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Structure & Function 1 > Gene Expression > Flashcards

Gene Expression Flashcards

1
Q

Prokaryotic Transcription

A
  • in cytoplasm
  • coupled transcription and translation
  • no definite phase of occurrence
  • one RNA polymerase
  • no initiation factors
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2
Q

Eukaryotic Transcription

A
  • in nucleus
  • occurs in G1 and G2
  • three RNA polymerases
  • multiple general transcription factors
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3
Q

What is a control element?

A
  • non-coding DNA segments
  • regulate transcription by binding transcription factors
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4
Q

What is a promoter?

A

a sequence of DNA bound by the first components of the pre-initiation complex

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5
Q

What is an enhancer?

A
  • distal control elements
  • short nucleotide segments that influence the rate of transcription
  • may be thousands of nucleotides away from the promoter
  • may be bound by silencer/repressor proteins
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6
Q

What is an intron?

A
  • interrupt the coding sequence
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7
Q

Define transcription

A

the process by which the information in a strand of DNA is copied into a new molecule of messenger RNA (mRNA)

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8
Q

Different RNA polymerases

A
  • RNA polymerase I; produces pre-rRNA
  • RNA polymerase II; produces pre-mRNA
  • RNA polymerase III; produces pre-tRNA
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9
Q

Four steps of transcription

A

1) Initiation
2) Elongation
3) Termination
4) Processing

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10
Q

INITIATION

A

Unwinding of DNA
- RNA polymerase binds to the template strand via the pre-initiation complex
- chromatin remodelling exposes the promoter
- pre-initiation complex binds to recognition site on promoter

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11
Q

ELONGATION

A
  • RNA polymerase moves along the template strand, synthesising a pre-mRNA molecule
  • pre-mRNA is processed; capping, splicing & polyadenylation
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12
Q

TERMINATION

A
  • addition of additional adenine nucleotides at the 3’ end of the RNA transcript
  • POLYADENYLATION
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13
Q

PROCESSING

A
  • introns are removed and exons are spliced together to form a mature mRNA molecule one single protein-coding sequence
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14
Q

Pre-mRNA processing

A
  • cap added at 5’ end
  • tail added at 3’ end
  • glutynaltransferase attaches methylated GTP cap to 5’ end
  • splicing; removal of introns by spliceosomes
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15
Q

Purposes of 5’ end capping

A
  • Regulation of nuclear export
  • Prevention of degradation by exonucleases
  • Promotion of translation
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16
Q

Poly-A tail addition

A
  • polyadenylation signals; bind cleavage factors
  • poly-A polymerase adds about 100-250 adenine nucleotides to cut 3’ end
  • forms a poly-A tail
  • stabilises the transcript, aids in transcription termination and exportation from nucleus to cytosol
17
Q

Translation overview

A
  • mRNA moves into the cytoplasm
  • becomes associated with ribosomes
  • tRNA with correct anticodon carries amino acid to mRNA
  • anticodon-codon complementary base pairing occurs
  • peptide chain is transferred from resident tRNA to incoming tRNA
    -tRNA departs and will pick up another AA
18
Q

Three steps of translation

A
  • initiation
  • elongation
    -termination
19
Q

Structure of the ribosome

A
  • Large ribosomal subunit (50s) contains three slots for tRNAs
  • Ribosome slides from 5’ to 3’ end
  • A —> P —-> E
  • aminoacyl-tRNA, peptidyl-tRNA & exit
  • small ribosomal subunit (30s) has the mRNA binding site
20
Q

Structure of tRNA

A
  • acceptor stem at 3’ end has amino acid attachment site
  • anticodon read 3’-5’ antiparallel to codon mRNA
21
Q

tRNA wobble

A
  • “Wobble position” at 5’ end of anticodon
  • allows the same tRNA to recognise multiple codons for amino acid it carries
  • allows for fewer tRNA molecules
22
Q

Loading tRNA with correct amino acid

A
  • Enzymes called aminoacyl-tRNA synthases specific for each AA
  • recognise the AA and the suitable tRNA molecule
  • uses ATP
23
Q

INITIATION; translation

A
  • small ribosomal subunit and initiator tRNA binds to the 5’ end cap
  • complex moves along in the 3’ direction
  • tRNA molecule binds to the codon via it’s anticodon
24
Q

What is the sequence of initiator tRNA?

A

UAC

25
Q

ELONGATION; translation

A
  • second tRNA molecule binds at A site
  • amino acid at the P site is covalently attached via a peptide bond to the amino acid at site A
  • tRNA at the P site is de-acylated (no AA)
  • ribosome moves along in 5’-3’ direction
  • de-acylated tRNA moves to E point (exit) and is released
26
Q

Stop codon sequences

A

UAA
UAG
UGA

27
Q

TERMINATION; translation

A
  • elongation and translocation continue until a stop codon is reached
  • stop codons don’t recruit a tRNA but a release factor that signals for translation to stop
  • the polypeptide is released and two ribosomal subunits separate
  • polypeptide is ready for post-translational modifications

Structure & Function 1 (11 decks)

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