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Phospholipids main function?



Main function of steroids

Component of many hormones, cholesterol


Describe the structure of fatty acids

Long hydrocarbon chain with terminal carboxylic acid group
Hydrocarbon chain: saturated (no double bonds), monounsaturated (1 C=C), polyunsaturated (2+ C=C)

Unsaturation causes kink in chain
All naturally occurring unsaturated fats are in cis formation whereas trans unsaturated fats found in manufacture of food


Compare saturated and unsaturated fats

Palmitic (C16) is a saturated fat, MP 69.9
Oleic (C18) is monounsaturated, MP 13.4 - C=C makes packing of molecule difficult

Most animal fats are saturated whereas most fish and plant fats are unsaturated


What is glycerol and what is its importance?

Three C substance that forms backbone of fatty acids in fats
Important component of triglycerides and phospholipids


What is triglyceride and describe its structure

Main component of vegetable oil and animal fats formed from the esterification of 3 fatty acids with glycerol

Has chemical structure CH2COOHR-CHCOOHR'-CH2COOHR"; Rs are long alkyl groups
The fatty acids can be all same, different or 2 the same


What is the importance of triglycerides?

Metabolism: contain 2X energy as carbs and proteins
Storage and transport form of fats
High levels linked to atherosclerosis (heart disease, stroke)


What is the role of adipocytes and adipose tissue?

Adipocytes specialised for synthesis and storage of triglycerides
Found in subcutaneous layer and in abdominal layer
Subcutaneous fat provides insulation


What is lipolysis?

Breakdown of triglycerides into glycerol and fatty acids with release of energy
Fatty acids released into blood, circulate body


Describe the catabolism of glycerol

Converted to glyceraldehyde 3-P and then glucose OR enter TCA depending on ATP supply


Describe the catabolism of fatty acids

Enzymes remove 2C atoms at a time to acetyl CoA to enter TCA


Describe the process of FA activation

Acetyl-CoA synthases esterify long chain FAs to acyl-CoA
Is ATP dependant


Describe the process of FA oxidation

Acyl-CoA dehydrogenase removes H2 from acyl-CoA, NAD is reduced to NADH2, acetyl-CoA oxidised to trans-enoyl-CoA
enoyl-CoA hydratase, hydrates trans-enoyl-CoA to B-hydroxyacyl-CoA
B-hydroxyacyl-CoA dehydrogenase oxides B-..-CoA to B-ketoacyl-CoA
Acyl-CoAacetyl-transferase moves acetyl forming acyl-CoA (2Cs shorter) + acetyl-CoA


What is lipogenesis?

Synthesis of lipids (anabolism) from smaller units
Mainly occurs in liver and adipose tissue in conditions of excess sugar as glucose converted to glycogen
It doesn't appear to be essential


Compare glucose and fructose

Glucose used in cells throughout body, fructose only in liver
Glucose converted to glycogen, some to FAs and triglycerides
Fructose converted to acetyl them FAs and triglycerides


What are essential fatty acids?

FAs that are required in human diet as humans lack specific enzyme so cannot be synthesised by the body


What can a deficiency of a-linoleic acid and linoleic acid lead to?

Dry scaly rash, decreased growth (children/infants), susceptibility to infection, poor wound healing

Present in variety of foods, represent omega 3 and 6 category of lipid structure


Describe the structure of phospholipids

2 FAs and P group attached to glycerol
FAs from hydrophobic tail, P and its attachment form hydrophilic head


What is meant by amphipathic?

Molecule with both hydrophobic and hydrophilic groups


Describe saturation in phospholipids

1 chain saturated, other not
Degree of saturation alters ability of molecules to pack, affects fluidity


What is the function of cholesterol?

Controls permeability of membrane
Makes membrane less flexible due to rigid steroid ring


Describe glycolipid structure

2 hydrophobic tails, hydrophilic region with 2+ sugar residues i.e. phospholipids without P


What is the function of glycolipids?

Make up 5% of outer monolayer
Sugar groups exposed on cell surface protect and modulate membrane function
Insulating agents in nerve cells (gangliosides)


Describe the structure of steroids

Lipids characterised by C skeleton of 4 fused rings


What is the role of steroids?

Cholesterol: high levels cause atherosclerosis
Hormones: testosterone, oestrogen, cortisol (synthesised from cholesterol) control metabolism, development of sexual characteristics, immune functions


What is a lipoprotein?

Biochemical assembly that contains both proteins and lipids


What is the function of lipoproteins?

Transport insoluble lipids in plasma
Non-polar lipids (triglycerides) contained in hydrophobic centre, polar lipids (phospholipids) form coat


What are apoproteins?

Protein components of lipoproteins
Interact with cellular receptors and determine the metabolic fate of lipoproteins


Explain LDL and HDL

LDLs carry FAs in blood for use by cells but also deposit on artery walls (bad)
HDLs carry LDLs away from artery walls (good)


What are some of the ways to treat hypercholesrerolemia?

Reduce intake (egg yolk, liver, oily fish)
Reduce absorption uptake - zetia, ezetro, niacin
Statins - block enzyme in synthesis of cholesterol