RNA and Protein Synthesis How are Genes Expressed?

Genes and Proteins Genes are instructions for assembling proteins. How do proteins result in phenotype? Many proteins are enzymes that catalyze and regulate chemical reactions. Some genes may do things like code for enzyme that produces pigment in a flower. Proteins are key to almost everything a cell does!

The Roles of RNA and DNA RNa DNA “blueprints”/Recipe Card Disposable Used on the job “master plan”/Cookbook Contain all of the information/recipes Kept safely in an office/ kitchen (nucleus)

Structure of RNA vs. DNA RNA DNA Made of nucleotides Sugar = ribose Single strand Uracil (instead of Thymine) Made of nucleotides Sugar = deoxyribose Double strand Thymine

Types of RNA Most are involved in protein synthesis. 3 Types: 1. messenger RNA (mRNA) Carry copies of the protein-assembling instructions from DNA to ribosomes 2. ribosomal RNA (rRNA) One component of ribosomes, which direct the assembly of amino acids into proteins 3. transfer RNA (tRNA) Bring amino acids to the ribosome according to the mRNA’s coded message

Transcription Definition: the copying of a nucleotide sequence of DNA into a complementary sequence in RNA RNA polymerase binds to DNA at “promoters” (specific base sequences that tell the enzyme where to start making RNA). It then separates the DNA strands and uses one strand as a template from which nucleotides are assembled into a strand of RNA.

RNA editing Before it is functional, a newly made RNA strand is modified. Pieces called “introns” (intervening sequences) are cut out, while… Pieces called “exons” (expressed sequences) are spliced back together. A cap and a tail are added to complete the process. Why? Perhaps to enable formation of multiple RNA molecules from the same gene. Hairpins, polyadenylation, associated proteins – controls translation

The Genetic Code Proteins are made of linked amino acids… “Polypeptides” 20 different amino acids Sequence of amino acids determines properties of the protein (hydrophobic, polar, charged) The language of the mRNA instructions is the “genetic code.” Each word is 3 nucleotides long – a “codon” – and specifies a certain amino acid.

Translation Ribosomes are the cellular factories that read and follow the instructions for creating a polypeptide. Translation: decoding information from messenger RNA to produce proteins. The mRNA molecule made during transcription attaches to a ribosome. Transfer RNAs (tRNA) bring amino acids to build the polypeptide (protein). Anticodons of tRNA complement each codon.

Translation The ribosome connects the amino acids to each other with peptide bonds. Once amino acids are delivered, the tRNAs are released. The protein continues to grow until a stop codon is reached. The newly formed polypeptide is released.