1. How an Organism’s
DNA Genotype
Produces Its
Phenotype

2. • Genotype- genetic make-up; the
sequence of nucleotides
• Phenotype- organism’s specific traits
• The chain of command is from DNA in the nucleus of the cell to
RNA to protein synthesis in the cytoplasm
Two Major Stages
 Transcription- the transfer of genetic
information from the DNA into an RNA
molecule
 Translation- the transfer of the information in
the RNA into a protein

3. Gene- Enzyme- Protein- Polypeptide
• One Gene- One Enzyme
 Archibald Garrod- suggested that genes dictate phenotypes
through enzymes, the proteins that catalyze chemical processes
(1909).
 George Beadle and Edward Tatum- formulated the one gene-
one enzyme hypothesis (the function of an individual gene is
dictated the production of a specific enzyme)
• One Gene- One Protein
 The one gene- one protein hypothesis was modified and
extended beyond enzymes to include all types of proteins.
• One Gene- One Polypeptide
 It was discovered that many proteins have one or more different
polypeptide chains, and each polypeptide is specified by its own
gene.

4. To understand how genetic
information passes from genotype to
phenotype, we need to see how the
chemical language of DNA is
translated into the different chemical
language of polypeptides.

5. From Nucleotide Sequence to Amino
Acid Sequence: An Overview
• DNA & RNA- polymers made
of monomers in specific
sequences that carry
information in English.
 In DNA the monomers are four
types of nucleotides, which
differ in nitrogenous bases (A,
T, C and G).
 In RNA the same is true
although it has U instead of T.

6. Specific sequences of bases, each with
a beginning and an end, make up the
genes on a DNA strand. A typical gene
consists of thousands of nucleotides, and
a DNA molecule may contain thousands of
genes.

7. Transcription
• Process when DNA is transcribed and the
results to RNA molecule.
 Because the nucleic acid language of DNA has simply
been rewritten (transcribed) as a sequence of bases of
RNA; the language is still that of nucleic acids.
Translation
• Conversion of nucleic acid into the
polypeptide language
 polypeptides are polymers, but the monomers that make
them up- the letters of the polypeptide alphabet- are 20
amino acids common to all organisms

8. Triplet Code
• Basis of the flow of information from gene
to protein.
• The smallest “words” of uniform length
that can specify al the amino acids.

9. Codons
• The genetic instructions for the amino acid
sequence of a polypeptide chain are
written in RNA and DNA as a series of
three-base words called codons.
• 1st codon was deciphered in 1961 by
Marshall Nirenberg

10. The Dictionary of the Genetic
Code (Listed by RNA codons)
• Triplet AUG has a dual
function
 Codes for amino acid
methionine (Met)
 Provide signal for the start
of polypeptide chain.
• Three of the other codons do
not designate amino acids.
They are the stop codons that
instruct the ribosomes to end
the polypeptide (UAA,UAG,
UGA)
• Tryptophan (Trp)- the only
codon for the amino acid (but
most amino acids are specified
but two or more codons)

11. The Genetic Code
• The set of rules relating nucleotide
sequence to amino acid sequence.
• Notice in the dictionary that there is
redundancy but no ambiguity.
 For example, although codons UUU and UUC both
specify phenylalanine (redundancy), neither of them ever
represents any other amino acid (ambiguity).

12. Transcription: From DNA to RNA
• An RNA molecule is transcribed from a
DNA by a process similar to DNA
replication.
• RNA polymerase- the transcription
enzyme that links the RNA nucleotides.
3 Stages
Initiation of Transcription
RNA Elongation
Termination of Transcription

13. Initiation of Transcription
• Promoter- nucleotide sequence signaling
the start of transcription which is located at
the start of the gene
– a specific place where RNA polymerase
attaches.
– dictates which of the two strands is to be
transcribed.
• Initiation- 1st phase; the attachment of
RNA polymerase to the promoter and the
start of RNA synthesis.

14. RNA Elongation
• Elongation- 2nd phase; RNA grows longer
• The RNA strand peels away from its DNA
template, allowing two separated DNA
strands to come back together in the
region already transcribed.

15. Termination of Transcription
• Termination- 3rd phase; RNA polymerase
reaches a special sequence of bases in
the DNA template.
• Terminator- term for the special sequence
that the RNA reaches.
– Signals the end of the gene
• The polymerase molecules detaches from
the RNA molecule and the gene.

16. The transcription of an
entire gene occurs in 3
phases.
As RNA nucleotides
base-pair one by one
with DNA bases on one
DNA strand (called the
template strand), the
RNA polymerase links
the RNA nucleotides
into an RNA Chain. The
green shape in the
background is the RNA
polymerase.

17. The Processing of Eukaryotic RNA
• Messenger RNA (mRNA)- the result of
transcription in prokaryotic cells, wherein
RNA transcribed from the gene immediately
functions as the messenger molecule.
• RNA Processing- or modification on RNA in
transcribed in eukaryotic cells before
translation
• Thru these processes the “final draft” of the
eukaryotic mRNA is ready for translation

18. RNA Processing
• Capping- addition of extra nucleotides to
the ends of the RNA transcript.
 Cap and Tail- the additions; protects the RNA fro attack
by cellular enzymes and help ribosomes recognize the
RNA as mRNA.
• Tailing- made by noncoding stretches of
nucleotides that interrupts the nucleotides
that actually code for amino acids.
 introns- internal noncoding regions
 extrons- the coding region; the parts of the gene that are
expressed.

19. • RNA splicing- The process before the
RNA leaves the nucleus, the introns are
removed and the exons are joined to
produce an mRNA molecule with a
continuous coding sequence.