1. From Gene to Protein: Transcription & RNA Processing
Chapter

2. Important Terms to Know…
25% of students confuse these terms in FRQs!!
Replication
Copying of DNA prior to cell division (DNA  DNA)
Not prior to transcription!
Transcription
Making mRNA copy from DNA prior to protein synthesis (DNA  RNA)
Translation
Decoding mRNA and making a protein (RNA  Protein)

3. 17.1
Genes specify proteins via transcription and translation

4. Understanding Genes  Proteins
Scientists connected metabolic disorders to genes
Ex: alkaptonuria
Urine blackens when exposed to air due to missing enzyme that metabolizes alkapton
Beadle & Tatum studied bread mold
Introduced mutations and saw that mutating certain genes caused metabolic defects
One gene, one enzyme hypothesis
Not all proteins are metabolic (ex: keratin), so hypothesis is now one gene, one polypeptide

5. 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

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

7. 3* Types of RNA mRNA: carries DNA message from nucleus to cytoplasm
tRNA: carries amino acids from cytoplasm to ribosome
rRNA: forms part of ribosomes
*other types of RNA exist but we will talk about those later

8. Steps in Gene Expression
Transcription
RNA processing (eukaryotes only)
Translation
Prokaryote
Steps occur simultaneously
Eukaryote
Steps are separate

9. 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
NOT ambiguous: each codon codes for 1 amino acid

10. 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

11. 17.2
Transcription is the DNA-directed synthesis of RNA

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

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

14. Transcription: Elongation
RNA polymerase moves along template strand of DNA adding complimentary RNA nucleotides
Reads in 3’5’ direction
This means mRNA is synthesized 5’3’ direction
A – U; G – C

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

17. 17.3
Eukaryotic cells modify RNA after transcription

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