BY: DR. JYOTISH KUMAR JHA

DEPARTMENT OF ORAL MEDICINE AND RADIOLOGY

CELL BIOLOGY

CONTENTS : Definition: Characteristics of cells: Structure of cells Structure of cell membrane: Applied physiology of cell membrane: 1)Cytoplasm: 2)Rough Endoplasmic Reticulum: 3)Smooth Endoplasmic Reticulum: 4)Golgi apparatus: 5)Lysosomes: 6)Perioxisomes:

7)Mitochondria : 8)Ribosomes: Nucleus Function of nucleus DNA RNA TRANSCRIPTION AND TRASNSLATION CELL DIVISION TYPES OF CELL DIVISION MITOSIS

CELL CYCLE DIFFERENCE BETWEEN MITOSIS AND

MEIOSIS LIST OF CHROMOSOMAL

ABNORMALITIES CHROMOSOMAL ABERRATION APOPTOSIS CELL JUNCTON VIRUS ENTRY TO CELL

TERM WAS COINED BY” ROBERT HOOK” (1635-1703)

DEFINED AS STRUCTURAL AND FUNCTIONAL UNIT OF LIFE

GENERAL CHARACTERISTICS OF CELL• Needs nutrition & oxygen• Eliminates carbon dioxide & other

metabolic wastes• Shows immediate response to the

entrance of invaders• Reproduces by division

STRUCTURE OF CELL

Each cell is formed by a cell body and a membrane covering the cell body known as cell membrane or plasma membrane

The cell body has two parts namely the nucleus and the cytoplasm surrounding the nucleus.

Thus the structure of a cell is studied under 3 headings…

I. Cell membraneII. CytoplasmIII. nucleus

CELL MEMBRANE

Protective sheath covering the cell body

Separates the fluid outside the cell called extracellular fluid(ECF) and the fluid inside the cell called intracellular fluid(ICF)

COMPOSITION OF CELL MEMBRANE 1. PROTEINS(55%)2. LIPIDS(40%)3. CARBOHYDRATES(5%)

STRUCTURE OF CELL MEMBRANE

THREE PROPSED MODELSW ARE

1. Danielli-Davson model

2. Unit membrane model

3. The fluid mosaic model

THE CELL MEMBANE is a three layered membrane.

MICROSCOPIC STUDY REVEALS

Central electron-lucent layer called LIPID LAYER formed by lipid protein

• MAJOR LIPIDS PRESENT ARE

1. PHOSPHOLIPIDS

2. CHOLESTROL

functional significance of this layer is that it forms a semi permeable membrane and allows only fat soluble substances to pass through ie oxygen, carbon dioxide &alcohol

2 electron-dense layer one on either side of central layer called PROTEIN LAYER formed by protein substances.

MAJOR PROTEIN PRESENT ARE

3. Integral Protein

4. Peripheral Protein

Functional significance of protein layer1. Integral protein provide the

structural integrity of cell membrane2. Channel protein- for diffusion of

water soluble substances like glucose and electrolyte

3. Carrier protein4. Receptor protein5. Antigen

APPLIED PHYSIOLOGY ON CELL MEMBRANE

LIPID soluble material in the ECE, when come in contact with cell membrane get dissolved in the oily cell membrane then enter the cytoplasm. Thus lipid soluble drugs easily pass the blood-brain barrier(BBB)

In the cell membrane of fungus ergosterol is present instead of cholestrol, drugs are present which get attached with ergosterol and damage them and thus the fungal cell membrane is damaged and last death

such drugs are AMPHOTERECIN B. AMB used against fungal infection

1. CYTOPLASM

ORGANELLES IN CYTOPLASM1. ENDOPLASMIC RETICULUM 2 TYPES rough endoplasmic reticulum smooth endoplasmic reticulum function of rough endoplasmic reticulum2. synthesis of protein3. degradation of worn out organelles function of smooth endoplasmic reticulum4. synthesis of lipids and steroids5. storage and metabolism of calcium6. degradation of toxic substances in liver

GOLGI APPARATUS1. present in all cells except red blood

cells2. has two faces or ends cis face and

trans face, cis face is close to endoplasmic reticulum and trans face near the cell membrane

function of golgi apparatus• processing, labelling and delivery of

proteins and lipids in different parts of cell

LYSOSOMES 1. membrane bound vesicular organelles

found throughout the cytoplasm 2. Formed by golgi apparatus3. Enzymes synthesized in RER are

processed and packed in the form of vesicles in the golgi apparatus

4. Then these vesicles are pinched off from golgi apparatus and become the lysosomes

TYPES OF LYSOSOMES1. PRIMARY LYSOSOMES -- one that is

pinched off from the golgi apparatus and is inactive

2. SECONDARY LYSOSOMES – a active lysosome formed by fusion of primary lysosome with phagosome or endosome

FUNCTION OF LYSOSOMES1. Degradation on macromolecules like

bacteria2. Degradation of worn out organelles 3. Secretory function

PEROXISOMES

FUNCTION OF PEROXISOMES1. Degradation of toxic substances like

hydrogen peroxide – present in liver cells which is a major organ for detoxification

2. Oxygen utilization3. Breakdown of excess fatty acids4. Acceleration of gluconeogenesis from fats5. Degradation of purin to uric acid6. Role in the formation of myelin and bile

acids

CENTROSOME AND CENTRIOLES

Situated near the centre of the cell close to the nucleus

Responsible for the movement of chromosomes during cell division

MITOCHONDRIA

Rod like oval structure Bilayered membranous organelle Outer membrane smooth and encloses the

contents of mitocondria Inner membrane folded in the form of shelf

called cristae Cristae contains many enzymes and other

protein molecules which are involved in respiration and synthesis of ATP

Move freely in cytoplasm and capable of self reproduction

FUNCTION OF MITOCONDRIA

Production of energy– called POWER HOUSE OF CELL – required for cellular function – produced during oxidation of digested food particles like proteins,crbohdrates and lipids

Synthesis of ATP apoptosis

RIBOSOMES

Granular and small dot like structure Made up of proteins(35%) and RNA(65%) FUNCTION OF RIBOSOMES SYNTHESIS OF PROTEIN mRNA passes genetic code for protein synthesis

from nucleus to ribosomeRibosomes arrange the amino acids into small

units of proteinRibosomes attached with ER are involved in

protein synthesis like enzymatic protein,harmonal protein and proteina of cell membrane

There are two types of cells:

1) Prokaryotic Cells

2) Eukaryotic Cells

These are two distinct types of cells with STRUCTURAL differences.

Traits of Prokaryotes: (pro-care-ee-ohts)

1. They do not have a nucleus, and their genetic material is not stored in the nucleus.

2. They have some organelles, but not many.

3. They are less complicated that eukaryotes.

4. All bacteria are prokaryotes.

Eukaryote CellA more complex cell with

a nucleus and many

organelles.

Traits of Eukaryotes: (you-care-ee-othts)

1. They all have a nucleus where the genetic material of the cell is stored.

2. They have many organelles that work together to help the cell function.

COMPARISON OF PLANT AND ANIMAL CELL

NUCLEUS

located near centre of cell and is mostly spherical in shape.

STRUCTURE OF NUCLEUS

Covered by nuclear membrane and it encloses the structures called nucleo plasm and nucleolus

NUCLEAR MEMBRANE

Double layered and porous in nature

Allows nucleoplasm to communicate with cytoplasm

NUCLEOPLASMGel like ground substance of the

nucleusContains large quantities of the

genetic materials in the form of deoxyribonucleic acid(DNA) which form the gene

DNA made of thread like material known as chromatin

NUCLEOLIo One or more nucleoli are present in

each nucleuso Nucleolus contains ribonucleic

acid(RNA) and some proteins similar to those found in ribosomes

FUNCTION OF NUCLEUS1. Control of all the activities of the

cell2. Synthesis of RNA3. Sending genetic instruction to the

cytoplasm for protein synthesis through mRNA

4. Control of cell division through genes

5. Storage of hereditary information

DNA Genetic information of an organism is stored

in genes of DNA DNA forms the chemical basis of hereditary

characters Carrier for genetic information to the

offspring Contains instruction for the synthesis of

proteins in the ribosome DNA present in nucleus is responsible for

synthesis of RNA

RNA Formed from DNA Regulates the synthesis of proteins in

the ribosome TYPES

I. MESSENGER RNA (mRNA) carries genetic code of amino acid

sequence for synthesis of protein from the DNA to cytoplasm

TRANSFER RNA(tRNA) Responsible for decoding the genetic

message present in mRNARIBOSOMAL RNA(rRNA) Present within ribosome and is

responsible for the assembly of proteins from amino acids in the ribosomes

TRANSCRIPTION Copying of genetic material from DNA to

RNA Transcription of genetic codes in nucleus formation of m RNA copying of message from DNA to m

RNA

m RNA enter the cytoplasm and

activate the ribosome for protein synthesis

TRANSLATION Process of protein synthesis in ribosomes ribosomes get attached to mRNA codons of mRNA recognized

by complimentary base of tRNA called anticodons

according to sequence of base of anticodon different amino acids transported from cytoplasm to ribosomes

rRNA assemble the proteins from amino acids and attach to RER

BINARY FUSIONBINARY

FUSIONBINARY FUSION

MITOSIS

MEIOSIS

The Cell Cycle

LIST OF CHROSOMAL ABNORMALITIES

NUMERICAL ABNORMALITIESa) Aneuploidyb) Trisomic(2n+1)c) Monosomic(2n-1) STRUCTURAL ABNORMALITIESa. DOWN’S SYNDROMEb. EDWARDS SYNDROMEc. PATAU’S SYNDROME

SEX CHROMOSOME DISORDER1) KLINEFELTER’S SYNDROME2) TURNER’S SYNDROME3) FRAGILE X SYNDROME

CHROMOSOME ABERRATION

Useful marker for radiation injury Observed in irradiated cells at the time of

mitosis when the DNA condenses to form chromosome

If radiation exposure occurs after DNA synthesis(ie in G2 or mid or late S) only one arm of affected chromosome is broken

If radiation occurs before DNA replication(ie in G1 or early S) then break in both the arms

APOPTOSIS

Defined as programmed cell death under genetic control

A normal phenomenon and in essential for normal development of the body

FUNCTIONAL SIGNIFICANCE Main function is to remove unwanted

cells without causing any stress or damage to the neighboring cells

SIGNIFICANCE1) Vital role in cellular homeostasis2) Useful for removal of a cell that is

damaged by a virus of a toxin beyond repair

3) Essential event during the development and in adult stage

ROLE OF MITOCONDRIA IN APOPTOSIS

external or internal stimuli initiate apoptosis by activating the proteases CASPASES

Normally caspases suppressed by apoptosis inhibiting factor(AIF)

WHEN CELL RECEIVE APOPTOSIS STIMULI… mitochondria release two proteins

1. CYTOCHROME C 2. SECOND MITOCONDRIA-DERIVED

ACTIVATOR OF CASPASES(SMAC)

SMAC inactivates AIF SMAC +AIF to form apoptosome

activates CASPASES CYTOCHROME C also facilitate

caspase activation

APOPTOTIC PROCESS

CELL JUNCTION

It is the connection between the neighboring cells

THREE TYPES1. OCCLUDING JUNCTION- prevent intercellular

exchange of substances

2. COMMUNICATING JUNCTION-permits intercellular exchange of substances

3. ANCHORING JUNCTION-provide strength to the cells

OCCLUDING JUNCTION prevent movement of ions and

molecule from one cell to another cell

TIGHT JUNCTION/ZONA OCCLUDENS belong to this category Present in the apical margin of

epithelial and endothelial cells in intestinal mucosa,walls of renal tubules,capillary wall

STRUCTURE OF TIGHT JUNCTION

FUNCTION OF TIGHT JUNCTION1. Holds the neighboring cell of tissues firmly

for strength and stability2. In epithelial and endothelial cells function

as selective diffusion barrier between neighboring cells

3. Prevents lateral movement of integral proteins and lipids in cell membrane

4. In brain capillaries form blood-brain barrier allowing only lipid soluble drugs and steroids to pass through