Nucleic Acids and DNA/RNA

Nucleic Acids

• Nucleic acids store information for cellular growth and reproduction.
• They transfer genetic information from one generation to the next.
• There are two types of nucleic acids: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).
• Both DNA and RNA are polymers consisting of long chains of monomers called nucleotides.

Nucleotides

• Nucleotides contain three components: a nitrogenous base, a pentose sugar, and a phosphate group.
• Nitrogenous bases are non-protein, cyclic compounds having nitrogen.
• There are two types of nitrogenous bases: Purines (with two rings) and Pyrimidines (with one ring).
• Pentose sugars are ribose (in RNA) and deoxyribose (in DNA).
• The sugar and phosphate group form the backbone of nucleic acids, while the nitrogenous bases project inward from the backbone.

Nucleosides and Nucleotides

• A nucleoside consists of a nitrogenous base linked by a glycosidic bond to C1’ of a ribose or deoxyribose.
• A nucleotide is a nucleoside that forms a phosphate ester with the C5’ OH group of ribose or deoxyribose.

Functions of Nucleotides

• Nucleotides are energy carriers, electron carriers, coenzymes, and activators of metabolites.
• They are also involved in the expression and transmission of genetic information.

Nucleotide as Energy Carrier

• Nucleotides carry chemical energy in cells in the form of nucleoside mono-, di-, and triphosphates.
• Hydrolysis of nucleoside triphosphates provides the chemical energy to drive a wide variety of cellular reactions.

Central Dogma

• The central dogma is the process by which genetic information is transferred from DNA to RNA to proteins.

DNA and RNA Structure

• DNA is a double-stranded helix with two strands of nucleotides that wind together in opposite directions.
• The base pairs are arranged in step-like pairs and held together by hydrogen bonding.
• RNA is single-stranded and transmits information from DNA to make proteins.

Types of RNA

• There are three major classes of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• mRNA carries genetic information from DNA to the ribosomes.
• tRNA brings amino acids to the ribosome to make proteins.
• rRNA makes up 2/3 of ribosomes where protein synthesis takes place.

Genetic Code

• The genetic code is a collection of base sequences that corresponds to each amino acid.
• It is a triplet of nucleotides that code for 20 amino acids.

mRNA

• mRNA has a long sequence of adenine nucleotides (a “poly-A tail”) on the 3’-end of the RNA chain.
• It also has a “cap” on the 5’-end consisting of a molecule of 7-methylguanosine.

tRNA

• tRNA has a triplet called an anticodon that complements a codon on mRNA.
• It bonds to a specific amino acid at the acceptor stem.

rRNA

• rRNA is found in association with several proteins as components of the ribosomes.
• There are three distinct sizes of rRNA: 23S, 16S, and 5S in prokaryotes, and 28S, 18S, 5.8S, and 5S in eukaryotes.

Differences between DNA and RNA

• DNA is double-stranded, while RNA is single-stranded.
• DNA has deoxyribose sugar, while RNA has ribose sugar.
• DNA has thymine as a pyrimidine base, while RNA has uracil.
• DNA is found in the nucleus and mitochondria, while RNA is found in the nucleus, mitochondria, and cytoplasm.