7' Expression of Genetic Information 1

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7. Expression of Genetic Information (1)
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Relationship between Genes and Proteins

• The intermediates RNAs
• Assembled as complimentary copy of one strand of
  DNA
• RNA synthesis termed transcription
• Sequence retains the information of the gene

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Relationship between Genes and Proteins

• The intermediate messenger mRNA
• Use of mRNA allows separate information
• Storage
• Utilization
• mRNA moving into cytoplasm and serves as template
  for aa assembly into proteins
• Allows amplification of synthetic output

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Relationship between Genes and Proteins

• RNAs
• Proteins synthesized in the process of
  translation
• Participation of multiple components
• Including ribosomes
• Nonspecific components
• Composition
• Large and small subunits
• RNA and protein
• Assembled function disassembled
• ribosomal RNA (rRNA)
• Bind other molecules
• Structural support
• Catalyse linking of aa in formation of
  polypeptides

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Relationship between Genes and Proteins

• RNAs
• Transfer RNAs (tRNAs)
• Translate mRNA code into aa sequence of
  polypeptide
• tRNAs and rRNAs have long half-lives
• Complex secondary and tertiary structures
• Fold into complex 3-dimensional shapes
• Diverse array of functions
• Folding follows rules complementary base pairs
• Stems and loops
• Contain non-standard base pairs
• Contain modified nitrogenous bases

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Relationship between Genes and Proteins

• Transcription basics
• Process DNA information for synthesis of RNA
• Enzymes DNA-dependent RNA polymerases or RNA
  polymerases
• DNA provides the template
• First step association of RNA polymerase with
  DNA template
• Site on DNA which binds polymerase is termed the
  promotor
• RNA polymerases need help to recognize promotor

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Relationship between Genes and Proteins

• Transcription basics
• Helper proteins are transcription factors
• Promotor contains
• Binding site for polymerase
• Which DNA strand is transcribed
• Site of commencement of transcription
• Polymerase moves along DNA from 3 to 5
• DNA temporarily unwound
• RNA assembled from its 5 to 3
• DNA double helix reforms

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Relationship between Genes and Proteins

• Transcription basics

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Relationship between Genes and Proteins

• Transcription RNA Processing
• Eukaryotic cells 3 transcribing enzymes
• RNA polymerase I
• Larger rRNAs 28S, 18S, 5.8S
• Ribosomal RNAs
• RNA polymerase II
• mRNAs
• Small nuclear RNAs (snRNAs)
• RNA polymerase III
• Low mw RNAs
• tRNAs
• 5S rRNA
• Also some snRNAs

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Relationship between Genes and Proteins

• Transcription RNA Processing
• Transcription factors have multiple roles
• Binding of polymerases
• Initiation of transcription
• Elongation
• Termination

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Relationship between Genes and Proteins

• Transcription RNA Processing
• All three RNA types derived from precursor RNA
• Longer than the product
• Termed primary transcript or pre-RNA
• Associated with protein as they are synthesized
• Processed into smaller transcripts
• Processing assisted by small nuclear RNAs
  (snRNAs)

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs
• 80 of cellular RNA
• DNA codons repeated hundreds of times
• Called rDNA
• Clustered
• Human genome 5 clusters on different
  chromosomes
• Gathered into nucleoli
• Function in producing ribosomes

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs Synthesizing the precursor
• Genes on DNA in tandem arrangement

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs Synthesizing the precursor
• Each branch a nascent rRNA transcript
• Dark granule base of each fibril RNA
  polymerase I

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs Synthesizing the precursor
• Shorter fibrils closer to transcription
  initiation site
• Length of DNA between short and longest fibrils
  a single transcription unit

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs Synthesizing the precursor
• DNA fiber between transcription units
  nontranscribed spacer

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs processing the precursor
• Eukaryotic ribosomes have four distinct rRNAs
• Three in large subunit
• One in small subunit
• In humans
• Large subunit contains 28S, 5.8S 5S
• Small subunit contains 18S
• 28S, 18S and 5.8S derived from the pre-RNA
• 5S from separate RNA from outside nucleolus

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Relationship between Genes and Proteins

• Transcription RNA Processing
• rRNAs processing the precursor
• Two peculiarities of pre-RNA
• Large numbers of methylated nucleotides
• Psuedouridine residues
• All modifications occur posttranscriptionally
• Altered nucleotides at specific positions
• Clustered
• All altered nucleotides remain in final product
• Some unaltered nucleotide sections are discarded
• Function of altered domains unclear
• Protection from enzymatic cleavage
• May promote correct folding

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Relationship between Genes and Proteins

• Transcription rRNA Processing

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Relationship between Genes and Proteins

• Transcription rRNA Processing

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Relationship between Genes and Proteins

• Transcription rRNA Processing

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Relationship between Genes and Proteins

• Transcription rRNA Processing
• Role of small nucleolar RNAs (snoRNAs)
• Packaged with proteins to form small nucleolar
  ribonucleoproteins (snoRNPs)
• snoRNPS associate with rRNA before it is fully
  transcribed
• Two groups of snoRNAs
• U3 antisense
• Antisense forms an RNA duplex
• Recognition site for enzymes which modify pre-RNA

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Relationship between Genes and Proteins

• Transcription rRNA Processing
• Nucleolus also site for assembly of two ribosomal
  subunits
• Two types of proteins associated
• Proteins which remain in the ribosome
• Proteins which cleave RNA precursors and proteins
  which protect sites from cleavage

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Relationship between Genes and Proteins

• Transcription rRNA Processing
• Synthesis and processing of 5S rRNA
• Coded by a large number of genes outside of the
  nucleolus
• Transcribed by RNA polymerase III
• 5 end remains unchanged
• 3 end is truncated
• Following synthesis 5S rRNA is transported to
  nucleolus
• Incorporated into assembly of large ribosomal
  subunit

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Relationship between Genes and Proteins

• Transcription rRNA Processing