GI: RNA and Protein Synthesis

Question 1

When is mRNA made?

Answer 1

During transcription.

Question 2

What does mRNA do?

Answer 2

Carries the genetic code from the DNA to the ribosomes, where it is used to make a protein during translation.

Question 3

mRNA

Answer 3

Single polynucleotide strand.

Question 4

In mRNA, what are groups of three adjacent bases called?

Answer 4

Codons

Question 5

What does tRNA do?

Answer 5

Involved in translation - carries the amino acids that are used to make proteins to the ribosomes.

Question 6

Anticodon

Answer 6

Specific sequence of three bases at one end of the tRNA molecule.

Question 7

Single polynucleotide strand.

Answer 7

mRNA

Question 8

Specific sequence of three bases at one end of the tRNA molecule.

Answer 8

Anticodon

Question 9

In addition to anticodons, what do tRNA molecules have?

Answer 9

An amino acid binding site at the other end.

Question 10

Describe the shape of a tRNA molecule:

Answer 10

Single polynucleotide strans that’s folded into a clover shape.

Held together by hydrogen bonds between specific base pairs.

Question 11

What is the first stage of protein synthesis?

Answer 11

Transcription - an mRNA copy of a gene is made from DNA.

Question 12

Where does transcription take place in prokaryotes?

Answer 12

In the cytoplasm - as prokaryotes don’t have a nucleus.

Question 13

Where does transcription take place in eukaryotic cells?

Answer 13

Nucleus.

Question 14

Describe the process of transcription:

8 points

Answer 14

1. RNA polymerase attaches to DNA double helix at beginning of gene.
2. DNA helicase attached to RNA polymerase breaks hydrogen bonds and strands separate, the molecule uncoils and the bases are exposed.
3. One strand is used as a template to make mRNA.
4. RNA polymerase lines up free nucleotides along exposed bases on template - complementary base pairing - and joins them together.
5. RNA polymerase moves along DNA, separating the strands and assembling mRNA.
6. Hydrogen bonds reform between uncoiled strands of DNA and the strands coil back into a double helix.
7. RNA polymerase reaches a stop signal and mRNA detaches from DNA.
8. In eukaryotes, mRNA moves out of nucleus through nuclear pore and attaches to a ribosome in cytoplasm.

Question 15

pre-mRNA

Answer 15

mRNA strands containing introns and exons.

Question 16

What additional step occurs in transcription within eukaryotes that does not occur in prokaryotes?

Answer 16

Splicing - introns are removed from pre-mRNA and exons are joined together.

Forms mRNA strands, which then leave the nucleus for the next stage of protein synthesis.

Takes place in nucleus.

Question 17

What is the second stage of protein synthesis?

Answer 17

Translation - amino acids are joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA.

Question 18

Where does translation occur within eukaryotes and prokaryotes?

Answer 18

At the ribosomes in the cytoplasm.

Question 19

Describe the process of translation:

7 points.

Answer 19

1. mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it - ATP provides energy for bond between amino acid and tRNA.
2. tRNA molecule, with an anticodon complementary to 1st codon on mRNA, attaches to mRNA via specific base pairing.
3. 2nd tRNA molecule attaches to the next codon in mRNA.
4. Two amino acids attached to tRNA molecules are joined by peptide bond - 1st tRNA molecule moves away, leaving amino acid behind.
5. 3rd tRNA molecule binds to next codon on mRNA - its amino acid binds to first two and 2nd tRNA molecule moves away.
6. Process continues producing a chain of linked amino acids until there’s a stp signal on the mRNA.
7. Polypeptide chain moves away from the ribosome and translation is complete.