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Summary Molecular Biology of the Cell 2 (book) (WBFA007-04)
Summary Regenerative Medicine
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Biochemistry
Biochemistry - part 2
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Biochemistry 2
Biomolecular structures - LIPIDS
Definition - Multiple hydrocarbon groups and few oxygen or polar groups
Often called FATS but also includes OILS
Heterogeneous group
Properties
insolubility in water
soluble in non-polar solvents such as chloroform, hydrocarbons, benzene etc.
proteins (enzymes that catalyst the reactions) don’t like being in an aqueous environment.
Why are they important
Energy store
Membrane structure
Hormones and signaling compounds – derived from cholesterol and signal over short ranges
Lipids can be grouped into:
Complex lipids - most common in nature. e.g. phospholipids
Simple lipids - small proportion but many have specific functions. e.g. cholesterol, prostacyclin
Complex Lipids
Made from other smaller components put together
Major part is made of FATTY ACIDS
Nomenclature of fatty acids
SYSTEMATIC NAMES - Number of carbons in chain (in Latin) with ‘-oic acid’ on end or ‘-oate’ if ionised
form.
If there are double bonds these are indicated with a number. e.g. cis-9-hexadecanoate
The double bond is between the 9th and 10th carbons starting the numbering from the carboxyl
carbon
COMMON NAMES - Appear to be random but often relate to the source from which the fatty acid was first
isolated. e.g. palmitate from palm oil
, Complex Lipids – Triacyl Glycerols
Complex Lipids – Phospholipids
Fatty Acid chain length and double bonds
, Chain length has a significant effect on the extent of inter-chain interaction
Longer chain - more interaction
Double bonds also significantly affect the inter-chain interaction
Double bonds - less interaction
The extent of interaction has an effect on the fluidity of bilayers
Hence organisms vary widely in the composition of the FAs that they contain within their membrane
forming lipids
The composition reflects a number of things including growth temperature and membrane function
AMPHIPATHIC molecules
Sometimes termed 'SCHIZOPHRENIC' molecules
Free fatty acids, phospholipids, glycolipids, sphingolipids, ceramides etc are amphipathic
Such molecules when added to water form a monolayer with the hydrophobic hydrocarbon chains
projecting from the water
Vigorous shaking can produce micelles
The process is not driven by free energy but by entropy
Close packing of hydrocarbon tails excludes water leading to an increase in entropy
Bilayers can also form from this type of molecule
Vigorous shaking of bilayers produces liposomes, which are much larger than micelles
Triacylglycerols are neutral and hence are NOT amphipathic
Triacylglycerols pack closely to exclude water, so taking up less space – ideal for a concentrated energy
store
Introduction to lipid metabolism
Fatty acids are the most common lipid molecules
Fatty acids can be metabolised to release energy and generate ATP
Where do the Fatty acids come from?
Diet – about 30-40% of calories are from fatty acids
Adipose tissue – fat storage cells can release fat when needed
De novo synthesis – made from carbohydrates and some amino acids
Digestion of fats begins in the small intestine Requires input from two other organs
LIVER & PANCREAS
LIVER
Liver produces and releases, via the gall bladder, BILE
Bile contains a number of slightly
different compounds, called bile
acids & bile salts, derived from
cholesterol - these act as detergents
emulsifying the lipids and forming
small droplets of fat
PANCREAS
, Pancreas produces digestive enzymes and bicarbonate solution
- the enzymes involved in fat digestion are called LIPASES
Action of pancreatic lipases
Triacylglycerol lipase
Catalyses the hydrolysis of triacylglycerols at their 1 & 3 positions
Triacylglycerol (95% of dietary fat)
1,2 diacylglycerol + fatty acid
2 acylglycerol + fatty acid
Triacylglycerol lipase
At the water-lipid interface so surface area for lipase to attach to is important
Fatty acids and 2 acylglycerol are then able to diffuse in to intestinal epithelial cells .i.e. cells lining the
intestine
Once inside the cells these components are reconstituted into triacylglycerols
Phospholipase A2
Acts upon phospholipids to aid their digestion by removal of the fatty
acid residue from position C2
TRANSPORT OF LIPIDS
Lipoprotein complexes are used to transport the majority of lipids in the blood stream
The complexes are classified by density but there is overlap in composition from one type to the next
Lipoprotein complexes
Essentially, lipid droplets surrounded by proteins and
phospholipids that make them soluble in blood
Some free fatty acids can be transported in blood,
solubilised by binding to serum albumin
LIPOPROTEIN LIPASE
Present on capillary surfaces of the tissues that absorb lipid from the blood .i.e. mammary, muscle and
adipose tissues
The enzyme is activated by the Apo-CII component of chylomicrons
This is able to breakdown the triacylglycerols into fatty acids and monoacylglycerol
These are able to diffuse out of the chylomicrons and in to the cells of the tissue
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