The Function and Structure of Lipids in Living Organisms

Lipids are a group of organic compounds that are fatty acids and include Oils, Fats, Waxes and Steroids. They are also all insoluble in water because they are non-polar but are soluble in solvents, which is why solvents are often used in home cleaning products like oven cleaners and drain cleaners to remove build-up’s of fats and oils. Also lipids like wax can be very useful and vital for many creatures such as bird and semi-aquatic mammals which use them to make their feathers fur waterproof. Similarly humans use keratin in the epidermis and oil produced by the sebaceous glands help to make their skin waterproof(1).

The structure of lipids

Lipids similar to carbohydrates contain carbon, oxygen and hydrogen, but in lipids the proportion of oxygen is a lot lower than carbohydrates. Also lipids are insoluble in water because they are non-polar which means that the positive and negative charges cancel out each other so it doesn’t have a positive or negative charge but they are soluble in organic solvents such as ethane and methane because they are also non-polar.

This is a preview of the whole essay

Fatty acids can be saturated or unsaturated depending on their carbon bonding and can be told apart easily because of their state at room temperature, ether solid or liquid. Saturated fatty acids are made up of hydrogen, oxygen and carbon, the carbon in the saturated fatty acid has single bonds and it is bonded to the maximum number of atoms that it can bond with. Because of this it is a strait chain which means that it can be closely packed with other chains which means that it is a solid at room temperature. Saturated fats are directly responsible for high cholesterol levels because they are LDL’s (low-density lipoproteins) or “bad” cholesterol which causes blocked arteries and increase your chance of heart disease (which may lead to a heart attack).This happens when fat builds up in the walls of your arteries and over time causes the artery walls to harden to an extent where arteries become narrowed and blood flow to the heart is slowed down or blocked. The blood carries oxygen to the heart and around the body and if not enough blood and oxygen reach parts of your body then they will start to weaken and you may suffer from chest pain. If the blood supply to the heart is completely cut off by a blockage you will then have a heart attack.

Unsaturated fatty acids also contain hydrogen, oxygen and carbon but the bonds between some of the carbon atoms are double bond so carbon is not bonded to the maximum number of atoms that it could bond with the result of this is a chain with kinks in it. A result of this is that they cannot closely pack together like the unsaturated chains, this means that they form liquids at room temperature. This is very useful for animals such as artic fish because unsaturated fatty acids are liquids over a larger range which is important for them because if there cell membranes were made up of saturated fatty acids then the membrane would be solid and the fish would not be able to survive, yet other artic fish like beluga whales need saturated fat for isolation which makes up half their body weight (There blubber is roughly about 10cm thick)(2). Unsaturated fatty acids are known as HDL’s (High-density lipoprotein) or “good” cholesterol these are the opposite of LDL’s and actually prevent cholesterol build up in arteries. They are also dancer because they contain a higher proportion of protein to cholesterol.

Triglycerides and Phospholipids

Triglycerides are made from glycerol and 3 fatty acids. The bond is formed in a condensation reaction between the hydroxyl group (-OH) from the glycerol and the carboxyl group (-COOH) of the fatty acids. When they join water molecules are given off (condensation reaction) and a ester bond is formed between them (This type of reaction is known as a esterification reaction. The nature of the lipid formed (solid or liquid at room temperature e) is dependent on whether fatty acid is saturated or unsaturated.

Phospholipids are the main component of a cellular membrane. Thy consist of a glycerol attached to two fatty acid chains and a phosphate group which is attracted to water (hydrophilic) while the fatty acid end repels (hydrophobic). The hydrophobic end turns inwards in the membrane to form a phospholipid bilayer(3).

Steroids

Although steroids are classed as lipids, their structure is quite a bit different to the other types of lipids. Steroids have a basic structure of three rings made of 6 carbon atoms each and a fourth ring that contains 5 carbon atoms. Examples of steroids include both the male and female sex hormones (testosterone (male) and oestrogen (female)) which control the reproductive systems and puberty in both males and females. Also the hormones cortisol (releases in response to stress and increases blood sugar levels) and aldosterone (increases the reabsorption of sodium ions and water)(3).

Waxy and Oily Layers

The epidermis covers the lower and upper sides of the leaf. Each side is composed of a single layer of closely-packed rectangular cells. The layers are translucent and are covered with a waxy cuticle on the outer wall. The epidermis stops water loss but allows a small amount to go through it also photosynthesis, respiration and gaseous-exchange as well as protecting the internal tissue.

The gland that waterproofs a parrot's feathers is called the uropygial gland. The uropygial gland is also known as the oil gland. It's present in most species of bird, and it's relatively large in some aquatic species. In certain species this gland is not present (for example Macaws don't have this gland).

By Maxwell Taylor 14/9/2011

Peer Reviews

Here's what a star student thought of this essay

PicturePerfect

1st of Apr 2012

Quality of writing

Unfortunately the quality of writing in this piece of work is below average. There are a fair few spelling mistakes, there are also occasions in which words have been omitted. In addition the candidate sometimes fails to use the plural for certain words and there are some problems with grammar. The candidate doesn't always use commas appropriately, when you read through your work, you should have a comma in every place that you naturally stop to take a breath. Though the essay flows well, the problems with the quality of writing and grammar make it difficult to read at times, therefore the essay is not as fluent as it could be. Many of the issues I have highlighted could have been eradicated if the candidate had proof read their work and been thorough when using spell check.

Level of analysis

This essay goes into a reasonable level of detail and the information provided is scientifically accurate. The candidate shows evidence of independent research, for example they have discussed the way in which cleaning products works. Which shows an interest in the subject youÃ¢â‚¬â„¢re discussing and makes the essay more enjoyable to read. In addition the candidate has shown a board subject knowledge as they have linked in other key points from the Biology specification, for example in the second paragraph s/he has mentioned the link between high cholesterol levels and increased risk of heart disease. However there is no real conclusion to this essay. A conclusion should summarise your key points and ideas (in this case the main reasons why lipids are important). This brings the essay to a close and gives you a chance to leave the reader with a good impression.

Response to question

Though the candidate uses the first paragraph to describe what a lipid is, there is no clear introduction, after the first sentence the candidate jumps straight into the body of the essay. An introduction should set out what you plan to discuss, introduce your main topic and provide simple facts that will lead you into your main topic of discussion. In addition this gives you a chance to catch the readers attention. The candidates response to the set topic is fairly explicit, they provide relevant scientific details and develop the discussion to include other relevant topics.

Did you find this review helpful? Join our team of reviewers and help other students learn