3.10. PROTEIN SYNTHESIS

Question 1

What is mRNA (messenger RNA)?

Answer 1

Makes a copy of DNA base sequence (Uracil instead of Thymine) through transcription.
Uses Codons instead of triplets.

Question 2

What is tRNA (transfer RNA)?

Answer 2

consists of a single RNA strand about 80 nucleotides long and has an anticodon instead of a codon/triplet. Used in translation.

Question 2

What is tRNA (transfer RNA)?

Answer 2

consists of a single RNA strand about 80 nucleotides long and has an anticodon instead of a codon/triplet. Used in translation.

Question 3

What are the 3 stages of translation/ transcription?

Answer 3

Initiation, elongation and termination.

Question 4

What is the definition of transcription?

Answer 4

process of making a copy of something

Question 5

What is the definition of translation?

Answer 5

process of conversion of something from one form to another

Question 6

What is the central dogma?

Answer 6

More than a law - never wrong. i.e. DNA replication

Question 7

What happens in the initiation stage of transcription?

Answer 7

RNA polymerase binds to the promoter region of DNA.
DNA is unzipped to make two strands of DNA.
Antisense strand acts as a template strand for mRNA.
This is so mRNA has the same base sequence as the sense strand (U instead of T).

Question 8

What is the antisense strand of DNA?

Answer 8

Holds no code and is complimentary to the sense DNA strand. This is the strand copied in transcription.

Question 9

What is the sense strand of DNA?

Answer 9

Holds the triplet code for the sequence of amino acids.

Question 10

What happens in the elongation stage of transcription?

Answer 10

RNA polymerase travels along the antisense strand matching complimentary base sequences for mRNA molecule.

Question 11

How fast can RNA polymerase synthesize mRNA?

Answer 11

at 40-80 nucleotides per second

Question 12

What happens in the termination stage of transcription?

Answer 12

RNA polymerase will encounter a sequence of DNA bases that will terminate production of mRNA and RNA polymerase will detach and release mRNA.
- The mRNA molecule is free to leave the nucleus through nuclear pores and DNA rewinds into helix.

Question 13

What are ribosomes?

Answer 13

Ribosomes are made of two components: ribosomal RNA (rRNA) and proteins.
- complex macromolecular machines, and the site of biological protein synthesis.

Question 14

What are the two subunits of ribosomes?

Answer 14

• small ribosomal subunit that reads the mRNA
• large ribosomal subunit with two binding sites for tRNA molecules and a catalytic site for joining amino acids together

Question 15

What is the initiation stage of translation?

Answer 15

small ribosomal subunit binds to the mRNA at the universal start codon - AUG - with UAC (tRNA) by complimentary base pairing.
This happens at the amino acid receptor site.
- large ribosomal subunit now joins to make a ribosome.

Question 16

What is the promoter region?

Answer 16

Region near the beginning of a gene of DNA - where transcription beginnings.

Question 17

What is a receptor site?

Answer 17

One end of a tRNA molecule

Question 18

How many tRNA molecules are there for every codon?

Answer 18

1 tRNA per codon

Question 19

What is the elongation stage (part1) of translation?

Answer 19

Where a second tRNA molecule with another anticodon binds to mRNA, and a second amino acid is brought into the second tRNA binding site on the ribosome.
- Catalytic site creates a peptide bond between methionine and the second amino acid by a condensation reaction. this is in the 2nd binding site of the ribosome.

Question 20

What is the catalytic site on a ribosome?

Answer 20

called Peptidyl Transferase and is made of RNA.

Question 21

What is the 2nd part of elongation in translation?

Answer 21

First tRNA detaches from the ribosome and will bind to a fresh amino acid, and the ribosomes move along mRNA by one codon to allow the 2nd amino acid biding site to be clear.
- when a 3rd tRNA molecule with another anticodon binds by complimentary base pairing to codon on mRNA and a third amino acid is brought into the cleared tRNA binding site on the ribosome.

Question 22

What is the 3rd part of elongation in translation?

Answer 22

The catalytic site on the ribosome creates a peptide bond between the combined amino acid and the new amino acid by a condensation reaction.
- process repeats again and again.

Question 23

How fast do ribosomes work?

Answer 23

At a maximum of 60 amino acids joined per second.

Question 24

What happens in the termination stage of translation?

Answer 24

Continues until the ribosome encounters a stop codon on the mRNA.
These cause the ribosomal subunits to detach from each other and the mRNA.
- The polypeptide will fold up into its final shape and will undergo POST TRANSLATIONAL MODIFICATION to fold into a protein at the Golgi.

Question 25

What are the stop codons in RNA and DNA?

Answer 25

• UAG/ TAG
• UAA/ TAA
• UGA/ TGA