1. Gene mutations
Stem cells and totipotency
Gene mutations might arise during DNA replication. They include
addition, deletion, substitution, inversion, duplication and
translocation of bases. Gene mutations occur spontaneously. The
mutation rate is increased by mutagenic agents.
Mutations can result in a different amino acid sequence in the
encoded polypeptide.
• Some gene mutations change only one triplet code. Due to the
degenerate nature of the genetic code, not all such mutations result
in a change to the encoded amino acid.
• Some gene mutations change the nature of all base triplets
downstream from the mutation, ie result in a frame shift. Students
should be able to relate the nature of a gene mutation to its effect
on the encoded polypeptide.
Totipotent cells can divide and produce any type of body cell. During
development, totipotent cells translate only part of their DNA,
resulting in cell specialisation. Totipotent cells occur only for a
limited time in early mammalian embryos. Pluripotent cells are found
in embryos; multipotent and unipotent cells are found in mature
mammals and can divide to form a limited number of different cell
types.
• Pluripotent stem cells can divide in unlimited numbers and can be
used in treating human disorders.
• Unipotent cells, exemplified by the formation of cardiomyocytes.
• Induced pluripotent stem cells (iPS cells) can be produced from
adult somatic cells using appropriate protein transcription factors.
Substitution
Deletion
Addition duplication
Inversion
Translocation
Frame shift
Exam question
Explain how a single base substitution causes a change in the structure
of a polypeptide
,1. Change in (sequence of) amino acid(s)/primary structure;
2. Change in hydrogen/ionic/disulfide bonds;
3. Alters tertiary structure;
Causes of mutations + mutagenic agents
High energy ionising radiation
Chemicals
Totipotent – cells that can mature into any body cell such as fertilised eggs
and zygotes + the early cells that derive from these cells. In specialised cells,
only part of the DNA of a cell is translated into proteins. Genes are prevented
from expressing themselves by preventing transcription so preventing the
production of mRNA. And by preventing translation.
Pluripotent – found in embryos and can differentiate into almost any type of
cell e.g. embryonic and foetal stem cells
Multipotent – found in adults and can differentiate into a limited number of
specialised cells – usually develop into cells of a particular type e.g. stem cells in
bond marrow can produce any types of blood cell. Examples are adult stem
cells and umbilical cord stem cells.
Unipotent – can only differentiate into a single type of cell – derived from
multipotent stem cells and are made in adult tissue. Examples are
cardiomyocytes which are heart muscle cells that can divide to produce heart
tissue.
iPS – type of pluripotent cell that is produced from unipotent stem cells – they
are genetically altered to make them acquire the characteristics of embryonic
stem cells- this involves inducing genes and transcription factors within the cell
to express themselves. The fact that these genes are able to be reactivated
shows that adult stem cells retain the same genetic information as embryonic
stem cells. They are not exactly the same as embryonic stem cells though – they
are capable of self renewal and can divide indefinitely to provide a limitless
supply.
Regulation of transcription and translation
In eukaryotes, transcription of target genes can be stimulated or
inhibited when specific transcriptional factors move from the
cytoplasm into the nucleus. The role of the steroid hormone,
oestrogen, in initiating transcription. Epigenetic control of gene
expression in eukaryotes.
For transcription to begin, the gene is switched on by transcription factors
Each transcription factor has a site that binds to a specific base
sequence of the DNA in the nucleus
, When it binds, it causes this region of DNA to begin transcription
When a gene is not being expressed, the site on the transcription factor
that binds to DNA is not active
As it is inactive it cannot cause transcription
Transcription factors bind the promotor region of DNA and allow
RNA polymerase to bind
The role of oestrogen in transcription
Oestrogen is a lipid soluble molecule and
therefore diffuses easily through the
phospholipid bilayer of CSM’s
Once inside the cytoplasm, oestrogen
binds with a site on a receptor of the
transcription factor. The shape of this site
and the shape of the oestrogen are
complementary.
By binding, the oestrogen changes the
shape of the DNA binding site on the
transcription factor which can now bind to
DNA as it is activated
The transcription factor can now enter the
nucleus through a nuclear pore and bind
to specific base sequences on the DNA
Epigenetic control of gene expression
Epigenetics involves heritable changes in gene function, without
changes to the base sequence of DNA. These changes are caused by
changes in the environment that inhibit transcription by:
• increased methylation of the DNA or
• decreased acetylation of associated histones.
The relevance of epigenetics on the development and treatment of
disease, especially cancer. In eukaryotes and some prokaryotes,
translation of the mRNA produced from target genes can be inhibited
by RNA interference (RNAi).
Stem cells and totipotency
Gene mutations might arise during DNA replication. They include
addition, deletion, substitution, inversion, duplication and
translocation of bases. Gene mutations occur spontaneously. The
mutation rate is increased by mutagenic agents.
Mutations can result in a different amino acid sequence in the
encoded polypeptide.
• Some gene mutations change only one triplet code. Due to the
degenerate nature of the genetic code, not all such mutations result
in a change to the encoded amino acid.
• Some gene mutations change the nature of all base triplets
downstream from the mutation, ie result in a frame shift. Students
should be able to relate the nature of a gene mutation to its effect
on the encoded polypeptide.
Totipotent cells can divide and produce any type of body cell. During
development, totipotent cells translate only part of their DNA,
resulting in cell specialisation. Totipotent cells occur only for a
limited time in early mammalian embryos. Pluripotent cells are found
in embryos; multipotent and unipotent cells are found in mature
mammals and can divide to form a limited number of different cell
types.
• Pluripotent stem cells can divide in unlimited numbers and can be
used in treating human disorders.
• Unipotent cells, exemplified by the formation of cardiomyocytes.
• Induced pluripotent stem cells (iPS cells) can be produced from
adult somatic cells using appropriate protein transcription factors.
Substitution
Deletion
Addition duplication
Inversion
Translocation
Frame shift
Exam question
Explain how a single base substitution causes a change in the structure
of a polypeptide
,1. Change in (sequence of) amino acid(s)/primary structure;
2. Change in hydrogen/ionic/disulfide bonds;
3. Alters tertiary structure;
Causes of mutations + mutagenic agents
High energy ionising radiation
Chemicals
Totipotent – cells that can mature into any body cell such as fertilised eggs
and zygotes + the early cells that derive from these cells. In specialised cells,
only part of the DNA of a cell is translated into proteins. Genes are prevented
from expressing themselves by preventing transcription so preventing the
production of mRNA. And by preventing translation.
Pluripotent – found in embryos and can differentiate into almost any type of
cell e.g. embryonic and foetal stem cells
Multipotent – found in adults and can differentiate into a limited number of
specialised cells – usually develop into cells of a particular type e.g. stem cells in
bond marrow can produce any types of blood cell. Examples are adult stem
cells and umbilical cord stem cells.
Unipotent – can only differentiate into a single type of cell – derived from
multipotent stem cells and are made in adult tissue. Examples are
cardiomyocytes which are heart muscle cells that can divide to produce heart
tissue.
iPS – type of pluripotent cell that is produced from unipotent stem cells – they
are genetically altered to make them acquire the characteristics of embryonic
stem cells- this involves inducing genes and transcription factors within the cell
to express themselves. The fact that these genes are able to be reactivated
shows that adult stem cells retain the same genetic information as embryonic
stem cells. They are not exactly the same as embryonic stem cells though – they
are capable of self renewal and can divide indefinitely to provide a limitless
supply.
Regulation of transcription and translation
In eukaryotes, transcription of target genes can be stimulated or
inhibited when specific transcriptional factors move from the
cytoplasm into the nucleus. The role of the steroid hormone,
oestrogen, in initiating transcription. Epigenetic control of gene
expression in eukaryotes.
For transcription to begin, the gene is switched on by transcription factors
Each transcription factor has a site that binds to a specific base
sequence of the DNA in the nucleus
, When it binds, it causes this region of DNA to begin transcription
When a gene is not being expressed, the site on the transcription factor
that binds to DNA is not active
As it is inactive it cannot cause transcription
Transcription factors bind the promotor region of DNA and allow
RNA polymerase to bind
The role of oestrogen in transcription
Oestrogen is a lipid soluble molecule and
therefore diffuses easily through the
phospholipid bilayer of CSM’s
Once inside the cytoplasm, oestrogen
binds with a site on a receptor of the
transcription factor. The shape of this site
and the shape of the oestrogen are
complementary.
By binding, the oestrogen changes the
shape of the DNA binding site on the
transcription factor which can now bind to
DNA as it is activated
The transcription factor can now enter the
nucleus through a nuclear pore and bind
to specific base sequences on the DNA
Epigenetic control of gene expression
Epigenetics involves heritable changes in gene function, without
changes to the base sequence of DNA. These changes are caused by
changes in the environment that inhibit transcription by:
• increased methylation of the DNA or
• decreased acetylation of associated histones.
The relevance of epigenetics on the development and treatment of
disease, especially cancer. In eukaryotes and some prokaryotes,
translation of the mRNA produced from target genes can be inhibited
by RNA interference (RNAi).
