1. Chapter 17 Hon. Adv. Biology Notes 11/29/10
From Gene to Protein
Chapter 17
Hon. Adv. Biology Notes
11/29/10

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)

16. 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. Chapter 18: Genetics of Viruses and Bacteria
Part 1: Viruses
Part 2: Bacteria

19. What is a Virus? Infectious particle consisting of a genome
either single- or double-stranded
either RNA or DNA
inclosed in a capsid - protein that surrounds it.
Replicate using metabolic machinery of host cells: bacteria, plant, animal
Possibly evolved from plasmids or transposons

20. TMV
The search for the cause of tobacco mosaic disease led to discovery of viruses.
No microbe could be found and no agent could be filtered out
Crystallization of infectious particle.

21. Structural components of viruses
Genome: genes are contained on a single linear or circular nucleic acid molecule
Capsid: protein shell, often large numbers of identical subunits (capsomeres)
rod-shaped (helical)
polyhedral
complex
Envelope: derived from membranes of hosts

22. What is a “phage”? Bacteriophage: complex viruses that attack bacteria
Host Range: proteins on the outside of virus only recognize a few specific receptors on host cell surfaces.

23. Three patterns of Genome Replication
DNA viruses
RNA viruses
retroviruses
reverse transcriptase

24. Viral Life Cycles
Lytic cycle
Lysogenic cycle

25. Defenses against Infection
restriction enzymes
barriers
antibodies
vaccines

26. Viroids and Prions and Viral Evolution

27. Chapter 18 (part 2): The Genetics of Bacteria
short generation span aids their evolutionary adaptation to changing environments
circular bacterial chromosome found tightly packed in a region called the nucleoid.
100x the DNA of a virus
1/1000 of the DNA of a eukaryote
plasmids are also found in many strains
genetic recombination produces new strains

28. Binary Fission
replication of chromosome proceeds in two directions from the single point of origin prior to binary fission.
See diagram on board.
Due to semiconservative replication, most bacteria in a colony are identical.

29. Genetic Recombination: Bacteria
Transformation: (recall Griffith’s exp.)
bacteria take up naked DNA
Transduction: (recall Hershey and Chase)
phages transfer genes from one bacterium to another
generalized and specialized transduction
Conjugation and Plasmids
2 cells temporarily join by appendages called sex pili

30. Closer Look at Conjugation
bacteria join and transfer DNA thru pili
ability to form pili and donate DNA depends on the presence of an F factor
if the F factor is on the F plasmid they are called F+; after conjugation the F- (female) is converted into an F+ (male)
Hfr cells; F factor inserted into chromosome
R plasmids: inheritance of resistance

31. Key Terms for Review!!
See the key terms on the Campbell Place website for important terms for Ch !!!