Download Gene Regulation and Mutation Notes and Questions

Gene Regulation and Mutation
Notes and Questions
How do mutations affect a cell?
Main Idea
• Gene expression is regulated by the cell, and
mutations can affect this expression.
• Gene regulation is the ability of an organism to
control which genes are transcribed in response
to the environment.
Prokaryote Gene Regulation
Prokaryotes are simple.
• In prokaryotes, an operon often controls the
transcription of genes in response to changes in
the environment.
• An operon is a section of DNA that contains the
genes for the proteins needed for a specific
metabolic pathway.
• A regulatory gene “turns on and off”
transcription.
Eukaryotic Gene Regulation
Eukaryotes have many more genes than
prokaryotes.
How is transcription controlled?
• Transcription factors (type of protein) ensure
that a gene is used at the right time and that
proteins are made in the right amount.
• The complex structure of eukaryotic DNA also
regulates transcription.
Some transcription factors guide the
binding of RNA polymerase to a
promoter. This determines which protein
will be made.
Hox Genes (Homeobox genes)
• Hox genes code for transcription factors and control
differentiation – (process through which all cells
become specialized in shape and function)
• Hox genes are used in embryo
development and are active in
different zones of the embryo and
control what body part will develop
in different parts of the embryo.
• Hox genes are responsible for the
general body pattern of most
animals.
RNA Interference
• Another way eukaryotic genes are regulated is
RNA interference (RNAi). Small segments of
RNA bind to mRNA and prevent parts of mRNA
from being translated. (Protein Synthesis)
• RNA interference can stop the mRNA from
translating its message.
Recall that every cell contains
an entire set of the
organism’s DNA. Only a
small segment of the DNA is
used for each specialized cell
to do its job. Only the part of
the DNA that is needed will
be used in protein synthesis.
Mutations
• A mutation is a permanent change that occurs in
a cell’s DNA.
• A mutation in a gene sequence (protein
synthesis) can change the protein that is made.
• Types of Mutations:
▫ Point mutations, insertion, deletion
• A mutation in DNA changes the amino acid base
sequence.
• A different amino acid or series of amino acids
are incorporated into the protein that is made on
the ribosome. The result can be a malfunction of
the protein. Mutated proteins often do not
work. Remember the shape is very important to
its function (or ability to do its “job)
• A mutation can affect a single nucleotide or a
large segment of DNA.
Types of Mutations – Point Mutations
• Point mutations (Base-pair substitutions) - a mutation
in which one nucleotide base replaces another
• Point mutations affect only one codon, so they affect only
one amino acid in a peptide chain
• It may or may not have serious effects on an organism. It
depends on where the mutation occurs and how it affects
the protein for which it codes
• It can be harmless
• Muscular dystrophy is an example of a disease caused by
a point mutation. (nonsense – early STOP codon due to
the wrong amino acid)
• Muscular dystrophy is progressive muscle disorder
characterized by the weakening of many muscles in the
body.
Types of Mutations - Insertion
• Insertion is the addition of one or more bases into a
nucleotide sequence
• This can change many amino acids in the
polypeptide chain, thus changing the protein
• It causes a “frameshift” in the mRNA bases, thus
causing the wrong amino acid to be added to the
polypeptide chain.
• Crohn’s disease is caused by an insertion. Crohn’s is
a chronic inflammation of the intestinal tract,
producing diarrhea, abdominal pain, nausea, fever
and weight loss.
Types of Mutations - Deletion
• Deletion – one or more bases is removed from a
nucleotide sequence
• A different amino acid is put into the peptide
chain, thus changing the protein
• Cystic fibrosis, a disease characterized by
abnormally thick mucus in the lungs, intestines,
and pancreas, is an example of a mutation
caused by a deletion.
Frameshift
• Both insertion and deletion result in a
frameshift.
• A frameshift is simply a shift (to the left or right)
in the nitrogen bases, resulting in new codons.
• A frameshift changes the number of bases in a
sequence.
Types of Mutations - Chromosomal
• Point mutations, insertions, and base deletions
affect only a single gene or segment of DNA.
• A chromosomal mutation affects the entire
chromosome.
• Chromosomal mutations change the number of
genes in a chromosome or the organization of
the chromosome.
• We will cover more of this
with genetics.
The order of amino acids is similar to the order of letters and
words in a sentence. If a slight change happens, the meaning
can change.
Fragile X
• An example of a mutation is Fragile X.
• Fragile X syndrome is due to many extra
repeated CGG units near the end of the X
chromosome, making the lower tip of the X
chromosome appear fragile.
Protein Folding and Stability
• Substitutions can lead to genetic disorders
• Substitutions can change both the folding and
stability of the protein
Compare the order
• An example is sickle-cell disease
of the amino acids
in the normal chain
vs the mutated
chain. What is the
difference?
Causes of Mutation
• Mutations can occur spontaneously.
• DNA polymerase can make a mistake.
• Chemicals and radiation also can
damage DNA.
• High-energy forms of radiation, such
as X rays and gamma rays, are highly
mutagenic.
• A mutagen is any agent that changes
the DNA of an organism.
• Thymines can stick together causing a
kink in the DNA. The bases will not
bond correctly.
Body-cell v. Sex-cell Mutation
• Somatic cell mutations are not passed on to the
next generation. Somatic cells are cells in the
body that are not sex cells.
• Mutations that occur in sex cells are passed on to
the organism’s offspring and will be present in
every cell of the offspring. The mutations may
not change how the cells function or may have
serious effects on the organism.