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RNA and Protein Synthesis. Structure of RNA. Ribonucleic acid or RNA is a single stranded nucleic acid. It contains the sugar ribose. RNA contains the base pairs adenine, uracil, guanine, and cytosine. Types of RNA. RNA is important in the creation of proteins or protein synthesis.
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Structure of RNA • Ribonucleic acid or RNA is a single stranded nucleic acid. • It contains the sugar ribose. • RNA contains the base pairs adenine, uracil, guanine, and cytosine
Types of RNA • RNA is important in the creation of proteins or protein synthesis. • There are three main types of RNA: • Messenger RNA • Ribosomal RNA • Transfer RNA
Messenger RNA/mRNA • Most genes carry instruction for assembling amino acids into proteins. • The RNA molecule that carries the copies of these instructions from the DNA to the ribosome is the messenger RNA.
Ribosomal RNA/rRNA • Proteins are assembled on ribosomes. • Ribosomal RNA is a part of the ribosome that helps in the construction of the protein.
Transfer RNA/tRNA • During the construction of a protein, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by the coded message in the mRNA. • The transfer of amino acids is done by tRNA.
Transcription • RNA molecules are produced by copying part of the DNA sequence into a complementary sequence in RNA…this is called transcription. • In order for transcription to occur, an enzyme called RNA polymerase is required.
RNA Polymerase • RNA polymerase binds to and separates the DNA strands. • Then RNA polymerase uses one strand of DNA as a template from which the nucleotides are assembled into a strand of RNA. • RNA polymerase knows were to start and stop because it binds to an area called a promoter, which has a specific DNA sequence. • RNA will stop at a similar signal in the DNA once the new RNA is completed.
RNA Editing • The DNA of eukaryotes does sometimes carry sequences of nucleotides that are not involved in coding for proteins. These are called introns. • The sequences that code for proteins are called exons because they are expressed. • When RNA molecules are formed, both introns and exons are copied. • The introns are cut out while the molecule is still in the nucleus, the exons are then spliced together making the mRNA molecule.
Genetic Code • Proteins are made by the joining of amino acids into long chains called polypeptides. • There are only 20 different amino acids, but these combine to make all of the protein in your body. • The language of mRNA is called the genetic code. • RNA is written in a language with only four letters: AUGC
The Genetic Code • In order for the language of the RNA to be translated into amino acids it must be read as three letter words. • Each three letter word is called a codon. • A codon is three nucleotides (AUGC) that code for a specific amino acid. • UCGCACGGU – if this is the mRNA • UCG-CAC- GGG – are the codons • Serine-Histidine-Glycine – are the amino acids
The Genetic Code • Because there are four different bases there are 64 combinations. (4 x4 x4) • The codon AUG signifies a start or initation. • UGA, UAA, UAG are stop codons • All of these sequences can be decoded using the codon chart.
Translation • The ability to read and put together the genetic information to build the proteins is done by the ribosome. • The decoding of the message of the mRNA into the polypeptide (protein) is the process called translation.
Translation • Messenger RNA is transcribed in the nucleus. • mRNA then attaches to a ribosome, each codon moves through the ribosome, until it finds the start codon. • The ribosome continues to read the mRNA chain and the tRNA brings the appropriate amino acid to the ribosome. • The tRNA matches the mRNA by using three unpaired bases known as anticodons.
Translation • The tRNA anticodons match as follows: • If the mRNA codes AUG, the tRNA anticodon is UAC • If the mRNA codes UUC, the tRNA anticodon is AAG. • The tRNA anticodon is what determine which amino acid will be brought to the ribosome.
Translation • As the tRNA is bringing the amino acid to the ribosome the next tRNA is attaching to the ribosome. • This process works like an assembly line, until it reaches the stop codon. • Each new tRNA, brings a new amino acid, and the peptide bonds create the new protein. • Once the stop codon is reached, the protein, and the mRNA are released from the ribosome and translation is complete. http://www.biostudio.com/demo_freeman_protein_synthesis.htm
