RNA and Protein Synthesis

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  • RNA and Protein Synthesis
    • Types of RNA
      • Messenger: Made during transcription. Carries genetic code from DNA to ribosomes, used to make protein during translation. Single polynucleotide strand. Three adjacent bases in mRNA= codon
      • Transfer: Involved in translation. Carries amino acid to ribosomes. Single polynucleotide strand folded into clover shape. Hydrogen bonds between specific base pairs hold molecule in shape. every tRNA has specific sequence of three bases at one end called anticodon. Have amino acid binding site at other end
    • 1. Transcription
      • mRNA copy of gene made from DNA
      • Takes place in nucleus in eukaryotic cells
      • 1) RNA polymerase attaches to DNA at beginning of gene
      • 2) H bonds between two DNA strands break. Separates strands. DNA uncoils, exposing some bases
      • 3) One strand used as template to make mRNA copy
      • 4) RNA polymerase lines up free RNA nucleotides alongside exposed bases on template. Free bases attracted to exposed ones. Complementary base pairing means mRNA complementary copy of DNA template. T replaced with U
      • 5) Once RNA nucleotides paired up with complementary pairs, joined together by RNA polymerase- forming mRNA molecule
      • 6) RNA polymerase moves along DNA, separates strands- assembles mRNA strand
      • 7) Hydrogen bonds between uncoiled strands re form, strands coil back into double helix
      • 8) When RNA reaches DNA sequence called stop signal, stops making mRNA, detaches from DNA
      • 9) mRNA move sout of nucleus through nuclear pore, attached to ribosome
    • Eukaryotes/ Prokaryotes
      • Eukaryotes: Introns/exons both copied into mRNA. This is pre mRNA. Splicing occurs- introns removed, exons joined together, forms mRNA strands. Takes place in nucleus. mRNA leaves nucleus for translation
      • Prokaryotes: mRNA produced directly from DNA. No splicing
    • 2. Translation
      • Occurs in ribosomes/cytoplasm
      • Amino acids joined together to make polypeptide chain following sequence of codons carried by mRNA
      • 1) mRNA attaches itself to ribosome and tRNA molecules carryamino acids to it. ATP provides energy needed for bond between amino acid and tRNA molecule to form
      • 2) tRNA molecule carrying amino acid with anticodon complementary to first codon on mRNA attaches itself to mRNA by specific base pairing
      • 3) Second tRNA molecule attaches to next codon on mRNA in same way
      • 4) Two amino acids attached to tRNA joined by peptide bond. First tRNA moves away
      • 5) Third tRNA molecule bins to next codon on mRNA. Its amino acid binds to first two, second tRNA moves away
      • 6) Process continues, producing polypeptide chain until there is a stop signal on mRNA
      • 7) Polypeptide chain moves away from ribosme


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