Concept discussion

[Scooby]

That is so interesting; so basically the inner-membrane of a mitochondrion is beleived to be the plasma membrane of the prokaryote + the vesicle that the mitochondrion was held in when engulfed, but not digested, by eukaryotic cells, is believed to have formed the outer-membrane of the mitochondria. That is quite interesting.

It's like chloroplasts. I guess you can say that chloroplasts are made up of the grana (small discs containing the green-pigment chlorophyll) and stroma (containing enzymes for photosynthesis and other dissolved substances in solution form). Can we say the inner membrane is believed to be the plasma membrane, whilst the outer membrane is believed to be that of the vesicle it was held in when engulfed, but not digested?

Just making sure that the double-membrane theory can be applied to both chloroplasts AND mitochondria

Yup, endosymbiosis applies to mitochondria and chloroplasts

[Yacoubb]

Thank you.

So when we come to justify the endosymbiotic theory of evolution, would valid points be:
* mitochondria/chloroplasts have their own DNA.
* the presence of ribosomes within mitochondria/chloroplasts.
* the presence of a double (inner- and outer-) membrane on the structure of mitochondria/chloroplasts

I don't think a potential question that asks that ^ on an exam would require any more points to justify this theory?

[alondouek]

Actually, it's quite likely there would be a question (or possibly only a Multiple Choice) on the Endosymbiotic Theory; I've certainly seen it before.

All those points are valid mitochondrial DNA = mtDNA, chloroplast DNA = ctDNA or cpDNA. Both mtDNA and ctDNA molecules are circular.

Here's a ctDNA molecule:


And an mtDNA molecule:


Not really necessary to know either of the structures of these in detail, but it's still fascinating to see which sequences code for what.

[Yacoubb]

It certainly is fascinating - perhaps even learning the importance of DNA, ribsomoes and inner- and outer-membranes would be handy.

DNA -
The genetic information that codes for the proteins produced by mitochondria/chloroplasts codes for proteins produced by mitochondria or chloroplasts.

Ribosomes -
The synthesis of proteins (e.g enzymes required in photosynthesis [chloroplasts] or aerobic respiration [aerobic respiration].

Membranes:
Would that just be a structural assistance to these organelles, like a protective layer?!

[alondouek]

It certainly is fascinating - perhaps even learning the importance of DNA, ribsomoes and inner- and outer-membranes would be handy.

DNA -
The genetic information that codes for the proteins produced by mitochondria/chloroplasts codes for proteins produced by mitochondria or chloroplasts.

Ribosomes -
The synthesis of proteins (e.g enzymes required in photosynthesis [chloroplasts] or aerobic respiration [aerobic respiration].

Membranes:
Would that just be a structural assistance to these organelles, like a protective layer?!

Well, let's take a sequential look at it - we'll use mtDNA as the basis for the example.

As we can see, the mtDNA molecule has various regions for coding rRNA (a component of the ribosome) and tRNA (required for translation. Therefore, we can see that the rRNA- and tRNA-encoding genes (orange and yellow respectively in the diagram), when translated, work in conjunction with the translation of the regions required for the synthesis of proteins (green areas).

The areas in the diagram labelled "NADH dehydrogenase subunits" are needed in the construction of the enzyme of NADH dehydrogenase - which fulfils the following reaction:

NADH + H⁺ + acceptor <---> NAD⁺ + reduced acceptor

You might recognise this reaction as a side-reaction in aerobic respiration.

There is a region that codes for the cytochrome oxidase enzyme. This also fulfils an important reaction in mitochondrial aerobic respiration:

4 Fe²⁺-cytochrome c + 8 H⁺_in + O₂ ---> 4 Fe³⁺-cytochrome c + 2 H₂O + 4 H⁺_out

Wikipedia summarises this reaction well:

"Two electrons are passed from two cytochrome c's, through the Cu_A and cytochrome a sites to the cytochrome a₃- Cu_B binuclear center, reducing the metals to the Fe⁺² form and Cu⁺¹. The hydroxide ligand is protonated and lost as water, creating a void between the metals that is filled by O₂. The oxygen is rapidly reduced, with two electrons coming from the Fe⁺²cytochrome a₃, which is converted to the ferryl oxo form (Fe+4=O). The oxygen atom close to Cu_B picks up one electron from Cu⁺¹, and a second electron and a proton from the hydroxyl of Tyr(244), which becomes a tyrosyl radical: The second oxygen is converted to a hydroxide ion by picking up two electrons and a proton. A third electron arising from another cytochrome c is passed through the first two electron carriers to the cytochrome a₃- Cu_B binuclear center, and this electron and two protons convert the tyrosyl radical back to Tyr, and the hydroxide bound to Cu_B⁺² to a water molecule. The fourth electron from another cytochrome c flows through Cu_A and cytochrome a to the cytochrome a₃- Cu_B binuclear center, reducing the Fe⁺⁴=O to Fe⁺³, with the oxygen atom picking up a proton simultaneously, regenerating this oxygen as a hydroxide ion coordinated in the middle of the cytochrome a₃- Cu_B center as it was at the start of this cycle. The net process is that four reduced cytochrome c's are used, along with 4 protons, to reduce O₂ to two water molecules."

As you can see, this is quite complicated and nowhere even near VCE level. More briefly, you can see that it is the other side reaction in aerobic respiration.

Finally, we come to the ATP synthase region of the mtDNA molecule (the lightest green regions).

ATP synthase is involved in the 'main', energy-producing reaction of aerobic respiration:
ADP + P_i ---> ATP, where ADP and P_i are joined together by ATP synthase

The membranes serve the same purpose as in other cells/unicellular organisms - partly structural, needed for diffusion of various materials, the site of certain chemical reactions (Electron Transport Chain in this case - thanks Scooby!) etc.

[Scooby]

It certainly is fascinating - perhaps even learning the importance of DNA, ribsomoes and inner- and outer-membranes would be handy.

DNA -
The genetic information that codes for the proteins produced by mitochondria/chloroplasts codes for proteins produced by mitochondria or chloroplasts.

Ribosomes -
The synthesis of proteins (e.g enzymes required in photosynthesis [chloroplasts] or aerobic respiration [aerobic respiration].

Membranes:
Would that just be a structural assistance to these organelles, like a protective layer?!

Inner mitochondrial membrane is also the site of the electron transport chain

[pi]

Well, membranes have a broader role than *just* structural support

[Yacoubb]

Inner mitochondrial membrane is also the site of the electron transport chain

That of course comes when investigating aerobic respiration - that is, Kreb's Cycle takes place in the matrix of mitochondria and the Electron Transport Cahin takes place in the Cristae of the Mitochondria.

So the cristae are practically the inner folds that form when the inner mitochondrial folds and forms these compartments that are filled with fluid. The matrix of mitochondria are the spaces in between the cristae that are filled with fluids. Probably knowing the significance of each compartment in Cellular respiration is essential

[Yacoubb]

Finally, we come to the ATP synthase region of the mtDNA molecule (the lightest green regions).

Glad you said that; I just face-palmed LOL! But no I think what I've mentioned below about knowing the compartments of mitochondria in relation to aerobic respiration, and also a little bit on how to justify the endosymbiotic theory of evolution.

Okay lets start discussing the Nucleus. Now the nucleus is found exclusively in eukaryotic organisms and contains the genetic code and hereditary information DNA of an organism that determines how it functions, behaves, the appearance of the organism, proteins produced for controlling cellular functions, etc. The nucleus is surrounded by a double membrane; it is relatively large compared to other organelles. It contains chrosomes and the nucleolus

Four structures/complexes that are discussed when describing the nucleus:
* nucleus
* nuclear membrane
* nucleolus
* centriole

Nuclear membrane: a double membrane holds the nucleus structure, and it contains many pores on the surface. It seperates the nucleoplasm (the contents including genetic material within the nucleus), seperating it from other organelles/structures that are immersed in the cell's cytosol. It also regulates movement of material between the cytoplasm and the nucleus.

Nucleolus: a granular structure in the nucleus; a nucleoprotein (nucleic acid + protein). The ribosomal RNA that forms part of the structure of ribosomes found in the cytoplasm is synthesised in the nucleolus.

Centriole: a pair of cylindrical structures made up of smaller tubes that form the spindle during cell division along the equator of the cell.

Important key terms:

Protoplasm = cytosol + all organelles including the nucleus.

Cytoplasm = cytosol + all organelles except the nucleus.

That is handy because if you were asked to distinguish between the two, all your answer would have to be is that protoplasm includes all the organelles including the nucleus + cytosol whereas cytoplasm refers to cytosol + all organelles with the exception of the nucleus.

Feel free to add Ooh, and also, the nucleus is basically the control centre of the cell, due to the fact that it contains the genetic code and information that manufactures/synthesises proteins used to control cellular functions and activity.

Constructive criticism would be appreciated

[Scooby]

Okay lets start discussing the Nucleus. Now the nucleus is found exclusively in eukaryotic organisms and contains the genetic code and hereditary information DNA of an organism that determines how it functions, behaves, the appearance of the organism, proteins produced for controlling cellular functions, etc. The nucleus is surrounded by a double membrane; it is relatively large compared to other organelles. It contains chrosomes and the nucleolus

Be very careful there. The appearance of an organism and its behaviour, etc, are determined both by its genetic material and environmental factors

[Yacoubb]

So I just wanted to mention if the following definition of DNA is acceptable:

DNA, Deoxyribose Nucleic Acid, is the genetic code and hereditary information of an organism that determines the proteome of an organism that control cellular functions and the overall function of an organism.

I've excluded the bit on appearance, because good point, phenotypes are practically determined by the genotype of an organism + the environmental factors/conditions they are around.

Is all the other information valid? Or accurate rather?!

[Bad Student]

I think it would be better if you said:

DNA, Deoxyribonucleic Acid, is a molecule which contains the genetic code and hereditary information of an organism that determines the proteome of an organism that control cellular functions and the overall function of an organism.

[Yacoubb]

Yeah valid point; it is a molecule + not just anything; specific is better. Thanks for the handy tip

[Yacoubb]

Ribosomes: organelles that are present in both prokaryotes and eukaryotes that synthesises and manufactures proteins.

* Ribosomes are not held in a membrane.
* Condensation reaction where amino acids are chemically bonded by peptide bonds, and a polypeptide is synthesised within the ribosome.
* Amino acids that make up the primary sequence of a polypeptide are determined by the genetic code found in DNA.
* Ribosomes are actually made up partly of rRNA (i.e. ribosomal RNA)

Feel free to add on.

[Yacoubb]

Oh and constructive criticism please!!