Lecture notes : cell biology summarize for viva examination

 

Cell biology :

Cell: it is the structural and functional unit living body

Types of cells

1.        Prokaryotic : no nucleus     2.Eukaryotic: have nucleus 

Cell components : Cell membrane, cytoplasm and nucleus

1.       Cytoplasm

•       Cytosole

•       Organelles : membranous and -non-membranous

•       Inclusion

2.       Nucleus

•          Nuclear membrane

•          Nucleolus

•          Nucleoplasm

•          Chromatin

 

Cell membrane : fluid mosaic model of cell membrane

•          The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.

•          Fluid mosaic model  is composed of –

1.        A phospholipid bilayer : polar:  hydrophilic head and   non-polar : hydrophobic tail)

2.       Cholesterol

3.       Two types of protein (  integral protein): some are partially embedded  , some are fully extended called transmembrane protein & peripheral proteins )

Carbohydrate : when attached to the phospholipids called glycolipid and when attached to the protein is called glycoprotein

 

Functions of cell membrane:

1. Forms the cell boundary 2. Ion and nutrient transport 3. Act as a site of receptors 4. Cell to cell adhesions

 

Exocytosis : It is the  process in which substances leave the cell

 

Endocytosis : It is the process in which substances enter the cell

Protoplasm is the content of the cell including the cell membrane, cytoplasm and the cell nucleus

 Cytoplasm is the jelly like substance surrounding the nucleus within the cell membrane. The cytoplasm contains the cell organelles like mitochondria, ribosomes etc

Cytosol: Part of the cytoplasm within which organelles are embedded. It contains many soluble protein, ions and metabolites

Organelles: They are sub-cellular elements, each of which performs a specific function that is essential for cell life

 Inclusion: Temporary , non living structure , consist of pigment granules, lipid droplets and glycogen 

Organelles are two types

 Membranous

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Mitochondria

Golgi complex

Lysosomes

Peroxisomes

Non-membranous

Microfilaments

Intermediate filaments

Microtubules

Centrioles

Ribosomes

Membranous organelles

Rough ER

It is the site of protein synthesis/  Modify newly synthesized protein

Smooth ER : lipid and steroid synthesis

Golgi complex post- translational modification, packages and places an address on product

Peroxisomes maintain the amount of H2O2 in the cell

Lysosomes

lysosomes digest, phagocytosed, microorganisms, cell debris, damaged or excessive cell organelles

The mitochondria are double membranous, elongated, rod shaped structures that vary in size, shape and number according to the function of the cells.

Structure: outward to inward

The outer mitochondrial membrane,

The intermembrane space (the space between the outer and inner membranes),

The inner mitochondrial membrane,

The cristae space (formed by infoldings of the inner membrane), and

The matrix (space within the inner membrane) contain mitochondrial DNA

function:

Synthesis ATP (also known as power house of cell)

Maintain body temperature

Non-membranous organelles

The cytoskeleton	It is a complex network of    -microtubules,    -microfilaments and    -intermediate filaments	•       Cell motility •       Cell adhesion •       Intracellular and extracellular transport •       Maintenance of cellular skeleton
Centriole	they are non-membranous, small, cylindrical structures formed by microtubules situated near the nucleus	•       Basal body formation •       Mitotic spindle formation
Ribosomes	They are non membranous, small, dark-staining granules .	Synthesis of protein by translating from m-RNA

Cell cycle

Cyclic changes of a cell involving interphase and mitosis is known as the cell cycle.

There are two stages of cell cycle

1.       Inter-phase : There are three phases of inter-phase

                                         -G1, S and G2 phase

2.       Mitosis

Interphase : The phase between two mitoses is called inter-phase

Phase	Duration	Synthesize
The G1 phase it began at the end of M phase	6-12 hrs	Growth of cell Formation of RNA and protein synthesis
S phase	it is about 7 to 10 hrs in duration	DNA synthesis
G2 phase	•          1hr	Preparation for mitosis Growth

	Duration
Mitosis	1 hr

G0: Some terminally differentiated cells leave the cell cycle after the M phase and enter Go phase

•       Example : neuron

            

Cell division: It is a process that increases the number of cells, permit renewal of cell populations and allows wound repair.  There are two types of cell division mitosis and meiosis

Difference between mitosis and meiosis

Topics	Mitosis	Meiosis
Occurs in	mitosis cell division increase number of somatic cells, immature germ cells	meiosis cell division produces mature germ cell
number of daughter cell produce after  division	2	4
chromosome number of daughter cells after cell division	Remain same diploid (46)	Reduces by half haploid (23)
identical / non-identical	identical (genetically same)	non-identical (genetically different)
one/ two division processes	one division process	two division process
cross over	not occurred	occurred
Pairing of homologus chromosome	Not occurred	Occurred
Function	Takes part in general growth and  healing and repair.	Takes part in the formation of gametes and maintenance of chromosome number.

Mitosis :  It is a process in which one parents cell produce two daughter cells, those are identical to that of the parent cell. The major purpose of mitosis is for growth and to replace worn out cells.

By mitosis, the number of somatic and immature germ cells ( oogonia  and spermatogonia) are increased

 

Prophase	Individualization of chromosomes
Metaphase	Chromosomes arranged in equatorial plane Disappearance of nuclear envelope and nucleolus
Anaphase	Longitudinal splitting of chromosomes
Telophase	Nuclear envelope and Nucleolar formation

Meiosis : It involves two cells division process in which one gamete cell produce four daughter cells, those are  non-identical containing half the number of chromosomes and half the DNA found in somatic cells

Meiosis division produces mature germ cells (ovum and spermatozoa )

Importance of meiosis: It keep the consistency of the chromosome number from generation to generation.

 recombination of genetic material is occurred in this cell division

 

Meiosis I: Prophase I
Leptotene	Pairing of homologous chromosome
Zygotene	Synapsis occurred (synapsis means the close association of homologous chromosomes )
Pachytene	Crossing over occurred (transposition of DNA stands between homologous pairs of chromosomes)
Diplotene	chiasmata formation (Homologous chromosomes  begins  to separate )
Diakinesis	The nucleolus and nuclear membrane disappears Spindle and asters formation
Metaphase I	Homologus chromosomes lie parallel to the equatorial plate
Anaphase I and Telophase I	Homologous chromosomes separate and moves to each pole and form two haploid cells (2n amount of DNA)
Meiosis II	Chromosomes of each cell are split longitudinally and moves to each pole of cell and formed two haploid cells (n amount of DNA )

Comparison between Meiosis in Males and Females

Topics	Meiosis in Males	Meiosis in Females
Definition	It is a continuous process which starts from puberty and remains throughout life.	This process may take over 40 years from start to finish.
Occurs at	Seminiferous tubules of the testicles	ovary
Name of immature cell	Primary spermatocyte	Primary oocyte
Chromosome number of immature cell	Diploid , 44 XY	Diploid, 44XX
Name of mature cell after meiotic division	Spermatozoa	Ovum
Chromosome number of mature cell	Haploid, 22X and 22Y	Haploid, 22X
Number of cells after meiotic division	4 gametes are form	Single ovum and three polar body
Time	Completed in days or weeks	Delayed for months or years
Cell Division	Symmetric	Asymmetric
Start time	Begins around puberty	Begins before birth

Comparison/ difference between Meiosis in Males and Females

general histology : Intercellular junctions

Intercellular junctions

These are several types of membrane modifications that present on the lateral membranes of many epithelial cells

Zonula occludens/ occluding or tight junctions

It forms a collar around each cell immediately beneath the cell surface( apical region).

It is impermeable limiting the movement of water & other molecules through the intercellular space

Zonula adherens

•          This junction encircles the cell and provides for the adhesion of one cell to its neighbor.

•          The intercellular space of zonula adherens contain a relatively electron-lucent material of unknown composition which forms a strong bond between the opposing membrane surfaces.

•          The cytoplasmic aspect of the membrane provides anchorage for the fine meshwork of microfilaments making up the terminal web

•          The terminal web: is a specialization of the actin cytoskeleton lying immediately beneath the cell surface.

Desmosomes

•      It is a disk-shaped structure at the surface of one cell that is matched with an identical structure  at the surface of the adjacent cell.

•      The cell membrane in this region are very straight and are frequently some what further apart.

•      Desmosomes numbers are greatest in stratified squamous epithelia, providing structural integrity at surfaces subject to considerable mechanical stress

Electron microscopic features of  gap junctions

•          Cell membranes of adjacent cells  are closely apposed

•          Connexon: individual unit of the gap junction

•          Connexins: each connexon is form by six gap junction protein, which join together leaving a hydrophilic pore

•          Location: any where along the lateral membranes of epithelial cells.

•          Function: creates a conduit between two adjacent cells for passage of small ions and informational micro molecules

•          It is found in nearly all mammalian tissues except skeleton muscle. Examples: cardiac muscle, embryonic epithelia

  

Histology slide : Summary of tissue preparation with mcq

 

Histology slide 

Tissue preparation

 Under the light microscope, tissues are examined via a light beam that is transmitted through the tissue. But the tissue and organs are usually too thick for light to pass through them. For this region tissues have to sectioned to obtain thin, translucent sections. Before making the histological slide tissue has to pass though some preparation processes. Following are the steps of tissue preparations of histological slide.

Steps of tissue preparation for study  

1. Selecting parts of tissue: part of an organ selected and cut. The best thickness are 3-5mm
2. Fixation: The process of avoiding tissue damage from bacteria or autolysis(cell digestion by cells own enzymes) by the help of some chemicals (fixatives) is called fixative. Name of fixatives: Formaline: Formaldehyde  is a gaseous substance but 40% of it soluble in water. In tissue prepation we uses  :10% formaldehyde(CH20) solution in water.
• Uses of formalin: used as a disinfectant or to preserve biological specimens.
•  Health hazards: short time exposure:  irritation of eye,skin, mucosa of nose and throat, it is  carcinogenic substance  but not teratogenic.
• Precurtion during use of formalin :
•  Exposure to mild formalin for 8 hrs /per day or 40 hrs in a week is safe. Formalin is not absorbed through skin so mild formalin can be handling for short time. After handling wash hand with soap and plenty of water for few min. For long term handling use gloves. Contamination of eye with formalin: wash eye with water for 15 min and consult with ophthalmologist.

Dehydration : after fixation, tissue must be dehydrate by graded series of ethanol and water, usually from the 70% to 100% 

Clearing : after dehydration, tissue must be clean with xylene.

3. Infiltration: after clearing  tissue must be infiltrate with paraffin.

 What is paraffin: for infiltration, tissue must place into a container containing liquid paraffin and place it  in an incubator at the temperature of 58-60 C  

4. After that tissue must be place in a cash for embedding or block formation
5. then sectioning with microtome : now block of the tissue cut by microtome ( a cutting instrument ) 
6. Staining: unfortunately tissues are colourless can not be observe in microscope. So need to be stain. For staining rehydration is necessary. Rehydration is done by graded ethanol and water from 100% to 70%.
7. In routine staining hematoxilin and eosin

Name of the staining and its components:

Basophilic : Tissue components that stain more with basic dye is called basophilic

Acidophilia : tissue components that stain more with acidic dye is called acidophilic

Colour of different components of tissue:

• nucleus light blue to  dark blue
• Cytoplasm and extra-cellular matrix  light pink to red 
7. Dehydration: after staining tissue need to be dehydrate again for long preservation.
8. Clearing: after dehydration tissue need to be clean with xylene. 
9. Amounting: DPX. This chemical place above the tissue and covered by coverslip for long term use.
10. Now a histological slide is ready for study.
11. (Write T for True and F for False)

12. 1.        Name the fixative which is used in histology

    i)                     40% formaldehyde

    ii)                   xylene

    iii)                 paraffin

    iv)                  osmium tetroxide

    v)                   DPX

    2.        Following are the disadvantage of formaline ?

    i)                     preservation of tissue

    ii)                   irritant of skin, mucosa of nose and throat

    iii)                 teratogenic( harmful for fetus)

    iv)                  carcinogenic

    v)                   disinfected

    3.        Following is/are the clearing agent/agents

    i)                     paraffin

    ii)                   formaline

    iii)                 alcohol

    iv)                  xylene

    v)                   eosin

    4.        Following instrument is/are used for cutting paraffin block.

    i)                     slide

    ii)                   knife

    iii)                 coverslip

    iv)                  microtome

    v)                   oven

    5.        Following staining are commonly used in histology lab

    i)                     silver stain

    ii)                    eosin stain

    iii)                 Giemsa stain

    iv)                  Azan stain

    v)                   Hematoxylin stain

    6.        Following statements are true

    i)                     formaldehyde is a gas , 40% of it soluble in water

    ii)                   plastic resins uses as embedding materials

    iii)                 mixture of alcohol and water from 70%-100% causes rehydration

    iv)                  tissue component with negative charge stain more with basic dye

    v)                   Exposure to mild formalin for 8 hrs /per day or 40 hrs in a week is safe.

    7.        Following are the sequence of tissue preparation

    i)                     embedding, fixation , clearing , infiltration

    ii)                   embedding, infiltration, clearing , fixation

    iii)                         fixation, dehydration, clearing, infiltration, embedding

    iv)                  fixation, rehydration, clearing, infiltration, embedding

    v)                   sectioning tissue, fixation, dehydration, clearing, infiltration, embedding

    8.        Following structures are stain blue in hematoxyline and eosin stain

    i)                     Nucleus

    ii)                   Cell membrane

    iii)                 Matrix of cartilage

    iv)                  Cytoplasm

    v)                   Collagen fibres

    9.           Following structures are stain pink  in hematoxyline and eosin stain

    i)                     cytoplasm

    ii)                   nucleus

    iii)                 nucleolus

    iv)                  collagen fibres

    v)                   mitochodria

    10.     Before amounting following steps are done

    i)                     clearing

    ii)                   rehydration

    iii)                 dehydration

    iv)                  tissue section covered by DPX

    v)                   tissue section covered by cover slip