14 RNA molecules and RNA processing

What type of colinearity are prokaryotes

Continuous colinearity

• most bacteria don’t have introns and thus its amino acids can be proportional to the number of nucleotides

• this allows transcription and translation to occur simultaneously

What type of colinearity are Eukaryotes

Discontinuos colinearity

• the presence of introns in pre-mRNA results in DNA to loop out representing regions that are non-coding

• once introns are taken out then it can be said that they are continuously colinear

The number of nucleotides in a gene is proportional to the number of amino acids in the protein

Colinear

Introns are removed from what?

pre-mRNA to yield mature mRNA

________ tend to be longer than _____, and most eukaryotic genes contain more noncoding nucleotides than coding nucleotides.

Introns; exons

Idea that introns were absent from ancient organisms but were later acquired by eukaryotes

Intron Late Hypothesis

Idea that early ancestors of bacteria, archaea, and eukaryotes possessed introns that were later lost by prokaryotes and simple eukaryotes.

Intron Early Hypothesis

A DNA sequence that encodes an RNA molecule or the entire DNA sequence required to transcribe and encode an RNA molecule

Gene

Why aren’t mRNAs modified in prokaryotes?

They don’t have introns that need to be removed from splicing and thus can go straight to the cytoplasm

Do ribosomes carry genetic information?

No

Where is mRNA synthesized for Bacteria?

In the cytoplasm which allows it to undergo transcription and translation at the same time

Serves as an intermediate to carry genetic information from the DNA to ribosome to translate into protein

mRNA

a sequence of nucleotides at the 5 ′ end of the mRNA that does not encode any of the amino acids of a protein; called the leader

5’ Untranslated Region (UTR)

In bacteria, what is included in the 5’ UTR

The Shine Dalgarno Sequence

• a consensus sequence

• location where ribosome binds during translation

• upstream of the start codon

The part of mRNA consisting of the nucleotides that specify the amino acid sequence of a protein

Protein Coding Region

Sequence of nucleotides at the 3 ′ end of mRNA that is not translated into amino acids

• affects the stability of the mRNA

• helps regulate the translation of the mRNA protein-coding sequence

3’ Untranslated Region (UTR)

Why aren’t rRNA and tRNA 5’ capped?

They are not made from RNA polymerase II which contains the capping mechanism

Purpose of 5’ capping in eukaryotes?

• allows recognition of mRNA by small ribosomal subunits which can then allow translation

• Increases mRNA stability

• Influences removal of introns

Purpose of pol (A) tail addition?

• increases mRNA stability

• aids in export of mRNA to cytoplasm

• aids in attachment of ribosome to mRNA

Where does RNA splicing take place?

In the nucleus

True or False: Splicing occurs co-transcriptionally, which means that transcription and splicing take place at the same time

True

What do most mRNA introns begin and end with?

GU and end in AG

Adenine nucleotide in nuclear pre-mRNA introns that lies 18 to 40 nucleotides upstream of the 3 ′ splice site

• takes part in formation of lariat

• deletion of this sequence prevents splicing

Branch Point

Large complex consisting of several RNAs and many proteins that splices protein-encoding pre-mRNA

• contains five snRNPs (U1, U2, U4, U5, and U6)

• snRNPs are made of snRNAs and other proteins

  • snRNP= small nuclear ribonucleoprotein

Spliceosome

Process in which a single pre-mRNA can be spliced in more than one way to produce different types of mRNA

• 70% of human genes undergo this type of splicing

• splicing may be different in tissues or at different times in the cell cycle or life cycle

Alternative Splicing

True or False: The anticodon of the tRNA pairs with the codon in the mRNA

True

tRNA is considered a

Adapter molecule

Multiple ribosomal RNA genes are

• dispersed in prokaryotes

• clustered in eukaryotes