DNA and Protein Synthesis

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DNA and Protein Synthesis
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DNA Does 2 Important Things in a Cell

• 1)DNA is capable of replicating itself. Every
  time a cell divides, each DNA strand makes an
  exact copy of itself.
• 2)DNA directs the production of proteins in the
  cell. DNA contains the instructions on how to
  make proteins.

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The Importance of Proteins

• Proteins are the workhorses of the cell. They
  build all of the important structures and carry
  on most of the important cellular functions.
• What types of proteins are made determine
  everything about the organism and how it
  functions.

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Review of Protein Structure

• Proteins are large polymers made of long chains
  of amino acids.
• Amino Acids bind together with peptide bonds.
• A proteins final shape determines its function.
  This shape is determined by its amino acid
  sequence.

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Protein Structure

• Proteins are made by ribosomes.
• Amino acids are put together in a long chain
  which then folds and bends to determine the final
  shape.
• Remember Shape equals function!
• So, it is VERY important that the amino acid
  sequence is correct!

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What determines the correct amino acid sequence
in a protein?

• The DNA in a cell determines the sequence of
  amino acids in a protein.
• The DNA sequence is a code that determines which
  amino acid is first, which is second, etc.

DNA determines protein
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DNA leads from afar..

• The DNA in a cells nucleus determines the
  sequence of amino acids that are put together at
  the ribosome.
• Yet, the DNA never leaves the nucleus!
• How does the DNA do this?

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Chromosomes to Genes
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Messenger RNA (mRNA)

• DNA is able to tell the ribosome how to build
  the protein by sending a messenger.
• This comes in the form of an RNA molecule.
• Therefore, this is called messenger RNA, or mRNA.

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From DNA to Protein

• Protein Synthesis has 2 main processes
• 1) Transcription (to write) making a mRNA
  molecule
• 2) Translation (to read) making the protein,
  using the mRNA as a guide.
• Together, these are called Gene Expression

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RNA A Major Player

• Three types of RNA are used in protein building
• mRNAmessenger RNA (made in nucleuscarries the
  genetic code)
• tRNAtransfer RNA (brings amino acids to the
  ribosome)
• rRNAribosomal RNA (what ribosomes are made of)

Ribonucleic Acid
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RNA Vs. DNA

• RNA differs from DNA in 3 ways
• RNA is single-stranded DNA is double-stranded
• RNA has Ribose DNA has Deoxyribose
• RNA has Uracil DNA has Thymine

Uracil is found in RNA only
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• RNA Vs. DNA

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Transcription Reading the Gene

• During transcription, the information in a
  particular segment of DNA (a gene) is copied into
  mRNA
• Step 1
• RNA polymerase binds to a specific sequence of
  bases on the DNA called the Promoter. This is the
  start code.

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Transcription Reading the Gene

• Step 2 Helicases unwind the DNA strand in front
  of the promoter region.
• Step 3 RNA polymerase adds and links
  complementary RNA bases on one side of the DNA,
  following base pairing rules. (Exception Adenine
  in DNA bonds to Uracil)

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Transcription

• The RNA polymerase eventually reaches a stop
  location in the DNA.
• This stop signal is a sequence of bases that
  marks the end of each gene.
• The result is a single strand of RNA

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The Genetic Code

• To make a correct protein, the amino acids must
  be put in the proper sequence.
• Each segment of 3 nucleotides in DNA codes for 1
  amino acid.
• Each triplet of DNA bases makes a triplet of mRNA
  basescalled a Codon.

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Codons of mRNA
What amino acid comes from the code AUC? GGG? CGA?
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Translation RNA to Proteins

• Translation is the process of converting the
  language of RNA into the language of proteins
  (amino acid sequences.)
• Translation involves mRNA, tRNA, and rRNA.

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tRNA Transfer RNA

• Each tRNA is folded into a compact shape.
• There are 2 important places on each tRNA
• Terminal endhas 3 bases which match up to mRNA.
  This is the Anticodon.
• Amino Acid attachment site

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Translation, Step 1 Start Codon

• After leaving the nucleus, the mRNA joins with a
  ribosome and tRNA.
• The mRNA start codon, AUG, signals the beginning
  of a protein.
• The tRNA carrying Methionine binds to the start
  codon.

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Translation Step 2A new tRNA arrives.

• A new tRNA arrives and binds to the next codon on
  the mRNA.
• A peptide bond forms between the first amino acid
  and the second amino acid.
• The first tRNA detaches and leaves its amino acid
  behind.

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The Ribosome Moves down the mRNA

• The ribosome moves one codon down the mRNA
  strand.
• Because the anticodon (on the tRNA) is attached
  to the codon, they move together as a unit.
• The amino acid chain grows as each new one binds.

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Translation, Step 3 Releasing the protein

• The process ends when a stop codon is reached.
• The amino acid chain is released, the ribosome
  complex and mRNA strand fall apart.

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Protein Synthesis Animations

• http//bioweb.uwlax.edu/genweb/molecular/theory/tr
  anslation/trans1.swf
• http//www.youtube.com/watch?v983lhh20rGYfeature
  related
• http//www.youtube.com/watch?NR1featureendscree
  nvIkq9AcBcohA