Use real CAIE Biology questions to distinguish primary transcript from mature mRNA, explain intron removal and exon joining, and apply cap/poly(A) tail functions.
Smooth muscle is a tissue composed of smooth muscle cells. The cells contain cytoplasm packed with proteins that are involved in contraction and relaxation.
Caldesmon is a large protein with a number of binding sites to attach to other proteins.
Caldesmon exists in two different forms, H-caldesmon and L-caldesmon.
H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells.
L -caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein.
- Caldesmon is coded for by a gene known as CALD1.
- CALD1 has 17 exons.
- The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon.
Researchers now know that the two different forms of caldesmon are the result of events occurring directly after transcription of DNA. Changes occur to the primary transcript that is formed by DNA transcription.
Suggest how the smooth muscle cells and non-muscle cells can produce different forms of caldesmon from the same primary transcript.
any two from:
differences owing to, RNA / gene, splicing ;
A primary transcript for RNA
A ref. to alternative splicing
R DNA splicing
R mutation occurring during gene splicing
(differences occur during) removal of, introns / non-coding sequences ;
R if introns described as bases / nucleotides / codons
R different number of introns removed / some introns remain
exons / coding sequences, detail ;
e.g. joined differently / in a different combination in middle (of transcript), removed / not included for repeating sequence, removed / not included
(so) messenger RNA / mRNA, formed is different ;