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BIOL1007 > RNA > Flashcards

RNA Flashcards

1
Q

Tell me the differences between the strucutre of DNA and RNA ?

A
  1. RNA contains the pentose sugar of ribose as opposed to the deoxyribose sugar in DNA
  2. containd Uracil rather than thymine
  3. single stranded rather than double stranded. this is so it can form well-defined secondary structures
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2
Q

Tell me the 6 types of RNA and their roles

A
  1. mRNA: messenger RNA, a template for protein synthesis
  2. rRNA: ribosomal RNA, major component of ribosomes
  3. tRNA: transfer RNA, carries amino acids in their activated forms to the ribosome
  4. snRNA: small nucleuar RNA, participates in RNA splicing
  5. miRNA: micro RNA, binds to mRNA and inhibits their translation
  6. siRNA: small interfering RNA, bind to mRNA and promote degradation
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3
Q

How is RNA produced?

A

Via transcription

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4
Q

What are the different stages of transcription?

A
  1. initiation
  2. elongation
  3. termination
  4. processing
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5
Q

What happens in the initiation stage of transcription?

A
  1. DNA unwinds and seperates
  2. RNA polymerase binds to the promoter of the template strand
  3. RNA synthesis occurs in the 5’–> 3’ direction (antiparallel to the DNA strand)
  4. RNA forms
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6
Q

RNA polymerase has an subunit and an initiation factor. What are each of these and their role.

Whats a Holoenzyme?

A

The subunit is called a2ßß’w. This is the subunit of the core enzyme RNA polymerase and is involved in catalytic activity

The initiation factor is σ. This directs the enzymes to the correct initiation sites

Holoenzyme is formed from a combination of enzyme with coenzyme

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7
Q

Whats the start of transcription marked by and what is this?

A

Promotors, these interact with different transcriptional factors and RNA polymerase to initiate the process

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8
Q

In prokaryotes whats located at position -35 and -10 on the genome when +1 marks the start of RNA and what are these?

In Eukaryotes whats located at position -75 and -25 on the genomes when +1 marks the start of RNA and what are these?

A

Prokaryotes

Position -35: A consensus sequence (TTGACA)

Position -10: Pribnow box (AT-rich region)

Eukaryotes

Position -75: CAAT box (sometimes present)

Position -25: Hogness box (TATA box)

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9
Q

What occurs in the elongation stage of transcription?

Whats used in this stage in prokaryotes?

A
  1. RNA polymerase moves along the template strand, synthesing an RNA molecule
  2. NTPs (nucleoside triphosphates) are added to the 3; end of RNA

NOTE: in prokaryotes, RNA polymerase is a holoenzyme consisting of a number of subunits including a sigma factor (transcription factor)

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10
Q

Whats are NTPs?

  • uses
  • what DNA and RNA synthesis use
  • why its synthesised within the cell
A
  • building blocks of DNA and RNA
  • source of energy for cellular reactions
  • involved in signalling pathways
  • not absorbed well, so synthesise within the cell
  • DNA synthesis uses dNTPs whilst RNA synthesis uses NTPs
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11
Q

What two ways can the termination stage of transcription in prokaryotes occur?

A

In prokaryotes there are two ways that transcription can be terminated

  1. Rho-dependant termination
  2. Rho-independant termination
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12
Q

Tell me about the Rho-dependant termination in prokaryotes?

A
  1. it requires a protein known as a Rho factor
  2. Rho moves along the molecule in the 5’ –> 3’ direction and encourages the dissociation of the DNA template and RNA polymerase
  3. disrupts the transcriptional complex
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13
Q

Tell me about the Rho-indepedant terminator in prokaryotes?

A
  1. a self-annealing hairpin structure is formed
  2. the hairpin formation causes the RNA polymerase to stall and become unstable
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14
Q

How does termination of transcription occur in eukaroytes?

A
  1. terminator signals that are associated with RNA polymerase II are detected and trigger the termination process
  2. Additional adenine nucleotides are added to the 3’ end od the RNA transcript (a process known as polyadenylation)
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15
Q

Whats polyadenylation?

A

the addition of a PolyA tail to an mRNA

this tail consisits of multiple AMPs (stretch of RNA which only has adenine bases)

Part of the procee that produces mature mRNA for translation

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16
Q

Whats the biggest difference between DNA-RNA replication in prokaryotes and eukaryotes?

A

in prokarytoes, transcription and translation occur at the same time

in eukaryotes there is compartmentalisation which means that translation cannot occur until transcription is complete.

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17
Q

What occurs in the processing process of transcription?

A
  1. preribosomal RNA is spliced where the introns are removed which then leads to the formation of mature RNA
  2. normal base pairing rules where thymine is replaced with uracil in RNA
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18
Q

How is eukaryotic pre-mRNA processed?

A
  1. addition of PolyA tail to 3’ end of RNA transcript
  2. Addition of a cap to 5’ end (important initiation of translation)
19
Q

what are the main factors that influence gene expression?

A
  1. nuclear membrane-seperate transcription and translation
  2. RNA processing
  3. Complex transcriptional regulation
20
Q

In eukaryotes, what are the 3 types of RNA polymerase and what are their roles?

A
  1. RNA polymerase I: produces rRNA (18s, 5.8s and 28s)
  2. RNA polymerase II: produces mRNA
  3. RNA polymerase III: produces tRNA and 5s rRNA
21
Q

What is the name of the large complex involved in splicing?

A

spliceosomes

22
Q

What are spliceosomes?

A
  • have GU at 5’ end and AG at 3’ end
  • assembles from 5 small nuclear RNAs (snRNA) and protein facotrs
  • removes introns from pre-mRNA
23
Q

Whats alternative splicing?

A
  • a single gene coding for multiple proteins
  • particlular exons may be excluded from the final processed mRNA
24
Q

Give an example of a protein formed from a single gene via alternative splicing ?

A

Fibronectin

25
Q

Whats Fibronectin- how is it formed- and Fibronectin mRNA?

A

Fibronectin: a component to the extracellular matrix- fibroblasts secrete fibronectin

Fibronectin mRNA: includes the exons EIIIB and EIIIA- these encode amino acids that bond tightly to proteins in the fibroblasts plasma membrane

26
Q

Hepatocytes do not produce the exons EIIIB and EIIIA what does this mean for fibronectin ?

A

This allows the fibronectin to be secreted and circulate freely in the blood stream to help clot formation (will not incorrectly adhere to fibroblasts)

27
Q

whats ß-thalassemia and what can it lead to?

A

this is a blood disorder that reduces the production of haemoglobin.

it can lead to incorrect splicing

28
Q

changing single nucleotide’s can lead to mutations in splice site. name 3 types of things that can happen from these single nucleotide changes?

A
  1. exon skipping
  2. activating a cryptic splice site
  3. new exon incorporation
29
Q

when genes are expressed all the time, what is this known as?

A

constitutive expression

30
Q

What is meant by the term regulated expression?

A

A gene expressed under certain conditions or at certain times. they require something to activate them

31
Q

Whats means by the term polycistronic mRNA?

A

an mRNA that encodes several proteins

32
Q

whats Allolactose?

What effect does it have on the lac operon?

A

A disaccharide similar to lactose- side product of beta-galactosidase reacton (by product of lactose)

Allolactose binds to the repressor protein and prevents it from binding to the operator

this means that when lactose is present these genes are switched on

33
Q

Tell me what happens when lactose is present and when lactose isn’t present with the lac operon?

A

When lactose is present:

  1. RNA polymerase binds to the regulatory gene and transcribes it
  2. this leads to the production of a repressor protein from the translation of mRNA
  3. A lactose inducer binds to the repressor protein and renders it inactive as its conformation is changed
  4. this allows RNA polymerase to bind to the promotor region
  5. transcription of the genes LAC z/y/a occurs

Lac z produces: beta galactosidase

Lac y produces: lactose permease

Lac a produces: acetylase

When lactose isn’t present:

  1. RNA polymerase binds to the regulatory region and transcribes it
  2. mRNA is then translated which leads to the production of the repressor protein
  3. the repressor protein the binds to the operator region
  4. this blocks RNA polymerase from binding to the promotor region
  5. the genes z/y/a are not transcribed which means the enzymes for lactose metabolism are not produced
34
Q

Whats the trp operon?

A

An operon that leads to the synthesis of tryptophan

35
Q

Tell me the stages to the expression of the genes for typtophan on the operon, when trp is present and when it isnt present

A

When trp is present:

  1. RNA binds to the regulatory gene which leads to the production of the repressor protein
  2. the corepressor (tryptophan) binds to the repressor protein and changes its conformation
  3. the protein then binds to the operator region forming a repressor- corepressor complex which is active
  4. This blocks RNA polymerase from binding to the promotor region so the genes are not transcribed

When trp isn’t present:

  1. RNA polymerase binds to the regulatory gene and transcibes it leading to the formation of the repressor protein
  2. this repressor protein is inactive if no trp binds to it
  3. this allows RNA polymerase to bind to the promotor region
  4. the genes a/b/c/d/e are therefore transcribed
  5. this produces the enzymes for tryptophan synthesis
36
Q

What direction does the production for tryptohan and lactose enzymes occur in?

A

the 5’ to 3’ direction

37
Q

What are the 4 stages to how transcription is controlled?

A
  1. chromatin remodelling
  2. exposure of a promoter
  3. assembly of proteins
  4. attachment of RNA polymerase
38
Q

whats are basal transcription factors?

why are they important?

A

they bind to promotors and are common in most genes.

They have to be there in order for RNA polymerase to bind and start transcription

39
Q

what are regulatory transcription factors?

A

they bind to promoters and are specific for particular genes

40
Q

What does miRNA regulate?

A

gene expression

41
Q

How is miRNA produced?

A

they are synthesised as a precursor fron nuclear DNA and then processed (in both the nucleus and cytoplasm) into miRNA

42
Q

whats miRNA’s function? What does it’s function lead to?

A

base-pairing complementary sequences within mRNA which results in the silencing of speciifc mRNAs and repression of protein translation

43
Q
A

BIOL1007 (8 decks)

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