Cell Organelles and Their Functions

Introduction
Genetics: the science, which deals with the principles of heredity and variation.
Heredity: transmission of characters from parents to their off spring.
Variation: Differences for various characters among the individuals of the same species.
Types of variation: 1. Environmental and 2. Hereditary
1. Heredity variation: Variation observed among the individuals of the same species due to difference in their genetic constitution is termed as heredity variation.
2. Environmental variation: Two individuals with the same genotype may become different in phenotype when they come into contact with different conditions of food, temp., light, humidity and other external factors. Such differences among organisms of same heredity are called as an environmental variation.
Environment: can be defined as sum total of an external conditions which influence on organism.
Plant genetics: A branch of genetics, which deals with inheritance and variation of characters in plant species.
Cytology: cytology may be defined as that branch of science, which deals with the morphology and physiology of the cell.
Cytogenetics: Combined study of cytology and genetics.
History Events (cytology and Genetics)

|Year |Events |
|1665 |R. Hooke – Introduced the term “cell” |
|1830 |J. E. Purkinje– Introduced the term “protoplasm” |
|1833 |Brown discovered the cell nucleus in flowering plant Tredescantia |
|1834 |Von Mohl described cell division and emphasized the importance of protoplasm |
|1838 |M. J. Schleiden – cell concept in plants |
|1839 |T. Schwann applied the cell concept to animals |
|1846 |K. Nageli showed that plant cells arise from the division of pre-existing cells |
|1855 |R. Virchow – confirmed the principle that cell arise only from pre-existing cells. (Omnis cellula e cellula) |
|1865 |G. Mendel (1822-1884) developed the fundamental principles of heredity. |
| |“Father of Genetics” |
|1882 |W. Fleming – proposed the term meiosis |
|1888 |W. Waldeyer – introduced the term chromosome |
| |Strasburger showed that the chromosome number is halved in the cell when gametes are formed |
|1892 |A. Weismann – Germplasm theory |
|1900 |Karl Correns, Hugo de Vries and E. Tschermak rediscovered the fundamental principles of heredity |
|1902 |Mc - Clung identified the sex – chromosome in Hemiptera |
| |W. S. Sutton showed significance of reduction division; proposed the chromosome theory of heredity |
|1905 |Farmer coined the term meiosis with J. E. Moore |
|1906 |Bateson coined the term “Genetics” |
|1909 |Johannsen coined the terms Gene, Genotypes and Phenotypes |
|1915 |T. H. Morgan – correlated genetic studies with cytological studies in Drosophila |
|1927 |Muller studied the mutation through X – rays in animals |
|1932 |Knoll and Ruska produced one of first electron microscope |
|1946 |Muller received the Noble Prize for radiation genetics work |
|1953 |Watson and Crick proposed a model for the DNA molecules |
|1958 |Beadle, Tatum and Lederberg received the Noble Prize for in field of Genetics |
|1959 |Sanger received the Noble Prize for determination of amino acid sequence in insulin |
| |Ochoa received the Noble Prize for the in vitro synthesis of polyribonucleotides |
|1959 |Kornberg received the Noble Prize for the in vitro synthesis of polydeoxy ribonucleotides |
|1962 |Watson and Crick with Wilkins received the Noble Prize for their model of the DNA molecule |
|1965 |Lwoff, Monod and Jacob received the Noble Prize for the concept of mRNA; Operon and episomes |
|1968 |Holley, Khorana and Nirenberg received the Noble Prize for the delineation of the genetic code and molecular |
| |mechanisms of protein synthesis |
Structural differences between Eukaryotic and Prokaryotic cells

| |Prokaryotic cell |Eukaryotic cell |
|1. |Nucleus is absent and not surrounded by membrane |The nucleus is enclosed by two concentric unit membrane |
|2. |DNA is naked and not complex with histones |DNA is complex with histone and non-histone protein to form |
| | |chromatin fibers |
|3. |The amount of DNA per cell is small fraction |The amount of DNA per cell is many fold greater |
|4. |Cytoplasm does not have E. R. and other except |Cytoplasm contains several membranous structures e.g. E.R., |
| |chromatophores in photosynthetic bacteria and blue green algae|golgi bodies, lysosomes etc. |
|5. |Mitochondria and chloroplast absent but algae have chloroplast|Cells contain mitochondria and chloroplast with grana |
| |without grana | |
|6. |Spindle fibers are absent |During cell division spindle fibers organized |
|7. |Chromosomes are attached to plasma lemma |Chromosomes ends are attached with the nuclear membrane |
|8. |All ribosomes are free in the cytoplasm |Most of the ribosomes are attached to E.R. and some are free |
| | |in cytoplasm |
|9. |Nucleolus is absent |Nucleolus is present in the nucleus |

Differentiate between Plant Cells and Animal Cells

| |Plant cells |Animal cells |
|1. |Cell wall present. |Cell wall absent |
|2. |Chloroplasts present. |Chloroplasts absent. |
|3. |Plastids occur in cytoplasm. |Plastids are absent. |
|4. |Centrioles present only in cells of lower plant forms. |Centrioles are present. |
|5. |Large vacuoles filled with cell sap. |Vacuoles, if present are small and contractile or temporary |
| | |vesicles. |

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PLANT CELL

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ANIMAL CELL

CELL STRUCTURE AND ORGANELLES

Cell: A basic unit of structure and function in all living organisms.
Plant cell: A structural and physiological unit of plant, which have protoplasm.
Cell organelles: various bound structures that are found within a cell such as nucleus, plastids, mitochondria, endoplasmic reticulum, etc.,

CELL

Non-living inclusions Living materials

Nucleus Cytoplasm 1. Nuclear membrane 1. Plasma-membrane 2. Nucleoplasm 2. Endoplasmic reticulum 3. Chromatin 3. Ribosomes 4. Nucleolus 4. Golgi body 5. Vacuoles 6. Mitochondria 7. Plastids 8. Lysosomes 9. Centrosomes 10. Microtubules

Cell wall: ▪ It is the outermost part of the cell and is always non-living (Rigid and Strong) though produced and maintained by living protoplasm. ▪ The cell wall is found only in plants and absent in animals.
Functions:
1. To protect inner parts of cell. 2. To give a definite shape of the cell. 3. To provide mechanical support.
Plasma lemma OR Plama membrane: • The cytoplasm is surrounded on the outer side by a thin and flexible membrane. • It presents both in plant and animal cell. • Composed of lipids and proteins.
Functions:
1. It regulates the passage in and out of the cell. 2. It acts as a selectively permeable membrane. 3. It checks the entry of toxic elements from out side into the cytoplasm. 4. It permits only passage for molecules like minerals into the cell and restricts their outward movement.
Protoplasm:
➢ The substances that provide life- plants/animals. ➢ It is granular, semi fluid –translucent. ➢ Protoplasm is differentiated into Cytoplasm and Nucleus.
Cytoplasm:
➢ There are a variety of structure remain suspended such as living and non-living. ➢ Non-living: not membrane bounded – lipid drops, starch granules. ➢ Living: they are membrane bounded.
Cytoplasmic inclusions (Non-living): ➢ These are not metabolic active parts but they are storage sites of end product. ➢ Suspended in cytoplasmic matrix ➢ It includes oil drops, yolk granules, pigments, starch granules etc.

Cytoplsmic organelles: ➢ Organells are membrane bounded, living structures ➢ They performed important activities like biosynthesis, metabolic and respiratory ➢ They are also engaged in transportation and storage of food material and reproduction
Microtubules:
➢ Complex structure made up of 13 individual protofilaments arrange to form hallow cylinder ➢ Transportation of small molecules produce fibres during cell division
Endoplasmic Reticulum (E.R.): ➢ The term E. R. was first used by Porter in 1948 to describe a fine Reticulum in the endoplasmic cells. ➢ It is thread or tube like- floating in cytoplasm on which ribosomes are attached.
Two Types:
1. Smooth E. R.: ➢ Outer and inner surfaces are regular and they do not have attached ribosome, no protein synthesis.
2. Rough E. R.: ➢ Outer and inner membrane found attached with ribosomes ➢ It actively involved in protein synthesis. ➢ Rough and Smooth ER change into each other as per needs of cells.
Functions:
1. It is associated with or base for the synthesis of proteins (rough ER), lipids and phospholipids (both ER) 2. Provide channel for the transportation of synthesized material to various parts 3. Provide controlled passage for the export of m-RNA from nucleus to rough ER 4. Several enzymes are embedded in the membrane e.g. glucose-6-phosphate, ATPase etc.
Golgi complex: ➢ Golgi complex was first describing Camilo Golgi in 1822 in nerve cells of cat and owl ➢ A structure like stalk of filament arranged one above the other ➢ Composed – lamellae, tubules, vesicles and vacuoles
Function:
1. Packaging of food materials such as proteins, lipids and phospholipids for transport to other cells. 2. It secrete many granules and lysosomes (originated from golgibodies).
Lysosomes:
➢ The term Lysosome was first used by Dave in 1955 ➢ In plant cell they are bounded storage granules and contain hydrolylic digestive enzymes
Function:
➢ Digestion of intracellular substances and foreign particles, which comes in the cell by pinocytosis and phagocytosis.
Cytoplasmic Vacuoles: ➢ Small or large sized liquid filled structure ➢ More in number and large size in plant cell ➢ The vacuoles of plant cells are bounded by single, semi-permiable membrane known as tonoplast
Function:
1. Storage and transmission of the materials and maintenance of internal pressure. 2. It contains water, phenol, alkloids, pigment salts and other secretory products.
Ribosomes:
They are small organelles- composed of RNA + Protein that play vital roe in protein synthesis
Three kinds of ribosomes: Each ribosome is composed of two structural units 1. Mitochondrion – 70s 2. Chloroplastic – 70s 3. Cytoplasmic – 80s s = sedimentation co-efficient, Sved berg units ➢ They remain attached with the membrane of ER by the 60s subunits ➢ They are the site of protein synthesis
Function: To carry out protein synthesis with the help of m-RNA

Mitochondria: ➢ They are cylindrical bodies, rod like structure or spherical granules lying free in cytoplasm ➢ Randomly distributed throughout cytoplasm ➢ They are bounded by two membranes of lipo-proteins ➢ They arise by fission of pre-existing mitochondria, on an average cell may have 200-800 mitochondria
Function:
1. It involved in respiration, oxidation of food (carbohydrates, amino acids and fatty acids) and metabolism of energy (powerhouse of cell) 2. They contain circular DNA molecules and ribosomes so they are capable of synthesis of certain proteins 3. Since they contain DNA, they contribute to heredity by way of cytoplasmic inheritance
Plastids:
Plastids are highly specialized living protoplasmic bodies of the cytoplasm
They may be coloured or colourless 1. Leucoplasts – colourless 2. Chromoplasts – coloured but other than green viz., plucoxanthin, phycocyanin – Function not known 3. Chloroplasts – coloured
The plastids are associated with the formation of starch, chlorophyll and other cytoplasmic products
Leucoplasts:
➢ Colourless, in storage, roots, underground stems ➢ Function: Store starch and lipids, Sugar convert into starch
Chloroplasts:
➢ They are green in coloured due to chlorophyll, found in plant parts which are exposed to the light ➢ The contain DNA, Ribosome and complete protein synthetic machinery
Function: Photosynthesis
Chromoplasts:
➢ They contain pigments of different colour – yellow, orange and red. ➢ Present in petals of flowers and fruits ➢ The colouring matter associated with them are Xanthophyll and Carotene
Nucleus and it’s structure:
Nucleus:
➢ The nucleus was first discovered by Robert Brown in 1833, since nucleus contains chromosomes of genes is called as controlling center of the cell ➢ The organelle containing chromosomes and nucleolus and surrounded by a typical nuclear envelope composed of two concentric membranes ➢ Usually spherical or oval shape ➢ Larger in active cell than in resting cells ➢ Store house of almost all the genetic information
It consists of four structures: 1. Nuclear membrane 2. Nucleoplasm (karyolimph) 3. Nuclear reticulum (chromatin) 4. Nucleous
1. Nuclear Membrane: ➢ Nucleus is enclosed by two membranes of lipo-proteins, which separated nucleus from cytoplasm and membranes are not continuous but they are broken at several places is known as nuclear pores ➢ Space between two nuclear membrane is known as peri nuclear space ➢ Outer membrane is attached with ER on which ribosomes are present
Function:
1. It facilitates and regulates nucleo-cytoplasmic interaction 2. The nuclear pores regulate the exchange of micro molecules i.e. protein, r-RNA, m-RNA etc.

2. Nucleoplasm: ➢ The watery substances in higher nucleolus and chromatin are present which is surrounded by nuclear membrane is called Nucleoplasm or Nuclear sap or Karyolymph ➢ It is shapeless contains dissolved phosphorus ribose sugar proteins nucleotides and had nucleic acids
3. Nucleolus: ➢ In higher organisms, every cell nucleus has a spherical, darkly stained colloidal body, which can be easily seen and generally disappear during cell division ➢ It is associated with a particular nucleolar organizing chromosome ➢ Chemically, it is composed of large amount of ribosomal proteins and ribosomal RNA
Functions:
1. Biogenesis of ribosomes 2. Stores all proteins of ribosomes 3. Provide energy for nuclear activities
4. Nuclear Reticulum (chromatin fibers): ➢ Nucleoplasm contains many thread like, coiled and much elongated structures ➢ During cell division – mitosis and meiosis – chromatin fibers becomes thick ribbon like structure which are known as chromosomes
Function:
1. Chromatin fibers are the basic unit 2. They are also fundamental basis of inheritance since they contain the genetic material
On the basis of stainability Cohn (1964) classified chromatin in two parts: 1. Heterochromatin 2. Euchromatin