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Biology 211 > Translation: The Cast of Characters > Flashcards

Translation: The Cast of Characters Flashcards

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1
Q

what is translation, what does it involve?

A

key step to the production of protein molecules, involving a change in language from the nucleotide base sequence of an mRNA molecule to the amino acid sequence of a polypeptide chain

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2
Q

what happens during the process of translation?

A

a sequence of mRNA nucleotides, read as triplet codons, specifies the order in which amino acids are added to a growing polypeptide chain

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3
Q

what do ribosomes do in translation? What about RNA?

A

ribosomes serve as the intracellular site for translation, while RNA molecules are the agents that ensure insertion of the correct amino acid at each position in the polypeptide

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4
Q

the cellular machinery for translating mRNAs into polypeptides involves 5 major components:

A
  1. ribosomes that carry out the process of polypeptide synthesis
  2. tRNA molecules that align amino acids in the correct order along the mRNA template
  3. aminoacyl-tRNA synthesases that attach amino acids to their appropriate tRNA molecules
  4. mRNA molecules that encode the amino acids sequence information for the polypeptides being synthesized
  5. protein factors that facilitate sever steps in the translation process
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5
Q

The Ribosome Carries Out Polypeptide Synthesis

  • ribosomes play a central role in…
  • what do they do?
A
  • protein synthesis
  • orient the mRNA and amino acid carrying tRNAs so the genetic code can be read accurately and catalyzing peptide bond formation to link amino acids into a polypeptide
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6
Q

The Ribosome Carries Out Polypeptide Synthesis

  • ribosomes are particles made of …
  • In euk… (2)
  • In prok…. (2)
A 
-ribosomal RNA(rRNA) and protein 
In euk.. 
-free in the cytosol
-bound to ER and outer nuclear envelope 
In prok... 
-ribosomes are smaller 
-bacterial ribosomes are sensitive to different inhibitors of protein synthesis and are composed of fewer proteins and smaller and fewer RNA molecules
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7
Q

The Ribosome Carries Out Polypeptide Synthesis
shape of a typical bacterial ribosome?
-subunits?
-whole S value?

A
  • 2 subunits, large and small (50S and 30S)

- whole S value= 70S

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8
Q

The Ribosome Carries Out Polypeptide Synthesis
shape of typical euk ribosome?
-subunits?
-whole S value?

A
  • 2 subunits, large and small, (60S and 40S)

- whole S value= 80S

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9
Q

The Ribosome Carries Out Polypeptide Synthesis

what does rRNA do?

A

performs many of the key functions of ribosomes

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10
Q

The Ribosome Carries Out Polypeptide Synthesis:

Four sites on the ribosome are particularly important for protein synthesis..

A
  1. mRNA binding site
  2. three sites where tRNA can bind:
    - an A (aminoacyl) site that binds each newly arriving tRNA with its attached amino acid
    - a P (peptidyl) sirte where the tRNA carrying the polypeptide chain resides
    - an E (exit) site from which tRNAs leave the ribosome, after they have discharged their amino acids
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11
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:

what is a tRNA molecule?

A

-tRNA molecule is an adapter: binds a specific amino acid and the mRNA sequences that specify the amino acid

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12
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:

each ‘adapter’ molecule (tRNA) posses two sites..

A
  1. one that binds to a specific amino acid

2. the other recognizes an mRNA base sequence coding for this amino acid

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13
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:

tRNAs are linked to their corresponding amino acids by…

A

an ester bond that joins the amino acid to the 2’- or 3’- hydroxyl group of the adenine (A) nucleotide located at the 3’- end of all tRNA molecules

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14
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:

selection of the correct amino acid for each tRNA is the responsibility of…

A

the enzymes that catalyze formation of the ester bond

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15
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:
by convention, the name of the amino acid that attached to a given tRNA is indicated by…
ex?

A

a superscript

ex tRNA molecules specific for alanine are identified as tRNA^Ala

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16
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:
once the amino acid is attached, the tRNA i called an.
-what is said about the tRNA?
-what is said about the amino acid? .

A

aminoacyl tRNA

  • tRNA is said to be in its charged form
  • amino acid is said to be activated
17
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:

tRNA molecules can recognize codons in mRNA because ..

A

each tRNA posses an anticodonm which is a special trinucleotide sequence located within one of the loops of the tRNA molecules

18
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:
the anticodon of each tRNA is complementary to..
therefore anticodons allow..

A

one or more mRNA codons that specify the amino acid being carried by that tRNA
therefore anticodons allow tRNA molecules to recognize codons in mRNA by complementary base pairing

19
Q

Transfer RNA Molecules Bring Amino Acids to the Ribosome:
some tRNA molecules recognize more than one codon..
-what does the wobble hypothesis allow for?
example?

A

Wobble hypothesis: allows for some unexpected base pairing

  • nucleotide inosine is able to pair with U,C, or A and is often found in the wobble position of the anticodon
  • this allows for several codons to specify one amino acid
20
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
before a tRNA moelcule can bring its amino acid to the ribosome, that amino acid must be…
-what is the enzyme aminoacyl-tRNA synthetase responsible for?

A

attached covalently to the tRNA

-enzyme responsible for the linking of amino acids to their corresponding tRNAs is called aminoacyl-tRNA synthetase

21
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
cells typically have how many aminoacyl-tRNA synthetases?

A

20 differnt aminoacyl-tRNA synthetases, one for each of the 20 amino acids commonly used in protein synthesis

22
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
what do aminoacyl-tRNA synthetases do and how do they do it?

A

catalyze the attachment of amino acids to their corresponding tRNAs via an ester bond using ATP hydrolysis

23
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
in the product, aminioacyl-tRNA, the ester bond is said to be ..? what does this mean? what is this process also referred to as? why?

A
  • high energy bond
  • this means that hydrolysis of the bond releases sufficient energy to drive formation of the peptide bond that will eventually join the amino acid to a growing polypeptide chain
  • this process is also referred to as amino acid activation because it links an amino acid to its proper tRNA as well as activates it for subsequent peptide bond formation
24
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
how do aminoacyl-tRNA synthetases identify the correct tRNA for each amino acid?

A

both the anticodon and the 3’ end of the tRNAare needed to specify the correct amino acid

25
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
what happens after addition of the amino acid to the tRNA molecule?

A

aminoacyl-tRNA synthetases proofread the final product to ensure the correct amino acid was added

26
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
where does the “proofreading” of the final product occur?

A

preformed by a site on the synthetase molecule that recognizes incorrect amino acids and releases them by hydrolyzing the bond that links that amino acid to the tRNA

27
Q

Aminoacyl-tRNA Synthetases Link Amino Acids to the Correct Transfer RNAs:
what happens once the correct amino acid has been added to the tRNA?

A

it is the tRNA itself that recognizes the appropriate codon in the mRNA

28
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
what do sequences of codons in mRNAs direct?
HENCE?

A

direct the order in which amino acids are linked together in protein synthesis
HENCE: mRNA that happens to bind to a given ribosome will determine which polypeptide that ribosome will manufacture

29
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
In eukaryotes, transcription…
in prokaryotes,…

A
  • transcription takes place in the nucleus and protein synthesis is mainly a cytoplasmic event, the mRNA must first be exported from the nucleus
  • in prok. transcription and translation are usually coupled events
30
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
at the heart of each mRNA molecule is the..

A

its message, ie the sequence of nucleotides that encodes a polypeptide

31
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
mRNA also possess sequences at each end that are not translated…
1. untranslated sequence at 5’ end?
2. untranslated sequence at 3’ end?

A
  1. the untranslated sequence at the 5’ end of an mRNA precedes the start codon, which is the first codon to be translated ( AUG is most common start codon)
  2. the untranslated sequence at the 3’ end follows the stop codon, which signals the end of translation ( UAG, UAA, UGA)
32
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
included in the untranslated regions of euk. mRNAs are..

A
  • a 5’ cap and

- a 3’ poly(A) tail

33
Q

Messenger RNA Brings Polypeptide Coding Information to the Ribosome:
in euk. each mRNA typically encodes… compared to bacterial/archaea?

A

a single polypeptide

bacterial and archaeal may encode several

34
Q

Protein Factors are Required for the Initiation, Elongation, and Termination or Polypeptide Chains:
INFO

A

some of these protein factors are required for initiating the translation process, others for elongating the growing polypeptide chain, and still others for terminating polypeptide synthesis

Biology 211 (46 decks)

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