Chapter 17, Problem 1IQ

1. a. In what three ways does RNA differ from DNA?
2. b. Fill in the following sequence in the flow of genetic information, often called the central dogma. Above each arrow, write the name of the process involved.

Figure 17.6 The codon table for mRNA. The three nucleotide bases of an mRNA codon are designated here as the first, second, and third bases, reading in the 5′ ® 3′ direction along the mRNA. The codon AUG not only stands for the amino acid methionine (Met, or M) but also functions as a “start” signal for ribosomes to begin translating the mRNA at that point. Three of the 64 codons function as “stop” signals, marking where ribosomes end translation. Both one- and three-letter codes are shown for the amino acids; see Figure 5.14 for the full names.

VISUAL SKILLS A segment in the middle of an mRNA has the sequence 5′-AGAGAACCGCGA-3′. Using the codon table, translate this sequence, assuming the first three nucleotides are a codon.

Summary Introduction

To determine: Three ways in which ribonucleic acid (RNA) differs from deoxyribonucleic acid (DNA).

Introduction: Nucleic acids are the major organic molecules of all living organisms. Nucleic acids are made of three major components, such as nitrogenous base, pentose sugar, and phosphate group. The two major nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA carries the genetic information from one generation to other generation. DNA controls the synthesis of RNA in the cell. RNA is responsible for the synthesis of protein molecules.

Explanation of Solution

Three ways in which DNA differ from RNA are given below:

Criteria	DNA	RNA
Pentose sugar	DNA contains deoxyribose pentose sugar.	RNA contains ribose pentose sugar.
Nitrogenous base	DNA has 4 nitrogenous bases, namely adenine, cytosine, guanine, and thiamine.	RNA has 4 nitrogenous bases, namely adenine, cytosine, guanine, and uracil.
Strand	DNA is double-stranded.	RNA is single-stranded.

Summary Introduction

To fill and name: The given sequence in the flow of genetic information and the process involved in it.

Introduction: The central dogma of biology explains the flow of information from genes to protein by two processes. These two processes are transcription and translation.

Explanation of Solution

The given sequence in the flow of genetic information and the process involved in it is as follows:

$\text{DNA}\underrightarrow{\text{transcription}}\text{RNA}\underrightarrow{\text{translation}}\text{protein}$

Transcription is a process in which a DNA sequence is converted into a functional piece of RNA. In the initiation of transcription, RNA polymerase binds to the sequence of DNA, and then the unbinding of DNA strand takes place. RNA polymerase adds the RNA bases to the DNA that creates a single strand of mRNA. RNA polymerase detaches from the sequence, and the newly formed sequence of mRNA is released into the nuclear fluid, and then it leaves the nucleus.

After the transcription, the newly formed mRNA enters the cytosol. In the cytosol, processed mRNA associates with many ribosomes. The complex of ribosome-mRNA starts the process of translation. At the initiation of translation, anticodons that appear on tRNA attaches with the mRNA codon. This attachment of tRNA and mRNA codon corrects the orientation of newly arrived amino acids. These amino acids are linked together by a peptide bond, and a peptide chain starts to grow.

Conclusion

Transcription is the formation of RNA from a DNA sequence and through the process of translation, protein is formed from the RNA.