PROTEIN SYNTHESIS Flow of Genetic Information The flow of genetic information can be symbolized as: DNA RNA Protein This is also known as: The central dogma of molecular biology Protein Proteins are made of amino acids linked together by peptide bonds 20 different amino acids exist Amino acid chains are called polypeptides RNA DNA alone cannot tell your cells how to make proteins. It needs the help of RNA, ribonucleic acid, the middle player in the central dogma of molecular biology. DNA "lives" in the nucleus, but proteins are made on the ribosomes in the cytoplasm How does the genetic information get from the nucleus to the cytoplasm? RNA is the answer. RNA v DNA RNA, like DNA, is a nucleic acid. However, RNA differs from DNA in several ways. In addition to being smaller than DNA, RNA also Consists of one nucleotide chain instead of two. Contains the nitrogen base uracil (U) instead of thymine. Contains the sugar ribose instead of deoxyribose. Types of RNA There are three main types of RNA, all of which are involved in making proteins.
Messenger RNA (mrna) copies the genetic instructions from DNA in the nucleus, and carries them to the cytoplasm. Ribosomal RNA (rrna) helps form ribosomes, where proteins are assembled. Transfer RNA (trna) brings amino acids to ribosomes, where they are joined together to form proteins. Messenger RNA Long Straight chain of nucleotides Made in the nucleus Copies DNA & leaves through nuclear pores Contains the Nitrogen Bases Nitrogen bases A, G, C, T ( no T ) Carries the information for a specific protein Made up of 500 to 1000 nucleotides long Sequence of 3 bases called codons AUG methionine or start codon UAA, UAG, or UGA stop codon Ribosomal RNA (rrna) rrna is a single strand 100 to 3000 nucleotides long Globular in shape Made inside the nucleus of a cell Associates with proteins to form ribosomes Site of protein synthesis
Transfer RNA (trna) Clover leaf shape Single stranded molecule with attachment site at one end for an amino acid Opposite end has three nucleotide bases called the anticodon The Genetic Code A codon designates an amino acid An amino acid may have more than one codon There are 20 amino acids, but 64 possible codons Some codons tell the ribosome to stop translating Protein Synthesis The production or synthesis of polypeptide chains (proteins) Two phases: Transcription and Translation mrna must be processed before it leaves the nucleus of eukaryotic cells Transcription Translation Transcription The process of copying the sequence of one strand of DNA, the template strand mrna copies the template strand Requires the enzyme RNA polymerase During transcription, RNA polymerase binds to DNA and separates the DNA strands RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
mrna Processing (Extra Detail) Introns, non-functional segments of DNA are snipped out of the chain Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase A guanine triphosphate cap is added to the 5 end of the newly copied mrna A poly A tail is added to the 3 end of the RNA The newly processed mrna can then leave the nucleus Ribosomes Made of a large and small subunit Composed of rrna (40%) and proteins (60%) Have two sites for trna attachment --- P & A Translation mrna leaves the nucleus through its pores and goes to the ribosomes Translation is the process of decoding the mrna into a polypeptide chain Ribosomes read mrna three bases or one codon at a time and construct the proteins
Steps of Translation During translation, amino acids are assembled from information encoded in mrna. As the mrna codons move through the ribosome, trna s add specific amino acids to the growing polypeptide chain. The process continues until a stop codon is reached and the newly made protein is released.
Protein Synthesis: