Question

what is mRNA sequence?

Answer 1

mRNA is a sequence of ribonucleotides. it is the template for protein synthesis through ribosomes.

you get mRNA from DNA through transcription. the resulting pre-mRNA is then
spliced (all non-coding sequence gets cut out),
capped (against digestion) and, in case of eukaryotes,
polyadenylated (protects against digestion, increases translation activity, takes part in the release from the ribosome after translation).

Answer 2

another question:
why is start codon important for the proper reading of the mRna strand?

Answer 3

because you can theoretically have 3 different reading frames. imagine a sequence like this:


AAUGUCUGAUCUAGCA.

first reading frame:
AAU GUC UGA UCU AGC A

second one:
A AUG UCU GAU CUA GCA

third one:
AA UGU CUG AUC UAG CA

as you see, those will translate into profoundly different protein sequences. having a single start codon (AUG) tells your ribosome where to start a sensemaking amino acid sequence. the cell has various stop codons btw, to prevent excessie nonsense translation.

Answer 4

another one sorry for asking you :
what happen is start codon is improperly placed?