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L5 - Extra-Nuclear Genomes
and Mitochondrial Disorders
Introduction to extra-nuclear inheritance
The first thing we’re going to look at is why we have extra-nuclear inheritance.
As you know, most traits segregate during meiosis and show Mendelian
inheritance, that is, you have one allele coming from your mother and one allele
coming from your father.
However, some characteristics or phenotypes or traits are not determined by
DNA in the nucleus and do not show Mendelian inheritance.
These traits are determined by DNA outside the nucleus. So this DNA is called
extra, or outside, extra-nuclear DNA. Where do we find extra-nuclear DNA?
We find extra-nuclear DNA in the mitochondria, mitochondrial organelles, and in
the chloroplast organelles, and they each have a unique, specialised function.
The specialised function of the mitochondria, shown in the picture on this slide,
is to release energy from nutrients and convert it into ATP during respiration.
The main function of the mitochondria is respiration. Now remember,
mitochondria are found in plants and animal cells. It’s found in all eukaryotic
cells.
In this picture, we see a picture of a
mitochondria, a mitochondria is a
cigar-shaped organelle, which
contains a double membrane, an
outer membrane and an inner
membrane. And in the inner
membrane or at the inner
membrane, we have the main
enzymes of respiration.
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 1
, The chloroplasts, as you know, are only found in plants and they capture sun or
solar energy and store it as carbohydrates during photosynthesis. So the first
thing we’re going to look at is mitochondrial DNA, what does it look like, how big
is it, how many copies of mitochondrial DNA do we have. You have more than
one mitochondria inside a cell because making energy is a fundamental process
of cells.
Mitochondrial DNA (mtDNA)
The mitochondria consists of two membranes. It’s a double-membraned
structure. And it has an inner membrane and an outer membrane. And then the
inner membrane structures project into a matrix. The mitochondrial DNA is found
in the matrix of the mitochondria.
The mitochondrial DNA isn’t just free-floating. It’s found in a little structure called
a nucleoid.
Now, a nucleoid is not a nucleus.
A nucleoid is a structure that has condensed DNA.
The condensed DNA is NOT condensed with histone. There are no histones
involved.
The nucleoids, typically one nucleoid will typically contain 3-5 molecules of
mitochondrial DNA tangled together.
The mitochondrial DNA is circular and so it exists in a supercoiled structure.
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 2
, So the nucleoids are found in the matrix of the mitochondria and the nucleoids
consist of about 4/5 molecules of mitochondrial DNA.
How many nucleoids do you have in one mitochondrial organelle? Well, you
have about, depending on the cell type, as little as 10 or as many as 40 or 50.
So you have about 30 nucleoids in each mitochondria. Just go over this again.
The DNA of the mitochondria is found in the nucleoid.
The nucleoid is composed of about 4/5 molecules of mitochondrial DNA
condensed. And you have about 30 or so nucleoids in a mitochondria. That’s in
one mitochondria.
Remember that you normally have more than one mitochondria cell.
A cell could have as many as 40 or 50 mitochondria in one cell.
The number of mitochondria you have in a cell depends on the function of the
cell and it depends on the actual cell and tissue type.
So, now we know that you have mitochondrial DNA inside mitochondria. We
know that there’s many copies of the mitochondrial DNA. They’re bound in
nucleoids.
There’s many nucleoids and there are many mitochondria per cell. So how big is
the mitochondrial genome, and what is the gene content of the mitochondrial
genome?
Well, both the size of the
mitochondria genome varies
between organisms and the gene
content can vary between
organisms.
You can clearly see that the mitochondrial genome size is way, way smaller than
the human nuclear genome.
Plants have larger mitochondrial genomes than animals.
The nuclear DNA divides in the synthesis phase before cell division for mitosis.
You can only divide the DNA, the nuclear DNA, once you’ve doubled it.
When do mitochondria double in preparation for cell division?
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 3
L5 - Extra-Nuclear Genomes
and Mitochondrial Disorders
Introduction to extra-nuclear inheritance
The first thing we’re going to look at is why we have extra-nuclear inheritance.
As you know, most traits segregate during meiosis and show Mendelian
inheritance, that is, you have one allele coming from your mother and one allele
coming from your father.
However, some characteristics or phenotypes or traits are not determined by
DNA in the nucleus and do not show Mendelian inheritance.
These traits are determined by DNA outside the nucleus. So this DNA is called
extra, or outside, extra-nuclear DNA. Where do we find extra-nuclear DNA?
We find extra-nuclear DNA in the mitochondria, mitochondrial organelles, and in
the chloroplast organelles, and they each have a unique, specialised function.
The specialised function of the mitochondria, shown in the picture on this slide,
is to release energy from nutrients and convert it into ATP during respiration.
The main function of the mitochondria is respiration. Now remember,
mitochondria are found in plants and animal cells. It’s found in all eukaryotic
cells.
In this picture, we see a picture of a
mitochondria, a mitochondria is a
cigar-shaped organelle, which
contains a double membrane, an
outer membrane and an inner
membrane. And in the inner
membrane or at the inner
membrane, we have the main
enzymes of respiration.
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 1
, The chloroplasts, as you know, are only found in plants and they capture sun or
solar energy and store it as carbohydrates during photosynthesis. So the first
thing we’re going to look at is mitochondrial DNA, what does it look like, how big
is it, how many copies of mitochondrial DNA do we have. You have more than
one mitochondria inside a cell because making energy is a fundamental process
of cells.
Mitochondrial DNA (mtDNA)
The mitochondria consists of two membranes. It’s a double-membraned
structure. And it has an inner membrane and an outer membrane. And then the
inner membrane structures project into a matrix. The mitochondrial DNA is found
in the matrix of the mitochondria.
The mitochondrial DNA isn’t just free-floating. It’s found in a little structure called
a nucleoid.
Now, a nucleoid is not a nucleus.
A nucleoid is a structure that has condensed DNA.
The condensed DNA is NOT condensed with histone. There are no histones
involved.
The nucleoids, typically one nucleoid will typically contain 3-5 molecules of
mitochondrial DNA tangled together.
The mitochondrial DNA is circular and so it exists in a supercoiled structure.
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 2
, So the nucleoids are found in the matrix of the mitochondria and the nucleoids
consist of about 4/5 molecules of mitochondrial DNA.
How many nucleoids do you have in one mitochondrial organelle? Well, you
have about, depending on the cell type, as little as 10 or as many as 40 or 50.
So you have about 30 nucleoids in each mitochondria. Just go over this again.
The DNA of the mitochondria is found in the nucleoid.
The nucleoid is composed of about 4/5 molecules of mitochondrial DNA
condensed. And you have about 30 or so nucleoids in a mitochondria. That’s in
one mitochondria.
Remember that you normally have more than one mitochondria cell.
A cell could have as many as 40 or 50 mitochondria in one cell.
The number of mitochondria you have in a cell depends on the function of the
cell and it depends on the actual cell and tissue type.
So, now we know that you have mitochondrial DNA inside mitochondria. We
know that there’s many copies of the mitochondrial DNA. They’re bound in
nucleoids.
There’s many nucleoids and there are many mitochondria per cell. So how big is
the mitochondrial genome, and what is the gene content of the mitochondrial
genome?
Well, both the size of the
mitochondria genome varies
between organisms and the gene
content can vary between
organisms.
You can clearly see that the mitochondrial genome size is way, way smaller than
the human nuclear genome.
Plants have larger mitochondrial genomes than animals.
The nuclear DNA divides in the synthesis phase before cell division for mitosis.
You can only divide the DNA, the nuclear DNA, once you’ve doubled it.
When do mitochondria double in preparation for cell division?
L5 - Extra-Nuclear Genomes and Mitochondrial Disorders 3
