RNA Protein synthesis DNA vs RNA DNA can

RNA & Protein synthesis

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

How are genes expressed? • Genes are coded DNA instructions that control the production of proteins within the cell. • The 1 st 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 Nitrogenous Base Ribose Sugar

RNA Structure ate Phosph Group Nitrogenous Base Ribose Sugar

Types of RNA • RNA’s assemble amino acids into proteins • There are 3 types of RNA – Messenger RNA (m. RNA) – Ribosomal RNA (r. RNA) – Transfer RNA (t. RNA)

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 m. RNA

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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: RNA: ACTGTGGACCT 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 m. RNA = 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 m. RNA to make proteins. • m. RNA instructs amino acids on t. RNA to join together in the ribosome containing r. RNA http: //www. johnkyrk. com/DNAtranslation. html

What is t. RNA again? • Transfer RNA brings amino acids to the ribosome. • One end of the t. RNA has an amino acid, the other end has 3 bases called the anticodon, that are complementary to one of the m. RNA 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: Codons: UCGCACGGU 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 1 st 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 m. RNA: GGUCUAUCCAAA codons: GGU-CUA-UCC-AAA t. RNA: CCA-GAU-AGG-UUU Amino acids for the m. RNA codons on t. RNA’s: Glycine-Leucine-Serine-Lysine