Mitochondrion Structure Flashcards
What are the compartments of a mitochondrion
Outer membrane
Inter-membrane space
Inner membrane - cristae
Matrix
Describe the outer membrane:
Contains equal amounts of protein and phospholipids
Contains porin molecules which are large aqueous channels, allowing entry of molecules
Permeable to nutrient molecules, ions, ATP and ADP
Contains enzymes involved in mitochondrial lipid synthesis
Describe the inter-membrane space:
Contains enzymes that use ATP to phosphorylate other nucleotides
It is the compartment into which H+ ions are pumped
It has a low pH due to the H+ ions
Content of the intermembrane space is in continuous contact with the cellular cytoplasm through the porin channels and is similar in composition
Describe the inner membrane:
Contains the complexes of the electron transport chain and ATP synthetase complex
The lipid bilayer contains the phospholipid cardiolipin
Permeable only to O2, CO2, H2O
Contains three types of protein:
1 - proteins for redox reactions of electron transport chain
2 - proteins for synthesis of ATP
3 - transport proteins for movement of molecules into and out of matrix
An electrochemical gradient is established (drives ATP synthase)
The inner membrane must be impermeable to ions / small charged molecules
Describe the cristae:
The inner membrane has folds called cristae that project into the matrix
This gives increased surface area for complexes and proteins that aid in production of ATP
In a hepatocyte cristae constitute about a third of total cell membrane
The number of cristae is three times greater in the mitochondria of cardiomyocytes than in the mitochondria of hepatocytes
This reflects the greater demand for ATP in the cardiac muscle
Describe the mitochondrial matrix:
Matrix contains hundreds of enzymes which are involved in:
- oxidation of pyruvate and fatty acids
- the Citric Acid cycle
- synthesis of mitochondrial ribosomes, tRNAs, and mitochondrial DNA
Contains several copies of mitochondrial DNA, mitochondrial ribosomes, mitochondrial tRNAs, and enzymes required for gene expression
Besides these, it has oxygen, carbon dioxide and other recyclable intermediates
Describe mitochondrial inheritance:
Maternal inheritance - only the egg contributes mitochondria to the embryo, while sperm mitochondria are typically destroyed after fertilisation
Non-mendelian inheritance
Both males and females can inherit mitochondrial diseases, but only females pass them on to their offspring
Describe the production of mitochondria:
Biogenesis - process by which new mitochondria are produced
Replication -they replicate independently of the cell via fission
Coordination with Nuclear Genes
Regulation
In mitosis, each daughter cell receives half the mitochondria present in parent cell
Relate microtubules to mitochondria:
Microtubules provide tracks for mitochondrial movement, ensuring proper distribution throughout the cell
Microtubules regulate mitochondrial fission and fusion
Microtubules play a role in mitochondrial anchoring - positioning mitochondria in regions with high energy demands
During mitosis, microtubules ensure equal distribution of mitochondria between daughter cells.
How is old and damaged mitochondria destroyed ?
Autophagy controls mitochondrial numbers by wrapping endoplasmic reticulum membranes around the mitochondrion. Lysosomes, from the Golgi complex, join autophagic vacuole, containing hydrolases attached to mannose 6 phosphate receptors.
Acid pH removes hydrolases, recycling them.
Describe the mitochondrial genome:
Circular double stranded DNA
Encodes 37 genes: 13 protein-coding, 22 tRNAs, 2 rRNAs
Lacks introns and is densely packed with coding sequences
Replicates independently of the nuclear genome
Maternally inherited and highly susceptible to mutations
Discuss the origin of the mitochondria in symbiosis:
Mitochondria originated as free living aerobic bacteria that were engulfed by an ancestral anaerobic eucaryote
Instead of being digested, a symbiotic relationship was formed as there was a mutual benefit
Over time, mitochondria became permanent organelles within eukaryotic cells
Happened 1.5 billion years ago
Discuss the bacterial origin of the mitochondria:
Mitochondria originated from a free-living alpha-proteobacterium that was engulfed by a primitive eukaryotic cell
Bacterium provided the host cell with a more efficient way to produce energy through aerobic respiration, while the host cell offered protection and nutrients
Bacterium lost many of its genes, either transferring them to the host nucleus or becoming redundant, leading to the formation of modern mitochondria.
Mitochondria still retain key features of their bacterial origin, including a circular genome, binary fission replication, and double membranes
What is the evidence for the bacterial origin of mitochondria ?
New mitochondria are formed only through binary fission, the form of cell division used by bacteria
If a cell’s mitochondria are removed, the cell does not have the means to create new ones.
Transport proteins called porins are found in the outer membranes of mitochondria and are also found in bacterial cell membranes.
Mitochondria contain circular DNA molecules that are similar to the DNA of bacteria both in size and structure
Mitochondrial ribosomes are more similar to those of bacteria (70S) than those of eukaryotes (80S)
Horizontal transfer of mitochondrial genes to the host nucleus over time.
What are the 2 genetic systems that produce mitochondrial proteins ?
Mitochondrial DNA - encodes a small number of essential proteins involved in mitochondrial energy production
Nuclear DNA - encodes the vast majority of mitochondrial proteins, which are synthesized in the cytoplasm and imported into the mitochondria for proper function
