Ribosome

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Ribosome

• a presentation by Erin Husson

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Just a quick overview of what were going to
cover

• What ribosome is and what its subunits are
• The purpose of ribosome
• The process of protein synthesis, including
• DNA to mRNA (transcription)
• mRNA to protein (translation)
• Initiation
• Elongation
• End of translation

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Just a quick overview of what were going to
cover

• Structures of the two ribosome subunits
• The larger subunit
• The smaller subunit
• RNAs relation to their structure

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What is ribosome?

• Ribosome - protein synthesizer consisting of two
  subunits
• Larger one, 50S, is upper picture. Smaller is
  30S
• (They look the same size here because of space
  restrictions.)

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50S and 30S???

• Related to their respective sizes. Numbers
  actually measures of how quickly each subunit
  sinks to the bottom of a container of liquid when
  spun in a centrifuge
• One subunit smaller than other, but both are
  larger than average protein

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A couple more nifty pictures

• 50S (left) and 30S. This time you can see them
  from different angles, through different style of
  picture

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So whats the purpose of ribosome?

• Ribosome basically a protein factory. Subunits
  each have role in making of proteins
• To understand exactly what each subunit does,
  its necessary to walk through protein synthesis
  step by step

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Protein synthesis

• Process starts from DNA through transcription
• Translation is where ribosome comes in.
  Translation occurs when protein formed from code
  on mRNA
• Ribosome carries out the translation of the
  nucleotide triplets

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Protein synthesis

• Chart - visual image of transcription and
  translation in protein synthesizing
• DNA and RNA have nucleotides that determine kind
  of protein
• 3 nucleotides 1 amino acid of a protein

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Ribosome and RNA

• mRNA with code for proteins located at 30S
  subunit
• tRNAs responsible for carrying amino acids to
  mRNA. Each tRNA has own nucleotide triplet which
  binds to matching triplet on mRNA, ex., tRNA with
  code AAA (triple adenine) would match up with
  mRNA that has code UUU (triple uracil)

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InitiationThe first phase of translation

• Translation begins when mRNA attaches to the 30S
• tRNA comes and binds to mRNA where nucleotide
  code matches
• This triggers 50S binding to 30S. 50S is where
  all tRNAs will bind. Now we move on to elongation

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ElongationThe second phase

• Two binding sites on 50S A site and P site,
  which aid in continuing translation
• First tRNA connected at A site. Now moves to P
  site as another tRNA approaches
• Second tRNA binds to A site

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Elongation (continued)

• Peptide bond forms between amino acids of tRNAs
  (methionine and proline)
• First tRNA now detached from its amino acid, and
  it leaves ribosome. Second tRNA still has
  proline and methionine attached

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Elongation (continued)

• The tRNA left now moves to P site. Ribosome
  ready to accept another tRNA and continue process
• Each tRNA adds another amino acid to growing
  peptide chain (thus elongation)
• Eventually process has to finish, however

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End of translation

• Ribosome was moving along nucleotide triplets one
  by one
• Ribosome reaches stop codon, peptide chain
  finished. Last tRNA leaves ribosome, leaving
  behind completed peptide chain

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End of translation (continued)

• Ribosome separates from mRNA
• Ribosome subunits also separate, and will remain
  this way until another mRNA comes along to
  restart the process

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Still awake?Its Pop Quiz Time!!!

• Heres a little quiz on what weve covered so
  far, just to keep your brain alert.
• First question
• What are the two subunits of ribosome known as,
  and which is which?
• Answer 50S (the larger one) and 30S (the smaller
  one)

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Another question

• (This ones multiple choice!)
• The process of converting code on the mRNA into a
  protein is called?
• A. Transition
• B. Transduction
• C. Translation
• D. Transcription

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And now

• Thats the end of the quiz (whew)!
• Any questions so far?
• Okay, thats taken care of. And now, without
  further ado, we move on to

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Structures of the subunits

• 50S and 30S besides difference in size, also have
  somewhat different structures
• Both are rather complicated, since theyre much
  larger than average protein
• Well cover structure of 50S first

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The 50S subunit

• This part of ribosome contains site where new
  peptide bonds are formed when proteins are
  synthesized
• mRNA would be located horizontally in groove
  across middle
• To help with protein synthesis, subunit uses
  adenine RNA nucleotide, shown by green dot in
  center

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The 50S subunit

• This part of ribosome contains site where new
  peptide bonds are formed when proteins are
  synthesized
• mRNA would be located horizontally in groove
  across middle
• To help with protein synthesis, subunit uses
  adenine RNA nucleotide, shown by green dot in
  center

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The 50S subunit

• 50S made of two RNA strands a long one, shown in
  an orangey color, and shorter one, shown in
  yellow
• Blue things in the picture are a few of many
  proteins that have bound to ribosomes surface
• Many of proteins have long tails that go inside
  ribosome and keep the RNA strands in place

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A bit more on 50S

• 50S is quite rigid, folded and packed so well
  that its virtually immobile within its structure
• Contrasts with structure of 30S, which well now
  move to

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The 30S subunit

• Unlike 50S, 30S is fairly flexible
• It needs to have movable regions because, when it
  shifts from one mRNA nucleotide triplet to
  another, movement is necessary to aid this
  process
• 30S controls flow of information during protein
  synthesis

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The 30S subunit

• 30S finds an mRNA and then makes sure that each
  tRNA is matched up correctly on mRNA
• Its been suggested that mRNA enters through
  small hole in 30S (shown here in center of left
  side)

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The 30S subunit

• 30S finds an mRNA and then makes sure that each
  tRNA is matched up correctly on mRNA
• Its been suggested that mRNA enters through
  small hole in 30S (shown here in center of left
  side)

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The 30S subunit

• mRNA then extends up into the place where
  translation occurs, located in cleft between top
  part, head, and bottom part, body

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Structure and RNA

• Recently discovered - about two-thirds of
  ribosomes mass made up of RNA
• Most important functions of ribosome performed by
  RNA. This has been found because of atomic
  knowledge of structures of 50S and 30S and their
  assemblage into 70S
• (One might logically think it to be 80S, but it
  really isnt)

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Concluding

• Although a good amount of progress has been made
  in figuring out structures of 50S and 30S, there
  is probably still a lot that hasnt been
  deciphered yet
• Its somewhat difficult to find out structures
  because, as mentioned earlier, theyre relatively
  large. Hopefully more will be discovered about
  them in the future

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Guess whatIts Quiz Time again!

• This is the last one, I promise. Its a piece of
  cake anywaywell, if you were paying attention,
  that is.
• Ribosome is primarily made up of?
• A. DNA
• B. RNA
• C. Proteins
• Glad thats over, huh? Now to summarize what we
  covered

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To summarize

• Ribosome protein synthesizer consisting of two
  subunits, 50S and 30S
• Protein synthesis starts from DNA, which carries
  the code for making the proteins. The DNA is
  converted to mRNA by transcription, and mRNA,
  in turn, is converted to protein by translation
• Ribosome translates nucleotide triplets on mRNA
  into proteins

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To summarize

• tRNAs carry amino acids to ribosome to be linked
  together by the ribosome. One by one, they bind
  to the ribosome, add their amino acid to the
  chain, and then depart
• 50S and 30S made primarily of RNA and are both
  larger than the average protein. 50S has rather
  rigid structure, while 30S has fairly flexible
  one. Not all about them has been discovered yet,
  but significant progress has been made in that
  respect

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The End

• Thats a wrap!
• Any questions?