module 7 lec 2

Question 1

Who cracked the genetic code in 1961?

Answer 1

Marshall Nirenberg and Heinrich Matthaei.

Question 2

What codon did Nirenberg and Matthaei use to discover phenylalanine?

Answer 2

They used UUU, which codes for phenylalanine.

Question 3

What other tools did Khorana use to further crack the code?

Answer 3

Khorana used polynucleotides like polydinucleotides, polytrinucleotides, and polytetranucleotides.

Question 4

What was the outcome of using these polynucleotides?

Answer 4

Researchers could read amino acid sequences and deduce corresponding codons

Question 5

Was the genetic code fully resolved?

Answer 5

No, there was still some ambiguity in the code.

Question 6

Who helped Nirenberg resolve the ambiguities in the genetic code?

Answer 6

Philip Leder.

Question 7

How did Nirenberg and Leder resolve the ambiguities of the genetic code?

Answer 7

hey used trinucleotide mRNAs of known sequence, tRNAs charged with radioactive amino acids, and ribosomes.

Question 8

What was the role of tRNAs in Nirenberg and Leder’s experiment?

Answer 8

tRNAs were charged with radioactive amino acids to help identify which codons corresponded to which amino acids.

Question 9

What are nonsense codons?

Answer 9

Nonsense codons are stop codons that signal the end of translation.

Question 10

How many nonsense codons are there in the genetic code?

Answer 10

There are three nonsense codons: UAA, UAG, and UGA.

Question 11

What is the role of nonsense codons in protein synthesis?

Answer 11

They terminate translation, causing the ribosome to release the newly synthesized polypeptide.

Question 12

What do nonsense codons do?

Answer 12

Nonsense codons terminate the polypeptide chain during translation.

Question 13

What are the three nonsense codons (stop codons)?

Answer 13

The three stop codons are UAA (ochre), UAG (amber), and UGA (opal).

Question 14

What is another name for nonsense codons?

Answer 14

Nonsense codons are also called stop codons.

Question 15

What does the 5’ to 3’ direction of mRNA correspond to in polypeptide synthesis?

Answer 15

It corresponds to the N-terminal to C-terminal direction of the polypeptide. and its the rna like strand

Question 16

Which strand of DNA serves as the template for mRNA?

Answer 16

The template strand of DNA is used to synthesize mRNA.

Question 17

What is the other strand of DNA called in relation to mRNA?

Answer 17

The other strand is the RNA-like strand, which has the same sequence as the mRNA (except for uracil replacing thymine).

Question 18

Is the genetic code the same for all organisms?

Answer 18

Yes, the genetic code is almost universal for all living organisms.

Question 19

Can mRNA from one organism be used to generate protein in another organism?

Answer 19

Yes, translational systems can use mRNA from one organism to generate protein in another.

Question 20

What are some exceptions to the universal genetic code?

Answer 20

Exceptions include some mitochondrial genomes and certain ciliates.

Question 21

Where are messenger RNAs made?

Answer 21

mRNAs are made in the nucleus.

Question 22

Where do messenger RNAs travel after being made in the nucleus?

Answer 22

They travel to the cytoplasm.

Question 23

What was the role of mRNA originally thought to be?

Answer 23

It was thought to transport DNA information from the nucleus to the cytoplasm as an intermediate molecule.

Question 24

Where does protein synthesis take place?

Answer 24

Protein synthesis occurs in the cytoplasm.

Question 25

What enzyme catalyzes transcription?

Answer 25

RNA polymerase catalyzes transcription.

Question 26

What signals RNA polymerase where to begin transcription?

Answer 26

Promoters signal RNA polymerase where to start.

Question 27

In which direction does RNA polymerase add nucleotides during transcription?

Answer 27

RNA polymerase adds nucleotides in the 5’ to 3’ direction.

Question 28

What tells RNA polymerase when to stop transcription?

Answer 28

Terminator sequences signal when to stop transcription.