Dory's Biology Questions Thread

[GenesForLife]

Are mitochondria immobile or do they move within the cell?

http://jcb.rupress.org/content/167/4/661.abstract

Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1–2 μM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate– or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2199926/

Using fluorescent membrane potential sensing dyes to stain budding yeast, mitochondria are resolved as tubular organelles aligned in radial arrays that converge at the bud neck. Time-lapse fluorescence microscopy reveals region-specific, directed mitochondrial movement during polarized yeast cell growth and mitotic cell division. Mitochondria in the central region of the mother cell move linearly towards the bud, traverse the bud neck, and progress towards the bud tip at an average velocity of 49 +/- 21 nm/sec. In contrast, mitochondria in the peripheral region of the mother cell and at the bud tip display significantly less movement. Yeast strains containing temperature sensitive lethal mutations in the actin gene show abnormal mitochondrial distribution. No mitochondrial movement is evident in these mutants after short-term shift to semi-permissive temperatures. Thus, the actin cytoskeleton is important for normal mitochondrial movement during inheritance. To determine the possible role of known myosin genes in yeast mitochondrial motility, we investigated mitochondrial inheritance in myo1, myo2, myo3 and myo4 single mutants and in a myo2, myo4 double mutant. Mitochondrial spatial arrangement and motility are not significantly affected by these mutations. We used a microfilament sliding assay to examine motor activity on isolated yeast mitochondria. Rhodamine-phalloidin labeled yeast actin filaments bind to immobilized yeast mitochondria, as well as unilamellar, right- side-out, sealed mitochondrial outer membrane vesicles. In the presence of low levels of ATP (0.1-100 microM), we observed F-actin sliding on immobilized yeast mitochondria. In the presence of high levels of ATP (500 microM-2 mM), bound filaments are released from mitochondria and mitochondrial outer membranes. The maximum velocity of mitochondria- driven microfilament sliding (23 +/- 11 nm/sec) is similar to that of mitochondrial movement in living cells. This motor activity requires hydrolysis of ATP, does not require cytosolic extracts, is sensitive to protease treatment, and displays an ATP concentration dependence similar to that of members of the myosin family of actin-based motors. This is the first demonstration of an actin-based motor activity in a defined organelle population.

The JCB is open access and you can grab the full text of both papers.

[Dory]

Until it is degraded, it is free to be recycled...

Why would it be degraded? Why does the cell care if it floats around in its cytoplasm? It's not like it's getting rusty or anything.

Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules.

I'm surprised to find out that mito are immobile. I thought that together with symbiosis they've lost all mobility.

[GenesForLife]

Until it is degraded, it is free to be recycled...

Why would it be degraded? Why does the cell care if it floats around in its cytoplasm? It's not like it's getting rusty or anything.

Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules.

I'm surprised to find out that mito are mobile. I thought that together with symbiosis they've lost all mobility.

FIFY.

[GenesForLife]

Until it is degraded, it is free to be recycled...

Why would it be degraded? Why does the cell care if it floats around in its cytoplasm? It's not like it's getting rusty or anything.

There would be an advantage for any cell that can break down complex polymers into monomers which can be used to make polymers again as the situation demands, suppose you need nucleotides for replication, it would make sense to obtain nucleotides from now superfluous polymers to do the same. The idea for metabolic efficiency is being able to synthesize as much as you need while minimizing external intake, which again would have evolutionary advantages as in some degree of independence from external food sources. Any metabolic configuration that evolves and ends up with the above features will give its bearers an evolutionary advantage.

That is one reason, secondly, I'd like to bring this up...

From the earliest comparisons of RNA production with steady-state levels, it has been clear that cells transcribe more RNA than they accumulate, implying the existence of active RNA degradation systems. In general, RNA is degraded at the end of its useful life, which is long for a ribosomal RNA but very short for excised introns or spacer fragments, and is closely regulated for most mRNA species. RNA molecules with defects in processing, folding, or assembly with proteins are identified and rapidly degraded by the surveillance machinery. Because RNA degradation is ubiquitous in all cells, it is clear that it must be carefully controlled to accurately recognize target RNAs. How this is achieved is perhaps the most pressing question in the field.

Again this would have advantages in recycling now superfluous polymers to raw material for further anabolism.

http://www.cell.com/abstract/S0092-8674%2809%2900067-1

I will try to procure a copy of the paper from a friend.

[Dory]

There would be an advantage for any cell that can break down complex polymers into monomers which can be used to make polymers again as the situation demands,

All you needed to say.



....New question--

Why should there be sexual dimorphism in pine cones?

[GenesForLife]

is your name Tomas Sorensen on Yahoo answers?

http://answers.yahoo.com/question/index ... 316AACZnJi

Why should there be sexual dimorphism in pine cones?

I'll come back to the question as and when time permits, I have some phone calls to make.

[Dory]

is your name Tomas Sorensen on Yahoo answers?

http://answers.yahoo.com/question/index ... 316AACZnJi

Why should there be sexual dimorphism in pine cones?

I'll come back to the question as and when time permits, I have some phone calls to make.

No, Thomas is a dude name, I am not a dude! But, I do browse this section awful lot...and whatever perplexes me I post here hoping you'd help me figure it out. This is my YA profile btw... http://answers.yahoo.com/my/my;_ylt=Aif ... Qt.;_ylv=3 ...

Anyway, I tried to google for the answer, as I always do, before looking to you. About 20% of my questions come from YA, the other 80% are self-occuring.

When it comes to sexual dimorphism among plants genotypes, it rather perplexed me. Does it help to generate more diversity of possible pollinators somehow?

By the way...look at this!

http://rationalia.com/forum/viewtopic.php?f=76&t=16199

[Dory]

Can herbivores digest meat?

[Dory]

Why can't insects grow huge?

[GenesForLife]

Why can't insects grow huge?

Abstract

Background

The correlations between Phanerozoic atmospheric oxygen fluctuations and insect body size suggest that higher oxygen levels facilitate the evolution of larger size in insects.
Methods and Principal Findings

Testing this hypothesis we selected Drosophila melanogaster for large size in three oxygen atmospheric partial pressures (aPO2). Fly body sizes increased by 15% during 11 generations of size selection in 21 and 40 kPa aPO2. However, in 10 kPa aPO2, sizes were strongly reduced. Beginning at the 12th generation, flies were returned to normoxia. All flies had similar, enlarged sizes relative to the starting populations, demonstrating that selection for large size had functionally equivalent genetic effects on size that were independent of aPO2.

Significance

Hypoxia provided a physical constraint on body size even in a tiny insect strongly selected for larger mass, supporting the hypothesis that Triassic hypoxia may have contributed to a reduction in insect size.

http://www.plosone.org/article/info%3Ad ... ne.0003876

ScienceDaily (Aug. 12, 2007) — Researchers at the U.S. Department of Energy's Argonne National Laboratory have cast new light on why the giant insects that lived millions of years ago disappeared.

In the late Paleozoic Era, with atmospheric oxygen levels reaching record highs, some insects evolved into giants. When oxygen levels returned to lower levels, the insect giants went extinct.

The basis of this gigantism is thought to lie in the insect respiratory system. In contrast to vertebrates, where blood transports oxygen from the lung to the cell, insects deliver oxygen directly through a network of blind-ending tracheal tubes. As insects get bigger, this type of oxygen transport becomes far less effective. But if the atmospheric oxygen levels increase, as they did in the late Paleozoic, then longer tracheal tubes can work. This would allow larger-sized insects—even giants—to evolve.

Recent research published in the journal Proceedings of the National Academy of Science helps confirm the hypothesis that the tracheal system actually limits how big insects can be. The research provides a specific explanation for what limits size in beetles: the constriction leading to the legs.

A collaborative team of researchers from Argonne's Advanced Photon Source (APS), Midwestern University and Arizona State University wanted to study how beetles' tracheal systems change as their body sizes increase. The team took advantage of richly detailed X-ray images they produced at the APS to examine the dimensions of tracheal tubes in four beetle species, ranging in body mass by a factor of 1,000.

Overall, they found that larger beetle species devote a disproportionately greater fraction of their body to tracheal tubes than do smaller species.

The team focused in particular on the passageways that lead from the body core to the head and to the legs. They reasoned that these orifices may be bottlenecks for tracheal tubes, limiting how much oxygen can be delivered to the extremities.

“We were surprised to find that the effect is most pronounced in the orifices leading to the legs, where more and more of the space is taken up by tracheal tubes in larger species,” said Alex Kaiser, biologist at Midwestern University.

They then examined the tracheal measurements of the four species to see if they could predict the largest size of currently living beetles. The head data predicted an unrealistically large, foot-long beetle. In contrast, the leg data predicted a beetle that nicely matches the size of the largest living beetle, Titaneus giganteus .

“This study is a first step toward understanding what controls body size in insects. It's the legs that count in the beetles studied here, but what matters for the other hundreds of thousands of beetle species and millions of insect species overall is still an open question,” said Jake Socha, Argonne biologist.

Funding for this work was supported by the National Science Foundation. Use of the APS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

http://www.sciencedaily.com/releases/20 ... 194908.htm

[GenesForLife]

Re: The pinecones...

One must note that microspores (or male gametes) do not need to contain extra sources of nutrition for instance whereas megaspores do, as these, after fertilization, contain the zygote and thus need to nourish the zygote, in the range of possible pinecone configurations, the most evolutionarily selectable one would be minimizing the resources needed to produce male gametes while maximizing nutrient availability to the zygote. This would also explain the dimorphism between ovaries and antheridia in gymnosperms, and eggs and sperm cells in metazoans.



PS One must also note that the female cones contain ovules which receive microspores.

[Dory]

Re: The pinecones...

One must note that microspores (or male gametes) do not need to contain extra sources of nutrition for instance whereas megaspores do, as these, after fertilization, contain the zygote and thus need to nourish the zygote, in the range of possible pinecone configurations, the most evolutionarily selectable one would be minimizing the resources needed to produce male gametes while maximizing nutrient availability to the zygote. This would also explain the dimorphism between ovaries and antheridia in gymnosperms, and eggs and sperm cells in metazoans.

First sentence is all you needed to say, the rest after this becomes self-explanatory (in my mind ) thanks!!!

[Dory]

By the way...do you have the names of those giant Paleozoic insects? I'd like to see some artist renditions

Oh and this should be a simple one

Can herbivores digest meat?

[GenesForLife]

Can herbivores digest meat?

Digestion shouldn't be a problem, given that the basic biomolecular constituents of meat aren't very different from plant material, except for relative concentrations.

[GenesForLife]

try Meganeura, a giant dragonfly.