Flashcards in Exam 3 Deck (288)
Where in a cell does splicing occur?
Where in a cell does transcription occur? (eukaryotes)
Where in a cell does translation occur? (eukaryotes)
Translating the ‘language’ of nucleic acids into the language of proteins (nucleotides into amino acids)
What is codon usage bias?
Different species prefer different codons for the same amino acid
True or False: The AUG codon for methionine is the most common start codon in both eukaryotes and prokaryotes
--> In prokaryotes, a specialized form of methionine is used for the initiating methionine known as N-formyl methionine, though
True or False: The start codon in translation signifies the C terminal of the protein
FALSE: The start codon signifies the N-terminal of the protein
What are the three stop codons?
UAA, UAG, UGA
What is the difference between methionine (Met) and N-formylmethionine (fMet)?
N-formylmethionine has a H-C=O group on its N-group
--> Draw this!
True or False: Despite the slight difference between Met and nMet, eukaryotes can't recognize nMet as foreign
FALSE: The eukaryotic immune system recognizes proteins with fMet as foreign
Where is nMet used (which types of cells)?
In prokaryotes, mitochondria, and chloroplasts
What establishes the reading frame in translation?
The initiator AUG
Definition: Reading frame
The reading frame is the phase in which 3 nucleotides are read into amino acids. There are 3 potential reading frames and the AUG specifies which frame is used.
Definition: Open reading frame
An open reading frame is the series of codons that come between the initiation AUG and the first Stop codon
What are the three types of point mutations?
Silent, Missense, and Nonsense
Describe a silent mutation
A point mutation that does not end up making a difference in the amino acid that is coded (due to redundancy of the genetic code)
Describe a missense mutation
A point mutation that results in one amino acid being changed
--> Normally not that big of a problem
Describe a nonsense mutation
A point mutation that changes a regular codon to a stop codon, resulting in premature ending of the protein
--> Usually results in a loss of function, may or may not be a big deal
What are tRNAs?
- A class of noncoding RNAs made by RNA Pol III
- Adapters that link the sequence of the RNA to the sequence of the protein
What is at the 3' end of tRNA?
A single-stranded 'CCA' at the 3’-end that links to the amino acid
What is the anticodon of tRNA?
A sequence of 3 nucleotides that can base pair with the codon of the mRNA
How does tRNA fold into its cloverleaf shape?
- By intramolecular base pairing with 4 regions that are double-helical
True or False: tRNAs have about 10% of their bases modified before they leave the nucleus
Why are tRNAs chemically modified?
Modifications are crucial for tRNA structure, function, and stability
-Modifications of specific positions affect the behavior of tRNAs during translation
-Some modifications, such as pseudouridines, make the tRNA more rigid whereas others such as dihydrouridines make it more flexible
-Some modifications are essential for ‘charging’ the tRNA with correct amino acid
True or False: Hypermodified tRNAs are targeted for degradation
FALSE: HYPOmodified tRNAs are targeted for degradation
What does Wobble Base Pairing do?
Allows some tRNAs to recognize more than 1 codon because it doesn’t require a perfect match in the 3rd position of the codon
--> i.e. non-standard Watson-Crick pairing
What is the first step of decoding the genetic code? What enzyme does this?
-Linking the correct amino acid to the tRNA is the first step
-This is done by aminoacyl tRNA synthetases
What is an aminoacyl tRNA?
A tRNA with the amino acid attached to it
Describe the bond that forms between the amino acid and the 3' end of tRNA
- An ester bond forms between the acid of the amino acid and the 3’ hydroxyl of the ribose at the 3’-end of the tRNA.
- This is a high energy bond.
- This energy is used later to link the amino acid to the growing protein chain.
- Because of the high energy bond, an amino acid linked to a tRNA is sometimes said to be ‘activated’