Flagella and cillia

[Greg Boyles]

In the case of phytoplankton, both these examples of nanomachinery give individual phytoplankton the ability to move purposely in a specific direction, i.e. to move towards the ocean surface by night and down to the ocean depths by day.

 

In the thread "how life begins" I saw and watched the series of youtube videos about abiogenesis and particularly the one about how the flagellum probably developed.

 

The flagelleum simply rotates and a kink towards the end allows it to provide thrust.

 

Question

 

How can a flagellum that simply rotates give the cell the ability to move in a specific direction?

 

With fish and worms etc there are various muscles associated with the propulsion structure that allows it to move in specific ways and therefore provide thrust in a specific direction. But there is apparently no such way to differentially move a flagellum.

[CaptainPanic]

How can a flagellum that simply rotates give the cell the ability to move in a specific direction?

With the risk of being wrong (I'm no expert), I propose an answer:

 

I do not think the flagellum gives the cell the ability to move in a specific direction. It just allows to to move somewhere else (which is already better than being stationary).

If single cell organisms deliberately move up and down in the ocean at all, I think they do it by slight changes in overall density (buoyancy).

I cannot provide any links, because I admit that this is just an educated guess instead of an answer.

 

A quick search btw suggests that the phytoplankton doesn't move up and down. It's zooplankton that moves up and down. Again, just a couple of Google hits that told me that... not years of study.

[Greg Boyles]

With the risk of being wrong (I'm no expert), I propose an answer:

 

I do not think the flagellum gives the cell the ability to move in a specific direction. It just allows to to move somewhere else (which is already better than being stationary).

If single cell organisms deliberately move up and down in the ocean at all, I think they do it by slight changes in overall density (buoyancy).

I cannot provide any links, because I admit that this is just an educated guess instead of an answer.

 

A quick search btw suggests that the phytoplankton doesn't move up and down. It's zooplankton that moves up and down. Again, just a couple of Google hits that told me that... not years of study.

 

Yes, that's right it was zooplankton rather than phytoplankton. Does zooplankton include single cells with flagella or simple multicellular animals with multiple flagella or cillia? If so same question.

[CharonY]

One think I have to mention first is that flagella is used as a term both for eukaryotic as well as for prokaryotic systems. However, while the functions are similar, structurally they are not related.

That being said, the best understood and common chemotactic orientation using flagella is the run-and-tumble mechanism. Essentially linear movements are broken up by random tumbles in which the organism reorients its path (randomly) and then starts moving again. The trick is that the frequency of the tumble is dependent on the taxis. I.e. in the case of positive taxis the tumble frequency is reduced while swimming towards the attractant, and increased, if moving away from it. This model for flagellar-mediated taxis has been derived from bacterial motility and elements are also found in zooplankton. But there are also other motility patterns indicating that more mechanism exists (depending on species) and likely include more mechanisms.

 

Note that zooplankton includes a wide array of organisms, independent on the presence of flagella per se. Basically any smallish animal drifting in water can be considered one, which includes e.g. metazoa in various developmental stages.

[Greg Boyles]

Note that zooplankton includes a wide array of organisms, independent on the presence of flagella per se. Basically any smallish animal drifting in water can be considered one, which includes e.g. metazoa in various developmental stages.

 

Yes I was aware of that which is why I asked if it included single cell organisms. Larvae probably have rundimentary muscles grouped around their appendages which allows them to move them differentially.

 

With flagellated single cells........how do they tumble differentially? That implies they have some sort of spoiler system on their surface (like an aircraft) that can differentially create drag. How? Or is that still subject to ongoing research?

[Essay]

With flagellated single cells........how do they tumble differentially? That implies they have some sort of spoiler system on their surface (like an aircraft) that can differentially create drag. How? Or is that still subject to ongoing research?

 

Even with unflagellated cells, chemiosmosis, or any differential in a chemical (nutrient or nutrient-associated) gradient [humus], can redirect or reorient a cell. Signal reception is often associated with mechanical or structural changes that then cause directed movement....

 

...if I understand the book I've been browsing this summer:

 

1. Bacterial growth and form

Author: Koch, Arthur L.

Published: 2001

Call Number: QR84.5 .K63 2001

Status: Checked Out

 

~

[CharonY]

With flagellated single cells........how do they tumble differentially? That implies they have some sort of spoiler system on their surface (like an aircraft) that can differentially create drag. How? Or is that still subject to ongoing research?

 

I am not sure what you mean with differentially. Do you mean how the frequency is controlled? The system is overall very simple but incredibly clever. To clarify, the tumble is induced by either stopping flagellar movement or by rotating it the other way round. The latter is the case in some bacteria and it results that the flagella (which in this case are organized in a bundle) become disorganized and induce a random tumbling of the cell. The tumbling can therefore be partially active (unorganized movement) or, depending on cell size and morphology be a combination of diffusion, momentum and liquid viscosity.

 

The trick is that the activity of the regulator that determines the movement of the flagellar motor is directly coupled to the concentration that the cell senses.

 

There are other types of movements, of course which utilize a number of mechanisms.

[Greg Boyles]

I am not sure what you mean with differentially. Do you mean how the frequency is controlled? The system is overall very simple but incredibly clever. To clarify, the tumble is induced by either stopping flagellar movement or by rotating it the other way round. The latter is the case in some bacteria and it results that the flagella (which in this case are organized in a bundle) become disorganized and induce a random tumbling of the cell. The tumbling can therefore be partially active (unorganized movement) or, depending on cell size and morphology be a combination of diffusion, momentum and liquid viscosity.

 

The trick is that the activity of the regulator that determines the movement of the flagellar motor is directly coupled to the concentration that the cell senses.

 

There are other types of movements, of course which utilize a number of mechanisms.

 

 

It seems to me that a flagellated cell is like a speed boat with a propellor but no rudder. I don't undertand how it can move in specific direction given differential chemoctactic signals from its surface.

 

Where is the equivalent of its rudder or teleost fish fins?

 

Or is it all down to pure chance? Some cells happen to tumble in or are defelcted in the right direction and some don't. But because there are always so many that the chances that some cells will end up in the right place and survive to reproduce is overwhelming?

 

Think about it in terms of spermatazoa finding their way up the fallopian tubes to meet the ovum.

Edited August 6, 2011 by Greg Boyles

[CharonY]

As I mentioned, the direction is coupled to the tumble frequency. If it is on the right track it tumbles less and moves towards it. If it deviates, tumble frequency increases and will continue to do so until they are on the right track and the tumble frequency gets reduced.

 

How they are oriented due to the tumble is by chance. But since the frequency is gradient dependent, the net movement will be towards the attractant. Essentially it is a random walk with a net movement towards the attractant (or away from a repellant).

 

So, no, it is not a pure chance event.

[Greg Boyles]

As I mentioned, the direction is coupled to the tumble frequency. If it is on the right track it tumbles less and moves towards it. If it deviates, tumble frequency increases and will continue to do so until they are on the right track and the tumble frequency gets reduced.

 

How they are oriented due to the tumble is by chance. But since the frequency is gradient dependent, the net movement will be towards the attractant. Essentially it is a random walk with a net movement towards the attractant (or away from a repellant).

 

So, no, it is not a pure chance event.

 

OK but what causes the tumbling? And what is the mechanism by which the rate of tumble can be varied in response to chemotactic signals?

 

This implies that there is some sort of spoiler system over the cell surface that is analagous to fish fins.

 

Or in the case of a speed boat with no rudder, it must be analagous to the passengers on one side of the boat dipping their legs in the water so that it creates differential drag that causes the boat to gradually turn in that direction.

 

Facinating pondering such questions and it sometimes makes me miss the scientific community and the pure discovery and problem solving that science involves. One thing that I have found myself particularly talented at in the landscaping, home rennovation, horticulture and weed control world is problem solving.

Edited August 7, 2011 by Greg Boyles