8.3 - Structures of Ribonucleic Acid

• what does messenger RNA (mRNA) do?

  transfers DNA code from nucleus to ribosomes in the cytoplasm

  leaves nucleus via nuclear pores because it's small enough
• what's a codon?

  sequence of 3 buses on mRNA that codes for a single amino acid
• what's a genome?

  complete set of genes in an organism
• what's a proteome?

  the full range of proteins produced by the genome

  sometimes called complete proteome where proteome means the proteins produced by a given type of cell under certain conditions
• RNA Structure

  polymer made of mononucleotide monomers, single stranded

  each mononucleotide is made of ribose (pentose sugar), organic bases ( A, G, C, U) and a phosphate group
• types of RNot in protein synthesis

  messenger RNA (mRNA)

  transfer RNA (tRNA)
• structure of mRNA

  single polynucleotide strand

  base sequence is determined by sequences of bases on a length of DNA in transcription
• what does mRNA do?

  leaves nucleus via nuclear pores and associates with ribosomes & acts as a template for protein synthesis
• how is mRNA Structure suited to its function?

  contains genetic information as codons and sequence of Codons determines amino acid sequence Of polypeptide

  small & single stranded so can leave the nucleus via nuclear pores
• What is tRNA?

  a small molecule made of around 80 nucleotides
• structure of tRNA

  single polynucleotide strand folded into a clover shape with one and extending more (where amino acid can attach - amino acid binding site)

  hydrogen bonds hold molecule in shape

  on the opposite end there's a sequence of 3 bases (anticodon) complementary to codon on mRNA
• why must there be as many tRNA molecules as there are coding triplets?

  because the genetic code is non-overlapping- each triplet codes for just one amino acid

  so each tRNA is specific to one aminoacid & has an anticodon specific to that amino acid
• What's the function of tRNA?

  carry amino acids to growing polypeptide chain

  translation
• how is ERNA structurally suited to its role?

  has anticodon which is complementary (base pairing) with codon of MRNA

  has end chain for attaching amino acids so can carry them to growing polypeptide chain
• comparing DNA, mRNA & tRNA - polynucleotide chain

  DNA: double polynucleotide chain

  mRNA: Single polynucleotide chain

  tRNA: single polynucleotide chain
• comparing DNA, mRNA & tRNA - size largest to smallest

  DNA

  mRNA

  tRNA
• comparing DNA, mRNA & tRNA - shape

  DNA: double helix

  mRNA: single helix

  tRNA: clover shaped
• comparing DNA, mRNA & tRNA - pentose sugar

  DNA: deoxyribose

  mRNA & tRNA: ribose
• comparing DNA, mRNA & tRNA - organic bases

  DNA: A, T, C, G

  mRNA & tRNA: A, U, C, G
• comparing DNA, mRNA & tRNA - location

  DNA: Nucleus

  mRNA & tRNA : manufactured in the nucleus but found throughout cell
• comparing DNA, mRNA & tRNA - quantities

  DNA: constant for all cells of a species exept gametes

  mRNA & tRNA: varies from cell to cell & with level of metabolic activity
• comparing DNA, mRNA & tRNA - most to least stable 


  DNA, tRNA, mRNA