Chapter 8, Problem 2P

Match the hypothesis from the left column to the observation from the right column that gave rise to it.

a.	existence of an inter-mediate messenger between DNA and protein	1.	two mutations affecting the same amino acid can recombine to give wild type
b.	the genetic code is nonoverlapping	2.	one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
c.	the codon is more than one nucleotide	3.	artificial messages containing certain codons produced shorter proteins than messages not containing those codons
d.	the genetic code is based on triplets of bases	4.	protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
e.	stop codons exist and terminate translation	5.	artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
f.	the amino acid sequence of a protein depends on the base sequence of an mRNA	6.	single base substitutions affect only one amino acid in the protein chain

Summary Introduction

a.

To match:

The hypothesis “existence of an inter-mediate messenger between DNA and protein” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

RNA molecules are the intermediate messenger that migrate to the cytoplasm. They arise in the nucleus from the transcription of DNA sequence information and then move to the cytoplasm, where they determine the order of amino acids during protein synthesis.

Answer to Problem 2P

Correct answer:

Existence of an inter-mediate messenger between DNA and protein: protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus.

Explanation of Solution

Existence of an intermediate messenger between DNA and protein means that the mRNA acts as an intermediate between the DNA and protein synthesis. This is observed as the protein synthesis occurs in cytoplasm and DNA resides in the nucleus. RNA was a prime candidate for this intermediary information-carrying molecule. Therefore, an intermediate is required.

Summary Introduction

b.

To determine:

The hypothesis “the genetic code is nonoverlapping” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

The DNA regions that encode proteins are called genes. The information in the DNA of genes dictates, through a genetic code, the order of amino acids in a protein molecule.

Answer to Problem 2P

Correct answer:

The genetic code is nonoverlapping: single base substitutions affect only one amino acid in the protein chain.

Explanation of Solution

The genetic code is non-overlapping. This is because three nucleotides are specific to each amino acid. Each nucleotide is a part of one triplet codon. This is observed when the single base substitution affects one amino acid in the polypeptide chain.

Summary Introduction

c.

To determine:

The hypothesis “the codon is more than one nucleotide” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

groups of three nucleotides represent all 20 amino acids. Each nucleotide triplet is called a codon. Each codon, designated by the bases defining its three nucleotides, specifies one amino acid.

Answer to Problem 2P

Correct answer:

the codon is more than one nucleotide: two mutations affecting the same amino acid can recombine to give wild type.

Explanation of Solution

The codon is more than one nucleotide can be observed when two mutations affect the same amino acid, and then they recombine to give the wild type. This is due to the three nucleotides present in a codon.

Summary Introduction

d.

To determine:

The hypothesis “the genetic code is based on triplets of bases” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

The linear bases of DNA are copied through molecular complementarity into the linear bases of RNA. The bases of RNA are read three at a time (that is, as triplets) to encode the amino acid subunits of proteins.

Answer to Problem 2P

Correct answer:

The genetic code is based on triplets of bases: single base substitutions affect only one amino acid in the protein chain.

Explanation of Solution

The genetic code is non-overlapping. This is because three nucleotides are specific to each amino acid. Each nucleotide is a part of one triplet codon. This is observed when the single base substitution affects one amino acid in the polypeptide chain.

Summary Introduction

e.

To determine:

The hypothesis “stop codons exist and terminate translation” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

Stop codons are triplets that do not correspond to an amino acid and instead signal termination of transcription. They are nonsense codons such as UAA, UGA, UAG.

Answer to Problem 2P

Correct answer:

Stop codons exist and terminate translation: stop codon exists and. artificial messages containing certain codons produced shorter proteins than messages not containing those codons.

Explanation of Solution

Stop codons exist and terminate translation is referred to the translation gets terminated when the ribosome reaches a stop codon. This is observed when artificial messages containing certain codons produced shorter proteins than the messages which do not contain these codons.

Summary Introduction

f.

To determine:

The hypothesis “the amino acid sequence of a protein depends on the base sequence of an mRNA” to the appropriate observation among the options given below,

1. two mutations affecting the same amino acid can recombine to give wild type
2. one or two base deletions (or insertions) in a gene disrupt its function; three base deletions (or insertions) are often compatible with function
3. artificial messages containing certain codons produced shorter proteins than messages not containing those codons
4. protein synthesis occurs in the cytoplasm, while DNA resides in the nucleus
5. artificial messages with different base sequences gave rise to different proteins in an in vitro translation system
6. single base substitutions affect only one amino acid in the protein chain

Introduction:

Biochemists obtained cellular extracts with the addition of mRNA that are synthesized polypeptides in a test tube. These extracts produced are called in vitro translational systems.

Answer to Problem 2P

Correct answer:

The amino acid sequence of a protein depends on the base sequence of an mRNA: artificial messages with different base sequences gave rise to different proteins in an in vitro translation system.

Explanation of Solution

The amino acid sequence of a protein depends on the base sequence of an mRNA. This is observed when artificial messages with different base sequences will produce different proteins in an in-vitro translation system. The synthesis of artificial mRNAs containing only a few codons of known composition. When added to in vitro translational systems, these simple, synthetic mRNAs directed the formation of simple polypeptides.