4.2: Nucleic acids - protein synthesis

Question 1

what are the 2 steps of protein synthesis

Answer 1

transcription -> translation

Question 2

where does transcription occur for protein synthesis

Answer 2

nucleus

Question 3

where does translation occur for protein synthesis

Answer 3

cytoplasm

Question 4

list and describe the sequence for the process of transcription of the DNA in the nucleus

Answer 4

1 - RNA polymerase binds to DNA at the gene to be unwound and copied
2 - A helicase unzips DNA (H bonds between the polynucleotides break)
3 - Only one of the DNA strands is used as a template
4 - free RNA nucleotides align themselves opposite the complementary DNA base pairs
5 - G - C, U - A
6 - RNA polymerase moves along the strand joining nucleotides forming single stranded pre-mRNA
7 - the mRNA now carries complementary codons, which will code for specific amino acids
8 - at the end of the gene sequence mRNA is detached and DNA rewinds into a double helix
9 - mRNA leaves the nucleus through the nuclear pores to the cytoplasm where it attached to ribosomes consisting of rRNA and protein

Question 5

describe the process of post transcriptional modification of mRNA in the nucleus

Answer 5

1 - Introns are cut out of pre-mRNA strand
2 - Exons are then spliced (joined) together
3 - DNA ligase joins sections of (exons) DNA together to produce a mature mRNA strand

Question 6

list 3 differences between DNA replication and transcription

Answer 6

DNA repl = DNA polymerase, free DNA nucleotides, 2 template strands
Transcr = RNA polymerase, free RNA nucleotides, 1 template strand

Question 7

list and describe the sequence for the process of translation of mRNA in the cytoplasm

Answer 7

1 - amino acid in cytoplasm activated by ATP and attached to specific tRNA molecule via a specific linkage
2 - amino acid attaches at opposite end of tRNA to the anticodon
3 - tRNA molecules bring specific amino acids to the mRNA
4 - first tRNA’s anticodon complementary base pairs to the start codon of mRNA
5 - tRNA forms hydrogen bonds with mRNA
6 - another tRNA complementary base pairs to the 2nd codon of the mRNA
7 - ribosomal enzymes catalyse formation of peptide bond between an amino acid on one tRNA and the forming polypeptide on the other tRNA
8 - first tRNA is release and returns to the cytoplasmic pool to attach to the same specific amino acid
9 - ribosome moves along mRNA one codon at a time so that tRNA can fill the next vacant slot
10 - each amino acid can then form a peptide bond with the last member of the chain until a stop codon is reached

Question 8

describe the process of post translational modification of the polypeptide formed in the cytoplasm

Answer 8

1 - removal of Met (start codon) from start of primary structure
2 - RER buds off transport vesicles containing the polypeptide, transported to the golgi body for chemical modification (addition of functional group) and for packaging into lysosomes or secretory vesicles