RNA Transcription and Processing

Question 1

What are the components of a nucleotide?

Answer 1

phosphate, deoxyribose sugar, and a nitrogen base (C, G, A, T)

Question 2

What is transcription?

Answer 2

The process by which RNA chains are made from DNA template strands

Question 3

What is RNA made of/what does it stand for?

Answer 3

ribonucleic acid

Question 4

What type of bonds are the bases in RNA connected by?

Answer 4

phosphodiester bonds like DNA

Question 5

What’s different about RNA structure vs. DNA?

Answer 5

Antiparallel strands! One strand is in the 5’ to 3’ direction the other in the 3’ to 5’ direction

The two strands are of opposite polarity

Question 6

What are the purine bases for RNA?

Answer 6

A or G

Question 7

What are the pyrimidine bases for RNA?

Answer 7

U or C

Question 8

What’s the major difference between DNA and RNA formation of base pairs?

Answer 8

DNA forms base pairs with adjacent strands of DNA

RNA forms base pairs with itself within the RNA molecule

Question 9

What hybrid structure is critical to the process of transcription?

Answer 9

RNA forms a hybrid with DNA strand by way of base-pairing

Question 10

What is rRNA?

Answer 10

Ribosomal RNA

The majority of RNA in the cells is this type

95% of all RNA

Question 11

What are the 3 major species of rRNA?

Answer 11

28S, 18S and 5.8S

Question 12

What is tRNA?

Answer 12

Transfer RNA that brings amino acids to the ribosome for protein synthesis

Structural RNA molecules which serve as adaptors for translating the information in the sequence of mRNAs into specific amion acids

There is at least 1 tRNA per amino acid

Has cloverleaf structure

Question 13

Which RNA species is the most stable?

Answer 13

rRNA

Question 14

Which is more stable tRNA or mRNA?

Answer 14

tRNA

Question 15

What happens at the acceptor stem of the tRNA?

Answer 15

That’s where the amino acid attachment site is

Question 16

What happens at the anticodon loop at the bottom of all tRNAs?

Answer 16

That’s where binding to codons along the mRNA will occur

Question 17

Which other RNA types are found in the nucleus?

Answer 17

ncRNA (noncoding RNA)

miRNA (micro RNA)

Question 18

What do micro RNA do?

Answer 18

They help regulate gene expression by binding to other RNA molecules to form hybrids

Question 19

Are mRNA stable?

Answer 19

no

Question 20

How are mRNAs degraded?

Answer 20

RNAses

Question 21

What is the structure of a mRNA?

Answer 21

guanine methylated cap, nontranslated sequence, coding sequence, nontranslated trailing, poly A tail

Question 22

Why do you want mRNA to be unstable?

Answer 22

Because the cell needs to be able to make and degrade mRNAs as it needs them - quickly and efficiently

Question 23

Which items are necessary for RNA Transcription?

Answer 23

DNA, Transcription Factors, RNA polymerase and ATP

Question 24

What does RNA polymerase 1 do?

Answer 24

makes rRNA

Question 25

What does RNA pol 2 do?

Answer 25

Makes mRNA

Question 26

What does RNA polymerase 3 do?

Answer 26

makes tRNA and other small RNA

Question 27

How many RNA polymerases do plants have?

Answer 27

5

Question 28

What are the steps of RNATranscription?

Answer 28

The promotor box including TATA box (usually) markes the binding site for TFIID transcription factors at the initiation site

Other transcription factors IIA and IIB attach too

This complex prepares for successful binding of RNA polymerase which binds now

Then more transcription factors come in to complete the complex.

Energy is released into the system

RNA polymerase 2 synthesizes RNA template from strand of DNA

Factors Release

RNA polymerase dissociates and releases the new RNA strand

Modifications can facilitate this whole process especially local unwinding of the DNA to faciliate transfer

Question 29

What signals RNA synthesis promoters?

Answer 29

DNA sequences

Question 30

According to Dr. Mickelson there are 4 distinct steps to RNA transcription - what are they?

Answer 30

1) Biinding of RNA polymease and local unwinding of DNA
2) Initiation of RNA synthesis
3) Elongation of RNA
4) Termination

Each step requires energy!

Question 31

How are pre-mRNA’s processed?

Answer 31

1) Cap placed on 5’ end
2) Poly A tail put on 3’ end
3) Introns spliced out - producing mature transcript with exons next to each other
4) mRNA ready to leave the nucleus to go to the cytoplasm to be translated to protein

Question 32

What is the dystrophin gene?

Answer 32

it codes for a protein important in maintaining the sarcolema of muscle cells

Question 33

Which gene is mutated in the case of muscular dystrophy?

Answer 33

Dystrophin gene!

mutation near splice junction so the spliceosome can’t catalyze the event to remove the introns!

Question 34

Why is the dystrophin gene so important or significant?

Answer 34

It is the largest gene in any animal or human genome - it’s introns are huge so it’s mostly introns

Without a functioning gene the muscles become more fragile, they break and atrophy :(

Question 35

How are introns removed from the pre-mRNA transcript?

Answer 35

Spiceosome activity - splice junction recognition

Question 36

What is a spliceosome?

Answer 36

A large ribonucleoprotein complex that catalyzes the removal of introns from a pre-mRNA transcript

Question 37

How does a spliceosome remove the introns from a pre-mRNA?

Answer 37

U1 and U2 are catalytic and can break mRNA molecule at exon/intron junction and splice two pieces together

5’ end of intron has a GU to signal U1’s landing

3’ end has AG to signal U2’s landing

Question 38

Does the spliceosome only occur in one tissue type?

Answer 38

no. the splicing reaction can occur in a tissue specific form - any tissue