DNA and genomics II Flashcards
what are the components of a gene
the promoter, transcription unit, and a termination sequence
why is the genetic code a triplet code
with 3 nucleotides coding for 1 a.a., the protein can contain up to 4^3=64 diff codes; more than sufficient to code for 20 a.a
these 64 codons form the set of instructions that tells a cell the order in which a.a. are to be joined to form a protein
key features of transcription
- synthesis in 5’ to 3 direction
- catalysed by RNA polymerase
- formation of ssRNA
- complementary base pairing
- recognition sequence
points of comparison between DNA and RNA
d/ss, size, stability, location, sugar residue, ratio of bases, bases, structural variation, forms, amount
brief description of transcription
DNA is used as a template to synthesise the pre-mature mRNA/mRNA by complementary base pairing of gene nucleotides and is catalysed by RNA polymerase.
pre-mature mRNA will undergo post-transcriptional modification where a 5’ cap and poly-A tail is added
two steps that occur at transcription’s termination stage
- release of mRNA chain
- RNA polymerase disassosciates
–> terminates transcription
define translation
process in which a sequence of ribonucleotides in mRNA is used as a template to synthesise a specific sequence of amino acid in a polypeptide by complementary base pairing
how is the translation initiation complex formed
- small ribosomal subunit and initiator tRNA assemble at start codon AUG downstream of 5’ end–> initiate translation
- binding of large ribosomal subunit completes the ribosome and will form the translation initiation complex
describe amino acid activation
- each specific a.a. is covalently attached to a specific tRNA molecule with a specific anticodon at its 3’ CCA stem, forming an aminoacyl-tRNA; catalysed by 20 different enzymes, one for each a.a.; known as aminoacyl-tRNA synthetases
- enzyme has specific complementary conformation and charge to the a.a. tRNA attached to and the specific tRNA with specific anticodon
why simultaneous transcription and translation only occur in prokaryotes
prokaryotes do not have membrane-bound nuclei, thus the processes of transcription, translation occur simultaneously