Bellwork: What are the main differences between RNA and DNA

RNA Section 3.1

What is RNA? Another type of nucleic acid A working copy of DNA Does not matter if it is damaged or destroyed Used to direct the production of proteins that determines an organisms characteristics

What are the differences between RNA and DNA? There are 3 key differences 1) sugar is Ribose rather than De- oxy ribose 2) RNA is generally single stranded 3) RNA contains Uracil rather than Thymine Chemical differences make it easier for a cell to distinguish between RNA and DNA

Functions of RNA Main function – protein synthesis 3 types of RNA Controls assembly of amino acids into proteins 3 types of RNA Messenger RNA Carry information from the DNA to other parts of the cell Ribosomal RNA Ribosomes are made of ribosomal RNA and proteins Transfer RNA Transfers amino acids to the ribosome as/when they are needed

RNA synthesis Transcription Prokaryotes Eukaryotes Segments of DNA serve as template to produce complementary RNA molecules Prokaryotes RNA synthesis and Protein synthesis occurs in the cytoplasm Eukaryotes RNA produced in the nucleus Transcription occurs in the cytoplasm The enzyme RNA polymerase controls transcription One gene can produce hundreds or thousands of RNA molecules

Promoters RNA polymerase will only bind to areas of DNA where a promoter is present Promoter = region of RNA that has specific base sequences Similar signals cause transcription to stop

RNA editing RNA needs a bit of tweaking before it can be put into action Chunks are cut out of them and discarded – introns In eukaryotes, introns are taken out of pre-mRNA molecules whilst they are in the nucleus What is left – exons, are spliced back together to form the final mRNA

Why does RNA polymerase make more than it needs? Scientists still aren’t sure Some pre-mRNA molecules may be cut/spliced in different ways in different tissues – so a single gene can produce several forms of RNA Intron and Exons may play a role in evolution Small changes in DNA sequences can have a large effect on how genes affect cellular function

Summary RNA is a working copy of the DNA Made from small sections of DNA (transcription) RNA polymerase Promoters indicate which part of DNA to use Three key types of RNA Messenger Ribosomal Transfer More is made than needed Introns discarded Exons kept