Cell cycle

BHARAT INSTITUTE OF TECNOLOGY

Mr.B.CHAKRAPANI M.pharm (ph.D)ASSISTANT PROFESSOR

DEPARTMENT OF PHARMACOLOGY

MANGALAPALLY,IBRAHIMPATNAM(M), R.R Dist.

CELL

Cells

Tissues

Organs

Systems

Organism

Check points and the cell cycle

6-12 h

S G1

6-8 h

G2 M

3-4 h 1 h

Cell Cycle

G1

Cell Cycle

Eric Niederhoffer

SIU-SOM

G0

6-8 h

DNA, RNA, Protein

3-4 h

RNA, Protein

1 h

Mitosis, Cytokinesis

S

G2 Cyc D’sCDK4,6

Cyc B/ACDK1

Cyc ACDK2

M

Cyc ECDK2

6-12 h RNA, Protein

p53pRb

LaminH1Abl

Necrosis vs. Apoptosis

Principle Sites of Damage in Cell Injury

Direct Physical ActionMajor problems are hemorrhage & ischemia

Ionizing Radiation

Ionizes H2O into H+ & OH-

OH- attaches to DNA & prevents cell reproduction

DNA mutations

Toxic Molecular Injury

Dose related

Microbes

Toxins can interfere with protein synthesis or utilization of O2

Inflammatory & Immune Reactions

• Due to cell injury & then in turn causes injury

Stages in cellular response to stress and injurious stimuli

Cell reaction to stimuli

CELL CYCLE

G1 PHASE

G1 Phase– This is the phase in which the cell

spends almost all of its time. It is the normal phase of the cell. The cell is doing what ever that cell was

designed to do. For example: a skin cell would function as a skin

cell during G1 and a liver cell would function as a liver cell during G1.

S PHASE

S phase – the s phase is the phase during

which dna replication is occurring. Out of sight of most people’s ability to see, the

dna is undergoing replication so, at the end

of the s phase, there would be two complete

sets of dna in the nucleus of that cell. In the s phase the cell has copied the contents

of its nucleus

G2 PHASE

G2 Phase- In this phase, the cell makes copies of the important organelles found in the cytoplasm.

If a cell is going to divided, it needs enough mitochondria, (power plants) endoplasmic reticulum, (highways) and so on to support itself after cell division.

If there are not enough mitochondria in one of the new cells, that cell will die and the main purpose of cell division, to make two cells out of one cell, will be for nothing.

In G2 phase, the important organelles in the cytoplasm are copied to ensure that the two new cells will have enough organelles each to survive.

M-PHASE

M Phase- This phase is the phase during

which the nucleus divides into two nuclei.There are four parts to this phase;

1) PROPHASE,

2) METAPHASE,

3) ANAPHASE ,

4) TELOPHASE. At the end of the M Phase, there will temporarily

be a single cell with two nuclei.

PROPHASE

Prophase – Spindle fibers form, Chromosomes shorten, thicken and become visible (under a microscope) and the nuclear membrane begins to dissolve.

PROPHASE

METAPHASE

Spindle fibers move the chromosomes, which have their copies wrapped around themselves, to the middle of the nucleus and line them up.

ANAPHASE

Spindle fibers shorten and pull the identical chromosomes away from each other to the opposite side of the nucleus.

TELOPHASE

Spindle fibers dissolve, chromosomes lengthen out and become invisible again, nuclear membrane reforms around both sets of separated chromosomes.

CYTOKINESIS

The cytoplasm divides leaving you with two identical cells, each with one nucleus.

MEIO

SIS

FOR

MATIO

N

ETIOLOGY of Cell Injury

GENETIC CAUSES

ACQUIRED CAUSES

GENETIC CAUSES

THE GENETIC CAUSES OF VARIOUS DISEASES:

1. Developmental defects

2. Cytogenetic defects: chromosomal abnormalities

3. Single gene defects:Mendelian disorders

4. Multifactorial inheritance disorders

5. Other pediatric diseases

ACQUIRED CAUSES

1. HYPOXIA AND ISCHAEMIA

2. PHYSICAL AGENTS

3. CHEMICAL AGENTS AND DRUGS

4. MICROBIAL AGENTS

5. IMMUNOLOGIC AGENTS

6. NUTRITIONAL DERANGEMENTS

7. PHYCHOLOGICAL FACTORS

HYPOXIA AND ISCHAEMIA

Cells of different tissues essentially require oxygen to generate energy and perform metabolic functions.

Deficiency of oxygen or hypoxia results in failure to carry out these activates by the cells.

Hypoxia is the most common cause of cell injury.

HYPOXIA AND ISCHAEMIA

THE CAUSES OF HYPOXIA ARE AS UNDER:The most common mechanism of hypoxic cell

injury is by reduced supply of blood to cells .i.e. ischemia.

How ever , oxygen deprivation of tissues may result from other causes as well e.g: In anemia , carbon monoxide –poisoning, cardio respiratory in sufficiency, and increased demand of tissues.

All disease occurs because of cell injury

Either because of the injury itself or the repair process that follows

Mechanisms of Cell Injury

Ischemic injury

Principle Sites of Damage in Cell Injury

NECROSIS