The mitotic cell cycle
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The document provides information about chromosomes and their structure. It discusses that chromosomes are made up of DNA tightly coiled around histone proteins. Chromosomes contain genes and appear as rod-shaped structures during cell division. The document also describes the different parts of a chromosome including the centromere, telomeres, and chromatin. It discusses the role of chromosomes in genetic inheritance, cell division and differentiation.
The mitotic cell cycle
- 1. Unit-5 The Mitotic Cell Cycle - By Suman Tiwari (M.Sc. , M. Ed.)
- 3. Chromosomes • The word chromosome comes from the chrom0, "colour") and somes "bodies“.The term was coined by the German scientist Waldeyer, referring to the term chromatin, which was itself introduced by Flemming, who discovered cell division. • In the nucleus of each cell, the DNA (2 nm wide and 1.8 metres long)molecule is packaged into thread-like structures called chromosomes. • Each chromosome is made up of DNA tightly coiled many times around proteins called histones(Basic) that support its structure. • They appear as rod shaped dark stained bodies during the metaphase stage of mitosis when cells are stained with a suitable basic dye and viewed under a light microscope.
- 4. • Chromatin referred to as the loosely coiled form of chromosomes during the interphase of the cell cycle • Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells • DNA + Structural protein that gives it the shape • DNA molecules are wrapped around histone protein
- 5. • During interphase (the period of the cell cycle where the cell is not dividing), two types of chromatin can be distinguished: • Euchromatin, which consists of DNA that is active, e.g., being expressed as protein. • Heterochromatin, which consists of mostly inactive DNA. It seems to serve structural purposes during the chromosomal stages. Heterochromatin can be further distinguished into two types: • Constitutive heterochromatin, which is never expressed. It is located around the centromere and usually contains repetitive sequences. • Facultative heterochromatin, which is sometimes expressed. Chromosomes
- 6. Chromosomes
- 7. Chromosomes
- 8. • In eukaryotes the chromosomes are multiple large, linear and are present in the nucleus of the cell. • Each chromosome typically has one centromere and one or two arms that project from the centromere. • Structurally, each chromosome has three parts— • Pellicle • Matrix • Chromonemata Chromosomes
- 9. • Pellicle • It is the outer envelope around the substance of chromosome. • It is very thin and is formed of achromatic substances. • Matrix • It is the ground substance of chromosome which contains the chromonemata. • It is also formed of non-genic materials. • Chromonemata • Embedded in the matrix of each chromosome are two identical, spirally coiled threads, the chromonemata. • The two chromonemata are also tightly coiled together that they appear as single thread of about 800A thickness. • Each chromonemata consists of about 8 mi-crofibrils, each of which is formed of a double helix of DNA.
- 10. • In mitotic metaphase chromosomes, the following structural feature (except chromomere) can be seen under the light microscope: • (1) Chromatid, • (2) Chromonema, • (4) Centromere, • (5) Secondary constriction or Nucleolar organizer, • (6)Telomere and • (7) Satellite. Chromosomes
- 11. • A small structure in the chromonema, marked by a constriction which is recognised as permanent structure in the chromosome is termed as the centromere. • At this point the two chromonemata are joined together. • It is known as centromere or kinetochore or primary constriction. • It divides the chromosome into two sections, or “arms.”The short arm of the chromosome is labeled the “p arm.”The long arm of the chromosome is labeled the “q arm.” • Its position is constant for a given type of chromosome and forms a feature of identification. • The chromosomes are attached to spindle fibres at this region during cell division. Centromere
- 12. • The chromosome besides having the primary constriction or the centromere possesses secondary constriction at any point of the chromosome. • Constant in their position and extent, these constrictions are useful in identifying particular chromosomes in a set. • The chromosome region distal to the secondary constriction i.e., the region between the secondary constriction and the nearest telomere is known as satellite. • Therefore, chromosomes having secondary constrictions are called satellite chromosomes or sat-chromosomes. • Nucleolus is always associated with the secondary constriction of sat-chromosomes.There-fore, secondary constrictions are also called nucleolus organiser region (NOR) and sat-chromo-somes are often referred to as nucleolus organiser chromosomes. Secondary constriction
- 14. • These are specialized ends of a chromosome which exhibits physiological differentiation and polarity. • Each extremity of the chromosome due to its polarity prevents other chromosomal seg-ments to be fused with it.The chromosomal ends are known as the telomeres. • If a chromosome breaks, the broken ends can fuse with each other due to lack of telomere. Telomeres https://www.youtube.com /watch?v=CfsE_klDhhM
- 15. • Importance ofTelomere: • Telomere sealed the ends of the chromosomes • Made of DNA with short base sequences, repeating many times – no useful information • They make sure the end of the DNA molecules are not left out during the replication by making them longer – so the last bit of information won’t be left out • Performed by the enzyme telomerase • In cells without telomere – those that are differentiated, the end can be left out, making each new copy of the DNA incomplete – this is theorized to be the cause of ageing. Telomeres
- 16. • Human chromosomes are of two types : • autosomes • sex chromosomes • Genetic traits that are linked to the sex of the person are passed on through the sex chromosomes. • The rest of the genetic information is present in the autosomes. • Humans have 23 pairs of chromosomes in their cells, of which 22 pairs are autosomes and one pair of sex chromosomes, making a total of 46 chromosomes in each cell. Types of Chromosomes
- 17. • Monocentric with one centromere. • Dicentric with two centromeres. • Polycentric with more than two centromeres • Acentric without centromere. Such chromosomes represent freshly broken segments of chromosomes which do not survive for long. • Diffused or non-located with indistinct centromere diffused throughout the length of chromosome. On the Basis of Number of Centromeres Types of Chromosomes
- 18. • Telocentric are rod-shaped chromosomes with centromere occupying the terminal position, so that the chromosome has just one arm. • Acrocentric are also rod-shaped chromosomes with centromere occupying a sub-terminal position. One arm is very long and the other is very short. • Sub-metacentric chromosomes are with centromere slightly away from the mid-point so that the two arms are unequal. • Metacentric areV-shaped chromosomes in which centromere lies in the middle of chro-mosome so that the two arms are almost equal. On the Basis of Location of Centromere Types of Chromosomes
- 20. • The number of the chromosomes is constant for a particular species. • Genetic Code Storage: Chromosome contains the genetic material that is required by the organism to develop and grow. DNA molecules are made of chain of units called genes. Genes are those sections of the DNA which code for specific proteins required by the cell for its proper functioning. • Sex Determination: Humans have 23 pairs of chromosomes out of which one pair is the sex chromosome. Females have two X chromosomes and males have one X and oneY chromosome.The sex of the child is determined by the chromosome passed down by the male. If X chromosome is passed out of XY chromosome, the child will be a female and if aY chromosome is passed, a male child develops. Role of Chromosomes
- 21. • Control of Cell Division: Chromosomes check successful division of cells during the process of mitosis.The chromosomes of the parent cells insure that the correct information is passed on to the daughter cells required by the cell to grow and develop correctly. • Formation of Proteins and Storage:The chromosomes direct the sequences of proteins formed in our body and also maintain the order of DNA.The proteins are also stored in the coiled structure of the chromosomes.These proteins bound to the DNA help in proper packaging of the DNA. Role of Chromosomes
- 22. • Gamete: a mature reproductive cell with half the number of chromosomes e.g. egg/ sperm cell • Homologous pair: A pair of chromosomes that code for the same type of proteins • Haploid: n copies of Chromosomes or half the usual number • Diploid: 2n copies of chromosomes or the full set of chromosomes • When two haploid cells fuse – they form a diploid cell • That diploid cell called Zygote divides by mitosis • After which they can differentiate into different cells • Some of the cells differentiate into germ cell and become the gonads
- 23. • Nucleosome: DNA wrapped around histones making 1⅔ turns (equivalent to 147 base pairs) • Nucleosome is 11nm wide, 6nm long; • Made of 8 histone molecules • Linker DNA is also held by a histone • Nucleosomes line up to form a fibre 10nm wide which is further coiled to a supercoil, involving non-histone molecules thus the DNA (1.8mlong, 2nm wide) is packed in nucleus (6um diameter) Structure of Nucleosome
- 24. Nuclear division producing two genetically identical daughter nuclei, each containing the same no. of chromosomes as the parent. Sister chromatids contain DNA with identical genes which is key to precise nuclear division (when each chromatid goes into each daughter cell, it makes them genetically identical). • The cell cycle: 3 phases • interphase • nuclear division and • cell division. Mitosis
- 25. • Interphase: cell grows to its normal size after cell division, and synthesises important substances eg proteins. • Growth 1 phase: gap after cell division and before S phase. -Prepares for growth and DNA synthesis (S phase) by producing RNA, proteins and enzymes. - If there are insufficient growth factors, or when cell has reached its maximum size, cell will not divide and remain in G zero. • S phase: synthesis of DNA (in euchromatin form) so each chromosome consists of two identical chromatids (short phase). - Chromatin also replicates along with DNA so histones are replicated (for M phase) • Growth 2 phase: gap after S phase and before nuclear division (prepares for mitosis) - New DNA checked, and errors are repaired. - Sharp increase in the production of tubulin to make - microtubules for the formation of mitotic spindle. - Nuclear envelope envelopes nucleus. Mitosis
- 26. • Cell division: • Nuclear division: division of nuclei at M phase. • Growth stops temporarily during mitosis. Mitosis
- 27. Note: nuclear envelope breaks down into vesicles during prophase and reassembles when the vesicles fuse to form the envelope back at telophase • Cytokinesis: division of cytoplasm between daughter cells, last stage of cell division. • Significance of mitosis: • Growth: clones produced allow growth of multicellular organism from unicellular zygote. • Immune response: The cloning of B- andT- lymphocytes during the immune response is dependent on mitosis. • Replacement of cells and repair of tissues: cells die and are replaced by GI cells; rapid in skin, lining of gut, and to regenerate whole parts of body. • Asexual reproduction: production new individual by a single parent. In unicellular organisms, cell division results in reproduction. In multicellular organisms, new individual produced bud off from parent. Mitosis
- 28. Cells that divide repeatedly by mitosis, and differentiate into specialized cells , each new cell has the potential to remain a stem cell.The extent of the power of a stem cell to produce different cell types is variable and is referred to as its potency. There are three different kinds: • Totipotent: cells that can divide repeatedly to form any other cell in the body, eg: zygote • Pluripotent: embryotic stem cells that lead to development of the embryo and later the adult.They are not specialized into placenta. • Multipotent: Adult stem cells that are only able to produce a few types of cells eg stem cells in bone marrow. Stem Cells
- 29. • Zygote for example • Some cells specialized • Some cells lost the ability– becoming pluripotent Totipotent Cells
- 30. • Can form all the cells that will lead to the development of the embryo and later the adult • Embryonic stem cells are pluripotent • Basically it can give rise to any cell that forms the body Pluripotent Cells
- 31. • Cells become more committed with its role during adulthood – the cell loses the ability to divide • Some are no longer pluripotent/totipotent • They became multipotent • Can divide many numbers of times – but only of a specific type of cells • Red Blood Cells – an example Multipotent Cells
- 32. • The introduction of new adult stem cells into damaged tissue to treat disease or injury • Bone marrow transplantation for leukemia for example • Might be able to cure Parkinson’s, Huntington’s diseases • There are still experiments on growing new organs Stem Cell Therapy
- 33. • Cancers = uncontrolled Mitosis • Carcinogens: A substance that can cause cancer • Benign –Tumors that do not spread from its site of origin • Malignant (One that interferes with body function eg. Blocks blood vessel/ intestine) Cancer
- 34. • Starts: Mutation that creates an oncogenes (genes that are mutated) – from carcinogen • Usually mutated cell is destroyed – however cancer cells escape detection • Doesn’t respond to signals from the body – just DIVIDE • Tumors get bigger – changes in characteristics • Blood vessels and lymph vessels begin supplying the tumor • Invades other tissue – Metastasis – spreads across the body Cancer
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