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LS 3 Final > Lecture 13: Translation Machinery & Genetic Code > Flashcards

Lecture 13: Translation Machinery & Genetic Code Flashcards

1
Q

In prokaryotes, transcription and translation occur ________

A

simultaneously

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2
Q

Function of mRNA

A

Carry genetic information transcribed from DNA in form of codons

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3
Q

What are codons?

A

3-nucleotide sequences, each of which specifies a particular amino acid

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4
Q

Direction that ribosome reads mRNA and moves in

A

5’ to 3’

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5
Q

Direction of polypeptide synthesis

A

N to C

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6
Q

How long is one tRNA?

A

74-93 nucleotides (small RNA chain)

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7
Q

Function of tRNA

A

Read codons in the mRNA through base pairing with their own anticodon and bring the corresponding amino acid

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8
Q

Function of rRNA

A

Associate with set of proteins to form ribosomes

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9
Q

What do ribosomes do?

A

Bind tRNAs associated with amino acids and move along the mRNA, catalyze get assembly of amino acids into polypeptide chains

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10
Q

What does large subunit of ribosome (rRNA) do?

A

Catalyze reaction to form peptide bonds between AAs

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11
Q

What does small subunit of ribosome (rRNA) do?

A

Recognize where translation starts (specific sequence)

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12
Q

What does it mean that the DNA code is degenerate?

A

More than one triplet code for each AA (4 bases, 3 letter code, so 4^3 means 64 possibilities, which is more than enough for 20 AAs)

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13
Q

Stop codons

A

UAA, UAG, UGA

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14
Q

Start codon

A

AUG (also the AA codon for methionine)

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15
Q

In a codon, which bases are the most important?

A

The first two

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16
Q

Positive correlation between _____ of codons and ______ of the amino acid (except ______)

A

Number, frequency, Arg

17
Q

What are the exceptions to the AUG start codon and where do they occur?

A

GUG and UUG in prokaryotes, CUG in eukaryotes

18
Q

What is the open reading frame?

A

Sequence of codons that runs from a specific start codon to a stop codon; must be long enough to make a functional polypeptide

19
Q

Each nucleotide is part of only one codon, which means the genetic code is?

A

Non-overlapping

20
Q

How was it determined that the genetic code is non-overlapping?

A

In mutant proteins, there is only ONE amino acid substitution; if it were overlapping more than one AA would change

21
Q

Frameshift mutation

A

Insertion or deletion of bases not in multiples of 3, shifting the entire AA sequence (shift in the ORF)

22
Q

Components of tRNA

A

3 loops (inc. anticodon loop), acceptor stem

23
Q

Structure of tRNA’s anticodon loop

A

Contains anticodon region, which is complementary to a codon in mRNA

24
Q

Where does an AA attach to tRNA and how?

A

AA covalently attaches to acceptor stem at 3’ end (at CCA, the sequence at the 3’ tail)

25
Q

How does tRNA recognize and attach to the correct AA?

A

Enzymes called aminoacyl-tRNA synthetases covalently attach each AA to the correct tRNA (occurs before reaching ribosome) - most cells have 20 ARS’s, one per AA)

26
Q

How are aminoacyl-tRNA synthetases named? Give example.

A

seryl-tRNA synthetases for serine

27
Q

How many ARS’s (aminoacyl-tRNA synthetases) does each AA have?

A

One: it recognizes all the codon(s) for that AA

28
Q

How else does an ARS recognize the right tRNA?

A

Segments on the acceptor end, and bases elsewhere in the molecule, like nucleotide 73 (discriminator base)

29
Q

How and where are AAs linked to tRNAs by ARS’s?

A

Covalently linked to tRNAs at the 2’ or 3’ OH - this requires ATP (ATP to AMP)

30
Q

What molecule is responsible for proofreading in the attachment of tRNA to AA?

A

ARS (ribosome, AA, and tRNA don’t know if a mistake has been made); can remove an incorrect AA

31
Q

How can 61 different codons be read when cells have less than 61 different tRNAs?

A

One tRNA anticodon can recognize more than one codon corresponding to one AA

32
Q

How can one tRNA recognize more than one codon?

A

“Wobble” position: 3rd base (3’) in mRNA codon = 1st base (5’) in tRNA anticodon is more flexible

33
Q

How many H bonds between each base pairing?

A

2 between A and U/T, 3 between C and G

34
Q

What is inosine?

A

Rare base found in tRNA, often in the anticodon

35
Q

What can inosine base pair with, and where?`

A

Can base pair with A, C, or U in wobble position of mRNA codon (3rd position)

36
Q

Basic process of translation

A

mRNA used as template to make proteins

LS 3 Final (5 decks)

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