The Cell Cycle and How Cells Divide E-CLIP EIS Teaching – Learning Strategies / Procedures

Biology Secondary 6, duration 60 min.

Teacher: Mr.Wichai Likitponrak

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Look at this Picture!

What is

this?

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Introduction by this VDO!!!

https://www.youtube.com/watch?v=vA8aMpHwYh0

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Phases of the Cell Cycle

The cell cycle consists of

◦ Interphase – normal cell activity

◦ The mitotic phase – cell divsion

INTERPHASE

Growth

G 1

(DNA synthesis)

Growth

G2

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Cell Division An integral part of the cell cycle

Results in genetically identical daughter cells

Cells duplicate their genetic material

◦ Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

20 µm 100 µm 200 µm

(a) Reproduction. An amoeba,

a single-celled eukaryote, is

dividing into two cells. Each

new cell will be an individual

organism (LM).

(b) Growth and development.

This micrograph shows a

sand dollar embryo shortly after

the fertilized egg divided, forming

two cells (LM).

(c) Tissue renewal. These dividing

bone marrow cells (arrow) will

give rise to new blood cells (LM).

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Structure of Chromosomes

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Chromosome Duplication 0.5 µm

Chromosome

duplication

(including DNA

synthesis)

Centromere

Separation

of sister

chromatids

Sister

chromatids

Centrometers Sister chromatids

A eukaryotic cell has multiple

chromosomes, one of which is

represented here. Before

duplication, each chromosome

has a single DNA molecule.

Once duplicated, a chromosome

consists of two sister chromatids

connected at the centromere. Each

chromatid contains a copy of the

DNA molecule.

Mechanical processes separate

the sister chromatids into two

chromosomes and distribute

them to two daughter cells.

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Structure of Chromosomes The centromere is a constricted region of the

chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores.

Kinetochores serve as points of attachment for microtubules that move the chromosomes during cell division:

Metaphase chromosome

Kinetochore

Kinetochore microtubules

Centromere region of chromosome

Sister Chromatids

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Phases of the Cell Cycle Interphase

◦ G1 - primary growth

◦ S - genome replicated

◦ G2 - secondary growth

M - mitosis

C - cytokinesis

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Mitosis Some haploid & diploid cells divide by mitosis. Each new cell receives one copy of every

chromosome that was present in the original cell. Produces 2 new cells that are both genetically

identical to the original cell.

DNA duplication

during interphase

Mitosis

Diploid Cell

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Mitotic Division of an Animal Cell

G2 OF INTERPHASE PROPHASE PROMETAPHASE

Centrosomes

(with centriole pairs) Chromatin

(duplicated)

Early mitotic

spindle

Aster

Centromere

Fragments

of nuclear

envelope

Kinetochore

Nucleolus Nuclear

envelope

Plasma

membrane

Chromosome, consisting

of two sister chromatids

Kinetochore

microtubule

Nonkinetochore

microtubules

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METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Spindle

Metaphase

plate Nucleolus

forming

Cleavage

furrow

Nuclear

envelope

forming Centrosome at

one spindle pole

Daughter

chromosomes

Mitotic Division of an Animal Cell

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Mitosis in a plant cell

1 Prophase.

The chromatin

is condensing.

The nucleolus is

beginning to

disappear.

Although not

yet visible

in the micrograph,

the mitotic spindle is

staring to from.

Prometaphase.

We now see discrete

chromosomes; each

consists of two

identical sister

chromatids. Later

in prometaphase, the

nuclear envelop will

fragment.

Metaphase. The

spindle is complete,

and the chromosomes,

attached to microtubules

at their kinetochores,

are all at the metaphase

plate.

Anaphase. The

chromatids of each

chromosome have

separated, and the

daughter chromosomes

are moving to the ends

of cell as their

kinetochore

microtubles shorten.

Telophase. Daughter

nuclei are forming.

Meanwhile, cytokinesis

has started: The cell

plate, which will

divided the cytoplasm

in two, is growing

toward the perimeter

of the parent cell.

2 3 4 5

Nucleus

Nucleolus Chromosome Chromatine

condensing

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Meiosis Reduces the chromosome number such

that each daughter

Cell has a haploid set of chromosomes

Ensures that the next generation will have:

◦ Diploid number of chromosome

◦ Exchange of genetic information (combination of traits

◦ that differs from that of either parent)

Only diploid cells can divide by meiosis.

Prior to meiosis I, DNA replication occurs.

During meiosis, there will be two nuclear divisions, and the result will be four haploid nuclei.

No replication of DNA occurs between meiosis I and meiosis II.

Interphase

Homologous pair

of chromosomes

in diploid parent cell

Chromosomes

replicate

Homologous pair of replicated chromosomes

Sister

chromatids Diploid cell with

replicated

chromosomes

1

2

Homologous

chromosomes

separate

Haploid cells with

replicated chromosomes

Sister chromatids

separate

Haploid cells with unreplicated chromosomes

Meiosis I

Meiosis II

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Meiosis Phases Meiosis involves the same four phases seen in mitosis

prophase metaphase anaphase telophase

They are repeated during both meiosis I and meiosis II. The period of time between meiosis I and meiosis II is

called interkinesis. No replication of DNA occurs during interkinesis because

the DNA is already duplicated.

Prophase I

of meiosis

Tetrad

Nonsister

chromatids

Chiasma,

site of

crossing

over

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Sister chromatids

Chiasmata

Spindle

Centromere (with kinetochore)

Metaphase plate

Homologous chromosomes separate

Sister chromatids remain attached

Microtubule attached to kinetochore

Tetrad

PROPHASE I METAPHASE I ANAPHASE I

Homologous chromosomes

(red and blue) pair and

exchange segments; 2n = 6

in this example

Pairs of homologous chromosomes split up

Tetrads line up

Meiosis I is very important to variation (crossing over)

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Meiosis II is very similar to mitosis

Cleavage furrow

PROPHASE II METAPHASE II ANAPHASE II TELOPHASE I AND

CYTOKINESIS TELOPHASE II AND

CYTOKINESIS

Sister chromatids separate

Haploid daughter cells forming

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A Comparison of Mitosis and Meiosis

Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell

Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell

The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis

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MITOSIS MEIOSIS

Prophase

Duplicated chromosome

(two sister chromatids)

Chromosome

replication

Chromosome

replication

Parent cell

(before chromosome replication)

Chiasma (site of

crossing over) MEIOSIS I

Prophase I

Tetrad formed by

synapsis of homologous

chromosomes

Metaphase

Chromosomes

positioned at the

metaphase plate

Tetrads

positioned at the

metaphase plate

Metaphase I

Anaphase I

Telophase I

Haploid

n = 3

MEIOSIS II

Daughter

cells of

meiosis I

Homologues

separate

during

anaphase I;

sister

chromatids

remain together

Daughter cells of meiosis II

n n n n

Sister chromatids separate during anaphase II

Anaphase

Telophase

Sister chromatids

separate during

anaphase

2n 2n

Daughter cells

of mitosis

2n = 6

A Comparison Of Mitosis And Meiosis

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Assignment:

Worksheet

Pages 7-9

◦1.1, 1.2 and 1.3

Sent me back in this class !!!