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S293 The Fats of Life

OU S293 Course Description

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17th March 2005

Well, isn't this a sight for sore eyes on a dark, dismal Thursday!!

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12th January 2005

I posted my ECA on Monday (10th) and received the card back from the OU to say they received it, this morning. Fingers crossed that it was enough! S293 was, by far, my least favourite course.

Summary of Lipids, adipose tissue and a long, healthy liefe - and the Epilogue

Vitamins A and D (and a few others) are lipids and certain fatty acids are dietary essentials. These nutrients can be stored, and supplies are passed from mother to offspring, so symptoms of deficiencies appear only slowly in animals eating inadequate diets.

Aspirin (and related drugs) work by inhibiting the synthesis of certain lipid-derived messenger molecules.

The adipose tissue associated with lymph nodes and similar immune tissue has special properties that enable it to contribute to immune responses.

Dietary lipids modulate immune responses, possibly via the associated adipose tissue.

High levels of fat in the form of lipoproteins cause damage to the lining of blood vessels, thereby producing constrictions that impede blood flow, eventually causing strokes and/or heart atacks. Polyunsaturated fatty acids, especially thos of the n-2 family, protect people against atherosclerosis. Animals whose natural diet is low in fat are very susceptible, while many carnivores can tolerate very fatty diets.

Long-term obesity promotes heart disease and diabetes, as well as increasing the risk of accidents.

Impaired control of appetite, over consumption of fatty foods, weak thermogenesis and lack of exercise all contribute to human obesity.

Both rats and people adapt to restricted diets, enabling them to gain weight on less food.

Most drugs that alter energy expenditure or appetite have dangerous side-effects. Preventing overeating by surgical constriction of the stomach is effective but is a major operation.

1st December

Though these books couldn't exactly be classed as "un-put-downable", I'm fairly rattling through the material now. I wonder why that is?!

Summary of People and their adipose tissue

There are few hard facts, but there is much speculation, about the evolutionary origins of human obesity.

Many large primates as well as ourselves are partly carnivorous. Modern people are not as completely adapted to the meat diet as cats or snakes.

The skills required for predation may promote the evolution of intelligence, and a diet rich in animal fats may favour social behaviour. The digestion of animal food also produces less heat than that of plants, reducing the risk of overheating.

Compared to other mammals, humans grow very slowly both before and after birth and suckle for a long time. Compared to other mammals, energy ulilization by the neonate's brain is high, and that of the muscles low, so the very high fat diet provided by cows' or goats' milk is not appropriate.

Because of the large quantity of heat generated by the metabolism of the brain, humans seem to be better adapted for dissipating heat than conserving it. Modern people tolerate cold well, perhaps because the adipose tissue itself can be thermogenic, but wearing clothes reduces the capacity, and may contribute to becoming obese.

Sex differences in the distribution of adipose tissue in mammals are minimal except in humans. Hair reduction increased the visibility of body shape, promoting the evolution of changes in the distribution of adipose tissue as an indicator of sexual and social status.

Non-human apes do not have waists. The waist arises from changes in the shape of the pelvis associated with walking upright and is a distinctively human, as well as distinctively female, feature.

Some Stone Age people were obese but changes in diet with animal husbandry and agriculture probably increased the prevalence of obesity.

29th November

*Some* of this is becoming very slightly more interesting. But I'm still reading without taking anything in or wanting to understand, it seems - as when I get to the questions at the end of the chapters, I don't have a clue what they're talking about! I think I'm going to try to finish off this course, pronto - so that I can then relax over just S180 - although that ECA looks harder than the S293 one (probably famous last words ...)

Summary of The Use of Lipids and Adipose Tissue

Migrating animals fatten before the journey, and may 'refuel' on the way by stopping at places where suitable food is abundant. The amount of fat they can carry and thus the distance they can travel without feeding depends upon body size, weather conditions and other factors.

Fatter animals are often healthier and produce better sexual displays during the mating season, thus enabling them to attract more and/or better partners.

The energetic demands of lactation are much greater than those of gestation for most mammals, and lipid reserves built up during pregnancy are reclaimed during lactation. Biochemical changes direct lipids from the adipose tissue to the mammary glands to support the synthesis of milk.

Most mammals are born lean but fatten during suckling, in the cases of some marine mammals at a spectacularly high rate. The young's adipose tissue grows very fast during this period, with new adipocytes forming and maturing.

The unborn fetus uses mainly glucose for energy metabolism and lipids are incorporated into the membranes of growing cells. After birth, energy metabolism switches to using mainly fatty acids, but some still end up in structural roles. In this capacity, the chemical composition of the fatty acids that the mother supplies to her offspring is important.

In fish, birds and reptiles, the lipids in egg yolk supply energy and structural materials for growth before hatching; their composition is particularly important for maturation of the brain and eye.

The fatty acid composition of the mother's diet during the weeks before the eggs are laid is important for their hatching success.

In most species, parent birds feed their chicks, often on foods other than their own adult diet. The breeding success of captive animals can be much improved by providing an appropriate diet that the parents can feed to the young.

The more elaborate and efficient control of adipose tissue in mammals may have evolved as an adaptation to 'manage' the competing demands of lactation and supporting the mother's own body.

Eating and digesting food require much energy, which can be supplied from adipose tissue. Animals in which reserves are insufficient lose their appetite and enter terminal decline.

To be metabolized during hibernation, tricylglycerols must remain liquid (ie not forzen) at low temperatures. A high proportion of unsaturated fatty acids lowers the freezing temperature of mixtures of triacylglycerols. Animals choose food rich in unsaturated fatty acids while fattening just before hibernating, and their metabolism preferentially sequesters such fatty acids in the adipose tissue.

Some animals remain active but minimize energy expenditure by reducing their adipose stores during winter.

The proportion of adipose tissue in superficial depots is greater in larger animals, and since their surface area is also proportionately smaller, it becomes chicker. However, superficial adipose tissue is adapted to function as thermal insulation only in marine mammals.

Tough, metabolically inert adipose tissue supports and protects other tissues in paws and in human feet and hands, and around the eyes and cheeks.

19th November

Goodness - that chapter was dreadful!! I don't feel that I read most of it (well, I know I didn't). I sort of floated over the words - nothing went in. It *could* be interesting, I'm sure of that - but the book is sooooooooooooooo badly put together that it becomes sooooooooooooo boring.

Summary of Lipids in Action

Tricylglycerols and phospholipids are too big and too insoluble to be absorved by the gut without first being broken down into fatty acids and glycerol by digestion.

The digestion of lipids is hastened by their emulsification by churning in the stomach and by reaction with bile salts, but is still slower than that of most other components of food.

Lipases are enzymes that break ester bonds of acylglycerols, releasing fatty acids and glycerol which are small enough to pass through cell membranes. Some lipases are very specific, working well only on triacylglycerols of certain compositions. Only specialized lipases attack the ester bond in waxes efficiently.

Undigested triacylglycerols act as laxatives. Olestra is a synthetic lipid designed to be indigestible.

Lipoproteins are very large assemblages of molecules that transport lipids around the body. An enzyme called lipoprotein lipase attack lipoproteins, releasing fatty acids which are then taken up by adjacent cells, usually those that synthesized and secreted the lipoprotein lipase.

Because fatty acids themselves pass intact from gut to cells, their composition provides information about an animal's diet, and to a lesser extent, its mode of digestion.

The isotopic composition of the carbon atoms in fatty acids (and in principle, those of other biological molecules) provides information about their origin, especially whether they first entered a living organism in the sea or on land.

The energy that would be released when lipids are burnt (ie fully oxidized) is converted in living cells into a form (ATP) in which it can be utilized to drive other biochemical processes. Fatty acids are broken down in the mitochondria to carbon dioxide and water.

During fasting and strenuous exercise, adipocytes in different adipose depots do not contribute equally to the lipids circulating in the blood. the muscles of many animals, including humans, need glucose as well as lipid to support vigorous exercise.

Plants can convert fatty acids into glucose, which is converted into cellulose, their principal skeletal material. Seed lipids are packed into numerous very tiny vesicles (instead of the single larger droplet in white adipocytes), which may speed up the growth of seedlings by bringing more lipids into contact with the enzymes that metabolize them.

Steroid hormones derived from cholesterol include oestrogen and other sex hormones. Particular polyunsaturated fatty acids are the raw materials for the synthesis of certain messenger molecules, including prostaglandins, leukotrienes and thromoxanes, which usually occur transiently and at very low concentrations.

8th November

Oh boy - it's not improving all that much (at all). I'm reading through it fairly quickly, in order to get an overall impression - or generalisation - or whatever! Bound to have to read whole chunks again.

Summary of Diverse Lipids in Biology and Technology

The common names for many fatty acids derive from the source from which they were first extracted, or some from physical property.

Saturated fatty acids have only single carbon-to-carbon bonds; unsaturated fatty acids have at least one double carbon-to-carbon bond.

Monunsaturated (monoenoic) fatty acids have one pair of carbons atoms linked by a double bond, polyunsaturated (polyenoic) fatty acids have two or more such bonds.

The positions of double bonds (or other features) are identified by counting carbon atoms starting from the methyl (CH3) end, written as the n (or ω, omega) number, eg n-3, n-6 etc.

Many highly unsaturated fatty acids react chemically with atmospheric oxygen; 'drying' oils, in which such fatty acids are abundant, polymerize to form a tough surface. Similar processes in edible oils make them 'rancid'. The chemical changes are accelerated by higher temperatures and bright sunlight.

A wide variety of fatty acids are found in plant lipids, especially those of seeds, and in algae and microbes. The exact composition depends upon the climate as well as on the species of the plant.

The composition of animal lipids depends mostly upon what the animal has been eating, but many animals can introduce certain chemical modifications to fatty acids.

Double bonds of the cis configuration are commoner in natural fats, especially those of animals, than are trans bonds. The cis bonds between carbon atoms bend the molecule more than the trans bonds do.

Chemical hydrogenation resembles frementation processes in the rumen of cattle. It rearranges the types of bonds between carbon atoms and saturates unsaturated bonds in fatty acids, thus altering some of their physical properties (eg melting temperature) and chemical properties (eg tendency to react with oxygen).

Natural antioxidants prevent unwanted oxidation of fatty acids (ie of those in membranes). Many antioxidants found in animals come from eating leaves, flowers, fruits and other plant parts that are exposed to bright light.

Some natural fats are toxic to animals, including humans. The toxins protect the plants that synthesize them from herbivores.

5th November

I appear to be hurtling through this - but I'm not really. I have to keep reading to stop the eyelids closing ....

Summary of Adipose Tissues

Adipocytes are cells found only in vertebrate animals that are specialized for storing triacylglycerols. Adipocytes can undergo large changes in size and, as animal cells go, can become exceptionally big.

Like other cells, adipocytes are bounded by membranes that contain various receptors that bind to messenger molecules and enable the adipocytes to communicate with each other and with the nervous system and other tissues.

Adipose tissue is composed mainly of adipocytes and in mammals is found in many discrete depots, each characterized by adipocytes of a certain relative size (and by various biochemical properties). Corresponding (homologous) depots can be recognized in most kinds of mammals.

Different groups of mammals differ in proportions of the total adipose tissue situated in different depots. Some larger animals, especially primates (humans, apes and monkeys), have additional depots not found in other groups.

The adipocytes of larger mammals are themselves larger relative to fatness; although larger animals have more adipocytes, they do not have as many as would be expected if all the increase in size of the adipose tissue was due only to having more cells.

Carnivorous (meat-eating) mammals have more, smaller adipocytes than herbivores (plant-eaters) of similar body size.

Nearly all humans have more adipocytes than would be expected from comparison with other animals. The minimum fatness of humans is about the same as the average for wild animals.

Various instruments are used to measure fatness in animals and people, and the data are summarized as various kinds of mathematical formulae.

Most animals are fat only at certain stages of their lives (eg while being fed by the parents) and/or their fatness varies seasonally. Most naturally obese animals live in places where food supply is very erratic, particularly arctic regions.

Natural fatness does not necessarily impair fitness, though fatter animsla re often at greater risk from predators. Some widespread kinds of animals become fat over only part of their range.

Natural obesity usually involves the enlargement of existing adipocytes more than the formation of many more such cells.

4th November

Plodding on!! Biochemistry is not the most rivetting of things ....

Summary of Lipids in Life

Fats are frozen oils and both are called lipids.

Fatty acids are chains of carbon and hydrogen atoms, ranging in number from just a few to dozens, with an acid group (-COOH or -COO-H+) at one end.

Glycerol is an alcohol with three -OH groups.

The most abundant natural lipids are triacylglycerols (glycerol linked by ester bonds to three fatty acids) and phospholipids (glycerol linked by ester bonds to two fatty acids and to a third entity containing phosphate).

Making the ester bond between glycerol and fatty acids (or other component) is called esterification and entails the release of one water molicule for each bond formed; the reverse reaction, in which the ester bond of the lipid is broken by the addition of a water molecule, is called lipolysis.

Lipids mix well with each other and with alcohol and many other 'organic' solvents, but not with water.

Most lipids are less dense than water so they float on it.

The melting temperature of many biological lipids is close to the temperatures at which most organisms live. Smaller lipids evaporate at these temperatures and many have a powerful and distinctive smell.

Short-chain fatty acids have fewer than eight carbon atoms, medium-chain fatty acids have 8-12 and long-chain fatty acids have more than 12 carbon atoms. Those with even numbers of carbon atoms are commoner.

Triacylglycerols are the main storage lipids and phospholipids form the membranes within and around cells.

Cell types differ greatly in the proportion of membranes and hence in the abundance of phospholipids that they contain. Neurons are rich in membranes, which have many special properties that are central to the functioning of the nervous system.

2nd November

On a dreary, dank November morning, as the American people prepare to go cast their votes - I was woken at 7:30am with the Fats course materials!

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Introduction to fats
Introduction to fatty tissues
Diverse fatty acids
Lipids in action
The functions of fattening
The functions of fat
Fat people
Fat and health
Study Period 1: Lipids in life
Study Period 2: Adipose tissues
Study Period 3: Diverse lipids in biology and technology
Study Period 4: How the body handles lipids
Study Period 5: The uses of lipids and adipose tissue
Study Period 6: People and their adipose tissue
Study Period 7: Lipids, adipose tissue and a long, healthy life
Reprints collection

+ the usual study notes, assignments etc - and a video, "Too fat, too young", "The fatbusters", "Fat cats, thin mice".

14th October 2004

I have registered for this course, starting in November. It can't be as bad as S292. Can it?

More and more people, including many small children, are worried about their diet and where their food comes from. This course is designed to help you understand many of the scientific issues involved, from how to interpret the labels on food packaging to why people differ so much in how readily they lose or gain weight. The approach integrates scientific concepts developed from the study of people, wild and laboratory animals, plants and microbes with information from ecology, palaeontology and archaeology.

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