Unit 3 - The control of gene
expression
Mutations
What is a mutation?
A change in the base sequence of DNA randomly occurring
during DNA replication
When are mutations likely to occur?
During DNA replication (in Synthesis phase of mitosis)
What can increase the likelihood of a mutation?
- carcinogens
- rate of mutation can be increased by mutagenic agents
What are the mutagenic agents?
- ultraviolet radiation
- ionising radiation
- some chemicals
- some viruses
They increase the rate of mutation in different ways:
Acting as a Base
- analog chemicals can substitute for a base in DNA replication, changing the base
sequence of the new DNA
- e.g 5-bromouracil can substitute for thymine, pairing with guanine instead of
adenine
Altering Bases
- some chemicals can delete or alter bases
- e.g Alkylating agents can add alkyl group to guanine so it binds with thymine
instead of cytosine
Changing the structure of DNA
- some types of radiation can change the structure of DNA, causing issues in DNA
replication
- e.g UV radiation can cause adjacent thymine bases to group together
, Type of mutation Effect on DNA Effect on amino Consequence
acid sequence
Substitution One or more bases Unlikely to change 1 different amino acid
are swapped for DNA sequence (DNA un sequence ->
another is degenerate) protein function likely
ATCCGT -> ATCCTT the same
Addition Bases are added change amino acid Many amino acids
ATCCGT -> ATACCGT sequence - frame different = different
shift = different tertiary structure =
amino acids protein function
changed
Deletion Bases are removed change amino acid Many amino acids
ATCCGT -> ATCCT sequence - frame different = different
shift = different tertiary structure =
amino acids protein function
changed
Inversion Sequence of bases Changed amino acid Protein could have
reversed sequence in section different tertiary
ATCCGT ->TGCCTA reversed structure
Duplication One or more bases Changes amino acid Many amino acids
are repeated sequence in section different = different
ATCCGCGCGT and could change tertiary structure =
amino acids after as protein function
could cause a changed
frameshift
Translocation Sequence of bases Could cause Many amino acids
moved from one frameshift different = different
location to another Puts new bases next tertiary structure =
to each other where protein function
the sequence was changed
removed and where it
is moved to.
What is a genetic disorder?
An abnormal condition that a person inherits through genes or chromosomes
What are hereditary mutations?
Mutations passed from parents to the offspring via gametes
How may a mutation have a positive effect?
Increase the functionality of a protein or the expression of a particular gene which
gives the individual an advantageous trait- creates differential survival. For example, a
mutation of the CCR5 Th cell receptor protein increases AIDS resistance
Explain how a mutation can lead to a non-functioning enzyme
- A change in the base sequence of DNA occurs. In the nucleus, DNA is transcribed to
produce pre-mRNA.
, - The introns are spliced to produce mRNA with an
altered (or many in a frame shift) codon which
moves to and attaches to the ribosomes where
translation begins.
- A different specific tRNA molecule brings a different specific amino acid and
complementary base pairs with the new codon (via anticodon.) This alters the
primary structure of the protein and secondary/tertiary bonding patterns.
- Creates a different tertiary structure of the enzyme/protein so that it is no longer
specific to the substrate/receptor to the molecule etc.
Genetic Fingerprinting and PCR
Introns
Noncoding segments of nucleic acid that lie between coding sequences. This is where
the VNTRs are found
Exons
Coding segments of eukaryotic DNA, these code for proteins
VNTRs
variable number of tandem repeats, sections of repeated DNA sequences found at
specific locations on certain chromosomes; the number of repeats in a particular VNTR
can vary from person to person
Promotor Region
A regulatory region a short distance upstream from the 5' end
of a transcription start site that acts as the binding site for
RNA polymerase. A region of DNA to which RNA polymerase
binds in order to initiate transcription, after the transcriptional
factors bind
Transcriptional factor
in eukaryotes, protein required for the initiation of transcription by RNA polymerase
PCR
A technique for amplifying DNA in vitro by incubating with special primers, DNA
polymerase molecules, and nucleotides.
Stages of PCR
expression
Mutations
What is a mutation?
A change in the base sequence of DNA randomly occurring
during DNA replication
When are mutations likely to occur?
During DNA replication (in Synthesis phase of mitosis)
What can increase the likelihood of a mutation?
- carcinogens
- rate of mutation can be increased by mutagenic agents
What are the mutagenic agents?
- ultraviolet radiation
- ionising radiation
- some chemicals
- some viruses
They increase the rate of mutation in different ways:
Acting as a Base
- analog chemicals can substitute for a base in DNA replication, changing the base
sequence of the new DNA
- e.g 5-bromouracil can substitute for thymine, pairing with guanine instead of
adenine
Altering Bases
- some chemicals can delete or alter bases
- e.g Alkylating agents can add alkyl group to guanine so it binds with thymine
instead of cytosine
Changing the structure of DNA
- some types of radiation can change the structure of DNA, causing issues in DNA
replication
- e.g UV radiation can cause adjacent thymine bases to group together
, Type of mutation Effect on DNA Effect on amino Consequence
acid sequence
Substitution One or more bases Unlikely to change 1 different amino acid
are swapped for DNA sequence (DNA un sequence ->
another is degenerate) protein function likely
ATCCGT -> ATCCTT the same
Addition Bases are added change amino acid Many amino acids
ATCCGT -> ATACCGT sequence - frame different = different
shift = different tertiary structure =
amino acids protein function
changed
Deletion Bases are removed change amino acid Many amino acids
ATCCGT -> ATCCT sequence - frame different = different
shift = different tertiary structure =
amino acids protein function
changed
Inversion Sequence of bases Changed amino acid Protein could have
reversed sequence in section different tertiary
ATCCGT ->TGCCTA reversed structure
Duplication One or more bases Changes amino acid Many amino acids
are repeated sequence in section different = different
ATCCGCGCGT and could change tertiary structure =
amino acids after as protein function
could cause a changed
frameshift
Translocation Sequence of bases Could cause Many amino acids
moved from one frameshift different = different
location to another Puts new bases next tertiary structure =
to each other where protein function
the sequence was changed
removed and where it
is moved to.
What is a genetic disorder?
An abnormal condition that a person inherits through genes or chromosomes
What are hereditary mutations?
Mutations passed from parents to the offspring via gametes
How may a mutation have a positive effect?
Increase the functionality of a protein or the expression of a particular gene which
gives the individual an advantageous trait- creates differential survival. For example, a
mutation of the CCR5 Th cell receptor protein increases AIDS resistance
Explain how a mutation can lead to a non-functioning enzyme
- A change in the base sequence of DNA occurs. In the nucleus, DNA is transcribed to
produce pre-mRNA.
, - The introns are spliced to produce mRNA with an
altered (or many in a frame shift) codon which
moves to and attaches to the ribosomes where
translation begins.
- A different specific tRNA molecule brings a different specific amino acid and
complementary base pairs with the new codon (via anticodon.) This alters the
primary structure of the protein and secondary/tertiary bonding patterns.
- Creates a different tertiary structure of the enzyme/protein so that it is no longer
specific to the substrate/receptor to the molecule etc.
Genetic Fingerprinting and PCR
Introns
Noncoding segments of nucleic acid that lie between coding sequences. This is where
the VNTRs are found
Exons
Coding segments of eukaryotic DNA, these code for proteins
VNTRs
variable number of tandem repeats, sections of repeated DNA sequences found at
specific locations on certain chromosomes; the number of repeats in a particular VNTR
can vary from person to person
Promotor Region
A regulatory region a short distance upstream from the 5' end
of a transcription start site that acts as the binding site for
RNA polymerase. A region of DNA to which RNA polymerase
binds in order to initiate transcription, after the transcriptional
factors bind
Transcriptional factor
in eukaryotes, protein required for the initiation of transcription by RNA polymerase
PCR
A technique for amplifying DNA in vitro by incubating with special primers, DNA
polymerase molecules, and nucleotides.
Stages of PCR
