5.6 - Polypeptide synthesis - transcription and splicing Flashcards
What is the first (summarised) step in polypeptide synthesis?
DNA provides the instructions in the form of a long sequence of nucleotides and the bases they possess.
What is the second (summarised) step in polypeptide synthesis?
A complementary section of part of this sequence is made up as pre-mRNA. TRANSCRIPTION.
What is the third (summarised) step in polypeptide synthesis?
pre-mRNA modified to mRNA by removing the introns (bases copied from non-functional DNA). SPLICING.
What is the fourth (summarised) step in polypeptide synthesis?
mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide. TRANSLATION.
What is the definition of transcription?
The process of making pre-mRNA using part of the DNA as a template.
What is the first step of transcription?
DNA Helicase acts on a specific region of the DNA molecule, breaking the H-bonds between the bases, causing the 2 strands to separate. Exposes the nucleotide bases in region.
What is the second step of transcription?
RNA polymerase moves along the template strand of DNA, causing the nucleotides on this strand to join with individual complementary nucleotides from the pool present in the nucleus.
What is the third step of transcription?
As RNA polymerase adds the nucleotides one at a time to form a strand of pre-mRNA, the DNA strands rejoin behind it. Only about 12 base pairs exposed at any one time.
What is the final step of transcription?
When RNA polymerase reaches a particular sequence of bases on the DNA which it recognises as a stop code, it detaches. Production of pre-mRNA is complete.
What are exons?
Sections of DNA that code for proteins.
What are introns?
Sections of DNA that do NOT code for proteins.
What is the definition of splicing?
When intervening, non-functional introns are removed and the functional axons are joined together.
Does splicing occur in eukaryotic, prokaryotic or both?
Eukaryotic cells.
How are certain disorders (e.g. Alzheimer’s disease) caused?
By splicing failures leading to non-functional polypeptides being produced. Caused by a mutation.
Do the exon sections always rejoin in the same order?
No. A single gene can code for up to 12 different proteins.
