Polypeptide synthesis

Question 1

What are the two stages of protein synthesis?

Answer 1

-transcription
-translation

Question 2

Describe transcription

Answer 2

-hydrogen bonds between complimentary bases break and a part of the DNA molecule unwinds
-the gene is now exposed and acts as a template for a complementary copy to be made by a mRNA
-free RNA nucleotides pair up via hydrogen bonds with their complimentary bases and sugar-phosphate groups of RNA are bonded by RNA polymerase to form the backbone
-after transcription the DNA re-forms and the mRNA leaves the nucleus through a pore in the nuclear envelope

Question 3

What are pre-mRNA molecules?

Answer 3

the whole gene containing intones and exons of a certain gene

Question 4

What happens before the pre-mRNA exits the nucleus? Describe it.

Answer 4

Splicing
-non-coding sections removed (introns)
-coding sections joined together (exons)
-mRNA molecule carries only the coding sequences (exons)

Question 5

Describe translation

Answer 5

-occurs in the cytoplasm where there are free molecules of tRNA which have a triplet of unpaired bases at one end (anticodon) and a region where a specific amino acid can attach at the other
-mRNA attaches to a ribosome and tRNA molecules bind with their specific amino acids and bring them to the mRNA molecule
-the anticodon on the tRNA pairs with a complimentary codon on the mRNA molecule
-two tRNA molecules fit onto the ribosome at any one time
-a peptide bond forms between two amino acids, this requires energy (ATP) provided by mitochondria
-process continues until a stop codon is reached