Chapter 14.1-2: mRNA

Question 1

Colinear/colinearity

Answer 1

number of nucleotides in a gene should be proportional to the number of amino acids in the encoded protein (bacteria and many viruses)

Question 2

Noncolinear

Answer 2

DNA much longer than mRNA - demonstrated through hybridization (eukaryotes)

Question 3

Introns are removed by ___ _________. And are categorized by _____

Answer 3

RNA Splicing

How they are removed, splicing mechanism

Question 4

Type of intron: Nuclear pre-mRNA

Answer 4

protein-encoding genes in the nucleus of eukaryotes (Spliceosomal)

Question 5

Type of intron: tRNA

Answer 5

tRNA genes of eubacteria, archaea, and eukaryotes

Enzymatic

Question 6

What is considered part of the gene?

Answer 6

DNA (exons & introns) 
RNA sequences NOT translated into protein, including...
Transcription Unit
Promoter
RNA coding sequence
Terminator

Question 7

Function of mRNA

Answer 7

template for protein synthesis; it carries genetic information from DNA to a ribosome and helps to assemble amino acids in their correct order.

Question 8

Structure of mRNA

Answer 8

1. 5’ untranslated region (5’UTR or leader sequence), can be shine-Dalgarno sequence (ribosome binding site in bacteria)
2. Protein coding region
3. 3’ UTR- stability and translation

Question 9

pre-mRNA

Answer 9

immature single strand of mRNA, that contains exons and introns

Question 10

Addition of 5’ Cap

Answer 10

A nucleotide with 7-methylguanine; 5’-5’ bond is attached to the 5’-end of the RNA. NOT PHOSPHODIESTER. Cap-binding proteins recognize and attach the cap.

1. Facilitates binding of ribosome to 5’ end to initiate translation
2. Increases mRNA stability
3. Enhances RNA splicing
4. Enhances intron removal

Question 11

Addition of poly(A) tail

Answer 11

~50-250 adenine nucleotides are added to the 3’-end of the mRNA.

Added by cleavage and polyadenylation at 3’ end

1. Increase stability of mRNA
2. facilitates binding of ribosome to mRNA
3. Plays a role in export of mRNA into cytoplasm

Question 12

RNA splicing

Main function, consensus sequences

Answer 12

Main function: Removes noncoding introns from pre-mRNA using consensus sequences
5’: GU A/G AGU: splice site
3’: CAGG
Branch point: Adenine “A”, ~18-40 nucleotides upstream of 3’ splice site

Question 13

Other functions of RNA splicing

Answer 13

1. Removes introns
2. Facilitates export of mRNA to cytoplasm,
3. Allows for multiple proteins to be produced through alternative splicing

Question 14

RNA splicing: Spliceosome

Answer 14

Five RNA molecules + 300 proteins

Where splicing takes place

Question 15

RNA Splicing Process (release Lariat)

Answer 15

1. pre-mRNA cut at 5’ site
   5’ end attaches to branch point forming lariat. G bonds with A through transesterification (ester exchange with alcohol)
2. Cut at 3’ splice site, and 3’ end of exon 1 becomes covalently attached to the 5’ end of exon 2. Lariat is released.

Question 16

If a splice site were mutated so that splicing did not take place, what would the effect be on protein encoded by the mRNA?

a. it would be shorter than normal
b. it would be longer than normal
c. it would be the same length but would have different amino acids

Answer 16

a. it would be shorter

WHY? Because introns usually early stop codons.

Question 17

Nuclear Organization of pre-mRNA processing: intron removal, mRNA processing, and transcription take place at

Answer 17

the same site in the nucleus

Question 18

Minor Splicing

Answer 18

Use different types of consensus sequences & snRNAs

Question 19

Self-splicing introns (groups 1&2)

Answer 19

in some rRNA genes in protists and mitochondria genes in fungi

Group 1- Nine Stemmed Loops, Large intron removed by splicing

Group 2- intron removed by lariat structure

Question 20

Alternative processing pathways

Answer 20

1. Multiple 3’ cleavage sites
2. Alternative Splicing- one 3’ cleavage site, but alternative RNA splicing, either two introns removed, or counts it as one big intron and takes an exon with it.

Question 21

Estimated that more than ___% of human genes undergo alternative splicing

Answer 21

90%

Question 22

Alternative 3’ cleavage sites results in
a. multiple genes of different length.

b. multiple genes of pre-mRNA of different length.
c. multiple mRNAs of different length.
d. All of the above.

Answer 22

c. mRNAs of different length

Question 23

RNA editing after transcription: Why?

Answer 23

So protein amino acid sequence differs from encoded gene.

Some nuclear genes in mammalian cells and in some mitochondrial genes in plant cells.

Can include insertion, deletion of nucleotides, and conversion of bases

gRNA plays role

Question 24

Guide RNA (gRNA) is template for ____, ____ and _____ of bases

Answer 24

Addition, deletion, and alteration

Question 25

Overview of mRNA production

Answer 25

1. preMRNA transcribed
2. 5’ cap added
3. Cleavage at 3’ end is 10 bp downstream of consensus
4. Poly(A) tail
5. Introns removed