AP Biology
Chapter 17 Guided Reading Assignment
1. What did Garrod mean by “inborn errors of metabolism?”
Garrod was the first to suggest that genes dictate phenotypes through enzymes that
catalyze specific chemical reactions in the cell. Garrod postulated that the symptoms
of an inherited disease reflect a person’sinability to make a particular enzyme.
2. Describe the Beadle and Tatum experiment with mold in detail – use the diagram
below to help. The logic behind both the experiment and the results are critical.
Tatum and Beadle where inquiring if individual genes specified the enzymes that function in
a biochemical pathway. Working with the mold Neurospora crassa, they isolated mutants
that required arginine in their growth medium. Research showed that the mutants fell into
three different classes that each was defective in a different gene. This experiment tested
there one gene- one enzyme hypothesis and their postulated arginine-synthesizing pathway.
In this experiment, they grew their 3 different mutants and four different conditions.
Wild Type/ Class 1/ Class 2/ Class 3
Condition Mutants Mutants Mutants CLASSES OF
NEUROSPORA
Minimal Medium (MM) CRASA
control.
1. Can grow with or without any
MM + Ornithine supplements.
2. Can grow on ornithine ,
citrulline, or arginine
MM + Citrulline 3. Can grow only on citrulline or
arginine
4. Absolutely require arginine to
MM + Arginine grow.
( control)
1 2 3 4
Wild Type/ Class 1/ Class 2/ Class 3
Mutants Mutants Mutants
P P= Precursor
Enzyme A
Gene A O=Ornithine
O C= Citrulline
Enzyme B
Gene B A=Arginine.
C
Gene C Enzyme C
A
3. What was Beadle and Tatum’s final hypothesis?
Beadle and Tatum’s final hypothesis was “ one gene-one polypeptide
, hypothesis”.
(a) Bacterial Cell. In a
bacterial cell, which
lacks a nucleus, mRNA
produced by
transcription is
Transcription immediately translated
without additional
Translation processing.
DNA
(b) Eukaryotic cell. The
Transcription nucleus provides a separate
mRNA
Translation compartment for
Ribosome transcription. The original
DNA RNA transcript, called pre-
Polypeptide mRNA
mRNA, is processed in
various ways before leaving
Ribosome the nucleus as mRNA.
Polypeptide
RNA Processing
Nuclear envelope
Pre-mRNA
4. Why does the “code” have to be in triplets and not singles or doubles?
Triplets of nucleotide bases are the smallest units of uniform length that cancode for all the
amino acids. If each arrangement of three consecutive bases speficies an amino acids,
there are 64 possible code words, which are more than enough to specify all the amino
acids. If each nucleotide basewere translated into an amino acid, only four of the 20 amino
acids would bespecified. A two-base sequence would only give 16 possible arrangements,
either one would not be enough.
5. What is the template strand? The DNA strand that provides the pattern, or
template for ordering the sequence of nucleotides in an RNA transcript.
6. Compare and contrast the codon and anticodon? A codon is a three-nucleotide
sequence that specifies a particular amino acid or termination signal; the basic unit
of the genetic code. An anti-codon is a nucleotide triplet that recognizes a particular
complementary codon on a mRNA molecule.
Chapter 17 Guided Reading Assignment
1. What did Garrod mean by “inborn errors of metabolism?”
Garrod was the first to suggest that genes dictate phenotypes through enzymes that
catalyze specific chemical reactions in the cell. Garrod postulated that the symptoms
of an inherited disease reflect a person’sinability to make a particular enzyme.
2. Describe the Beadle and Tatum experiment with mold in detail – use the diagram
below to help. The logic behind both the experiment and the results are critical.
Tatum and Beadle where inquiring if individual genes specified the enzymes that function in
a biochemical pathway. Working with the mold Neurospora crassa, they isolated mutants
that required arginine in their growth medium. Research showed that the mutants fell into
three different classes that each was defective in a different gene. This experiment tested
there one gene- one enzyme hypothesis and their postulated arginine-synthesizing pathway.
In this experiment, they grew their 3 different mutants and four different conditions.
Wild Type/ Class 1/ Class 2/ Class 3
Condition Mutants Mutants Mutants CLASSES OF
NEUROSPORA
Minimal Medium (MM) CRASA
control.
1. Can grow with or without any
MM + Ornithine supplements.
2. Can grow on ornithine ,
citrulline, or arginine
MM + Citrulline 3. Can grow only on citrulline or
arginine
4. Absolutely require arginine to
MM + Arginine grow.
( control)
1 2 3 4
Wild Type/ Class 1/ Class 2/ Class 3
Mutants Mutants Mutants
P P= Precursor
Enzyme A
Gene A O=Ornithine
O C= Citrulline
Enzyme B
Gene B A=Arginine.
C
Gene C Enzyme C
A
3. What was Beadle and Tatum’s final hypothesis?
Beadle and Tatum’s final hypothesis was “ one gene-one polypeptide
, hypothesis”.
(a) Bacterial Cell. In a
bacterial cell, which
lacks a nucleus, mRNA
produced by
transcription is
Transcription immediately translated
without additional
Translation processing.
DNA
(b) Eukaryotic cell. The
Transcription nucleus provides a separate
mRNA
Translation compartment for
Ribosome transcription. The original
DNA RNA transcript, called pre-
Polypeptide mRNA
mRNA, is processed in
various ways before leaving
Ribosome the nucleus as mRNA.
Polypeptide
RNA Processing
Nuclear envelope
Pre-mRNA
4. Why does the “code” have to be in triplets and not singles or doubles?
Triplets of nucleotide bases are the smallest units of uniform length that cancode for all the
amino acids. If each arrangement of three consecutive bases speficies an amino acids,
there are 64 possible code words, which are more than enough to specify all the amino
acids. If each nucleotide basewere translated into an amino acid, only four of the 20 amino
acids would bespecified. A two-base sequence would only give 16 possible arrangements,
either one would not be enough.
5. What is the template strand? The DNA strand that provides the pattern, or
template for ordering the sequence of nucleotides in an RNA transcript.
6. Compare and contrast the codon and anticodon? A codon is a three-nucleotide
sequence that specifies a particular amino acid or termination signal; the basic unit
of the genetic code. An anti-codon is a nucleotide triplet that recognizes a particular
complementary codon on a mRNA molecule.
