Lipids, Aggregates and Steroids

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What are lipids?
A type of biological molecule and includes all compounds solubilised from cells by organic solvent
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What are the functions of lipids (6)
Storage in cells, thermal insulation, energy reserve, electrical insulation, cell recognition and cell membranes
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What are the three common saturated fatty acids?
Stearic, palmitic and myristic acid
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What are the two common unsaturated fatty acids?
Palmitoleic, and oleic acid
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What are the two common polyunsaturated fatty acids?
Linoleic and linolenic acid
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How do you work out if a fatty acid is omega 3 or omega 6?
Count from the last carbon (methyl) up to the first C=C bond
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What are the three key points about bacterial fatty acids?
Rarely polyunsaturated, often branched and sometimes hydroxylated
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What are simple triglycerides?
Glycerol molecule with a ester bond to a single type of fatty acid
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What are mixed triglycerides?
Glycerol molecule with a ester bond to two or more types of fatty acid
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Why do unsaturated fatty acids have a lower melting point?
The C=C bond causes a disruption (kink) in structure, van der Waals interactions are not as strong so less energy is required to overcome forces
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In which phase are fats at room temperature?
Solids
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In which phase are oils at room temperature?
Liquids
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In which phase are waxes at room temperature?
Semi-solid at room temperature
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Plant oils are rich in which type of fatty acids?
Unsaturated fatty acid triglycerides (liquid at room temperature)
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Fish oils are rich in which type of fatty acids?
Polyunsaturated fatty acid triglycerides (liquid at room temperature)
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What are three types of complex lipids?
Glycerophospholipids (based on glycerol), sphingolipids (based on sphingosine) and steroids (based on cholesterol)
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What do glycerophospholipids consist of?
Hydrocarbon tail (hydrophobe) ester bonded to glycerol molecule which is ester bonded to a phosphate group (hydrophile) bonded to X (side group - leads to classes of glycerophospholipids)
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What does a sphingosine consist of?
OH groups, NH3+, C=C bond and hydrocarbon chain etc.
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What do sphingomyelins (sphingophospholipids) consist of?
Phosphatidycholine head group, n-acyl fatty acid derivative of sphingosine (ceramide) - major component of nerve cell myelin sheath
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What are cerebrosides?
Simplest form of glycolipid, have a single sugar residue as polar head group e.g. galactocerebrosides (head group is galactose - prevalent in nerve cell membrane)
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What are gangliosides?
Complex glycolipids, ceramides with oligosaccharide as polar head group, at least one residue of which is sialic acid (makes up significant amount of brain lipid and involved in cell recognition/blood groups)
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What is SDS?
Sodium dodecyl sulfate
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Lipids which give a conical shape can be combined to form what?
Micelles
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What are the uses of micelles?
Used to remove stains e.g. in washing powder
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Which type of molecules forms an inverse conical shape?
Phosphatidyethanolamines
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What is formed when inverse conical shapes are put together?
Reverse micelle (able to pass through membranes) - apply to skin
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Which type of molecules form a cylinder shape?
Phosphatidycholines
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These cylinder shapes form what?
Monolayer, bilayer
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Describe lipid bilayer demonstration (5)
RBCs homogenised and membranes isolated by centrifugation, membrane pellet treated with acetone, acetone solution of membrane lipids spread as monolayer on (Langmuir) trough, area of monomolecular film measured, area of film compared with SA of cells
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What were the errors made in this demonstration?
Film area = 2 x cell SA, cell membrane (2 molecules thick), RBCs SA underestimated and acetone extraction has a yield of only 70-80%
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What is transverse lipid diffusion?
Rare/energetically difficult (forcing hydrophilic head into a hydrophobic region of bilayer), involves a lipid being flipped within a bilayer
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What is lateral lipid diffusion?
Determined by photo-bleaching recovery experiments, involvement movement of lipid across monolayer within bilayer (maintains same molecular environment/rapid)
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How does fluidity vary with temperature?
Higher temperature leads to more fluidity (more permeable). Lower temperature leads to less fluidity (less permeable)
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What is a significant feature in the structure of steroids?
Contains carbon rings/molecule is not flat (learn ring labels and numbering system)
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Atoms/groups oriented above the ring plane are what?
Beta
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Atoms/groups oriented below the ring plane are what?
Alpha
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What are cholestanes?
A class of steroids, 27 carbon skeleton e.g. cholesterol
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Cholesterol is a precursor for what other substances?
Bile acids, steroid hormones and vitamin D
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Is cholesterol present in prokaryotes?
Cholesterol is largely absent in prokaryotes (e.g. bacteria)
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Give examples of other sterols (in plants and fungi)
Stigmasterol and fungi
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What are the forms cholesterol which can be taken up by cells?
LDL complexes, cholesterol, phospholipids, triglycerides and proteins
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What are estranes?
A class of steroids, 18 carbon skeleton e.g. estradiol
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What is estradiol?
Principal female sex hormone, produced in the ovaries, responsible for development and maintenance of female sex characteristics. Major effects on brain functioning and bone metabolism
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What is ethinylestradiol?
A derivative of estradiol, a major component of hormonal oral contraceptives
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What are androstanes?
A class of steroid, 19 carbon skeleton e.g. testosterone
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What is testosterone?
Male sex hormone, synthesised in the testes, responsible for development/maintenance of male sex characteristics produces from progesterone (e.g. of anabolic steroid)
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What are anabolic steroids used for?
Can be used by athletes to improve performance but considered as a form of doping in most sports (testosterone: epitestosterone ratio measured)
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What are the side effects of anabolic steroids?
Increased aggression, paranoia, confusion, insomnia (in men sterility/breasts, in women shrunken breasts and facial hair)
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What are pregnanes?
A class of steroid, 21 carbon skeleton e.g. progesterone
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What is progesterone?
Produced in the corpus luteum, responsible for changes in (luteal phase of) the menstrual cycle, controls differentiation of mammary glands
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How is progesterone manufactured?
By semi-synthesis from the steroid, diosgenin, obtained from yams
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What is progesterone used for?
To support pregnancy following IVF
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What does high levels of blood cholesterol increase the risk of?
Coronary heart disease and disease of the arteries
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What are the rich sources of cholesterol?
Eggs, offal and shellfish
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What are LDLs?
Takes cholesterol from liver to cells - may cause harmful build up in blood vessels
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What are HDLs?
Take cholesterol from cells back to the liver where it's broken down and excreted
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Which hormones are in the adrenal glands?
Glucocorticoids e.g. cortisol (hydrocortisone - carbohydrate metabolism, stress management, effects immune system, also an anti-inflammation steroid) and mineralocorticoids e.g. aldosterone
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Where are bile acids synthesised?
In the liver from cholesterol e.g. cholic acid (bile salts facilitates the formation of lipid micelles to promote lipid digestion)
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Amphotericin preferentially complexes with what instead of cholesterol?
Fungal ergosterol
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Card 2

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What are the functions of lipids (6)

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Storage in cells, thermal insulation, energy reserve, electrical insulation, cell recognition and cell membranes

Card 3

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What are the three common saturated fatty acids?

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Card 4

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What are the two common unsaturated fatty acids?

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Card 5

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What are the two common polyunsaturated fatty acids?

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