6.6 Nucleic Acids

Short Introduction Nucleic acids are the most important organic biomolecules which store and transfer hereditary information from one generation to the next. There are two main types of nucleic acids: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA). Both types of nucleic acids are made up of many units called nucleotides.

Main Idea

Nucleic acids (DNA and RNA) are polymers of nucleotides that store and transmit genetic information. Each nucleotide consists of a pentose sugar, a nitrogenous base, and a phosphate group. DNA is a double-stranded helix that stores hereditary information, while RNA is a single-stranded molecule that helps convert this information into proteins. The flow of genetic information from DNA to RNA to proteins is known as the central dogma of molecular biology.

Core Concept

Structure of Nucleotide Each nucleotide is made up of three components: generated by DeepSeek to PDF

1. Pentose (5C Sugar): Deoxyribose in DNA, Ribose in RNA. 2. Nitrogen-containing ring structure called a nitrogen base, attached at the first carbon of the pentose sugar. 3. Phosphate group attached with the fifth carbon of the pentose sugar. Nitrogen Bases (Two Main Types): Purines: Nitrogen-containing double-ring structures (Adenine and Guanine). Pyrimidines: Nitrogen-containing single-ring structures (Cytosine, Thymine, and Uracil). Nucleotides in DNA and RNA: DNA consists of four types of nucleotides called deoxyribonucleotides. Each can have one of the bases: Adenine, Cytosine, Guanine, and Thymine. RNA consists of four types of nucleotides called ribonucleotides. Each can have one of the bases: Adenine, Cytosine, Guanine, and Uracil. So, DNA nucleotides can have Thymine, while RNA nucleotides can have Uracil. Structure of DNA DNA is a polynucleotide made of many deoxyribonucleotides. Each next nucleotide binds through its phosphate at the 3rd carbon of the pentose sugar of the previous nucleotide. Watson and Crick Model of DNA (Main Points): 1. The DNA molecule is double-stranded like a ladder, and both strands are coiled around each other like a helix. 2. Both strands are antiparallel (oppositely oriented). 3. The backbone (uprights) of the molecule is composed of sugar and phosphate parts, while bases form the rungs. 4. The amount of adenine (A) = thymine (T) and cytosine (C) = guanine (G). 5. Base pairing is highly specific: Adenine pairs with Thymine (one strand with the other), and Cytosine pairs with Guanine. The sequence of nucleotides in one strand is complementary to the sequence in the other strand. 6. Both strands are held by weak hydrogen bonds. There are two hydrogen bonds between A and T, and three hydrogen bonds between C and G. 7. The diameter of the double helix is uniform and is about 2 nm. Function of DNA (Genes) as Carrier of Hereditary Information Heredity is the transmission of characters from one generation to the next. It is important for the continuity of all life forms. During cell division, chromatin fibres condense and fold to form chromosomes. A small piece of a huge DNA molecule in the chromosome is called a gene. Genes store and control hereditary information. Each chromosome is made up of a large number of genes. The total number of genes found in the complete set of chromosomes of an organism is called its genome. During sexual reproduction, gametes (sperm and egg) are produced by meiosis. They contain chromosomes (set of genes) of the parent generation. At fertilization, male and female gametes fuse to form a zygote. Thus, genes of both parents are transferred to the zygote, which develops into the offspring. This is how DNA (genes) carries hereditary generated by DeepSeek to PDF

information from one generation to the next. Structure of RNA RNA is a polynucleotide helical chain like DNA, but it is a single-stranded nucleic acid. In RNA, the pentose sugar ribose is present instead of deoxyribose. RNA differs from DNA in having uracil nucleotide instead of thymine. Nitrogen bases of RNA are overhung because they are not bonded to nitrogen bases of another (complementary) strand like DNA. The sequence of nucleotides in RNA is synthesized by using the sequence of nucleotides in DNA by the process of transcription. Function of RNA in Converting Hereditary Information into Useful Proteins After synthesis in the nucleus, RNA is transported to the cytoplasm. RNA is an intermediate molecule for controlling heredity. The primary function of RNA is to synthesize proteins by the process of translation. Types and Functions of RNA: 1. Messenger RNA (mRNA): Carries the message of DNA from the nucleus to the cytoplasm for protein synthesis. 2. Transfer RNA (tRNA): Transfers amino acids to ribosomes during protein synthesis. 3. Ribosomal RNA (rRNA): Component of ribosomes. It combines with ribosomal proteins to form units of ribosomes, which are the factory of proteins. Flow of Genetic Information (Central Dogma) DNA (genes) contain information needed for the synthesis of proteins. The flow of biological information from DNA to RNA and from RNA to protein is known as the "central dogma of molecular biology" or "central dogma of life". Proteins are the main structural and functional molecules of living organisms. The correct primary structure of any protein is primarily determined by DNA. Protein synthesis takes place in two sequential steps: transcription and translation. Together, transcription and translation are known as gene expression. Transcription: The first step of gene expression that involves the formation of an RNA molecule from DNA. Both DNA strands of a gene unwind from each other. Only one strand of DNA is copied. The nucleotide sequence of one DNA strand (coding strand) is copied in the form of mRNA. After the gene is copied to mRNA, both strands of DNA coil together again into their normal double- stranded shape. Translation: The mRNA synthesized in the nucleus moves into the cytoplasm where it binds to the ribosome. The mRNA message (codes) is translated by ribosomes, which link amino acids to form a polypeptide chain with a specific sequence of amino acids. Different types of tRNAs transfer amino acids to the ribosome as per the sequence of codes in mRNA.

Detailed Explanation

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Nucleic acids are the molecules that carry the genetic blueprint of life. They are essential for storing, transmitting, and expressing genetic information. 1. Nucleotides: The building blocks of nucleic acids are nucleotides. Each nucleotide consists of a pentose sugar (ribose in RNA, deoxyribose in DNA), a nitrogenous base (purine or pyrimidine), and a phosphate group. The nitrogenous bases are of two types: purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). 2. DNA Structure: DNA is a double-stranded helix. The two strands are antiparallel (they run in opposite directions). The sugar-phosphate backbone is on the outside, and the nitrogenous bases are on the inside, forming the rungs of the ladder. Base pairing is specific: A pairs with T (two hydrogen bonds), and C pairs with G (three hydrogen bonds). The two strands are complementary, meaning the sequence of one strand determines the sequence of the other. The diameter of the helix is about 2 nm. 3. DNA Function: DNA stores genetic information in its sequence of bases. A gene is a segment of DNA that codes for a protein or RNA molecule. The complete set of genes in an organism is its genome. During sexual reproduction, gametes carry genes from the parents to the offspring, ensuring heredity. 4. RNA Structure: RNA is single-stranded and contains ribose sugar and uracil instead of thymine. The bases are not bonded to a complementary strand, so they are "overhung." RNA is synthesized from DNA by transcription. 5. RNA Function: RNA acts as an intermediate between DNA and protein. There are three types of RNA: mRNA carries the genetic message from DNA to the ribosome. tRNA transfers amino acids to the ribosome during protein synthesis. rRNA is a component of ribosomes, which are the sites of protein synthesis. 6. Central Dogma: The flow of information from DNA → RNA → protein is the central dogma of molecular biology. Transcription (DNA → RNA) occurs in the nucleus, and translation (RNA → protein) occurs in the cytoplasm on ribosomes. Together, these processes constitute gene expression.

Intermediate Level

Nucleic acids are polymers of nucleotides that store and transmit genetic information. There are two types: DNA and RNA. A nucleotide consists of a pentose sugar (ribose in RNA, deoxyribose in DNA), a nitrogenous base (purine: adenine, guanine; pyrimidine: cytosine, thymine in DNA, uracil in RNA), and a phosphate group. DNA is a double-stranded helix (Watson and Crick model). The strands are antiparallel; the sugar-phosphate backbone is on the outside and bases on the inside. Base pairing is specific: A=T (two hydrogen bonds), C≡G (three hydrogen bonds). The diameter is about 2 nm. DNA stores hereditary information in genes. A gene is a segment of generated by DeepSeek to PDF

DNA on a chromosome. The genome is the complete set of genes. Gametes transmit genes from parents to offspring. RNA is single-stranded, contains ribose and uracil, and is synthesized from DNA by transcription. There are three types: mRNA (carries message from DNA to ribosome), tRNA (transfers amino acids), and rRNA (component of ribosomes). The flow of information from DNA → RNA → protein is the central dogma. Protein synthesis involves transcription (DNA → mRNA) and translation (mRNA → polypeptide).

Important Points

• 1. Nucleic acids store and transfer hereditary information from one generation to the next.
• 2. Two main types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
• 3. Both are made of units called nucleotides.
• 4. Nucleotide structure: Pentose sugar (deoxyribose in DNA, ribose in RNA), nitrogen base, and phosphate
• group.
• 5. Purines (double-ring): Adenine and Guanine.
• 6. Pyrimidines (single-ring): Cytosine, Thymine, and Uracil.
• 7. DNA nucleotides: A, C, G, T. RNA nucleotides: A, C, G, U.
• 8. DNA structure (Watson and Crick): Double-stranded helix, antiparallel, sugar-phosphate backbone,
• bases as rungs, A=T and C=G, A-T has 2 H-bonds, C-G has 3 H-bonds, diameter ~2 nm.
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• 9. Gene: A small piece of DNA on a chromosome that stores and controls hereditary information.
• 10. Genome: The total number of genes in the complete set of chromosomes of an organism.
• 11. Gametes carry genes from parents to offspring; at fertilization, they fuse to form a zygote.
• 12. RNA structure: Single-stranded, contains ribose and uracil, bases are overhung, synthesized by
• transcription.
• 13. Types of RNA: mRNA (carries message), tRNA (transfers amino acids), rRNA (component of ribosomes).
• 14. Central dogma: Flow of information from DNA → RNA → protein.
• 15. Transcription: Formation of RNA from DNA (in the nucleus).
• 16. Translation: Synthesis of polypeptide from mRNA (in the cytoplasm on ribosomes).
• 17. Gene expression = transcription + translation.
• 18. Friedrich Miescher isolated "nuclein" from the nucleus of human pus cells (later called nucleic acid).

Remember

• Nucleic acids = DNA + RNA (polymers of nucleotides).
• Nucleotide = pentose sugar + nitrogen base + phosphate.
• Purines = Adenine, Guanine (double-ring).
• Pyrimidines = Cytosine, Thymine (DNA), Uracil (RNA) (single-ring).
• DNA: double helix, antiparallel, A=T, C≡G, 2 nm diameter.
• RNA: single-stranded, ribose, uracil, overhung bases.
• Gene = DNA segment on chromosome (hereditary unit).
• Genome = total genes in an organism.
• Central dogma: DNA → RNA → protein.
• Transcription: DNA → RNA (nucleus).
• Translation: mRNA → protein (cytoplasm/ribosome).
• Types of RNA: mRNA (message), tRNA (amino acid transfer), rRNA (ribosome component).
• Miescher = discovered nuclein (nucleic acid).

Common Mistakes

• 1. Confusing DNA and RNA sugars: DNA has deoxyribose; RNA has ribose.
• 2. Mixing up the bases: DNA has Thymine (T); RNA has Uracil (U) instead.
• 3. Thinking DNA is single-stranded: DNA is double-stranded; RNA is single-stranded.
• 4. Confusing transcription and translation: Transcription is DNA → RNA; translation is RNA → protein.
• 5. Thinking purines are single-ringed: Purines (A, G) are double-ringed; pyrimidines (C, T, U) are single-
• ringed.
• 6. Forgetting the number of hydrogen bonds: A=T has 2; C≡G has 3.
• 7. Thinking genes are found outside chromosomes: Genes are segments of DNA on chromosomes.
• 8. Mixing up the types of RNA: mRNA carries the message; tRNA transfers amino acids; rRNA is part of the
• ribosome.
• 9. Forgetting that RNA is synthesized from DNA: RNA is synthesized by transcription using DNA as a
• template.
• 10. Thinking the central dogma is DNA → protein directly: The central dogma is DNA → RNA → protein.

Quick Revision

• Nucleic acids are the organic biomolecules that store and transfer hereditary information. They are of two types:
• DNA and RNA, both made of nucleotides. Each nucleotide has a pentose sugar (deoxyribose in DNA, ribose in RNA),
• a nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine, uracil), and a phosphate group. DNA
• is a double-stranded helix (Watson and Crick model), with antiparallel strands, specific base pairing (A=T, C≡G), and
• a diameter of about 2 nm. A gene is a segment of DNA on a chromosome that stores hereditary information; the
• genome is the complete set of genes. RNA is single-stranded, contains ribose and uracil, and is synthesized by
• transcription. The three types of RNA are mRNA (carries the message), tRNA (transfers amino acids), and rRNA
• (component of ribosomes). The flow of genetic information from DNA to RNA to protein is the central dogma.
• Transcription (DNA → RNA) occurs in the nucleus; translation (RNA → protein) occurs in the cytoplasm on
• ribosomes. Together they constitute gene expression.

60-Second Revision

• Nucleic acids = DNA + RNA (polymers of nucleotides).
• Nucleotide = pentose sugar + nitrogen base + phosphate.
• Purines = A, G (double-ring).
• Pyrimidines = C, T (DNA), U (RNA) (single-ring).
• DNA: double helix, antiparallel, A=T (2 H-bonds), C≡G (3 H-bonds), 2 nm.
• RNA: single-stranded, ribose, uracil, overhung bases.
• Gene = DNA segment on chromosome.
• Genome = total genes in an organism.
• Central dogma: DNA → RNA → protein.
• Transcription: DNA → RNA (nucleus).
• Translation: mRNA → protein (cytoplasm/ribosome).
• Types of RNA: mRNA (message), tRNA (amino acid transfer), rRNA (ribosome component).
• Miescher = discovered nuclein.
• Frequently Asked Questions (FAQs)
• Q1. What are nucleic acids? Answer: Nucleic acids are the most important organic biomolecules which store and
• transfer hereditary information from one generation to the next. There are two main types: Deoxyribonucleic Acid
• (DNA) and Ribonucleic Acid (RNA).
• Q2. What is a nucleotide? Answer: A nucleotide is the basic unit of nucleic acids. Each nucleotide is made up of
• three components: a pentose sugar (deoxyribose in DNA, ribose in RNA), a nitrogen-containing ring structure called
• a nitrogen base, and a phosphate group.
• generated by DeepSeek to PDF

• Q3. What are purines and pyrimidines? Answer: Purines are nitrogen-containing double-ring structures (Adenine
• and Guanine). Pyrimidines are nitrogen-containing single-ring structures (Cytosine, Thymine, and Uracil).
• Q4. How does DNA differ from RNA in terms of bases? Answer: DNA nucleotides can have Thymine, while RNA
• nucleotides can have Uracil as a nitrogen base.
• Q5. What are the main points of the Watson and Crick model of DNA? Answer: The main points are:
• 1. DNA is double-stranded and coiled like a helix.
• 2. Both strands are antiparallel.
• 3. The backbone is composed of sugar and phosphate; bases form the rungs.
• 4. Amount of adenine = thymine and cytosine = guanine.
• 5. Base pairing is specific: Adenine pairs with thymine, cytosine pairs with guanine.
• 6. Both strands are held by weak hydrogen bonds (two between A and T, three between C and G).
• 7. The diameter of the double helix is about 2 nm.
• Q6. What is a gene? Answer: A small piece of a huge DNA molecule in the chromosome is called a gene. Genes
• store and control hereditary information.
• Q7. What is a genome? Answer: The total number of genes found in the complete set of chromosomes of an
• organism is called the genome of that organism.
• Q8. What are the three types of RNA and their functions? Answer:
• Messenger RNA (mRNA): Carries the message of DNA from the nucleus to the cytoplasm for protein
• synthesis.
• Transfer RNA (tRNA): Transfers amino acids to ribosomes during protein synthesis.
• Ribosomal RNA (rRNA): Component of ribosomes; combines with ribosomal proteins to form units of
• ribosomes.
• Q9. What is the central dogma of molecular biology? Answer: The flow of biological information from DNA to
• RNA and from RNA to protein is known as the central dogma of molecular biology (or central dogma of life).
• Q10. What is the difference between transcription and translation? Answer: Transcription is the first step of
• gene expression that involves the formation of an RNA molecule from DNA. Translation is the process in which the
• mRNA message is translated by ribosomes, which link amino acids to form a polypeptide chain with a specific
• sequence of amino acids.
• Multiple Choice Questions (MCQs)
• Q1. The building blocks of nucleic acids are: A. Amino acids B. Nucleotides C. Monosaccharides D. Fatty acids
• Correct Answer: B Explanation: Nucleic acids are made up of many units called nucleotides.
• Q2. Which sugar is found in DNA? A. Ribose B. Deoxyribose C. Glucose D. Fructose Correct Answer: B Explanation:
• DNA contains the pentose sugar deoxyribose.
• Q3. Which of the following is a purine? A. Cytosine B. Thymine C. Adenine D. Uracil Correct Answer: C Explanation:
• Adenine and guanine are purines (double-ring).
• Q4. Which base is found in RNA but not in DNA? A. Thymine B. Uracil C. Guanine D. Cytosine Correct Answer: B
• Explanation: RNA contains uracil instead of thymine.
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• Q5. According to the Watson and Crick model, how many hydrogen bonds are between adenine and thymine? A.
• One B. Two C. Three D. Four Correct Answer: B Explanation: There are two hydrogen bonds between adenine and
• thymine.
• Q6. The diameter of the DNA double helix is about: A. 1 nm B. 2 nm C. 3 nm D. 4 nm Correct Answer: B Explanation:
• The diameter of the double helix of DNA is about 2 nm.
• Q7. A small piece of DNA on a chromosome that stores hereditary information is called a: A. Nucleotide B. Gene C.
• Genome D. Codon Correct Answer: B Explanation: A gene is a small piece of a huge DNA molecule in the
• chromosome.
• Q8. Which type of RNA carries the message of DNA from the nucleus to the cytoplasm? A. tRNA B. rRNA C. mRNA
• D. siRNA Correct Answer: C Explanation: Messenger RNA (mRNA) carries the message of DNA from the nucleus to
• the cytoplasm.
• Q9. The flow of information from DNA to RNA to protein is called the: A. Central dogma B. Transcription C.
• Translation D. Replication Correct Answer: A Explanation: The flow of biological information from DNA to RNA and
• from RNA to protein is known as the central dogma.
• Q10. Which type of RNA is a component of ribosomes? A. mRNA B. tRNA C. rRNA D. None of the above Correct
• Answer: C Explanation: Ribosomal RNA (rRNA) is a component of ribosomes.
• Chapter 6: Molecular Biology is now fully complete (all 6 subtopics covered: 6.1 through 6.6).
• Reply "next" if you would like to begin Chapter 7: Metabolism, starting with Subtopic 1: 7.1 Metabolism and Its
• Types.