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