Note Outline – Mutations
Mutations
 Point mutations =
o Silent mutation =

o
Missense =
o
Nonsense =
When do mutations affect the next generation?
Point Mutation Leads to Sickle Cell Anemia
 What kind of mutation?

What structure has the mutation?
Mutations
 Frameshift =
o
Insertions =
o
Deletions =
Review Questions
1. If proteins were composed of only 12 different kinds of amino acids, what
would be the small-est possible codon size in a genetic system with four
different nucleotides?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 12
2. A portion of the genetic code is UUU = phenylalanine, GCC = alanine, AAA
= lysine, and CCC = proline. Assume the correct code places the amino acids
phenylalanine, alanine, and lysine in a protein (in that order). Which of the
following DNA sequences would substitute proline for alanine?
(A) AAA-CGG-TTA
(B) AAT-CGG-TTT
(D) AAA-GGG-TTT
(E) AAA-CCC-TTT
(C) AAA-CCG-TTT
3. What is the relationship among DNA, a gene, and a chromosome?
(A) A chromosome contains hundreds of genes, which are composed of protein.
(B) A chromosome contains hundreds of genes, which are composed of DNA.
(C) A gene contains hundreds of chromosomes, which are composed of protein.
(D) A gene is composed of DNA, but there is no relationship to a chromosome.
(E) A gene contains hundreds of chromosomes, which are composed of DNA.
4. A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA
codon is
(A) TTT
(B) UUA
(C) UUU
(D) AAA
(E) either UAA or TAA, depending on wobble in the first base.
5. A part of an mRNA molecule with the following sequence is being read by a ribosome:
5' CCG-ACG 3' (mRNA). The following activated transfer RNA molecules are available.
Two of them can correctly match the mRNA so that a dipeptide can form.
The dipeptide that will form will be
(A) cysteine-alanine
(B) proline-threonine
(D) alanine-alanine
(E) threonine-glycine
(C) glycine-cysteine
tRNA Anticodon
Amino Acid
GGC
Proline
CGU
Alanine
UGC
Threonine
CCG
Glycine
ACG
Cysteine
CGG
Alanine
Control of Prokaryotic (Bacterial) Genes
Prokaryotic Gene Control
 Bacteria need to respond quickly to ______________________________________________________________
 Transcription and translation happen simultaneously… they are “______________________________”
o _____________________________ is what is regulated
 Lack of _____________________ makes this very efficient!
Prokaryotic Control Mechanism
 Gene Regulation
o Instead of blocking ___________________________________, block _________________________ of
genes for all enzymes in tryptophan pathway
 Saves __________________ by not wasting it on unnecessary ___________________________.
Gene Regulation in Bacteria
 Cells vary amount of specific enzymes by _________________________________________________________.
o Turn genes ________ or turn genes ________
 Turn genes OFF example: If bacterium has enough tryptophan then it doesn’t need to make
enzymes used to _____________ tryptophan
 Turn genes ON example: if bacterium encounters new sugar (energy source), like lactose, then it
needs to start making enzymes used to ___________ lactose
Bacteria Group Genes Together
 Operon =
o Example = all enzymes in a metabolic pathway
o TWO TYPES =
 Structures of an operon
o Promoter =
 Single promoter controls transcription of all genes in operon
 Transcribed as one unit and a single mRNA is made
o Operator =
Repressor Operon: Tryptophan
Synthesis pathway model – when
excess tryptophan is present, it binds to
tryp repressor protein and triggers
repressor to bind to DNA…blocks
(represses) transcription
What happens when tryptophan is
present?
Tryptophan is _________________ regulator of repressor protein
Inducible Operon: Lactose
Digestive pathway model – when
lactose is present, binds to lac
repressor protein and triggers
repressor to release DNA…induces
transcription
What happens when lactose is
present?
Lactose is ____________________ regulator of repressor protein
Up Regulation – increase the rate!
Example = CAP/cAMP system
When lactose is present and glucose is low:



cAMP is _____________
cAMP activates Catabolite Activator Protein _____
Increases the rate of transcription by 100x!
Operon Summary
 Repressible Operon
o Usually functions in _________________ pathways
 Synthesizing end products
o When end product is in excess, cell allocates
resources to other uses
 Inducible Operon
o Usually functions in _________________ pathways
 Digesting nutrients to simpler molecules
o Produce enzymes only when nutrient is available
 Cell avoids making proteins that have
nothing to do, cell allocates resources to other uses.
Control of Eukaryotic Genes
The Big Questions
 How are genes turned on and off in eukaryotes?
 How do cells with the same genes differentiate to perform completely different, specialized functions?
Evolution of Gene Regulation
 Prokaryotes =
o
o

Must respond quickly to changes in external environment
Gene Regulation =
Eukaryotes =
o Evolved to maintain constant internal conditions while facing changing external conditions
o Regulate body as a whole
 Growth and development
 Specialization
 Must coordinate the body as a whole rather than serve the needs of individual cells
Points of Control
 _______________________ of transcription and translation allows for _________________________________.
1. DNA Packing
 How do you fit all that DNA into the nucleus?
 DNA ______________________ and __________________________
 Nucleosomes =
o 1st level of __________________________
o Histone proteins =
 Degree of packing of DNA ____________________________________________________________________
o ____________________ wrapped around histones
 No _____________________________
 Genes __________________________
o Heterochromatin =
o Euchromatin =
 DNA Methylation
o DNA methylation ____________________ transcription factors (no transcription)
 Genes ______________________
 Attachment of ___________________ groups to cytosine
 Nearly permanent inactivation of genes
 Histone Acetylation
o Acetylation of histones ___________________________________
o Loosely wrapped around histones
 Enables transcription
 Genes turned ____________
 Attachment of acetyl groups to histones
 Conformational change in _________________________________
 Transcription factors have __________________________________________________
2. Transcription Initiation
 Control regions on ________________
o Promoter =
o
Enhancer =
3. Post-Transcriptional Control
 Alternative _________________________________
o Variable processing of ___________________ creates different _______________________________
4. Regulation of mRNA Degradation
 Lifespan of mRNA determines amount of __________________________________________________
o mRNA can last from hours to weeks
 5’ cap and 3’ tail prevent _________________________________
5. Control of Translation
 Block ____________________ stage of translation
o Regulatory proteins attach to 5’ end of mRNA
 Prevent _______________________ to ribosome and initiator _________________
 Block translation of _________________ to __________________
6. Protein Processing
 _______________________, cleaving, adding sugar groups, targeting for transport
7. Protein Degradation
 ________________________ tagging = marked for
_______________________________
 ________________________ degradation (dismantles protein)