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How does an amoeba move?

How does an amoeba move?


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Simple question. It forms a pseudopod, and then flows in to it. But how does it move its material to form a pseudopod? And even so, if it is floating in water, what is it pushing against so that part of it holds still and part can move forward? It would be like trying to move while wearing ice skates by pushing your arms forward in the air: no net force is transferred.


It has a cytoskeleton, a network of fibers stretched across the cell which it can shorten and expand (by adding or subtracting actin monomers which build them) in a coordinated manner to more-less arbitrary change shape.

According to this paper, on surfaces they generally can adhere to it using membrane protein structures, thus the locomotion occurs due to friction.

To swim, they generate bumps near the front end of the cell and move them towards the back, similarly to how a swimmer uses hands.


Amoeba

An amoeba is a highly motile eukaryotic, unicellular organism. Typically belonging to the kingdom protozoa, it moves in an “amoeboid” fashion. As such, microbiologists often use the term “amoeboid”, to refer to a specific type of movement and amoebae interchangeably. Interestingly, amoebae are not a distinct taxonomic group and are, instead, characterized based on their “amoeboid” movement rather than distinct morphological characteristics. Moreover, even members of the same species can appear dissimilar. Amebae species can be found in all major eukaryotic lineages, including fungi, algae, and even animals.

Amoebae contain an endoplasm that is granular in nature. This granular endoplasm contains the nucleus and various engulfed food vacuoles. In addition, amoebae are eukaryotic by definition and possess a unique nucleus that contains a central karyosome with a thin layer of beaded chromatin coating the inner nuclear membrane however, unlike many eukaryotes, amoebae are anaerobic. Thus, amoebae contain no mitochondria and generate ATP exclusively via anaerobic means.

Amoebas can be classified as free-living and parasitic. Parasitic amoebas are ubiquitous and often parasitize higher vertebrates and invertebrates alike. Only a limited number of amoeba species are capable of infecting humans, and typically invade the intestine. Specifically, only Entamoebahistolytica represents a true human pathogen, which infects the gastrointestinal tract. A second gut pathogen, Dientamoeba fragilis, is commonly mistaken as an amoeba owing to its similar morphology under a light microscope. Indeed, D. fragilis was originally misclassified as an amoeba however, modern methods have identified it as a nonflagellate trichomonad parasite. Interestingly, some free-living amoebas can cause opportunistic infections in humans, leading to eye infections, as well as various neurological, and cutaneous (skin) infections.


Contents

Sol-gel theory Edit

The protoplasm of an amoeba is made up of an outer layer termed the ectoplasm which surrounds an inner portion called the endoplasm. The ectoplasm consists of a gelatinous semisolid called plasma gel whereas the endoplasm is made up of a less viscous fluid called plasma sol. The ectoplasm owes its highly viscous state, in part, to the cross-linking actomyosin complex. Locomotion of an amoeba is thought to occur due to the sol-gel conversion of the protoplasm within its cell. 'Sol-gel conversion describes the contraction and relaxation events which are enforced by osmotic pressure and other ionic charges.' [4]

For example, when an amoeba moves, it extends a gelatinous, cytosolic pseudopodium, which then results in the more fluid cytosol (plasma sol) flowing after the gelatinous portion (plasma gel) where it congeals at the end of the pseudopodium. This results in the extension of this appendage. On the opposite (posterior) end of the cell, plasma gel is then converted to plasma sol and streamed toward the advancing pseudopodium. As long as the cell has a way to grapple the substratum, repetition of this process guides the cell forward. Inside the amoeba, there are proteins that can be activated to convert the gel into the more liquid sol state.

Cytoplasm consist largely of actin and actin is regulated by actin binding proteins. Actin binding proteins are in turn regulated by calcium ions hence, calcium ions are very important in the sol-gel conversion process. [1] [4]

Amoeboid movement modalities Edit

Actin-driven motility Edit

Based on some mathematical models, recent studies hypothesize a novel biological model for collective biomechanical and molecular mechanisms of cellular motion. [5] It is proposed that microdomains weave the texture of cytoskeleton and their interactions mark the location for formation of new adhesion sites. According to this model, microdomain signaling dynamics organize the cytoskeleton and its interaction with the substratum. As microdomains trigger and maintain active polymerization of actin filaments, their propagation and zigzagging motion on the membrane generate a highly interlinked network of curved or linear filaments oriented at a wide spectrum of angles to the cell boundary. It has also been proposed that microdomain interaction marks the formation of new focal adhesion sites at the cell periphery. The interaction of myosin with the actin network then generates membrane retraction/ruffling, retrograde flow, and contractile forces for forward motion. Finally, continuous application of stress on the old focal adhesion sites could result in the calcium-induced activation of calpain, and consequently the detachment of focal adhesions which completes the cycle.

In addition to actin polymerization, microtubules may also play an important role in cell migration where the formation of lamellipodia is involved. One experiment showed that although microtubules are not required for actin polymerization to create lamellipodial extensions, they are needed in order to afford cellular movement. [6]

Bleb-driven motility Edit

Another such proposed mechanism, the 'bleb-driven amoeboid locomotion' mechanism, suggests that the cell cortex actomyosin contracts to increase hydrostatic pressure inside the cell. Blebbing occurs in amoeboid cells when there is a roughly spherical protrusion in the cell membrane characterized by detachment from the actomyosin cortex. This mode of amoeboid movement requires that myosin II play a role in generating the hydrostatic pressure that causes the bleb to extend. [7] This is different from actin-driven locomotion where the protrusion created is by the actin polymerizing while remaining attached to the actomyosin cortex and physically pushing against the cell's barrier. During the bleb-driven amoeboid movement, the cytoplasmic sol-gel state is regulated. [1]

Blebbing can also be a sign of when a cell is undergoing apoptosis. [8]

It has also been observed that the blebs formed by motile cells undergo a roughly uniform life cycle that lasts approximately one minute. This includes a phase involving the initial outward expansion where the membrane breaks away from the membranous cytoskeleton. This is then followed by a short static phase where the hydrostatic pressure that has built up is just enough to maintain the size of the bleb. Following this is the last phase characterized by the bleb slowly retracting and the membrane being reintroduced to the cytoskeleton infrastructure. [9]

Cells may undergo fast transitions between blebbing and lamellipodium-based motility as a means of migration. However, the rate at which these transitions are made is still unknown. Tumor cells may also exhibit rapid transitions between amoeboid motility and mesenchymal motility, another form of cellular movement. [10]

Related movement mechanisms Edit

Dictyostelium cells and neutrophils can also swim, using a similar mechanism as for crawling. [11] [12]

Another unicellular form of movement shown in Euglena is known as metaboly. The basis of sol gel theory is interconversion of sol and gel.


Amoeba Movement

Amoeba propels itself by changing the structure of its body. We have explained the process in a way that would be easy for you to understand. Keep reading.

Amoeba propels itself by changing the structure of its body. We have explained the process in a way that would be easy for you to understand. Keep reading…

The scientific name of the most commonly found Amoeba is Amoeba proteus. It is interesting to know how an amoeba moves itself because the process is completely different from normal locomotion process of other living beings. An amoeba propels itself by changing the structure of its body. Basically it’s the cytoplasm and its variation in composition that aid in locomotion of the organism. Amoeba also extends the sides of its body to give rise to special structures known as pseudopodia, which enable it to “drag” itself.

An Overview of Movement of Amoeba

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The typical type of movement that an Amoeba exhibits is also called “amoeba-like movement”. The entire process is dependent on its anatomy and is based on a scientific theory, known as Sol-Gel theory. You first need to study the Sol-Gel theory in order to understand its movement.

Explaining The Sol-Gel Transition
The cytoplasm present inside the cell is capable of changing into different forms viz. from fluid to solid and vice versa. When the cytoplasm is in fluid state, it is known as plasmasol and when in solid or gel like state, is called the plasmagel. The interchange of these two states, i.e. from plasmasol to plasmagel is known as Sol-Gel theory, which is responsible for movement of amoeba.

Amoeba is capable of propelling itself only when its cytoplasm is in fluid state. First the amoeba attaches itself to a substrate. In the advancing end of its body, an ectoplasm is formed. Immediately the plasmasol flows through the center of the body towards the advancing end. Movement takes place when plasmasol flows. The plasmasol then gets converted to plasmagel by losing water. Locomotion stops at this stage as the cytoplasm becomes solid. This interchange of sol to gel is known as the sol-gel theory. Now, when the amoeba needs to propel itself once again, the gel transforms itself to sol by obtaining water from its uroid end. The process of formation of sol and gel is known as solation and gelation, respectively.

Formation of Pseudopodium
An amoeba forms protuberances from its body. These tentacles like extended structures, known as pseudopodium not only aid in locomotion but also helps in capturing preys. The number of pseudopodia they form ranges from one to a dozen. When the plasmasol flows towards the advancing end, the pseudopodium also extends and the amoeba drags itself. The pseudopodium is also connoted as false feet and it can develop from any part of the body. It grows in size and engulfs its prey by a technique known as phagocytosis. They shrink when phagocytosis is over. This way formation of pseudopodium and sol-gel transition enable it to move.

Interesting Facts about Amoeba

  • Amoeba belongs to the domain Eukaryota and kingdom Protista. It is classified under the phylum Plasmodroma and order Amoebida.
  • Amoeba is uninucleated, unicellular species. While a few species are too small to be seen with naked eyes, rest can be seen easily.
  • They are either freshwater or marine species. The parasitic protozoa is heterotrophic in nature and ingest food by the mechanism of phagocytosis.
  • They have porous body and thereby respire by passive diffusion. Oxygen diffuses in and carbon dioxide diffuses out from the pores present in its body.
  • The unicellular organism can maintain homeostatic regulation by the adaptive mechanism of osmoregulation. The contractile vacuoles present inside their body maintain osmotic balance (they store excess water and diffuse it through the pores, preventing its bursting in a hypotonic environment).
  • Amoeba also forms “blobs” to capture preys. When they sense their food or organisms on which they can prey upon, they quickly form different shapeless structures to engulf them. Thus, they are capable of detecting sense of stimuli and respond to the changes accordingly.

I hope you have been sufficed with the information you have been looking for regarding movement of amoeba from the content of this article. Despite being so tiny, it performs everything aptly. However, till date substantial research is going on to decipher other characteristic traits and mechanisms of amoeba.

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Reproduction and the spore state

Reproduction is almost always asexual, generally by by binary fission, though sometimes by multiple fission of the nucleus. During droughts or severe cold, amoeba withdraws all pseudopodia and secretes a tough coat or cyst. The cyst with its contents is called a spore. Each spore is very light and may be blown by the wind to new surroundings. Inside the cyst, the original animal divides to form numerous smaller individuals called amoebulae. In favorable conditions the cyst breaks down and releases them.


Parasitic Amoebas

Some amoeba are parasitic and cause serious illness and even death in humans. Entamoeba histolyticacause amebiasis, a condition resulting in diarrhea and stomach pain. These microbes also cause amebic dysentery, a severe form of amebiasis. Entamoeba histolytica travel through the digestive system and inhabit the large intestines. In rare cases, they can enter the bloodstream and infect the liver or brain.

Another type of amoeba, Naegleria fowleri, causes the brain disease amoebic meningoencephalitis. Also known as brain-eating amoeba, these organisms typically inhabit warm lakes, ponds, soil, and untreated pools. If N. fowleri enter the body though the nose, they can travel to the frontal lobe of the brain and cause a serious infection. The microbes feed on brain matter by releasing enzymes that dissolve brain tissue. N. fowleri infection in humans is rare but most often fatal.

Acanthamoeba cause the disease Acanthamoeba keratitis. This disease results from an infection of the cornea of the eye. Acanthamoeba keratitis can cause eye pain, vision problems, and may result in blindness if left untreated. Individuals who wear contact lenses most often experience this type of infection. Contact lenses can become contaminated with Acanthamoeba if they are not properly disinfected and stored, or if worn while showering or swimming. To reduce the risk of developing Acanthamoeba keratitis, the CDC recommends that you properly wash and dry your hands before handling contact lenses, clean or replace lenses when needed, and store lenses in a sterile solution.


The Cytoskeleton and Cell Movement

The cytoskeleton is the cytoplasmic structure that supports the cell, maintains its shape and holds or moves cell organelles. It is made of an extensive network of fibers dispersed in the cytoplasm and anchored in the plasma membrane. Its components are microtubules, microfilaments and intermediate filaments.

More Bite-Sized Q&As Below

2. What substances are microtubules made of? What structures and cellular processes are microtubules involved in?

Microtubules are made of consecutive dimers of the protein tubulin (each dimer contains an alpha and a beta tubulin). Microtubules play a role in cell division they are components of cilia and flagella and they also form centrioles.

3. What substances are microfilaments made of? What properties of these elements give motility to cells?

Microfilaments are made of actin (a protein). The contractile bond between actin and myosin as well as other cytoplasmic proteins gives microfilaments the ability to promote cell movement.

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Cell Movement

4. What are cell movements? What causes these movements?

Cell movements are movements carried out by cell structures, such as the movements of cilia and flagella, pseudopod movements (in amoeba, macrophages, etc.), the cyclosis of the cytoplasm and sarcomere contractions in muscle cells.

Cell movements can be created by the action of the cytoskeleton, by differences in viscosity between cytoplasmic regions and by intracellular contraction systems.

5. What are cilia and flagella? How do these structures produce movements? What are some examples of ciliated and flagellated cells in humans?

Cilia and flagella are structures found in some prokaryotes as well in some eukaryotic cells. They play a role in the defense, nutrition and movement roles of cells. In the eukaryotic cells of protists and animals, they originate from centrioles that migrate towards the plasma membrane and differentiate into structures projected outside the cell. Each cilium or flagellum is made of nine peripheral pairs of microtubules and one central pair all covered by the membrane. (In bacteria, flagella are made of a protein called flagellin bacteria can also contain fimbria made of pilin.)

At the base of each cilium or flagellum in the plasma membrane, there are proteins that work as molecular motors, providing movement for these structures by consuming energy. Due to this energy consumption, ciliated or flagellated eukaryotic cells have a large number of mitochondria.

In humans, ciliated cells can be found, for example, in the bronchial and tracheal epithelium. In these tissues, the cilia have the defensive function of sweeping away mucous and foreign substances that enter the airway. Sperm cells are a typical example of flagellated cells. Their flagellum is responsible for the propulsion necessary to move them towards the ovule.

6. How does amoeboid movement occur? What are examples of organisms and cells that use this type of movement?

Amoeboid movements are created by cytoplasmic movements and plasma membrane projections called pseudopods. Their formation actively changes the external shape of some portions of the cell surface, making it move along a substratum. Pseudopods are created from differences in viscosity between neighboring regions of the cytoplasm near the plasma membrane and from the contractile action of microfilaments.

Amoeboid movements occur, for example, in amoebas (a protozoan), organisms that use their movement to find food. Leukocytes, which are cells of the immune system, when attracted by chemical substances (immune mediators), use amoeboid movements to exit capillaries in areas of tissue damage to carry out their role in the inflammatory process.

7. What are some examples of movement produced by the contraction of the sarcomeres of muscle cells?

The holding of a cup of coffee, the peristaltic movements of the bowels, heartbeat and even a smile are examples of movement created by the contraction of the sarcomeres of muscle cells. This contraction is a type of cell movement.

8. What is cyclosis?

Cyclosis is a type of internal cell movement in which a directional flow of circulating material is created and maintained in the cytoplasm through the action of microfilaments. Cyclosis is more easily observed in plant cells.

Now that you have finished studying Cytoskeleton and Cell Movement, these are your options:


What Is the Function of Amoeba?

An amoeba functions as a part of the food web as a consumer and scavenger. This organism feeds on dead matter as well as other small organisms such as algae and protozoans. The amoeba in turn provides food for water fleas and mussels.

The amoeba is a single-celled organism called a protozoan that usually lives in water or inside other organisms as a parasite. This organism doesn't have a rigid shape, but it is made of a flexible material that changes shape as needed. An amoeba is made of protoplasm, a viscous, clear material with a cell membrane separating the ectoplasm and the endoplasm, or the outer and inner parts of the cell. The endoplasm contains the nucleus of the cell.

While most amoebas are too small to see with the naked eye, some of the common and giant species grow large enough to see without the aid of a microscope. While most species are harmless, including the parasitic ones, a few can cause real damage. The Entamoeba histolytica causes fatal dysentery in living organisms. The Naegleria fowleri is a deadly amoeba that finds its way to the brain and uses it as a food source. It is found in warm or hot water such as lakes, untreated swimming pools, hot springs and aquariums.


Amoeba

An amoeba is a one-celled creature that is among the simplest of all living organisms. Most amoebas are so small that they can only be seen though a microscope. There they look like tiny blobs of colorless jelly.

Amoebas are found in fresh and salt water. They also live in the moist body parts of other animals and in moist soil. At least six types of amoebas are found in human beings.

An amoeba has few parts. It has a thin covering called a membrane. Inside is a nucleus, food vacuoles, and a contractile vacuole. The food vacuoles digest food. The contractile vacuole gets rid of extra water.

Amoebas move by changing their shape. First, an amoeba extends a part of its jellylike body outward, like a stubby finger projecting out of a closed fist. This projection is called a pseudopod, or false foot. The amoeba then slowly pours the main part of its body into the pseudopod, which makes the pseudopod grow bigger and bigger. Eventually the pseudopod gets so big that it becomes the whole body. New pseudopods form as old ones disappear.

For food, amoebas depend mainly on plants and other one-celled animals. Amoebas use their pseudopods as mouths. The pseudopods reach out to surround the food and flow over it.

To reproduce, the nucleus of the amoeba simply splits into two pieces. The two halves pull apart, and each half takes part of the cytoplasm. In this way, a single amoeba becomes two.


Comments

Linda Crampton (author) from British Columbia, Canada on September 24, 2015:

Thank you very much, Vellur. I appreciate your visit.

Nithya Venkat from Dubai on September 23, 2015:

An extensive and well-researched article about amoebas. Interesting and informative, took me back to my college days.

Linda Crampton (author) from British Columbia, Canada on June 30, 2013:

Thanks for the comment and the vote, DDE.

Devika Primić from Dubrovnik, Croatia on June 30, 2013:

Amoebas in Pond Water and the Human Body, a well thought of hub on this topic and I found it to be informative, voted up and interesting.

Linda Crampton (author) from British Columbia, Canada on June 07, 2013:

Thank you for the visit and the comment, mylindaelliot!

mylindaelliott from Louisiana on June 07, 2013:

I did not realize some of those diseases were caused by an organism that was an amoeba. This was such an interesting hub.

Linda Crampton (author) from British Columbia, Canada on June 06, 2013:

Thank you very much, Deb. I appreciate your comment!

Deb Hirt from Stillwater, OK on June 06, 2013:

I was fascinated with the amoeba during my school days, so this brought back a lot for me. A very good piece that was easy to understand, with a lot of good material to fill in the gaps.

Linda Crampton (author) from British Columbia, Canada on June 05, 2013:

Hi, drbj. Thank you for the comment. It is very interesting to watch amoebas! The spelling is confusing, though. I wish there weren&apost so many variations!

drbj and sherry from south Florida on June 05, 2013:

I could easily become addicted to microscopic amoeba watching, Alicia. Fascinating! I learned to spell the word as amoeba so now when I see the various spelling variations of the word, I believe those spellings are all wrong!

Linda Crampton (author) from British Columbia, Canada on June 05, 2013:

Thanks for the comment, Eddy. Amoebas are so interesting. Examining them under a microscope was one of the highlights of my school science classes, too!

Eiddwen from Wales on June 05, 2013:

This was so interesting Alicia I can remember learning all about amoebas in school but nothing since. Remembered a great deal and thanks for sharing.

Linda Crampton (author) from British Columbia, Canada on June 04, 2013:

Hi, Nell. Yes, the thought of amoebas invading the blood or organs is horrible! Thank you for the visit and the comment.

Nell Rose from England on June 04, 2013:

Fascinating hub, and reading about the brain one and the Amoebic Dysentery does give us a yuck factor! lol! seriously, this was interesting as I had never really known about them before, nell

Linda Crampton (author) from British Columbia, Canada on June 04, 2013:

Thank you very much for the comment, Peg. I&aposm sorry that your coworker died from meningitis. I&aposve read that in the early stage of the disease PAM can resemble bacterial meningitis.

Linda Crampton (author) from British Columbia, Canada on June 04, 2013:

Thank you very much for the comment, the vote and the share, Bill! There are devices that can attach a film camera to a microscope. Digital microscopes can send a microscope image to a computer. The photos and videos that can be obtained are often fascinating!

Peg Cole from Northeast of Dallas, Texas on June 04, 2013:

This is like a mini refresher course in Biology 101 which I took so many years ago. How fascinating all this stuff is to me now. Unfortunately, it wasn&apost way back then. Your videos are interesting and I learned a lot here.

A coworker of mine passed away after being diagnosed with meningitis of the brain. He had severe flu-like symptoms that got much worse. He passed within 5 days. I wonder if it was P.A.M.

Bill De Giulio from Massachusetts on June 04, 2013:

Hi Alicia. Fascinating video, especially watching the amoeba catch its prey. How do they film this stuff?

Very interesting Hub. Thanks again for the education. Voted up, shared, etc.

Linda Crampton (author) from British Columbia, Canada on June 04, 2013:

Thanks for the comment, Sue. I appreciate it. Luckily, there isn&apost a test!

Susan Bailey from South Yorkshire, UK on June 04, 2013:

Very interesting Alicia. I&aposm learning a lot but I hope you don&apost test me on my knowledge!

Linda Crampton (author) from British Columbia, Canada on June 04, 2013:

Thanks for the comment, Bill. Yes, a whole new world becomes visible under a microscope! It&aposs amazing what we miss with our unaided eyes.

Bill Holland from Olympia, WA on June 04, 2013:

Watching them through a microscope is fascinating and I recommend it for everyone. great information for this former science teacher.


Watch the video: 2020 Amoeba Reproduction: Cell Division (June 2022).


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