Chapter 11The Continuity of Life: Cellular

Reproduction• 11.1 What is the role of cellular

reproduction in the lives of individual cells & entire organism?

• 11.2 How is DNA in eukaryotic cells organized into chromosomes

• 11.3 How do cells reproduce by mitotic cell division

• 11.4 How is the cell cycle controlled?

Chapter 11The Continuity of Life: Cellular

Reproduction• 11.5 What do so many organisms

reproduce sexually?• 11.6 How does meiotic cell division

produce haploid cells?• 11.7 How do mitotic and meiotic cell

division occur in the life cycle of eukaryotes?

• 11.6 How do meiosis and sexual reproduction produce genetic variability?

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual

Cells and Entire Organisms?

• Sexual reproduction is the union of gametes (like a sperm and egg)

• Asexual reproduction is just one parent dividing

• Cell division in eukaryotes enables asexual reproduction

bud

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual

Cells and Entire Organisms?

• The prokaryotic cell cycle consists of growth and binary fission

• Binary fission means splitting in two

• Creates 2 identical cells except for mutations (caused by copying mistakes)

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual

Cells and Entire Organisms?

• The eukaryotic cell cycle consists of interphase and cell division

• Often cells only divide when they receive signals, such as growth hormones

Some never divide, like muscle and nerve cells

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual

Cells and Entire Organisms?

• There are two types of cell division in eukaryotic cells:

– Mitotic cell division –> produces two daughter cells that are genetically identical with the same number of chromosomes

– Meiotic cell division -> produces four daughter cells with half the chromosomes (gametes)

meiosis in testes

meiosis inovaries

egg

fertilizationsperm

embryo

babymitosis,differentiation,and growth

mitosis,differentiation, and growth

mitosis,differentiation,and growth

fertilizedegg

Section 11.2 Outline• 11.2 How Is DNA in Eukaryotic Cells

Organized into Chromosomes?– The Eukaryotic Chromosome Consists of a

DNA Double Helix Bound to Proteins– Eukaryotic Chromosomes Usually Occur in

Homologous Pairs with Similar Genetic Information

– A Karyotype Reveals Chromosomal Types and Ploidy

nucleosome: DNA wrapped around histone proteins(10 nm diameter)

histone proteins

DNA (2 nm diameter)

chromosome:coils gathered ontoprotein scaffold(200 nm diameter)

DNA coils

coiled nucleosomes(30 nm diameter)

proteinscaffold

nucleosome: DNA wrapped aroundhistone proteins(10 nm diameter)

chromosome:coils gathered ontoprotein scaffold(200 nm diameter)

histone proteins

DNA (2 nm diameter)

DNA coils

coiled nucleosomes(30 nm diameter)

proteinscaffold

genes

centromere

telomeres

sisterchromatids

duplicatedchromosome(2 DNA double helices)

centromere means middle body

sister chromatids centromere

independentdaughterchromosomes,each with oneidentical DNAdouble helix

autosomes

sex chromosomes

11.2 How Is DNA in Eukaryotic Cells Organized into Chromosomes?

• Eukaryotic chromosomes usually occur in homologous pairs with similar genetic information

• Cells with pairs of homologous chromosomes are called diploid for double. (2n)

• Gametes are haploids for half. (1n)

Section 11.3 Outline

• 11.3 How Do Cells Reproduce by Mitotic Cell Division?

– Mitosis Consists of Four Phases– Events of Mitotic Prophase– Events of Mitotic Metaphase– Events of Mitotic Anaphase– Events of Mitotic Telophase– Cytokinesis

INTERPHASE

LATE INTERPHASE

nuclearenvelope chromatin

nucleolus

centriolepairs

Duplicated chromosomes inrelaxed state; duplicated centrioles remain clustered.

MITOSIS

beginning ofspindle formation

condensingchromosomes

Chromosomes condense and shorten; spindle microtubules begin to form between separating centriole pairs.

EARLY PROPHASE

LATE PROPHASE

kinetochore

pole

pole

Nucleolus disappears; nuclear envelope breaks down; spindle microtubules attach to the kinetochore of each sister chromatid.

METAPHASE

spindlemicrotubules

Kinetochores interact; spindle microtubules line up chromosomes at cell's equator.

ANAPHASE

"free" spindlefibers

Sister chromatids separate and move to opposite poles of the cell; spindle microtubules push poles apart.

chromosomesextending

nuclear envelopere-forming

One set of chromosomes reaches each pole and relaxes into extended state; nuclear envelopes start to form around each set; spindle microtubules begin to disappear.

TELOPHASE

Cell divides in two; each daughter cell receives one nucleus and about half of the cytoplasm.

CYTOKINESIS

Spindles disappear, intact nuclear envelopes form, chromosomes extend completely, and the nucleolus reappears.

INTERPHASE OFDAUGHTER CELLS

The waist completelypinches off, formingtwo daughter cells.

The microfilament ringcontracts, pinchingin the cell's “waist.”

Microfilaments form a ring around the cell's equator.

Cytokinesis in an Animal Cell

Complete separation of daughter cells.

Vesicles fuse to form a new cell wall (red) and plasma membrane (yellow) between daughter cells.

cell wall

Golgi complex

plasma membranecarbohydrate-filled vesicles

Carbohydrate-filled vesicles bud off the Golgi complex and move to the equator of the cell.

Cytokinesis in an Plant Cell

Section 11.4 Outline• 11.4 How Is the Cell Cycle Controlled?

– The Activities of Specific Enzymes Drive the Cell Cycle

– Checkpoints Control Progression Through the Cell Cycle

Enzymes Drive the Cell Cycle

– The cell cycle is driven by proteins called Cyclin-dependent kinases, or Cdk’s

– Kinases are enzymes that phosphorylate (add a phosphate group to) other proteins, stimulating or inhibiting their activity

– Cdk’s are active only when they bind to other proteins called cyclins

Enzymes Drive the Cell Cycle• Cell division occurs when growth

factors bind to cell surface receptors, which leads to cyclin synthesis

• Cyclins then bind to and activate specific Cdk’s

Checkpoints Control Cell Cycle

• Although Cdk’s drive the cell cycle, multiple checkpoints ensure that– The cell successfully completes DNA

synthesis during interphase – Proper chromosome movements occur

during mitotic cell division

Checkpoints Control Cell Cycle

• There are three major checkpoints in the eukaryotic cell cycle, each regulated by protein complexes– G1 to S:

– G2 to mitosis

– Metaphase to anaphase

Checkpoints Control Cell Cycle

• G1 to S: Ensures that the cell’s DNA is suitable for replication– p53 protein expressed when DNA is

damaged• Inhibits replication• Stimulates synthesis of DNA repair

enzymes• Triggers cell death (apoptosis) if damage

can’t be repaired

11.6 Why Do So Many Organisms Reproduce Sexually?

• Mutations in DNA are the ultimate source of genetic variability

• Sexual reproduction may combine different parental alleles in a single offspring

• Creates lot of variation

gene 1 gene 2

same alleles different alleles

Mutations are the raw material for evolution

Section 11.6 Outline• 11.6 How Does Meiotic Cell Division

Produce Haploid Cells?– Meiosis Separates Homologous Chromosomes

to Produce Haploid Daughter Nuclei– Fusion of Gametes Keeps Chromosome Number

Constant Between Generations– Events of Meiotic Prophase I– Events of Meiotic Metaphase I

Section 11.6 Outline• 11.6 How Does Meiotic Cell Division

Produce Haploid Cells? (continued)– Events of Meiotic Anaphase I and Telophase I– Summary of Events of Meiosis II

sisterchromatids

homologouschromosomes

Copyright © 2005 Pearson Prentice Hall, Inc.

Both members of a pair of homologous chromosomes are replicated prior to meiosis

During meiosis I, each daughter cell receives one member of each pair of homologous chromosomes

During meiosis II, sister chromatids separate into independent chromosomes (1n)

meioticcell division

fertilization

2n

2n

2n n

n

pair of homologous,duplicated chromosomes

sisterchromatids ofone duplicatedhomologue

Duplicated homologous chromosomes pair up side by side.Copyright © 2005 Pearson Prentice Hall, Inc.

protein strandsjoining duplicatedchromosomes

direction of“zipper”formation

Protein strands “zip” the homologous chromosomes together.

Copyright © 2005 Pearson Prentice Hall, Inc.

recombinationenzymes

Recombination enzymes bind to the joined chromosomes.

Copyright © 2005 Pearson Prentice Hall, Inc.

chiasma

Recombination enzymessnip chromatids apart and reattach the free ends. Chiasmata (the sites of crossing over) form whenone end of the paternal chromatid (yellow) attaches to the other end of a maternal chromatid (purple).

Copyright © 2005 Pearson Prentice Hall, Inc.

Recombination enzymes and protein zippers leave. Chiasmata remain, helping to hold homologous chromosomes together.

chiasma

Copyright © 2005 Pearson Prentice Hall, Inc.

Crossing overGenetic recombination

spindlemicrotubules

duplicatedchromosomes

Mitosis Meiosis I

Section 11.7 Outline• 11.7 When Do Mitotic and Meiotic Cell

Divisions Occur in the Life Cycles of Eukaryotes?

– In Haploid Life Cycles, the Majority of the Cycle Consists of Haploid Cells

– In Diploid Life Cycles, the Majority of the Cycle Consists of Diploid Cells

– In Alternation-of-Generation Life Cycles, There Are Both Diploid and Haploid Multicellular Stages

11.8 How Do Meiosis and Sexual Reproduction Produce Genetic

Variability?

• Shuffling of homologues creates novel combinations of chromosomes

• Crossing over creates chromosomes with novel combinations of genes

• Fusion of gametes adds further genetic variability to the offspring

Independent Assortment

There are 2 choices for each spot.

223 ≈ 8 million different gametes each human can make without even considering crossing over