Lipids are made up of carbon, hydrogen and oxygen (phospholipids also contain phosphate) and are found in a wide variety of organisms from bacteria to eukaryotes where they perform a wide variety of useful functions. This essay will expand on these functions to describe the role of lipids. There are several types of lipid including triglycerides, steroids, waxes and phospholipids. Triglycerides are made up of three fatty acids combined with glycerol by an ester linkage meaning they are predominantly hydrophobic.
They are combined in a condensation reaction where water is released.
Phospholipids and similar except one of the fatty acid tails is replaced by a charged phosphate group. This means phospholipids are made up of two parts as the phosphate head is hydrophilic while the tail is hydrophobic. This mean it is polar so when placed in water they position themselves so as the tail is as far away from the water as possible and the head is as close to the water as possible.
However the distinct similarity between these two types of lipid is that they both have fatty acids chains that can either be saturated (carbon carbon single bonds) or unsaturated (at least 1 carbon -carbon double bond) Due to the chains without a double bond being able to pack more closely together they have a higher melting point than unsaturated fats. Steroids however have a different structure and are cyclic lipids with various side groups. Cholesterol is an example of a steroid. It is important in the cell membrane as it stabilises it ensuring it does not become to like a fluid.
If this were the case they would become too permeable to certain substances. However at the same time it prevents it becoming too rigid so cholesterol helps to prevent the cell membrane to maintain the correct consistency. However cholesterol is not the only lipid important for the plasma membrane, phospholipids are also essential. Due to their hydrophobic tails and hydrophilic heads they from a bilayer with the heads face the water and the fatty acid tails backing onto other fatty acid tails This structure is extremely important as it allows lipid soluble substances to enter and leave the while preventing water soluble substances.
Also as the phospholipids can move relative to each other it gives the membrane a flexible structure Waxes are a type of lipid that are very important to plants as they provide a waxy cuticle which is a waterproof layer. This waxy cuticle prevents water loss by preventing evaporation from the surface of the plant. The thicker the cuticle the smaller the water loss therefore plants such as xerophytes have particularly thick cuticles to enable the xerophytes to survive in a hot climate.
This type of waterproofing is also evident in mammals when the produce an oily secretion from the sebaceous glands in the skin. Animals such as penguins live in cold environment and therefore heat conservation is essential for survival. It is here that triglycerides are essential to provide insulation. As added triglycerides make the organism bigger they reduce the surface area to volume ratio and therefore reduce the amount of heat lost to the environment. In addition lipids are used to insulate neurones.
Wrapped around axons are schwann and the membranes of these contain a lipid called myelin. This myelin speeds up the rate of conductance of impulses as nerve impulses as the lipid insulated the nerve so impulses jump between nodes of ranvier. As well as providing insulation triglycerides provide buoyancy as lipids are less dense that water so large amounts of triglyceride reduce the density of an animal. This is an important feature in mammals such as seals as it enables them to move to the surface of the water for ventilation.
Many animals carry out aerobic respiration and for this glucose is essential. Typically triglycerides are an energy store but if glucose is not available they can be used as the respiratory substrate. They are a very good respiratory substrate yielding twice as many molecules of ATP as a molecule of glucose. Despite being a hormone oestrogen is an example of a steroid lipid and is important in the control of fertility and reproduction. The oestrogen causes the rebuilding of the uterus lining after menstruation making it suitable for an egg to be implanted.
In addition when oestrogen levels are high it stimulates the pituitary gland to produce LH which subsequently causes the ovary to release its egg. The steroid progesterone then maintains the thick lining of the uterus and also inhibits the release of LH and FSH. However oestrogen can trigger certain types of cancer such as breast cancer through the activation of certain transcriptional factors. In conclusion without lipids the compartmentalisation of substances by organelles in eukaryotes and the menstrual cycle would not be possible throwing many processes into disarray.
Cite this Structure and Function of Lipids
Structure and Function of Lipids. (2016, Nov 13). Retrieved from https://graduateway.com/structure-and-function-of-lipids/