Nucleic acids, ATP, Genetic information, Protein synthesis & Enzymes



  • Both are polynucleotides...
  • DNA
    • Two anti parallel strands
    • Very long
    • Adenine, cytosine, guanine and thymine
    • Store genetic infomation
  • RNA
    • One strand
    • Relatively short
    • Adenine, cytosine, guanine and uracil
    • Transfer genetic infomation & forms ribosomes with proteins

                                               Image result for DNA vs RNA

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DNA Double helix & replication

  • Polynecleotides are made up of nucelotide monomers joined togther by phosphodiester bonds (condensation reaction)
  • DNA double helix is held together by Hydrogen (H) bonds between complementary base pairs
    • 2 H bonds between Adenine and Thymine
    • 3 H bonds between Cytosine and Guanine
  • Semi-conservative replication hypothesis is where when DNA replicates the new DNA will have one strand which is the orginal and one which is new
    • DNA helicase breaks the H bonds between the base pairs
    • Free nucleotides complementary base pair to the exposed strands
    • DNA polymerase catalyses condensation reactions to join adjacent nucleotides, forming phosphodiester bonds

                                                  Image result for semi conservative dna

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  • ATP to ADP
    • Hydrolysis reaction, ATP hydrolase enzyme, releases energy
  • ADP to ATP       
    • Condenstaion reaction, ATP synthase enzyme, requires energy
  • The hydrolysis of ATP can be coupled to energy-requiring reaction and used to phosphorylate compounds
  • The condensation of ADP to form ATP can occur during respiration and photosynthesis                                                                                                                                                                     Image result for atp structure
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Genetic Infomation

  • In prokaryotic cells, DNA molecules are short, circular and not associated with proteins 
  • In eukaryotes, the nucleus conatins very long, linear DNA molecules associated with proteins called histones. Together they produce a chromosome.
  • The mitochondria and chloroplasts have their own DNA which is short, circular and not associated with a protein
  • Genome = full set of DNA found in an organism
  • Proteasome = full range of porteins that can be synthesised from the genome
  • Gene = a section of DNA that codes for polypeptides and functional RNA located at a fixed locus on a DNA molecule
  • Codon = 3 DNA bases which code for a specific amino acid
  • The genetic code is universal, non-overlapping and degenerate
  • In eukaryotes, sections of the nuclear DNA do not code for polypeptides (introns)
    • Exons are the sections of DNA that code for amino acid sequence
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Protein Synthesis

  • Transcription = the processes of makng messenger RNA from a DNA template
  • DNA helicase breaks theHydrogen bonds between the DNA helix, free RNA nucleotides base pair with the exposed DNA template strand
  • In prokaryotes transcription results directly in the production of mRNA from DNA
  • In eukaryotes, transcription results in the production of pre-mRNA; which is then spliced to form mRNA
  • Translation
    • the process of making proteins by forming a specific sequence of amino acids based on coded instructions in the mRNA
    • RNA polymerase catalyses phosphodiester bonds between adiacent RNA nucleotides and the mRNA strand detaches, allowing the DNA helix to reform
  • mRNA attaches to a ribosome on the RER, tRNA carries the corresponding amino acid to each codon on the mRNA one at a time, with an enzyme catalysing the formation of a peptide bond between the amino acids using ATP, until a stop codon is reached and the peptide is released, folding into its tertiary structure
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  • Enzymes are biological catalysts that speed up the rate of a reaction and remains unchanged and reusable at the end of the reaction. they lower the activation energy needed
  • The lock and key model proposed that each substrate is a key that only fits a specific lock or enzyme
    • The alternative induced fit model has been proposed
  • Induced fit
    • the specificity of enzymes is due to the tertiary structure of its active site
    • allowing complementary binding to substrates
  • Enzymes catalyse both intra and extracellular reactions that determine structure and functions from cellular to the whole organism
    • Catalase intracellularly breaks down hydrogen peroxide into water and oxygen
    • Amylase is secreted from the salivary glands and pancreas to extracellularly break down starch. Requires Cl- cofactor
    • Trypsin is secreted from the pancreas to extracellularly break down proteins
  • Some enzymes are made as inactive and require another enzyme to catalyse them
  • Some enxymes require a cofactor, which is a substance which must be present to enable an enzyme to catalyse a reaction at an appropriate rate
    • Coenzymes form temporary associations and are derived from vitamins
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Enzymes continued...

  • The temperature coefficent (Q10) for a specific reaction is the effect of a 10oc rise in temperature on the rate of reaction
  • Factors effecting enzynme activity include
    • pH
    • Temperature
    • Enzyme concentration
    • Substrate concentration
    • competitive and non competitive inhibitor concentration

Image result for enzyme structure a level biology active and allosteric site

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