DNA Biology and Technology

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• DNA Biology and Technology

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What must DNA do?
21.1 DNA and RNA structure and function

• Replicate to be passed on to the next generation
• Store information
• Undergo mutations to provide genetic diversity

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DNA structure A review
21.1 DNA and RNA structure and function

• Double-stranded helix
• Composed of repeating nucleotides (made of a
  pentose sugar, phosphate and a nitrogenous base)
• Sugar and phosphate make up the backbone while
  the bases make up the rungs of the ladder
• Bases have complementary pairing with cytosine
  (C) pairs with guanine (G) and adenine (A) pairs
  with thymine (T)

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DNA structure
21.1 DNA and RNA structure and function
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How does DNA replicate?
21.1 DNA and RNA structure and function

• The two strands unwind by breaking the H bonds
• Complementary nucleotides are added to each
  strand by DNA polymerase
• Each new double-stranded helix is made of one new
  strand and one old strand (semiconservative
  replication)
• The sequence of bases makes each individual unique

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DNA replication
21.1 DNA and RNA structure and function
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RNA structure and function
21.1 DNA and RNA structure and function

• Single-stranded
• Composed of repeating nucleotides
• Sugar-phosphate backbone
• Bases are A, C, G and uracil (U)
• Three types of RNA
• Ribosomal (rRNA) joins with proteins to form
  ribosomes
• Messenger (mRNA) carries genetic information
  from DNA to the ribosomes
• Transfer (tRNA) transfers amino acids to a
  ribosome where they are added to a forming
  protein

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RNA structure
21.1 DNA and RNA structure and function
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Comparing DNA and RNA
21.1 DNA and RNA structure and function

• Similarities
• Are nucleic acids
• Are made of nucleotides
• Have sugar-phosphate backbones
• Are found in the nucleus

• Differences
• DNA is double stranded while RNA is single
  stranded
• DNA has T while RNA has U
• RNA is also found in the cytoplasm as well as the
  nucleus while DNA is not

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Proteins A review
21.2 Gene expression

• Composed of subunits of amino acids
• Sequence of amino acids determines the shape of
  the protein
• Synthesized at the ribosomes
• Important for diverse functions in the body
  including hormones, enzymes and transport
• Can denature causing a loss of function

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Proteins A review of structure
21.2 Gene expression
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2 steps of gene expression
21.2 Gene expression

• Transcription DNA is read to make a mRNA in the
  nucleus of our cells
• Translation Reading the mRNA to make a protein
  in the cytoplasm

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Overview of transcription and translation
21.2 Gene expression
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The genetic code
21.2 Gene expression

• Made of 4 bases
• Bases act as a code for amino acids in
  translation
• Every 3 bases on the mRNA is called a codon that
  codes for a particular amino acid in translation

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1. Transcription
21.2 Gene expression

• mRNA is made from a DNA template
• mRNA is processed before leaving the nucleus
• mRNA moves to the ribosomes to be read
• Every 3 bases on the mRNA is called a codon and
  codes for a particular amino acid in translation

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Processing of mRNA after transcription
21.2 Gene expression

• Modifications of mRNA
• One end of the RNA is capped
• Introns removed
• Poly-A tail is added

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2. Translation
21.2 Gene expression

• 3 steps
• Initiation mRNA binds to the small ribosomal
  subunit and causes 2 ribosomal units to associate
• Elongation polypeptide lengthens
• tRNA picks up an amino acid
• tRNA has an anticodon that is complementary to
  the codon on the mRNA
• tRNA anticodon binds to the codon and drops off
  an amino acid to the growing polypeptide
• Termination a stop codon on the mRNA causes the
  ribosome to fall off the mRNA

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Visualizing the 3 steps of translation
21.2 Gene expression
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Regulation of gene expression
21.2 Gene expression

• 4 levels
• 1. Transcriptional control (nucleus)
• e.g. chromatin density and transcription factors
• 2. Posttranscriptional control (nucleus)
• e.g. mRNA processing
• 3. Translational control (cytoplasm)
• e.g. Differential ability of mRNA to bind
  ribosomes
• 4. Posttranslational control (cytoplasm)
• e.g. changes to the protein to make it functional

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An example of transcriptional control
21.2 Gene expression
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What did we learn from the human genome project
(HGP)?
21.3 Genomics

• Humans consist of about 3 billion bases and
  25,000 genes
• Human genome sequenced in 2003
• There are many polymorphisms or small regions of
  DNA that vary among individuals were identified
• Genome size is not correlated with the number of
  genes or complexity of the organisms

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What is the next step in the HGP?
21.3 Genomics

• Functional genomics
• Understanding how the 25,000 genes function
• Understanding the function of gene deserts (82
  regions that make up 3 of the genome lacking
  identifiable genes)
• Comparative genomics
• Help understand how species have evolved
• Comparing genomes may help identify base
  sequences that cause human illness
• Help in our understanding of gene regulation

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New endeavors
21.3 Genomics

• Proteomics the study of the structure, function
  and interactions of cell proteins
• Can be difficult to study because
• protein concentrations differ greatly between
  cells
• protein location, concentration interactions
  differ from minute to minute
• understanding proteins may lead to the discovery
  of better drugs
• Bioinformatics the application of computer
  technologies to study the genome

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How can we modify a persons genome?
21.3 Genomics

• Gene therapy - insertion of genetic material
  into human cells to treat a disorder
• Ex vivo therapy cells are removed for a person
  altered and then returned to the patient
• In vivo therapy a gene is directly inserted
  into an individual through a vector (e.g.
  viruses) or directly injected to replace mutated
  genes or to restore normal controls over gene
  activity
• Gene therapy has been most successful in treating
  cancer

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Ex vivo gene therapy
21.3 Genomics
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DNA technology terms
21.4 DNA technology

• Genetic engineering altering DNA in bacteria,
  viruses, plants and animal cells through
  recombinant DNA techonology
• Recombinant DNA contains DNA from 2 or more
  different sources
• Transgenic organisms organisms that have a
  foreign gene inserted into them
• Biotechnology using natural biological systems
  to create a product or to achieve an end desired
  by humans

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DNA technology
21.4 DNA technology

• Gene cloning through recombinant DNA
• Polymerase chain reaction (PCR)
• DNA fingerprinting
• Biotechnology products from bacteria, plants and
  animals

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1. Gene cloning
21.4 DNA technology

• Recombinant DNA contains DNA from 2 or more
  different sources that allows genes to be copies
• An example using bacteria to clone the human
  insulin gene
• Restriction enzyme used to cut the vector
  (plasmid) and the human DNA with the insulin gene
• DNA ligase seals together the insulin gene and
  the plasmid
• Bacterial cells uptake plasmid and the gene is
  copied and product can be made

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Visualizing gene cloning
21.4 DNA technology
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2. Polymerase chain reaction (PCR)
21.4 DNA technology

• Used to clone small pieces of DNA
• Important for amplifying DNA for analysis such as
  in DNA fingerprinting

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3. DNA fingerprinting
21.4 DNA technology

• Fragments are separated by their charge/size
  ratios
• Results in a distinctive pattern for each
  individual
• Often used for paternity or to identify an
  individual at a crime scene or unknown body
  remains

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4. Biotechnology products Transgenic bacteria
21.4 DNA technology

• Important uses
• Insulin
• Human growthhormone (HGH)
• Clotting factor VIII
• Tissue plasminogen activator (t-PA)
• Hepatitis B vaccine
• Bioremediation cleaning up theenvironment such
  as oil degradingbacteria

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4. Biotechnology products Transgenic plants
21.4 DNA technology

• Important uses
• Produce human proteins in their seeds such as
  hormones, clotting factors and antibodies
• Plants resistant to herbicides
• Plants resistant to insects
• Plants resistant to frost
• Corn, soybean and cotton plants are commonly
  genetically altered
• In 2001
• 72 million acres of transgenic crops worldwide
• 26 of US corn crops were transgenic crops

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4. Biotechnology products Transgenic plants
21.4 DNA technology
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Health focus Ecological concern about BT crops
21.4 DNA technology

• Resistance increasing in the target pest
• Exchange of genetic material between the
  transgenic plant and a related species
• Concern about the impact of BT crops on nontarget
  species

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4. Biotechnology products Transgenic animals
21.4 DNA technology

• Gene is inserted into the egg that when
  fertilized will develop into a transgenic animal
• Current uses
• Gene pharming production of pharmaceuticals in
  the milk of farm animals
• Larger animals includes fish, cows, pigs,
  rabbits and sheep
• Mouse models the use of mice for various gene
  studies
• Xenotransplantation pigs can express human
  proteins on their organs making it easier to
  transplant them into humans