Question

Compare DNA and RNA is these ways. (a) Monosaccharide units (b) Principal purine and pyrimidine bases (c) Primary structure (d) Location in the cell (e) Function in the cell

Short answer

Question: Compare DNA and RNA in terms of (a) monosaccharide units, (b) principal purine and pyrimidine bases, (c) primary structure, (d) location in the cell, and (e) function in the cell. Answer: (a) DNA's monosaccharide unit is deoxyribose sugar, while RNA's is ribose sugar. (b) DNA contains adenine, guanine, cytosine, and thymine, while RNA contains adenine, guanine, cytosine, and uracil. (c) DNA's primary structure is double-stranded, while RNA is single-stranded. (d) DNA is primarily located in the nucleus, whereas RNA is found in both the nucleus and cytoplasm. (e) DNA carries genetic information, while RNA plays various roles such as mRNA (carrying information), tRNA (transferring amino acids), and rRNA (structural support and catalyzing peptide bond formation).

Step-by-step solution

(a) Monosaccharide units

DNA and RNA are both nucleic acids, which are composed of monomeric units called nucleotides. Each nucleotide consists of a monosaccharide unit, a phosphate group, and a nitrogenous base. The monosaccharide units for DNA and RNA are slightly different: DNA has a deoxyribose sugar, while RNA has a ribose sugar. The main difference between these two sugars is that the deoxyribose sugar (in DNA) lacks an oxygen atom at the 2' carbon position that is present in the ribose sugar (in RNA).

(b) Principal purine and pyrimidine bases

The nitrogenous bases present in DNA and RNA are classified into purines and pyrimidines. The principal purine bases are adenine (A) and guanine (G) in both DNA and RNA. The principal pyrimidine bases are cytosine (C) and thymine (T) in DNA, while in RNA, thymine is replaced by uracil (U). In other words, DNA contains A, G, C, and T as its bases, whereas RNA contains A, G, C, and U.

(c) Primary structure

The primary structure of a nucleic acid refers to the sequence of nucleotides. In both DNA and RNA, the primary structure is formed by the covalent linkage of nucleotides via phosphodiester bonds. In these bonds, the phosphate group of one nucleotide is linked to the 3' carbon of the adjacent nucleotide's sugar molecule. This creates a sugar-phosphate backbone with the nitrogenous bases pointing outwards. The primary structure of DNA is generally double-stranded, forming a double helix, while RNA usually exists as a single-stranded molecule that can fold into various secondary structures.

(d) Location in the cell

DNA is primarily located in the nucleus of eukaryotic cells, while RNA can be found in both the nucleus and the cytoplasm. In prokaryotic cells, which lack a nucleus, both DNA and RNA are found in the cytoplasm. In some cases, DNA can also be found in cell organelles such as mitochondria and chloroplasts (in plants).

(e) Function in the cell

DNA is the carrier of genetic information and is responsible for the transmission of genetic traits from one generation to the next. It serves as the template for RNA synthesis during transcription. RNA, on the other hand, plays several roles in the cell. The three major types of RNA are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). mRNA carries genetic information from the DNA to the ribosomes, where proteins are synthesized. tRNA plays a crucial role in protein synthesis by transferring specific amino acids to the growing polypeptide chain. rRNA is a major component of ribosomes, providing structural support and catalyzing peptide bond formation.

Key concepts

DNA vs RNA

When comparing DNA and RNA, it's helpful to think of them as the genetic bookkeepers of life. Both DNA and RNA are nucleic acids, but they have distinct differences.

DNA, or deoxyribonucleic acid, contains deoxyribose as its sugar component, while RNA, or ribonucleic acid, contains ribose. This difference matters because deoxyribose has one less oxygen atom than ribose.

Moreover, the nitrogenous bases differ slightly. In DNA, the bases include adenine (A), guanine (G), cytosine (C), and thymine (T). In RNA, thymine is replaced with uracil (U). Another significant variance is their structure: DNA is mostly double-stranded, forming the well-known double helix, while RNA is typically single-stranded and can fold into various shapes.

Monosaccharide Units

Monosaccharide units are a central part of nucleic acids. They form the backbone of both DNA and RNA. These units are sugars that link together with other components to form nucleotides.

In DNA, the monosaccharide is deoxyribose, a sugar missing an oxygen atom compared to its counterpart in RNA, ribose. This very small structural difference is critical: it affects the stability and function of the nucleic acids.

DNA’s deoxyribose gives DNA more stability, fitting for its role in long-term genetic storage. In contrast, RNA’s ribose makes it more reactive, which supports its various functions, such as catalysis and protein synthesis.

Nitrogenous Bases

Nitrogenous bases are the core components that make up the genetic code. They are purines and pyrimidines. In both DNA and RNA, the purines include adenine (A) and guanine (G). Purines are the double-ringed structures in the genetic structure.

On the other hand, pyrimidines in DNA are cytosine (C) and thymine (T). In RNA, cytosine (C) is joined by uracil (U) instead of thymine. These bases bond in specific ways: A pairs with T (or U in the case of RNA) and C pairs with G.

This specific pairing is crucial as it ensures the accurate copying of genetic information during cell division and protein synthesis.

Cellular Function of DNA and RNA

DNA and RNA serve as the blueprints of life and play distinct roles in cellular function.

DNA's primary role is to store and transmit genetic information. It ensures that genetic instructions are sent from one generation to the next. As a template for RNA synthesis, DNA guides cellular activities via transcription processes.

RNA transfers information, mainly as messenger RNA (mRNA), and plays a critical part in protein synthesis.

• mRNA carries genetic information from DNA to the ribosome.
• Transfer RNA (tRNA) brings amino acids to ribosomes during protein synthesis.
• Ribosomal RNA (rRNA) structures ribosomes and catalyzes protein synthesis.

These functions allow cells to produce proteins essential for life's various processes.

Nucleotide Primary Structure

The primary structure of nucleotides is foundational to understanding nucleic acids. It is all about the sequence of nucleotides linked by phosphodiester bonds.

These bonds connect the phosphate group of one nucleotide to the 3' carbon of the sugar of the next nucleotide. The sequence itself is not merely a list of nucleotides, but a highly organized chain that dictates genetic information.

In DNA, this structure forms the iconic double helix, stabilizing the genetic material. In RNA, the structure is usually single-stranded, flexible, and capable of folding into complex shapes necessary for its functions.

Understanding nucleotide primary structures is crucial in grasping how genetic information is stored, replicated, and translated into proteins.