Cell and Method Of Cell Study

• Cells are the smallest structural and functional unit if life.99% of its weight is made by carbon ,hydrogen, oxygen, phosphate and sulphur.
• The average human cell size is 5-50m.Ovum is the largest human cell wherease the neuron is the longest cell.
• Cells are fundamentally of two different types:

1. Eukaryotic

Nucleus= present
Cell division =Mitotic
Membrane bound organelles=present
Cell wall content= Sterol
DNA with histones= Present
Ribosomes= 40s+60s=80s.

1. Prokaryotic

Nucleus= Absent
Cell division =Binary Fission
Membrane bound organelles=absent
Cell wall content= Peptidoglycans
DNA with histones= absent
Ribosomes = 30s+50s = 70s

• light microscope is most commonly used for ye examination of histological sections by trans-illumination. It is bsed in the interaction of photons and tissues components. It has magnification of 1000-1500.
• Microtome is the instrument used to prepare thin selection for the histological studies.
• Electron microscope is based on interaction of electrons and tissue component.It has magnification of 4000,000-6000,000.The only electron microscope present in Nepal is TUTH.
• The resolving power of a microscope depends mainly on the quality of its objectives lens.The ocular lens only enlarges the image obtained by the objective.
• Fractional is thee process by which all cells organelles are separated from the cell.

Structure of the mammalian cell

1. Cell membrane(Plasma membrane)
2. Protoplasm-It includes Nucleus and Cytoplasm. 

        a.Nucleus: - Nuclear membrane, Nucleolus, Nucleoplasm, Chromatin.
        b.Cytoplasm has organelles and inclusion bodies

        

        Membranous Organelles: Mitchoondria, Endoplasmic recticulum, Golgi complex.

       Non-Membranous Organelles: Ribosomes, Centrosomes, Microfilaments, Micro-tubules.Cytoskeleton is formed         by micro-tubules and micro-filaments.

        Inclusion:  Glycogen, Fat globules, Pigments granules

Components of mammalian cell

1. Plasma membrane :

• Semi Permeable membrane
• Has 2 layers of phospholipids with some proteins embedded in it

Function:

• Maintains shape, holds cell together.
• Protects and prevents entry of harmful substances.
• Cell to cell communication
• Involves in immune response and neurotransmission

     2.  Endoplasmic recticulum(EndoSkeleton):

• It is made of network of tubules.it is of 2 typea.
• SER(Smooth ER)-It is ER without ribosomes on cell surface.
• RER(Rough ER)-It has ribosomes on the cell surface.

Function:

SER

• Steroid and lipt synthesis, Detixification.
• Sarcoplasmic recticulum is a type of SER that regulates calcium level.

RER  

• protein synthesis     

      3. Ribosomes:

• Spherical in shape and is made of proteins and RNA.

Function:

• Protein synthesis

     4. Golgi bodies:

• Are stack of flattened membrane sacs.

Function:

• Stores, modifies and packages secretion of cells
• syntheses of polysaccharides and hormones.

      5. Mitochondria:

• Double layer 
• Liver contain maximum number if mitochondria.
• Sperm molecules doesn't contribute mitochondria to Zygote.
• Cristae are minor or folds present in mitochondria.

Function:

• Power house of cell, ATP synthesis.
• Enzymes are present at different sites.
• Most of the kerbs's cycle enzymes in matrix.
• Respiratory chain,ATP production in inner
• mitochondrial membrane.
• lipid synthesis and fatty acid metabolism in outer mitochondrial membrane.

      5. Lysosomes:

•        Suicide bag (atom bomb of cells) 

Function:

• Contains hydrolytic enzymes that digest materials.

      6. Centroiles:

• Cylindrical structures made of micro-tubes

Function:

• Helps in cell division as they form the poles of nuclear spindle.

      7. Nucleolus:

•  Spherical structure compose of of RNA (t-RNA)protein
• Absent in sperm

Function:

• Protein synthesis
• t-RNA synthesis

      8. Microtubules:

• Made of protein tubulin

Function:

• Helps in movement of cell, like sperm tail, chromosomes movement in cell division.

      9. Microfilaments:

• Made of polymers of actin and myosin

Function:

• Movement and support

    10. Chromosomal material:

• Coiled stands of DNA and proteins.

Function:

• Controls protein synthesis and cell reproduction

Cell Cycle

• It is relation between mitosis / meiosis and inter-phase in tissues with cell turnover
• Depending on the type of cell it is variable.
• It is divided into mitosis and inter-phase.

Interphase

• The principle event is replication of chromosomal components.
• Nucleus attains its maximum size.
• It is a long phase and account for 90% of cell cycle.
• It is divided into three phases:-

     1. Facultivate/Stable cells: They don't divide for long time.Eg: Cells of liver,kidney & smooth muscle.

               2. Permanent cells: Cells that have completely lost the ability to divide.Eg: Nerve cell

               3. Labile cells: Cells that have divided continuously.Eg:Lymphoid and Epithelial cell.

Mitosis(Dividing Phase)

• It includes karyokinesis- division of nucleus & cytokinesis-division of cytoplasm.
• There are 4 phases of mitosis: Prophase, Metaphase, Anaphase, Telophase.
• Mitotic index: It is proportion of cells , in a tissue, which are inmitosis at a particular point of time.
• Colchicine inhibits microtubule assembly during metaphase of mitosis , which is used in karyotyping.
• Meiosis II is similar to mitosis whereas Meiosis I is a reduction division.Prophase of Meiosis I is divided into 5 phases as:

1. Leptotene - bouquet stage, beaded stage.
2. Zygotene - homologus chromosome fromation, synapsis
3. Pachytene - Tetrad formation
4. Diplotene - Chiasmata formation
5. Diakinesis - Terminalization