Bio

• DNA directs the production of proteins via RNA
• Genetic information flows from DNA to RNA to protein
• Transcription creates a molecule of RNA from a molecule of DNA
• Translation involves the coordination of three kinds of RNA
• Translation creates a molecule of protein via the genetic code
• RNA acts as an intermediate link between DNA in the nucleus and protein synthesis in the cytoplasm
• RNA is a chain of nucleotides composed of ribose, phosphate group, and a nitrogen-containing base
• Sugar in RNA is ribose (Sugar in DNA is deoxyribose; missing an oxygen atom)
• RNA has the base uracil in place of thymine
• RNA is a single strand of nucleotides (DNA is double-stranded)
• Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA
• RNA is evolutionary older than DNA
• Thymine is methylated form of Uracil, and so gives a more stabilized structure to DNA
• Transcription converts a gene into a single-stranded RNA molecule
• RNA polymerase recognizes the transcription start site (promoter) of a gene, splits open the double-stranded DNA and transcribes just the template strand of DNA, stringing together a complementary strand of RNA nucleotides
• The new mRNA strand is processed (mRNA processing)
• The mRNA transcript moves to the cytoplasm for translation
• Methylated 5’ Cap helps the mRNA strand bind to a ribosome and prevents the strand from being broken down too fast
• Poly (A) tail helps the mRNA molecule exit the nucleus and adds stability to the mRNA
• RNA splicing: Noncoding sections called introns are removed from the mRNA
• Introns are noncoding sections of DNA
• Exons are coding sections of DNA
• After mRNA is transcribed, all introns are cut out and exons are joined together before mRNA leaves the nucleus. This mechanism allows various combinations of exons, resulting in different proteins
• Introns may protect DNA against harmful mutations and regulate gene expression
• Both transcription and replication occur within the nucleus
• Both transcription and replication are catalyzed by large, complex enzymes (Polymerases)
• Both transcription and replication involve unwinding of the DNA double helix
• Translation converts an mRNA message into a polypeptide, or protein
• Both transcription and replication involve complementary base pairings to the DNA strand
• A three-nucleotide sequence (codon) codes for an amino acid
• If one nucleotide coded for one amino acid, RNA could code for only four amino acids
• If two nucleotides coded for one amino acid, RNA could code for 16 amino acids
• If three nucleotides coded for one amino acid, RNA could code for 64 amino acids (enough to cover the 20 amino acids)
• Many amino acids are coded for by more than one codon
• Codons are read, without spaces, as a series of three non-overlapping nucleotides (Reading frame)
• Ribosome is needed for translation
• There are three stop codons (UAA, UAG, UGA) and one start codon (AUG - methionine)
• Changing the reading frame completely changes the resulting protein (Frameshift mutation)
• Small subunit holds onto the mRNA strand, Large subunit catalyzes the reaction that forms the bonds between amino acids
• Ribosomes are also made of RNA (rRNA)