DNA and protein synthesis - the basics

Question 1

what is transcription: overview sentence:
what is one distinct feature of mRNA and why is this needed?
where is the ribosome found in the cell?

Answer 1

• a complementary mRNA copy of one of gene ON THE DNA is created in the nucleus
• much shorter than DNA to be able to carry the genetic code to the ribosome in the cytoplasm
• cytoplasm

Question 2

describe the process of transcription: (5)

Answer 2

• dna helix unwinds to expose the bases which act as a template. only one chain of dna is used
• the unwinding is catalysed by dna helicase which breaks the hydrogen bonds between the bases
• free mRNA nucleotides in the nucleus align opposite complementary dna bases
• the enzyme RNA polymerase bonds RNA nucleotides to form the RNA polymer chain: pre MRNA
• one entire gene is copied and once done so the pre mrna is modified to become mrna in which the introns aka non coding regions are spliced out by a protein called a splicesome to only remain with the exons

Question 3

describe the process of translation: (5)

Answer 3

• the mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm. the ribosome attaches to the start codon
• tRNA molecule aligns opposite the start codon with a complementary anti codon. THIS IS HELD IN PLACE BY THE RIBOSOME
• the ribosome moves along the mRNA molecule to allow another complementary tRNA to attach itself onto the next codon
• the two amino acids that have been delivered by the tRNA molecule are joined together by a peptide bond. this requires atp and is also catalysed by an enzyme
• this will continue until the ribosome reaches the stop codon at the end of the mRNA molecule. the stop codon doesn’t code for an amino acid so the ribosome detaches. a polypeptide chain is formed