Gene expression

• Gene expression involves the transcription and translation of DNA sequences
• Only a fraction of the genes in a cell are expressed
• Transcription and translation involve three types of RNA: mRNA, tRNA, rRNA
• RNA is single-stranded and composed of nucleotides containing ribose sugar, phosphate, and one of four bases: cytosine, guanine, adenine, and uracil
• Messenger RNA (mRNA) carries a copy of the DNA code from the nucleus to the ribosome
• Transfer RNA (tRNA) carries its specific amino acid to the ribosome
• Ribosomal RNA (rRNA) and proteins form the ribosome
• mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm
• Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid
• RNA polymerase moves along DNA unwinding the double helix and synthesizes a primary transcript of mRNA from RNA nucleotides by complementary base pairing
• Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids
• Peptide bonds join the amino acids together
• Different proteins can be expressed from one gene depending on which exons are retained
• Polypeptide chains fold to form the three-dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids
• Transcription


  The process of copying genetic information from DNA into RNA.
• Translation


  The process of translating genetic information from RNA into a protein.
• DNA


  The double-stranded molecule that contains the genetic code for all living organisms.
• RNA polymerase


  The enzyme that catalyzes the transcription of DNA into RNA.
• mRNA


  The single-stranded RNA molecule that is synthesized during transcription and serves as the template for protein synthesis.
• Ribosomes


  The complexes of RNA and protein that facilitate the translation of mRNA into protein.
• tRNA


  The small RNA molecules that deliver amino acids to the ribosome during translation.
• Amino acids


  The building blocks of proteins.