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MBG*2040 > MBG PART TWO: Lecture 6 > Flashcards

MBG PART TWO: Lecture 6 Flashcards

1
Q

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

A

A continuous sequence of amino acids in the protein

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2
Q

What is the number of nucleotides proportional to?

A

The number of amino acids (3:1)

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3
Q

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

A

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

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4
Q

What is the Protein Coding Region?

A

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

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5
Q

What is 3’UTR?

A

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

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6
Q

How can transcription and translation occur in prokaryotes?

A

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

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7
Q

What happens to the mRNA in Eukaryotes?

A

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

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8
Q

In Eukaryotes, what happens to the template strand?

A

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.

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9
Q

What are exons?

A

Coding sequences

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10
Q

What are introns?

A

Non-Coding Sequences

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11
Q

How do you remove introns?

A

RNA splicing along with additional RNA processing

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12
Q

Why is the removal of introns required?

A

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

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13
Q

What can exons vary in?

A

Length and relative position on the gene.

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14
Q

What type of introns and exons are the best studied?

A

Nuclear pre-mRNA introns and exons

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15
Q

What does splicing of the introns require?

A

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

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16
Q

What can introns influence?

A

How genes are expressed

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17
Q

What do some introns have?

A

Self-splicing capabilities

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18
Q

What are introns removed from?

A

pre-mRNA by the action of the splicesome.

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19
Q

What does addition to 5’ cap do?

A

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

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20
Q

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

A

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

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21
Q

What does RNA splicing do?

A

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

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22
Q

What does RNA editing do?

A

Alters nucleotide sequence of mRNA.

23
Q

How is RNA transcription initiated?

A

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

24
Q

How does RNA processing work with the 5’ cap?

A

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

25
Q

Where can methyl groups be added to?

A
  • 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.
26
Q

What is added to the first and second transcribed nucleotide?

A

CH3 group

27
Q

What is not transcribed?

A

Methyl Guanosine

28
Q

What might be added adenine if present?

A

One extra CH3 group

29
Q

Where is Pre-mRNA cleaved?

A

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

30
Q

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

A

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

31
Q

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

A

5 - 250 A’s are added.

32
Q

How are A’s added?

A

Without a template.

33
Q

What is the Poly A consensus sequence?

A

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

34
Q

What does the Poly A Consensus sequence affect?

A

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

35
Q

What is RNA splicing?

A

Removal of introns from pre-mRNA

36
Q

What must removal of introns be?

A

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

37
Q

What does EVERY intron have?

A

Three conserved sequences that are required for its precise removal

38
Q

What are the three conserved sequences?

A

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.

39
Q

What does a spliceosome contain?

A

Five small nuclear RNAs (snRNAs)

40
Q

What do the snRNAs associate with?

A

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

41
Q

What does Each snRNP contain?

A

One snRNA molecule and multiple proteins.

42
Q

How many snRNPs does the spliceosome contain?

A

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

43
Q

What do snRNAs of the splice some form?

A

Complementary base pairing with the pre-mRNA

44
Q

Where does U1 attach?

A

To the 5’ splice site

45
Q

Where does U2 attach?

A

To the branch point

46
Q

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

A

The spliceosome

47
Q

What is Step 1 of RNA splicing?

A

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.

48
Q

What is Step 2 of RNA splicing?

A

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

49
Q

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

A

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)

50
Q

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

A

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

51
Q

What happens to U1 and U4?

A

They are released

52
Q

Where does base pairing occur?

A

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

53
Q

What is transesterification?

A

One phosphodiester linkage is replaced by another

54
Q

What do the two transesterification reactions by U6 cause?

A

Joining of two exons together and releasing the Lariat

MBG*2040 (26 decks)

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