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Fundamentals of the Living Cell > RNA Synthesis > Flashcards

RNA Synthesis Flashcards

1
Q

What is the main function of chromosomes ?

A

To carry genes

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2
Q

What is a gene?

A
  • Unit of heredity: contains instructions for an organisms phenotype
  • DNA segment containing instructions for making a particular product
  • includes regulatory genes and structural genes
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3
Q

What is transcription?

A

The synthesis of mRNA from DNA

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4
Q

What is translation?

A

Protein production from the mRNA transcript

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5
Q

How many RNA types are found in the cell and what are they?

A
  • 3

- mRNA, tRNA and rRNA

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6
Q

What are the main differences between RNA and DNA?

A
  • RNA HAS ribose not deoxyribose
  • RNA has uracil instead of thymine
  • RNA is single stranded
  • RNA shorter than DNA
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7
Q

Where is RNA made?

A

In the nucleus

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8
Q

How are sa attached to tRNA?

A

By aminoacyl tRNA synthases

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9
Q

How does RNA Pol know where to start transcribing?

A
  • In prok/euk DNA, there are regions called promoter regions

- They are specific sequence of nucleotides that bind with RNA Pol

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10
Q

Where is the TATA box found?

A

25 nucleotides to the start of where the gene is found

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11
Q

What are the requirements for transcription?

A
  • RNA Pol II
  • rNTPs
  • Promoter regions
  • Transcription factors (forms pre-initiation complex)
  • Enhancers and silencers
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12
Q

Describe initiation

A
  • Transcription Factor II D binds to the promoter region (Tata- box Binding Protein is a subunit of TFIID tata binding protein)
  • TFIIB binds to the TBP and it links RNA polymerase to the TFIID
  • WHEN RNA polymerase binds to the TFIIB it is already associated with TFIIF
  • TFIIE and TFIIH associate with RNA polymerase
  • TFIIH unwinds the DNA around the initiation site (cistron) and phosphorylated the RNA polymerase II
    ATP is needed
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13
Q

Describe elongation

A
  • RNA Polymerase moving along DNA synthesizing the RNA which is released at the other end
  • Transcription Bubble formed which is 12 - 14 bps.
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14
Q

Describe termination

A
  • Near the stop codon there is a sequence called AAUAAA which is the polyadenylation signal or the termination signal which is after the stop codon.
  • A specific endonuclease recognizes the termination signal. The CSPF is the enzyme that does the cleavage after the termination signal.
  • Polyadenylate polymerase adds 250 adenines to the end of the 3’ end of the pre-mRNA and this is called the poly A tail.
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15
Q

When does capping occur and what is it’s importance?

A
  • When mRNA is still being transcribed
  • Acts as a marker of RNA Pol to transcribed RNA
  • Stimulates splicing
  • Protects from any nucleus attack
  • Enables multiple ribosomes to translate simultaneously
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16
Q

Describe the capping mechanism

A
  • Forms a capping enzyme complex of methyl transferase, triphosphatase and gunnel transferase
  • Triphosphatase removes a phosphate group from mRNA
  • Guanyl transferase transfers G to 5’ end
  • Methyl transferase transfers methyl group to the 7th position on G
17
Q

Where does the the polyadenylation occur?

A
  • At the beginning of the 3’ end
  • Within the mRNA transcript there is a cleavage signal that is recognised by a specific endonuclease
  • poly A pol. adds around 200 ‘A’s
18
Q

What are the requirements of polyadenylation?

A
  • CPSF: Cleavage and polyadenylation specificity factor
  • CSTF: Cleavage stimulation factor
  • Poly A Pol.
  • PABP: Poly A binding protein stims Poly A Pol
19
Q

What is the purpose of capping and polyadenylation?

A

1) Stabilty: prevents degradation in the nucleus and cytoplasm
2) Transport: ensures mRNA is intact
3) Integrity prior translation: so cell does not waste energy translating incomplete/ incorrect mRNA

20
Q

What is splicing?

A

The removal of introns and the joining of axons

21
Q

Describe splicing

A
  • GU recognised by an RNA within the splicer zone where protein binds
  • Protein undergoes conformation and cleaves 5’ splice site
  • Ends join to form lariat like structure
  • Cleavage at 3’ splice site and exons join together
22
Q

What is alternative splicing?

A
  • Ligations of exons can differ so the sequence of mature mRNA changes
  • The proteins made may have similar functions as there are common exons, but different function as the sequence of exons differs.
23
Q

How is RNA exported out of the nucleus?

A
  • tRNA and microRNAs bind directly to export receptors.
  • Large RNAs such as ribosomal RNAs and mRNA recruit specific adaptor proteins.
  • They are exported through the nuclear pores
24
Q

What proteins bind to mRNA for export from nucelus?

A
  • Cap binding complex: recognises cap
  • TREX: transcriptional-coupled export complex
  • EJC: exon-junction complex recognises successful splicing events

Fundamentals of the Living Cell (31 decks)

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