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Genetics > Lesson 7 Translation > Flashcards

Lesson 7 Translation Flashcards

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Biology 101 flashcards
1
Q

What is an inborn error of metabolism?

A

A relationship between the function of gene and the production of enzymes.

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2
Q

What did Beadle and Tatum’s Experiments with Neurospora lead to?

A

The One Gene-One Enzyme theory

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3
Q

What is a loss of function allele?

A

A gene that loses its function causes a defect.

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4
Q

What is the genetic code? How is it read?

A

A sequence of bases within an mRNA molecule.

Read in groups of three nucleotides.

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5
Q

How many types of bases are there?

A
  1. A, U, G, C
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6
Q

How many different codon arrangements exist?

A

4 to the third power or 64

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7
Q

What is meant by saying genetic code is degenerate?

A

There are more codon than amino acids. More than one codon specifies the same amino acid.

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8
Q

What is the wobble base?

A

The third base in the codon, which is usually the degenerate base.

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9
Q

Experiment 13A: Deciphering the Genetic Code

What was the hypothesis of the experiment?

A

The sequence of bases in RNA determines the incorporation of specific amino acids into a polypeptide.

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10
Q

Experiment 13A; Deciphering the Genetic Code

How were the data interpreted?

A

Investigators were able to determine how many Us or G’s in the codon for a specific amino acid, but not the order of those bases.

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11
Q

Primary structure of a polypeptide

A

Amino acid sequence

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12
Q

What is a quaternary structure? What are its subunits?

A

Structure of a protein made up of more than one polypeptide. Each polypeptide is a subunit of the protein.

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13
Q

What kind of functions do proteins carry out?

A

A myriad of cellular functions, including the synthesis of all of a cell’s molecules and macromolecules.

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14
Q

What does the function of tRNA depend on?

A

The specificity between the amino acid it carries and its anticodon.

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15
Q

What is the function of tRNA?

A

To recognize the codon within an mRNA and carry the correct amino acids to the site of polypeptide synthesis.

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16
Q

How do mRNA and tRNA bind?

A

The anticodon in a tRNA molecules binds to a codon in mRNA because of their complementary sequences.

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17
Q

Of what codons is the genetic code made?

A

The genetic code has 3 stop codons and 61 different codons that specify the 20 amino acids.

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18
Q

Experiment 13B: Translation, mRNA, tRNA

What is the hypothesis?

A

Codon recognition is dictated only by the tRNA anticodon; the chemical structure of the amino acid attached does not play a role.

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19
Q

Experiment 13B: Translation, mRNA, tRNA

What does Raney nickel do?

A

It converts cysteine to alanine. It was the only way to find an alanine in the experiment because the only codon in the template were U any G.

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20
Q

How does Raney nickel convert cysteine to alanine?

A

It removes the -SH group. It does not remove the 14C label within the cysteine.

21
Q

Experiment 13B: Translation, mRNA, tRNA

Why was column chromatography used?

A

To separate the amino acids. Alanine and cysteine come out in different fractions.

22
Q

Experiment 13B: Translation, mRNA, tRNA

How were the data interpreted?

A

In the control, the radioactivity was mostly with cysteine. In other set, the radioactivity was mostly with alanine. This means tRNA incorporated alanine into the polypeptides. It was tRNAcys codons that incorporated the amino acid, so it depends on tRNA and mRNA, no on amino acid itself.

23
Q

What common structural features do tRNAs share?

A

They have a secondary structure that is described as a cloverleaf pattern. There are three stem/loop structures, a variable region, an acceptor stem, and a 3’ single-stranded region.

24
Q

Where is the anticodon located on tRNA?

A

In the second stem/loop region.

25
Q

What are aminoacyl-tRNA synthetase enzymes?

A

Enzymes that catalyze the attachment of amino acids to tRNA molecules. There are twenty different ones.

26
Q

What is a charged tRNA?

A

A charged tRNA has an amino acid attached to its 3’ end by an ester bond.

27
Q

Where does the wobble position occur?

A

Between the first base (meaning first base in the 5’ to 3’ direction) in the anticodon ant the third base in the mRNA

28
Q

What is the wobble hypothesis?

A

The first two positions pair strictly according to AU/GC rule. Third position can tolerate certain types of mismatches.

29
Q

What kind of ribosomes do prokaryotes and eukaryotes have?

A

Prokaryotes: one type of ribosomes found within bacterial cytoplasm.
Eukaryotes: biochemically distinct ribosomes in different cellular locations.

30
Q

What does each ribosomes contain?

A

Several rRNA molecules and many proteins.

31
Q

Where does synthesis of eukaryotic rRNA occur? Ribosomes?

A

In structure he nucleus. In the cytosol.

32
Q

Where does assembly of rRNAs and ribosomal proteins to make the 40S and 60S occur? What happens to them after they are assembled?

A

In the nucleolus.

The 40S and 60S are then exported into the cytosol and assemble to form an 80S ribosomes during translation.

33
Q

What are the stages of translation?

A

Initiation, elongation, termination.

34
Q

What happens during translation initiation?

A

Initiator tRNA recognizes the start codon in an mRNA, as the small and large ribosomal subunits assemble.

35
Q

In bacteria, what is the binding of the mRNA to the 30S ribosomal unit dependent on?

A

complementarity between short region of mRNA and rRNA within the 30S subunit.

36
Q

In bacteria, what is the ribosomal binding site or Shine-Dalgarno sequence?

A

A sequence found in bacterial mRNAs involved in the binding of the mRNA to the 30S subunit.

37
Q

How is assembly of initiation complex of eukaryotes different from that of prokaryotes?

A

A key difference is the recognition of the start codon. Most eukaryotic. mRNAs contain a 7-methylguanosine caprmi structure at the 5’ end of the RNA. The recognition of this cap structure is of central importance in the initial binding of mRNA to the ribosomes.

38
Q

In eukaryotic translation initiation, what happens after recognition of the 5’ cap?

A

The next step is to locate the AUG start codon that is somewhere downstream from the 5’ cap structure. This occurs by a scanning mechanism. In some cases, but not all, the first AUG codon that it encounters is used as a start codon. In some cases the scanning ribosomes passes over the first AUG start codon and chooses another AUG codon that is farther down the mRNA.

39
Q

What role does the sequence of nucleotides around the AUG codon play in determining selection of AUG?

A

There is a consensus sequence for optimal start codon recognition. Initiation relies on the correct sequence around the start codon.

40
Q

During elongation stage, how does the tRNA transfer an amino acid to the growing polypeptide chain?

A

The tRNA progresses from the A to the P to the E site. A new tRNA carrying a single amino acid first binds to the A site. This binding occurs because the anticodon in the tRNA is complementary to the codon in the mRNA.

The formation of a peptide bond between the amino acid in the A site and the growing polypeptide chain occurs via a peptidyl transfer reaction. A covalent bond forms between the last amino acid in the polypeptide chain and the amino acid on the newest tRNA. The polypeptide chain is thereby transferred to the tRNA in the A site. The peptidyl transfer reaction is catalyzed by an enzyme complex known as peptidyltransferase, which is composed of several proteins and rRNA.

After this step, the ribosomes moves, or translocates, to the next codon in the mRNA. This moves the tRNAs in the P and A sites to the E and P sites, respectively. The next codon in the mRNA is now exposed in the empty A site. Finally, uncharged tRNA exits the E site and the cycle begins all over again.

41
Q

What is a peptidyl transfer reaction?

A

How a peptide bond is formed between the amino acid in the A site and the growing polypeptide chain.

42
Q

What is a peptidyltransferase?

A

An enzyme that is composed of several proteins and rRNA that catalyzes the peptidyl transfer reaction.

43
Q

When does termination occur?

A

When the mRNA reaches a stop codon.

44
Q

What recognizes the termination codon?

A

Proteins known as release factors.

45
Q

What happens when the release factors recognize the stop codon?

A

The release factors bind, and the bond between the polypeptide and the tRNA is hydrolyzed. The polypeptide is then released from the ribosomes and the entire complex disassembles.

46
Q

What is the directionality of a polypeptide chain?

A

From its amino terminus to its carboxyl terminus.

47
Q

What bond is formed during each cycle of elongation?

A

A peptide bond is formed between the carboxyl group in the last amino acid in the polypeptide chain and the amino group in the next amino acid to be added to the chain.

48
Q

Where is the first amino acid of the polypeptide chain located?

A

At the N-terminal or amino-terminal end of the polypeptide. The term N-terminal comes from the presence of a nitrogen atom at this end.

49
Q

Where is the last amino acid of the polypeptide chain located?

A

The Cd-terminal or carboxyl-terminal end

Genetics (12 decks)

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