Protein Synthesis

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Protein Synthesis Review
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Review!!

• http//learn.genetics.utah.edu/content/begin/tour/
  

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An Overview

• Genes on chromosomes need to be transcribed into
  RNA, and then translated by ribosomes into
  protein.
• Genes act by directing the production of only ONE
  protein each.
• This is known as the one gene-one enzyme
  hypothesis.
• An error in gene sequence can result in a change
  in protein sequence, shape, and therefore
  function.
• TRY THIS Activity p 233, Translating the Code.

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Overview

• DNA in the nucleus is TRANSCRIBED into a
  complementary RNA message that moves to the
  cytoplasm. (copied from one medium to another)
• Numerous RNA copies can move to different
  ribosomes.

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Overview

• The ribosomes TRANSLATE the message into
  Polypeptide chains and process into proteins
  (convert into a different language).
• Transcription involves the copying of information
  in DNA into mRNA
• Translation involves ribosomes using mRNA as
  blueprint to synthesize a protein composed of
  amino acids.

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A Cool Visual

• http//www.youtube.com/watch?v41_Ne5mS2ls

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RNA

• ribose sugar with a hydroxyl on 2 Carbon
• uracil replaces the base thymine and pairs with
  adenine
• single stranded

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3 Types of RNA

• Messenger RNA (mRNA) varies in length, end
  product of transcription of a gene, moves to the
  ribosome
• Transfer RNA (tRNA) delivers amino acids to the
  ribosomes for translation. Shaped like a
  cloverleaf very short.
• Ribosomal RNA (rRNA) binds with protein to make
  ribosomes

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Step 1 - Transcription

• Within the nucleus, the
• DNA of a particular gene
• unwinds and separates.
• One strand of the DNA is
• transcribed into
• messenger RNA (mRNA)
• in a process called
• transcription.

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Transcription Making mRNA
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Transcription divided into three sequential
processes

• Initiation
• RNA polymerase binds to DNA at specific site
  known as promoter, near the beginning of the
  gene. (usually high of A Tonly 2 bonds to
  break!)
• Elongation
• Enzyme RNA polymerase puts together the
  appropriate ribonucleotides and builds the mRNA
  transcript

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• Termination
• Shortly after RNA polymerase passes the end of a
  gene, recognizes signal to stop transcribing
• mRNA transcript then is completely released from
  the DNA and will exit the nucleus
• http//www.youtube.com/watch?vztPkv7wc3yU

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The Final Touches

• the mRNA must be prepared to leave the nucleus.
  A 5 cap is added (for protection), and a poly A
  tail is added to the 3 end
• The mRNA contains regions of code that do not
  make the protein (introns). Introns are removed
  by spliceosomes.
• Spliceosomes join exons (coding regions)
  together.
• The mRNA strand leaves the nucleus and binds with
  ribosomes in the cytoplasm.

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• P 249, Q 1-6

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Step 2 Translation

• Once mRNA enters cytoplasm, it is ready to be
  translation
• Ribosomes made up of two parts a large subunit
  (60s) and a small subunit (40s). Bind to the
  mRNA (recognizing the 5 cap)
• Must be lined up correctly to the proper reading
  frame (reading triplets correctly)

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tRNA

• tRNA delivers amino acids to the polypeptide
  building site (ribosome)
• tRNA is a small single stranded nucleic acid,
  resembles a cloverleaf
• one arm anticodon (sequence of three bases
  complementary to mRNA)
• 3 end has acceptor site for a particular amino
  acid
• this recognition by tRNA of mRNA is facilitated
  through complimentary base pairing.
• every tRNA carries only one specific amino acid
• therefore there must be at least 20 (20-64)
  different tRNAs

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Translation
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Translation

• The mRNA consists of nucleotides that code for a
  specific amino acid. The code is in triplet
  called a CODON (3 nucleotides 1 amino acid).
  Amino acids are brought into place by a molecule
  known as transfer RNA (tRNA). This process is
  known as translation. Peptide bonds occur b/w
  amino acids.

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Building the Chain

• First codon recognized is start (AUG-methionine)-
  aligns the reading frame
• ribosome contains two sites for tRNA an A
  (acceptor) site and a P (peptide) site.
• tRNA (Met- AUG) enters the P site.
• the rest of the tRNA enter at the A site and form
  peptide bonds between the amino acids as the
  chain forms.

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• Ribosome translocates one codon over and
  continues the chain until it reaches a stop
  codon. (UGA, UAG, UAA)
• A release factor protein dismantles the complex,
  releasing the polypeptide chain.
• Enzymes may cleave the chain at specific places

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(No Transcript)
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http//www.youtube.com/user/ndsuvirtualcellp/a/44
B161B3F290FC23/0/5bLEDd-PSTQ
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(No Transcript)
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Protein Synthesis

• Once all the triplet codes (Codons) are read and
  the amino acids are brought into place, the
  completed protein travels through the ER to the
  Golgi.
• The Golgi modifies the structure and packages it
  into a vesicle.
• Vesicle moves to the membrane and is released by
  exocytosis.