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MED-109 Biology II > Topic 4: gene expression > Flashcards

Topic 4: gene expression Flashcards

1
Q

Define RNA

A
  • Intermediate between genes + proteins which they code for
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2
Q

Define transcription

A
  • DNA directed synthesis of RNA
  • Produces mRNA
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3
Q

Define translation

A
  • Synthesis of polypeptide under mRNA
  • Occurs in ribosomes
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4
Q

Difference in gene expression between prokaryote + eukaryote

A

PROKARYOTES:
- No nuclear envelope to seperate transcription + translation
- mRNA immediately translated without RNA processing
- Translation can start before end of transcription
EUKARYOTES:
- Nuclear envelope separates
- Transcription in nucleus
- RNA processing = RNA transcripts modified to mRNA
- Translation in cytoplasm

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5
Q

Explain the triplet code

A
  • Info flow from gene = triplet code
  • Transcribed into complementary mRNA triplet = codon
  • Codon = specific amino acid
  • Genes translated into amino acid change = polypeptide chain
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6
Q

Describe the template DNA strand

A
  • Template DNA strand in transcription = 3’-5’ strand
  • RNA polymerase synthesizes RNA in 5’-3’ using DNA template
  • RNA transcripts = single stranded
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7
Q

What direction do the codons read duing translation?

A
  • Translation = codons read in 5’-3’ direction by ribosomes
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8
Q

Describe the genetic code

A
  • 64 codons
  • 61 = produce amino acids
  • 3 = UAA + UAG + UGA = stop signals = end translation
  • AUG = methionine + start codon
  • Only 2 amino acids
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9
Q

Describe the genetic code characteristics

A

1) Redundant = more than 1 codon encode for amino acid
2) Not ambiguous = each codon specify only 1 amino acid
3) Codons must be read in correct reading frame = specified polypeptide produced

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10
Q

Describe the evolution of the genetic code

A
  • Nearly universal = bacteria = complex animals
  • Genes can be transcribed + translated after bein transplanted = e.g. genetically modified bacteria
  • Bacteria programmed by insertion of human genes for medical use = e.g. insulin
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11
Q

Describe the structure of RNA

A
  • Prduced by transcription of DNA
  • Single strand consits of ribonucleotides
  • Nitrogenous base = AU + GC
  • Pentose sugar = ribose
  • Phosphate group
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12
Q

Types of RNA

A
  • mRNA = translated into proteins
  • rRNA = part of ribosome structure
  • tRNA = transfers amino acids to polypeptide chain during translation
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13
Q

What is the function of RNA polymerase in transcription?

A
  • Is RNA polymerase II
  • RNA polymerase catalyzes transcription
  • Transcription starts with binding of RNA polymerase to DNA region = promoter
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14
Q

Give the molecular components of transcription

A

1) Promoter
2) Terminator
3) Transcription unit

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15
Q

Define the promoter

A
  • DNA sequence where RNA polymerase attaches
  • On 5’ end
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16
Q

Define the terminator

A
  • Sequence signalling end of trnascription in bacteria NOT eukaryotes
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17
Q

Define the transcription unit

A
  • Part of DNA transcribed
  • Bacterica = only 1 RNA polymerase
  • Eukaryotes = 3 types of RNA polymerase
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18
Q

Describe RNA polymerase

A
  • Synthesizes RNA using DNA template strand
  • Only transcribes 1 of 2 DNA strands = 3’-5’
  • Adds nucleuoside triphosphates in 5’-3’
  • Doesn’t need RNA primer for adding NTP
19
Q

Types of RNA polymerase

A

1) RNA polymerase I = rRNA synthesis
2) RNA polymerase II = mRNA + snRNA synthesis
3) RNA polymerase III = tRNA + small RNA

20
Q

Stages of transcription

A

1) Initiation = RNA polymerase binds to promoter
2) Elongation = add NTP to 5’-3’
3) Termination = RNA transcript released from DNA

21
Q

What are the parts of initiation?

A
  • Promoters = signal initiation by binding RNA polymerase II
  • General transcription factors = proteins mediate binding of RNA P + promoter > initiation
  • Transcription initiation complex = transcription factors + RNA P > bound to promoter
  • TATA box = sequence within promoter responsible for assembly of initiation complex
22
Q

Stages of initiation

A

1) General transcription factors bind to TATA box within promoter
2) RNA polymerase binds to promoter

23
Q

Describe elongation of RNA

A
  • Untwisting of double helix
  • Addition of nucleotides to 3’
  • Gene can be transcribed by several RNA polymerases simultaneously = large amounts of proteins produced at a specific time
24
Q

Describe termination

A

BACTERIA:
- RNA polymerase at end of terminator sequence
- mRNA translated without being processed
- Translation can start before termination
EUKARYOTE:
- RNA P transcribes polyadenylation signal = AAUAAA
- RNA transcript released 10-35 nucleotides after signal

25
Describe RNA processing
1) Addition of 5' Cap = modified guanine nucleotide at 5' end 2) Addition of poly-A tail at 3' = 50-200 adenine 3) RNA splicing = removal of segments from transcript
26
What is the role of RNA end modifications?
- Facilitate export of mRNA from nucleus - Protect mRNA from degradation by hydrolytic enzymes - Help ribosomes attach to 5' during translation
27
Describe RNA splicing
- Introns = non-coding - Exoms = coding regions - Splicing removes introns + joins exons = final mRNA molecule - Using spliceosomes = large complex of snRNPs = interact with sites on intron = release it + join 2 exons
28
What is ribozymes?
- Catalytic RNA molecule = function enzyme - Found in prokaryotes + lower eukaryotes - Role in RNA splicing - Discovery ruled out belief that biological catalysts are proteins
29
What is alternative splicing?
- Production of different proteins from same pre-mRNA transcript = different combos
30
Describe the functional role of alternative splicing
- Genes can encode for 1+ polypeptide depending on which segment treated as as exons during splicing - Proteins = modular architecture consisting of different domains - Different exons = code for different domains - Exon shuffling = evolution of new proteins
31
Give the molecular components of translation
1) mRNA 2) tRNA = transfer amino acids from cytoplasm to ribosome 3) Ribosomes = couple mRNA + tRNA + add amino acid = growing polypeptide
32
Describe tRNA
- Translator = reads nucleic acid codons = interprets as amino acid - Single RNA strand - Clover leaf - Carries specific amino on end - Has anticodon on other end = base pairs complementary codon on mRNA
33
Describe dirction of translation
- Ribosome reads mRNA in 5'-3' direction - Polypeptide synthesis = N terminal to C terminal
34
Describe ribosomes
- Proteins + rRNA - 2 subunits - Facilitates base pairing between tRNA anticodons + mRNA codons - Tetracycline + streptomycin = inactivates prokaryotic ribosomes NOT eukaryotic = treats bacterial infections
35
Describe the difference between eukaryotic/prokaryotic ribosomes
PROKARYOTIC: - Smaller - 70S - Small subunit = 30S - Large subunit = 50S EUKARYOTIC: - Small subunit = 40S - Large subunit = 60S
36
Describe the ribosome binding sites
1) P site = holds tRNA carrying growing polypeptide chain 2) A site = tolds tRNA carrying next amino acid 3) E site = discharges tRNA to exit ribosome
37
Types of ribosomes
1) Free = not bound to ER = synthesis of cytosolic proteins 2) Bound = bound to ER = synthesis of secreted/membrane bound proteins
38
Describe polyribosomes
- Group of free ribosomes in cytosol - Enable cells to make many copies of poly peptides quickly - Each mRNA translated simultaneously by many ribosomes
39
Stages of translation
1) Initiation 2) Elongation 3) Termination
40
Describe initiation
- Small ribosomal subunit binds with 5- cap on mRNA + initiator tRNA - Subunit moves along mRNA until reaches = start codon = AUG within Kozak sequence - Initiation factors induce binding of large subunit - Form translation initiation complex = mRNA + tRNAi + both subunits - GTP = energy for assembly of initiation complex
41
Describe initiation in bacteria
- Small ribosomal subunit = binds to Shine-Dalgarno sequence = upstream from start codon - AUG = P site
42
Describe elongation
1) Codon recognition by tRNA = transfer of aminoacyl-tRNA from cytosol to position A 2) Peptide bond formation = attachment of new amino to growing chain via peptide bond - Peptidyl transferase = part of large subunit = catalyzes peptide bond 3) Translocation = tRNA translocates from A to P + mRNA moves 3 nucleotides
43
Describe termination
- Stop codon reached on mRNA = A site - UAG + UAA + AGA
44
Describe post transational modifications
- Amino + sugar/lipid/phosphate group - Polypeptides activated by enzymes = cleave them - Polypeptides + polypeptide = subunit of proteins

MED-109 Biology II (6 decks)

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