CHAPTER 17: FROM GENE TO PROTEIN
THE CONNECTION BETWEEN GENES AND PROTEINS
I.
THE STUDY OF METABOLIC DEFECTS PROVIDED EVIDENCE THAT GENES SPECIFY PROTEINS
Garrod’s Hypothesis–
A. How Genes Control Metabolism: One Gene—One Enzyme
1. Beadle and Ephrussi–
2. Beadle and Tatum; Neurospora crassa (see Figure 17.1 p. 305)
a) minimal medium–
b) complete growth medium–
c) the experiment–
d) one gene-one enzyme–
B. One Gene-One Polypeptide–
II.
TRANSCRIPTION AND TRANSLATION ARE THE TWO MAIN STEPS FROM GENE TO PROTEIN: AN
OVERVIEW
A. Similarities and Differences between RNA and DNA
1. Both polymers of nucleotides
2. Deoxyribose–
Ribose–
3. Thymine–
Uracil–
B. Linear sequence of nucleotides in DNA ultimately determines the linear sequence of amino
acids in a protein
C. Transcription of RNA from DNA–
messenger RNA–
D. Translation of mRNA to protein–
E. Differences between prokaryotes and eukaryotes–
RNA processing– primary transcript–
III.
IN THE GENETIC CODE, NUCLEOTIDE TRIPLETS SPECIFY AMINO ACIDS
A. How many nucleotides are needed to code an amino acid
1. triplet code–
template strand–
codons–
2. DNAmRNAprotein– the central dogma–
B. Cracking the Genetic Code–Marshall Nirenberg
1. poly U–
2. *cell-free-extract–
3. start codon–
AUG–
Methionine–
4. 61 codons; code an amino acid–
redundancy but no ambiguity–
5. stop codons–
6. reading frame–
C. The Genetic Code Must Have Evolved Very Early in the History of Life
1. Universality–
Exceptions–
THE SYNTHESIS AND PROCESSING OF RNA
IV.
TRANSCRIPTION IS THE DNA-DIRECTED SYNTHESIS OF RNA: A CLOSER LOOK
A. RNA polymerases–
promoters–
terminator–
transcription unit–
B. RNA Polymerase Binding and Initiation of Transcription
1. transcription factors–
transcription initiation complex–
2. TATA box–a crucial promoter DNA sequence
C. Elongation of the RNA Strand
1. Untwists and opens a short segment of DNA–
2. Linking incoming RNA nucleotides to the 3’ end–
3. Peeling away of the mRNA–
4. DNA re-forms a double helix–
5. Simultaneous transcription–
D. Termination of Transcription–
termination site–
termination sequence–
V.
EUKARYOTIC CELLS MODIFY RNA AFTER TRANSCRIPTION
A. Alteration of mRNA Ends
1. 5” cap–
leader sequence–
2. poly-A tail–
trailer sequence–
B. Split Genes and RNA Splicing
1. heterogeneous nuclear RNA–
2. introns–
exons–
split genes–
3. RNA splicing–
4. small nuclear ribonucleoproteins (snRNPs)–
5. spliceosome–
C. Ribozymes–
D. The Functional and Evolutionary Importance of Introns
1. regulatory role of introns–
2. alternative RNA splicing–
protein diversity–
domains–
THE SYNTHESIS OF PROTEINS
VI.
TRANSLATION IS THE RNA-DIRECTED SYNTHESIS OF A POLYPEPTIDE: A CLOSER LOOK
A. The Structure and Function of Transfer RNA
1. Structure–
2. Function–
3. Anticodon–
4. Wobble–
B. Aminoacyl-tRNA Synthetases
C. Ribosomes
1. Ribosomal RNA–
2. Subunits–
3. P site–
A site–
E site–
D. Building a Polypeptide
1. Initiation–
initiator codon–
initiator tRNA–
initiation factors–
2. Elongation
a) codon recognition–
b) peptide bond formation–
**peptidyl transferase–
c) translocation–
3. Termination–
termination codon–
release factor–
E. Polyribosomes–
F. From Polypeptide to Functional Protein–
post-translational modification–
VII.
SOME POLYPEPTIDES HAVE SIGNAL SEQUENCES THAT TARGET THEM TO SPECIFIC
DESTINATIONS IN THE CELL (see Figure 17.21 p. 320)
A. Signal Peptide–
Signal Recognition Particle–
B. Signal Recognition Particle Receptor–
Translocation Complex
VIII. RNA PLAYS MULTIPLE ROLES IN THE CELL: A REVIEW
IX.
COMPARING PROTEIN SYNTHESIS IN PROKARYOTES AND EUKARYOTES: A REVIEW
A. Prokaryotes–
B. Eukaryotic cells–
X.
POINT MUTATIONS CAN AFFECT PROTEIN STRUCTURE AND FUNCTION
A. Types of Point Mutations
1. Substitutions–
a) base-pair substitution–
b) missense mutation–
c) nonsense mutation–
2. Insertions or Deletions
a) base-pair insertion–
b) base-pair deletion–
c) frameshift mutation–
B. Mutagens–
XI.
WHAT IS A GENE? Revisiting the question