Nucleic Acids: Structure, Function, and Genetic Information

Nucleic Acids

Definition and Role

Nucleic acids are biological macromolecules that store, transmit, and express genetic information in living organisms. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• Gene: A segment of DNA containing instructions to build a protein.

• Gene Expression: The process by which genetic information is used to synthesize proteins, involving transcription and translation.

• Transcription: DNA is copied into messenger RNA (mRNA).

• Translation: mRNA is used as a template to assemble amino acids into proteins.

Monomer: Nucleotide

Structure of Nucleotides

Nucleic acids are polymers made of nucleotide monomers. Each nucleotide consists of three components:

• Phosphate group

• Five-carbon sugar (pentose): either deoxyribose (in DNA) or ribose (in RNA)

• Nitrogenous base: Purines or Pyrimidines

Nitrogenous Bases

• Purines: Double-ring structure; adenine (A) and guanine (G)

• Pyrimidines: Single-ring structure; cytosine (C), thymine (T) (DNA only), and uracil (U) (RNA only)

Sugar Component

• Deoxyribose: Found in DNA; lacks an oxygen atom at the 2' carbon

• Ribose: Found in RNA; contains an oxygen atom at the 2' carbon

Nucleotide Polymers

Formation and Bonding

Nucleotides are joined together by phosphodiester bonds to form nucleic acid polymers.

• Bonds form between the phosphate group of one nucleotide and the sugar of the next.

• The 5' end of a nucleic acid has a phosphate group; the 3' end has a hydroxyl group.

Directionality

• Nucleic acids have directionality: 5' to 3' ends.

• During synthesis, nucleotides are added to the 3' end.

Central Dogma of Molecular Biology

Flow of Genetic Information

• DNA → RNA → Protein

• DNA is transcribed into RNA, which is then translated into protein.

Nucleic acids encode the information needed to make proteins, which perform essential cellular functions.

Structure of DNA and RNA

DNA Structure

• Double helix: Two strands twisted around each other.

• Base pairing: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

• Strands run in opposite directions (antiparallel).

• Complementarity: Ensures accurate replication and transmission of genetic information.

RNA Structure

• Single-stranded: RNA usually exists as a single strand.

• Can fold into complex shapes, but does not form a double helix like DNA.

• Contains uracil (U) instead of thymine (T).

Summary Table: DNA vs. RNA

Feature	DNA	RNA
Strands	Double-stranded	Single-stranded
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Function	Stores genetic information	Transmits genetic information, protein synthesis

Key Equations

• Phosphodiester bond formation: $\text{Nucleotide}_1 + \text{Nucleotide}_2 \rightarrow \text{Nucleotide}_1\text{-}P\text{-}O\text{-}Nucleotide_2$

• Central Dogma: $\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$

Example

• Example of base pairing: In a DNA molecule, if one strand has the sequence 5'-ATCG-3', the complementary strand will be 3'-TAGC-5'.

Additional info: The notes briefly mention the importance of antiparallel strands and complementarity for accurate replication, which is essential for cell division and inheritance.