16-cell cycle and mitosis part 1

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Chapter 12

The Cell Cycle 

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Cell Division

http://www.youtube.com/watch?v=rgLJrvoX_qo 

http://www.youtube.com/watch?v=DD3IQknCEdc 

Interphase  Prophase  Prometaphase 

Metaphase  Anaphase  Telophase  Cytokinesis 

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Cell Division

Cell Division  – creation of new cells (daughter cells)

by division of pre-existing cell (parent cell)

Why do cells divide?

Do cells divide continuously?

Parent Cell

Daughter Cells

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Why do cells divide?

Cell Division  – creation of new cells (daughter cells)

by division of pre-existing cell (parent cell)

Purposes:

Growth of multicellular organisms

Repair of damaged tissues and

renewal of old cells

Reproduction  – production of offspring

Asexual – utilizes mitosis

Sexual – utilizes meiosis

Parent Cell

Daughter Cells

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Do Cells Divide Continuously?

Cell Division Stage – M (mitotic) Stage 

Division of the nucleus (division of genetic material) 

Mitosis  – used for asexual reproduction, growth and repair 

Meiosis  – used for sexual reproduction

Division of the cytoplasm – Cytokinesis

Preparation Stage  – Interphase

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Interphase: Preparing for Cell

Division

G1 of Interphase (gap 1) - Interval of Growth

Number of organelles doubles

Materials (such as proteins) needed for DNA synthesis are

produced Stage at which normal cell functions occur

S of Interphase (synthesis) - DNA Replication

Chromosomes (DNA and proteins) are duplicated

G2 of Interphase (gap 2) - Preparation for Division

Proteins needed for cell division (such as tubulin) aresynthesized

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The Cell Cycle

What is G0 ?

Stage occupied by cells that are arrested  (not dividing)

Cells can perform normal functions in this stage 

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Mitosis & MeiosisKeeping it all straight!

The lifecycle of sexually reproducing organisms requires

two kinds of nuclear division – mitosis and meiosis

MEIOSIS

(2n n) 

Egg  Sperm 

Gameteshaploid (n) 

Fertilized eggdiploid (2n) 

Cell divisionsresponsible for growth(addition of somatic cells) 

In animals, meiosis occurs priorto production of eggs and sperm 

Adultdiploid (2n) 

The key to keeping

it all straight…

knowing the

terminology !

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Genetic Material Terminology

Chromosome  – single, long molecule of DNA and its

associated proteins (linear in eukaryotes); this DNA-

protein complex is called chromatin

Non-Dividing Cells (Interphase): diffuse, threadlike DNA 

Dividing Cells (M phase): chromosomes are in duplicated

and condensed form 

NOTE: Table 12.1 in your text is very helpful!

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Chromatin

DNA

histonecore 

DNA

Non-Dividing

Dividing

Length of DNA in one human cell = ~2 m!

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Genetic Material Terminology

Each chromosome contains a particular set of genes

Gene  – a section of DNA that carries instructions for

building a protein (influences hereditary traits)Example: flower color gene

Allele  – different versions of the same gene

Example: “white” allele and “purple” allele 

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Genetic Material Terminology

The human genome* contains

46 chromosomes 

Different species have different

numbers of chromosomes

*genome - complete set of genetic information 

karyotype of human cell

SpeciesChromosome Number

(Diploid) 

Human 46

Kangaroo 12

Shrimp 254

Mosquito 6

Algae 148

Pea 14

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Genetic Material Terminology

The chromosomes are

arranged in pairs called

homologouschromosomes 

karyotype of human cell

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Genetic Material Terminology

Homologous Chromosomes  – pair of same “kind” of

chromosomes – similar in size, shape, and gene

content (Note: alleles may differ)

one chromosome is inherited from mother

one chromosome is inherited from father

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Genetic Material Terminology

Each chromosome may exist in… 

An unduplicated  form (prior to DNA replication in S phase or

after cell division), or… 

A duplicated   form (following S phase)

Each copy is called a chromatid 

one chromosome (unduplicated)

one chromosome (duplicated)

chromatid

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Genetic Material Terminology

Sister chromatids – the two chromatids

of a duplicated chromosome

Contain identical  genetic information

Associated with one another along

entire length

Centromere  – specialized region at which sister

chromatids are joined

Kinetochore  – protein complexes on either side

of centromere; site at which spindle fibers attach

(more later…) 

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Homologous Chromosomes v.

Sister Chromatids

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Ploidy 

Ploidy  – number of sets of chromosomes in a cell 

Cells that have two chromosomes of each “kind” (i.e. have

homologous pairs of chromosomes) are called diploid (2n)

Example: somatic (body) cells 

Cells that have one chromosome of each “kind” are called

haploid (n)Example: gametes (sperm and egg)

What is the value of n for humans?

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Human Lifecycle:Diploid & Haploid Stages

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DNA Replication in S Phase

How many

chromosomes are in

each cell?Count the centromeres!

4 replicatedchromosomes

4 unreplicatedchromosomes

Are these cells haploidor diploid?

How do you know?

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Lifecycle of Sexually Reproducing Organisms:

Requires Mitosis and  Meiosis

MEIOSIS(2n n) 

Amount o f

hereditary m aterial

is reduced by half  

Egg  Sperm 

Gameteshaploid (n) 

Normal amount of

hereditary m aterial

is restored  Fertilized eggdiploid (2n) 

Cell divisionsresponsible for growth(addition of somatic cells) 

In animals, meiosis occurs priorto production of eggs and sperm 

Adultdiploid (2n) 

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Mitosis & Meiosis

Mitosis - used for growth, repair, & asexual

reproduction

duplication division

2n 2n

Meiosis - used for sexual reproduction reduction division

2n n

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Mitosis: Features 

Occurs in somatic (body) cells -

involved in growth and repair

Produces 2 daughter nuclei 

Daughter nuclei are diploid (like

parent nucleus)

Daughter cells are clones 

(genetically identical) of parent

cell and each other

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Mitosis: Overview  

G1  S PHASE AND G2  MITOSIS

Sisterchromatids

Parent cell:4 replicatedchromosomes

Replicatedchromosomescondense at thestart of mitosis.

Parent cell:4 unreplicatedchromosomes

Chromosom es are shown par t ia lly

condensed to make them vis ible  

During mitosis, sisterchromatids separate.

Two daughter cells areformed by cytokinesis.

Daughter cells:contain thesamecomplement ofchromosomes asthe parent cell.

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Mitosis

Mitosis is a continuous process, but it is typically

broken into steps for descriptive purposes

Prophase Prometaphase

Metaphase

Anaphase

Telophase

Remember: prior to the start of mitosis, the

chromosomes are replicated (in S phase) 

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Prophase

Chromatin condenses

Nuclear envelope begins to break down

Nucleolus disappears

Centrosomes move to opposite poles

Mitotic Spindle begins to form

ProphaseEarly Prophase

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Mitotic Spindle

Mitotic Spindle - system of microtubules; orients chromosomes

and provides mechanical force used to separate chromosomes into

daughter cells

Forms between two centrosomes (microtubule organizingcenters)

Each contains a pair of centrioles and radiating asters 

(microtubule bundles)

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Mitotic Spindle

Types of Spindle Fibers:

Kinetochore (centromeric) spindle fibers

attach to kinetochores on the surface of centromeres pull chromosomes

Polar spindle fibers

spindle fibers that extend beyond midpoint of cell

push cell poles apart

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Prometaphase

Nuclear envelope completely broken down

Kinetochores appear on each side of centromeres

Kinetochore microtubules contact chromosomes

Push-pull forces of the spindle apparatus - begin to align

chromosomes at center of cell

Prometaphase

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Metaphase

Mitotic spindle is fully formed

All chromosomes are lined up at the metaphase plate

(spindle equator) at the end of metaphase

Metaphase

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Anaphase

Centromeres divide

Sister chromatids separate

Daughter chromosomes pulled (along kinetochore spindle

fibers)/pushed (by polar spindle fibers) to opposite poles of cell

Finished when equivalent (and complete) collections of chromosomes arelocated at the two poles of the cell  

 Anaphase

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Chromosome Movement

Motor proteins (dynein and others) on kinetochores

“walk” the chromosomes down microtubules (kinetochore

spindle fibers)

Microtubules shorten from kinetochore endMicrotubules 

Fiberscontaining

motorproteins 

Kinetochoreplates 

Tubulinsubunits 

 – 

+ 

+ 

Chromosome 

Chromosomemovement 

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Telophase

(basically the reverse of prophase) 

Mitotic spindle disassembles

Nuclear envelope reassembles around daughternuclei

Chromosomes decondense

Nucleolus reappears

Finished when two daughter nuclei have formed - each areclones of one another and of the parent cell  

Telophase

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Cell Division and the Cell Cycle

Preparation Phase  – Interphase

Cell Division Phase – M (mitotic) Phase 

Division of the nucleus (division of genetic material) 

Mitosis  – used for asexual reproduction, growth and repair 

Meiosis  – used for sexual reproduction

Division of the cytoplasm – Cytokinesis

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Cytokinesis

Cytokinesis

mechanism that splits

cytoplasm into daughtercells

usually occurs

immediately followingmitosis

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Cytokinesis in Animal Cells

Formation of a cleavage furrow - due to band of actin

 filaments working in association with myosin beneath

plasma membrane

Cytoplasm is pinched in two

Mitosis is over, and

the spindle is nowdisassembling.

Band of actin filaments

(contractile ring) at the formerspindle equator contracts.

The contractions

continue and cutthe cell in two.

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Cytokinesis in Animal Cells

Formation of a cleavage furrow - due to band of actin

 filaments working in association with myosin beneath

plasma membrane

Cytoplasm is pinched in two

 Myosin

“Head” region

 Actin

When myosin’s “head” attaches to actin and moves,

the actin filament slides

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Cytokinesis in Plant Cells

Formation of a cell plate

Vesicles filled with wall-building material fuse along cellequator

Cell plate thickens to become a crosswall - divides the

parent cell into two daughter cells

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Cytokinesis in Plant Cells

cell wall

formerspindleequator

cell plate

vesiclesconverging

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Mitosis and Cytokinesis

Interphase  Prophase  Prometaphase 

Metaphase  Anaphase  Telophase  Cytokinesis 

http://highered.mcgraw-hill.com/olc/dl/120073/bio14.swf  

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Mitosis and Cytokinesis

Animal Cell:http://www.youtube.com/watch?v=DD3IQknCEdc&feature=related 

Plant Cell:http://www.youtube.com/watch?v=aDAw2Zg4IgE&feature=related 

Prokaryotic Cell Division: Binary

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Prokaryotic Cell Division: Binary

Fission

Prokaryotic cell

division is

often very fast!

Some

antibiotic

s inhibit

cell wall

synthesis