Chromosome (girja pd. patel)

Chromosome-structure and function

1. K . G . ART’S & SCIENCE COLLEGE RAIGARH ( C . G .) Session - 2019-20 Deparment of Zoology & Research Center Subject :- Molecular and Cell Biology. Seminar topic :- Chromosome. Guided by Submitted by Proff. Anita Pandey mam . Girja Prasad Patel M.Sc. I Sem. Zoology

2. CHROMOSOME SYNOPSIS :- Introduction. Definition. History of Chromosome. Morphology of Chromosome. Prokaryotic & Eukaryotic Chromosome. Structure of Chromosome. Region of Chromosome. Types of Chromosome. Composition of Chromosome. Model of Chromosome. Function of Chromosome. Conclusion. Reference.

3. 1. INTRODUCTION :- “Chromosome ” is a combination of two words i.e. Greek “ Chroma ” = colour and “ Soma ”= body. A Chromosome is thread-like, self-replicating genetic structure is called “ Chromosome ”. It made up of proteins and a molecule of DNA (Deoxyriboribo nucleic acid). It is located inside the nucleus. Only visible during Cell division. Chromosome are seen during metaphase stage of mitosis when the cells are stained with suitable dye and viewed under light microscope. Chromosomes are the vehicle of heridity means they are passed on from parents to offspring.

4. 2. DEFINITION :- Chromosome is the main part of the living cells which control all activity and heridity function of cell that are called Chromosome . 3. HISTORY OF CHROMOSOME :- W. Hofmeister (1848) First discovered chromosome in the dividing pollen mother cells. Strasburger (1875) First observed chromosome during cell division. Waldeyer (1888) The term chromosome however was first used .

5. 4. MORPHOLOGY OF CHROMOSOME :- Mitotic metaphase is the most suitable stage for studies on chromosome morphology. The number of chromosomes varies from species to species. Generally the chromosomes are arranged in pairs. A pair of similar chromosome is called homologous Chromosome . The size of chromosomes range 0.1 micron to 30 microns The diameter varies from 0.2micron to 2 micron in general plant have larger chromosome than animals. The length of the human Chromosome from 4 micron to 6 microns.

6. SHAPE OF CHROMOSOME :- The shape of the chromosomes is changeable from phase to phase in continuous process of the cell growth and cell division. Chromosome contain clear zone, known as “ Centromere ” or “ Kinetochore ” along their length. Centromere divide’s the chromosome into two parts, each part is called “ Chromosome arm ”. The position of centromere varies from chromosome to chromosome and it provides different shapes to the chromosome.

7. 5. PROKARYOTIC & EUKARYOTIC CHROMOSOME :- PROKARYOTIC CHROMOSOME :- Found in cytoplasm. Circular chromosome. Single chromosome + plasmid. Made up of only DNA. Copies it’s chromosomes and divideds immediately.

8. EUKARYOTIC CHROMOSOME :- Found ie nucleus. Linear chromosomes. Many chromosome usually 10-50 chromosome in somatic cells. Made up DNA, Histone proteins. Copies it’s chromosome grows cell and then divides equally through mitosis.

9. 6. STRUCTURE OF CHROMOSOME :- The detail structure of chromosome varies from cell to cell major changes are associated with cell division. It is a prominent structure during prophase of cell division. Each chromosome contains one DNA Molecule. The DNA is coiled tightly around proteins called Histone. These protein structural support to a Chromosomes and allow the very long DNA molecule to form a compact shape and fit inside the nucleus of a cell. A.) Pellicle & Matrix :- Each chromosome is bounded by a membrane called “Pellicle”. It is very thin and is formed of achromatic substance. This membrane encloses a jelly like substance which is usually called Matrix. In the matrix is present the chromonemata. The matrix is also formed of achromatic or nongenic material.

10. B.) Chromonemata :- with in the matrix of each chromosome are found embedded two identical spirally coiled threads the Chromonemata or chromonemated fibrils. Both Chromonemata are so tightly coiled that they appear as a single thread of about 800 A° thickness.. C.) Chromomere :- during interphase , some bead like structure are found along the length of the chromosomes which are called Chromomere. These are actually accumulated chromatin material and tightly folded regions of DNA. D.) Centromere :- Centromere is the chromosomal region that hold sister chromatid together. The Centromere contain complex system of fibers called kinatochore . Each centromere contain two kinatochore lined with chromosomal arms. Also termed as primary constriction . Darkly stained region.

11. In humans the centromere contains 1-10 million base pair of DNA. Kinetochore are made up of protein fiber and microtibules which asist in the formation of spindle during mitosis and meiosis. E.) Arm’s :- Each chromosome has two arms labeled “p” (the shorter of the two) and “q” (the longer arm). The “p” arm is named for “ pelit ” meaning “ short ”. The “q” arm is named to French word “ queue ” meaning “ tail ”. Two arm divided at cemtromere. They can be connected in either metacentric,sub-metacentric, acrocemtric, telocentric manner. F.) Constriction :- A typical chromosome has narrow called “Constriction”. They are two types of constriction namely – primary constriction and secondary constriction.

12. Primary constriction :- is made of centromere and kinetochore . The shape of the chromosomes is determined by the primary constriction situated at the meeting point of the arms of the chromosomes. Secondary constriction :- is a darkly stained constricted area. It is associated with the formation of nucleolus. So they are refer as “ nucleolar organizer ” . G.) Satellite region :- The part of the chromosome which is present beyond the secondary constriction is called “ satellite region ” or “ trabant ”. The varies in size according to the position of the secondary constriction. If secondary constriction is very close to an end of the chromosome the satellite may be a baiely perceptible dot. The chromosome having satellite is called “ Sat Chromosome”.

13. H.) Telomere :- Derived from the greek nouns “ telos ” = end and “ meros ” = part . The ends of a chromosome are called “ Telomere ”. They play critical roles in chromosome replication and maintainance of chromosomal length. The telomere are highly stable and telomere of different chromosomes do not fuse . 7. REGION OF CHROMOSOME :- (1.) HETEROCHROMATIN :- Darkly stained due to which it is called “ Heterochromatin ”. At that region chromatin fold it self forming a highly condensed structure. Largely transcriptionally inactive preventing gene expression due to its tightly packing.

14. (2.) EUCHROMATIN :- Lightly stained as they are loosely packed regions. It is transcriptionally active allowing expression. 92% of human genome consists of euchromatin. 8. TYPES OF CHROMOSOME :- A.) AUTOSOME & ALLOSOME OR SEX CHROMOSOME :- AUTOSOME :- These are present in all cells of all organism. Autosome that are the same size (structure) are called homologous. In human there are 22 pairs of chromosome. ALLOSOME OR SEX CHROMOSOME :- Chromosome that are connected with the determination of sex are called sex chromosome.

15. Allosome are non-homologous. There are two types of sex chromosome ‘ X ’ and ‘Y ’. ‘X’- chromosome is found in both male and female. ‘ Y ’-chromosome is found in only male. In human last one pair (23 rd pair) of chromosome is sex chromosome.

16. B.) BASED ON THE POSITION OF THE CENTROMERE :- 1.) Metecentric :- these chromosome are V-shaped. they have arms equal in length having cemtromere in the center. Exa . Human chromosome 1&3. 2.) Sub - Metecentric :- these chromosome are L-shaped. they have arms unequal in length. Exa . Human chromosome 4-12. 3.) Acrocentric :- the chromosome are J-shaped. these is rod-like chromosome. having a very small arm and a very long arm. having centromere severaly offset from center leading. Exa . Human chromosome 13,15,21,22.

17. 4.) Telocentric :- the chromosome are I-shaped. having centromere at very end of chromosome. human don’t have this type of chromosome but found in other species like mice.

18. C.) BASED ON THE NUMBER OF CENTROMERE :- 1.) Acentric :- without centromere. 2.) Monocentric :- with one centromere. 3.) Dicemtric :- with two centromere. Eg . Wheat, Maize . 4.) Polycentric :- with more then one centromere. Eg . Ascaris, Luzula . D.) SPECIAL TYPE OF CHROMOSOME :- I.) Polytene Chromosome : These are also giant chromosome but relatively smaller than Lambrush chromosome. Found nuclei of the Salivery gland cells of the larvae of dipterans. (like Drossofila have usually long and wide chromosome.)

19. 100 or 200 times in size of the chromosome in other body cell of the organism. They are discovered by “ Balbiani ” (1881) and named “ Koller ”. Function :- Highly condansed of DNA so that highly transcriptionally active because highly protein require for development.

20. II.) Lambrush Chromosome :- These are the largest chromosome found in the Diplotene stage of Mitotic Prophase (I) of Amphibians Oocyte (Fishes, reptile & Birds). They can be seen with nached eye. These loops give it a brush-like appearance that is why these are called “Lambrush chromosome”. Discovered by “ Ruckert ” in 1892. Function :- I. Synthesis of RNA. II. Formation of yolk material.

21. 9. COMPOSITION OF CHROMOSOME :- Chemical Composition :- I.) DNA – 40% II.) RNA – 1.5%(helps in synthesis of chromosomal fibers). III.) Histone (Protein) – 50% IV.) Non-Histone (Protein) – 8.5% V.) Some amount of calcium which is attached with DNA. DNA is the chief and most significant part of the chromosome. DNA :- a.) Nitrogenous Base :- purine & pyrimidine. b.) Pentose suger . c.) Phosohate group. Protein :- a.)Histone protein. b.) Non- Histone protein :- Tubulin- alpha & beta, Myosine

22. a.) Histone protein :- Histone are the basic proteins (positively charge) in lysine and arginine amino acids. Histone are highly alkalins proteins found in Eukaryotic cell nuclei that package and order the DNA into structural units called nucleosome . The histones are classified on the bases of structural differences, Molecular weight and lysine /arginine ratio. All amino acid of the histone protein are in direct contact with the DNA (negatively charged due to presence of phosphate group) or other histone. The five classes of histones are H1/H5, H2A, H2B, H3, and H4. Histones H2A, H2B, H3 and H4 are known as the core histones. While histones H1/H5 are known as the linker histones. H1, H2A & H2B are rich in lysine whereas H3 & H4 are arginine rich.

23. Histone octamer has a structural core of an H3, H4 tetramer associated with two H2A, H2B dimers.

24. 10. MODEL OF CHROMOSOME :- NUCLEOSOME MODEL :- 1974 Roger Kormberg discovers nucleosome who won Nobel Prize in 2006. Nucleosome model is the most acceptable model of chromatin. Nucleosome are the fundamental repeating units of chromatin. The nucleosome consist of a core particle of eight histone protein and DNA that wraps around the core. The nucleosome core composed of a disc shaped structure of eight histone protein. The nucleosome core composed of two molecule of each of the four Histone H2B, H2A, H3&H4 and his structure is called Histone Octamer. Each Histone core encircled by 1.8 turn of DNA. This 1.8 turn of DNA represents about 146 bp. The H1 histone play are very important role in the formation of the 30-nm fiber.

25. The Linker DNA region in the 30-nm structure are variably bent and twisted to attain the folding pattern. This 30-nm fiber are further folded to form the metaphase chromosome during cell division.

26. 11. FUNCTION OF CHROMOSOME :- they have following functions :- Genetic code storage :- contains genetic material by organism to develop and grow in the form of gene. Sex determination :- help in determining sex like in human XX-chromosome determine female while XY determine male. Control of cell division :- the chromosome of parent cell insure that correct information and number is passed on a daughter cells during mitosis. Formation of protein & storage :- Chromosome direct protein formed in our body and also stored in the chromosomes in the form of histone protein that help in proper packaging of DNA. Crossing over and aberrations of chromosomes introduce variations in population. They transmit heredity information from generation to generation.

27. 12. CONCLUSION :- The chromosome of a cell are in the nucleus. Their number is fixed and definite. This is carry the genetic information generation to generation because called heridity vehicle. 13. REFERENCE :- Albert bruss . Gerald karp . C. B. Pawar . Singh & Tomar . By Internet. THANK YOU