1. Chapter 17 Hon. Adv. Biology Notes 12/01/06
From Gene to Protein
Chapter 17
Hon. Adv. Biology Notes
12/01/06

2. Connection between Genes and Proteins
Evidence that genes specify proteins
Overview: “Central Dogma of Molecular Genetics”
“The Code” – nucleotide triplets specify a.a.’s
Evolution of the code
Synthesis and Processing of RNA
A closer look: Transcription
RNA processing occurs in eukaryotic cells
Synthesis of Protein
A closer look: Translation
Signal peptides – target specific cell destinations
Review: Roles of RNA in the cell
Review: Comparison of protein synthesis in prokaryotes and eukaryotes
Point mutations can affect protein structure and function
Wrap-up: “So, What is a gene?”

3. Lecture Objectives Compare the structure of RNA with that of DNA.
Summarize the process of transcription.
Relate the role of codons to the sequence of amino acids that results after translation.
Outline the major steps of translation.
Discuss the evolutionary significance of the genetic code.

4. Figure 17.1 Beadle and Tatum’s evidence for the one gene-one enzyme hypothesis

5. RNA vs. DNA
there are 3 major differences between the 2 forms of nucleic acids
Composition of sugar backbone (reflects name)
RNA - ribonucleic acid (ribose)
DNA - deoxyribonucleic acid (deoxyribose)
number of strands: RNA = 1 and DNA = 2
RNA does not have thymine as a nitrogen base, instead uracil (U) is substituted in its place (back)

6. Central Dogma of Molecular Genetics
Explains the flow of information from gene to protein.
Replication: flow of gene from one generation to the next
Transcription: flow of info from DNA to RNA
Translation: conversion of info from nucleic acid language into protein

7. Transfer of Information from DNA to RNA
Transcription: mRNA production, or the synthesis of other types of RNA
Short segment of DNA (gene) is transcribed into mRNA for movement out of the nucleus to the ribosome
DNA is used as a template to make a complementary piece of “messenger RNA”. This requires the aid of the RNA polymerase enzyme.

8. Translation: Protein Synthesis
mRNA transcript arrives at the ribosome to act as the genetic code for protein assembly
proteins are composed of a unique sequence of amino acids.
mRNA carries the code for the order and type of amino acids to be included in the protein. The “genetic code” is the unique order of triplet codons located on the mRNA strand. (back)

9. The Genetic Code: Three-Nucleotide “Words”
Genetic Code The genetic code (codons) used by most organisms to translate mRNA is nearly universal. Sometimes called a triplet code.

10. Figure 17.3 The triplet code

11. Figure 17.4 The dictionary of the genetic code

12. What does a “Gene” really do?
It is simply a blueprint in the DNA that tells how to build a protein.
“WHO” we are genetically is really just a collection of “WHAT” proteins are expressed in our phenotype.
Figure A tobacco plant expressing a firefly gene
(back)

13. Evolution of the Genetic Code
must have evolved very early in the history of life…. Why?
Answer: nearly universal, shared by organisms from the simplest bacteria to complex plants and animals
Ex. CCG codes for the amino acid proline in every organism ever studied (back)

14. The Synthesis/Processing of RNA
The Stages of Transcription
initiation
elongation
termination
RNA processing occurs in eukaryotes
alteration of mRNA ends
RNA splicing
ribozymes
introns (back)

15. Protein Synthesis (Translation)
structure and function of tRNA
aminoacyl-tRNA synthetases
ribosomes
building a polypeptide
initiation
elongation
termination
signal peptides target protein destinations (back)

17. Point Mutations types of point mutations Results of point mutations
base-pair substitutions
insertions
deletions
Results of point mutations
silent mutation
missense mutations
nonsense mutations
frameshift mutations (back)

18. Key Terms for Review!!