Biochemistry of genetics and molecular genetics

A slide on genetics

1. Basic Molecular Genetics NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA MUHAMMAD BAWA YUSUF PhD (Medical Biochemistry and Molecular Therapeutics)

2. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA DNA & RNA

3. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Vocabulary of DNA Genetics—The study of genes & heredity Trait-- inherited characteristic determined by the presence and expression of dominant and/or recessive alleles. Gene-- a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc.)

4. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 4 Definations Molecular biology ; the study of biology at the molecular level. Molecular biology ; the study of gene structure and functions at the molecular level to understand the molecular basis of hereditary, genetic variation, and the expression patterns of genes. The Molecular biology field overlaps with other areas, particularly genetics and biochemistry .

5. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 5 The Genome The genome of an organism is the totality of genetic information and is encoded in the DNA (or, for some viruses, RNA ). commons . wikimedia . org / wiki / Image : Genome . jpg

6. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 6 All living things are grouped into three domain: Eukaryotes; Prokaryotes and Archaea. Three Domain of Life

7. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Cell The cell is the smallest living unit, the basic structural and functional unit of all living things. Some organisms, such as most bacteria , are unicellular (consist of a single cell). Other organisms, such as humans , are multicellular.

8. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Cell Cells are stacked together to make up structures, tissues and organs. Most cells have got the same information and resources and the same basic material. Cells can take many shapes depending on their function. Function of cells Secretion (Produce enzymes). Store sugars or fat. Brain cells for memory and intelligence. Muscle cells to contract. Skin cell to perform a protective coating. Defense, such as white blood cells.

9. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Eukaryotic Cell Eukaryotes are generally more advanced than prokaryotes . There are many unicellular organisms which are eukaryotic, but all cells in multicellular organisms are eukaryotic. Eukaryotic cells are found in animals; plants; fungi and protists cell.

10. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Eukaryotic Cell Cell with a true nucleus , where the genetic material is surrounded by a membrane; Eukaryotic genome is more complex than that of prokaryotes and distributed among multiple chromosomes; Eukaryotic DNA is linear ; Eukaryotic DNA is complexed with proteins called " histones; Numerous membrane - bound organelles; Complex internal structure; Cell division by mitosis.

11. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Prokaryotic Cell Unicellular organisms, found in all environments . These include bacteria and archaea. Without a nucleus ; no nuclear membrane ( genetic material dispersed throughout cytoplasm ; No membrane - bound organelles ; Cell contains only one circular DNA molecule contained in the cytoplasm; DNA is naked (no histone); Simple internal structure ; and Cell division by simple binary fission .

12. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Archaea Archaea are prokaryotes; organisms without nucleus but some aspect of their molecular biology are more similar to those of eukaryotes.

13. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Eukaryotic Cell Cycle Eukaryotic Cell Cycle : defined as the sequence of events that occurs during the lifetime of a cell and is traditionally divided into four phases: G1 = Growth and preparation of the chromosomes for replication S = Synthesis of DNA G2 = Preparation for mitosis M = Mitosis

14. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Central Dogma of Molecular Biology The flow of genetic information as follows:

15. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 15 Deoxyribonucleic Acid (DNA) Deoxyribonucleic Acid (DNA), the genetic material of all cellular organisms and most viruses, the gigantic molecule which is used to encode genetic information for all life on Earth.

16. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Thread like structure. Located in the cell nucleus. The storage place for all genetic information. The number of chromosomes varies from one species to another. The Chromosome

17. In normal human cell DNA contained in the nucleus, arranged in 23 pairs of chromosomes ; 22 pairs of chromosomes (autosomes) ; the 23 chromosome pair determines the sex of individual and is composed of either two (x) chromosomes (female) or an (x) and (y) chromosome (male). DNA Facts Chromosomes are made of DNA Deoxyribonucleic Acid (DNA) Molecule that stores genetic information in cells Copies itself exactly for new cells

18. Early Work NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 1. Friedrich Miescher, 1869, first isolates a substance from the nucleus of cells that he calls “ nuclein .” His student, Richard Altmann, calls the substance “nucleic acid.” 2. Biochemists identify two types of nucleic acids, later called RNA and DNA. 3. In 1929, Phoebus Levine at the Rockefeller center identifies the four bases of DNA.

19. What Does DNA Do? NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 1. Though early researchers knew that DNA was found in chromosomes, they doubted that it was the hereditary material. There were only four bases. How could for bases code for all sorts of proteins? 2. Some researchers, including Linus Pauling, thought that the protein also found in chromosomes was probably the hereditary factor.

20. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA How do we know that all of our genetic information comes from DNA? What type of experiment would you design to determine that DNA is the source of all genetic information?

21. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation Frederick Griffiths was a bacteriologist studying pneumonia He discovered two types of bacteria: Smooth colonies Rough colonies CONCLUSION: The smooth colonies must carry the disease!

22. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation When heat was applied to the deadly smooth type… And injected into a mouse… The mouse lived!

23. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Griffith injected the heat-killed type and the non-deadly rough type of bacteria. The bacteria “transformed” itself from the heated non-deadly type to the deadly type. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation

24. Griffith’s Experiment NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA

25. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Griffith’s Experiment did not prove that DNA was responsible for transformation How would you design an experiment to prove that DNA was responsible for transformation?

26. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Avery, McCarty, and MacLeod Repeated Griffith’s Experiment Oswald Avery Maclyn McCarty Colin MacLeod

27. Oswald Avery NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Avery continued working with Griffith’s findings in hope of discovering what factor in bacteria carried the trait of virulence. Isolated proteins, carbohydrates, nucleic acids and applied them to non-virulent bacteria. Only nucleic acids (DNA) caused a change.

28. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Avery’s Work

29. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA How did DNA: 1. Store information? 2. Duplicate itself easily? These questions would be answered by discovering DNA’s structure

30. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Race to Discover DNA’s Structure

31. The Race to Discover DNA’s Structure Linus Pauling 1940s Discovered the alpha-helical structure of proteins.

32. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Race to Discover DNA’s Structure Maurice Wilkins Rosalind Franklin X-Ray diffraction image of DNA taken by Franklin in 1951

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34. The Race to Discover DNA’s Structure NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Chargaff studied DNA itself, in hopes of providing some clues about its structure. Discovered that there are always equal amounts of the bases Adenine and Thymine, and equal amounts of Cytosine and Guanine. Chargaff proposed that these bases pair with one another in some way

35. The Race to Discover DNA’s Structure 1950 Chargaff’s Rule: Equal amounts of A denine and T hymine, and equal amounts of G uanine and C ytosine Erwin Chargaff Why do you think the bases match up this way? Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow Purine + Pyrimidine = Perfect Fit from X-ray data

36. When Watson, Crick and Wilkins got their Nobel prize awards in 1962, Rosalind Franklin was cheated of deserved recognition in part by her early death from cancer in 1958. Rosalind Franklin and Maurice Wilkins took DNA X-ray photos that were essential to the discovery of the double helix of DNA by James Watson and Francis Crick in 1953.

37. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Race to Discover DNA’s Structure was Over

38. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA DNA Structure DNA is a polymer (composed of repeating subunits called nucleotides) 2 long strands Each a chain of nucleotides

39. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Nucleotides Consists of… Phosphate Carbon sugar (deoxyribose) Nitrogen base

40. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Adenine and Guanine are PURINES Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

41. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Thymine and Cytosine are PYRIDAMINES Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

42. DNA structure DNA is made up of four bases. RNA also has four bases, but has uracil instead of thymine.

43. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA DNA Strand Each nucleotide bonds to the next one to form a strand. The two strands twist around a central axis to form a double helix. Sides of the ladder alternate phosphate and sugar (deoxyribose) Rungs are held together by Hydrogen bonds

44. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Base Pair Rule Adenine can bond only with Thymine A-T or T-A (2 H bonds) Cytosine can bond only with Guanine C-G or G-C (3 H bonds) This is called the BASE PAIR RULE

45. Nitrogenous Bases Those 4 bases (ATCG) have endless combinations Just like the letters of the alphabet can combine to make an infinite number of words. The two strands are said to be complimentary That means that if you have GAATAC on one side you will have _ _ _ _ _ _ on the other.

46. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA DNA Forms

47. Genomic organization: DNA by the Numbers Each cell has about 3 meters of DNA. The average human has 300 trillion cells. The average human has enough DNA to go from the earth to the sun about 400 to 600 times. DNA has a diameter of only 0.000000002 meters . All humans are 99.9% identical 0.1% gives clues about diseases The earth is 150 billion meters or 93 million miles from the sun.

48. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Eukaryotic Chromatin Eukaryotic chromatin is folded in several ways. The first order of folding involves structures called nucleosomes , which have a core of histones, around which the DNA winds ( four pairs of histones H2A, H2B,H3 and H4 in a wedge shaped disc, around it wrapped a stretch of 147 bp of DNA ).

49. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Thread like structure. Located in the cell nucleus. The storage place for all genetic information. The number of chromosomes varies from one species to another. The Chromosome

50. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA In normal human cell DNA contained in the nucleus, arranged in 23 pairs of chromosomes ; 22 pairs of chromosomes (autosomes) ; the 23 chromosome pair determines the sex of individual and is composed of either two (x) chromosomes (female) or an (x) and (y) chromosome (male). The Chromosome

51. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The basic units of inheritance; it is a segment within a very long strand of DNA with specific instruction for the production of one specific protein. Genes located on chromosome on it's place or locus . About 30,000 genes code for most proteins that perform life functions The Gene

52. DNA Replication Before cells divide, they must double their DNA so that each cell gets identical copies of the DNA strands. DNA replication helps assure that the bases are copied correctly. Enzymes carry out the process.

53. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Replication The process by which DNA makes a copy of itself Why does DNA need to copy? Cells divide for an organism to grow or reproduce Every new cell needs a copy of DNA In DNA replication enzymes work to unwind and separate the double helix and add complimentary nucleotides to the exposed strands

54. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Replication DNA replication is semi-conservative. When it makes a copy, one half of the old strand is ALWAYS kept in the new strand This helps reduce the number of copy errors.

55. DNA Replication DNA helicases—break H-bonds linking bases DNA polymerases—move along each of the strands, adding nucleotides, according to base pairing rules.

56. DNA Replication The result is two exact copies of the original DNA Each new double helix is composed of one original DNA strand and one new strand. Semi-conservative

57. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Mitochondrial DNA Mitochondria is a membrane-enclosed organelle found in most eukaryotic cells .These organelles range from 1–10 micrometers ( μm ) in size. Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP). Mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth . Mitochondria have been implicated in several human diseases, including mental disorders ,cardiac dysfunction, [ and may play a role in the aging process. Mitochondria has its own DNA.

58. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Mitochondrial DNA Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function . Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation . Oxidative phosphorylation is a process that uses oxygen and simple sugars to create adenosine triphosphate ( ATP ) , the cell's main energy source . The remaining genes provide instructions for making molecules called transfer RNAs ( tRNAs ) and ribosomal RNAs ( rRNAs ) . Mitochondrial genes are among the estimated 20,000 to 25,000 total genes in the human genome .

59. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Function of The DNA Deoxyribonucleic Acid ( DNA ), the gigantic molecule which is used to encode genetic information for all life on Earth. The chemical basis of hereditary and genetic variation are related to DNA. DNA directs the synthesis of RNA which in turn directs protein synthesis .

60. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Genetic Code The purine and pyrmidine bases of the DNA molecule are the letters or alphabet of the genetic code. All information contained in DNA represented by four letters: A,T,C,G. Three nucleotides of DNA (1st, 2nd and 3rd) form triplet codons. A group of codons constitute the genetic code, that can be translated into amino acid of proteins. RNA Codon tRNA Amino Acids

61. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Genetic Code The sequence of codons in the mRNA defines the primary structure of the final protein. Since there are 64 possible codons, most amino acids have more than one possible codon. Out of the 64 possible 3-base codons, 61 specify amino acids; the other three are stop signals (UAG, UAA, or UGA).

62. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The RNA Three major classes of RNA : messenger (mRNA), transfer (tRNA) and ribosomal (rRNA). Minor classes of RNA include small nuclear RNA ; small nucleolar RNA;………..

63. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The RNA The concentration of purine and pyrimidine bases do not necessarily equal one another in RNA because RNA is single stranded. However, the single strand of RNA is capable of folding back on itself like a hairpin and acquiring double strand structure.

64. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Messenger RNA mRNA molecules represent transcripts of structural genes that encode all the information necessary for the synthesis of a single type polypeptide of protein. mRNA ; intermediate carrier of genetic information; deliver genetic information to the cytoplasm where protein synthesis take place. The mRNA also contains regions that are not translated: in eukaryotes this includes the 5' untranslated region, 3' untranslated region, 5' capand poly-A tail.

65. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Transfer RNA(tRNA) All tRNAs share a common secondary structure represented by a coverleaf. They have four-paired stems defining three stem loops (the D loop, anticodon loop, and T loop) and the acceptor stem to which amino acids are added in the charging step. RNA molecules that carry amino acids to the growing polypeptide.

66. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Ribosomal RNA (rRNA) Ribosomal RNA (rRNA) is the central component of the ribosome, the function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation by providing peptidyl transferase activity.

67. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Ribosomes Ribosomes ; Factory for protein synthesis; are composed of ribosomal RNA and ribosomal proteins (known as a Ribonucleoproteinor RNP). They translate messenger RNA (mRNA) to build polypeptide chains using amino acids delivered by transfer RNA (tRNA) .

68. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Ribosomes Eukaryotic ribosomes are larger. They consist of two subunits; a 60S subunit holds (three rRNAs 5S, 5.8S , 28S and about 40 proteins) and a 40S subunit contains (an18S rRNA and about 30 proteins) , which come together to form an 80S particle compared with prokaryotic 70S ribosome

69. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Most mRNA are translated by more than one ribosome at a time; the result, a structure in which many ribosomes translate an mRNA in tandem, is called a polysomes. Polysomes

70. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA The Protein Proteins are the basic building materials of a cell, made by cell itself; the final product of most genes. Proteins are chain like polymers of a few or many thousands of amino acids. Amino acids are represented by codons, which are 3-nucleotide RNA sequences. Amino acids joined together by peptide bonds ( polypeptide) . Proteins can be composed of one or more polypeptide chains. Proteins have many functions: provide structure that help cells integrity and shape (e.g. collagen in bone); serve as enzymes and hormones; bind and carry substance and control of activities of genes….

71. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 71 Four levels of a protein's structure: Primary structure: Formed by joining the amino acid sequence into a polypeptide . Secondary structure: Different conformation that can be taken by the polypeptide: alpha helix and strands of beta sheet. Tertiary structure : Result from folding the secondary structure components of the polypeptide into three-dimensional configuration. Quaternary structure : complex of several protein molecules or polypeptide chains, usually called protein subunits, which function as part of the larger assembly or protein complex.

72. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 72 Protein Structure

73. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 73 Gene Expression Gene expression process by which a gene product (an RNA or polypeptide ) is made. In transcription steps , RNA polymerase make a copy of information in the gene (complementary RNA) (mRNA) complementary to one strands of DNA. In translation step , ribosomes read a messenger RNA and make protein according to its instruction. Thus any change in gene sequence may lead to change in the protein product.

74. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 74 Types of control in Eukaryotes Transcriptional, prevent transcription, prevent mRNA from being synthesized. Posttranscriptional, control mRNA after it has been produced. Translational, prevent translation; involve protein factors needed for translation. Posttranslational, after the protein has been produced.

75. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 75 Mutation Mutation include both gross alteration of chromosome and more subtle alteration to specific gene sequence. Gross chromosomal aberrations include: large deletions; addition and translocation (reciprocal and nonreciprocal). Mutation in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene. Point mutations are the result of the substitution of a single base. Frame-shift mutations occur when the reading frame of the gene is shifted by addition or deletion of one or more bases.

76. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 76 Mutation Mutations can have harmful, beneficial, neutral, or uncertain effects on health and may be inherited as autosomal dominant, autosomal recessive, or X - linked traits . Mutations that cause serious disability early in life are usually rare because of their adverse effect on life expectancy and reproduction .

77. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA Common Tools in Molecular Biology Nucleic acid fractionation Polymerase chain reaction Probes, Hybridization Vector, Molecular cloning Nucleic acid enzymes Microarray DNA sequencing Electrophoretic separation of nucleic acid Detection of genes: *DNA: Southern blotting; inSitu hybridization; FISH Technique *RNA: Northern blotting *Protein: Western blotting, immunohistochemistry

78. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 78 Human Genome Project Goals Identify all the approximately 20,000-25,000 genes in human DNA, Determine the sequences of the 3 billion chemical base pairs that make up human DNA, store this information in databases, Improve tools for data analysis, transfer related technologies to the private sector, and Address the ethical, legal, and social issues (ELSI) that may arise from the project.

79. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 79 Molecular Biology : Uses Various methods in molecular biology diagnose the different human diseases; diagnosis of an infectious agent, in malignancy, the presence of the genetic disease and in transplantation, paternity and forensic analysis. The Most Recent Applied Technologies Genetic engineering DNA finger-printing in the social and forensic science. Pre and postnatal diagnosis of inherited diseases. Gene therapy. Drug Design.

80. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 80 Molecular biology is facilitating research in many field including biochemistry, microbiology, immunology and genetics,…………………… Molecular biology allows the laboratory to be predictive in nature, it gives information that the patients may be at risk for disease (future).

81. 81 Glossary Alleles are forms of the same gene with small differences in their sequence of DNA bases. Exon (Coding DNA): A gene sequence contains protein coding information. Introns ( intervening sequence) (A noncoding DNA sequence ): Intervening stretches of DNA that separate exons. Primary transcript: The initial production of gene transcription in the nucleus; an RNA containing copies of all exons and introns. RNA gene or non-coding RNA gene : RNA molecule that is not translated into a protein. Noncoding RNA genes produce transcripts that exert their function without ever producing proteins. Non-coding RNA genes include transfer RNA (tRNA) and ribosomal RNA (rRNA), small RNAs such as snoRNAs, microRNAs, siRNAs and piRNAs and lastly long ncRNAs. Enhancers and silencers: are DNA elements that stimulate or depress the transcription of associated genes; they rely on tissue specific binding proteins for their activities; sometimes a DNA elements can act either as an enhancer or silencer depending on what is bound to it. Activators: Additional gene-specific transcription factors that can bind to enhancer and help in transcription activation . Open reading frame (ORF) : A reading frame that is uninterrupted by translation stop codon (reading frame that contains a start codon and the subsequent translated region, but no stop codon). Directionality: in molecular biology, refers to the end-to-end chemical orientation of a single strand of nucleic acid. The chemical convention of naming carbon atoms in the nucleotide sugar-ring numerically gives rise to a 5' end and a 3' end ( "five prime end" and "three prime end"). The relative positions of structures along a strand of nucleic acid, including genes, transcription factors, and polymerases are usually noted as being either upstream (towards the 5' end) or downstream (towards the 3' end). 3' flanking region: Present adjacent to 3' end of the gene; often contain sequences which affect the formation of the 3` end of the message and may contain enhancers or protein binding sites. 5' flanking region: A region adjacent to 5' end of the gene. It is not transcribed into RNA; it contains the promoter. May contain enhancers or other protein binding sites . 3' untranslated region: The three prime untranslated region (3' UTR) is a particular section of messenger RNA (mRNA). It follows the coding region. It is a region of the DNA which is transcribed into mRNA and becomes the 3' end or the message, Several regulatory sequences are found in the 3' UTR. The 3' untranslated region may affect the translation efficiency of the mRNA or the stability of the mRNA. It also has sequences which are required for the addition of the poly(A) tail to the message (including one known as the "hexanucleotide", AAUAAA ). 5' untranslated region: The five prime untranslated region ( 5' UTR ), also known as the leader sequence , is a particular section of messenger RNA (mRNA) and the DNA that codes for it. It is a region of a gene which is transcribed into mRNA. It starts at the site (where transcription begins) and ends just before the start codon (usually AUG) of the coding region. It usually contains a ribosome binding site (RBS), in bacteria also known as the Shine Dalgarno sequence (AGGAGGU). In prokaryotic mRNA the 5' UTR is normally short. Some viruses and cellular genes have unusual long structured 5' UTRs which may have roles in gene expression. Several regulatory sequences may be found in the 5' UTR . Reverse Transcription: Some viruses (such as HIV, the cause of AIDS ), have the ability to transcribe RNA into DNA.

82. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA 82 Thank You

83. NASARAWA STATE UNIVERSITY, KEFFI, NIGERIA DNA Replication The double helix did explain how DNA copies itself We will study this process, DNA replication , in more detail

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