Lake Tahoe Community College
Fall Qtr
Bio 101
Instructor: Sue Kloss
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Chapter 17 – From Gene to Protein
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Chapter 17
I. Gene expression: “one gene, one polypeptide”
A. DNA genotype is expressed as proteins
1. genes specify proteins
2. proteins – structure/function of bodies.
3. review classes of proteins?
4. DNA specifies the synthesis of proteins thru 2 major steps = transcription and translation
5. Fig. 10.6a. DNA ______>RNA_______> proteins
transcription
translation
6. enzymes are responsible for producing reactions in biochemical pathways.
7. If a person lacks a particular enzyme, they can’t complete the pathway
8. inheriting a defective gene causes lack of particular enzymes.
9. Beadle and Tatum -- 1 gene, 1 protein. Now its 1 gene, 1 polypeptide, but not always
II. Flow of Genetic Information from DNA to RNA to Protein
A. Transcription and translation
1. Transcription
2. Translation
3. mRNA
4. ribosomes
5. pre-mRNA or primary transcript
B. Genetic Information written in codons is translated into protein sequences
1. codons
2. template strand
3. transcription
4. translation
5. reading frame
C. code of life
1. two different codons can code for same amino acid
2. redundancy in the code, but no ambiguity
3. A mutation might still code for the same protein.
4. AUG is the start codon; UAA, UAG and UGA = stop
6. almost all organisms share the code
7. This is why we can have GMO’s.
III. Transcription produces genetic messages in the form of RNA
A. transcription is the transfer of information from DNA to RNA
2. very similar to DNA synthesis
3. RNA polymerase
4. template DNA strand
5. promoter and terminator
6. transcription initiation complex and TATA box
7. There are 3 phases to transcription
a. Initiation – RNA polymerase attaches to template strand of DNA and unwinds it
b. Elongation
c. Termination
B. Eukaryotic RNA is “processed” before it leaves the nucleus
1. Alteration of mRNA ends
2. Split genes and mRNA splicing
a. splicing
b. alternative RNA splicing
3. introns and exons
IV. Translation
A. Transfer RNA Molecules Serve as Interpreters During Translation
B. Structure and function of tRNA
1. Anticodon
2. Aminoacyl tRNA synthetases
3. Ribosomal structure
a. E, P, A sites
C. Ribosomes build Polypeptides
1. polypeptide factories in a cell – the ribosomes
2. ribosomes consist of 2 subunits
3. tRNA anticodons and mRNA codons fit on ribosomes during this process
D. An Initiation Codon Marks the Start of an mRNA Message
1. Translation has the same 3 phases as transcription
a. initiation
b. elongation
c. termination
2. Initiation is very important because of reading frame errors
3. translation initiation complex
4. initiation factors
5. start codon
E. Elongation Adds Amino Acids to the Polypeptide Chain Until a Stop Codon Terminates Translation
1. Once initiation is complete, amino acids are added one at a time till translation is complete
2. Each amino acid that is added onto the growing chain does so in 3 steps
a. codon recognition
b. peptide bond formation
c. translocation 3. termination.
4. release factor
J. Review
1. typically, several ribosomes (polyribosome) will be translating the same mRNA
2. it takes about a minute for an mRNA to be translated into an average sized polypeptide
3. after translation, the completed polypeptides fold and coil into their 3D shapes
4. a gene- a region of DNA that codes for a polypeptide or RNA
K. completing and targeting the functional protein
1. during synthesis, a functional protein will coil and fold spontaneously
2. other modifications may be required
3. targeting to specific locations
L. Mutations can change the meaning of genes
1. Point Mutation is change in nucleotide sequence
2. can be in a single base pair, or a large sequence
a. substitutions
b. insertions and deletions
3. several mutations have no effect because of redundancy
4. mutagens
a. electromagnetic radiation
b. chemical mutagens
c. mutagens usually carcinogenic and vice versa
Chapter 17 Lesson Objectives
1. Briefly explain and draw a model to show how information flows from gene to protein.
2. Distinguish between transcription and translation.
3. Compare where transcription and translation occur in prokaryotes and in eukaryotes.
4. Define codon and explain the relationship between the linear sequence of codons on mRNA and the linear sequence of
amino acids in a polypeptide.
5. Explain why polypeptides begin with methionine when they are synthesized.
6. Explain what it means to say that the genetic code is redundant and unambiguous.
7. Explain the significance of the reading frame during translation.
8. Explain the evolutionary significance of a nearly universal genetic code.
9. Explain how RNA polymerase recognizes where transcription should begin. Describe the promoter, the terminator, and the
transcription unit.
10. Explain the general process of transcription, including initiation, elongation, and termination.
11. Explain how RNA is modified after transcription in eukaryotic cells.
12. Draw and label, and then describe the functional and evolutionary significance of introns and exons.
13. Diagram the structure and annotate to explain the functions of tRNA.
14. Describe the structure and functions of ribosomes.
15. Describe the process of translation (including initiation, elongation, and termination) and explain which enzymes, protein
factors, and energy sources are needed for each stage.
16. Describe how a polypeptide must be modified before it becomes fully functional.
17. Compare protein synthesis in prokaryotes and in eukaryotes.
18. Define point mutations. Distinguish between base-pair substitutions and base-pair insertions and give examples.
19. Draw and label the processes that occur to change this segment of DNA into a protein.
TACCAACGAAAGAAAACC
a. Label and define the names of the 2 major steps in this process.
b. Label the following terms in your drawings. DNA, RNA polymerase, mRNA, tRNA, small ribosomal subunit, large
ribosomal subunit, codon, anticodon, P site, A site, E site, amino acid, polypeptide, translocation
c. Using the structures listed above, LIST briefly the chain of events that would occur in the correct order to change
the DNA segment into a protein.
d. Show the polypeptide you would expect to see as a result of the processes you explained, from the DNA
sequence above.