Chapter 14

How many introns are present on a gene that consists of 5 exons? 4 5 6 None of the above answers is correct. 7

4

Intron

A non-coding, intervening sequence within a eukaryotic gene. -Interfere -One to many (exons-1)

Exon

A segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence. -Expressed -Exon first and last

List the post-transcriptional modifications

Addition of the 5' cap 3' cleavage and addition of the poly-A tail RNA splicing RNA editing

Which mechanism allows for more than one polypeptide to be encoded by a single gene? RNA methylation Regulated transcription Self-splicing of introns RNA interference Alternative RNA splicing

Alternative RNA splicing

crRNA

CRISPR RNA; small RNA molecules found in prokaryotes that assist in the destruction of foreign DNA

RNA editing relies on ___________________ to perform its function. piwi RNA Micro RNA Guide RNA transfer RNA

Guide RNA

Kozak Sequence

Helps the ribosome identify the start codon in eukaryotes

lncRNA

Long non-coding RNA; function is mostly unknown

miRNA

Micro RNA; small RNA molecule produced by cleavage of double stranded RNA arising from small hairpins within the RNA that is mostly single stranded. The miRNAs combine with proteins to form a complex that binds (imperfectly) to mRNA molecules and inhibits their translation.

RNA Splicing

Process by which the introns are removed from RNA transcripts and the remaining exons are joined together.

RNA Editing

Process in which the protein-coding sequence of an mRNA is altered after transcription. The amino acids specified by the altered mRNA are different from those predicted from the nucleotide sequence of the gene encoding the protein.

Guide RNA

RNA molecule that serves as a template for an alteration made in mRNA during RNA editing

Which of the following statements regarding gene structure is false? Intron cleavage and exon splicing are both mediated by protein enzymes. The number of introns found in organisms is species specific. The amino acid sequence of a polypeptide can be precisely predicted by the nucleotide sequence of the gene that encodes it. The number of exons is always less than the number of introns in a gene. All of the above statement are NOT false.

The number of exons is always less than the number of introns in a gene.

Shine-Dalgarno Sequence

The site of initiation of translation in prokaryotes

Which of the following statements about bacterial mRNA transcript is TRUE? The Shine−Dalgarno box associates with an RNA component in the large subunit of ribosomes. Unlike eukaryotes, bacterial mRNA transcripts do not typically contain untranslated regions. Most of bacterial genes contain a large number of introns and small number of exons. None of these is the correct answer. Transcription and translation take place simultaneously in bacterial cells.

Transcription and translation take place simultaneously in bacterial cells.

Which of the following spliceosomal components specifically recognizes and binds to the branch point of the intron during pre-mRNA splicing? U6 U1 U2 U3 U5

U2

Which of the following best defines the term translation? Using DNA as a template to make RNA Using RNA as a template to make DNA. Using protein as a template to make RNA. Using DNA as a template to make DNA Using RNA as a template to make protein.

Using RNA as a template to make protein.

Untranslated Region

segment of the RNA molecule that are not translated into protein. These regions lie before (upstream or 5') and after (downstream or 3') the protein-coding region

siRNA

small interfering RNA; single stranded RNA molecule produced by the celavage and processing of double stranded RNA; binds to complementary sequences in mRNA and brings about the cleavage and degradation of the mRNA -Some siRNAs bind to complementary sequences in DNA and bring about their methylation

Explain the function of each of the post -transcriptional modifications

· Addition of the 5' cap: Facilitates binding of ribosomes 5' end of mRNA, increases mRNA stability, enhances RNA splicing. · 3' cleavage and addition of poly(A) tail: Increases stability of mRNA, facilitates binding of ribosome to mRNA. · RNA splicing: Removed noncoding introns from pre-mRNA, facilitates exports of mRNA to cytoplasm, allows for multiple proteins to be produced through alternative splicing. · RNA editing: Alters nucleotide sequence of mRNA.

Discuss alternative splicing: why would this evolve?

· Alternative splicing is when a single pre-mRNA can be spliced in more than one way to produce different types of mRNA. This would evolve to allow for more variation in proteins that have different functions throughout the cell.

Briefly discuss the concept of collinearity and it refers to gene and mRNA structure

· Collinearity is a concept that there is a direct correspondence between the nucleotide sequence of a gene and the continuous sequence of amino acids in a protein. We always see the start codon first, and then exon 1, intron 1, exon 2, intron 2, etc. in that order, and then a stop codon.

List and briefly discuss the two types of self-splicing introns

· Group I Intron: Process of self-splicing is internal to whole structure · Group II Intron: Process of self-splicing is external to the whole structure

Discuss the basic structure of mature mRNA

· Mature messenger RNA is mRNA that is ready for translation. · Mature mRNA contains a 5' untranslated region, a start codon, a protein-coding region, a stop codon, and a 3' untranslated region end.

5' Cap

· Modified 5' end of eukaryotic mRNA consisting of an extra nucleotide (methylated) and methylation of the 2' position of the ribose sugar in one or more subsequent nucleotides. o Plays a role in the binding of the ribosome to mRNA and affects mRNA stability and the removal of introns. o Protects the 5' end from exonucleases.

What is RNA editing? Explain role of guide RNAs in RNA editing

· RNA editing is the process in which the protein-coding sequence of an mRNA is altered after transcription. The amino acids specified by the altered mRNA are different from those predicted from the nucleotide sequence of the gene encoding protein. · Guide RNAs serve as a template for the addition, deletion, or alteration of base. · Guide RNA adds nucleotides to the pre-mRNA that were not encoded by the DNA.

Poly-A Tail

· String of adenine nucleotides added to the 3' end of a eukaryotic mRNA after transcription. o Protection to prevent degradation by exonucleases and create longevity. o Necessary for the mRNA to be transported out of the nucleus (eukaryotes)

Explain the process of pre-mRNA splicing in nuclear genes

· We have our exon 1 and cut on the 5' splice site · We form the lariat structure · Exon 2 is cut from the 3' splice site · The 3' end of exon 1 and the 5' end of exon 2 are joined