B2 - Cell Division And Growth (Y10 - Spring 1) Flashcards
🟠 Denfinitions of DNA, a Cell, a Gene, Chromosomes, and Nucleus
DNA - The Chemical from which chromosomes are made.
Cell - The basic building block of a living organism.
Gene - A small packet of information controlling a characteristic.
Chromosomes - Thread-like structures holding genes.
Nucleus - The part of a cell that contains genetic information.
🟠 What happens in the Cell Cycle and Mitosis
Body cells divide in a series of stages known as the cell cycle. Cell division in this cycle involves the process of mitosis, and it produces 2 identical cells. As a result, all your normal body cells have the same chromosomes and so the same genetic information. Cell division by mitosis produces additional cells needed for growth and development in multicellular organisms, and for the replacement of worn out damaged cells.
In asexual repeoduction, the cells of the offspring are produced by mitosis from the cells of their parent. This ks why they contain exactly the same genes as their parents with little or no genetic information.
The cell cycle can take anywhere between less than 24 hours, up until sereveral years, this depends on the age of the person, as for a foetus/baby or child this will be quick, but for an adult it will not. The time that this division takes can tell you how fast your mitosis is. (This means as mitosis slows down, the more you seem to age, as it takes longer for new cells to create.) Mitosis is especially improtant when producing new cells and for replaceing dead cells (such as hair folicles, skin, blood, and the lining of your digestive system)
🟠 The cell cycle in a healthy human roughly follows the pattern of:
Stage 1: Interphase
This is the longest stage in the cycle. The cells grow bigger, while they also increase in their size and mass, and carry out normal cell activities. Most importantly, they replicate their DNA to form two copies of each chromosome ready for cell division. They also increase the number of sub-cellular structures such as mitochondria, ribosomes, and chloroplasts ready for the cell to divide.
Stage 2: Mitosis
In this process, the chomosome line up in the middle of the cell, and then one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides. Now, you essentially have a cell in each half, and all but stage 3 needs to take place.
Stage 3: Cytokenesis
This is the stage during which the cytoplasm and the cell membranes also divide to for, two identical ‘daughter’ cells.
🟠 When does the Cell Cycle happen/take place
In some parts of an animal or plant, mitotic cell division carries on rapidly all the time. For example, you constantly lose cells from the skin’s surface and make new cells to replace them. In fact, about 300 million of your body cells die every minute, so cell division by mitosis is very important. In a child, mitotic divisions produce new cells gaster than the old ones die. As an adult, cell death and mitosis keep more or less in balance. When you get very old, mitosis slows down and you show the typical signs of ageing.
🟢 What happens in the Differentiation In Animal Cells
In the early development of animal and plant embryos, the cells are unspecialised. Each one of them (known as a stem cell) can become any type of cell that is needed.
In animals, many types of cells become specialised very early in life. By the time a human baby is born, most of its cells are specialided to carry out a particular job, such as nerve cells, skin cells, or muscle cells. They habe differentiated. Some of their genes habe been switched on and others have been switched off. As a result, different types of specialised cells have differnt sub-cellular structures to carry out specific functions.
Most specialised cells can divide by mitosis, but they can only form the same sort of cell. Muscle cells divide to produce more muscle cells, for example. Some differentiated cells, such as red blood cells and skinncells, cannot divide at all and so adult stem cells replace dead or damaged cells. Nerve cells do not divide omce they have differntiated amd they are not replaced by stem cells. As a result, when nerve cells are damaged they are not usually replaced.
In a matural animal, little or no growth takes place. Cell division is almost entirely resitricted to repair and replacement of damaged cells and each differentiated cell type divides only to mak more of the same cells.
🟢 What happens in the Differentiation In Plant Cells
In contrast to animal cells, most plant cells are able to differntiate all through their lives. Undifferntiated cells are formed at active regions of the stems and roots, known as the meristems. In these areas, mitosis takes plsce almost continuously. The cells then elongate and grow before they finally differentiate.
Plants kepp growing allthough their lives at these ‘growing points’. The plant cells produced do not differentiate until they sre in their final position in the plant. Even the , the differentiation is not permanent. You can mive a plsnt cell from one part pf a plant to another. Thee it can redifferentiate and become a completely diifere t type of cell. You csnnnot do that with animal cells.
🟢 How Plants are Cloned
Producing identical offspring is known as cloning. Huge numbers of identical plant clones can be produced from a tiny piece of leaf tissue. This is because, in the right conditions, a plant cell will become unspecialised and undergo mitosis many times. Each of these undifferntiated cell produce more cells by mitosis. Given different conditions, thede will then differentisted to form tissues such as xylem, phloem, photosynthetic cells, and root hair cells that are needed to form a tiny new plant. The new plant will be identical to the original parent. It is difficult to clome animals because, as you have seen, most animal cells differentiate permanently early in embryo development. The cells cannot change back. As a result, artificial animal clones van only be made by cloning embryos in some way, although, adult cells can be used to make an embryo.
🟠 Why Stem Cells Are Needed (How People Suffer Without)
An egg and sperm cell fuse to form a zygote, a single new cell. That cell divides and becomes a hollow ball of cells - the embryo. The inner cells of this ball are the embryonic stem cell that differntiate to form all of the specialised cells of your body. Even when you are an adult, some of your stem cells remain. An adult stem cell is an undifferentiated cell of an organism that can give rise to many more cells of the same type. Certain other types of cell can also arise from stem cells by differentiaton (your bone marrow is a good source of adult stem cells).
Scientists now think there may be a tiny number of stem cells in most of the different tissues in your body, including your blood, brain, muscle, and liver. Many of your differentiated cells can divide in order to replace themselves, however, some tissues can’t do this and stem cells can stay in these tissues for years, only needed if the cells are injured or affected by disease. Then they start dividing to replace the different types of damaged cell.
🟠 Why Stem Cells Are Needed (How People Suffer Without)
Many people suffer and even die because parts of their body stop working properly. For example, spinal injuries can cause paralysis because the spinal nerves cannot repair themselves. Also, people with type 1 diabetes have to inject themselves with insulin every day because soecialised cells in their pancreas do not work. Millions of people would benefit if we could replace damaged or diseased parts of the body.
🟠 How Were Stem Cell Discovered And Are Used Today
In 1998, there was a breakthrough, as teo scientists managed to culture human embryonic stem cells, which are capable for forming other types of cell. Scientists hope that embryonic stem cells can be encouraged to grow into almost any different type of cell needed in the body. Already, scientists have used nerve cells grown from embryonic stem cells to restore some movement to the legs of paralysed rats in 2010, the first trials testing the safety of injecting cells grown from embryonic stem cells into the spinal chords of paralysed human patients were carried out. The scientists and doctors hope it will not be long before they can use stem cells to help people who have been paralysed to walk again.
In 2014, doctors transplanted embryonic stem cells into the eyes of people going blind as a result of macular degeneration. It was a small study to check the safety of the technique but all of the patients found they could see better. Larger trials are now taking place. Scientists are also using different types of stem cells to try and grow cells that are sensitive to blood sugar levels and produce the hormone of insulin to help treat people with disbetes.
🟠 What can Stem Cells In Plants be used for
The stem cells from the plant meristems can be used to make clones of the mature parent plant very quickly and economically. This is importnat as it gives us a way of producing large numbers of rare plants reliably and safely. Plant cloning also gives us a way of producing large populations of identical plants for research. This is important as scientists can change variables and observe the effects on genetically identical individuals.
Cloning large numbers of identical plants from the stem cells in plant meristems is also widely used in horticulture peoducing large numbers of plants such as orchids for sale. In agriculture, it is used to produced large numbers of identicsl crop plants with special features, such as disease resistance. For example, every bannana you eat is produced by a cloned plant.
🟠 Risks ans Concrns sureounding Embryonic Stem Cells
Progress in developing therapies using embryonic stem cell has been relatively slow, difficult, expensive, and hard to control. However, it is easy to forget that scientists have only been working with them for around 20 years. The signals that control cell differentiation are still not completely understood. Not suprisingly it is proving difficult to persuade embryonic stem cells to differentiate into the type of cells needed to treat patients.
Embryonic stem cells divide and grow rapidly. This is partly why they are potentially useful but there is some concern that embyonic stem cells might cause cancer if they are used to treat people. This has sometimes been a problem when they have been used to treat mice and in early human treatment for autoimmune diseases.
There is a risk that adult stem cells might be infected with viruses, and si could transfer the infections to patients. If stem cells from and adult are used to treat another unrelated person, they may trigger an immune response. The patient may need to take immunisuppressant drugs to stop their body rejecting the new cells. Scientists hope embryonic stem cell will solve this problem. This body of a mother does not reject the embryo, so they hope that embryonic stem cells will not be rejected by the patient.
🟠 Ethical Dilemmas with Stem Cells and some Public Opinions
Many Embryonic stem cells come from aborted embryos. Other come from spare embryos from fertitly treatment, donated because they will not otherwise used. Some people question the use of a potential human being as a source of cells, even to cure others. Some people feel that, as the embryo cannot give permission, using it as a violation of its numan rights. The religious beliefs of other mean they cannot accept any interference with the proces of human reproduction.
Some people feel that a great deal of money and time is being wasted on stem cell research that would be better spent on research into other areas of medicine. Yet in spite of all these concerns, there is a lot of investment into stem cell reserch as many scientists and doctors are convinved stem cells have the potential to benefit many people.
🟠 Positive new Stem Cell Information coming out of New Research
Scientists have founds embryonic stem cells in the umbilical cord blood of newborn babies and even in the amniotic fluid that surrounds the fetus as it grows. Using these instead of cells from spare embryos may help to overcome some of the ethical concerns about their use.
Scientists are also finding ways of growing adult stem cell, although so far they have only managed to develop them into a limited range of cell types. Adult stem been used successfully to treat some forms of heart disease and to grow some new organs such as tracheas (windpipes).
The area of stem cell research known as theraputic cloning has much potential but is proving very difficult. It involves using cells from an adult to produce a cloned early embryo of themselves. This would provide a source of perfectly matched embryonic stem cells. In theory, organs for the original donor. The new organs would bot be rejected by the body because they have been made from the body’s own cells have the same genes.
Scientists habe discovered stem cells in some of the tubes that connect the liver and the pancreas to the small intestine. They hsve managed to make these cells turn into the special insulin-producing cells in the pancreas that sre so important for controlling blood sugar. These are the cells that are missing or destroyed in people with type 1 diabetes. Scientists have transplanged these modified stem cells into diabetic mice, which wokeed to control the blood sugar levels. The next stage is to work tkwards the same success in human.
Stem cell research in the UK is being carried out for the following possible therapies:
- Spinal cord after injuries
- Diabetes
- Heart after damage in a heart attack
- Eyesight in the blind
- Damaged bone cartilage
🟠 How can Stem Cells help Eyesight in the Blind
Stem cells can help blind people and help help cure the blindness altogether. The stem cells are though to be able to regrow any retinal cells that may remain in the eye, and therefore will help it regrow and regenerate, to allow the sight.
