

Chromosome StructureChromosome Structure

Composed of 2 sister chromatids and a centromere.

Binary Fission of a ProkaryoteBinary Fission of a Prokaryote

The Cell CycleThe Cell Cycle Is the period from the beginning of one

mitosis to the beginning of the next Consists of interphase and M phase

Prophase

Metaphase Anaphase

Telophase

Interphase

Controls On The Cell CycleControls On The Cell Cycle

InterphaseInterphase

InterphaseInterphase

Is a period of intense activityIs a period of intense activity Proteins are madeProteins are made DNA copiedDNA copied ATP is made and utilizedATP is made and utilized Nucleus is synthesizing mRNA to direct Nucleus is synthesizing mRNA to direct

cellular activitiescellular activities

Interphase

Consists of G1, S, and G2

Cells do not move through the cycle at the same rate

G1 consists of cell growth and development; increase in supply of proteins, and synthesis of some organelles

S stands for synthesis: DNA replication occurs here

G2 synthesis of more organelles and the cell prepares for mitosis (shortest of the phases)

MitosisMitosis Division of the nucleusDivision of the nucleus Occurs in somatic orOccurs in somatic or

body cellsbody cells Can last from a fewCan last from a few

minutes to severalminutes to several

daysdays

Mitosis DiagramMitosis Diagram

Prophase (longest phase)Prophase (longest phase) Chromosomes become visible as they Chromosomes become visible as they

shorten and thickenshorten and thicken Disintegration of the nucleolus and the Disintegration of the nucleolus and the

nuclear envelopenuclear envelope Centrioles move apart Centrioles move apart Formation of the mitotic spindle fibersFormation of the mitotic spindle fibers Takes up about 50-60%Takes up about 50-60%

of mitosisof mitosis

Metaphase (shortest phase)Metaphase (shortest phase) Centrioles have reached the opposite Centrioles have reached the opposite

polespoles Chromosomes line up along the equator or Chromosomes line up along the equator or

middle of the cellmiddle of the cell Centromere of each chromosome is Centromere of each chromosome is

attached to a spindle fiberattached to a spindle fiber

Anaphase (3Anaphase (3rdrd phase) phase) Centromeres splitCentromeres split Spindle fibers draw chromatids to poles of Spindle fibers draw chromatids to poles of

cellscells Chromatids are now individual Chromatids are now individual

chromosomeschromosomes

TelophaseTelophase

Chromosomes have reached opposite polesChromosomes have reached opposite poles Chromosomes uncoil and become less distinctChromosomes uncoil and become less distinct Nuclear membrane begins to reform around Nuclear membrane begins to reform around

chromosomeschromosomes Spindle begins to break apartSpindle begins to break apart Nucleolus reappearsNucleolus reappears Cells begin to divide by formation of cell plate in Cells begin to divide by formation of cell plate in

plant cells and cleavage furrow in animal cellsplant cells and cleavage furrow in animal cells Formation of two new daughter cellsFormation of two new daughter cells

Telophase (final phase)Telophase (final phase)

CytokinesisCytokinesis Division of the cytoplasmDivision of the cytoplasm Occurs at the end of telophaseOccurs at the end of telophase Results in two identical daughter cellsResults in two identical daughter cells

Review of Mitotic StagesReview of Mitotic Stages

MeiosisMeiosis

The process of gamete formation in which The process of gamete formation in which the chromosome number is reduced to the chromosome number is reduced to half the normal numberhalf the normal number

Requires two nuclear divisions called Requires two nuclear divisions called Meiosis I and Meiosis IIMeiosis I and Meiosis II

Meiosis IMeiosis I

Interphase-the cell replicates its chromosomesInterphase-the cell replicates its chromosomes Prophase I-each pair of homologous chromosomes Prophase I-each pair of homologous chromosomes

comes together to form a four-part structure called tetradcomes together to form a four-part structure called tetrad Crossing Over-homologous chromosomes exchange Crossing Over-homologous chromosomes exchange

genetic materialgenetic material Metaphase I-homologous chromosomes line up in Metaphase I-homologous chromosomes line up in

tetrads independently of each othertetrads independently of each other Anaphase I-centromeres do not split, this ensures that Anaphase I-centromeres do not split, this ensures that

each new cell will receive only one chromosome from each new cell will receive only one chromosome from each homologous paireach homologous pair

Telophase I-each new cell has one half of the genetic Telophase I-each new cell has one half of the genetic informationinformation

Crossing overPairing of

homologous chromosomes

Chiasma formation

ChromosomesBreakage and joining

Recombinant chromosomes

Crossing Over AnimatedCrossing Over Animated

www.contexo.info/.../images/www.contexo.info/.../images/mimovchanged2.gifmimovchanged2.gif

Metaphase I Anaphase I

Telophase IProphase II

Prophase I

Meiosis IIMeiosis II

Prophase II

Metaphase II

Anaphase II

Telophase II

Result of MeiosisResult of Meiosis

4 Haploid cells Gametes4 Haploid cells Gametes

Meiosis begins by replicating Meiosis begins by replicating the chromosomesthe chromosomes

Centromeres Do Not Split at Meiosis I

Centromeres Split at Meiosis II

OogenesisOogenesis Process by which egg cells are madeProcess by which egg cells are made Results in four haploid gametesResults in four haploid gametes One functional ovum capable of One functional ovum capable of

fertilizationfertilization Three polar bodies disintegrateThree polar bodies disintegrate

SpermatogenesisSpermatogenesis Process by which sperm cells are Process by which sperm cells are

producedproduced Results in four functional sperm cellsResults in four functional sperm cells

2n1 cell division: 2 daughter cells

2 cell divisions: 4 product of meiosis

2n

2n

2n

n

n n

n

n=chromosome number

Somatic cellsSomatic cells

Cells in sexual cycleCells in sexual cycle

MITOSISMITOSIS

MEIOSISMEIOSIS

Final resultFinal result

 

Mitosis :two genetically identical diploid cells from one diploid parent cell

MitosisMitosisConservative process:Conservative process:Daughter cells genotypes identical Daughter cells genotypes identical to parental genotypesto parental genotypes

Diploid organismDiploid organism: two sets of chromosomes (one: two sets of chromosomes (one

from each parent); 2nfrom each parent); 2n

Meiosis : Four genetically different haploid cells;

from one diploid parent cell

MeiosisMeiosisPromotes variation among the product Promotes variation among the product of meiosis (crossing over)of meiosis (crossing over)

Haploid organismHaploid organism: one set of chromosomes; n: one set of chromosomes; n

Mitosis vs Meiosis Alike Both have the stages

PMAT Both go through

Cytokinesis Both divide and make

daughter cells Both are a form of

reproduction Both take place inside the

cell Chromosomes duplicate

and DNA replication occurs in each process

Different Mitosis produces two identical daughter cell,

meiosis produces four genetically different cells

Crossing over and tetrad formation (synapsis) occur in prophase I of Meiosis

The centromeres split in Anaphase II Mitosis has one division, Meiosis has two Mitosis occurs in somatic or body cells Meiosis occurs in reproductive organs;

producing gametes Mitosis is asexual reproduction Meiosis ensures sexual reproduction