Lecture 10 Flashcards

1
Q

Outline the general process of Transcription

A
  1. RNA polymerase, together with one or more transcription factors, binds to promoter DNA
  2. RNA polymerase creates a transcription bubble, which separates the two strands of DNA helix by breaking the hydrogen bonds between complementary DNA nucleotides
  3. RNA polymerase adds RNA nucleotides complementary to DNA
    strand
  4. RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form a new RNA strand
  5. Hydrogen bonds of the RNA-DNA helix break, freeing the new RNA strand
  6. In eukaryotes post transcriptional processing includes polyadenylation, 5’ capping, and splicing
  7. The RNA may remain in the nucleus or exit to the cytoplasm through the nuclear pore matrix via
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2
Q

What is responsible for all of the catalytic action of transcription? what else is involved in transcription?

A

RNA Polymerase II ; activator proteins

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3
Q

Does Transcription create superhelical tension?

A

yes, topoisomerase relieves the tension

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4
Q

When are new mRNA capped?

A

They are capped as soon as they emerge from the RNA polymerase

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5
Q

What must occur once the RNA polymerase is finished with one mRNA strand, before it can begin another round of transcription?

A

It must be dephosphorylated

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6
Q

“what are the steps involved in eukaryote mRNA processing prior to leaving the nucleus?”

A

5’ capping
RNA splicing (removes intron sequences ; lariats are formed here)
3’ polyadenylation (poly A tail)

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7
Q

What are the steps in capping mRNA? When does mRNA capping begin?

A

The 1st nucleotide is dephosphorylated

GMP is added in reverse linkage (5’ to 5’ instead of 5’ to 3’)

A methyl group is added to the guanosine

Capping begins when the mRNA is 25 nucleotides long

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8
Q

Explain how Introns are ID’ed and removed during splicing

A

Introns are flanked by sequences that are recognized by spliceosome RNA’s to ID where the cut needs to happen, and then RNA brings in other proteins to actually cut the intron out.

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9
Q

what performs splicing?

A

spliceosomes

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10
Q

explain the process of splicing

A

the 5’ end of the intron is ID’ed

the “A” near the 3’ splice site of the intron in ID’ed

the Lariat structure is formed

the 3’ end of the intron is cut

the 2 exons are then joined

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11
Q

Spliceosomes do not need to use ATP because they use energy already stored in the intron to exon bonds. True or False

A

False ; spliceosomes use ATP

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12
Q

List the 5 types of snRNP’s and what they are involved in

A

U1: ID’s 5’ end of intron

U2: binds to A

U4 and U5: work together to recruit proteins to make the conformational and enzymatic changes in splicing

U6: recognizes the 3’ end and works with U4 and U5

(there is no U3)

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13
Q

Why are mRNA sequences given a poly A tail?

A

it increases the stability of the sequence and makes it easier to be transported without being damaged.

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14
Q

define Consensus sequences in the process of transcription

A

signal that the mRNA needs to be clipped (this sequence is complete)

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15
Q

What is an exosome in the nucleus?

A

a protein complex that uses RNAses to digest damaged RNA sequences so that their nucleotides can be recycled

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16
Q

describe the exosome type found in blood, urine, and cultured medium of cell cultures.

A

cell-derived vesicles that contain various molecular constituents of their cells of origin.

contain enzymes, heat shock proteins, and cytoskeletal proteins

17
Q

What mediates the “handoff” of mRNA through the nuclear pores into the cytoplasm?

A

nuclear export receptor proteins

18
Q

What is the final quality control point for mRNA prior to Translation? how does it work?

A

nonsense mediated decay ; it eliminates mRNA’s that have premature stop codons

19
Q

what are miRNA’s? what do they do?

A

small, noncoding RNA molecules that function in RNA silencing and post-transcriptional regulation of gene expression

basically “guide” molecules in RNA silencing

20
Q

Dysregulation of miRNA’s is associated with what?

A

many human diseases, especially cancer and neurodevelopment disorders

21
Q

where are noncoding RNA’s synthesized and processed?

A

in the nucleus, just like all other RNA’s

22
Q

What is rRNA for? where does this occur?

A

rRNA’s (ribosomal RNA’s) code for ribosome subunits ; the rRNA is processed and assembled into ribosome subunits in the nucleolus

23
Q

what is the nucleolus?

A

a structure in the nucleus visible during interphase when it is producing more ribosomes

“ribosome factory”

24
Q

what is the size of a cell’s nucleolus associated with?

A

that particular cell’s need to produce proteins (it will need many ribosomes for this)

25
Q

explain the full process of ribosomal subunit processing/ maturation

A

rRNA’s are created and processed in the nucleolus

rRNA is made into ribosomal subunits in the nucleolus

final processing of the subunits does not occur until it is shipped through the nuclear pore into the cytoplasm

26
Q

where are most snoRNA’s assembled into snRNP’s?

A

cajal bodies (a type of aggregate in the nucleus)

27
Q

what is a scaffold protein?

A

attaches to the tail of RNA polymerase and keeps transcription accessor proteins in close proximity to the polymerase.