Please enable JavaScript.

Coggle requires JavaScript to display documents.

DNA (3.4.2 DNA + Protein Synthesis (Protein synthesis (Translation (In…

- - - - Messenger RNA (mRNA)
        
        Linear single strand
        Length depends on length of gene
        
        Formed in the nucleus of the cell by transcription of a DNA template by RNA polymerase
        Passes into cytoplasm where it is translated into a protein on the ribosomes
      - Transfer RNA (tRNA)
        
        Small single strand
        At least 20 different types (20 amino acids)
        
        Held in precise 3-D shape by internal hydrogen bonds
        Flattened = clover-leaf shape
        Normal, each base-paired region twisted to form a double helix
        Overall L-shaped molecule
        
        One free end of the molecule has a binding site for an amino acid
        Other end has Anticodon = 3 bases y which tRNA binds to codon of mRNA during translation
        Amino acid is specific to anticodon
      - Ribosomal RNA (rRNA)
        Makes up part of the structure of ribosomes
  - - - Genome = Complete set of genes in a cell
      - Proteome = Complete set of proteins which a cell is able to make
      - Sequence of bases on the DNA determines the order of amino acids in a protein
    - - Each set of 3 base = triplet codon
      - Degenerate: Some amino acids coded for by more than 1 codon
      - Some codon are start + stop signal, don't produce amino acid
        Start = AUG = Methionine - Removed from protein in Golgi
      - Universal code: same code in all living organisms
      - Non-overlapping: Each base part of 1 codon
  - - - Takes place in nucleus
      - DNA helicase breaks hydrogen bonds
        Unwinds DNA molecule at site of gene to be transcribed
        Bases exposed
      - Sense strand used as template to produce complementary mRNA
        RNA polymerase Indy to promoter
        Active RNA nucleotides found in nucleus hydrogen bond to exposed bases using rules of complementary base pairing
      - RNA polymerase joins nucleotides by condensation reactions to form sugar-phosphate backbone
        RNA polymerase reaches stop codon + detaches
        DNA returns to helical form
    - - Pre-mRNA formed needs to be processed to mRNA
      - Introns removed by RNA splicing:
        Complex of snRNP's attach to pre-mRNA at start + end of introns forming spliceosome complex
        mRNA bends + Introns forms loop
        Enzymes in complex cut RNA at start + end of intron
        Another enzyme joins exons together
        Only exons = mature mRNA
    - - At one end is an amino acid binding site
        At the other end is the anticodon
        Each tRNA molecule can only bind with a specific amino acid under the control of a specific enzyme
      - An amino acid bins to the active site of a specific enzyme
        ATP also binds to the active site
        AMP is linked to the swing acid with 2 Pi being released
        Creates correct shape in active site for specific tRNA to bind
        Amino acid transferred onto tRNA with AMP released
        Anticodon determines which tRNA can fit
    - - 2 ribosome sub-units lock onto ribosome binding site
        mRNA bound to small sub-unit so 2 codons exposed to large sub-unit in the P site + A site
      - First mRNA codon AUG recognised by tRNA with UAC anticodon
        Codon + anticodon hydrogen bond + Methionine starts chain
        Second complementary tRNA hydrogen bonds to next codon
      - Peptide Bond forms between amino acids
        Catalysed by Peptidyl Transferase enzyme in small sub-unit
      - Ribosome moves along mRNA to next codon
        Complementary tRNA anticodon H bonds + Peptide bond forms
        tRNA from first amino acid released into cytoplasm
      - Continues until ribosome reaches stop codon (release factor)
        Ribosome released
      - Polypeptide chain leave ribosome + is processed
        Takes up secondary + tertiary structure
        Further processing adds several chains = Quaternary structure
      - In general
        
        If a protein will be used in the cell it is synthesised on free ribosomes then released into cell cytoplasm
        
        Proteins for export are synthesised on ribosomes attached to rough ER then passed into ER + transported to Golgi for processing + packaging into vesicles for release
        
        As a ribosome is moving along a mRNA molecule, the free end becomes associated with another ribosome
        Any ribosomes translating same mRNA simultaneously increases rate of protein production
- - - - Can carry a large amount of information
    - - Each nucleotide consists of:
        Deoxyribose (pentose sugar)
        Phosphate group
        Organic/Nitrogenous base (adenine, thymine, cytosine, guanine)
      - Linked by condensation reactions
        Phosphate-sugar backbone held together by covalent phosphodiester bonds
    - - 2 helical polynucleotide chains coiled around each other
      - Chains run anti-parallel
      - Chains held together by hydrogen bonds between bases (A-T + C-G)
        Provide cumulative strength
        Easily broken so code can be accessed
      - Order of bases on each chain is unrestricted = unlimited code
      - Highly coiled + compact
        Supercoiling around histone proteins
      - Strong covalent phosphodiester bonds
        Stable + not easily corrupted
        H bonds protected inside molecule
      - Specific base pairingvallows for exact replication by semi-conservative method
  - - - Used Chemical components from smooth, pneumonia causing strain of bacteria to transform rough bacteria which did not cause pneumonia
        Purified DNA caused transformation
        Transforming ability destroyed when treated with DNAase
    - - Label protein capsule with radioactive sulfur + DNA with radioactive phosphorus, in separate bacteriophages
        Infect bacteria
        Mixed in blender so bacteria protein coats break off
        Centrifuged
        Some infected bacteria contained radioactive P
        None contained radioactive S
        Must be DNA that is passed on
- - - - DNA helicase breaks hydrogen bonds between polynucleotide chains, with energy from ATP, causing them to separate
        Each strand acts as a template
        Following specific rules of complementary base pairing, free activated nucleotides in the nucleus hydrogen bond to exposed bases
        DNA polymerase joins nucleotides by condensation reactions to form covalent phosphodiester bonds, creating backbone
        DNA polymerase can only add nucleotides onto 3' end as this has complementary shape to active site of enzyme
        New strand synthesised 5'->3' direction
        Leading strand is synthesised continuously
        Lagging strand synthesised discontinuously
    - - Produced "heavy" DNA using N15
        Transferred onto medium containing N14
        Left to replicate for 1/2/3 etc generations
        Remove sample after each generation
        Density of DNA analysed
      - Parental DNA heavy
        1 gen = middle band (hybrid)
        2 gen = light band + hybrid band