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UNIT 2 (Nucleic acids (DNA (The structure of DNA is a double helix model,…

- - - - A sugar with 5 carbon atoms which can be a ribose or a deoxyribose
      - A phosphate group
      - A nitrogenous base. Types: adenine (A), guanine (G), cytosine (C)), thymine (T) and urcail (U)
  - - - It is made up of two chromatin fibres called sister chromatids joined together in the centromere.
      - Types
        
        Metacentric: the centromere is in the middle of the chromosome and the arms have the same lenght
        
        Submetacentric: the centromere is further to one side and the arms are slightly inequal in lenght
        
        Acrocentric: the centromere is near one of the ends of the chromosome, making the armes very unequal
        
        Telocentric: the centromere is at the end of the chromosme, which makes visble only one arm.
      - They are structures formed by the condensation of the chromatin that appears when the cell is about to divide
      - Number of chromosomes
        
        The chromosomes are homologus in equal pairs of two
        
        Types
        
        Dipolid organisms: they have two sets of chromosomes or 2n.
        
        Hapolid organisms: they have a single set of chromosomes or n.
- - - - The DNA strand opens up and two strands are formed, one of them is used as a template to the the mRNA, which is formed by nucleotides with nitrogenous bases that are complementary to those in the DNA chain
      - The strand of mRNA separates form the DNA and leaves the cytoplasm, in this way, a transcription is transferred
      - The information stored in DNA is transferred to a mRNA molecule
    - - In the cytoplasm, the mRNA bonds to the ribosomes and the amino acids nond to the tRNA which transfers each amino acid to the mRNA.
      - Each aa recognises a specific codon and links to it to create a protei chain. Oncve all the mRNA chain has been read, the protein separates from the ribosome.
  - - - It is degenerate, most of the aa have more than one codon
      - It has codons that don't code for any aa, these are called termination codons. When the ribosmoe finds one of them, it separates from the RNA and ends the process
      - It is universal, in other words, it's identical in all living things
      - In most cases, AUG is the start codon.