Nucleic Acids: DNA & RNA Structure

Nucleic Acids: DNA & RNA Structure and Function

• Nucleic acids are linear polymers
• They store and pass genetic information

Nucleotide Structure

• Nucleotides are the building blocks
• Each nucleotide contains a phosphate group, a sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base
• Nitrogenous bases include purines (adenine, guanine) and pyrimidines (cytosine, thymine in DNA, uracil in RNA)

DNA Structure

• DNA is a double helix
• Two antiparallel strands wound around each other
• The strands are held together by hydrogen bonds between complementary nitrogenous bases (A with T, and G with C)
• DNA has a sugar-phosphate backbone

RNA Structure

• RNA is typically single-stranded
• The sugar in RNA is ribose
• The nitrogenous base uracil replaces thymine in RNA
• Several types of RNA exist including mRNA, tRNA, and rRNA
• Several other non-coding RNAs function in gene regulation

Chargaff's Rule

• In DNA, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine

DNA Packaging

• DNA is packaged into structures called chromosomes
• DNA wraps around proteins called histones to form nucleosomes
• Further packaging coils the nucleosomes into a tightly packed structure

Central Dogma

• DNA -> RNA -> Protein
• DNA replication makes copies of DNA
• Transcription converts DNA to RNA
• Translation converts RNA to protein

Types of RNA

• mRNA - carries the genetic code for protein synthesis
• tRNA - carries amino acids to the ribosome
• rRNA - forms the ribosome structure
• Other Types: snRNA (small nuclear RNA), snoRNA (small nucleolar RNA), miRNA (microRNA), siRNA, lncRNA (long non-coding RNA), and circRNA (circular RNA)

Gene Structure

• Genes are segments of DNA that code for proteins
• A gene contains an exon (region coding for protein) and intron (region not coding for protein)

Transcription

• Transcription is the process of making RNA from DNA
• RNA polymerase synthesizes RNA
• It proceeds in 3 stages: Initiation – Elongation – Termination

Translation

• Translation is the process of making protein from mRNA
• mRNA is read by ribosomes
• tRNA brings amino acids to the ribosome
• Amino acids are linked together to form a polypeptide chain
• The polypeptide chain folds into a functional protein

Gene and DNA - Differences

• Gene is a sequence of DNA or RNA that codes for a functional product
• DNA is a molecule composed of two strands forming a double helix carrying the genetic instructions needed in the growth, development, and functioning of all living organisms