Molecular Genetics


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DNA and RNA; Replication. Protein Synthesis

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Molecular Genetics

  1. 1. Mechanisms of Evolution: Genetics
  2. 2. Introduction to Genetics <ul><li>Genetics is the study of genes and the ways whereby they determine the traits of an organism </li></ul><ul><li>We cover the following concepts and principles of evolution based on genetics: </li></ul><ul><li>Biological Genetics </li></ul><ul><li>Chromosomes and Genes </li></ul><ul><li>Mitosis and Meiosis </li></ul><ul><li>Population Genetics </li></ul><ul><li>Molecular Biology </li></ul>
  3. 3. Key Concepts in Evolution: Natural Selection <ul><li>Species : A group of life forms (plants and animals) that can reproduce fertile offspring among themselves </li></ul><ul><li>Evolution : Change through time of biological species </li></ul><ul><li>Natural selection : Evolutionary change based on differential reproduction of the species within an environment </li></ul>
  4. 4. Key Concepts in Evolutionary Thought: Mutation <ul><li>Heredity: the transmission of all biological traits (inherited characteristic) from generation to generation </li></ul><ul><li>Chromosome : Body in the nucleus of the cell that contains the hereditary material: DNA and protein </li></ul><ul><li>Genes : A chromosomal segment with a specific function </li></ul><ul><li>Mutation : Alteration of genetic material giving rise to new life forms </li></ul>
  5. 5. Structure of Cell: Diagram <ul><li>To understand how genetics works, we must start with the cell </li></ul><ul><li>The next discussion follows this diagram of a cell and its components </li></ul>
  6. 6. Cell Structure: Description <ul><li>Cell : Smallest unit of the organism considered to be alive </li></ul><ul><li>Nucleus : Center of the cell, which contains genetic material (chromosomes, comprising the genes) </li></ul><ul><li>Nuclear Membrane : Membrane enclosing the nucleus </li></ul><ul><li>Cytoplasm : Jellylike material that make up the rest of the cell </li></ul><ul><li>Plasma Membrane : The membrane that keeps the cell in shape and allows entry and exit of certain material. </li></ul><ul><li>The diagram to the left show other specialized parts: nerve cell, white blood cell, sperm </li></ul>
  7. 7. Cells: Other Parts <ul><li>Proteins: The organic molecules that maintain the cells’ functions </li></ul><ul><li>Organelles: functional parts within cytoplasm </li></ul><ul><li>Ribosomes : organelles important to protein synthesis, as we will see </li></ul><ul><li>Mitochondria: organelles responsible for energy production; They have their own DNA whose regular mutations enable relative dating within a species, human in this case </li></ul>
  8. 8. Concepts of Genetics <ul><li>Trait: Any inborn feature of a living organism </li></ul><ul><li>Each organism contains a pair of genes for each trait </li></ul><ul><li>Each gene may have two or more alleles (variants) </li></ul><ul><li>Monogenic Trait: a trait coded by one gene for each trait (e.g., phenylthiocarbamide [PTC] taster vs. nontaster of the bitterness of brussels sprouts); </li></ul><ul><li>Mendelian Trait: This is a synonym for Monogenic trait </li></ul><ul><li>Polygenic: a trait coded by more than one gene (e.g. skin color, eye color) </li></ul>
  9. 9. Genes and Chromosomes <ul><li>In the cell nucleus is genetic material which determines our traits. </li></ul><ul><li>Chromosomes are long strands of molecules and protein; they come in pairs </li></ul><ul><li>Humans have 23 pairs of chromosomes, or 46 in all </li></ul><ul><li>Genes are units within chromosomes </li></ul><ul><li>Also in pairs, they occur in specific location, or loci , of the chromosomes </li></ul><ul><li>Each variant of a trait is determined by an allele of a gene </li></ul>
  10. 10. Genetic Composition: Genotype <ul><li>Genotype : Alleles of a gene possessed by an organism </li></ul><ul><li>Homozygous : Having two of the same allele in a gene pair </li></ul><ul><li>Heterozygous : Having two different alleles in a gene pair </li></ul>
  11. 11. Genetic Appearance: Phenotype <ul><li>Phenotype : Observable characteristics of an organism </li></ul><ul><li>Dominant : Allele of a pair that is expressed in the phenotype (e.g. PTC taster) </li></ul><ul><li>Recessive : Allele of a pair that is expressed only when homozygous (e.g. PTC nontaster, Blood Type O) </li></ul><ul><li>Codominant : Both alleles of a pair are expressed in the phenotype (e.g., Blood Type A and B) </li></ul><ul><li>Or four o’clock flowers: red, white—and pink </li></ul>
  12. 12. Cell Division <ul><li>Cell division is a constant process in all living forms. </li></ul><ul><li>There are two types of cell division: </li></ul><ul><li>Mitosis: The division of somatic or body cells </li></ul><ul><li>Meiosis: The division of gametes or sex cells: sperm in the males of any species and ovum (plural ova ) or egg in the females of any species </li></ul><ul><li>The next sections explain how these two types of cells divide. Refer to the diagram in the next panel </li></ul>
  13. 13. Mitosis: First Phases <ul><li>In the interphase , the cell is “at rest” between one division and the next </li></ul><ul><li>In the prophase , the chromosome double, from 46 (23 pairs) chromosomes to 92 (46 pairs) </li></ul><ul><li>They appear to “thicken” as each chromosome replicates itself. </li></ul><ul><li>The chromosomes are attached to each other at the center, forming an x; these are known as centromeres </li></ul>
  14. 14. Mitosis: Middle Phases <ul><li>In the prometaphase the nucleus dissolves, the chromosomes line up in the center, centrioles form at the opposite end of the cells, and spindle fibers (fibrils or microtubules) form between the centromeres of the chromosomes and the centrioles (top diagram) </li></ul><ul><li>In the metaphase, the chromosomes are lined up and the centrioles prepare to pull each new pair of chromosomes toward them using the spindle fibers) </li></ul>
  15. 15. Mitosis: End Phases <ul><li>In the anaphase, the fibrils anchored by the centrioles pull the chromosomes toward the center of each new cell </li></ul><ul><li>In the telophase, the fibrils and the centrioles dissolve and the wall forms between the two new cells </li></ul><ul><li>In cytokinesis , the walls are completely formed and the two new cells are in interphrase. </li></ul>
  16. 16. Meiosis: Introduction and Terms <ul><li>Meiosis refers to cell division of a fertilized egg in the reproductive process. </li></ul><ul><li>Gametes : sex cells </li></ul><ul><li>Sperm : male sex cells </li></ul><ul><li>Ovum : female sex cells </li></ul><ul><li>Each gamete (sex cell) </li></ul><ul><li>Contains half the normal number of chromosomes in cells </li></ul><ul><li>Contains 23 chromosomes in humans </li></ul>
  17. 17. Meiosis: Fertilization of an Ovum <ul><li>First, the sperm has fertilizes an ovum (above left) </li></ul><ul><li>Three million sperms enter the vagina; only one ultimately enters the ovum, roughly a third of the way down the Fallopian tube </li></ul><ul><li>The fertilized ovum (now a zygote ) is then implanted in the uterus </li></ul><ul><li>The rapid process of meiosis begins there </li></ul><ul><li>Of course, some couples don’t get it quite right (below left) </li></ul>
  18. 18. Meosis I: Beginning Phases <ul><li>In the prophase stage, the doubled chromosomes cross over, so some of the genes on one chromosome moves over to the other chromosome—and vice versa </li></ul><ul><li>Otherwise, the process is the same as mitosis </li></ul><ul><li>The prometaphase follow the same process as in mitosis: the chomosomes line up and the spindle fibers and centrioles are now in position. </li></ul>
  19. 19. Meiosis II: Early Middle Phases <ul><li>The first metaphase continues as mitosis; the chromosomes have been doubled and now line up. </li></ul><ul><li>The anaphase continues as in mitosis; the chromosomes are pulled apart by the spindle fibers and the centrioles </li></ul><ul><li>The telophase continues as in mitosis; the chromosomes are centered in the daughter cells and a new wall forms. </li></ul>
  20. 20. Meiosis III: Late Middle Phases <ul><li>In the interphase 2, the chromosomes remain lined up and the nucleus has not formed </li></ul><ul><li>In metaphase 2, there is only a pair of chromosomes in each cell; they remain lined up and the spindle fibers and the centrioles go into position </li></ul><ul><li>In anaphase 2, the chromosomes (now numbering 23 as haploids ) are pulled apart. </li></ul>
  21. 21. Meiosis IV: Final Phases <ul><li>In telephase 2, a wall forms between each of the cells and the nuclei start to form </li></ul><ul><li>In cytokinesis or interphase, the daughter cells remain with one pair of chromosomes. </li></ul><ul><li>On fertilization, the sperm will contribute half the chromosomes and the ovum contributes half to the offspring </li></ul>
  22. 22. End of Meiosis; Beginning of Mitosis: Fertilization of an Ovum <ul><li>When the couple copulates, the sperm fertilizes the egg (upper left) </li></ul><ul><li>In so doing, each parent contributes exactly half ot the chromosomes of the offspring cell </li></ul><ul><li>Three million sperms enter the vagina; only one ultimately enters the ovum, roughly a third of the way down the Fallopian tube </li></ul><ul><li>The fertilized ovum (now a zygote ) is then implanted in the uterus </li></ul><ul><li>The rapid process of mitosis of the zygote begins there </li></ul><ul><li>Of course, some couples don’t get it quite right (lower left) </li></ul>
  23. 23. Mendelian Genetics <ul><li>The appearance of an individual is derived from the cell divisions we just described </li></ul><ul><li>Traits are maintained in the organism through mitosis </li></ul><ul><li>They are transmitted from parent to offspring through meiosis </li></ul><ul><li>When haploid cells are united between couples to become diploid </li></ul><ul><li>Each parent contributes exactly half their makeup to their offspring </li></ul>
  24. 24. Individual Genetics; :Concepts <ul><li>Traits are inherited through the chromosomes and their constituent genes </li></ul><ul><li>The genetic composition of a trait is known as a genotype </li></ul><ul><li>A phenotype is a trait of a genotype that is visible or otherwise observable and can be measured </li></ul><ul><li>Homozygous traits are those with two identical alleles in a gene pair </li></ul><ul><li>Heterozygous traits are those with two different alleles in a gene pair </li></ul>
  25. 25. Individual Genetics: When Genotypes Become Phenotypes <ul><li>A dominant allele is one whose trait appears in both homozygous heterozygous combination </li></ul><ul><li>A recessive allele is one whose trait appears only in homozygous combination. </li></ul><ul><li>A codominant allele is one whose trait reflects the genetic combination of two different alleles </li></ul><ul><li>Punnett squares illustrate how these principles work </li></ul>
  26. 26. Case Study of Monogenic Trait: Tasters vs. Nontasters <ul><li>Most of us can taste the bitterness of Brussels sprouts </li></ul><ul><li>This is the ability to taste phenylthiocarbamide (PTC) </li></ul><ul><li>Tasters are dominant; nontasters are recessive </li></ul><ul><li>A Punnett Square allows us to determine the proportion of tasters vs. nontasters of PTC </li></ul><ul><li>This is a table that gives us a visual count of the allele for each trait. </li></ul>
  27. 27. PTC Tasters and Nontasters: Generation I <ul><li>Suppose one parent is a taster and the other is a nontaster in the first generation </li></ul><ul><li>All the offspring (Generation II) will be tasters in the second generation, as shown in the next panel. </li></ul><ul><li>To simplify, we use only a 2 X 2 table </li></ul>
  28. 28. Punnett Square of Tasters and Non-Tasters: Generation II <ul><li>t (nontaster) t (nontaster) </li></ul><ul><li>T (taster) Tt Tt </li></ul><ul><li>T (taster) Tt Tt </li></ul>
  29. 29. PHC Tasters and Nontasters: Generation II <ul><li>The second generation generate a new combination of phenotypes </li></ul><ul><li>The proportion is now 1 homozygote for PTC tasters, 1 homozygote for nontasters, and 2 heterozygotes for tasters/nontasters. </li></ul>
  30. 30. Punnett Square of Tasters and Non-Tasters: Generation III <ul><li> T (tasters t (nontasers) </li></ul><ul><li>T TT Tt </li></ul><ul><li>t Tt tt </li></ul>
  31. 31. Codominant Genes <ul><li>Some alleles are codominant: one trait does not trump the other </li></ul><ul><li>A species of flower, four-o’clocks, may come in red and white </li></ul><ul><li>Their hybrids thus come in pink in Generation II </li></ul><ul><li>In the Punnett Square, in Generation III, the proportion is 1:2:1 (one red, two pinks, and one white) </li></ul>
  32. 32. Mendel’s Laws: Law of Segregation <ul><li>Mendel found that there were three principles of inheritance resulting from the study of pea plants for seven characteristics. </li></ul><ul><li>In so doing, he found that traits of the parent generation do not blend in those of their offspring. </li></ul><ul><li>Rather, one gene for each trait is segregated from other genes for other traits. </li></ul><ul><li>Segregation : Separation of alleles in the formation of gametes (sex cells) </li></ul>
  33. 33. Mendel’s Law: Law of Independent Assortment <ul><li>Independent Assortment: differing traits are inherited independently of each other (genes on separate chromosomes) </li></ul><ul><li>For example whether a pea plant flower is violet or white is separated from smooth or wrinkled peas </li></ul><ul><li>In other words, a white flowering plant can yield either a wrinkled or a smooth pea; so can a violet flowering plant </li></ul><ul><li>So flower color is independent from smoothness of peas </li></ul><ul><li>The PHC assortments in the Punnett Squares are another example of this law. </li></ul>
  34. 34. Mendel’s Laws: Law of Recombination <ul><li>Though independent, genes can recombined to allow further genetic variety </li></ul><ul><li>In meiosis, some genes cross over, allowing even further variety. </li></ul>
  35. 35. Linkages <ul><li>Nevertheless, if alleles occur on the same chromosome, they will be inherited together. </li></ul><ul><li>Sex-linked traits are one example: secondary characteristic are linked to the primary characteristics (organs of reproduction </li></ul>
  36. 36. Molecular Biology: Basics <ul><li>All matter is made of atoms </li></ul><ul><li>Of the 92 atoms, 4 are essential to life: </li></ul><ul><li>--Carbon [C] --Oxygen [O] </li></ul><ul><li>--Hydrogen [H] --Nitrogen [N] </li></ul><ul><li>Others are also important: calcium, phosphorus </li></ul><ul><li>Atoms are joined together to form molecules </li></ul>
  37. 37. Molecular Biology: Molecules of Life <ul><li>Three molecules are essential </li></ul><ul><li>Carbohydrates : sugars and starches </li></ul><ul><li>Lipids: fats, oils, and waxes </li></ul><ul><li>Proteins: building blocks of cells </li></ul>
  38. 38. Protein <ul><li>Role of Proteins </li></ul><ul><li>To build cells </li></ul><ul><li>And maintain them in various ways </li></ul><ul><li>Amino acids: Any of 20 kinds of </li></ul><ul><li>long chains of basic units </li></ul><ul><li>that include C, O, H, and N </li></ul><ul><li>that form protein </li></ul>
  39. 39. Structure of DNA
  40. 40. Replication of DNA
  41. 41. Nucleic Acid <ul><li>Nucleic Acid : Long chains of molecules that convey genetic information </li></ul><ul><li>DNA and RNA are nucleic acids </li></ul><ul><li>Nucleotide: A unit of nucleic acid that comprises </li></ul><ul><li>Phosphate: Compound that combines phosphorus with other elements </li></ul><ul><li>Complex Sugar: aka pentose, a catchall name for sugars with five carbon atoms </li></ul><ul><li>Base: one of four nitrogen-based molecules in DNA </li></ul>
  42. 42. Defining DNA: Deoxyribonucleic Acid 1 <ul><li>DNA is a molecule carrying the genetic code </li></ul><ul><li>Picture DNA as a spiral ladder </li></ul><ul><li>Sides are composed of a </li></ul><ul><li>Complex sugar molecule (deoxyribose in DNA) </li></ul><ul><li>Phosphate molecule </li></ul><ul><li>“ Rungs” are the bases </li></ul>
  43. 43. Defining DNA: Deoxyribonucleic Acid 2 <ul><li>The Bases </li></ul><ul><li>Purines (defined as two connected rings of nitrogen): </li></ul><ul><li>Adenine (A) in DNA and RNA </li></ul><ul><li>Guanine (G) in DNA and RNA </li></ul><ul><li>Pyrimidine (defined as one ring of nitrogen): </li></ul><ul><li>Cytosine (C) in DNA and RNA </li></ul><ul><li>Thymine (T) in DNA </li></ul><ul><li>Uracil (U) takes T’s place in RNA </li></ul>
  44. 44. Defining DNA: Deoxyribonucleic Acid 3 <ul><li>Sugar and phosphate form the “sides” of a “ladder” </li></ul><ul><li>Bases are the rungs, that with hydrogen bonds link: </li></ul><ul><li>One specific purine with one specific pyramidine </li></ul><ul><li>Adenine (A) with thymine (T) (uracil [U] in RNA) </li></ul><ul><li>Cytosine [C] with guanine [G] </li></ul><ul><li>The phosphate, sugar, and base comprise the nucleotide </li></ul><ul><li>Triplets: three nucleotides (and three bases) </li></ul><ul><li>The chain of nucleotides is known as nucleic acid </li></ul><ul><li>DNA is one type of nucleic acid </li></ul>
  45. 45. Replication of DNA
  46. 46. Molecular Biology: Cell Division <ul><li>The DNA strands disconnect </li></ul><ul><li>They attract “floating” nucleotides from the nucleus </li></ul><ul><li>New nucleotide chains are formed </li></ul><ul><li>A connects with T </li></ul><ul><li>C connects with G </li></ul><ul><li>The DNA strands—core of the chromosomes </li></ul><ul><li>Form part of the new nuclei of the new cells </li></ul>
  47. 47. Protein Synthesis: mRNA
  48. 48. DNA and RNA <ul><li>DNA is “deoxyribose nucleic acid” </li></ul><ul><li>RNA is “ribose nucleic acid” </li></ul><ul><li>The differences: </li></ul><ul><li>DNA has one less oxygen molecule per sugar molecule than RNA </li></ul><ul><li>DNA is double-stranded (the double helix) </li></ul><ul><li>RNA is single-stranded </li></ul>
  49. 49. Molecular Biology: Synthesizing Protein 1 <ul><li>DNA strands “unzip” or disconnect </li></ul><ul><li>Messenger ribonucleic acid (mRNA) is attracted to opened “master” DNA </li></ul><ul><li>A connects with uracil (replacing T) </li></ul><ul><li>C connects with G </li></ul><ul><li>Each DNA triplet attracts a mRNA codon </li></ul><ul><li>Codon by codon, the mRNA string forms </li></ul><ul><li>When complete mRNA leaves nucleus </li></ul><ul><li>And goes to a ribosome </li></ul>
  50. 50. Molecular Biology: Synthesizing Protein 2. <ul><li>mRNA moves to the ribosomes in the cytoplasm </li></ul><ul><li>Each codon of the mRNA “attracts” </li></ul><ul><li>The complementary anticodon of the transfer RNA </li></ul><ul><li>Which bears the correct amino acid </li></ul><ul><li>synthesizes the correct amino acid </li></ul><ul><li>The tRNA “deposits” the amino acid </li></ul><ul><li>The amino acids are attached to each other to form proteins </li></ul>
  51. 51. Molecular Biology: Information Metaphor <ul><li>Codons: Three-based units that form code (“recipes”) for type of amino acid </li></ul><ul><li>Sequence of codons make up a chain of amino acids to make a protein </li></ul><ul><li>Term for process: protein synthesis </li></ul><ul><li>To summarize: </li></ul><ul><li>Base = Letter </li></ul><ul><li>Triplet/Codon/Anticodon = Word = Amino Acid </li></ul><ul><li>Gene = Sentence = Protein </li></ul>
  52. 52. Conclusion: What Has Been Covered <ul><li>Cellular genetics </li></ul><ul><li>Cell structure </li></ul><ul><li>Chromosomes </li></ul><ul><li>Genes </li></ul><ul><li>Cell division (mitosis and meiosis </li></ul><ul><li>Genotypes and Phenotypes </li></ul><ul><li>Dominant, Codominant, and Recessive Genes </li></ul><ul><li>Molecular Biology </li></ul><ul><li>Nucleic acid and nucleotides </li></ul><ul><li>Cell structure from another perspective </li></ul><ul><li>DNA and coding </li></ul><ul><li>RNA and protein synthesis </li></ul>