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![MicroQuestions
1. Describe the relationship between DNA, genes
and chromosome. [3]
2. Using the idea of molecular structure, describe
the structure of DNA and its function in leading
to a trait. [4]
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Molecular genetics 2014
This document discusses the learning objectives for a lesson on molecular genetics. It covers DNA structure and function, genes, genetic transfer between organisms, and the effects of genetic engineering on society. Specifically, it aims to explain how the human insulin gene can be inserted into bacterial DNA to produce human insulin through fermentation. It also aims to discuss the social and ethical implications of genetic engineering using a real-world example.
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Molecular genetics 2014
- 2. 2 Learning Objectives: (a) outlinethe relationship between DNA, genes and chromosomes. (b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides. (c) state the rule of complementary base pairing. (d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides. (e) state that each gene is a sequence of nucleotides, as part of a DNA molecule. (f) explain that genes may be transferred between cells
- 3. 3 Learning Objectives: (g) brieflyexplain how a gene that controls the production of human insulin can be inserted into bacterial DNA to produce human insulin in medical biotechnology. (h) outline the process of large-scale production of insulin using fermenters. (i) discuss the social and ethical implications of genetic engineering, with reference to a named example.
- 4. 4 "Cloning is allvery well in theory, but do you have any proof it can actually work?"
- 5. 5 1. We inherittraits from aunts, uncles, cousins and siblings because family members point out the resemblance between students and their relatives. 2. Some people think that most common traits are “better”. 3. Dominant alleles or traits are always the most common. 4. DNA is a living thing. 5. Only animal contains DNA. 6. Genes from one type organism will not function in a different type organism.
- 6. 6 1. Traits canonly be inherited from parents, and by extension, grandparents. 2. No. The traits simply show up more frequently in the human population. 3. Not necessary. ( A dominant trait may be quite rare, while a recessive trait may be the most common one observed.)
- 7. 7 × DNA isa living thing. × Genes from one type organism will not function in a different type organism. × Only animal cells contain DNA. 4. DNA is a molecule with instructions for a cell. 5. Plants also contain DNA 6. There is a genetic code common to all living things.
- 8. 20.1 DNA 20.2 Genes 20.3Transferring Genes between Organisms 20.4 Effects of Genetic Engineering on Society Chapter 20 Molecular Genetics
- 9. Learning Outcomes After thissection, you should be able to: • describe the basic unit of DNA – the nucleotide; • state and apply the rule of complementary base pairing. 20.1 DNA
- 10. 10 Chromosomes • Inheritable materialsin nucleus of a cell. Numerous genes are located on it. • Chromosomes can exist in coiled compact form or uncoiled extended form. • Cells undergoing cell division will contain chromosomes in coiled compact form.
- 11.
- 12. Function of DNA •It codes for the synthesis of polypeptides. • Many polypeptides will join together to form protein, which is responsible for your traits. 12
- 13. 13 Structure of DNA •A molecule that carries genetic information • The basic unit of DNA is known as nucleotide;
- 14. 14 adenine nucleotide thymine nucleotide guanine nucleotide cytosine nucleotide • Each nucleotide(basic unit) is a complex of three subunits: a) a sugar (deoxyribose/ribose) b) a phosphate group c) a nitrogenous base • Many nucleotides can be joined together to form polynucleotides.
- 15.
- 16. “Rule of basepairing” • Adenine (A) bonds with thymine (T) • Guanine (G) bonds with cytosine (C) These pairs of bases are called complementary bases.
- 17. • The DNAmolecule is made of two anti-parallel polynucleotide strands. (The two strands run in opposite directions.) • The bases on one strand form bonds with the bases on the other strand according to the rule of base pairing.
- 18.
- 19.
- 20. The two anti-parallelstrands of the DNA molecule coil to form a double helix three-dimensional structure. bases sugar-phosphate backbone coiling of DNA the double helix 3D structure of DNA
- 21. Coiling of DNA UncoiledDNA resemble a ladder (2D structure) Coiled DNA resemble a spiral staircase/ double-helix (3D structure)
- 22.
- 23. 23 Activity: Build YourDNA Model • Create a DNA model using materials of their own choice. • Suggested materials include straws, pipe cleaners, pasta • They should include a key that explains what each item represents. After you have completed their models, display the models to the whole class.
- 24.
- 25. Checkpoint 1 1. a)State the bases that are complementary to the bases on strand shown below: b) State the ratio of: (1) adenine : thymine, and (2) guanine : cytosine in the DNA of a cell. Answer: Answer: (1)1 : 1 (2)1 : 1
- 26. • What isthe base sequence of the DNA strand that would be complementary to the following single-stranded DNA molecule? GGATCTGATCCAGTCA A : GGAUCUGAUCCAGUCA B : CCTAGACTAGGTCAGT Checkpoint 2
- 27. • The percentof cytosine in a double-stranded DNA is 21. What is the percent of thymine in that DNA? A 21% B 29% Checkpoint 3
- 28. • According tobase pair rule, the percentage of As, Ts, Cs, and Gs should add up to 100%, because A C T G = = Adding all the bases together should make up 100% of the DNA molecule.
- 29. • The percentof adenine in a double-stranded DNA is 38. What is the percent of cytosine in that DNA? A 12% B 38% Checkpoint 4
- 30. • The percentof guanine in a double-stranded DNA is 14. What is the percent of adenine in that DNA? A 14% B 36% Checkpoint 5
- 31. © Boardworks Ltd2004 What’s the order? Let’s Recap !
- 32.
- 33. Investigation 13.2 : DNAExtraction of Onion 33
- 34. Add 10cm3 detergent To breaknuclear membrane Add 10cm3 of ethanol To separate out the DNA strand Add phenol red indicator Indicate presence of DNA
- 35. 20.1 DNA 20.2 Genes 20.3Transferring Genes between Organisms 20.4 Effects of Genetic Engineering on Society Chapter 20
- 36. Learning Outcomes After thissection, you should be able to: • state that DNA molecules contain the genetic code; • state what is meant by the genetic code; • state that a gene is a specific sequence of nucleotides in a DNA molecule that controls the production of a polypeptide. 20.2 Genes
- 37. What is agene? • It is a segment of DNA. • The nucleotide sequence in the gene determines the polypeptide formed. gene DNA polypeptide coded by the gene 20.2
- 38. • Three bases,or codon, code for one amino acid. • A chain of amino acids makes up one polypeptide, which later can be used to make proteins. Codon on DNA Example of amino acid coded for TAC Methionine (M) TAT Alanine (A) CAT Lysine (K) GAG Glutamic acid (E) ACA Serine (S)
- 39. “One gene, onepolypeptide” theory • The theory that each gene is responsible for the synthesis of a single polypeptide
- 40. What happens when thenucleotide sequence in a gene is altered? What happens when the nucleotide sequence in a gene is altered?
- 41. A change inthe nucleotide sequence of a gene is termed as gene mutation. A mutation may or may not lead to a change in the protein product. A change in the protein product may or may not lead to an observable phenotype. Recall Two examples of gene mutation was mentioned in Chapter 19. Can you state the two examples? (1)Albinism (2)Sickle-cell anaemia
- 42. Important! •A cell cannotdirectly use the DNA template to make proteins. It has to go through the following stages. How are proteins made? How are proteins made?
- 43. (a) Transcription: • Messagesin DNA template is copied into messenger RNA in the nucleus. • (b) Translation : messenger RNA carries the message to cytoplasm and ribosome helps to convert them into proteins. 44 (a) Transcription (b) Translation
- 44. MicroQuestions 1. Describe therelationship between DNA, genes and chromosome. [3] 2. Using the idea of molecular structure, describe the structure of DNA and its function in leading to a trait. [4] 45
- 45. 1) (a) •Gene isa segment of the DNA molecule . •Chromosomes are made of coiled DNA molecules. •DNA carries many genes along its length.
- 46. 1) (b) Function: DNA codesfor the synthesis of polypeptide. Polypeptides are used to make proteins , which are responsible for many traits. Structure of DNA: • Basic unit made of nucleotide • Nucleotide is made a phosphate group, a sugar and a base. • The 2 strands of polynucleotide joined together by the ‘complementary base pairing rule’ (A & T , G & C) • 2 strands are twisted to form a double helix 3D structure
- 48. DNA template transcription mRNA - RNA contains uracil(U) instead of thymine (T) polypeptide translation Pure Biology
- 49. It is atemporary molecule that is made when needed. It is a permanent molecule in the nucleus. It is a small soluble molecule.It is a large insoluble molecule. No fixed ratio between A and U and between G and C. Ratio of A:T and G:C is 1:1. Nitrogen-containing bases are adenine (A), uracil (U), guanine (G) and cytosine (C). Nitrogen-containing bases are adenine (A), thymine (T), guanine (G) and cytosine (C). Sugar unit is ribose.Sugar unit is deoxyribose. RNADNA (double helix) DNA vs. RNA Pure Biology
- 50. Transcription and translation 1 2 templatestrand gene unzips transcription ribosome mRNA mRNA molecule 3 attachment to ribosome Pure Biology
- 51. The biological moleculesinvolved are: (1) Amino acids - There are a total of 20 different amino acids. (2) Transfer RNA (tRNA) molecules - Each tRNA molecule has an amino acid attached. - The amino acid attached depends on the tRNA’s anticodon. (3) Ribosomes - Ribosomes help make polypeptides from mRNA molecules. (4) mRNA molecules Translation anticodon Pure Biology
- 52. Translation peptide bond amino acids attachedto tRNA ribosome codon first tRNA is released a new tRNA fits into the ribosome ribosome moves along the mRNA strand 1 2 Pure Biology
- 53. 3 polypeptide formed stop codon Amino acidsare continually attached until the ribosome reaches the stop codon on the mRNA. Upon encountering the stop codon, the ribosome leaves the mRNA. The complete polypeptide is produced. URL Pure Biology
- 54. 20.1 DNA 20.2 Genes 20.3Transferring Genes between Organisms 20.4 Effects of Genetic Engineering on Society Chapter 20 Pure Biology
- 55. Learning Outcomes After thissection, you should be able to: • define genetic engineering; • describe human insulin production as an example of an application of genetic engineering; • differentiate between selective breeding and genetic engineering. 20.3 Pure Biology
- 56. 57 “Pigs that glowin the dark”” • The scientists will use the transgenic pigs to study human disease. • Because the pig's genetic material encodes a protein that shows up as green, it is easy to spot. http://science.howstuffworks.com/framed.htm?parent=question388.htm&url=http://news.bb
- 57. • Genetic engineeringrefers to the manipulation of an organism’s genetic material. • It involves the transfer of genes from one organism to another. • This is done by the use of a vector. • A vector molecule is DNA molecule that is used to carry the gene or genes to be transferred. • Plasmids (circular DNA) from bacteria are commonly used as vectors. Genetic engineering
- 58. The process Isolate thedesired gene - Cut the gene using restriction enzymes. Insert the gene into the vector DNA - Restriction enzymes that were used to cut the desired gene are used to cut the vector DNA. - Both the cut vector DNA and gene are mixed together with DNA ligase, an enzyme that will help join the two molecules together. Insert the recombinant plasmids into bacteria - Mix recombinant plasmids with bacteria and heat- or electric-shock the cells. 1 2 3 20.3
- 59. • Mass productionof human insulin for type 1 diabetes patients was made possible through the use of genetic engineering. • The human insulin gene is transferred to bacterial cells that are able to express the gene. The product (insulin) can then be harvested. Producing human insulin Background: Type 1 diabetes is caused by the inability of the islets of Langerhans to produce sufficient insulin.
- 60. insulin gene cut usingrestriction enzyme sticky end DNA fragment that contains the insulin gene Isolating the human insulin gene 1
- 61. Inserting the geneinto the vector2 cut by same restriction enzyme sticky ends insulin gene inserted into plasmid insulin gene bacterial plasmid
- 62. Inserting the recombinant plasmidsinto bacteria 3 recombinant plasmid (bacterial plasmid with human insulin gene inserted) bacterial DNA recombinant plasmid transgenic bacterium
- 63. • The transgenicbacteria need to be burst open in order to extract the human insulin that is produced in the bacteria. • In order to obtain large amounts of human insulin, large amounts of transgenic bacteria need to be cultured. • This is done through the use of large sterile containers called fermenters. Large-scale production of human insulin
- 64. 66 Mass production of insulinin a fermenter Pure
- 65. • Creation oftransgenic plants that are resistant to herbicides. • Creation of transgenic plants that are pest-resistant. • Gene therapy – healthy genes can be transferred from one person to the cells of another person with defective genes. Other applications of genetic engineering 20.3
- 66. • Genes canbe transferred between organisms of different species (as shown in the production of insulin) and between organisms of the same species. • An example of gene transfer between organisms of the same species is the transfer of a pest-resistant gene from wild wheat plants to common wheat plants that are grown as crop. Note that: 20.3
- 67. Selective breeding vs.genetic engineering More efficient as transgenic organisms grow faster and may require less food Less efficient as organisms grow more slowly and may require more food A process which uses individual cells that reproduce rapidly in a small container in a laboratory. Slow process that involves several generations. Selection of genes before transfer eliminates the risk of transferring a defective gene. There is a possibility that defective genes will be transmitted to the offspring. Genes from an organism can be inserted into non-related species or different species. Organisms involved in selective breeding must be closely related or of the same species. Genetic engineeringSelective breeding
- 68. 20.1 DNA 20.2 Genes 20.3Transferring Genes between Organisms 20.4 Effects of Genetic Engineering on Society Chapter 20 Molecular Genetics
- 69. Learning Outcomes After thissection, you should be able to: • discuss the advantages and disadvantages of genetic engineering; • state the social and ethical implications of this technology.
- 70. Advantages of geneticengineering Nutritional quality of foods are improved. Development of foods designed to meet specific nutritional goals The use of costly pesticides that may damage the environment is reduced. Development of pesticide- resistant crops Farmers are able to grow crops in environmental conditions that are not favorable for cultivating most crops. Production of crops that grow in extreme conditions Drugs like human insulin become more affordable. Low cost production of medicines Benefits to societyApplications of genetic engineering
- 71. Disadvantages of geneticengineering Environmental hazards • Genetically-modified (GM) crop plants that produce insect toxins may result in the deaths of insects that feed on them and may result in loss of biodiversity. Economic hazards • If the prices of the seeds of modified crop plants are not regulated, poorer farmers may not have the financial capacity to benefit from this technology while richer farmers continue to get richer through the technology.
- 72. Disadvantages of geneticengineering Social and ethical hazards • Genetic engineering may lead to class distinctions. • Some religions do not approve of genetic engineering as it may not be appropriate to alter the natural genetic make-up of organisms. Health hazards • Genes that code for antibiotic resistance may be accidentally incorporated into bacteria that cause human diseases.
Editor's Notes
- #16 Note: The sugar-phosphate backbone is always the same whereas the bases are variable.
- #17 Note: Purines (adenine, guanine) always pair with pyrimidines (thymine, cytosine). Specific pairing between adenine and thymine, and guanine and cytosine occurs as optimum hydrogen bonding that can be established in those combinations. It is this specificity in base pairing that led to Edwin Chargaff’s finding that, in the DNA of a cell, the amount of adenine = the amount of thymine, and the amount of guanine = the amount of cytosine. (However, after learning of this, Chargaff did not come to the conclusion that specific base pairing occurs. This rule of base pairing was instead first proposed by Watson and Crick, the famous scientists that discovered the double helix structure of DNA.) Slide 11 (hidden) can be used to give students a visual representation of the hydrogen bonding between complementary bases. Slide 12 (hidden) contains directives for a mini project that requires students to find out more about Chargaff and his contributions to science. This topic can be used to bridge over to the discovery of the double helix structure of DNA by Watson and Crick. *To un-hide slides, go to ‘Normal View’ or ‘Slide Sorter’ and right click on the slide. Unselect ‘Hide Slide’.
- #18 Note: The diagram on the right, may be used to point out to students how the two strands in a DNA molecule are anti-parallel.
- #21 Note: If students have difficulty visualising the structure of the double helix, it may be helpful to state that the structure resembles a spiral staircase.
- #26 Note: The answer to the first question comes out step-wise.
- #35 Use this flowchart to explain the extraction of DNA in details. Describe the fact that the cell and nuclear membrane needs to be broken down before the DNA can be extracted.
- #38 Note: A DNA molecule can contain more than one gene along its length. A gene consists of two polynucleotide strands. One of the strands is termed the coding strand, while the other the non-coding strand. This will be further elaborated in slides describing protein synthesis. Other names for the coding strand: sense strand, non-template strand. Other names for the non-coding strand: antisense strand, template strand.
- #39 Note: The codon is also known as the triplet code. The genetic code can be in the form of DNA or RNA sequences. It is important that the students understand this and state, when answering questions, whether the codon/triplet code being mentioned is a DNA sequence or RNA sequence.
- #42 Note: Slide 19 (hidden) can be used for revision of the two examples of gene mutation that were covered in the chapter on heredity. *To un-hide slides, go to ‘Normal View’ or ‘Slide Sorter’ and right click on the slide. Unselect ‘Hide Slide’.
- #52 Note: The DNA strands unzip at the segment where the gene is located. Transcription occurs: The sequence of bases on one of the DNA strands (the template strand) is used to make the mRNA, following the rule of base pairing. Note that mRNA does not contain the thymine (T) base. Instead, adenine (A) in DNA pairs with uracil (U) in mRNA. The template strand refers to the non-coding strand. It is the DNA strand from which mRNA is made. The coding strand of the DNA is the strand that has the same base sequence as the mRNA molecule. The completed mRNA molecule leaves the nucleus through the nuclear pore and attaches to a ribosome in the cytoplasm. This is the start of translation.
- #53 Note: Amino acids and transfer RNA (tRNA) molecules are found in the cytoplasm. Anticodons are sequences that can bind to complementary codons on mRNA.
- #54 Note: Translation starts with an mRNA molecule attaching to a ribosome. Two tRNA molecules with the correct anticodons then attach to the mRNA codons. A peptide bond is formed between the two amino acids on the tRNA molecules. Once the peptide bond is formed, the ribosome moves one codon to the right of the mRNA. As the ribosome moves, the first tRNA is released and the third tRNA attaches to the ribosome. (continued on next slide)
- #55 Note: A stop codon on an mRNA molecule can be UGA, UAA or UAG. A stop codon has no corresponding tRNA molecule. Click on the Video-URL button to be directed to a website where an animation on mRNA translation can be found. (On the webpage, scroll down to Chapter 12, select Tutorial 12.3 select ‘Animation’) The animation lasts for about two minutes. Note that this animation clip contains more details than what is discussed in the textbook. Namely, There is mention of a start codon – which codes for Methionine. Reference is made to the E, P and A sites of the ribosome. tRNA that has an amino acid attached is referred to as amino-acyl tRNA. The chemistry behind peptide bond formation is briefly mentioned.
- #60 Note: The first step (Isolate the desired gene) can also be done using polymerase chain reaction (PCR) technology. The vector DNA mentioned in the second step is typically a bacterial plasmid. If PCR is used in the first step, the enzymes used to cut the vector DNA are selected based on the PCR primer design. Recombinant plasmids are plasmids that are made of DNA molecules that do not naturally exist together. In this case, the recombinant plasmid is made of DNA from two different organisms. When we heat shock or electric shock bacterial cells, we cause their cell surface pores to open. This increases the chance of the recombinant plasmid entering the cells. Other than insertion into bacterial cells, the recombinant plasmid can also be inserted into animal or plant cells using other methods (e.g. microinjection). This process will be pictorially shown in Slides 32 and 34 as an example of genetic engineering (producing human insulin in bacterial cells).
- #61 Tell students that an organism that acquires a foreign gene is called a transgenic organism. As such, the bacterial cell in which the human insulin gene is transferred into is termed transgenic bacterium. Note: The following slides show pictorially the process of genetically engineering a bacterium so that it expresses the gene for human insulin.
- #62 Note: The human chromosome containing the human insulin gene is identified and isolated. The portion of DNA that contains the gene is cut using a restriction enzyme. Usually an enzyme that produces sticky ends (as opposed to blunt ends) is used. (Sticky ends have ‘overhangs’ – The DNA molecules have ends that have nucleotides that are unpaired. Blunt ends do not have ‘overhangs’ – The DNA molecule ends with a base pair.) Slide 33 (hidden) shows an example of a sticky end and an example of a blunt end. Students can be asked for their opinions as to why sticky ends are preferred. *To un-hide slides, go to ‘Normal View’ or ‘Slide Sorter’ and right click on the slide. Unselect ‘Hide Slide’.
- #63 Note: EcoRI is an example of an enzyme that will produce sticky ends. As shown, the cut results in the DNA having some nucleotides that are unpaired. These unpaired nucleotides are called the DNA overhangs. SmaI is an example of an enzyme that will produce blunt ends. As shown, the cut results in the DNA ending with a base pair.
- #64 Note: The bacterial plasmid (vector) is cut with the same enzyme that was used to cut the gene. The gene fragment and the cut vector is mixed in a solution that contains DNA ligase. DNA ligase helps to join the two DNA fragments together.
- #65 Note: The recombinant plasmids are mixed with bacteria (usually E.coli). The bacteria are heat-shocked or given an electric shock. This opens up the pores on the bacteria cell surface such that the recombinant plasmids can enter. The bacteria with the recombinant plasmid will express the gene and produce human insulin. To extract and purify the human insulin in the bacteria for medical purposes, the bacteria will have to be burst open.
- #66 Note: Although the container used to culture large quantities of transgenic bacteria are called fermenters, the insulin production by transgenic bacteria is not a fermentation process.
- #68 Discuss the various components of a large-scale fermenter. Elaborate more on the various components and their function. Details can be found in the textbook.
- #69 Note: Examples: The gene that codes for the enzyme cyanamide hydratase (found in Myrothecium verrucaria, a soil fungus) is transferred to crop plants so that they are resistant to herbicides. Wild species of wheat contain a gene that confers resistance to the Hessian fly (a major wheat pest). This gene can be transferred to the common wheat plant, that is used as a crop plant, so that it is resistant to this pest. Gene therapy is used to treat patients with cystic fibrosis. Healthy genes are inserted into the lung cells of the patients. (The last two examples are examples of gene transfer between organisms of the same species.)
- #75 Note: (continued on next slide)
- #76 Note: More examples of each hazard are listed in the textbook. The next slide (hidden) contains directives for a class activity. Students are asked to listen to a discussion on the ethical implications of genetic engineering. After listening to the talk, the students are to form groups to prepare a presentation on their own views on genetic engineering. The full video is about an hour long. The video can be stopped at time 23:45 (After Topic 6: Improvement vs. Cure). Students should be sufficiently exposed to the nature of the debate on genetic engineering in these 23 plus minutes. *To un-hide slides, go to ‘Normal View’ or ‘Slide Sorter’ and right click on the slide. Unselect ‘Hide Slide’.
- #77 Note: The full video is about an hour long. The video can be stopped at time 23:45 (After Topic 6: Improvement vs. Cure). Students should be sufficiently exposed to the nature of the debate on genetic engineering in these 23 plus minutes.