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*Central Dogma

de Taza, Kaizette Mieje L.
de Leoz, Maria Sabrina C.
AAPD2F
*Central Dogma
       
           Click to edit the
           outline text format
           
               Second Outline
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                         Outline
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*Central Dogma
* Within each cell the genetic information flows from
  - DNA to RNA to protein.
* This flow of information is unidirectional and
  irreversible.
* The information carried within the DNA dictates the end
  product (protein) that will be synthesized.
  - This information is the genetic code.
* Conversion of DNA encoded information to RNA
  -is called transcription.
* The information from a mRNA is then translated to an
  amino acid sequence in the corresponding protein
*Proteins
*Building blocks are Amino acids

*AA’s are joined between the carboxyl end
 of one AA to the amino group of the other
 – One water molecule is lost
 – Enzyme called peptidyl transferase is involved
*Protein Structures
*Four Levels Protein
      Structure
*Deducing the Genetic
                       Code it was a mystery
*Before the genetic code was cracked,
 as to how four nucleotides could encode for 20 amino
 acids.


*One or two nucleotides representing each amino acid
 would not suffice
 – A one-letter code could specify four amino acids
 – A two letter code could specify 16 (42 = 16)
 – To accommodate 20, at least three letters are needed (43 = 64)


*therefore 3 letters to a codon was the most likely
 option
* Reversion of a deletion frameshift
 mutation by a nearby addition mutation
*The Genetic Code is a
                 triplet different mutants in the
                              code
*   Recombination between two
    same position resulted in wild-type E.Coli:
    – One codon consists of more than one nucleotide.


* The addition of 3 nucleotides results in 1 additional
    amino acid in the protein


*The deletion of 3 nucleotides results in 1 less amino
    acid in the protein
Central dogma
* Most amino acids are encoded
            by multiple codons
*There are potentially 64 codons, and only 20
 amino acids.


* If each amino acid is encoded by only one codon,
 – there would be 44 codons which would not code for
 any amino acid.


* This would imply that more than 50% of the time,
 a frame shift would result in a codon that would
 be a ‘nonsense’ codon.
 – This was contrary to experimental observations
*Characteristics of the
                Genetic Code
*It is a triplet code.
 – Each three-nucleotide codon in the mRNA specifies one amino
 acid


*It is comma free.
 – mRNA is read three bases at a time without skipping any bases.


* It is non-overlapping/non-ambiguous.
 – Each nucleotide is part of only one codon and is read only once
 during translation.


*It is almost universal.
 – In nearly all organisms, most codons have the same amino acid
*It is degenerate.
 – Of 20 amino acids, 18 are encoded by 2 or more
 codons.
*The code has start and stop signals.
 – AUG is the usual start signal and defines the
 open reading frame.
* Stop signals are codons with no
 corresponding tRNA
 – the nonsense or chain-terminating codons.
 – generally three stop codons: UAG, UAA, and
 UGA.
*The
         Genetic
           Code

    Click to edit the outline text
    format
     
         Second Outline Level
           −   Third Outline Level
                  
                      Fourth Outline
                      Level
                        −   Fifth Outline
                            Level
                        −   Sixth Outline
                            Level
                        −   Seventh
                            Outline
*The Genetic Code Is
  Non-Overlapping
*Universality of the
                  Genetic Code
* All living beings use the same genetic code.
* Genetic code evolved early in life, and has remained
 constant over billions of years because of the lack of
 tolerance for change.
* Some exceptions exist:
 – in some ciliates, there is only one nonsense codon.
* In eukaryotic mitochondria, there are some changes:
 – e.g.: in yeast, CUA codes for Thr instead of Leu.
* The impact of this change in these organisms/organelles
 may not be as drastic, since there are very few proteins
 encoded by these systems, allowing evolution of the
 genetic code.
*Thank You!

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Central dogma

  • 1. *Central Dogma de Taza, Kaizette Mieje L. de Leoz, Maria Sabrina C. AAPD2F
  • 2. *Central Dogma  Click to edit the outline text format  Second Outline Level − Third Outline Level  Fourth Outline Level − Fifth Outline Level − Sixth Outline Level − Seventh
  • 3. *Central Dogma * Within each cell the genetic information flows from - DNA to RNA to protein. * This flow of information is unidirectional and irreversible. * The information carried within the DNA dictates the end product (protein) that will be synthesized. - This information is the genetic code. * Conversion of DNA encoded information to RNA -is called transcription. * The information from a mRNA is then translated to an amino acid sequence in the corresponding protein
  • 4. *Proteins *Building blocks are Amino acids *AA’s are joined between the carboxyl end of one AA to the amino group of the other – One water molecule is lost – Enzyme called peptidyl transferase is involved
  • 7. *Deducing the Genetic Code it was a mystery *Before the genetic code was cracked, as to how four nucleotides could encode for 20 amino acids. *One or two nucleotides representing each amino acid would not suffice – A one-letter code could specify four amino acids – A two letter code could specify 16 (42 = 16) – To accommodate 20, at least three letters are needed (43 = 64) *therefore 3 letters to a codon was the most likely option
  • 8. * Reversion of a deletion frameshift mutation by a nearby addition mutation
  • 9. *The Genetic Code is a triplet different mutants in the code * Recombination between two same position resulted in wild-type E.Coli: – One codon consists of more than one nucleotide. * The addition of 3 nucleotides results in 1 additional amino acid in the protein *The deletion of 3 nucleotides results in 1 less amino acid in the protein
  • 11. * Most amino acids are encoded by multiple codons *There are potentially 64 codons, and only 20 amino acids. * If each amino acid is encoded by only one codon, – there would be 44 codons which would not code for any amino acid. * This would imply that more than 50% of the time, a frame shift would result in a codon that would be a ‘nonsense’ codon. – This was contrary to experimental observations
  • 12. *Characteristics of the Genetic Code *It is a triplet code. – Each three-nucleotide codon in the mRNA specifies one amino acid *It is comma free. – mRNA is read three bases at a time without skipping any bases. * It is non-overlapping/non-ambiguous. – Each nucleotide is part of only one codon and is read only once during translation. *It is almost universal. – In nearly all organisms, most codons have the same amino acid
  • 13. *It is degenerate. – Of 20 amino acids, 18 are encoded by 2 or more codons. *The code has start and stop signals. – AUG is the usual start signal and defines the open reading frame. * Stop signals are codons with no corresponding tRNA – the nonsense or chain-terminating codons. – generally three stop codons: UAG, UAA, and UGA.
  • 14. *The Genetic Code  Click to edit the outline text format  Second Outline Level − Third Outline Level  Fourth Outline Level − Fifth Outline Level − Sixth Outline Level − Seventh Outline
  • 15. *The Genetic Code Is Non-Overlapping
  • 16. *Universality of the Genetic Code * All living beings use the same genetic code. * Genetic code evolved early in life, and has remained constant over billions of years because of the lack of tolerance for change. * Some exceptions exist: – in some ciliates, there is only one nonsense codon. * In eukaryotic mitochondria, there are some changes: – e.g.: in yeast, CUA codes for Thr instead of Leu. * The impact of this change in these organisms/organelles may not be as drastic, since there are very few proteins encoded by these systems, allowing evolution of the genetic code.