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1.6 Nucleic Acids

5 min readapril 5, 2023

Danna Esther Gelfand

Danna Esther Gelfand

Jed Quiaoit

Jed Quiaoit

Danna Esther Gelfand

Danna Esther Gelfand

Jed Quiaoit

Jed Quiaoit

are large complex molecules that play a crucial role in the storage, transmission, and expression of hereditary information. They are made up of monomers called , which consist of a 5-carbon sugar, a nitrogenous base, and a phosphate group. There are two main types of : deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material that stores the instructions for building proteins, while RNA is involved in the synthesis of proteins from the instructions stored in DNA. 🍭 are a specific unit of inheritance that contain the instructions for synthesizing particular proteins. They are made of DNA and are found on . The sequence of in a gene determines the sequence of amino acids in a particular protein, which in turn determines the protein's function. 🔧

Deoxyribonucleic Acid

Deoxyribonucleic acid (DNA) is a molecule that stores and transmits genetic information. It is responsible for directing its own replication, causing the synthesis of messenger RNA (mRNA), and using mRNA to control protein synthesis. The sugar in DNA is deoxyribose.

have a linear sequence of that are linked by covalent bonds. The sequence is defined by the presence of a hydroxyl group (-OH) on the 3' carbon of one nucleotide and a phosphate group on the 5' carbon of the next nucleotide. During DNA and RNA synthesis, are added to the 3' end of the growing strand, forming covalent bonds between adjacent . This process is essential for the replication and expression of genetic information. 🧠

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F1000px-Difference_DNA_RNA-EN_BW.png?alt=media&token=b9c00616-6e21-420a-9543-4c46b2548c38

Image courtesy of Wikimedia Commons.

Purines and Pyrimidines

The nitrogenous bases in are important because they are the key players in the genetic code. There are five nitrogenous bases in total: cytosine (C), thymine (T), uracil (U), adenine (A), and guanine (G). 

Uracil is only found in RNA, while thymine is only found in DNA. The nitrogenous bases can be divided into two categories: and

  • , which include adenine (A) and guanine (G), have a double-ring structure.

  • , which include thymine (T), cytosine (C), and uracil (U), have a single-ring structure. 

Each purine pairs with a pyrimidine, bonded together with . This base-pairing allows for the stability and accuracy of DNA replication and the transmission of genetic information from one generation to the next.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-LBvAGc86duLR.png?alt=media&token=af574353-2bfa-4384-9045-e30aee56e75c

Image courtesy of EpoMedicine

Chargaff’s Rule

of and

  • Adenine pairs with thymine (A-T); two hydrogen bonds when pairing the bases.

  • Guanine pairs with Cytosine (G-C); three hydrogen bonds when pairing the bases.

DNA is arranged in a made of two strands of held together by hydrogen bonds. Each strand of DNA consists of a that keeps the connected with the strand. RNA (ribonucleic acid) tends to be single-stranded, yet also has a . The three types of RNA you should know: mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).

A prime (ʹ) identifies the carbon atoms in the ribose, such as the 2ʹ carbon or 5ʹ carbon. DNA is structured as an antiparallel , with each strand running in opposite 5’ to 3’ orientation, and the 5’ end of one molecule is paired with the 3’ end of the other molecule and vice versa.

Example (with Arithmetic)

A researcher isolates a sample of DNA from a species of plant and finds that it contains the following amounts of the four nitrogenous bases: adenine (A) = 40%, thymine (T) = 40%, and cytosine (C) = 10%.

According to Chargaff's rule, what is the percentage of guanine in the sample?

To solve this problem, we can use Chargaff's rule, which states that in a double-stranded DNA molecule, the percentage of A is equal to the percentage of T, and the percentage of G is equal to the percentage of C.

Since the percentage of A in the sample is 40% and the percentage of T is 20%, we know that the percentage of G must be equal to the percentage of C, which is 10%. Therefore, the percentage of guanine in the sample is 10%!

DNA vs. RNA

While it's highly unlikely for an AP Biology standalone MCQ or FRQ to ask about the similarities and differences between DNA and RNA, it's important to learn the foundational knowledge to answer more complex, application-centered questions down the road!

⭐ Key similarities between the two:

  • Both are , meaning they are made up of .

  • in both DNA and RNA consist of a sugar molecule, a phosphate group, and a nitrogenous base.

  • Both contain the nitrogenous bases adenine, guanine, and cytosine.

  • Both are involved in the transmission of genetic information.

  • Both play important roles in the synthesis and regulation of proteins.

⭐ Key differences between the two:

  • The sugar molecule that they contain. DNA contains deoxyribose, which is a sugar molecule with one less oxygen atom compared to ribose, the sugar molecule found in RNA. Another difference is the presence of different nitrogenous bases. 

  • Nitrogenous bases. DNA contains the bases adenine, guanine, cytosine, and thymine, while RNA contains the bases adenine, guanine, cytosine, and uracil.

  • Structure. DNA is usually double-stranded, meaning it has two complementary strands that are held together by hydrogen bonds. RNA, on the other hand, is usually single-stranded, although some RNA molecules may be partially or fully double-stranded. 

  • Orientation and directionality for DNA. Uniquely In double-stranded DNA, the two strands are oriented in opposite directions, with one strand running 5' to 3' and the other running 3' to 5'. This is known as antiparallel orientation.

These structural differences between DNA and RNA are important because they contribute to the unique functions of these two types of . DNA is responsible for storing genetic information and transmitting it to future generations, while RNA plays a variety of roles in the synthesis and regulation of proteins, as well as other cellular processes.


-----

Key Terms to Review (22)

Adenine (A)

: Adenine is one of the four nitrogenous bases found in DNA and RNA molecules. In DNA, it pairs with thymine (T), while in RNA it pairs with uracil (U).

Antiparallel Orientation

: In biology, antiparallel orientation refers to the opposite arrangement of the sugar-phosphate backbones in a DNA double helix. One strand runs from 5' to 3' direction, and the other runs from 3' to 5'.

Base Pairing Rules

: The base pairing rules refer to the way in which DNA bases pair up. Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).

Chargaff’s Rule

: Chargaff's Rule states that in DNA, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C).

Chromosomes

: Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made up of protein and a single molecule of deoxyribonucleic acid (DNA).

Cytosine (C)

: Cytosine is another one of the four nitrogenous bases found in both DNA and RNA molecules. In both cases, it pairs with guanine (G).

Deoxyribonucleic Acid (DNA)

: DNA is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses.

Double Helix

: A double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA.

Genes

: Genes are segments of DNA that carry hereditary information and have specific functions in living organisms.

Guanine (G)

: Guanine is one of the four nucleobases in the nucleic acids DNA and RNA. It pairs with cytosine (C) through three hydrogen bonds.

Hydrogen-Bonding

: Hydrogen bonding is an attractive force between polar molecules where hydrogen is bound to a highly electronegative atom such as oxygen, nitrogen or fluorine.

Messenger RNA (mRNA)

: mRNA is a type of RNA that carries genetic information from the DNA in the nucleus to the cytoplasm, where it serves as a template for protein synthesis.

Nucleic Acids

: Nucleic acids are large biomolecules essential for all known forms of life. They include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which carry genetic information.

Nucleotides

: Nucleotides are the basic building blocks of DNA and RNA. They consist of a sugar, a phosphate group, and a nitrogenous base.

Purines

: Purines are one of the two types of nitrogenous bases found in nucleotides, which make up DNA and RNA. The two purines are adenine (A) and guanine (G).

Pyrimidines

: Pyrimidines are one of the two types of nitrogenous bases found in nucleotides, which make up DNA and RNA. The three pyrimidines are cytosine (C), thymine (T), and uracil (U).

Ribonucleic Acid (RNA)

: RNA is a molecule similar to DNA that plays a crucial role in coding, decoding, regulation, and expression of genes.

Ribosomal RNA (rRNA)

: rRNA is part of ribosomes, serving as structural components and also catalyzing peptide bond formation. It's essential for protein synthesis in all living organisms.

Sugar-Phosphate Backbone

: The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. It consists of alternating sugar and phosphate groups, to which nitrogenous bases are attached.

Thymine (T)

: Thymine is one of the four main nucleobases found in the nucleic acid DNA. It pairs with adenine.

Transfer RNA (tRNA)

: tRNA is a type of RNA that transports specific amino acids to the ribosome during protein synthesis. Each tRNA has an anticodon that pairs with an mRNA codon.

Uracil (U)

: Uracil is a nitrogenous base found only in RNA. It replaces thymine from DNA and pairs with adenine during transcription.

1.6 Nucleic Acids

5 min readapril 5, 2023

Danna Esther Gelfand

Danna Esther Gelfand

Jed Quiaoit

Jed Quiaoit

Danna Esther Gelfand

Danna Esther Gelfand

Jed Quiaoit

Jed Quiaoit

are large complex molecules that play a crucial role in the storage, transmission, and expression of hereditary information. They are made up of monomers called , which consist of a 5-carbon sugar, a nitrogenous base, and a phosphate group. There are two main types of : deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material that stores the instructions for building proteins, while RNA is involved in the synthesis of proteins from the instructions stored in DNA. 🍭 are a specific unit of inheritance that contain the instructions for synthesizing particular proteins. They are made of DNA and are found on . The sequence of in a gene determines the sequence of amino acids in a particular protein, which in turn determines the protein's function. 🔧

Deoxyribonucleic Acid

Deoxyribonucleic acid (DNA) is a molecule that stores and transmits genetic information. It is responsible for directing its own replication, causing the synthesis of messenger RNA (mRNA), and using mRNA to control protein synthesis. The sugar in DNA is deoxyribose.

have a linear sequence of that are linked by covalent bonds. The sequence is defined by the presence of a hydroxyl group (-OH) on the 3' carbon of one nucleotide and a phosphate group on the 5' carbon of the next nucleotide. During DNA and RNA synthesis, are added to the 3' end of the growing strand, forming covalent bonds between adjacent . This process is essential for the replication and expression of genetic information. 🧠

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F1000px-Difference_DNA_RNA-EN_BW.png?alt=media&token=b9c00616-6e21-420a-9543-4c46b2548c38

Image courtesy of Wikimedia Commons.

Purines and Pyrimidines

The nitrogenous bases in are important because they are the key players in the genetic code. There are five nitrogenous bases in total: cytosine (C), thymine (T), uracil (U), adenine (A), and guanine (G). 

Uracil is only found in RNA, while thymine is only found in DNA. The nitrogenous bases can be divided into two categories: and

  • , which include adenine (A) and guanine (G), have a double-ring structure.

  • , which include thymine (T), cytosine (C), and uracil (U), have a single-ring structure. 

Each purine pairs with a pyrimidine, bonded together with . This base-pairing allows for the stability and accuracy of DNA replication and the transmission of genetic information from one generation to the next.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-LBvAGc86duLR.png?alt=media&token=af574353-2bfa-4384-9045-e30aee56e75c

Image courtesy of EpoMedicine

Chargaff’s Rule

of and

  • Adenine pairs with thymine (A-T); two hydrogen bonds when pairing the bases.

  • Guanine pairs with Cytosine (G-C); three hydrogen bonds when pairing the bases.

DNA is arranged in a made of two strands of held together by hydrogen bonds. Each strand of DNA consists of a that keeps the connected with the strand. RNA (ribonucleic acid) tends to be single-stranded, yet also has a . The three types of RNA you should know: mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).

A prime (ʹ) identifies the carbon atoms in the ribose, such as the 2ʹ carbon or 5ʹ carbon. DNA is structured as an antiparallel , with each strand running in opposite 5’ to 3’ orientation, and the 5’ end of one molecule is paired with the 3’ end of the other molecule and vice versa.

Example (with Arithmetic)

A researcher isolates a sample of DNA from a species of plant and finds that it contains the following amounts of the four nitrogenous bases: adenine (A) = 40%, thymine (T) = 40%, and cytosine (C) = 10%.

According to Chargaff's rule, what is the percentage of guanine in the sample?

To solve this problem, we can use Chargaff's rule, which states that in a double-stranded DNA molecule, the percentage of A is equal to the percentage of T, and the percentage of G is equal to the percentage of C.

Since the percentage of A in the sample is 40% and the percentage of T is 20%, we know that the percentage of G must be equal to the percentage of C, which is 10%. Therefore, the percentage of guanine in the sample is 10%!

DNA vs. RNA

While it's highly unlikely for an AP Biology standalone MCQ or FRQ to ask about the similarities and differences between DNA and RNA, it's important to learn the foundational knowledge to answer more complex, application-centered questions down the road!

⭐ Key similarities between the two:

  • Both are , meaning they are made up of .

  • in both DNA and RNA consist of a sugar molecule, a phosphate group, and a nitrogenous base.

  • Both contain the nitrogenous bases adenine, guanine, and cytosine.

  • Both are involved in the transmission of genetic information.

  • Both play important roles in the synthesis and regulation of proteins.

⭐ Key differences between the two:

  • The sugar molecule that they contain. DNA contains deoxyribose, which is a sugar molecule with one less oxygen atom compared to ribose, the sugar molecule found in RNA. Another difference is the presence of different nitrogenous bases. 

  • Nitrogenous bases. DNA contains the bases adenine, guanine, cytosine, and thymine, while RNA contains the bases adenine, guanine, cytosine, and uracil.

  • Structure. DNA is usually double-stranded, meaning it has two complementary strands that are held together by hydrogen bonds. RNA, on the other hand, is usually single-stranded, although some RNA molecules may be partially or fully double-stranded. 

  • Orientation and directionality for DNA. Uniquely In double-stranded DNA, the two strands are oriented in opposite directions, with one strand running 5' to 3' and the other running 3' to 5'. This is known as antiparallel orientation.

These structural differences between DNA and RNA are important because they contribute to the unique functions of these two types of . DNA is responsible for storing genetic information and transmitting it to future generations, while RNA plays a variety of roles in the synthesis and regulation of proteins, as well as other cellular processes.


-----

Key Terms to Review (22)

Adenine (A)

: Adenine is one of the four nitrogenous bases found in DNA and RNA molecules. In DNA, it pairs with thymine (T), while in RNA it pairs with uracil (U).

Antiparallel Orientation

: In biology, antiparallel orientation refers to the opposite arrangement of the sugar-phosphate backbones in a DNA double helix. One strand runs from 5' to 3' direction, and the other runs from 3' to 5'.

Base Pairing Rules

: The base pairing rules refer to the way in which DNA bases pair up. Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).

Chargaff’s Rule

: Chargaff's Rule states that in DNA, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C).

Chromosomes

: Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made up of protein and a single molecule of deoxyribonucleic acid (DNA).

Cytosine (C)

: Cytosine is another one of the four nitrogenous bases found in both DNA and RNA molecules. In both cases, it pairs with guanine (G).

Deoxyribonucleic Acid (DNA)

: DNA is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses.

Double Helix

: A double helix refers to the structure formed by double-stranded molecules of nucleic acids such as DNA.

Genes

: Genes are segments of DNA that carry hereditary information and have specific functions in living organisms.

Guanine (G)

: Guanine is one of the four nucleobases in the nucleic acids DNA and RNA. It pairs with cytosine (C) through three hydrogen bonds.

Hydrogen-Bonding

: Hydrogen bonding is an attractive force between polar molecules where hydrogen is bound to a highly electronegative atom such as oxygen, nitrogen or fluorine.

Messenger RNA (mRNA)

: mRNA is a type of RNA that carries genetic information from the DNA in the nucleus to the cytoplasm, where it serves as a template for protein synthesis.

Nucleic Acids

: Nucleic acids are large biomolecules essential for all known forms of life. They include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which carry genetic information.

Nucleotides

: Nucleotides are the basic building blocks of DNA and RNA. They consist of a sugar, a phosphate group, and a nitrogenous base.

Purines

: Purines are one of the two types of nitrogenous bases found in nucleotides, which make up DNA and RNA. The two purines are adenine (A) and guanine (G).

Pyrimidines

: Pyrimidines are one of the two types of nitrogenous bases found in nucleotides, which make up DNA and RNA. The three pyrimidines are cytosine (C), thymine (T), and uracil (U).

Ribonucleic Acid (RNA)

: RNA is a molecule similar to DNA that plays a crucial role in coding, decoding, regulation, and expression of genes.

Ribosomal RNA (rRNA)

: rRNA is part of ribosomes, serving as structural components and also catalyzing peptide bond formation. It's essential for protein synthesis in all living organisms.

Sugar-Phosphate Backbone

: The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. It consists of alternating sugar and phosphate groups, to which nitrogenous bases are attached.

Thymine (T)

: Thymine is one of the four main nucleobases found in the nucleic acid DNA. It pairs with adenine.

Transfer RNA (tRNA)

: tRNA is a type of RNA that transports specific amino acids to the ribosome during protein synthesis. Each tRNA has an anticodon that pairs with an mRNA codon.

Uracil (U)

: Uracil is a nitrogenous base found only in RNA. It replaces thymine from DNA and pairs with adenine during transcription.


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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.