Molecular Biology of the Gene
One gene-one enzyme hypothesis
● The function of a gene is to dictate the production of a specific enzyme
Revisions
● Not all proteins are enzymes
● (ex. Keratin and insulin are examples of non enzyme proteins)
One gene-one polypeptide hypothesis
● Proteins are constructed from two or more different polypeptide chains
● Each polypeptide is specified by its own gene
Revisions
● Eukaryote genes can each code for a set of closely related polypeptides via
alternative splicing
● Few genes code for RNA
How RNA differs
● Contains ribose as its sugar instead of deoxyribose
● Nitrogenous base contains uracil rather than thymine
● Normally single stranded
Information flow from Gene to Protein
● Normally described in linguistic terms
● Both nucleic acids and proteins are polymers with specific sequences of
monomers conveying information
Transcription
● Synthesis of RNA
● DNA strand provided as template making new complementary strand used for
translation
● mRNA created to bring info from nucleus to the ribosomes
Translation
● Synthesis of polypeptide
● Uses information in the mRNA
● Translates the nucleotide sequence of mRNA into an amino acid sequence
● Ribosomes are site of translation
, Transcription and translation
Bacteria
● Both processes occur in the cytoplasm
Eukaryotes
● Transcription occurs in the nucleus
● Translation occurs in the cytoplasm
Relationship Between linear Sequence of Codons and Amino acids in Polypeptide
Codon - mRNA nucleotide triplets
● Written in 5’ → 3’ direction
● Amino acids created from a sequence of 3 base pairs
● Amino acids formed along the chain in the same direction as the sequence
● 3x the amount of nucleotides than amino acids
Start with Methionine…
● Functions as start codon and an amino acid
● Signals protein synthesizing machinery to begin translating
Redundant genetic code
● Redundancy is not random
● Act as synonyms for particular amino acid
● Doesn’t express ambiguity
● (ex. GAA and GAG both code for glutamic acid, neither specifiys for another
amino acid)
Reading frame
● While translating codon is read in triplets
● Extracts intended message from symbols based on groupings
Evolutionary significance Universal genetic code
● Language shared by living things indicates they must been operating very early
in history
● Present in common ancestors of present-day organisms
Transcription beginning → RNA polymerase attaches and initiates transcription
Terms
One gene-one enzyme hypothesis
● The function of a gene is to dictate the production of a specific enzyme
Revisions
● Not all proteins are enzymes
● (ex. Keratin and insulin are examples of non enzyme proteins)
One gene-one polypeptide hypothesis
● Proteins are constructed from two or more different polypeptide chains
● Each polypeptide is specified by its own gene
Revisions
● Eukaryote genes can each code for a set of closely related polypeptides via
alternative splicing
● Few genes code for RNA
How RNA differs
● Contains ribose as its sugar instead of deoxyribose
● Nitrogenous base contains uracil rather than thymine
● Normally single stranded
Information flow from Gene to Protein
● Normally described in linguistic terms
● Both nucleic acids and proteins are polymers with specific sequences of
monomers conveying information
Transcription
● Synthesis of RNA
● DNA strand provided as template making new complementary strand used for
translation
● mRNA created to bring info from nucleus to the ribosomes
Translation
● Synthesis of polypeptide
● Uses information in the mRNA
● Translates the nucleotide sequence of mRNA into an amino acid sequence
● Ribosomes are site of translation
, Transcription and translation
Bacteria
● Both processes occur in the cytoplasm
Eukaryotes
● Transcription occurs in the nucleus
● Translation occurs in the cytoplasm
Relationship Between linear Sequence of Codons and Amino acids in Polypeptide
Codon - mRNA nucleotide triplets
● Written in 5’ → 3’ direction
● Amino acids created from a sequence of 3 base pairs
● Amino acids formed along the chain in the same direction as the sequence
● 3x the amount of nucleotides than amino acids
Start with Methionine…
● Functions as start codon and an amino acid
● Signals protein synthesizing machinery to begin translating
Redundant genetic code
● Redundancy is not random
● Act as synonyms for particular amino acid
● Doesn’t express ambiguity
● (ex. GAA and GAG both code for glutamic acid, neither specifiys for another
amino acid)
Reading frame
● While translating codon is read in triplets
● Extracts intended message from symbols based on groupings
Evolutionary significance Universal genetic code
● Language shared by living things indicates they must been operating very early
in history
● Present in common ancestors of present-day organisms
Transcription beginning → RNA polymerase attaches and initiates transcription
Terms
