Lec 21

Question 1

mRNA

Answer 1

messenger RNA- contains codons for protein synthesis

Question 2

rRNA

Answer 2

ribosomal RNA-components of Ribosome

Question 3

tRNA

Answer 3

transfer RNA- brings amino acid to ribosome

Question 4

snRNA

Answer 4

small nuclear RNA- gene regulation and processing mRNA

Question 5

snoRNA

Answer 5

small nucleolar RNA- processing of rRNA

Question 6

scRNA

Answer 6

small cytoplasmic RNA-NOT SURE OF FUNCITON

Question 7

gRNA

Answer 7

guide RNA-RNA editing

Question 8

sirRNA

Answer 8

small interfering RNA-use in degrading mRNA

Question 9

miRNA

Answer 9

microRNA-used in decreasing translation

Question 10

Ribosomes

Answer 10

complex of rRNAs and protein
2 subunits in fully assembled ribosome
-ribosome does not fully assembly until translation

Question 11

Svedburg Unit

Answer 11

velocity of centrifugation (S)

-s units do not add

Question 12

Precursor rRNA

Answer 12

contains all rRNAs except 5s rRNA in eukaryotes

Question 13

Processing of rRNAs and snoRNA

Answer 13

(removing spaces)

• methylation occurs and identifies separate RNA-to-be molecules
• Pre-rRNA is then cleaved to produce distinct rRNA molecules
• In Eukaryotes snoRNAs help splice precursor into 18s, 5.8s, and 28s rRNA
• SnoRNAs combine with proteins to make snoRNPs. This process occurs in the nucleolus snores are sometimes transcribe from their own genes by RNA poly II or poly III but sometimes come from intro areas of the pre’mRNA molecules

Question 14

tRNA processing

Answer 14

• initial transcript contains several tRNA molecules
• tRNAs form secondary structure due to base pairing
• tRNAs are separated
• 5’ and 3’ ends are trimmed
• intron removed in eukaryotes
• 3’ end modified (CCA added) in eukaryotes
• Bases modified

**tRNA processing may include cleavage, splicing, base addition, and base modification

Question 15

What are the unusual bases that Transfer RNAs contain?

Answer 15

Inosine-derivative of Guanine
Pseudouridine (ribose attaches to 5 position of ring instead of 1 position)
Dihydrouridine- saturation of 5-6 double bond

Question 16

When does Capping the RNA (addition of 5’ cap) occur? What is the importance?

Answer 16

-capping occurs as soon as 5’ end of pre-mRNA is free of the RNA polymerase

Importance:

• gives mRNA stability
• Aids in RNA splicing efficiency
• Aids in translation efficiency since cap-bind proteins bind to the cap and the ribosome binds to cap-binding proteins

Question 17

Describe the process of capping RNA

Answer 17

• 1 phosphate is removed from 5’ end of RNA
• Guanine nucleotide triphosphate is added (sugar, phosphate, and base)(5’-5’ linkage)
• Methyl groups added to position 7 on guanine ring and to 2’ position of sugar of next two nucleotides

Question 18

What is the importance of 3’ PolyA tail

Answer 18

Protects the mRNA:

• tail length determines the stability
• tail shortens as mRNA ages
• when tail is to short, the mRNA is recycled

Helps initiate translation by aiding in attachment of ribosome to mRNA

Involved in termination of transcription

• since the 3’ end of the transcript is cleaved even though transcription still continues
• cleavage 11-30 nts downstream of consensus sequence

Question 19

Describe the of adding the 3’ polyA tail

Answer 19

• Pre-mRNA is cleave 11-30 nts downstream from consensus sequence
• 50-250 adenine nucleotides are added to the 3’ end by enzyme Poly(A) polymerase
• The poly-A tail allows mRNA to exist for a longer time in the cytoplasm before it is degraded and aids in attachment of ribosome

Question 20

Spliceosome

Answer 20

snRNPs and pre-mRNA complex

-structure at which introns are removed and eons are joined

Question 21

snRNPs

Answer 21

small nuclear ribonucleoproteins

• complex of protein + snRNA
• uridine rich so called U1, U2, etc.

Question 22

snRNAs

Answer 22

have regions complementary to ends of eons, sites in introns or sites on other snRNAs

Question 23

what is important for proper splicing?

Answer 23

Base-pairing between pre-mRNA and nRNA and between snRNAs

Question 24

What does splicing require?

Answer 24

critical sequences at 5’ splice site, 3’ splice site and branch point within the intron

Question 25

what is the process of mRNA splicing

Answer 25

Removing introns and joining exons

• cleavage at the 5’ splice site allows lariat formation by joining the 5’ end of the intron
• The guanine of intron binds to Adenine of branch site in a transesterification reaction
• Cleavage at the 3’ splice site occurs and eons are simultaneously joined
• snRNPs are CRITICAL in proper positioning for splicing and base-pairing is important in their binding to the RNA

Question 26

Where are most conserved regions located in splicing?

Answer 26

located in the intron

Question 27

RNA editing

Answer 27

defined as specific changes that are made to RNA after transcription

• RARE in nuclear RNA
• Frequent in organelle transcripts

Question 28

guide RNAs

Answer 28

aid in insertion and deletion types of editing

Question 29

fire and mello

Answer 29

injected darn into worm

• noticed that genes with nucleotide sequence was same as injected RNA had decreased expression (turned off particular gene)
• Can silence targeted gene by inhibiting translation

Question 30

RNAi

Answer 30

in eukaryotes shuts off gene expression using double stranded RNA

Question 31

Difference between sirens and miRNAs

Answer 31

siRNA:
Origin= mRNA, transposon, or virus
Target=genes from which they were transcribed

miRNA
origin-RNA transcribed from distinct gene
Target: genes other than those from which they were transcribed

Question 32

What are some potential uses for RNAi

Answer 32

studying gene function
Medicine: RNA interference in therapy
-Clinical trials in macular degeneration being conducted
-Possible problem if a gene with an accidentally similar sequence is also repressed