DNA, Genes & Biotechnology. Chapter 5

Transcription

1 DNA, Genes & Biotechnology Chapter 5

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3 What is DNA? (remember?!) DNA = deoxyribose nucleic acid Macromolecule that stores information Contains instructions for building all structures for all living things then why are we different from a fly or a flower or bacteria? In eukaryotes, arranged in linear pieces called chromosomes; DNA & associated proteins

4 Watson & Crick identified the structure of DNA, 1953

5 What is a gene? A specific sequence of DNA (~ 3000 base pairs long) that codes for a specific protein Alternate versions of a gene for the same trait are called alleles ex: trait is eye color; alleles are green or blue ex: trait is blood type; alleles are A, B or O

6 Not all DNA codes for protein HUGE non-coding regions occur both between and within genes; called introns Almost all eukaryotes have huge proportions of noncoding DNA In humans, genes make up only 5% of all DNA (!!) There is no relationship between the amount of coding DNA and the organism complexity Non-coding DNA s purpose remains a mystery

7 How does our DNA determine the way we look? Our inherited DNA specifies traits by directing synthesis of proteins In other words: proteins are the link between our genetic make up (genotype) and our physical appearance (phenotype)

8 Remember RNA? Ribonucleic acid A single stranded nucleic acid there are several types of RNA Has four nitrogenous bases like DNA A and U (uracil instead of T!) C and G Functions in protein synthesis

9 DNA directed protein synthesis Transcription DNA to mrna takes place in the nucleus Translation mrna to protein takes place in the cytoplasm

10 Transcription the details Initiation the enzyme, RNA polymerase, attaches to the promoter, a start here site on DNA indicating the start of a gene Elongation RNA polymerase builds a copy of the gene; the transcript copy called mrna b/c it can move elsewhere in the cell where the message can be translated Termination RNA polymerase reaches the terminator ( stop here ) at the end of a gene and detaches from the DNA the mrna is a free-floating single stranded copy of a gene Capping & editing ends of mrna are protected & introns are removed now the mrna can leave the nucleus

11 Transcription of a gene

12 DNA directed protein synthesis Transcription DNA to mrna takes place in the nucleus Translation mrna to protein takes place in the cytoplasm

13 Translation the basics Requires amino acids, ribosomes and trna trna is a 2 sided molecule there is a specific trna for each amino acid It takes 3 mrna bases to code for 1 amino acid; called a codon The amino acids attach together to form a protein

14 Translation the details Initiation ribosomes recognize a start codon on mrna & binds to it trna also recognizes start codon & binds to it with amino acid Elongation the next codon after the start specifies which amino acid carrying trna should bind to it ribosome facilitates the binding between the 1 st & 2 nd amino acids trna detaches to get another amino acid Termination ribosome reaches a stop codon & both ribosome & protein detach from mrna mrna can be read over & over again; eventually will be broken down

15 Transcription & translation

16 The genetic code The link between the codons in RNA & the amino acids of proteins Redundancy without ambiguity Nearly universal; this language is shared by almost all living things bacteria can transcribe human DNA & human cells can translate bacterial RNA

17 Transcription + translation = protein synthesis

18 Assuming these came from the same person, what do these different cell types have in common? They all have the exact same DNA

19 If all cells have the same DNA, how are different cells different? Because of control of gene expression an array of regulatory proteins interact with DNA to turn genes on or off in other words, regulatory proteins control which genes are transcribed, and when transcription will take place for multicellular eukaryotes, the default state for most genes seems to be off

20 Different genes = different functions Bone Cell Pancreas Cell Brain Cell

21 Types of regulatory proteins Activator proteins: bind to DNA to facilitate the attachment of the RNA polymerase to initiate transcription Repressor proteins: bind to DNA to inhibit the start of transcription Other proteins also involved... remember, many steps, many enzymes...

22 Additional means of regulating gene expression Remember capping & editing of mrna? the editing can occur in various ways with different results Some regulatory proteins block the translation of mrna or breakdown the mrna After translation, polypeptides may need alteration to become functional some polypeptides need to be cut into smaller units to become active Selective protein breakdown allows adjustment to the kinds and amounts of proteins in response to changes in environment

23 Mutation Any change in the nucleotide sequence of DNA Can involve large sections of a chromosome or a single nitrogenous base Result: a change in gene translation (this is not always a bad thing; creates new alleles)

24 Types of mutations Point mutations Base insertions or deletions Chromosomal aberrations

25 Point mutations The replacement of one nucleotide with another May have no effect due to redundancy of genetic code (a silent mutation) GAA and GAG both code for Glu (glutamic acid) May have big effect; protein does not function normally or is completely non-functional ex.: sickle-cell, protein is misshaped ex.: cystic fibrosis, amino acid sequence is too short (493 AA long instead of 1480)

26 Base insertions or deletions The addition or removal of one or more bases Often have serious consequences remember: mrna bases read in triplets (codons) the addition or subtraction of bases can alter the reading frame (triplet grouping) nitrogenous bases downstream of mutation will be regrouped into different codons Result: most likely a nonfunctional protein

27 Base deletion

28 Chromosomal aberrations Changes to the overall organization of genes on a chromosome complete deletion of an entire section of DNA moving a gene from one part of the chromosome to a different location on the same chromosome or onto another chromosome duplication of a gene with the new copy inserted elsewhere

29 Causes of mutations Spontaneous without outside cause Mutagens an external agent that induces mutation

30 Spontaneous mutations Occur during DNA replication or recombination an accident most errors are repaired by proofreader enzymes, but some get missed happpiness, bananana

31 Mutagens An external agent that induces mutation UV radiation from sunlight X-rays radioactive fallout from atomic bomb tests or nuclear accidents chemical weapons like mustard gas chemicals in tobacco chemicals in drugs thalidomide

32 Mutation summary 1. A mutated gene codes for nonfunctioning protein (very often an enzyme) 2. Non-functioning enzyme can t catalyze the reaction it normally would, halting the reaction 3. The molecule that would have reacted with enzyme accumulates 4. The accumulating chemical causes sickness and/or death

33 Are mutations heritable? Maybe... but only if they occur in the gamete producing cells

34 What can we do with all this knowledge regarding the structure & function DNA? Biotechnology is a field of biology where organisms, cells, & their molecules are modified to achieve practical benefits applications in medicine, agriculture & crime scene investigations modern emphasis is on genetic engineering, the manipulation of an organism s DNA by adding, deleting or transplanting genes from one organism to another using recombinant DNA techniques (combining DNA of 2 different species)

35 Uses of biotechnology In human health treat disease cure disease prevent disease In agriculture to create more nutritious food increase crop yields reduce environmental impact

36 Biotechnology in human health Treatment of disease Diabetes: insulin now made by E. coli bacteria in huge vats instead of obtaining from pigs and cattle Pituitary gland defects: human growth hormone (HGH) is responsible for stimulating growth in almost every part of the body; now produced like insulin instead of from obtaining from human cadavers

37 Biotechnology in human health Cure of disease uses gene therapy, the insertion of a functional gene into an individual s cells to replace a defective gene simple in concept, hard to successfully implement challenges difficult to get working gene into specific cells that need it difficult to get the working gene into enough cells & at the right rate to have an effect problems with the transfer organism (virus) getting into unintended cells for many diseases, the malfunctioning gene has not been identified, or the disease is caused by more than one malfunctioning gene only works on somatic cells; person can still pass on defective genes in gametes

38 Biotechnology in human health Prevention of disease Would you like to know if you were likely to develop a certain disease? Would you want to know if your children will be born with a genetic disease? Genetic testing possible Can test parents; healthy parents can be carriers of genetic diseases. ex. cystic fibrosis Can test embryo or fetus; get DNA sample from amniotic fluid or fetal cells. ex. Down syndrome Can test self; early detection has potential to enhance treatment. ex. Huntington s disease

39 Biotechnology in agriculture For 1000s of years, humans have been selectively breeding plants & animals for desirable traits, now doing it on a molecular level identify desirable trait from a plant, animal or bacteria & insert that gene into genome of another plant species creates genetically modified organisms (GMOs)

40 Benefits of GMOs Enhance taste, quality & nutrition of food vitamin A in rice; higher lycopene in tomatoes; sweeter or juicer fruit Reduce maturation time Increase size/yields more fruit per acre/more milk per cow, etc. can continue to feed the growing human population Increase plant stress tolerance Increase resistance to disease, pests & herbicides (Round Up ready) Production of vaccines

41 Negative impact (controversies) of GMO Technology advancements are outpacing risk assessment Potential human health impacts increase allergens, transfer antibiotic resistant markers, unknown effects Unintended transfers of transgenes through cross-pollination Unknown effects on other organisms monarch butterflies Loss of biodiversity in crop plants population less stable; high risk of rapid disease/pest destruction Domination of world food supply by a few companies (b/c they put patents on their plants) Tampering with nature by mixing genes; playing God

42 Did you know? Would you choose to purchase GMO if given the choice? How do you know if you are buying it or not?

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44 Biotechnology: DNA fingerprinting Did you know... everyone s DNA is 99.9% the SAME??! b/c we are all the same species and share a common ancestry BUT that means we each have about 3 million bases that are different from each other which make us unique DNA fingerprinting focuses on the unique parts of an individual s genome

45 DNA fingerprinting continued Some of our unique DNA contain VNTRs Variable Number of Tandem Repeats short sequences of bases that repeat over & over number of repeats differ for each chromosome of a pair one chromosome from each parent 13 different VNTR areas are usually looked at to make identifications &/or comparisons can take a DNA sample from suspect to see if it matches to DNA left on a victim, etc.

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47 How does genetic engineering work? Step 1: Isolate gene from donor organism requires use of restriction enzymes protect bacteria from invading virus DNA restriction enzymes recognize specific base sequences of 4-8 bases & cuts the DNA there so virus can no longer reproduce in bacteria there are dozens of restriction enzymes, each that recognize a different base sequence these are key tools of biotechnology

48 How does genetic engineering work? Step 2: amplify DNA pieces into useful quantities uses PCR (polymerase chain reaction) process allows virtually unlimited duplication of DNA segments DNA is heated & H-bonds between base pairs break and strands separate DNA polymerase & free nucleotides are added & complementary strands are created as DNA is cooled this heating & cooling can be repeated over & over

49 How does genetic engineering work? Step 3: Inserting foreign DNA into target organism creates transgenic organisms that contain DNA from donor species requires the use restriction enzymes and a plasmid, a circular DNA molecule that is separate from chromosomal DNA of a bacterium; sometimes viral DNA is used

50 How does genetic engineering work? Step 4: Grow bacterial colonies that contain gene of interest each time the bacteria divides, it is making a clone, a genetically identical cell it is possible to produce huge numbers of clones, each transcribing & translating the gene of interest Not all steps are used in all biotechnology applications; some use only one or a few