8.4 Polypeptide synthesis - Transcription and splicing

Question 1

What is the overall principle behind polypeptide synthesis

Answer 1

1. DNA provides the instructions in the form of long sequences of bases
2. A complementary section of part of this sequence is made in the form of a molecule called pre-mRNA - a process called transcription
3. The pre-mRNA is spliced to form mRNA
4. The mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide - a process called translation

Question 2

Describe the process of transcritpion

Answer 2

1. DNA helicase acts on a specific region of the DNA causing the two strands to separate and expose the nucleotide bases in that region
2. The nucleotide bases on one of the two DNA strands, known as the template strand, pair with their complementary nucleotides from the pool within the nucleus. RNA polymerase moves along the strand and joins the nucleotides together to form a pre-mRNA molecule
3. As the RNA polymerase adds the nucleotides one at a time, the DNA strands rejoin behind it.
4. When the RNA polymerase reaches a stop triplet code, it detaches, and the production of pre-mRNA is complete

Question 3

What is splicing of pre-mRNA

Answer 3

The process by which introns are removed, leaving just codon (exons) parts.

Question 4

Does splicing happen in prokaryotic cells

Answer 4

No, mRNA is just produced from transcription as introns arent present

Question 5

How does mRNA leave the nucleus

Answer 5

They are too large to diffuse out so they leave via a nuclear pore. Outside it is attracted to the ribosomes to which it becomes attached