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57 Cards in this Set
- Front
- Back
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What kind of molecule is tRNA and what does it link?
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1. Adapter molecule
2. Links mRNA codons to it's anti-codons |
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Each amino acid has its own adapter (tRNA). T or F?
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True
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There are two key events to make a protein with tRNA. What are they?
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1. tRNA must read mRNA codons correctly
2. tRNAs must deliver amino acids corresponding to each codon |
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What are the 3 primary functions of tRNA?
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1. Must be charged (carrying an amino acid)
2. Associates with mRNA molecules 3. Interacts with ribosomes |
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Where is the anticodon located on the tRNA? The amino attachment site? Hydrogen bonds?
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See illustration
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The sequence of the attachement site is ALWAYS ACC. T or F?
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False: It is always CCA
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______ different codons encode the ______ amino acids in all protiens
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61, 20
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Explain the wobble phenomenon
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The specificity for the base at the 3' end of the codon and the 5' end of the anti-codon are not always observed.
For example: The codons CGA, GCC and GCU can all be recognized by just one single species of tRNA. |
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Wobble does not allow the genetic code to be redundant. T or F?
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False: Wobble does not allow genetic code to be ambiguous
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What is a charged tRNA?
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A tRNA that has an amino acid attached to it
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Exactly how is a tRNA charged?
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The charge is "activated" by the enzyme Aminoacyl-tRNA snythase
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The small subunit ribosome is made up of what?
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One molecule of rRNA and 33 protiens
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The large subunit has three tRNA binding sites. What are they?
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A site (amino)
P site (polypeptide) E site (exit) |
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Illustration of how tRNA is charged
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See illustration
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What are some characteristics of the enzyme aminoacyl-tRNA synthase?
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1. Highly specific for each amino acid and it corresponding tRNA
2. Has three active sites that recognize ATP, a specific amino acid and a specific tRNA |
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Explain the purpose of the three sites (EPA) on the larger subunit.
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A: a charged tRNA anticodon binds to an mRNA codon
P: tRNA adds its amino acid to the growing chain E: tRNA sits here before being released from ribosome |
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The large subunit ribosome is made up of what?
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Three different molecules of rRNA and 49 protiens
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The ribosome has "fidelity function". What does this mean?
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It ensures that mRNA and tRNA interactions are accurate and that the bindings are appropriate
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In elongation, the large subunit catalyzes two reactions. What are they?
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1. Breaks bonds between tRNA in P site and its amino acid
2. Forms a peptide bond between the above acid and the acid on tRNA in the A site |
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How do codons and anticodons bind together?
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Hydrogen bonds
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During elongation, the first tRNA releases its amino acid. It then moves to the ______ site and becomes ______ again.
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E, charged
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Ribosomes are specific and can only make a certain protein. T or F?
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False: They are NOT specific and can make ANY protien
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During termination, stop codons bind to what type of protien?
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A protien release factor
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If no hydrogen bonds form between codons and anticodons, what probably happened?
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There was an incorrect base pairing - the ribsome will reject the tRNA
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In termination, what does the protein release factor do?
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Hydrolysizes the bond between the chain and tRNA on the P site (the chain separates from the ribosome)
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Translation has 3 steps. What are they?
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1. Initiation
2. Elongation 3. Termination |
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A single strand of mRNA can have MANY ribosomes on it creating MANY chains. What is this assemblage called?
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A polyribosome (or polysome)
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What does an initiation complex consist of?
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A charged tRNA, small ribsome unit that are both bound to mRNA
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Nucleus' mitochondria and chloroplasts have special receptor protiens that the chains (signal sequence) binds to. What are these protiens called?
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Docking protiens
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In prokaryotes, the rRNA fist binds to a special site on the mRNA. What is this special site?
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The Shine Dalgarno Sequence
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If a chain is destined for the ER, the chain's signal sequence binds to a ______ BEFORE translation is complete.
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Signal recognition particle
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In initiation, the small subunit binds to the ______ cap on the mRNA and moves until it reaches the start codon
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5'
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Illustration of translation occuring at the ER membrane.
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See illustration
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During initiation, the start codon is ALWAYS AUG. What amino acid does this code for?
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Methionine (MET) (It is sometimes removed after translation)
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Once a protien is inside the ER lumen, there are two types of signals that can direct the protein to its final destination. What are they?
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1. A certain sequence directs it to remain inside the ER
2. Sugars in the golgi result in glycoproteins and these end up at the plasma membrane OR vacuole in plants |
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During initiation, after the tRNA, mRNA and small subunit connect, what joins the complex?
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The large subunit (tRNA ends up in the P site of this unit)
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What is glycosylation modification?
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Addition of sugars to form glycoproteins. Important for targeting and recognition
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What are the "ingredients" that make up the "initiation factors"?
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mRNA, two ribosomal units (lrg and sml), and methionine-charged tRNA
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How are the ribosomal subunits bound together?
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Non-covalently (by ionic and hydrophobic forces)
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How is it determined which tRNA enters into the A site?
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Any tRNA whose anticodons is COMPLEMENTARY to the codon that is currently sitting in the A site
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In elongation, the incoming second tRNA enter the ______ site
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A
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Elongation catalyzes two reactions. Because of these two reactions, it is considered to have ______ activity.
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Peptidyl transferase
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During elongation, if rRNA is destroyed, all activity STOPS! Thus, rRNA is the ______ in peptidyl tranferase activity.
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Catalyst (this supports the idea that RNA evolved before DNA)
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All of the steps in elongation are assisted by ribosomal proteins. What are these proteins collectively called?
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Elongation factors
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The process of elongation ultimately produces what?
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A long polypeptide chain
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When is the only time a tRNA can "sit" in site E (the last slot)?
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If it has lost its amino acid (which occured in site P)
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When talking about codons, we are referring to ______ and when talking about anticodons, we are referring to ______.
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mRNA, tRNA
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When a stop codon (UAA for example) enters the A site, what happens?
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Translation ends
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What is the N terminus?
What is the C terminus? |
1. The start (methionine)
2. The end (last amino acid) |
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What happens to the subunits at the very end of translation?
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The separate
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Newly formed polypeptide chain have a sort of "address label". What is this called?
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A signal sequence
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What exactly do docking receptor proteins do?
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They form a channel to let the protein through
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What directs the polypeptide chain to the nucleus?
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A nuclear localization signal
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If a polypeptide chain is destined to travel to the ER, its signal sequence binds to a ______ BEFORE translation is complete.
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Signal recognition particle
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After translation, three different modifications can occur. What are they?
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1. Proteolysis
2. Glycosylation 3. Phosphorylation |
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What is proteolysis modification?
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Cleaving of a long chain with porteases - the fragments fold into different shapes
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What is phosphorylation modification?
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The addition of phosphate groups by protein kinases which alter the protein shape
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