RNA and Transcription Flashcards
Three forms of RNA
mRNA
rRNA = Binds with ribosomal proteins to form RNA (r = ribosomes)
tRNA
mRNA structure
Linear polypeptide chain
Single helix - No complementary base pairing
Average length of two kilobases
Contains codons
Uracil bases
tRNA structure
Folded clover leaf shape
Average length of 76-90 bases
Region of hydrogen basing
Amino acid binding site
Each with an anticodon complementary to an mRNA codon
(Amino acid binding site on top)
(Anticodon on bottom)
Genome
The complete set of gens within a cell
Proteome - The full range of proteins that a cell is able to produce
Protein synthesis
Translation and transcription
Transcrition
DNA -> mRNA e.g HIV transcription
Translation
mRNA -> Polypeptide
Transcrition
Only occurs in nucleus
Template strand and coding strand
Involves RNA Polymerase
Produced mRNA complementary to the template strand and identical to coding strand
Three stages of transcription
1) Initiation
2) Elongation
3) TERMINATION.
Initiation
RNA Polymerase binds to DNA at a promoter region upstream of the start codon
RNA Polymerase breaks hydrogen bonds between complementary DNA bases to expose them
One DNA strand can now act as a template and the other will be a coding strand
Elongatoin
Free nuclear RNA nucleotides align with their commentary bases on the exposed DNA template strand
RNA Polymerase moves along the molecule and joins together adjacent RNA nucleotides by phosphodiester bonds
Formation of a pre-mRNA molecule
Termination
RNA polymerase detaches once it recognises a stop codon at the termination site
Production of pre-mRNA is complete
Splicing of a pre-mRNA
Prokaryotic cells go from DNA -> mRNA
But eukaryotic cells go from DNA -> pre-mRNA -> mRNA
Eukaryotes need an extra step called splicing to produce mature mRNA ready for translation
Eukaryotic gens contain
both exons and introns but only exons are able to code for polypeptides
Intron and Exons
Introns - non-coding section of DNA
Exons - Coding section of DNA
Splicing for Pre-mRNA
Base sequence corresponding to introns and removed
Function exons join together
Catalysed by splicesome
Describe the process of translation (5 marks)
RNA polymerase attaches to promoter region on DNA strand and breaks hydrogen bonds between complementary bases between DNA strands (1)
One DNA strand now acts as a template and the other is a coding strand (1)
Free RNA nucleotides are attracted to bases on template strand by complementary base pairing (1)
Uracil replaces thymine and pairs with adenine (1)
RNA polymerase joins together RNA nucleotides with phosphodiester bonds (1)
Pre-mRNA detaches when stop codon is reached by RNA polymerase and is spliced to form RNA (1)
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