PHY 301AShort-Study Project

MITOCHONDRIA – It’s History, Structure and Function Nakul Surana

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Definition

o Mitochondria are well-defined cytoplasmic organelles of the cell which take part in a variety of cellular metabolic* functions

o The mitochondria are important as the fact that these organelles supply all the necessary biological energy of the cell, and they obtain this energy by oxidizing the substrates of the Krebs cycle.

* Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism.

When and How Often Did Mitochondria Arise?

o The oldest undisputedly eukaryotic(Contains nucleus) microfossils go back 1.45 billion years in the fossil record.

o Like eukaryotes themselves, mitochondria appear to have arisen only once in all of evolution.

o The best evidence for the single origin of mitochondria comes from a conserved set of clearly homologous and commonly inherited genes preserved in the mitochondrial DNA across all known eukaryotic groups.

HISTORY

There are currently two main, competing theories about the origin of mitochondria. They differ with regard to their assumptions concerning the nature of the host.

The traditional view posits that the host that acquired the mitochondrion was an anaerobic nucleus-bearing cell, a full-fledged eukaryote that was able to engulf the mitochondrion actively via phagocytosis.

The initial benefit of the symbiosis might have been the endosymbiont's ability to detoxify oxygen for the anaerobe host.

HISTORY

Shortcomings –

o Does not directly account for the ubiquity (state of being all the time) of mitochondria.

o The oxygen detoxification aspect is problematic, because toxic oxygen is produced via Mitochondria only (Like O2

-)

o This traditional view also does not directly account for anaerobic mitochondria 

HISTORY

o An alternative theory posits that the host that acquired the mitochondrion was a prokaryote (Without Nucleus).

o This view is linked to the idea that the ancestral mitochondrion was a metabolically versatile, facultative anaerobe

o The initial benefit of the symbiosis could have been the production of H2 by the endosymbiont as a source of energy and electrons for the archaebacterial host, which is posited to have been H2 dependent.

STRUCTURE

Functions

o Production of Energy, ATP Synthesis

o Production of heat: Non-shivering thermogenesis

o Role as independent units within eukaryotic cells: Mitochondria have mitochondrial DNA (mtDNA)

o Role in the process of apoptosis: (Programmed cell death)

o Storage of Ca2+ ions

Functions

Some of the functions of mitochondria depend on the type of cells in which they are located.

o contribution to synthesizing, breaking-down, and recycling biochemicals needed for cell functioning e.g. components of genetic material.

o contribution to synthesizing certain hormones e.g. oestrogen and testosterone.

o role in cholesterol metabolism

o role in neurotransmitter metabolism

o detoxification of ammonia in the urea cycle

Energy Production

This occurs by a process of cellular respiration, also known as aerobic respiration, which is dependent on the presence of oxygen. (When oxygen is limited, the chemicals that would otherwise be oxidized are, instead, metabolized by anaerobic respiration, via a process that is independent of the mitochondria.)

The 3 main stages in the overall process of aerobic cellular respiration are:

1.Glycolysis - splitting sugar molecules2.TCA Cycle3.Electron Transport

mtDNA

Mitochondria contain their own genetic material - which is independent of the cell in which they are located.

Mitochondrial DNA (mtDNA) is maternally inherited. At fertilization only nuclear DNA enters from the sperm because although the egg contains mitochondria, sperm cells do not. Sperm are so tiny that mitochondria would hamper their passage toward the egg. (Therefore exercise capacity e.g. for endurance sports tends to be maternally inherited. Maternal ancestral history can also be traced via mtDNA.)

mtDNA accounts for about 1% of the total cellular DNA

Application – Tracing Human eve

Mitochondrial Eve

o In 1987, Cann, Stoneking, and Wilson published an article on mtDNA

o Its main point was that "all mitochondrial DNAs stem from one woman" and that she probably lived around 200,000 years ago in Africa.

o This mtDNA, comes only from the mother and not from the Father

o mtDNA is transferred from mother to daughter, generation after generation. The mtDNA in the son, which he got from his mother, is a dead end street

o  However, the mitochondrial DNA gets transferred from generation to generation without any recombination. Only the normal mutation rate that occurs when DNA is replicated allows the mitochondrial DNA to change. 

It’s Methodology

o The mitochondrial data was determined using restriction analysis 

o They used African Americans rather than Africans from Africa to represent native Africans in their study.

o They used a program called PAUP to build a phylogenetic tree.

REFERENCES

http://www.mhrc.net/mitochondrialEve.htm http://www.nature.com/scitable/topicpage/the-origin-of-mitochondria-14232356 http://biology.tutorvista.com/animal-and-plant-cells/mitochondria.html