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MCAT Biochemistry > Ch 7 - RNA and Genetic Code > Flashcards

Ch 7 - RNA and Genetic Code Flashcards

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MCAT flashcards
1
Q

central dogma

A
  • DNA replication
  • DNA to RNA via transcription
    • opposite via reverse transcription
    • mRNA synthesized in 5-3 direction and is complementary to DNA template strand
  • RNA to protein via translation
    • translate RNA from 5-3 direction
    • synthesize protein from N terminus to C terminus
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2
Q

mRNA

A
  • specify amino acid sequence for proteins
  • transcribed via rna polymerase in the nucleus
  • read in codons
  • monocistronic - each mRNA molecule translates to one protein
    • eukaryotes
  • polycistronic - different proteins depending on where on mRNA translation begins
    • prokaryotes
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3
Q

tRNA

A
  • transfer RNA
  • anticodon to match codon on mRNA and retreive amino acid
  • charged (activated) - when connected to amino acid
  • aminoacyl-tRNA synthetase - activates amino acid
    • uses 2 high energy bonds from ATP
    • energy rich process
  • CCA sequence where amino acid binds to 3’ end of tRNA
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4
Q

rRNA

A
  • ribosomal RNA
  • synthesized in nucleolus
  • ribosomal machinery
  • ribozymes - enzyme made of RNA
  • important in splicing out introns
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5
Q

Codons

A
  • anticodons - antiparallel to codons
  • AUG - start codon (methionine)
  • stop codons - UGA, UAA, UAG
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6
Q

Mutations

A
  • silent/degenerate - due to wobble base
    • no change to amino acid
  • point - affect one nucleotide
    • missense - affect one amino acid
    • nonsense - introduce a stop codon
  • frameshift - nucleotides added or deleted
    • insertion or deletion
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7
Q

transcription

A
  • helicase and topoisomersae unwind and prevent supercoiling
  • synthesized from template strand
  • synthesized by RNA polymerase
    • RNA polymerase II - mRNA and snRNA in eukaryotes
    • RNA polymerase I - rRNA in nucleolus
    • RNA polymerase III - tRNA and rRNA
  • starts at promoter region
    • binds to TATA box
    • trasncription factors help polymerase bind
  • travel in 3-5 direction in order to synthesize in 5-3
  • +1 base is first to be transcribed
    • upstream from here are negative numbers
    • downstream are positive numbers
    • TATA box near -25
  • continue until termination sequence
  • DNA double helix reforms
  • hnRNA - heterogeneous nuclear RNA is unmodified transcript
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8
Q

Posttranscriptional processing

A
  • splicing: introns and exons
  • 5’ cap
  • 3’ poly A tail
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9
Q

Splicing

A
  • remove introns (noncoding sequences)
  • ligate exons (coding sequences) together
  • Spliceosome - snRNA and small nuclear ribonucleoproteins (snRNPs)(snurps)
    • recognize introns and remove
    • lariat - lasso shaped structure of intron
    • intron degraded
  • Alternatice splicing - make many different proteins from a limited number of genes
    • splice together in different ways
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10
Q

5’ Cap

A
  • 7-methylguanylate triphosphate cap
  • protect from degradation in cytoplasm
  • recognized by ribosome as the binding site
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11
Q

3’ Poly A tail

A
  • 3’ end of transcript
  • protect from degradation
  • longer tail will mean longer life outside of nucleus
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12
Q

Ribosome

A
  • A site - aminoacyl
  • P site - peptidyl
  • E site - exit
  • Eukaryotes - 4 rRNA strands
    • RNA polymerase I and III transcribe rRNA
      • polymerase I in the nucleolus
    • 40S and 60S subunits join to make 80S (whole ribosome)
  • Prokaryotes - 70S made from 50S and 30S subunits
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13
Q

Translation Initiation

A
  • eukaryotes - small subunit binds to 5’ cap
    • initiator tRNA binds anticodon to AUG in P site of ribosome
    • large subunit binds to small subunit
    • assisted by initiation factors
  • prokaryote - small subunit binds to Shane Dalgarno Sequence (5’ untranslated region)
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14
Q

Translation Elongation

A
  • ribosome moves 5-3
  • synthesize N to C terminus
  • A site - hold aminoacyl-tRNA complex, next amino acid, determined by codon
  • P site - hold growing peptide chain
    • form peptide bond - polypeptide transferred from P to A site tRNA via peptidyl transferase
      • GTP used
  • E site - uncharged tRNA pauses and then leaves
  • EF factors - elongation factors - locate and recruit amnioacyl tRNA and GTP, remove GTP
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15
Q

Translation Termination

A
  • release factor binds to terminal codon (stop codon)
    • UAA, UAG, UGA
  • add water to peptide chain - peptidyl transferase and termination factors hydrolyze peptide from last tRNA
  • released from P site
  • ribosome subunits dissociate
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16
Q

Posttrasnlational processing

A
  • chaperones - fold protein
  • cleavage - inactive peptide must be cleaved before active
  • phosphorylation - add PO4 2- via kinase
  • carboxylation - add carboxylic acid
  • glycosylation - add oligosaccharides in ER and golgi
  • prenylation - add lipids to membran bound enzymes
17
Q

signal sequences

A
  • designate destination for a protein
  • some direct to endoplasmic reticulum
    • ribosomes on ER to complete translation
  • then to Golgi apparatus and secrete via vesicle and exocytosis
18
Q

Prokaryote Gene expression

A
  • Operon - cluster of genes transcribed as a single mRNA
    • described by Jacob-Monod Model
    • strucutreal gene - protein of interest
    • operator site - binds repressor protein
    • promoter site - RNA polymerase binds
    • regulator gene - codes for repressor protein
  • Inducible and Repressible Systems
19
Q

Inducible System (operator system)

A
  • repressor binds to operator system and stops transcription
  • negative control - reduce transcription due to binding of molecule
  • Inducer binds to repressor to allow RNA polymerase to transcribe the gene
    • similar to competitive inhibition
  • ex. Lac operon (negative inducible)
    • only used when lactose is high and glucose is low
      • induced by presence of lactose
      • catabolite activator protein (CAP) - transcriptional activator when glucose is low
      • low glucose - high cAMP - binds to CAP - CAP conformational change - CAP bind to promoter - increase transcription of lactase gene
      • positive control - increase transcription of gene due to binding of molecule
20
Q

Repressible Systems

A
  • constant production of protein
  • repressor must bind to corepressor to be active
    • complex binds operator site
    • negative feeback
    • final structure may be the corepressor
  • trp operon - negative repressible
  • trp operon - tryptophan is high - acts as corepressor
    • repressor binds to operator when 2 tryptophans bound to it - stop making tryptophan
21
Q

Transciption factors

A
  • Eukaryotes
  • search DNA for DNA binding motifs
  • DNA binding domain - binds specific sequence in promoter region or DNA response element
  • Activation domain - binds other transcription factors and regulatory proteins
22
Q

Gene Amplification

A
  • increase transcription due to hormones, growth factors, intracellular conditions
  • Enhancers - several response elements (DNA sequences) grouped together to cause increase in transcription
    • form hairpin turn in DNA to mean up with promoter region
    • enhancer binds transcription factors that cooperate with the promoter region transcription factors
  • Gene duplication - can duplicate to have many duplicates on one chromosome
23
Q

Chromatin Structure

A
  • Heterochromatin - tightly coiled DNA, dark under microscope
  • Euchromatin - looser, light under microscope
    • genes are active
  • Histone acetylation - histone acetylase, acetylate lysine residue on histone proteins
    • decreases positive charge and weaken interaction with DNA
    • open chromatin and easier access
    • histone deacetylase - closes chromatin to decrease expression
  • DNA methylation - DNA methylase - add methyl group to cytosine and adenine
    • silences gene expression
    • heterochromatin is more methylated

MCAT Biochemistry (10 decks)

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