8.2 Wilson's disease The effects of a protein that is absent, or present but not doing its job, may not be evident for many years. This is called late onset, and is exemplified by Wilson's disease. Many molecules within the body require small amounts of minerals such as iron, magnesium or copper to function properly. There are mechanisms for absorbing these minerals from the diet. However, in excess, these same minerals can be toxic, as is the case with copper. So there are also mechanisms for getting rid
7.8 Summary of Section 7 This section has sought to illustrate the formation of connections between neurons and their targets by exploring a few examples. The picture that emerges is one of cells at different stages of development subjected to a vast array of signals. These signals are the medium through which environmental factors exert their effects. To some of these signals, some cells respond; to other signals, other cells respond. What a cell, a neuroblast, a growth cone actually does is dependent on the combina
7.6 Synaptogenesis The formation of synaptic connections is an essential property of nervous system development. Synapses are formed between neurons and also with targets that are not part of the nervous system, e.g. muscle. Axon terminals, under the direction of a variety of extracellular cues, grow towards particular targets. Once they arrive at the target, they stop growing and the growth cone changes to form a synapse. As with axon growth, the formation of the synapse is dependent on an interaction between
7.4 Elixirs of the nervous system: neurotrophins According to Section 7.2 axons obtain an elixir from targets at their synapses. Confirmation that there is indeed an elixir came from a series of events that reveals how much of science really works. Elmer Bucker, working with Hamburger in the mid-1940s, had removed a limb bud from a chick and replaced it with a tumour from
7.2 Selected to survive: studies of the PNS Viktor Hamburger carried out a series of classic embryologieal experiments over a period of about 30 years. He investigated the relationship between the size of target tissue in chick embryos and the size of the pool of neurons that innervated it. His technique was to remove or add target tissue to the tissue which would eventually form a limb, usually the hind limb, and is called the limb bud. A few days later he observed the effect of the tissue addition or removal on the pool of neurons de
7.1 Neuron proliferation There is a huge proliferation of neurons in early life. Even whilst that proliferation continues, some cells, e.g. neuroblasts, stop being able to divide. At some later stage the proliferation itself virtually ceases. It follows that cells switch from being able to divide, to being unable to divide, and that they switch at the appropriate time: the process of cell proliferation is controlled. The details of the control of proliferation are not yet understood and are not considered here. But o
5.4 Retinoic acid The retinoic acid story is both distressing and illuminating. It is distressing because with hindsight it is possible to see how the suffering of many people could have been averted. It is illuminating because we now understand much about how retinoic acid works. Retinoic acid is a natural product of vitamin A. It had been known since the 1930s that a lack of vitamin A, a vitamin A deficiency, led to fetal abnormalities. Subsequent studies in animals showed that an excess of vitamin A a
4.2 Licking/grooming-arched back nursing Rat mothers perform a number behaviours towards their pups: they build a nest for their pups, keep them in it and occasionally lick them and nurse them. (Rat fathers have a parental role too but it is not essential and the experimental set-up is simplified by his absence.) Licking occurs predominantly at the time when the dam arches her back and nurses her young, allowing a composite behaviour of licking/grooming-arched back nursing to be identified and recorded. If licking/grooming-arched ba
3.4 Sensitive periods The steroid hormone testosterone plays a major role in the development of mammals. In particular it is instrumental in causing differences between males and females. One well explored difference concerns play-fighting in young rodents. In the rat, play-fighting is a sequence which begins when one animal pounces on another. The pounce is followed by wrestling and/or boxing and the play-fight usually finishes with one animal on top of the other. A similar sequence of play-fighting is seen in yo
Learning outcomes After studying this unit you should be able to: recognise definitions and applications of each of the terms printed in bold in the text; critically evaluate statements about the influence of the genome on behaviour; explain the ways in which genetic and environmental factors influence the development of the nervous system; provide examples of the influence of genetic and environmental factors on the development of the nervous s
4.4.1 Phosphorus (P) Like calcium, phosphorus is important in the structure of bones and teeth. It is vital in the body as part of the molecules ATP and DNA, and is also a component of phospholipids, lipoproteins and many other proteins too. Phosphorus can occur, combined with oxygen, in phosphate ions and in this form it plays an important role in switching on and off metabolic pathways in cells. Phosphorus is widely available in the diet, from both plant and animal sources, such as meat, fish, eggs and dairy pr
Learning outcomes After studying this Unit you should know: that certain minerals are required in the body and that some minerals form essential structural components of tissues; that sodium, potassium, calcium and chloride ions are important in maintaining the correct composition of cells and of the tissue fluids around them (homeostasis); that some minerals are essential components of important molecules such as hormones and enzymes; that the correct
Acknowledgements Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence All other materials included in this unit are derived from content originated at the Open University. 1. Join the 200,000 studen
9 Summary In this unit you have found out that: The sensation of pain is caused by the release of a chemical (prostaglandin) that stimulates the nerve endings and sends an electrical message to the brain. Pain can be reduced if the formation of prostaglandin can be inhibited. Prostaglandin is formed, from arachidonic acid, in a cavity in the active site of the enzyme cyclooxygenase (COX). Geometrical isomerism
1.8 Enter aspirin! Aspirin is able to release part of its ester group (Figure 15) in a hydrolysis reaction. Look again at the structure of aspirin, 2.8, and identify this group on the molecule. It is known as an acetyl group and accounts for aspirin also being called acetylsalicylic acid. The acetyl group on aspirin is fairly easily removed and can be available for forming another ester with an —OH group on another molecule; in this case, part of the structure that makes up the inside of the cavi
Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: All other materials included in this unit are derived from content originated at the Open University.
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1 1.2 How DNA is replicated Cell division involving the nuclear division of mitosis produces two progeny cells, which contain identical genetic material, which is also identical with that of the original parent cell. This is how a fertilized egg grows into an adult many-celled organism. For one cell to become two new ones with identical genetic material, the DNA in each chromosome must undergo a process in which an identical copy is made. As noted above, Watson and Crick postulated that DNA base-pairing provides a
Learning outcomes After studying this unit you should understand: the basic composition and structure of DNA; what is meant by complementary DNA base pairing; how base pairing allows a mechanism for DNA replication; the number of DNA molecules within a chromosome.
5 Where does transcription occur in the cell? Up to now we have described the processes of transcription without considering where each occurs within the cell. Given that transcription — the production of mRNA — requires a DNA template, where do you think this process occur Introduction This unit explores how information contained in DNA is used, explaining the flow of information from DNA to RNA to protein. Also introduced are the concepts of transcription (as occurs between DNA and RNA) and translation. This unit is an adapted extract from the course Human genetics and health issues
(SK195)
SAQ 5
