Mitochondria and Peroxisomes Flashcards
(44 cards)
Importance of mitochondrial function
Mitochondrial functions are critical for cellular and organismal life. They have been central in driving the evolution of complex eukaryotic organisms.
Mitochondrial function has been implicated as a contributing factor to ageing and the development of ageing-related diseases such as cancer, cardiovascular diseases and dementia.
Why are mitochondria medically important?
Investigating mitochondrial disorders - a large group of inherited monogenic diseases affecting mitochondrial function.
The side effects of many commonly used antibiotics happen because they can inhibit mitochondrial function.
Importance of peroxisomes
Peroxisomes are far simpler organelles when compared to mitochondria.
But they have important roles in cellular metabolism.
Why are peroxisomes medically important?
Investigating peroxisomal disorders - a group of inherited diseases caused by mutations in peroxisomal proteins
What is the endosymbiotic theory related to the origin of mitochondria?
Mitochondria are present in all eukaryotic organisms
Approximately 2 billion years ago, the earth was colonised by bacteria while there was no complex life.- no eukaryotes, no multicellular life, and thus no animals or plants.
The endosymbiotic theory proposes that all the mitochondria that have existed can be traced back to one single prokaryotic cell
The prokaryote was engulfed by a primitive form of eukaryotic cell - the two cells formed a symbiotic relationship
The prokaryote is divided inside its host, producing daughter cells and increasing their number so that when the host cell divides, these daughter cells are also passed on
The prokaryote supposedly provided a functional advantage to the host cell, which then gave rise to all eukaryotic organisms that have lived
What is the importance of mitochondria and their evolutionary ancestor?
It enabled the evolution of complex life
Which eukaryotic cells do not contain mitochondria?
Some eukaryotes have lost mitochondria in evolution but retain a similar organelle
Mature red blood cells destroy their mitochondria
What is the structure of mitochondria?
Double membrane - inner and outer membranes
Intermembrane space - between the inner and outer membranes
Mitochondrial matrix - located within the inner membrane (this is where a large number of metabolic reactions occur)
Small circular genome - mitochondria have their own DNA
Where are the large protein complexes responsible for oxidative phosphorylation located?
Embedded in the inner mitochondrial membrane
What are the clues that mitochondria originate from a prokaryotic ancestor?
Presence of two membranes and a small circular genome (mitochondria have their own DNA)
What is the organisation of mitochondria highly dependent on?
Cell type
Examples of when mitochondria form networks
In skin fibroblast cells, mitochondria are interconnected and form networks with one another
This network is highly dynamic, whereby the mitochondria are constantly moving in the cell
Individual mitochondria can separate from the network, divide and fuse with other mitochondria (by fission and fusion)
Mitochondria are also highly abundant in cardiac cells (cardiomyocytes) and reside in distinct zones - distinct sub-cellular populations may perform zonal-specific functions necessary for cardiomyocyte function
How are mitochondria transported?
Mitochondria are transported on cytoskeletal microtubules
Mitochondria bind to dynein and kinesin proteins by adaptor proteins (milton and miro)
Milton and miro are located on the surface of mitochondria
Why is the transport of mitochondria important in neurons?
Mitochondria are channeled along axons and delivered to synapses where they are required for neuronal signalling and function
How is the prokaryotic origin of mitochondria reflected in their behaviour?
Like bacteria, mitochondria can divide and fuse with one another (by fission and fusion)
The process of increasing the number of mitochondria involves growing the mass of existing mitochondria, which are then able to undergo fission
Although it is known that the process of fusion is important for mitochondria, the physiological role is less clear
Why do macromolecules such as DNA and proteins become damaged in the mitochondria over time?
Due to oxidative insults
What process is involved in removing damaged mitochondria from the cell?
These damaged mitochondria are removed from the cell in the process of mitophagy (a form of autophagy)
What are the functions of mitochondria?
- To produce ATP in oxidative phosphorylation
- Anabolic synthesis of nucleotides which are required for DNA replication and growth
- Calcium homeostasis which is critical for muscle contraction
- Production of amino acids such as glutamate, which have a function as neurotransmitters
- Important in apoptosis - programmed cell death
- Involved in immune responses - there are protein receptors that detect invading viral RNA molecules and these protein receptors are located on the outer membrane of mitochondria (this activates an innate immune response)
Mitochondrial function has emerged as an important target for cancer therapy
What is the role of mitochondria in cellular energy metabolism?
Mitochondria play an important role in cellular energy metabolism as it is the site where most cellular ATP is generated
Nutrients in food are oxidised to produce acetyl coenzyme A, which is processed in the citric acid cycle (TCA/ Krebs cycle)
NADH and FADH are produced which serve as the electron donors in the electron transport chain - these electron donors are oxidised by the ETC and result in production of ATP
Citric acid cycle is the final common pathway for oxidation of fuel molecules, what are these fuel molecules?
Carbohydrates, fatty acids, and amino acids
Most fuel molecules enter the citric acid cycle as acetyl coenzyme A, where is this derived from?
Acetyl coenzyme A is derived from the metabolism of carbohydrates in the cytoplasm and from fatty acids metabolised by beta-oxidation in the mitochondria
The acetyl coenzyme A is completely oxidised to the carbon dioxide in the citric acid cycle
What are the two important functions of the citric acid cycle?
- To produce reduced electron donors NADH and FADH2 - these are used to produce ATP in oxidative phosphorylation (catabolic state - where energy is released during the breakdown of molecules)
- To provide biosynthetic precursors for the biosynthesis of fatty acids and amino acids (anabolic state - where energy is consumed in the formation of larger molecules)
Where does the citric acid cycle occur?
Citric acid cycle takes place in the mitochondrial matrix
What are and how many intermediates are there in the citric acid cycle?
9 intermediates, with the first one being citrate (made by combining acetyl coenzyme A and oxaloacetate)