What is the one-gene, one-enzyme hypothesis?
It claimed that each gene contained contains the
information required to make one enzyme.
What was the experimental evidence that supported this hypothesis?
Since arginine is synthesized in a metabolic pathway
with compounds called Ornithine and Citrulline as intermediaries
leading to argnine, Srb and Horowitz isolated mutant N. crassa
genes that cannot synthesize arginine and grow each type of mutant
on four different mediums
Medium not supplemented (No ornithine, citrulline,
Supplemented with ornithine (No citrulline, or
Supplemented with citrulline (No ornithine, or
Supplemented with arginine (No ornithine, or
The mutant cells were able to grow in some of these
media but not others and therefore fell into three distinct
classes each lacking a specific enzyme in the metabolic
What is the Central Dogma? Explain in words, and illustrate in
States that the sequence of bases in DNA specifies
the sequence of bases in an RNA molecule, which specifies the
sequence of amino acids in a protein.
Which of the steps in information flow within the cell
involves the transcription of information? Which involves
translation from one �language� to another? What are the principal
enzymes and molecules involved in these processes?
DNA is transcribed to RNA by RNA
Messenger RNA is translated into proteins by
Describe two exceptions to the central dogma.
Many genes code for RNA molecules that do not
function as mRNA and therefore are not translated into
In some cases, information flows from RNA back to
Explain the relationship between genotype and phenotype.
An organism�s genotype is determined by the sequence
of bases in its DNA while its phenotype is a product of the
proteins it produces.
Genotype is influenced DNA which is turned into
proteins which go on to influence phenotype.
How could a change in the base sequence of a gene lead to a
change in the phenotype of an organism?
A change in base sequence of a gene will cause a change in mRNA
sequence which changes the proteins that are synthesized and that
could cause changes in the phenotype of an organism.
Give two examples of how single amino acid substitutions can
affect protein function and the phenotype of an organism. [Refer to
section 3.2 on protein structure.]
A change in base sequence of a gene will cause a
change in mRNA sequence which changes the proteins that are
synthesized and that changes the phenotype of an organism.
In some individuals, hemoglobin has a valine instead
of a glutamate and this causes hemoglobin molecules that stick to
How can the 4 nucleotides present in DNA code for the 20
different amino acids found in proteins? How many
bases would be needed in a codon if there were five RNA bases
instead of four?
There are four different bases of ribonucleotides and a one
base code could specify for four different amino acids, but a three
base code could specify for 64 different amino acids which is more
than the required 20. The genetic code is redundant
and more than one triplet of bases might specify for the same
amino acid. Opens up the double helix and synthesizes
mRNA on the inside and is then closed back up Only
two bases would be needed.
What is a reading frame, and why is it important in translation?
A reading frame is the sequence of codons and it is
important because a single addition or deletion of a base in DNA
causes a loss in gene function.
When three bases were added or deleted, functional
proteins were produced.
Where in messenger RNA does protein synthesis begin and end?
Is there an amino acid that stops protein synthesis?
The start codon AUG signals that protein synthesis
should begin and the stop codons UAA, UAG, and UGA signal that the
protein is complete.
No, the stop codons end the translation.
List the key properties of the genetic code. What do these
Redundant: all amino acids except for methionine and
tryptophan are coded by more than one codon
Unambiguous: a single codon never codes for more than
one amino acid
Non-overlapping: once the ribosome locks on to the
first codon, it then reads each separate codon one after
Nearly universal: with a few minor exceptions, all
codons specify the same amino acids in all organisms
Conservative: when several codons specify the same
amino acids, the first two bases in those codons are almost
If a mutation or an error in translation or
transcription affects the third position in a codon, it is less
likely to change the amino acid in the final
Are all mutations deleterious to an organism? Explain.
No, some mutations can either neutral or beneficial
to an organism.