Chapter
12
Molecular Genetics
Prokaryote Gene Regulation
 Ability of an organism to control which genes
are transcribed in response to the
environment
 operon is a section of DNA that contains the
genes for the proteins needed for a specific
metabolic pathway.
 Operator
 Promoter
 Regulatory gene
 Genes coding for proteins
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
The Trp Operon
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
The Lac Operon
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
Eukaryote Gene Regulation
 Controlling transcription
 Transcription factors ensure that a
gene is used at the right time and that
proteins are made in the right amounts
 The complex structure of eukaryotic
DNA also regulates transcription.
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
Hox Genes
 Hox genes are
responsible for
the general body
pattern of most
animals.
Chapter
12
Molecular Genetics
12.4 Gene Regulation and Mutation
RNA Interference
 RNA interference can stop the mRNA
from translating its message.
Chapter
12
Molecular Genetics
12.3 Formative
Questions
Which shows the basic chain of events
in all organisms for reading and expressing
genes?
A. DNA
B. RNA
C. mRNA
RNA
DNA
protein
protein
rRNA
D. RNA processing
translation
tRNA
transcription
Chapter
12
Molecular Genetics
12.4 Formative
Questions
Why do eukaryotic cells need a
complex
control system to regulate the
expression
of genes?
Chapter
12
Molecular Genetics
12.4 Formative
Questions
A. All of an organism’s cells transcribe the same
genes.
B. Expression of incorrect genes can lead to
mutations.
C. Certain genes are expressed more frequently
than others are.
D. Different genes are expressed at different
times in an organism’s lifetime.
Chapter
12
Molecular Genetics
12.4 Formative
Questions
Which type of gene causes cells to
become specialized in structure in
function?
A. exon
B. Hox gene
C. intron
D. operon
Chapter
12
Molecular Genetics
Chapter Assessment
Questions
Explain how Hox genes affect an organism.
A. They determine size.
B. They determine body plan.
C. They determine sex.
D. They determine number
of body segments.
Chapter
12
Molecular Genetics
Standardized Test
Practice
What is this process called?
Chapter
12
Molecular Genetics
Standardized Test
Practice
A. mRNA processing
B. protein synthesis
C. transcription
D. translation
Chapter
12
Molecular Genetics
Standardized Test
Practice
How could RNA interference be
used
to treat diseases such as cancer and
diabetes?
Chapter
12
Molecular Genetics
Standardized Test
Practice
A. by activating genes to produce proteins that
can overcome the disease
B. by interfering with DNA replication in cells
affected by the disease
C. by preventing the translation of mRNA into
the genes associated with the disease
D. by shutting down protein synthesis in the
cells of diseased tissues
Eukaryotic Gene Regulation
Is the following sentence true or false?
Operons are frequently found in
eukaryotes.
False
Eukaryotic Gene Regulation:
How are eukaryotic genes usually
controlled?
Most are controlled individually and have
regulatory sequences that are much more
complex than those of the lac operon.
Eukaryotic Gene Regulation:
What is the function of the TATA box?
It seems to help position RNA polymerase
by marking a point just before the point
where transcription begins.
Eukaryotic Gene Regulation:
Eukaryotic promoters are usually found
just ____the TATA box, and they consist
of a series of short ____sequences.
before
DNA
Eukaryotic Gene Regulation:
List three ways in which proteins that bind to
enhancer sequences of a gene can work to
regulate gene expression.
a. They open up tightly packed chromatin.
b.. They help to attract RNA polymerase.
c. They block access to genes.
Eukaryotic Gene Regulation:
Why is gene regulation in eukaryotes more
complex than in prokaryotes?

All of the cells in a multicellular organism carry
the complete genetic code in their nucleus, but
only a few of the available genes can be
expressed in the appropriate cells of different
tissues.
Complex regulation allows for this specificity.
Development and Differentiation
What role do the hox genes play in the
development of an organism?
They control the differentiation of cells and
tissues in the embryo.
Development and Differentiation
 In fruit flies, a mutation affecting the hox genes
can replace a fly’s antennae with a
pair of legs.
 The function of the hox genes in humans seems
to be almost the same as it is in fruit
flies.
Development and Differentiation
Why do common patterns of genetic
control for development exist among
animals?
All the genes that control development
have descended from the genes of
common ancestors.
Mutagens
Ionizing radiation (X rays)
Nonionizing radiation (UV)
Natural and synthetic chemicals
Frameshift Mutations
Insertion

Extra base added into gene region
Deletion

Base removed from gene region
Both shift the reading frame
Result in many wrong amino acids
Frameshift Mutation
mRNA
parental DNA
arginine
glycine
tyrosine
tryptophan asparagine amino acids
altered mRNA
arginine
glycine
leucine
leucine
glutamate
DNA with
base insertion
altered aminoacid sequence
Figure 14.12
Page 234
Point mutations – mistakes with 1 nucleotide

Substitution of the wrong nucleotide (nitrogen base) in place
of correct one
Missense mutation – substitution of a base codes for a different
amino acid
Nonsense mutation – substitution of a base codes for a stop
Silent mutation – substitution of a base codes for same a.a.
Frameshift mutations – occur when a nucleotide is either inserted
or deleted, altering the “trios” of nitrogen bases (More severe
than point mutations because it affects all of the amino acids in
the protein after that point)
Gene mutations
Chromosomal mutations
Change in the number or structure of
the chromosomes




Deletion
Duplication
Inversion
Translocation
Think about this!
What types of mutations are most severe?
If a mutation happens in a skin cell, will it
get passed on to that person’s children?
What about an egg or sperm?
In what type of cells must mutations occur
in order to be passed on to offspring?