1. FROM GENE TO PROTEIN: TRANSCRIPTION & RNA PROCESSING Chapter 17

2. Important Terms to Know… 25% of students confuse these terms in free response questions!! Replication Copying of DNA prior to cell division (DNA  DNA) Transcription Making mRNA copy from DNA prior to protein synthesis (DNA  RNA) Translation Decoding mRNA and making a protein (RNA  Protein)

3. Central Dogma of Molecular Genetics: Crick Information coded in DNA is transcribed into mRNA and then translated into proteins DNA  RNA  protein Collectively known as gene expression

4. DNA vs. RNA RNA Double stranded Deoxyribose sugar Bases: A, T, C, G Remains in nucleus DNA Single stranded Ribose sugar Bases: A, U, C, G U pairs with A Found in nucleus or cytoplasm

5. 4 Types of RNA 1. mRNA: carries DNA message from nucleus to cytoplasm 2. tRNA: carries amino acids from cytoplasm to ribosome 3. rRNA: forms part of ribosomes 4. snRNA: involved in RNA processing (eukaryotes only)

6. Steps in Gene Expression 1. Transcription 2. RNA processing (eukaryotes only) 3. Translation Prokaryote Eukaryote

7. The Genetic Code Made of 3 letter codes: codons (found on mRNA) It is the same in almost all organisms Redundant: more than one codon for some AA’s

8. Overview of Protein Synthesis Begins with DNA Transcription: in nucleus, DNA message copied into mRNA mRNA is edited prior to leaving the nucleus (eukaryotes) Translation: mRNA message translated into amino acids at ribosomes

9. Transcription Components necessary: 1. RNA polymerase enzyme Separate DNA strand, add RNA nucleotides 5’  3’ 2. Promoter DNA sequence where transcription begins Different in prokaryotes and eukaryotes 3. Terminator DNA sequence where transcription ends Prokaryotes only 4. Transcription unit DNA to be transcribed into mRNA

10. Transcription: Initiation RNA polymerase recognizes and binds to promoter “upstream” of gene to be transcribed RNA polymerase unwinds DNA

11. Transcription: Elongation RNA polymerase moves along template strand of DNA adding complimentary RNA nucleotides 5’  3’ direction A – U; G – C

12. Transcription: Termination Terminator sequence in DNA is transcribed Signals to polymerase to detach from DNA and release transcript

14. RNA processing Eukaryotic mRNA must be modified: Exons: coding sequences of DNA (“ex”presed) Introns: non-coding regions, must be cut out by enzymes 5’ cap and poly-A tail added to protect mature mRNA