Biology DNA and RNA Structure and Function

DNA and RNA Structure and Function

• DNA stands for Deoxyribonucleic Acid
• RNA stands for Ribonucleic Acid
• DNA base pairing: Adenine (A) with Thymine (T), Cytosine (C) with Guanine (G)
• RNA base pairing: Adenine (A) with Uracil (U), Cytosine (C) with Guanine (G)
• Nucleotides are the building blocks of DNA and RNA
• Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base
• Base pairing is the specific pairing of nitrogenous bases

Transcription

• Transcription is the process of copying DNA into mRNA
• RNA polymerase synthesizes RNA during transcription
• Promoter regions signal the beginning of a gene, where RNA polymerase binds
• During Transcription, introns (non-coding regions) are removed from mRNA.
• The termination phase of transcription ends when RNA polymerase reaches a terminator sequence in DNA, causing the RNA strand to detach.
• mRNA processing modifies pre-mRNA (the initial mRNA transcript) to a mature mRNA, by adding a 5' cap, and a poly-A tail. These components protect mRNA from degradation and help in ribosome binding. Spliceosomes remove introns, joining exons forming the mature mRNA.

Translation

• Translation is the process of converting mRNA into a protein.
• Codons are sets of three nucleotides in mRNA that specify amino acids.
• tRNA (transfer RNA) brings the appropriate amino acids to the ribosome based on the codon sequence in mRNA.
• Ribosomes (composed of rRNA and protein) are the site of protein synthesis.
• The start codon (AUG) signals the beginning of protein synthesis, coding for methionine.
• Stop codons (UAA, UAG, UGA) signal the end of protein synthesis.
• Polypeptide chains are formed by linked amino acids; these eventually fold to form functional proteins.
• Release factors recognize stop codons and terminate protein synthesis, prompting the ribosome to release the polypeptide chain.
• There are 20 standard amino acids.

Protein Synthesis

• mRNA processing: the modification of mRNA after transcription, including adding a 5' cap and poly-A tail. Spliceosomes remove introns and join exons.
• Chaperone proteins help proteins fold correctly.
• Eukaryotic vs. prokaryotic transcription: Eukaryotic transcription occurs in the nucleus, while prokaryotic transcription occurs in the cytoplasm.
• Mutations can change the amino acid sequence of a protein, affecting its function and stability.
• Frameshift mutations occur when nucleotides are added or deleted, shifting the reading frame completely.

Central Dogma of Molecular Biology

• The central dogma states that genetic information flows from DNA to RNA to protein.