Microbiology Chapter 3

Intron

segment of DNA that is transcribed, but later removed from within the transcript by spicing together the sequences

RNA splicing

process of excising introns from RNA and connecting the exons into a continuous mRNA

primary RNA transcript

original unmodified RNA product corresponding to a transcription unit

Mature transcript

modified RNA transcript; modification may include the removal of intron sequences and alterations to the 5’ and 3’ ends

Exons

any part of a gene that will form a part of the final mature RNA produced by that gene after RNA splicing

region of the gene

length of precursor RNA

what separates individual coding regions?

genes

what does exon mutations effect?

polypeptide sequence

what does intron mutations effect?

RNA processing which may influence the sequence and/ or production of a polypeptide

does order of exons differentiate in genomic DNA and mRNA?

no

are the distances along the gene the same between genomic DNA and mRNA?

no

does base composition differ between introns and exons?

yes

is organization of exons maintained?

yes

cDNA

single-stranded DNA complementary to an RNA, synthesized from it by reverse transcription in vitro

does complementary DNA contain introns?

no

is the positions of introns usually conserved?

yes

can lengths of the introns that correspond to the exons vary?

yes

negative selection

mutations are deleterious

positive selection

mutations are benifital (i.e individual is able to produce more fertile progeny)

are exons usually conserved?

yes

why do introns evolve much more rapidly than exons?

less selective pressure to produce a functional polypeptide

overlapping gene

part of its sequence is found within part of the sequence of another gene

truncated protein

part of a full protein

alternative start

still starts at AUG but different spot

alternative splicing

certain exons are included or excluded in the mature mRNA- polypeptides differ by the presence or absence of certain regions

can the same pre-mRNA generate two different proteins?

yes

what percent of human genes are alternatively spliced?

95%

domains

independent functional protein modules

gene family

set of genes within a genome that encodes related or identical proteins or RNAs

what are gene families derived from?

duplication of an ancestral gene, followed by accumulation of changes in sequence between copies

KLF (kruppel-like factors)

gene family in humans

homologous genes (homologs)

share common features that preceded their evolutionary separation