Mitochondrial Genome Flashcards
Mitochondrial DNA is always passed on from the
Mother
Which process in the mitochondria generates ATP?
Oxidative Phosphorylation
Does not provide nearly as much ATP as oxidative phosphorylation
Anaerobic Phosphorylation
What are the four basic components of the mitochondria?
- ) Outer membrane
- ) Intermembrane space
- ) Inner membrane
- ) Matrix
The intermembrane space is made up of structural convolutions (fold) called
-The more you have, the more energy you will be able to make
Cristae
The oxidative phosphorylation machinery resides in the
Intermembrane space
Many of the nuclearly coded proteins residing in the mitochondrial matrix are used for processing
-oxidized within the matrix
Foodstuffs
The TCA cycle occurs in the
Mitochondrial matrix
Permeable to small molecules but impermeable to large molecules
-contains signaling receptors (Apoptotic receptors)
Outer mitochondrial membrane
Contains apoptotic proteins
Inermembrane space
Contains transport proteins and is where the electron transport chain takes place.
-It is the ATP synthesizing complex
Inner Mitochondrial membrane
Houses the proteins for the TCA cycle, lipid oxidation, transamination, mt DNA, and the mitochondrial protein synthesis machinery
Mitochondrial Matrix
Food from our diets (fats, carbs, protein) are metabolized through a process requiring oxygen to generate large amounts of
ATP
Says that mitochondria most likely evolved from engulfed bacteria
Endosymbiotic theory
There are two different types of mitochondrial proteins. One type, which is made from genomic DNA, and one type which is made from
Mitochondrial DNA
In mitochondria, both fission and fusion occur. The fission process is similar to the
Bacterial division process
If you start exercising a muscle, you will undergo
Fission
Circular DNA, which is proportional to the ATP requirement of the cell
Mitochondrial DNA
Mitochondrial DNA codes for 2
rRNAs (16S and 12S)
Codes for 22 tRNAs and 13 proteins
Mitochondrial DNA
The proteins that the mitochondria encodes are important for
Oxidative phosphorylation
The site where most of mitochondrial replication and transcription is controlled
-Allows replication to move faster
D loop (D = displacement)
Can replicate independently of the cell cycle
mt DNA
Which DNA polymerase functions in mitochondrial replication?
- Encoded by the nuclear genome
- has a proofreading and exonuclease activity
- more error prone than nuclear DNA polymerases
DNA polymerase ƴ
What is the helicase for mtDNA replication?
Twinkle
There are over 160 identified mutations that lead to disease in
DNA polymerase ƴ or Twinkle
Initiated from promoters generating polycistronic transcripts, which are then processed to produce the individual mRNA, rRNA, and tRNA molecules
Mitochondrial Transcription
Mitochondrial transcription requires what three things?
- ) mtRNA polymerase
- ) Transcription acticator (TFAM)
- ) Either mtTranscription factor B1 or B2
How many RNA polymerases are required for mitochondrial transcription?
1
The molecule that helps initiate mitochondrial transcription
-acts almost like a histone after replication
TFAM
When TFAM wraps the mtDNA, it becomes a
Nucleoid
Organelles about 1 micrometer in length in the cytoplasm of cells. There are typically 10-200 per cell, but there can be thousands of in a cell with very high-energy needs
Mitochondria
A typical lipid bilayer, which is permeable to small
molecules (
Outer Mitochondrial Membrane
Is the narrow space between the outer and
inner membranes.
-Houses apoptotic molecules, which lead to cell death
Intermembrane Space
Has many infoldings known as cristae, which
increase its surface area.
-A most unusual membrane, in having an extremely high protein content and in being impermeable to small as well as large molecules. Even K+ ions, Ca++ ions, ATP, ADP, protons and OH- groups cannot diffuse through
Inner mitochondrial membrane
The site of the electron transport chain and of oxidative phosphorylation
The inner mitochondrial membrane
The site of the TCA cycle and fatty acid oxidation.
-There are also small circular mitochondrial DNA molecules (mtDNA), which code for 13 polypeptide chains, which are all subunits involved in oxidative phosphorylation, and also for tRNA molecule and ribosomal RNA molecules.
Mitochondrial Matrix
The process of oxidative phosphorylation requires about 100 different polypeptide chains. Of these, 13 polypeptide chains are coded for by
mtDNA
Mitochondrial protein synthesis uses the rRNAs and tRNAs coded by the mtDNA, but the ribosomal proteins are all coded for by
Nuclear DNA
In the mitochondria, replication, transcription, and translation, are all controlled by
Imported nuclear proteins
Double stranded circular DNA, made up of 16,600 bases and no introns
Human mtDNA
The two strands of mtDNA differe in base composition. What are the two strands of the mtDNA called? Why?
- ) Heavy (H) strand: encodes more proteins
2. ) Light (L) strand
mtDNA contains only one significant non-coding region, which is called the
D-loop (displacement loop)
The site where most of replication and transcription is controlled
D-loop
Mitochondria replicate many times in their life cycle. They undergo division by
Fission
mtReplication starts with the H strand origin in the
D-loop
Binds single stranded DNA in mtDNA replication
mtSSB (mitochondrial single stranded binding protein)
Regulated at the non-coding D loop
Mitochondrial transcription
Unique in its ability to bind DNA non-specifically in addition to recognising specific sequences within promoter regions
TFAM
Packages mtDNA into nucleoids, facilitating
mtDNA replication and transcription, and
provides protection from DNA damage.
TFAM
Mitochondrial transcription proceeds bidirectionally, giving rise to
Polycistronic transcripts
tRNA processing enzyme that processes mtRNA
RNAse P
Human mitochondrial mRNAs have short
Poly(A) tails
Translation of the 13 polypeptides coded for by mtDNA takes place in the
Mitochondrial matrix
Is mtRNA capped?
No
Mitochondrial translation resembles
Bacterial translation
What are three distinctive features of mitochondrial genetics?
- ) Very high mtDNA mutation rate
- ) Maternal inheritance of mtDNA
- ) Random segregation of mitochondria and mtDNA
Has a DNA mutation rate that is 10-20 times that of nuclear genes
mtDNA
Why is mtDNA so prone to mutations?
Because of its proximity to oxidative phosphorylation which generates ROS
mtDNA also has no introns and little
Repair mechanism
From person to person, the mtDNA sequence differs on average by
4 nucleotides/ 1000 bp
The oocyte has a much larger cytoplasmic volume than sperm, so in the fertilized oocyte >99% of mitochondria are contributed by your
Mother
The small amount of mtDNA contributed by sperm gets
Inactivated
During cell division, mitosis and meiosis ensure coordinated segregation of chromosomes. However, during mitochondrial biogenesis, fission and fusion lead to a
Random distribution of mitochondria and mtDNA
When all the mtDNA in a cell are the same, it is known as
Homoplasmy
When there is a mixture of mutant and normal mtDNA in the same cell, it is called
Heteroplasmy
Tissues such as cardiac muscle, skeletal muscle, and CNS have very high
-each cell has a threshold level
ATP requirements
In a heteroplasmic cell, when the number of normal mtDNA drops below the threshold level, the respiration and ATP synthesis of the cell may be insufficient and lead to
Cell death
The number of mtDNA mutations increases with age
(especially deletions) and as a result, as you age, the levels of oxidative phosphorylation
-Why older people feel more tired
Decline
It is increasingly clear that some human pathological conditions are caused primarily or secondarily by defects in the process of
Oxidative phosphorylation
Mutations leading to defects in oxidative phosphorylation can be present either in
mtDNA or Nuclear DNA
When the inheritance pattern does not follow simple Mendelian inheritance, we can suspect the possibility of a
-Will have a maternal inheritance pattern
Defect in mtDNA
Because of the random distribution of mtDNA, the mutant mitochondria could exceed the threshold in one tissue in one family member, but not in another as a result, we may see
Variability in clinical consequences among family members
Maternal inheritance, variability in tissues and among family members, late onset, lactic acidosis, and massive mitochondrial proliferation in myofibers are all clinical features of defects in
mtDNA
As we age, there is often an increase in the number of
Mutant mtDNA
The most recognized abnormality in patients with mitochondrial disorders is
Lactic acidosis
Dysfunction in the ETC causes a decrease in the production of ATP. Low ATP levels result in an upregulation glycolysis, leading to an overproduction of
Lactate
Massive mitochondrial proliferation in myofibers appear around the mitochondrial periphery as
Ragged Red Fibers (RRFs)
Often include a large part of the mtDNA genome and affect more than 1 subunit
-increases with age, so the disease usually progresses with age
mtDNA deletions
Usually spontaneous and sporadic, and have symptoms including: ocular myopathy, lactic acidosis, hearing loss, and dementia
mtDNA deletions
Kearns-Sayre syndrome, characterized by progressive muscle weakness and retinopathy is an example of a disease caused by
mtDNA deletions
Base substitution mutations in the tRNA of mtDNA result in characteristic
RRFs of mitochondrial myopathy
Mutations in the tRNAs usually affect more than one
Subunit
A base substitution in the mitochondrial DNA (mtDNA) gene encoding tRNALys is the gene most commonly associated with the disease
MERRF (Monoclonic Epilepsy and Ragged Red Fiber Disease)
This mutation that causes MERRF leads to a reduction in mitochondrial protein synthesis, in particular of complexes I and IV, which have the most mitochondrial encoded subunits
A to G substitution at nucleotide 8344
A disease characterized by maternal inheritance that is an example of an mtDNA point mutation
Leber’s hereditary optic neuropathy (LHON)
The death of the optic nerve in LHON results in sudden onset in blindness, and this threshold is crossed when 80-90% of the mtDNA in a cell has the
Mutation
Which point mutation is the most common cause of LHON
Arg to HIS substitution in subunit 4 of NADH dehydrogenase
Most of the mtDNA point mutations leading to disease are found in
Complex I
What are the three different types of mtDNA mutations that lead to disease?
- ) mtDNA deletions
- ) Base substitution mutations in the tRNA
- ) mtDNA point mutations in protein coding genes
One major source of mitochondrial diseases is a mutation in the nuclear DNA region coding for
DNA polymerase ƴ
Tumor cells adapt to the requirements of unrestrained growth, in part by shifting from oxidative phosphorylation to glycolysis, known as the
-The decreased oxidative phosphorylation is promoted by defects in DNA polymerase POLγ and in mtDNA.
Warburg Effect
mtDNA encodes 13 polypeptide chains, which are all part of protein complexes involved in oxidative phosphorylation and are all embedded in the
Inner mitochondrial membrane
Four of the five mitochondrial complexes contain
Mitochondrial proteins
During early oogenesis, there is a substantial reduction in the amount of mtDNA present. This is known as the
Bottleneck affect
There is no mitochondrial division when germ cells are
-results in some cells getting a lot of mutated mtDNA and others getting none
Dividing
Can not pass mitochondrial diseases to any of their children
Affected Males
The point at which there are enough mtDNA mutations that we begin to see the phenotypic effect
Threshold effect
Level of Ox. Phos. decreases with age. When the amount of ATP produced falls below a certain threshold in a given tissue, a phenotype will be observed. This could be due to an increasing number of mutations with age or from
Random distribution of mutated mtDNAs
Due to heteroplasmy and the threshold effect,
different tissues harboring the same mtDNA mutation
may be affected to different
Degrees
Most mtDNA related sequences share the features of
Lactic acidosis and Massive mitochondrial proliferation (results in RRFs)
What two things happen as we age?
of mtDNA mutations increases, Ox. Phosphorylation decreases
Which organs are more frequently affected by mtDNA mutations?
Organs requiring a lot of energy
In mtDNA multiple mutations can lead to the same
Disease
Only 1/3 of mitochondrial diseases have
RRFs
Leigh Syndrome and LHON have no
RRFs
