Gene Expression

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Gene Expression Botany 130 Lectures 9
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Fig 11-2
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Fig 10-20
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Fig 10-21
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Fig 10-21
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Fig 10-22
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Fig 10-23
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DNA ? RNA ? Protein ? DNA ? RNA ?
Protein ? DNA ? RNA ? Protein ? DNA ?
RNA ? Protein ?
Successive generations of cells
Fig 11-3
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Transcription and translation happen in three
different places
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The unique roles of RNA

• Central Dogma DNA makes RNA makes protein
• Three types of RNA (mRNA, tRNA, rRNA)
• Messenger RNA carries the code from DNA that
  specifies the sequence of amino acids
• Transfer RNA translates the code - it carries an
  amino acid at one end and an anticodon at the
  other
• Ribosomal RNA makes up the ribosome, where the
  message is read and converted to protein

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Transcription Making mRNA
Fig 11-5
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Transfer RNA Interprets the code
Each tRNA gets a specific amino acid attached
by a different aminoacyl-tRNA synthetase. (there
have to be at least 20)
Fig 11-7
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The genetic code is one of the universal (nearly)
aspects of life

• The genetic code is degenerate
• DNA sequence uniquely identifies protein sequence
  but not the other way around
• Often, the last position does not matter

Fig 11-4
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Protein site
Aminoacyl site
Exit site
Fig 11-7
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All proteins begin with methionine
Fig 11-8
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Transcription is universal

• Transcription events are highly conserved among
  living organisms
• One difference is that bacteria have a smaller
  ribosome sensitive to different inhibitors
• Another is that prokaryotes start proteins with a
  special methionine that has formic acid attached
• Often, the beginning of a protein is modified,
  for example by loss of the formate and even the
  whole methionine

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Stope codons code for a release factor
Fig 11-8
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Fig 11-10
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Fig 11-10
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Polycistronic coding is common in bacteria
Fig 11-11
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An operon of bacteria
Fig 11-12
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Fig 11-14
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How can the extremely long DNA molecules of
eukaryotes be contained within a single cell?
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Transformation of plants

• Means introducing new genetic material
• Purposes
• Study how plants work
• Identified hormone binding proteins
• Sometimes means turning off genes
• Has been very successful, many fields of study
  have moved forward rapidly as a result

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Transformation of plants

• Make beneficial changes in crop plants
• Resistance to disease
• Papaya ringspot virus
• Resistance to insect attack (Bacillus
  thuringensis protein)
• This has reduced fungal attack, reducing
  aflatoxin levels in corn
• Modify sensitivity to herbicides
• Edible vaccines

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Percentage of crop that is now genetically
engineered?
Corn B.t. for resistance to corn borer insects.
reduced mycotoxins are among the benefits
Cotton B.t. allows much reduced usage of
pesticide
Soybeans Roundup-ready allows low-till farming
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Methods of Transformation

• Agrobacterium-mediated transformation
• Gene gun
• Both technologies introduce a gene into a cell,
  then allow a whole new plant to develop from that
  cell
• Need for selectable markers
• Callus culture

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Methods of Transformation Callus culture

• Use Murashige and Skoog medium
• Use hormone concentrations to grow callus, roots,
  or shoots

Makes use of the totipotency of plants
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Agrobacterium tumifaciens
Crown gall (left) is caused by Agrobacterium tumif
aciens. This bacterium has a plasmid (small
circle of DNA) that makes it virulent. The
virulence factors can be taken out and genes of
interest put in. Then, infecting callus cultures
allows some cells to be transformed.
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The Gene Gun
Blasts particles covered with DNA into plant
cells. Sometimes the DNA is expressed
transiently. Sometimes the DNA is incorporated
into the plants genes. These cells can be
selected (selectable markers) and used to grow
a new (transformed) plant
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Other Genetic Engineering Examples

• B.t. corn and Starlink
• The Terminator technology
• Putting Brazil nut proteins into soybeans
• Gluten sensitivity
• Soy allergy
• Golden rice

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Brazil nut proteins in soybeans

• Purpose improve the quality of soy bean protein
  for chicken feed
• Many nuts are allergenic
• Allergenicity of the protein was tested
• When found to be allergenic the Brazil nut
  protein was abandoned
• Failure or success?

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Transformation of plants

• Reduce inherent toxicity or allergenicity of
  plant proteins
• Many proteins, especially wheat gluten, are
  allergenic in part because of disulfide bonds. If
  the plant can be induced to not make those bonds,
  the gluten would no longer be allergenic and
  gluten-sensitive people could once again eat
  wheat products

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Transformation of plants

• Improve nutrition
• Golden rice, increased vitamin A and iron
• Technology still under development, all rights
  and patents given away

Why should that be controversial?
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"Biotech Perverts Get Out of Our Genes."
"The trouble is that if they admit there's one
good genetically modified product, then they
would have to admit there might be others"
Patrick Moore, a founder of Greenpeace who
became disillusioned with the movement.