Problem 10 - Biology of Humans: Concepts, Applications, and Issues

Question

Choose the incorrect statement: a. The base uracil is found in RNA but not in DNA. b. The two chains of RNA are held together by hydrogen bonds between the bases. c. Nucleotides are the monomers of nucleic acids. d. DNA molecules contain genes, which specify the sequence of amino acids in proteins.

Step-by-Step Solution

Answer

The incorrect statement is (b). RNA is typically single-stranded.

Step 1 - Identify the Base Found in RNA

The base uracil is found in RNA but not in DNA. DNA contains thymine instead of uracil. Therefore, statement (a) is correct.

Step 2 - Analyze RNA Structure

The statement 'The two chains of RNA are held together by hydrogen bonds between the bases' is incorrect. RNA is typically a single-stranded molecule, while DNA is double-stranded. Therefore, statement (b) is incorrect.

Step 3 - Verify Monomers of Nucleic Acids

Nucleotides are the monomers that make up nucleic acids, including both DNA and RNA. Hence, statement (c) is correct.

Step 4 - Confirm Function of DNA

DNA molecules contain genes, which specify the sequence of amino acids in proteins. This biological function is correctly described in statement (d).

Key Concepts

Nucleotides

Nucleotides are the building blocks of nucleic acids such as DNA and RNA. Each nucleotide consists of three components: a nitrogenous base, a five-carbon sugar (either ribose in RNA or deoxyribose in DNA), and one or more phosphate groups.
The nitrogenous bases are categorized into two types: purines and pyrimidines.
Purines include adenine (A) and guanine (G), while pyrimidines include cytosine (C), thymine (T), and uracil (U).
DNA uses adenine, guanine, cytosine, and thymine, whereas RNA uses adenine, guanine, cytosine, and uracil.
These nucleotides combine in specific sequences to form the genetic instructions necessary for life.

RNA Structure

RNA, or ribonucleic acid, is usually a single-stranded molecule. Unlike DNA, RNA contains the sugar ribose and the nitrogenous base uracil instead of thymine.
There are several types of RNA, each serving different functions in the cell:

• mRNA (messenger RNA): Carries genetic information from DNA to the ribosome, where proteins are synthesized.


• tRNA (transfer RNA): Delivers the correct amino acids to the ribosome during protein synthesis.


• rRNA (ribosomal RNA): Forms the core of the ribosome's structure and catalyzes protein synthesis.

The single-stranded nature of RNA allows it to fold into complex 3D shapes, which are crucial for its various functions.

DNA Function

DNA, or deoxyribonucleic acid, is the molecule that stores genetic information in living organisms. This genetic information is organized into units called genes, which code for proteins.
The sequence of nucleotides in a gene specifies the order of amino acids in a protein, which directly affects the protein's structure and function.
This process unfolds in two main steps:

• Transcription: DNA is transcribed into mRNA.


• Translation: The mRNA is then translated into a specific protein at the ribosome.

DNA's double-stranded structure, stabilized by hydrogen bonds between complementary base pairs (A with T and G with C), makes it ideal for replication and stable information storage.

Uracil

Uracil is one of the four nitrogenous bases found in RNA, pairing with adenine through hydrogen bonds.
Uracil differs from thymine (found in DNA) by lacking a methyl group at its 5-carbon position.
This subtle difference has significant biological implications, such as making RNA more prone to damage and less stable than DNA.
Uracil is crucial for the proper functioning of RNA in various roles, from coding and decoding genetic information to catalyzing biological reactions as part of ribozymes.