chapter introduction to molecular genetics 1.pptx

introduction to Genetics

1. Chapter one Introduction

2. Course objective At the end of this chapter, the student will be able to -Define the term genetics -Explain classification of genetics -Discuss history of genetics -Discuss nucleic acid overview

3. Course outline Definition of genetics History of genetics Classification of genetics -Classical genetics - Molecular genetics - Evolutionary genetics Nucleic acid overview

4. Introduction Genetics comes from ancient Greek word, genetikos , “genitive” and that from genesis, “origin” Genetics defined as the study of heredity and variation in living organism Genetics – study of how traits are passed from parent to offspring

5. Definition of terms Genetics = science of heredity study of what genes are, how they carry info, how they are replicated , passed along, and how expression of the info. determines characteristics of the organism. Genome = all the genes present in a cell or organism e.g. prokaryotes have 1 set of all their genes = haploid; while eukaryotes have 2 sets = diploid Chromosome = is a packaged and organized structure containing the DNA of a living organism. E.g. bacteria have 1 chromosome; humans have 46 chromosomes( 23 pairs ) Genes = A portion of a DNA molecule that serves as the basic unit of heredity. Is a segment of DNA that determines a trait is the unit of heredity

6. Cont… alleles: genes at the same location (locus) on homologous chromosomes, but that have different DNA sequences Genotype = the precise genetic makeup of an organism Phenotype = an observable characteristic of an o rganism Gene expression = turning the info. from the gene in DNA into the molecule it encodes, usually a protein. .

7. History of Genetics Domestication of plants & animals suggests prehistoric peoples recognized concept of heredity Traits passed from parent to offspring Selection of desirable traits – artificial selection Aristotle (4th century BC) speculated that female thought to supply what he called the “matter” and the male the “motion .” The Institutes of Manu, India female like that of the “field ”and of the male like that of the “ seed The ancient Babylonians knew that pollen from a male date palm tree must be applied to the pistils of a female tree to produce fruits .

8. Gregor Mendel (1822-1884 Systematically recorded results of crosses Theorized on nature of hereditary material Postulate mechanism of transfer of " Elementen " governing traits

9. Cont… In 1944-Ostwald Avery showed genes are composed of DNA In 1953-James Watson and Francis Crick describe physical structure of DNA. In 1990 human genome project, a large collaborative venture began, and provide the completes human DNA sequence in the year 2003

10. Classification of Genetics Genetics may classified into three classes: Classical, Molecular, and evolutionary genetics I-Classical Genetics Is the branch of genetics based solely on visible results of reproductive acts. It is the oldest discipline in the field of genetics , going back to the experiments on Mendelian inheritance by Gregor Mendel who made it possible to identify the basic mechanisms of heredity

11. Classification of Genetics, continued II- Molecular Genetics Is the field of biology that studies the structure and function of genes at a molecular level and thus employs methods of both molecular biology and genetics . The study of chromosomes and gene expression of an organism can give insight into heredity, genetic variation, and mutations.

12. Classification of Genetics, continued … III-Evolutionary genetics Is the broad field of studies that resulted from the integration of genetics and Darwinian evolution , called the 'modern synthesis‘ Populations evolve by changes in gene frequencies through: 1.  Genetic drift 2.  Gene flow 3.  Natural selection Focused on mechanism of evolutionary changes Change of gene frequencies in population over time. Charles Darwin, famous in the area of evolutionary genetics

13. Medical genetics Medical genetics is a branch of genetics focused on the study of t he inheritance of disease genes in families Mapping of disease genes to specific locations on the chromosomes Analysis of the molecular mechanism of through which genes cause disease The diagnosis and treatment of genetic diseases C ommunication of information regarding , the risk of genetic diseases, prognosis, and treatment of patients and their families.

14. Nucleic acid overview Nucleic acids are molecules that encode genetic information. Nucleic acids enable organisms to transfer genetic information from one generation to another . It contains the instructions needed to construct other components of cells, such as RNA and proteins. Includes DNA (deoxyribonucleic acid), and RNA (ribonucleic acid).

15. Nucleic Acids DNA/RNA Nucleic acids are polymers of nucleotides monomers

16. DNA 1953 - James Watson, Francis Crick, Rosalind Franklin & Maurice Wilkins Lead to understanding of mutation and relationship between DNA and proteins at a molecular level 1959 – “Central Dogma” DNA RNAprotein

17. Cont…… DNA consists of a double helical sugar-phosphate structure with the two strands held together by hydrogen bonding between adenine and thymine or cytosine and guanine bases DNA consists of a pair of strands of a sugar-phosphate backbone attached to a set of pyrimidine and purine bases The sugar is deoxyribose – ribose missing an oxygen atom at its carbon 2 position . Each DNA strand consists of alternating deoxyribose molecules connected by phosphodiester bonds from the position of one deoxyribose to the position of the next

18. Cont… The sugar unit is attached to a nitrogenous base by an N- glycosidic bond. The combination of a base and a pentose is called a Nucleoside . The base is attached to the 1' carbon atom of the pentose . If the sugar is a deoxyribose, a deoxyribonucleoside is produced and when the sugar is a ribose, a ribonucleoside is produced The purines contain a double ring structure known as a purine ring whereas the pyrimidines contain a single pyrimidine ring.

19. DNA Nucleotides “Bases

20. Two Hydrogen Bonds Three Hydrogen Bonds Base Pairing A -- T complementary Base Pairing G -- C complementary

21. Anti-Parallel - DNA is a double stranded molecule and orients in an anti-parallel fashion -orientation is in reference to the phosphodiester bonds.

22. Central dogma Is refers to transmission of information from DNA to DNA during its transmission from generation to generation through replication From DNA RNA Protein through gene expression

23. Central Dogma genetics focus DNA transcription RNA Protein translation Replication

24. DNA replication DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process occurs in all living organisms and is the basis for biological inheritance. DNA replication involves local unwinding of the double helix and copying a new strand from the base sequence of each parental strand DNA replication is semiconservative , meaning that each strand in the DNA double helix acts as a template for the synthesis of a new, complementary strand.

25. Cont … DNA replication requires the following components Template, Enzymes:( Helicase, Primase , DNA pol III, DNA pol I, DNA ligase) Primer (to prime synthesis ), dNTPs : d( deoxy ), N ( A,T,G,or C ) Energy .

26. Cont… Replication of duplex DNA is a complex process involving a group of enzyme activities. The first step in DNA replication is to ‘unzip’ the double helix structure of the DNA molecule by helicase enzyme which breaks the hydrogen bonds holding . The separation of the two single strands of DNA creates a ‘Y’ shape called a replication ‘fork’. The two separated strands will act as templates for making the new strands of DNA.

27. Cont… One of the strands is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strand. The other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand. A short piece of RNA called a primer (produced by an enzyme called primase ) comes along and binds complementary to the template A typical primer is about five to ten nucleotides long and acts as the starting point for DNA synthesis The RNA Primers are necessary for DNA Polymerase to bind Nucleotides to the 3' end DNA polymerase binds to the primers and then ‘walks’ along it, adding new complementary nucleotide bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction

28. Cont…. All the above steps of DNA replication are processed in the following three stages : Initiation , Elongation , and Termination . Initiation: involves recognition of an origin of replication by a complex of proteins, separation of the parental strands by helicase, then synthesis of daughter strands can be initiated at the replication fork.

29. Cont… Elongation : a primer sequence is added with complementary RNA nucleotides, which are then replaced by DNA nucleotides For 5 '-3' Template : The 3'-5' proceeding daughter is called leading strand because DNA Polymerase can "read" the template and continuously adds nucleotides. The 3'-5' template cannot be "read" by DNA Polymerase. The replication of this template is complicated and the new strand is called lagging strand

30. Cont… Example :

31. Cont… Termination: the RNA primers are removed and replaced by DNA through the activity of DNA polymerase I , the other polymerase involved in replication DNA polymerase III then fills in the gaps created by the excised bases. Finally, an enzyme called DNA ligase seals up the sequence of DNA into two continuous double strands . Enzymes called DNA polymerase III exonucleases “proofread” the new double helix structures and remove mispaired bases. Proof reading in 3 to 5 direction

32. Summery questions Define Genetics Explain the difference among classical, molecular and evolutionary genetics Mention at least 3 major historical events take place in the development of genetics, in the 21 st century What are the basic elements in the DNA nucleotide What is the difference between genotype and phenotype?

33. Cont….. 6. What are the important compounds that make up the DNA molecule? 7. How does DNA double strand constructed? 8. What is the central dogma of nucleic acid? 9. Explain about DNA replication processes

34. End THANK YOU