MBG PART TWO: Lecture 6

Question 1

What does a continuous sequence of nucleotides in the DNA encode?

Answer 1

A continuous sequence of amino acids in the protein

Question 2

What is the number of nucleotides proportional to?

Answer 2

The number of amino acids (3:1)

Question 3

What is the 5’ untranslated region (5’UTR)?

Answer 3

Does not code for amino acids. Binds to the ribosomal complex (not part of coding region)

Question 4

What is the Protein Coding Region?

Answer 4

Comprises the codons that specify the amino acids. Begins with a start codon and ends with a stop codon.

Question 5

What is 3’UTR?

Answer 5

Does not code for amino acids. Affects the stability of the mRNA and regulates its translation.

Question 6

How can transcription and translation occur in prokaryotes?

Answer 6

Simultaneously (no nucleus and the mRNA sequence direction corresponds to the DNA)

Question 7

What happens to the mRNA in Eukaryotes?

Answer 7

mRNA is extensively modified to translation and must be transported out of the nucleus.

Question 8

In Eukaryotes, what happens to the template strand?

Answer 8

The entire template strand of the gene produces a pre-mRNA which is then processes to make mature messenger mRNA that can be translated into protein.

Question 9

What are exons?

Answer 9

Coding sequences

Question 10

What are introns?

Answer 10

Non-Coding Sequences

Question 11

How do you remove introns?

Answer 11

RNA splicing along with additional RNA processing

Question 12

Why is the removal of introns required?

Answer 12

Too form the mRNA that will be translated into a polypeptide.

Question 13

What can exons vary in?

Answer 13

Length and relative position on the gene.

Question 14

What type of introns and exons are the best studied?

Answer 14

Nuclear pre-mRNA introns and exons

Question 15

What does splicing of the introns require?

Answer 15

A spliceosomal complex that contains a small nuclear RNAs (snRNAs) and proteins to remove the intron.

Question 16

What can introns influence?

Answer 16

How genes are expressed

Question 17

What do some introns have?

Answer 17

Self-splicing capabilities

Question 18

What are introns removed from?

Answer 18

pre-mRNA by the action of the splicesome.

Question 19

What does addition to 5’ cap do?

Answer 19

Facilitates binding of ribosome to 5’ end of mRNA, increases mRNA.

Question 20

What does the 3’ cleavage and addition of poly(A) tail do?

Answer 20

Increases stability of mRNA, facilitates binding of ribosome to mRNA.

Question 21

What does RNA splicing do?

Answer 21

Removes noncoding introns from pre-mRNA, facilitates export of mRNA to cytoplasm, allows fo multiple proteins to be produced through alternative

Question 22

What does RNA editing do?

Answer 22

Alters nucleotide sequence of mRNA.

Question 23

How is RNA transcription initiated?

Answer 23

When core RNA polymerase binds to the promoter with the help of sigma.

Question 24

How does RNA processing work with the 5’ cap?

Answer 24

One of the three phosphate groups at the 5’ end of the mRNA is removed and a guanine nucleotide is added. Methyl groups are added to position 7 of the base of the terminal guanine nucleotide

Question 25

Where can methyl groups be added to?

Answer 25

- 7' position of the terminal Guanine - 2' OH group of the sugar to the first and sometimes second nucleotide. - To adenine if it is the second nucleotide, sometimes.

Question 26

What is added to the first and second transcribed nucleotide?

Answer 26

CH3 group

Question 27

What is not transcribed?

Answer 27

Methyl Guanosine

Question 28

What might be added adenine if present?

Answer 28

One extra CH3 group

Question 29

Where is Pre-mRNA cleaved?

Answer 29

At a position from 11 to 30 nucleotides down-stream of the consensus sequence, in the 3' untranslated region

Question 30

Where does the addition of adenine nucleotides (polyadenylation) take place and what does it generate?

Answer 30

At the 3' end of the pre-mRNA, generating the poly(A)tail.

Question 31

How many Adenine's are added to the 3'end?

Answer 31

5 - 250 A's are added.

Question 32

How are A's added?

Answer 32

Without a template.

Question 33

What is the Poly A consensus sequence?

Answer 33

AAUAAA is the polyadenylation signal located 11 to 30 nucleotides upstream of the cleavage site

Question 34

What does the Poly A Consensus sequence affect?

Answer 34

The stability of mRNA, facilitates attachment of the ribosome and export out of the nucleus.

Question 35

What is RNA splicing?

Answer 35

Removal of introns from pre-mRNA

Question 36

What must removal of introns be?

Answer 36

Precise in order to properly fiuse the 3' end of one exon to the 5' end of the next exon.

Question 37

What does EVERY intron have?

Answer 37

Three conserved sequences that are required for its precise removal

Question 38

What are the three conserved sequences?

Answer 38

1.) 5' splice sequences containing the junction sequences GU 2.) 3' splice sequence containing the junction sequence AG 3.) Intron branch point: A conserved "A" residue located 18 - 40 nt upstream of 3' splice site.

Question 39

What does a spliceosome contain?

Answer 39

Five small nuclear RNAs (snRNAs)

Question 40

What do the snRNAs associate with?

Answer 40

About 300 small proteins to form small nuclear ribonucleoproteins (snRNPs)

Question 41

What does Each snRNP contain?

Answer 41

One snRNA molecule and multiple proteins.

Question 42

How many snRNPs does the spliceosome contain?

Answer 42

Five (U1, 2,4,5,6)

Question 43

What do snRNAs of the splice some form?

Answer 43

Complementary base pairing with the pre-mRNA

Question 44

Where does U1 attach?

Answer 44

To the 5' splice site

Question 45

Where does U2 attach?

Answer 45

To the branch point

Question 46

What does the addition of U4, U5, U6 join?

Answer 46

The spliceosome

Question 47

What is Step 1 of RNA splicing?

Answer 47

Pre/mRNA is cut at the 5' splice site and the 5' end of the intron attaches to the branch point. Called a Lariat. 5' phosphate of the G nucleotide binds with the 2' OH group of the A incueltodie at the branch point.

Question 48

What is Step 2 of RNA splicing?

Answer 48

Cut is made at the 3' splice site and simultaneously the 3' end of exon 1 becomes covalently attached to the 5' end of exon 2. Intron is released as lariat and degraded

Question 49

Why is RNA less stable than DNA and Why use it?

Answer 49

The presence of the unique 2'OH group in ribose causes it to react intramolecularly with the 3'OH site resulting in phosphate bond breakage (reactions due to electronegativity)

Question 50

What does the addition of U4,U5, and U6 cause?

Answer 50

A conformational change bringing the 5' splice site close to the branch

Question 51

What happens to U1 and U4?

Answer 51

They are released

Question 52

Where does base pairing occur?

Answer 52

Between U6 and U2 and between U6 and the 5' splice site

Question 53

What is transesterification?

Answer 53

One phosphodiester linkage is replaced by another

Question 54

What do the two transesterification reactions by U6 cause?

Answer 54

Joining of two exons together and releasing the Lariat