genetics

Introns

• part of the final mRNA strand

• generally absent from bacterial genomes

• code for a protein

• removed from initial mRNA strand prior to translation

Exons

• generally absent from bacterial genomes

• removed from initial mRNA strand prior to translation

• code for a protein

• part of the final mRNA strand

BOTH introns and exons

• code for a protein

• are present in eukaryotic genomes

• are present in the DNA used as the template for transcription

• are removed from the mRNA strand prior to translation

Suppose that RNA polymerase was transcribing a eukaryotic gene with several introns all contained within the coding region. In what order would the RNA polymerase encounter the elements in the DNA sequence of the gene?

• 3’ UTR, translation termination codon, splice donor site, translation initiation codon, 5’ UTR, promoter

• promoter, 5’ UTR, translation initiation codon, splice donor site, translation termination codon, 3’ UTR

• promoter, translation initiation codon, translation termination codon, 5’ UTR, 3’ UTR, splice donor site

• 3’ UTR, splice donor site, 5’ UTR, promoter, translation initiation codon, translation termination codon

If there is a mutation in the intron of a DNA segment, what would the outcome be of the mutation with regard to the ultimate protein that will form this sequence?

• Nothing. This mutation doesn’t affect a coding region. The protein will be unchanged.

• The corresponding amino acid is altered. The protein will be changed.

• An alternative splice site is formed. Two proteins of different lengths will be produced.

• This is a nonsense mutation. The protein will be truncated early and likely be nonfunctional.

What is the function of the spliceosome?

• adds a stretch of about 180 adenine nucleotides to the 3’ end of the mRNA

• transcribes ribosomal RNA and transfer RNA genes

• removes the Shine-Delgarno sequence from the 5’ end of the mRNA

• removes the introns and joins the exons to form the mature transcript

Why can alternative splicing of messenger RNAs be advantageous for eukaryotic organisms?

• allows for smaller genomes than bacteria

• increases variety of proteins that can be produced

• splices together introns instead of exons from newly transcribed mRNA

• allows exons from two different genes to be spliced into a new mRNA

How do the nucleus and ribosomes work together to generate a protein?

• The segment of DNA that contains a gene leaves the nucleus and is used by the ribosomes as instructions to synthesize a protein

• Ribosomes produce mRNA that migrates into the nucleus and uses a gene in the DNA as instructions to synthesize a specific protein

• Ribosomes migrate into the nucleus, attach to a gene in the DNA, and uses the gene as a transcript to synthesize a specific protein.

• In the nucleus, DNA is transcribed to mRNA, which the ribosomes use as instructions to synthesize a specific protein.

mRNA

• moves genetic information out of the nucleus and into the cytoplasm

• act as an enzyme for peptide synthesis

• contains nucleotide triplets that code for specific amino acids

• moves amino acids to the site of protein synthesis

rRNA

• moves genetic information out of the nucleus and into the cytoplasm

• acts as an enzyme for peptide synthesis

• has a convoluted structure with a 3-base sequence called an anticodon

• moves amino acids to the site of protein synthesis