Transcription Flashcards
Transcription
A stage during protein synthesis in which DNA is used as a template by being copied into mRNA thus used in translation so correct amino acids dependent on mRNA codons present
What enzymes are used in transcription?
Just RNA polymerase
How is DNA prepared to be transcribed?
RNA polymerase binds to DNA at start of gene (at start triplet) and the RNA polymerase present locally unwinds the DNA helix thus the 2 strands are separated (hydrogen bonds break)
This exposes the nucleotide bases that are in triplets to form a template strand
How does the template strand of DNA form mRNA, that carries the genetic code to synthesise a polypeptide?
By complementary base pairings , RNA nucleotides bind to the exposed bases (however nucleotide bases with U form bonds bonds to A)
Hydrogen bonds are formed between complementary base pairs
Where are free activated RNA nucleotides from?
In eukaryotes, the nucleoplasma
In prokaryotes, the cytoplasm
Triplet
In the DNA strand, 3 nucleotide bases that will encode for 1 amino acid
Codon
In the transcribed mRNA strand, 3 nucleotide bases that will encode for 1 amino acid
Triplet vs codon
Triplet = in dna strand
codon = in mRNA strand
They are complementary to each other by complementary base pairings
How is a molecule of mRNA actually joined together from the free activated nucleotides?
Because RNA polymerase catalyses the formation of phosphodiester bonds between the nucleotides = forms a single stranded polynucleotide mRNA
How is the whole length of DNA transcribed into mRNA?
Because RNA polymerase moves along the template, unwinded DNA assembling the mRNA strand by catalysing the condensation of mRNA nucleotides to form mRNA
What happens once the section of DNA has been copied? (once rna polymerase passes)
Hydrogen bonds between 2 polynucleotide strands will reform so it will coil back into double helix
When does transcription stop?
RNA polymerase reaches a base sequence which acts as a stop signal so this is copied as a stop codon and will detach from the DNA strand
What is the immediate strand of mRNA transcribed known as?
pre mRNA
Splicing
A process where introns in the pre RNA (non coding regions) are removed so mRNA only has exons left
Exons join together to form final complete mRNA strand
Complementary: template DNA strand, pre mRNA and final mRNA
pre mRNA’s codons are complementary to triplets in template DNA strand
by complementary base pairings
processed/ final mRNA is NOT complementary
