RNA & Protein synthesis

DNA vs. RNA DNA can be compared to the “master plan” of a builder RNA can be compared to the “disposable copies/blueprints” It goes to the protein-building ribosome site in the cytoplasm (job site) RNA is made from the DNA Single stranded Contains uracil Contains ribose DNA can be compared to the “master plan” of a builder It stays safely in the nucleus (office) Double stranded Contains thymine Contains deoxyribose

How are genes expressed? Genes are coded DNA instructions that control the production of proteins within the cell. The 1st step in decoding the DNA is to copy part of the nucleotide sequence into RNA RNA = ribonucleic acid The RNA’s make proteins

What is RNA? RNA consists of a long chain of nucleotides (like DNA) A sugar called ribose A phosphate group A nitrogenous base Adenine (A) Uracil (U) … not Thymine (T) Cytosine (C) Guanine (G) RNA is single-stranded

RNA Nucleotide Phosphate Group Ribose Sugar Nitrogenous Base

RNA Structure Phosphate Group Nitrogenous Base Ribose Sugar

Types of RNA RNA’s assemble amino acids into proteins There are 3 types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)

Messenger RNA Copies instructions in genes Serves as a “messenger” from the DNA to the cell

Ribosomal RNA Ribosomes make proteins Ribosomes are made of proteins and contain their own RNA

Transfer RNA Transfer amino acids to ribosomes based on specified codes in mRNA

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How is RNA made? RNA is made by transcription: DNA to RNA Transcription uses an 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 (stencil) from which nucleotides are assembled into a strand of RNA For example: DNA: ACTGTGGACCT RNA: UGACACCUGGA http://www.johnkyrk.com/DNAtranscription.html TRANSCRIPTION

The Genetic Code Remember: Proteins are chains of amino acids called polypeptides The order of the amino acids determines the properties of the protein The instructions for making different amino acids are in the mRNA = the genetic code The genetic codes is read 3 letters at a time, so each “word” is 3 bases long = codon

How are proteins made? Proteins are made by translation: RNA to protein Translation occurs in the cytoplasm During translation, the cell uses information from mRNA to make proteins. mRNA instructs amino acids on tRNA to join together in the ribosome containing rRNA http://www.johnkyrk.com/DNAtranslation.html

What is tRNA again? Transfer RNA brings amino acids to the ribosome. One end of the tRNA has an amino acid, the other end has 3 bases called the anticodon, that are complementary to one of the mRNA codons Amino acid Anticodon

Codons Three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide For example: RNA: UCGCACGGU Codons: UCG-CAC-GGU Amino acids: Serine-Histidine-Glycine There are 64 possible codon combinations, but there are only 20 amino acids! *More than one codon can code for an amino acid

When does it begin or end? There is 1 “start” codon that initiates protein synthesis if it is the 1st codon (otherwise it codes for an amino acid) AUG There are 3 “stop” codons that do not code for any amino acid and signify the end of a polypeptide. UAA UAG UGA

Let’s try to make a protein! DNA: CCAGATAGGTTT mRNA: GGUCUAUCCAAA codons: GGU-CUA-UCC-AAA tRNA: CCA-GAU-AGG-UUU Amino acids for the mRNA codons on tRNA’s: Glycine-Leucine-Serine-Lysine