cell cycle

• OVERVIEW OF THE CELL CYCLE

• INTRACELLULAR CONTROL OF THE

CELL CYCLE

• EXTRACELLULAR CONTROL OF

CELL DIVISION AND CELL GROWTH

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FLOW OF DISCUSSION1.Overview of the cell cycle

a. G1phase

b. S phase Interphase

c. G2 phase

d. Mitosis phase

* prophase, metaphase, anaphase, telophase, * cytokinesis

Meiosis

2.Intracellular Control of the Cell Cycle

a. Positive: Cyclin- dependent kinase & Cyclins

b. Negative: Rb & p53

3. Extracellular Control of the Cell Cycle

a. Mitogens

b. Growth factors

c. Survival factors

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OVERVIEW: THE KEY ROLES OF CELL

DIVISION

The ability of organisms to reproduce best distinguishes

living things from non-living matter.

The continuity of life is based upon the reproduction of

cells, or cell division.

Cell division is integral part of cell cycle.

OVERVIEW OF THE CELL CYCLE

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CELL CYCLE:

INTERPHASE

Interphase includes:

• G1 Phase:

• S Phase:

• G2 Phase:

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INTERPHASE: G1 PHASE

• Recovery from previous division

• Cell doubles its organelles

• Cell grows in size

• Accumulates raw materials for DNA synthesis (DNA replication)

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INTERPHASE: S PHASE

• DNA replication

• Proteins associated with DNA are synthesized

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INTERPHASE: G2 PHASE

• Between DNA replication and onset of mitosis

• Cell synthesizes proteins necessary for division

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CELL CYCLE: MITOSIS PHASE

Mitosis phase includes:

• Mitosis (karyokinesis)

• Nuclear division

• Daughter chromosomes

distributed to two daughter

nuclei

• Cytokinesis

• Cytoplasm division

• Results in two genetically

identical daughter cells

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CELL CYCLE: MITOSIS PHASE

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SIGNIFICANCE OF MITOSIS

• Permits growth and repair.

• In plants it retains the ability to

divide throughout the life of the

plant

• In mammals, mitosis is necessary:

• Fertilized egg becomes an

embryo

• Embryo becomes a fetus

• Allows a cut to heal or a broken

bone to mend

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MITOSIS PHASE: PROPHASEWhat’s happening?

• Chromatin condenses.

• Centrosomes separate, moving to opposite ends of the nucleus

• The centrosomes start to form a framework used to separate the two sister chromatids called the mitotic spindle, that is made of microtubules

• Nucleolus disappears

• Nuclear envelope disintegrates

What the cell looks like?

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MITOSIS PHASE: PROMETAPHASE

What’s happening?

• Nuclear envelope fragments

• Chromosomes become more condensed

• A kinetochore is formed at the centromere, the point where the sister chromatids are attached

• Microtubules attach at the kinetochores


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MITOSIS PHASE: METAPHASE

What’s happening?

• Chromosomes align on

an axis called the

metaphase plate

• Note: the spindle

consists of

microtubules, one

attached to each

chromosome


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MITOSIS PHASE: ANAPHASE

What’s happening?

• Each centromere splits

making two chromatids

free

• Each chromatid moves

toward a pole

• Cell begins to elongate,

caused by microtubules

not associated with the

kinetochore


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MITOSIS PHASE: TELOPHASEWhat’s happening?

• Formation of nuclear membrane and nucleolus

• Short and thick chromosomes begin to elongate to form long and thin chromatin

• Formation of the cleavagefurrow - a shallow groove in the cell near the old metaphase plate

• Cytokinesis = division of the cytoplasm


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RESULTS OF MITOSIS

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• Two daughter nuclei

• Each with same chromosome number as parent cell ( 2n)

• Genetically identical to each other and the parent cell

MEIOSIS

• Formation of Gametes (Eggs & Sperm)

• Called Reduction- division

• Preceded by interphase which includes

chromosome replication

• Two meiotic divisions

• Meiosis I and Meiosis II

• Original cell is diploid (2n)

• Four daughter cells produced that are

haploid (n)

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SIGNIFICANCE OF MEIOSIS

• Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

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SIGNIFICANCE OF MEIOSIS

• Meiosis must reduce the chromosome number by half

• Fertilization then restores the 2n number

from mom from dad child

meiosis reduces

genetic content

Too

much!

The

right

number!fatimaArivera

MEIOSIS I: PROPHASE I

Prophase I is further subdivided into

periods known as

•Leptotena

•Zygotena

•Pachytena

•Diplotena

•Diakinesis

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A physical exchange of

chromosome pieces

PROPHASE I

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METAPHASE I

Homologous pairs

of chromosomes

align along the

equator of the cell

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ANAPHASE I

Homologs separate and

move to opposite poles.

Sister chromatids remain

attached at their centromeres.

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TELOPHASE I

Nuclear envelopes

reassemble.

Spindle disappears.

Cytokinesis divides cell into

two.

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MEIOSIS II: PROPHASE II

Nuclear envelope

fragments.

Spindle forms.

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MEIOSIS II: METAPHASE II

Chromosomes align

along equator of cell.

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MEIOSIS II: ANAPHASE II

Sister chromatids

separate and move

to opposite poles.

Equator

Pole

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MEIOSIS II: TELOPHASE II

Nuclear envelope

assembles.

Chromosomes

decondense.

Spindle disappears.

Cytokinesis divides cell

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RESULTS OF MEIOSIS

• Four haploid cells with one

copy of each chromosome

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SUMMARY OF MEIOSIS I

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NucleusSpindle

fibersNuclear

envelope

EARLY

PROPHASE

I

LATE PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I &

CYTOKINESIS

SUMMARY OF MEIOSIS II

Prophase II Metaphase II Anaphase II Telophase II 4 I

Undentical

haploid

cellsfatimaArivera

Mitosis Meiosis

Number of

divisions1 2

Number of

daughter cells2 4

Genetically

identical?Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Germ cells

When Throughout life At sexual maturity

Role Growth and repair Sexual reproduction

COMPARISON OF DIVISIONS

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ANIMATION

FLOW OF DISCUSSION1.Overview of the cell cycle

a. G1phase


c. G2 phase

d. Mitosis phase


Meiosis





a. Mitogens

b. Growth factors

c. Survival factors

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Intracellular control of the cell

cycle

The cell cycle is controlled by

regulator molecules that either:

promote the process (positive)

stop it from progressing (negative)

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Positive: Cdks & Cyclins

Cyclins◦ The regulatory subunits of the protein

kinases that control the cell cycle

Cyclin-Dependent Kinases (Cdks)◦ The catalytic subunits of the protein

kinases

◦ Must be associated with a cyclin in order to be activated

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https://www.boundless.com/biology/cell-reproduction/control-of-the-cell-cycle/regulator-molecules-of-the-cell-cycle/images/fig-ch10_03_03/


Negative: Rb & p53

Tumor suppressor genes

Tumor suppressor gene codes for a

signaling protein in an inhibitory

pathway. If a tumor suppressor gene

mutates, the end result can be

active cell division.

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Negative: Rb & p53

◦ Retinoblastoma protein(Rb)

◦ prevents cell moving into S phase by

binding to a transcription factor

◦ When Rb is phosphorylated it cannot bind

so cell can move into S phase

◦ p53

◦ prevents damaged from dividing (by

inhibiting Rb pathway)

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Retinoblastoma protein (Rb)

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Rb halts the cell cycle by binding E2F. Rb releases its hold on E2F in

response to cell growth to advance the cell cycle.

• group of tumor-suppressor proteins



p53

p53 protein halts cell division if it detects

damaged DNA

options:

stimulates repair enzymes to fix DNA

forces cell into G0 resting stage

keeps cell in G1 arrest

causes apoptosis of damaged cell

ALL cancers have to shut down p53 activity

Cancer is essentially a failure of cell division

control

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p53 is theCell CycleEnforcer

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Major molecule players in the

cell cycle control

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Cyclin-dependent

kinases (Cdks)Cyclins

Cdk-cyclin complexP

regulatory proteinsphosphorylates cellular proteins

triggers passage through different stages of cell cycle

Generic cell cycle checkpoints

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Is environment favorable?

Is environment favorable?

Are all DNA replicated?Are all chromosomes

attached to the spindle?

The Cell Cycle_ Cyclins and Checkpoints.mp4

G1

S

G2M

G1 CheckpointG2 CheckpointM Checkpoint

G1 Cdk

G1 Cyclin

PActive G1 Cdk-Cyclin

• Growth factors• Nutritional state of cell• Size of cell

Degraded G1 Cyclin

Mitotic Cdk

Mitotic Cyclin

PActive Mitotic Cdk-Cyclin(MPF)

• Replication completed• DNA integrity

APC

Chromosomes attached at metaphase plate

Degraded Mitotic Cyclin

Control of the Cell Cycle

Control of the Cell Cycle.mp4

FLOW OF DISCUSSION

1.Overview of the cell cycle

a. G1phase


c. G2 phase

d. Mitosis phase


Meiosis





a. Mitogens

b. Growth factors

c. Survival factors

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EXTRACELLULAR CONTROL OF THE CELL

DIVISION AND CELL GROWTH

• What regulates cell size and cell

number?

• Regulated by extracellular signals

Mitogens stimulate cell division (PDGF)

• Growth factors • stimulate cell growth

• Survival Factors • inhibit apoptosis

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MITOGEN:

PLATELET DERIVED GROWTH FACTOR

PDGF is released by platelets in at the site of a wound

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GROWTH FACTORS

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• A signal transduction through phosphatidylinositol pathway

• Kinase cascade leads to increased translation

• Some factors stimulate both growth and cell cycle progression

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protein signals released by body

cells that stimulate other cells to

divide

density-dependent inhibition

crowded cells stop dividing

each cell binds a bit of growth factor

not enough activator left to trigger

division in any one cell

anchorage dependence

to divide cells must be attached to a

substrate

“touch sensor” receptors

GROWTH FACTORS

NORMAL CELLS NEED BOTH MITOGENS AND

“ANCHORAGE”- TO ENTER A NEW CELL

CYCLE

NERVE GROWTH FACTORS

CAN INFLUENCE BOTH

RATE AND DIRECTION OF

GROWTH

SURVIVAL FACTOR: MYOSTATIN• Myostatins are inhibitory factors that inhibit the proliferation of

myoblast that fuse to form skeletal muscle cells.

• Myostatin Mutants decrease apoptosis in muscle tissue

THANK YOU!

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cell cycle

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