To my knowledge plants do not have an uncontrolled growth disease similar to cancer. Is the function by which they avoid uncontrolled growth related to their cell wall and preventing damage to DNA/RNA? Is their telomerase special in some way in that it does not indefinitely replicate?
Plants do have uncontrolled tumorous growth. Though in almost all known cases, it is pathogen induced; such as in the case of the bacterium- Agrobacterium tumefaciens. Viruses can also induce plant tumors. Theoretically, the cell wall will pose a mechanical barrier to cell division. Also, cell wall synthesis is an extra biochemical step during cell division. Surely, the presence of a cell wall will disallow any metastasis if it might occur. There is an old article which says that cell wall structure differs between the normal plant tissue and the crown galls (tumor). However, this is with respect to Agrobacterium adsorption sites.
I am not aware of any natural plant tumor or the role of telomerase in plant tumorigenesis. However, there is one paper that says that telomerase dysfunction leads to disorganized growth.
Kefir: a powerful probiotics with anticancer properties
Probiotics and fermented milk products have attracted the attention of scientists from various fields, such as health care, industry and pharmacy. In recent years, reports have shown that dietary probiotics such as kefir have a great potential for cancer prevention and treatment. Kefir is fermented milk with Caucasian and Tibet origin, made from the incubation of kefir grains with raw milk or water. Kefir grains are a mixture of yeast and bacteria, living in a symbiotic association. Antibacterial, antifungal, anti-allergic and anti-inflammatory effects are some of the health beneficial properties of kefir grains. Furthermore, it is suggested that some of the bioactive compounds of kefir such as polysaccharides and peptides have great potential for inhibition of proliferation and induction of apoptosis in tumor cells. Many studies revealed that kefir acts on different cancers such as colorectal cancer, malignant T lymphocytes, breast cancer and lung carcinoma. In this review, we have focused on anticancer properties of kefir.
Normal Cell Division
There are several safeguards built into the cell division process to assure that cells do not divide unless they have completed the replication process correctly and that the environmental conditions in which the cells exist are favorable for cell division. Among others, there are systems to determine the following:
- Is the DNA fully replicated?
- Is the DNA damaged?
- Are there enough nutrients to support cell growth?
If these checks fail, normal cells will stop dividing until conditions are corrected. Cancer cells do not obey these rules and will continue to grow and divide.
Now that we have discussed the cell cycle, we will briefly address the ways in which cells are signaled to divide.
Most cells in the body are not actively dividing. They are performing their functions, such as the production of enzymes to digest food or helping to move the arms or legs. Only a small percentage of cells are actually going through the process just described.
Normal cell division requires constant signals (man standing on switch). When the signals are removed, the cells stop dividing.
Cells divide in response to external signals that 'tell' them to enter the cell cycle. These signals may take the form of estrogen or proteins such as platelet derived growth factor (PDGF). These signaling molecules, depicted as an X-shaped molecule in the animation below, bind to their target cells and send signals into the nucleus . The result is that the genes responsible for cell division are turned on and the cell divides. For example, a cut in the skin leads certain blood cells, platelets, to produce a growth factor (that causes the skin cells to reproduce and fill the wound. Cell division is a normal process that allows the replacement of dead cells.
Normal Cell Division II
What are the signals that make cells stop dividing?
A lack of positive external signals causes cells to stop dividing.
Cells are also able to sense their surroundings and respond to changes. For instance, if a cell senses that it is surrounded on all sides by other cells, it will stop dividing. In this way, cells will grow when needed but stop when their goal has been met. To revisit our wound example, the cells fill in the gap left by the wound but then they stop dividing when the gap has been sealed. Cancer cells do not exhibit contact inhibition. They grow even when they are surrounded by other cells causing a mass to form. The behavior of normal (top animation) and cancer cells (bottom animation) with regard to contact inhibition is depicted below.
The round containers in which the cells are depicted in the animations are called petri dishes. In the laboratory, cells are often grown in these, covered with a nutrient-rich liquid.
Most cells also seem to have a pre-programmed limit to the number of times that they can divide. Interestingly, the limit seems to be based, in part, on the cell's ability to maintain the integrity of its DNA. An enzyme , telomerase , is responsible for upkeep of the ends of the chromosomes. In adults, most of our cells don't utilize telomerase so they eventually die. In cancer cells, telomerase is often active and allows the cells to continue to divide indefinitely. For more information on telomerase, see the Cancer Genes section
The 10 commandments of cancer prevention
About one of every three Americans will develop some form of malignancy during his or her lifetime. Despite these grim statistics, doctors have made great progress in understanding the biology of cancer cells, and they have already been able to improve the diagnosis and treatment of cancer.
But instead of just waiting for new breakthroughs, you can do a lot to protect yourself right now. Screening tests can help detect malignancies in their earliest stages, but you should always be alert for symptoms of the disease. The American Cancer Society developed this simple reminder years ago:
- C: Change in bowel or bladder habits
- A: A sore that does not heal
- U: Unusual bleeding or discharge
- T: Thickening or lump in the breast or elsewhere
- I: Indigestion or difficulty in swallowing
- O: Obvious change in a wart or mole
- N: Nagging cough or hoarseness
It's a rough guide at best. The vast majority of such symptoms are caused by nonmalignant disorders, and cancers can produce symptoms that don't show up on the list, such as unexplained weight loss or fatigue. But it is a useful reminder to listen to your body and report sounds of distress to your doctor.
Early diagnosis is important, but can you go one better? Can you reduce your risk of getting cancer in the first place? It sounds too good to be true, but it's not. Scientists at the Harvard School of Public Health estimate that up to 75% of American cancer deaths can be prevented. The 10 commandments of cancer prevention are:
1. Avoid tobacco in all its forms, including exposure to secondhand smoke.You don't have to be an international scientist to understand how you can try to protect yourself and your family.
2. Eat properly. Reduce your consumption of saturated fat and red meat, which may increase the risk of colon cancer and a more aggressive form of prostate cancer. Increase your consumption of fruits, vegetables, and whole grains.
3. Exercise regularly. Physical activity has been linked to a reduced risk of colon cancer. Exercise also appears to reduce a woman's risk of breast and possibly reproductive cancers. Exercise will help protect you even if you don't lose weight.
4. Stay lean. Obesity increases the risk of many forms of cancer. Calories count if you need to slim down, take in fewer calories and burn more with exercise.
5. If you choose to drink, limit yourself to an average of one drink a day. Excess alcohol increases the risk of cancers of the mouth, larynx (voice box), esophagus (food pipe), liver, and colon it also increases a woman's risk of breast cancer. Smoking further increases the risk of many alcohol-induced malignancies.
6. Avoid unnecessary exposure to radiation. Get medical imaging studies only when you need them. Check your home for residential radon, which increases the risk of lung cancer. Protect yourself from ultraviolet radiation in sunlight, which increases the risk of melanomas and other skin cancers. But don't worry about electromagnetic radiation from high-voltage power lines or radiofrequency radiation from microwaves and cell phones. They do not cause cancer.
7. Avoid exposure to industrial and environmental toxins such as asbestos fibers, benzene, aromatic amines, and polychlorinated biphenyls (PCBs).
8. Avoid infections that contribute to cancer, including hepatitis viruses, HIV, and the human papillomavirus. Many are transmitted sexually or through contaminated needles.
9. Make quality sleep a priority. Admittedly, the evidence linking sleep to cancer is not strong. But poor and insufficient sleep increases is associated with weight gain, which is a cancer risk factor.
10. Get enough vitamin D. Many experts now recommend 800 to 1,000 IU a day, a goal that's nearly impossible to attain without taking a supplement. Although protection is far from proven, evidence suggests that vitamin D may help reduce the risk of prostate cancer, colon cancer, and other malignancies. But don't count on other supplements.
Stem cells and cancer
Some day, stem cells will be enlisted to help repair or replace damaged tissues and organs. They will rescue us from diseases for which drugs can only treat the symptoms. But they may have another role in our lives, one that is not so beneficial. They may in fact be the source of some, and possibly most cancers. Lurking somewhere within every tumor, some say, are a few stem cells that have lost their genetic marbles, so to speak - continuously supplying a malignant mass with cancerous cells.
Stem cells are key to our normal development and health from conception through adulthood. Embryonic stem cells produce the progenitors and patterns that determine how our organs, muscles, sinews, and skeletons are formed and how they are arranged in the body. After their work is done, they leave behind a guardian population of stem cells that repair each tissue as the need arises. When the stem cell divides into two, it creates one progenitor and renews itself. The progenitor continues its path of differentiation into mature, specialized cells, while the new stem cell waits for the next round when it is called upon to replenish tissue.
Stem cells survive much longer than ordinary cells, increasing the chance that they might accumulate genetic mutations. It might take only a few mutations for one cell to lose control over its self-renewal and growth and become the source of cancer.
The idea that the remnants of our embryonic past could lead to our demise through cancer is actually a longstanding hypothesis, tracing back to 1829. Throughout the mid-19th century, theories and observations accumulated that tumors were linked to embryonal tissue growth, culminating in a comprehensive “embryonal rest” theory put forward by Julius Cohnheim in 1875. The theory stated that tumors may arise from embryonic cells left over from development, and that lie dormant until activated to become cancerous.
Today’s theories about the involvement of stem cells in cancer are really an update of the embryonal rest theory, only now we know more precisely which types of cells are involved. This advance in knowledge, more than 150 years after the theory was first proposed, came about because we now know how to identify stem cells within tumors by the protein markers on their surface.
Searching for these markers, John Dick and colleagues at the University of Toronto confirmed in 1997 that certain types of leukemia originated from a subpopulation of stem cells. In 2003, Michael Clarke of the University of Michigan and now at Stanford, found cancer stem cells in breast tumors and demonstrated that most other cells in the tumor were incapable of seeding growth on their own. Others followed with similar discoveries in brain cancer, colon cancer, bone cancer and melanoma.
If tumors originate from just a few errant stem cells, it might explain why many treatments that reduce tumor mass fail to cure patients of cancer. Generally, these treatments target fast growing cells, which might leave the slow cycling stem cells untouched. Because they may be relatively protected from current treatment strategies, cancer stem cells are thought to be responsible for resistance to chemotherapy and the recurrence of disease.
A rationale for a new treatment strategy is emerging that specifically targets the cancer stem cells, which may only be a very small percentage of the total tumor mass. In combination with current treatments, however, these new treatments may lead to a more complete and durable response. A recent study completed by Markus Frank, Assistant Professor at Harvard Medical School, and Associate Faculty member of HSCI, identified a class of stem cells that initiate melanomas (skin cancer) in an animal model, and identified an antibody that slowed tumor growth by specifically targeting these stem cells. It was a first-time demonstration of this new therapeutic strategy.
The chance of the chemotherapy curing your cancer depends on the type of cancer you have.
- With some types of cancer, most people are cured by chemotherapy
- With other types of cancer, fewer people are completely cured
Examples of cancers where chemotherapy works very well are testicular cancer and Hodgkin lymphoma.
With some cancers, chemotherapy can't cure the cancer on its own. But it can help in combination with other types of treatment.
For example, many people with breast or bowel cancer have chemotherapy after surgery to help lower the risk of the cancer coming back.
With some cancers, if a cure is unlikely, your doctor may still suggest chemotherapy to:
- shrink the cancer
- relieve your symptoms
- give you a longer life by controlling the cancer or putting it into remission
Cell Wall Structure
Plant Cell Walls
The main component of the plant cell wall is cellulose, a carbohydrate that forms long fibers and gives the cell wall its rigidity. Cellulose fibers group together to form bundles called microfibrils. Other important carbohydrates include hemicellulose, pectin, and liginin. These carbohydrates form a network along with structural proteins to form the cell wall. Plant cells that are in the process of growing have primary cell walls, which are thin. Once the cells are fully grown, they develop secondary cell walls. The secondary cell wall is a thick layer that is formed on the inside of the primary cell wall. This layer is what is usually meant when referring to a plant’s cell wall. There is also another layer in between plant cells called the middle lamella it is pectin-rich and helps plant cells stick together.
The cell walls of plant cells help them maintain turgor pressure, which is the pressure of the cell membrane pressing against the cell wall. Ideally, plants cells should have lots of water within them, leading to high turgidity. Whereas a cell without a cell wall, such as an animal cell, can swell and burst of too much water diffuses into it, plants need to be in hypotonic solutions (more water inside than outside, leading to lots of water entering the cell) to maintain turgor pressure and their structural shape. The cell wall efficiently holds water in so that the cell does not burst. When turgor pressure is lost, a plant will begin to wilt. Turgor pressure is what gives plant cells their characteristic square shape the cells are full of water, so they fill up the space available and press against each other.
This diagram of a plant cell depicts the cell wall in green, surrounding the contents of the cell.
Algae Cell Walls
Algae are a diverse group, and the diversity in their cell walls reflects this. Some algae, such as green algae, have cell walls that are similar in structure to those of plants. Other algae, such as brown algae and red algae, have cellulose along with other polysaccharides or fibrils. Diatoms have cell walls that are made from silicic acid. Other important molecules in algal cell walls include mannans, xylans, and alginic acid.
Fungi Cell Walls
Bacteria and Archaea Cell Walls
The cell walls of bacteria usually contain the polysaccharide peptidoglycan, which is porous and lets small molecules through. Together, the cell membrane and cell wall are referred to as the cell envelope. The cell wall is an essential part of survival for many bacteria. It provides mechanical structure to bacteria, which are single-celled, and it also protects them from internal turgor pressure. Bacteria have higher concentration of molecules such as proteins within themselves as compared to their environment, so the cell wall stops water from rushing into the cell. Differences in cell wall thickness also make Gram staining possible. Gram staining is used for the general identification of bacteria bacteria with thick cell walls are gram-positive, while bacteria with thinner cell walls are gram-negative.
While archaea are similar in many ways to bacteria, hardly any archaeal walls contain peptidoglycan. There are several different types of cell walls in archaea. Some are composed of pseudopeptidoglycan, some have polysaccharides, some have glycoproteins, and others have surface-layer proteins (called an S-layer, which can also be found in bacteria).
How Cancer Works
Cancerous transformation results from changes of the DNA and the genes that control the cell cycle. Two types of genes normally control the cell cycle: proto-oncogenes, which start cell division and tumor-suppressor genes which turn off cell division. These two genes work together, one turning on cell division when the body needs to repair or replace tissue, and the other turning off cell division when the repairs have been made. If the proto-oncogenes become mutated, they can become oncogenes, genes that lead to uncontrolled cell division. Mutations in the tumor-suppressor genes result in the cell not having the ability to turn off cell division. Oncology is a branch of medicine that deals specifically with cancer.
MABs work by recognising and finding specific proteins on cancer cells.
Each MAB recognises one particular protein. So different MABs have to be made to target different types of cancer. Depending on the protein they are targeting, they work in different ways to kill the cancer cell. Or to stop it from growing.
Many different MABs are already available to treat cancer. Some are licensed to treat a particular type of cancer. And others can be effective against several types of cancer. Some newer types are still in clinical trials.
Ask your doctor or specialist nurse if MABs are used to treat your type of cancer and if they are suitable for you.
Critical Thinking Questions
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