B2 Flashcards
Cell division
What is a chromosome ?
- long, tightly packed string of DNA containing the entire genetic material of an organism
- found in pairs
[] 23 pairs in the whole human body
What is a gene ?
small section of DNA controlling (part of) the expression of a certain physical characteristic
How many chromosomes are found in a body cell vs a gamete ?
- body cell = 46
- gamete = 23
[] when one gamete fuses with another, they will make one (zygote) cell with the full 46 chromosomes
Why does the length of the cell cycle vary ?
- once puberty is over and the body is adult, the cell cycle in general in humans slows considerably
[] this is what causes aging
[] in childhood, the cell cycle is rather fast, in the foetal stage even faster, and in the embryonic stage it is rapid - also varies in length between the type of cells involved
Describe the first stage of the cell cycle
- stage 1: interphase
[] during this stage, the cell will grow and replicate all its DNA as well as its organelles
[] this is the longest stage by far, and the cell spends most time in this stage whilst also carrying out its normal functions - stage 2: mitosis
[] the cell prepares to be split, and pulls one complete set of DNA (splits the nucleus to do this) and organelles to opposite sides of the cell - stage 3: cytokinesis
[] the cytoplasm and cell membrane split
[] left with two identical daughter cells
Why is mitotic division of cells important to organisms ?
crucial to the growth, repair (of damaged tissue) and development of multicellular organisms
What is a stem cell ?
an undifferentiated cell that has the possibility of differentiating into any other type of specialised cell
What is the difference between embryonic stem cells and adult stem cells in animals ?
- embryonic stem cells
[] only produced when in the embryonic stage of development
[] can differentiate into ANY cell in an animal’s body, from nerve cells to skin cells etc. - adult stem cells
[] produced in the bone marrow
[] can only differentiate into a LIMITED RANGE of specialised cells, like red blood cells
[] exist to replenish other cells that cannot divide mitotically like most cells
How do stem cells differentiate ?
genes switch on or off in the cell, thus controlling the expression of characteristics once the cell develops and allowing it to take on specialised features
What is the difference between differentiation in animals and plants ?
-once animal cells are differentiate, THEY CANNOT RE-DIFFERENTIATE INTO DIFFERENT CELL TYPES
- plant cells are able to re-differentiate throughout their lives
Describe differentiation in plants
- undifferentiated stem cells are stored at the meristem in the roots and shoots of a plant
[] in these areas, mitosis and thus takes place almost constantly throughout a plant’s life
[] these stem cells elongate and grow before differentiating - plant cells can re-differentiate at any point during their lives
[] very useful if a predator or disease damages a (crucial) part of the plant - other cells can simply divide and re-differentiate to replace the lost part (or in the case of disease, wall off the diseased cells and then regrow there when the diseased region dies and falls off)
[] also useful to humans in terms of plant cloning
Why can you clone plants and not animals ?
- given the right conditions, a cutting of a plant will be able to grow into a full version of that plant
[] does this through re-differentiation of cells in contact with soil/water etc. to form root cells, xylem and phloem, and all other crucial cells to a plant
[] plant growth is often done solely through mitosis, which produces identical cells with the same genetic material; thus if one plant snipping is regrown into a full plant, the new plant is a clone of the old one - animal cells CANNOT re-differentiate like plant cells and so it is hard to clone animals without obtaining (embryonic) stem cells first
Where can adult stem cells be found in humans and why ?
areas of the body where a lot of cell division is needed (such as in the muscle tissue or when regrowth of the liver is needed) or where cells cannot divide by themselves (like nerve cells in the brain and red blood cells in the blood) usually have adult stem cells present
- bone marrow (most populous region of stem cells)
- blood
- brain
- muscle
- liver
- embryonic stem cells can also be found in the umbilical cords of newborns
What is stem cell therapy ?
the use of cloned stem cells prompted to differentiate into a certain type of cell in order to replace damaged or dead cells that cannot replace themselves
What do scientists hope that stem cell therapy can be used to treat ?
- macular degeneration
[] already some progress in this area; after a study in 2014 was done injecting embryonic cells into the eyes of those suffering from macular degeneration, it was found that a majority of patients were able to see better after - paralysis and nerve damage
- type 1 diabetes (to replace ill-functioning pancreatic cells with those that are able to produce insulin normally)
- infertility
[] producing functioning sperm and egg cells from embryonic stem cells - dementia
- growing organs for transplant
[] would reduce or negate the need for patients who have had a transplanted organ to take immunosuppressants (if the organ was grown from their own stem cells) as risk of rejection would be incredibly low
Why is cloning plants from the stem cells in their meristems useful ?
can produce a large number of the same plant quickly and economically, without making plant cuttings and thus destroying the parent plant
- useful in research of plants
- saving plants from extinction
- horticulture; producing a large number of a plant with specific, attractive characteristics (like uniquely coloured petals) for sale
- agriculture; cultivating a large population of a plant with a useful or desirable characteristic, like high yield of fruit, disease resistance, size etc.
[] fruits like bananas are all genetic clones of one parent plant and the current popular banana (the cavendish) was selected for its disease resistance, not shared by the gros michel banana that came before it
Where are embryonic stem cells for research and cell cloning sourced currently ?
- aborted embryos
- donated embryos (from IVF) that will not be used
- amniotic fluid
- umbilical cords of newborns
Describe the main problems with use of embryonic stem cells for medical treatments
- religious and ethical beliefs:
[] some people cannot accept the interference with human reproductive processes on account of religion
[] some people believe that life begins at conception, and so destroying aborted or spare/donated embryos to harvest the stem cells is murder
[] these people also may believe that, since the embryo cannot give consent to its use in science, it is a violation of human rights to destroy embryos and use them in scientific processes - financial and industry concerns:
[] stem cell research is extremely expensive to carry out, and progress is very slow; some feel that money and time are being wasted on stem cell research
[] it is proving difficult to prompt differentiation of embryonic stem cells into specific specialised cells, as the chemical signals that prompt cell differentiation are not presently understood in full; in this way, many embryos and embryonic stem cells are wasted during research - health risks/side effects:
[] some scientists have concern surrounding increased possibility of cancer when stem cell therapies are used on animals, due to the fast-dividing nature of embryonic stem cells; if division is not carefully controlled, some fear the development of tumours
[] this has already been a problem in mice who have had stem cell therapies as well as early human treatments for autoimmune diseases
[] risk of rejection of stem cells used in stem cell therapies, causing more problems than initially when used
How are scientists working to combat the main concerns, both ethical and scientific, surrounding use of embryonic stem cells for stem cell therapies ?
- sourcing embryonic stem cells from amniotic fluids and the umbilical cord instead of directly from spare/aborted embryos
[] this is a problem however, as sourcing of sufficient amounts of these cells can be difficult when done in this way - culturing adult stem cells instead of relying on embryonic stem cells
[] easier to source directly from the patient, meaning less risk of rejection
[] however so far have only been differentiated into a limited range of cells
[] harvesting of stem cells from bone marrow carries the risk of general anaesthesia - use of therapeutic cloning to reduce/negate risk of rejection
[] this is when the patient’s genetic material is inserted into an enucleated egg cell (original nucleus removed if not from the patient’s own body) to fertilise it
[] an embryo with the patient’s DNA is cultured and then destroyed to harvest the embryonic stem cells
[] this results in low/no risk of rejection to any transplant organs etc. put inside of the patient as it is their own genetic material, and thus the patient doesn’t need to take (as many) immunosuppressants, keeping them healthy in terms of immune system also
