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Part 3: The Continuity of Life How Genes Work Review
  1. DNA is made of molecules which are composed of . Each nucleotide has a central , a group and a base.
     
     
     
     
  2. The physical structure of DNA is a double : two strands of twisted around each other.
     
     
     
     
  3. DNA involves these steps:
     
     
     
     
     
     
     
     
  4. A simplistic model of cellular communication called the central views the genetic information flow from to in two steps: transcription and translation, resulting in the of a gene.
     
     
     
     
  5. Transcription takes place in the .
     
     
     
     
    • RNA binds to a region on the DNA called the to assemble a RNA transcript which contains coding regions called and noncoding regions called .
       
       
       
       
    • The exons are together to form mature RNA (mRNA) which exits the nucleus.
       
       
       
       
    • Sequences of 3 nucleotides on the mRNA serve as to translate the genetic code into sequences of acids, using a genetic .
     
     
     
     
  6. Translation takes place in the on .
     
     
     
     
    • The ribosome binds mRNA; in turn a RNA (tRNA), whose is complementary to the on the mRNA, binds to the complex.
       
       
       
       
    • The tRNA moves from the site to the site and exits at the site, adding a specific amino acid to the growing chain, until a codon on the mRNA is reached.
       
       
       
       
     
     
     
     
  7. Gene expression can be turned on or off by regulating access to the , which controls a cluster of genes that are transcribed together as a unit called an , as shown in prokaryotes.
     
     
     
     
    • The inducible lac operon is turned off in the absence of lactose when a binds to the . When lactose is present, the operon is turned on when acts as an inducer by inactivating the .
     
     
     
     
  8. A mutation is a change in the , due to errors in DNA or to damage from physical or chemical agents called .
       
       
       
       
    • Mutations that change a single base pair are called mutations caused by base .
       
       
       
       
    • Insertions and deletions can affect the reading and lead to mutations that affect large sections of the protein.
       
       
       
       
    • Some genes can move from one place on the chromosome to another through and result in either a mutated gene or abnormal of the gene.
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
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