13.1 Notes

The Role of DNA

• Cell separates the two strands od DNA and then uses base pairing to make a new complementary strand for each.

RNA: like DNA, is a nucleic acid that consists of a long chain of proteins.

• Genes contain coded DNA instructions that tell cells how to make proteins.

1. First step, copy base sequence of DNA into RNA.
2. Second step, RNA uses these instructions to direct the production of proteins.(determin characteristics of an organism.)

Comparing RNA and DNA

RNA                                                                      DNA
1. sugar is ribose                                                 1. sugar is deoxyribose
2. single stranded                                                2. double stranded
3. contains Uracil                                                 3. contains Thymine
4. leaves Nucleus and goes to Ribosomse         4. stays at Nucleus

• Because of differences enzymes can tell them apart

Functions of RNA

• Controlls the assembly of amino acids into proteins. Different types of RNA molecules specializes in different jobs.
• 1. Messenger RNA( mRNA): Carries instructions for proteins from the Nucleus to ribosomes in the cytoplasm.
• 2. Ribosomal RNA( rRNA): Forms an important part of both subunits of the ribosome.
• 3. Transfer RNA( tRNA): Carries amino acids to the ribosome and matches them to the coded mRNA message.

Transcription:
Segments of DNA serve as templates to produce complementary RNA molecules.

• In prokaryotes RNA synthesis and protein synthesis take place in cytoplasim.
• In eukaryotes RNA is poduced in Nucleus and then moves to cytpolasm to produce proteins

Transcription requires an enzyme RNA polymerase

• 1. Binds to DNA during transcription and separates DNA strands.
• 2. Uses strand of DNA as a template to produce a complementary strand of RNA

Promoters

RNA polymerase knows where to start and stop making a strand of RNA

• It binds to promoters, regions of DNA that have specific base sequence.
• Promoters signal in DNA molecule that show RNA polymerase exactly where to begin making RNA

RNA Editing

• RNA molecules need editing before they can be read.
• pre-mRNA molecules have bits cut out of them before they can go into action.

Introns: the portions that are cut out of the pre-mRNA also known as Exons( in eukaryotes) but the introns are taken out in the nucleus. The remaining pieces are then sliced back together to form the final mRNA.

• Introns and exons may play a role in evolution, making it possible for very small changes in DNA sequences to have dramatic effects on how genes affect cellular function.