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DNA (Proteins involved in replication and repair (Helicases (Enzyme that…

- - - - Makes strands available as template strands
  - - - Relieving the strain caused by unwinding
  - - - Restoring their original length and compensating for the shortening that occurs during cell replication
- - - - The cell keeps all 20 amino acids by synthesizing them from other compounds or by taking them up from the surrounding solution
    - - Base-pairs with a complementary codon on mRNA
    - - Enzymes that match up the correct tRNA and amino acid
    - - Aminoacyl-tRNA (A site)
        
        Holds the tRNA carrying the next amino acid to be added to the chain
      - Exit site (E site)
        
        Discharged tRNAs leave the ribosome from the site
      - Peptidyl-tRNA (P site)
        
        Holds the tRNA carrying the growing polypeptide chain
  - - - Codon recognition
        
        The anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site
      - Peptide bond formation
        
        A rRNA molecule catalyzes the formation of a peptide bond between the amino group of the new amino acid in the A site and the growing polypeptide in the P site
      - Translocation
        
        The ribosome translocates the tRNA in the A site to the P site and the empty tRNA is moved to the E site
    - - Elongation continues until a stop codon in the mRNA reaches the A site of the ribosome
        
        Hydrolysis breaks the bond between the completed polypeptide and the tRNA in the P site
        
        The polypeptide is released through the exit tunnel of the ribosome's large subunit
    - - Brings together mRNA, a tRNA bearing the first amino acid of the polypeptide, and two subunits of a ribosome
        
        The ribosomal subunit binds to a molecule of RNA and an initiator tRNA with an anticodon pairs with the codon in the RNA
        
        The tRNA carries an specific amino acid
      - In bacterial cells:
        
        mRNA binding site on the subunit recognizes a specific nucleotide sequence on the mRNA upstream of the start codon
- - - - DNA strands unwind and the polymerase initiates RNA synthesis at the start point on the template strand
    - - The polymerase elongates the RNA transcript 5'-->3'
        
        During the process, DNA strands re-form a double helix
    - - The RNA transcript is released and the polymerase detaches from the DNA
        
        Pre-mRNA is produced
    - - Separates two strands of DNA and joins RNA nucleotides complementary to the DNA template strand
        
        Assembles a polynucleotide in its 5'-->3' direction
        
        Can start a chain from scratch (they don't need a primer)
      - RNA polymerase attaches to the promoter, which is a specific sequence of nucleotides where transcription begins
- - - - When the cell is not dividing, chromatin exist in its dispersed form
  - - - Each chromosome consists of a DNA molecule and associated with proteins
- - - - The 5' end receives a 5' cap, a modified form of a guanine nucleotide added after transcription of the first 20-40 nucleotides
        
        Facilitate the export of the mature mRNA
        
        Protect mRNA from degradation by hydrolytic enzymes
      - At the 3' end, an enzyme adds 50-250 more adenine nucleotides forming a poly-A tail
        
        Help ribosomes attach the 5' end pf the mRNA once it reaches the cytoplasm
    - - Removal of large portions of RNA molecule
        
        Introns
        
        Noncoding segments of nucleic acid that lie in the coding regions
        
        Exons
        
        Coding regions that are eventually expressed by being translated into amino acid sequences
      - Spliceosome
        
        Several snRNPs joined with additional proteins
        
        snRNPs recognize the splice sites
        
        Cuts pre-mRNA releasing the intron for degradation and splices the exons together releasing mRNA that only contains exons
    - - RNA molecules that function as enzymes
        
        Such as a intron that catalyzes its own removal during RNA splicing
- - - - Pentose sugar called deoxyribose
      - A phosphate group
      - A nitrogenous base
        
        Guanine
        
        Thymine
        
        Cytosine
        
        Adenine
        
        The number of A and T bases are equal and the number of G and C bases are equal
        
        The base composition varies between species
        
        A purine will pair with a pyrimide
    - - Composed of two strands
        
        Hydrogen bonds hold one strand to the other
      - Strands are antiparallel
        
        Oriented in opposite directions
        
        The 5' end and the 3' end refer to the numbers assigned to the carbons in the sugar ring
  - - - Offspring inherit DNA from both parents
        
        This is due to DNA replication
    - - DNA carries hereditary material rather than the proteins
      - Transformation
        
        Change in phenotype and genotype due to the assimilation of external DNA by a cell