Protein synthesis

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  • Created by: Kayliss71
  • Created on: 31-05-18 08:55
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  • DNA,RNA & protein synthesis
    • DNA
      • Nuclear eukaryotic DNA is linear and associated with proteins
      • DNA is wound around histone proteins which help support the DNA, it is then coiled up very tightly to make a compact chromosome
      • Prokaryotic DNA is shorter and circular, it's not supported by histones. It condenses to fit in the cell by super coiling
      • DNA contains genes. A gene is a sequence of bases that code for a polypeptide or functional RNA
        • Functional RNA is RNA molecules that perform special tasks during protein synthesis (excludes mRNA)
      • In eukaryotic DNA genes that do code for polypeptides also contain sections that don't code for amino acids
        • Bits that do code are called exons
        • Bits that don't code are called introns and are removed during protein synthesis
      • Genes can exist in different forms called alleles, the order of the bases is slightly different so they code for slightly different versions of the same polypeptide
        • Alleles coding for the same characteristic will be found at the same locus on each chromosome in a homologous pair
    • RNA
      • There's more than one type of RNA
      • Messenger RNA is made during transcription. It carries the genetic code from the DNA to the ribosomes where its used to make a protein
      • Transfer RNA is involved in translation, it carries amino acids to the ribosomes. Its a single polynucleotide strand that's folded into a clover shape. Also has an anti codon at one end and an amino acid binding site at the other
    • Protein synthesis
      • Transcription is the first stage of protein synthesis
        • 1) Transcription starts when RNA polymerase attaches to the DNA at the beginning of a gene
        • 2) The hydrogen bonds between the DNA strands break and the DNA uncoils exposing some of the bases. One of the strands is then used as a template to make an mRNA copy
        • 3) The RNA polymerase lines up free RNA nucleotides alongside the exposed bases. Once the complementary bases are paired up with their specific bases they're joined together by RNA polymerase
        • 4) The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
        • 5) When RNA polymerase reaches a stop signal it stops making mRNA and detaches from the DNA. In eukaryotes mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm
      • Translation is the second stage of protein synthesis
        • 1) The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to it. ATP provides the energy to form the bond between the amino acid and tRNA
        • 2) A tRNA molecule attaches itself to the mRNA. A second tRNA molecule attaches itself to the next codon on the mRNA
        • 3) The two amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away leaving its amino acid behind. A third tRNA molecule binds to the next codon on the mRNA, its amino acids binds to the first two and the second tRNA molecule moves away
        • 4) This process continues, producing a chain of linked amino acids until there's a stop signal on the mRNA. The polypeptide chain moves away from the ribosome and translation is complete

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