SEL - 2LISNA HIDAYATI, M.Biotech.

OUTLINE

1. Pembelahan sel: amitosis, mitosis, dan

meiosis

2. Pengertian tentang sitoskeleton

Key Role: Pembelahan Sel

The continuity of life

Is based upon the reproduction of cells, or cell division

Key Role: Pembelahan Sel

Unicellular organisms

Reproduce by cell division100 m

(a) Reproduction. An amoeba,

a single-celled eukaryote, is

dividing into two cells. Each

new cell will be an individual

organism (LM).Figure 12.2 A

Key Role: Pembelahan Sel

Unicellular organisms

Reproduce by cell division100 m

(a) Reproduction. An amoeba,

a single-celled eukaryote, is

dividing into two cells. Each

new cell will be an individual

organism (LM).Figure 12.2 A

Key Role: Pembelahan Sel

Multicellular organisms depend on cell division for

Development from a fertilized cell

Growth

Repair 20 m200 m

(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).

Figure 12.2 B, C

Concept : Cell division 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

A cells endowment of DNA, its genetic information

Is called its genome

The DNA molecules in a cell

Are packaged into chromosomes

50 m

Figure 12.3

Eukaryotic chromosomes

Consist of chromatin, a complex of DNA and protein that condenses during cell division

In animals

Somatic cells have two sets of chromosomes

Gametes have one set of chromosomes

The Chromosomes

Each duplicated chromosome

Has two sister chromatids, which separate during cell division

0.5 m

Chromosome

duplication

(including DNA

synthesis)

Centromere

Separation

of sister

chromatids

Sister

chromatids

Centromeres 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.

Figure 12.4

Cell Division

Eukaryotic cell division consists of

Mitosis, the division of the nucleus

Cytokinesis, the division of the cytoplasm

In meiosis

Sex cells are produced after a reduction in chromosome number

Cell Cycle

The cell cycle consists of

The mitotic phase

Interphase

INTERPHASE

G1S

(DNA synthesis)

G2

Figure 12.5

INTERPHASE

can be divided into subphases

G1 phase

S phase

G2 phase

THE MITOTIC PHASE Is made up of mitosis and cytokinesis

Mitosis consists of five distinct phases

Prophase

Prometaphase

G2 OF

INTERPHASEPROPHASE 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 Figure 12.6

Nonkinetochore

microtubules

THE MITOTIC PHASE

Metaphase

Anaphase

Telophase

Centrosome at

one spindle pole

Daughter

chromosomes

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Spindle

Metaphaseplate Nucleolus

forming

Cleavage

furrow

Nuclear

envelope

formingFigure 12.6

The Mitotic Spindle:A Closer Look

The mitotic spindle

Is an apparatus of microtubules that controls chromosome movement during mitosis

Some spindle microtubules

Attach to the kinetochores of chromosomes and move the chromosomes to the metaphase plate

CentrosomeAster

Sister

chromatids

Metaphase

Plate

Kinetochores

Overlapping

nonkinetochore

microtubulesKinetochores

microtubules

Centrosome

ChromosomesMicrotubules0.5 m

1 m

Figure 12.7

Cytokinesis: A Closer Look

In animal cells

Cytokinesis occurs by a process known as cleavage, forming a cleavage furrow

Cleavage furrow

Contractile ring of

microfilamentsDaughter cells

100 m

(a) Cleavage of an animal cell (SEM)Figure 12.9 A

Cytokinesis: A Closer Look

In plant cells, during cytokinesis

A cell plate forms

Daughter cells

1 mVesicles

forming

cell plate

Wall of

patent cellCell plateNew cell wall

(b) Cell plate formation in a plant cell (SEM)Figure 12.9 B

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

NucleolusChromosomeChromatine

condensing

Figure 12.10

The cell cycle is regulated by a molecular control system

The frequency of cell division

Varies with the type of cell

These cell cycle differences

Result from regulation at the molecular level

The Cell Cycle Control System

The sequential events of the cell cycle Are directed by a distinct cell cycle control

system, which is similar to a clock

Figure 12.14

Control

system

G2 checkpoint

M checkpoint

G1 checkpoint

G1

S

G2M

The clock has specific checkpoints

Where the cell cycle stops until a go-ahead signal is received

G1 checkpoint

G1G1

G0

(a) If a cell receives a go-ahead signal at

the G1 checkpoint, the cell continues

on in the cell cycle.

(b) If a cell does not receive a go-ahead

signal at the G1checkpoint, the cell

exits the cell cycle and goes into G0, a

nondividing state.

Figure 12.15 A, B

The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases

Two types of regulatory proteins are involved in cell cycle control

Cyclins and cyclin-dependent kinases (Cdks)MPF

Cancer cells

Exhibit neither density-dependent inhibition nor anchorage dependence

25 m

Cancer cells do not exhibit

anchorage dependence or

density-dependent inhibition.

Cancer cells. Cancer cells usually

continue to divide well beyond a

single layer, forming a clump of

overlapping cells.

(b)

Figure 12.18 B

Loss of Cell Cycle Controls in Cancer Cells

Cancer cells

Do not respond normally to the bodys control mechanisms

Form tumors

Malignant tumors invade surrounding tissues and can metastasize

Exporting cancer cells to other parts of the body where they may form secondary tumors

Cancer cells invade

neighboring tissue.

2 A small percentage of

cancer cells may survive

and establish a new tumor

in another part of the body.

4Cancer cells spread

through lymph and

blood vessels to

other parts of the body.

3A tumor grows from a

single cancer cell.1

Tumor

Glandular

tissueCancer cell

Blood

vessel

Lymph

vessel

Metastatic

Tumor

Figure 12.19

Pembelahan Sel

1. Amitosis or direct cell division

2. Mitosis

3. Meiosis

AMITOSIS

Is the means of asexual reproduction

It happens in unicellular organisms like bacteria, yeast etc.

In this type the splitting of nucleus is followed by cytoplasmic constriction

Binary Fission

Prokaryotes (bacteria)

Reproduce by a type of cell division called binary fission

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

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

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Spindle

Metaphase

plate Nucleolus

forming

Cleavage

furrow

Nuclear

envelope

formingCentrosome at

one spindle pole

Daughter

chromosomes

Mitotic Division of an Animal Cell

Meiosis and Sexual Life Cycles

Living organisms are distinguished by their ability to reproduce their own kind

Heredity

Is the transmission of traits from one generation to the next

Variation

Shows that offspring differ somewhat in appearance from parents and siblings

Inheritance of Genes

Genes are segments of DNA, units of heredity

Offspring acquire genes from parents by inheriting chromosomes

Genetics is the scientific study of heredity and hereditary variation

Inheritance of Genes

Each gene in an organisms DNA has a specific locus on a certain chromosome

We inherit one set of chromosomes from our mother and one set from our father

Two parents give rise to offspring that have unique combinations of genes inherited from the two parents - sexual reproduction

Asexual Reproduction

In asexual reproduction, one parent produces genetically identical offspring by mitosis

Figure 13.2

Parent

Bud

0.5 mm

Sexual Reproduction Fertilization and meiosis alternate in sexual life cycles

A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism

Gametes

Diploid

multicellular

organism

Key

MEIOSIS FERTILIZATION

n

n

n

2n2nZygote

Haploid

Diploid

Mitosis

(a) Animals

Sex Cells - Gametes Unlike somatic cells, sperm and egg cells are

haploid cells, containing only one set of chromosomes

At sexual maturity the ovaries and testes produce haploid gametes by meiosis

Sexual Reproduction - The Human Life Cycle

During fertilization, sperm and ovum fuse forming a diploid zygote

The zygote develops into an adult organism

Haploid (n)

Diploid (2n)

Haploid gametes (n = 23)

Ovum (n)

Sperm

Cell (n)

MEIOSIS FERTILIZATION

Ovary Testis Diploid

zygote

(2n = 46)

Mitosis and

development

Multicellular diploid

adults (2n = 46)

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)

Meiosis

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.

Meiosis

Meiosis reduces the number of chromosome sets from diploid to haploid

Meiosis takes place in two sets of divisions

Meiosis I reduces the number of chromosomes from diploid to haploid

Meiosis II produces four haploid daughter cells

Figure 13.7

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

Meiosis Phases

Meiosis involves the same four phases seen in mitosis

prophasemetaphaseanaphasetelophase

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 interkinesisbecause the DNA is already duplicated.

Prophase I

Prophase I occupies more than 90% of the time required for meiosis

Chromosomes begin to condense

In synapsis, the 2 members of each homologous pair of chromosomes line up side-by-side, aligned gene by gene, to form a tetrad consisting of 4 chromatids

During synapsis, sometimes there is an exchange of homologous parts between non-sister chromatids. This exchange is called crossing over

Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred

Prophase I

of meiosis

Tetrad

Nonsister

chromatids

Chiasma,

site of

crossing

over

Metaphase I At metaphase I, tetrads line up at the metaphase plate, with one

chromosome facing each pole

Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad

Microtubules from the other pole are attached to the kinetochore of the other chromosome

Sisterchromatids

Chiasmata

Spindle

Centromere(with kinetochore)

Metaphaseplate

Homologouschromosomesseparate

Sister chromatidsremain attached

Microtubuleattached tokinetochore

Tetrad

PROPHASE I METAPHASE I ANAPHASE I

Homologous chromosomes

(red and blue) pair and

exchange segments; 2n = 6

in this example

Pairs of homologouschromosomes split up

Tetrads line up

Anaphase I

In anaphase I, pairs of homologous chromosomes separate

One chromosome moves toward each pole, guided by the spindle apparatus

Sister chromatids remain attached at the centromere and move as one unit toward the pole

Sisterchromatids

Chiasmata

Spindle

Centromere(with kinetochore)

Metaphaseplate

Homologouschromosomesseparate

Sister chromatidsremain attached

Microtubuleattached tokinetochore

Tetrad

PROPHASE I METAPHASE I ANAPHASE I

Homologous chromosomes

(red and blue) pair and

exchange segments; 2n = 6

in this example

Pairs of homologouschromosomes split up

Tetrads line up

Telophase I and Cytokinesis

In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids

Cytokinesis usually occurs simultaneously, forming two haploid daughter cells

In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms

No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated

Prophase II

Meiosis II is very similar to mitosis

In prophase II, a spindle apparatus forms

In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plate

Cleavagefurrow

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I AND

CYTOKINESISTELOPHASE II AND

CYTOKINESIS

Sister chromatidsseparate

Haploid daughter cellsforming

Metaphase II

At metaphase II, the sister chromatids are at the metaphase plate

Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical

The kinetochores of sister chromatids attach to microtubules extending from opposite poles

Cleavagefurrow

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I ANDCYTOKINESIS

TELOPHASE II ANDCYTOKINESIS

Sister chromatidsseparate

Haploid daughter cellsforming

Anaphase II

At anaphase II, the sister chromatids separate

The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles

Cleavagefurrow

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I AND

CYTOKINESISTELOPHASE II AND

CYTOKINESIS

Sister chromatidsseparate

Haploid daughter cellsforming

Telophase II and Cytokinesis

In telophase II, the chromosomes arrive at opposite poles

Nuclei form, and the chromosomes begin decondensing

Cytokinesis separates the cytoplasm

At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes

Each daughter cell is genetically distinct from the others and from the parent cell

Cleavagefurrow

PROPHASE II METAPHASE II ANAPHASE IITELOPHASE I ANDCYTOKINESIS

TELOPHASE II ANDCYTOKINESIS

Sister chromatidsseparate

Haploid daughter cellsforming

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

A Comparison Of Mitosis And Meiosis

Mitosis Meiosis

Tujuan: memperbanyak sel pada proses

pertumbuhan, mengganti sel rusak dan

reproduksi pada organisme bersel satu

Tujuan: mengurangi jumlah kromosom,

agar generasi berikutnya mempunyai

sel dengan jumlah kromosom tetap.

Tidak terjadi pertukaran genetik antara

kromosom-kromosom yang homolog

terjadi pertukaran genetik (pindah

silang) antara kromosom-kromosom

yang homolog

Terjadi pada sel tubuh, yaitu pada

proses pertumbuhan

Terjadi pada proses gametogenesis

(pembentukan sel gamet)

Sel yang melakukan pembelahan:

a. Sel haploid ( nn)

b. Sel diplodi (2n 2n)

Sel yang melakukan pembelahan:

Sel diploid 4 sel haploid

2n 2n n, n, n, n

Kandungan genetik sel-sel anakan

identik dengan sel induk

Kandungan genetik sel-sel anakan

berbeda satu sama lain dan berbeda

dengan sel induk

Comparison

Meiosis DNA

duplication followed by 2 cell divisions

Sysnapsis

Crossing-over

One diploid cell produces 4 haploid cells

Each new cell has a unique combination of genes

Mitosis

Homologous

chromosomes do not

pair up

No genetic exchange

between homologous

chromosomes

One diploid cell

produces 2 diploid

cells or one haploid

cell produces 2

haploid cells

New cells are

genetically identical to

original cell (except for

mutation)

Sexual Reproduction - The Human Life Cycle

During fertilization, sperm and ovum fuse forming a diploid zygote

The zygote develops into an adult organism

Haploid (n)Diploid (2n)

Haploid gametes (n = 23)

Ovum (n)

Sperm

Cell (n)

MEIOSIS FERTILIZATION

Ovary TestisDiploid

zygote

(2n = 46)

Mitosis and

development

Multicellular diploid

adults (2n = 46)

Spermatogenesis

Figure 27.8b, c

Oogenesis