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physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
physiology...protein
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physiology...protein

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  • The genetic code consists of successive “triplets” of bases—that is, each three successive bases is a code word. The successive triplets eventually control the sequence of amino acids in a protein molecule that is to be synthesized in the cell. Note in Figure 3–6 that the top strand of DNA, reading from left to right, has the genetic code GGC, AGA, CTT, the triplets being separated from one another by the arrows. As we follow this genetic code through we see that these three respective triplets are responsible for successive placement of the three amino acids, proline, serine, and glutamic acid, in a newly formed molecule of protein.
  • DNA Base RNA Baseguanine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cytosinecytosine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . guanineadenine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . uracilthymine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . adenineThree Different Types of RNA. There are three different types of RNA, each of which plays an independent and entirely different role in protein formation:1. Messenger RNA, which carries the genetic code to the cytoplasm for controlling the type of proteinformed.2. Transfer RNA, which transports activated amino acids to the ribosomes to be used in assembling the protein molecule.3. Ribosomal RNA, which, along with about 75 different proteins, forms ribosomes, the physical and chemical structures on which protein molecules are actually assembled.
  • Transcript

    • 1. C HAPT E R 212/3/2012 physiology Note series for midwifes 1
    • 2. INTRODUCTION• Some of the basic ideas of heredity have been known since antiquity, but a scientific understanding of how traits are passed from parent to offspring began with the Austrian monk Gregor Mendel (1822–84) and his famous experiments on garden peas. In the early twentieth century, the importance of Mendel’s work was realized and chromosomes were first seen with the microscope. Cytogenetics now uses techniques of cytology and microscopy to study chromosomes and their relationship to hereditary traits. Molecular genetics uses the techniques of biochemistry to study the structure and function of DNA. 12/3/2012 physiology Note series for midwifes 2
    • 3. Genes Genes -located in the nuclei of all cells of the body. Control heredity from parents to children, control day- today function of all the body’s cells by determining type of substances synthesized within the cell. Gene nucleic acid called deoxyribonucleic acid (DNA). It controls the formation of another nucleic acid, ribonucleic acid (RNA). RNA then spreads throughout the cell to control the formation of a specific protein. As there are more than 30,000 different genes in each cell, it is theoretically possible to form a very large number of different cellular proteins 12/3/2012 physiology Note series for midwifes 3
    • 4. Cont…12/3/2012 physiology Note series for midwifes 4
    • 5. Basic Building Blocks of DNA• Genes/ DNA is a polymer of nucleotides composing: 1. Sugar (deoxyribose), 2. Phosphoric acid,and 3. Four nitrogenous bases Nitrogenous bases- are grouped into 2 categories.i. Pyrimidines - Have a single carbon-nitrogen ring - Composes three bases: Cytosine (C), Thymine (T), and Uracil (U). 12/3/2012 physiology Note series for midwifes 5
    • 6. Cont…ii. Purines - Have double carbon-nitrogen rings - Composes adenine (A) and guanine (G)• The bases of DNA are C, T, A, and G, whereas the bases of RNA are C, U, A, and G. The first stage in the formation of DNA is to combine one molecule of phosphoric acid, one molecule of deoxyribose, and one of the four bases to form an acidic nucleotide.• Four separate nucleotides are thus formed, one for each of the four bases: a. Deoxyadenylic, b. Deoxythymidylic, c. Deoxyguanylic, and d. Deoxycytidylic acids. 12/3/2012 physiology Note series for midwifes 6
    • 7. Cont… Fig. 2.1 The basic building blocks of DNA.12/3/2012 physiology Note series for midwifes 7
    • 8. Cont… Figure 2–2: Deoxyadenylic acid, one of the nucleotides that make up DNA12/3/2012 physiology Note series for midwifes 8
    • 9. Cont…• The outer covering of the DNA strand is formed of phosphoric acid & deoxyribose sugar.• The interior of the strand of DNA is composed of the bases which connect two strands by hydrogen bond.• Each purine base adenine of one strand always bonds with a pyrimidine base thymine of the other strand, and• Each purine base guanine always bonds with a pyrimidine base cytosine.12/3/2012 physiology Note series for midwifes 9
    • 10. Cont… Figure 2.3- DNA Structure12/3/2012 physiology Note series for midwifes 10
    • 11. Cont…In the above figure , the sequence of complementary pairsof bases is CG,CG,GC,TA,CG,TA,GC,AT, and AT.Because of the looseness of the hydrogen bonds, the twostrands can pull apart with ease, and they do so many timesduring the course of their function in the cell. 12/3/2012 physiology Note series for midwifes 11
    • 12. GENETIC CODE The importance of DNA lies in its ability to control the formation of proteins in the cell. It does this by means of the so-called genetic code. When the two strands of a DNA molecule are split apart, this exposes the purine and pyrimidine bases projecting to the side of each DNA strand.• These projecting bases form the genetic code, that control the sequence of amino acids in a protein molecule which is to be synthesized in the cell.• The spilled DNA strand carries the genetic code. 12/3/2012 physiology Note series for midwifes 12
    • 13. GENETIC CODE cont… The spilled DNA template strand will be copied to RNA. DNA controls cytoplasmic chemicals through the process of transferring its code to RNA. This process of transforming DNA code to RNA code is called transcription. The RNA, in turn diffuses from nucleus through the nuclear pores in to the cytoplasmic compartment, where it controls protein synthesis. 12/3/2012 physiology Note series for midwifes 13
    • 14. GENETIC CODE cont…12/3/2012 physiology Note series for midwifes 14
    • 15. GENETIC CODE cont… G G C A G A C T T12/3/2012 physiology Note series for midwifes 15
    • 16. SYNTHESIS OF RNADuring synthesis of RNA:  The two strands of the DNA molecule separate temporarily One of these strands is used as a template for synthesis of an RNA molecule The code triplets in the DNA cause formation of complementary code triplets called codons in the RNA; Codons control the sequence of amino acids in a protein synthesis in the cell cytoplasm. 12/3/2012 physiology Note series for midwifes 16
    • 17. Basic Building Blocks of RNA RNA is a nucleic acid which formed from the polymer of nucleotide. The basic building blocks of RNA are almost the same as those of DNA, except for two differences. 1st – no deoxyribose sugar instead ribose sugar  2nd thymine is replaced by another pyrimidine, uracil. – Thus RNA nucleotide composed of: a. Phosphoric acid b. Ribose sugar & c. 4 nitrogenous bases ( uracil replaces thymine) 12/3/2012 physiology Note series for midwifes 17
    • 18. “Activation” of the RNA Nucleotides• The next step in the synthesis of RNA is “activation” of the RNA nucleotides by an enzyme, RNA polymerase.• This occurs by adding to each nucleotide two extra phosphate radicals to form triphosphates• These last two phosphates are combined with the nucleotide by high-energy phosphate bonds derived from ATP in the cell.12/3/2012 physiology Note series for midwifes 18
    • 19. Cont…12/3/2012 physiology Note series for midwifes 19
    • 20. Types of RNAThere are three different types of RNA.Each of them plays an independent and entirely different role in protein formation.1. Messenger RNA (mRNA)It carries the genetic code to the cytoplasm for controlling the type of protein formed.Their molecules are long, single RNA strands that are suspended in the cytoplasm.Composed of several hundred to several thousand RNA nucleotides in unpaired strandsThey contain codons that are exactly complementary to the code triplets of the DNA genes 12/3/2012 physiology Note series for midwifes 20
    • 21. Types of RNA cont…E.g. codons those carried by mRNA are CCG,UCU, and GAA.  These three are the codons for the amino acids proline, serine, and glutamic acid respectively. Codons mRNA Molecule 12/3/2012 physiology Note series for midwifes 21
    • 22. Types of RNA cont…2. Transfer RNAIt transports activated amino acids to the ribosomes to be used in assembling the protein molecule. Contains only about 80nucleotides, is a relatively small molecule in comparison with messenger RNA. Each type of transfer RNA combines specifically with 1 of the 20 amino acids that are to be incorporated into proteins. Each type of transfer RNA combines specifically with 1 of the 20 amino acids that are to be incorporated into proteins. 12/3/2012 physiology Note series for midwifes 22
    • 23. Types of RNA cont (tRNA)… Each specific type of tRNA recognizes a particular codon on the messenger RNA, in the ribosomes. This specific code is known as anticodon, which is again triplet of nucleotides. Each type of transfer RNA have specificity for a particular codon in the messenger RNA. 12/3/2012 Physiology Note series for midwifes 23
    • 24. Types of RNA cont (tRNA)…12/3/2012 physiology Note series for midwifes 24
    • 25. Types of RNA cont…3. Ribosomal RNAForms ribosomes the physical and chemical structures on which protein molecules are actually assembled. It constitutes about 60 per cent of the ribosome. The remainder of the ribosome is protein, containing about 75 types of proteins that are both structural proteins and enzymes needed in the manufacture of protein molecules. The ribosome is the physical structure on which protein molecules are actually synthesized 12/3/2012 physiology Note series for midwifes 25
    • 26. Protein Synthesis When a molecule of messenger RNA comes in contact with a ribosome, it travels through the ribosome. While mRNA travels through the ribosome, a protein molecule is formed by the process called Translation. Translation starting from the sequence of RNA bases called the “initiation chain” codon. The formation of protein end (stop) by signal of chain terminating codons. 12/3/2012 physiology Note series for midwifes 26
    • 27. Chemical steps of protein synthesis1. Activation of free amino acid--each amino acid is activated by a chemical process in which ATP combines with the amino acid to form an AMP complex with the amino acid, giving up two high-energy phosphate bonds in the process. AA + ATP AA-AMP+2P+ AA- AMP 12/3/2012 physiology Note series for midwifes 27
    • 28. Chemical steps cont…2. Combination of AA with tRNA--The activated amino acid, having an excess of energy, then combines with its specific transfer RNA to form an amino acid–tRNA complex and, at the same time, releases the adenosine monophosphate.tRNAAnticodons AA-AMP + tRNA AA-tRNA + AMP 12/3/2012 physiology Note series for midwifes 28
    • 29. Chemical steps cont…3. Temporary bond b/n tRNA & mRNA-the transfer RNA carrying the amino acid complex then comes in contact with the messenger RNA molecule in the ribosome, where the anticodon of the transfer RNA attaches temporarily to its specific codon of the messenger RNA, thus lining up the amino acid in appropriate sequence to form a protein molecule Under the influence of the enzyme peptidyl transferase peptide bonds are formed between the successive amino acids. Peptidyl transferase is one of the proteins in the ribosome. 12/3/2012 physiology Note series for midwifes 29
    • 30. Chemical steps cont… Thus peptidyl transferase adding progressively to the protein chain. These chemical events require energy from two additional high-energy phosphate bonds, making a total of four high-energy bonds used for each amino acid added to the protein chain. Thus, the synthesis of proteins is one of the most energy-consuming processes of the cell. 12/3/2012 physiology Note series for midwifes 30
    • 31. …. … .12/3/2012 physiology Note series for midwifes 31
    • 32. 12/3/2012 physiology Note series for midwifes 32
    • 33. Summery of Chemical steps of protein synthesis1. mRNA leaves the nucleus.2. Ribosome binds mRNA.3. tRNA binds an amino acid; binding consumes 1 ATP.4. tRNA anticodon binds to complementary mRNA codon.5. The preceding tRNA hands off the growing peptide to the new tRNA, and the ribosome links the new amino acid to the peptide.6. tRNA is released from the ribosome and is available to pick up a new amino acid and repeat the process.7. After translating the entire mRNA, ribosome dissociates into its two subunits.8. Ribosomal subunits rejoin to repeat the process with the same or another mRNA. 12/3/2012 physiology Note series for midwifes 33
    • 34. 12/3/2012 physiology Note series for midwifes 34
    • 35. 12/3/2012 physiology Note series for midwifes 35
    • 36. Control of Gene Function and Biochemical Activity in Cells The genes control both the physical and the chemical functions of the cells. However, the degree of activation of respective genes must be controlled as well; otherwise, some parts of the cell might overgrow or some chemical reactions might overact until they kill the cell. Each cell has powerful internal feedback control mechanisms that keep the various functional operations of the cell in step with one another. There are basically two methods by which the biochemical activities in the cell are controlled. 1. Genetic Regulation & 2. Enzyme Regulation 12/3/2012 physiology Note series for midwifes 36
    • 37. 1. Genetic Regulation Synthesis of a cellular biochemical product usually requires a series of reactions. Each of these reactions is catalyzed by a special protein enzyme. Formation of all the enzymes controlled by a sequence of genes located one after the other on the same chromosomal DNA strand. This area of the DNA strand is called an operon, and the genes responsible for forming the respective enzymes are called structural genes. The control mechanism is required to prevent over or under action of these enzymes in the process of synthesis. 12/3/2012 physiology Note series for midwifes 37
    • 38. Control of the Operon by a “Repressor Protein” The segment on the DNA strand is called the promoter. This is a group of nucleotides that has specific affinity for RNA polymerase. The promoter is an essential element for activating the operon. Additional band of nucleotides lying in the middle of the promoter is called a repressor operator. A “regulatory” protein bind to repressor operator and prevent attachment of RNA polymerase to the promoter, there by blocking transcription of the genes of this operon. Such a negative regulatory protein is called a repressor protein 12/3/2012 physiology Note series for midwifes 38
    • 39. Control of the Operon by an “Activator Protein” Another operator , called the activator operator, that lies adjacent to but ahead of the promoter. When a regulatory protein binds to this operator, it helps attract the RNA polymerase to the promoter, in this way activates the operon. Therefore, a regulatory protein of this type is called an activator protein. 12/3/2012 physiology Note series for midwifes 39
    • 40. In the above fig. , three respective structural genes are shownin an operon, and it is demonstrated that they control theformation of three respective enzymes that in turn causesynthesis of a specific intracellular product. 12/3/2012 physiology Note series for midwifes 40
    • 41. Negative Feedback Control of the OperonThe presence of a critical amount of a synthesized product in the cell can cause negative feedback inhibition of the operon that is responsible for its synthesis. It can do this either by causing :1. Regulatory repressor protein to bind at the repressor operator or2. By causing a regulatory activator protein to break its bond with the activator operator. In either of two case, the operon becomes inhibited. Therefore, once the required synthesized product has become abundant enough for proper cell function, the operon becomes dormant. 12/3/2012 physiology Note series for midwifes 41
    • 42. 2. Enzyme Regulation This is another means in which cellular biochemical activities are controlled by intracellular inhibitors or activators that act directly on specific intracellular enzymes. Thus, enzyme regulation represents a second category of mechanisms by which cellular biochemical functions can be controlled. Some chemical substances formed in the cell have direct feedback effects in the specific enzyme systems either to inhibit or activate the enzyme. 12/3/2012 physiology Note series for midwifes 42
    • 43. Cont….1. Enzyme Inhibition Enzyme inhibition is another example of negative feedback control. It is responsible for controlling intracellular concentrations of multiple amino acids, purines, pyrimidines, vitamins, and other substances.2. Enzyme Activation Enzymes that are normally inactive often can be activated when needed.• An example of this occurs when most of the ATP has been depleted in a cell, a considerable amount of cyclic adenosine monophosphate (cAMP) begins to be formed as a breakdown product of the ATP 12/3/2012 physiology Note series for midwifes 43
    • 44. Genetic Control of Cell Reproduction Cell reproduction is another example of the ubiquitous role that the DNA-genetic system plays in all life processes. The genes and their regulatory mechanisms determine the growth characteristics of the cells and also when or whether these cells will divide to form new cells. The period from 1st cell reproduction to the next cell reproduction is known as the life cycle of a cell. Life cycle of the cell is terminated by a series of distinct physical events called mitosis that cause division of the cell into two new daughter cells. 12/3/2012 physiology Note series for midwifes 44
    • 45. Cont… As is true of almost all other important events in the cell, reproduction begins in the nucleus itself. The first step is replication (duplication) of all DNA in the chromosomes. Only after this has occurred can mitosis take place. The DNA begins to be duplicated some 5 to 10 hours before mitosis, and this is completed in 4 to 8 hours. The net result is two exact replicas of all DNA. These replicas become the DNA in the two new daughter cells that will be formed at mitosis 12/3/2012 physiology Note series for midwifes 45
    • 46. Cont… Cell division is occur in either of two forms:1. Mitosis – is the actual process by which the cell splits into two new cells. - Involved in cell growth, differentiation and repair - Duplication of chromosomes resulted in two cells - Take place in all body cells except in sex cells2. Meiosis – Occurs only in reproductive cells – Is process in which oocyte & sperm formed – Reproduction in number of chromosomes/ the daughter cells have half of parents cell/haploid/ 12/3/2012 physiology Note series for midwifes 46
    • 47. Stages of cell reproduction. A, B, and C, Prophase. D,Prometaphase. E, Metaphase. F, Anaphase. G and H, Telophase. 12/3/2012 physiology Note series for midwifes 47
    • 48. Cell Differentiation Is special characteristic of cell growth and cell division It refers to changes in physical and functional properties of cells as they proliferate in the embryo to form the different bodily structures and organs. Differentiation results not from loss of genes but from selective repression of different genetic operons. The repressed genes never function again. 12/3/2012 physiology Note series for midwifes 48
    • 49. Cell Death The total number of cells is regulated not only by controlling the rate of cell division but also by controlling the rate of cell death. Cell death occur either pathologically or naturally. Pathological cell death called necrosis which is caused due to occlusion of a blood supply/ or injury to the cell  become swell & rupture. Natural cell death- when cells are no longer needed or become a threat to the organism, they undergo a suicidal programmed cell death, or apoptosis. This process involves a specific proteolytic cascade that causes the cell to shrink and condense, to disassemble its cytoskeleton, and to alter its cell surface so that a neighboring phagocytic cell, such as a macrophage, can attach to the cell membrane and digest the cell 12/3/2012 physiology Note series for midwifes 49
    • 50. Cell Death cont… Apoptosis is initiated by activation of a family of proteases called caspases. These are enzymes that are synthesized and stored in the cell as inactive procaspases. A tremendous amount of apoptosis occurs in tissues that are being remodeled during development. Even in adult humans, billions of cells die each hour in tissues such as the intestine and bone marrow and are replaced by new cells. Programmed cell death, however, is precisely balanced with the formation of new cells in healthy adults. Otherwise, the body’s tissues would shrink or grow excessively. 12/3/2012 physiology Note series for midwifes 50
    • 51. Cont… Abnormalities of apoptosis may play a key role in neurodegenerative diseases such as Alzheimer’s disease, as well as in cancer and autoimmune disorders. Some drugs that have been used successfully for chemotherapy appear to induce apoptosis in cancer cells. 12/3/2012 physiology Note series for midwifes 51
    • 52. Cancer Is excessive uncontrolled proliferation of cell Cancer is caused in all or almost all instances by mutation or by some other abnormal activation of cellular genes that control cell growth and cell mitosis. Cancer refers to malignant type of neoplasm. The abnormal genes are called oncogenes, as many as 100 different oncogenes have been discovered. Also present in all cells are antioncogenes, which suppress the activation of specific oncogenes. Therefore, loss of or inactivation of antioncogenes can allow activation of oncogenes that lead to cancer 12/3/2012 physiology Note series for midwifes 52
    • 53. Cont… So every body is an a risk to cancer, which result from unlucky occurrence, even though the probability of mutation increase due to exposure to certain. However, the probability of mutations can be increased many fold when a person is exposed to certain chemical, physical, or biological factors, including the following.1. Ionizing radiation- such as x-rays, gamma rays, and particle radiation from radioactive substances, and even ultraviolet light can predispose individuals to cancer 12/3/2012 physiology Note series for midwifes 53
    • 54. Cont…2. Chemical substances- Chemical substances that can cause mutation are called carcinogens.e.g. carcinogens from cigarette smokers3. Physical irritants also can lead to cancer, such as continued abrasion of the linings of the intestinal tract by some types of food.4. In many families, there is a strong hereditary tendency to cancer5. Certain type of virus cause some kinds of Ca e.g. leukemia 12/3/2012 physiology Note series for midwifes 54
    • 55. Cont… The major differences between the cancer cell and the normal cell are the following: (1) The cancer cell does not respect usual cellular growth limits; the reason for this is that these cells presumably do not require all the same growth factors that are necessary to cause growth of normal cells. (2) Cancer cells often are far less adhesive to one another than are normal cells. Therefore, they have a tendency to wander through the tissues, to enter the blood stream, and to be transported all through the body, where they form nidi for numerous new cancerous growths.(3) Some cancers also produce angiogenic factors that cause many new blood vessels to grow into the cancer, thus supplying the nutrients required for cancer growth.12/3/2012 physiology Note series for midwifes 55
    • 56. The End!12/3/2012 physiology Note series for midwifes 56

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