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Semester 1 > Metabolism S5 - Lipid transport and by-products of energy production > Flashcards

Metabolism S5 - Lipid transport and by-products of energy production Flashcards

1
Q

Why are lipids associated with proteins in the blood?

A

They are insoluble in water

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2
Q

What are the two methods of lipid transport in the blood?

A

Lipoproteins or albumin (less than 2%)

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3
Q

Lipoprotein disorders are associated with what main clinically important disease?

A

Atherosclerosis

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4
Q

What is the general structure of lipoproteins?

A

Hydrophilic surface coat - apoproteins, cholesterol and phospholipids

Hydrophobic core - TAGs, Cholesterol esters

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5
Q

How is the structure of lipoproteins maintained?

A

LCAT convert cholesterol to cholesterol esters when core is removed to maintain shape

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6
Q

What structural role do apoproteins play?

A
  • Involved in packaging non-water soluble lipids into soluble form
  • This is possible as they contain a hydrophobic region that interacts with the lipid molecule and hydrophilic region that interacts with water
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7
Q

What functional role do apoproteins play?

A
  • May be involved in activation of enzymes
  • Recognition of cell surface receptors
  • Transport of lipids
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8
Q

What do chylomicrons transport and to which destination?

A

TAGs

Intestine to adipose tissue

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9
Q

What do VLDLs transport and to which destination?

A

TAGs

Liver to adipose tissue

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10
Q

What do LDLs transport and to which destination?

A

Cholesterol

Liver to tissue

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11
Q

What do HDLs transport and to which destination?

A

Cholesterol

Tissues to the liver

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12
Q

All cells (except red blood cells) are able to synthesise _______ from acetyl CoA and could satisfy their requirements by biosynthesis. In practice, all cells appear to prefer the uptake of ________ ________ circulating in plasma _________

A

Cholesterol

Pre-formed cholesterol

Lipoproteins

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13
Q

Tissues obtain the _______ they need from LDLs by the process of _______ ________ _______. LDL particles are taken up by the cell and the cholesterol released inside the cell

A

Cholesterol

Receptor mediated endocytosis

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14
Q

Outline receptor mediated endocytosis of cholesterol

A
  • Cells requiring cholesterol synthesise LDL receptors that are exposed on the cell surface
  • These receptors recognise and bind specific apoproteins (Apo B100) on the surface of the LDL
  • The LDL receptor with its bound LDL is then endocytose by the cell and subjected to lysosomal digestion
  • Cholesterol can be stored (as cholesterol esters) or used by the cell
  • This also inhibits the synthesis of cholesterol by the cell and reduces the synthesis and exposure of LDL receptors.
  • This prevents the cell from accumulating too much cholesterol
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15
Q

Describe Type III hyperlipoproteinaemia

A
  • Raised LDL and chylomicron remnants
  • Associated with coronary artery disease
  • Caused by defective apoprotein E
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16
Q

Describe Type IV hyperlipoproteinaemia

A
  • Raised VLDLs
  • Associated with coronary artery disease
  • Defect unknown
17
Q

Describe Type V hyperlipoproteinaemia

A
  • Raised chylomicrons and VLDL in fasting plasma
  • Associated with coronary heart disease
  • Defect unknown
18
Q

What type hyperlipoproteinaemia is familial cholesterolaemia

A

IIa

19
Q

List some treatments for hyperlipoproteinaemia

A
  • Reduce cholesterol and TAGs in the diet
  • Statins: inhibits HMG-CoA reductase to prevent cholesterol synthesis from acetyl-CoA
  • Bile Salt sequestrants: lower cholesterol by increasing its disposal from the body. They bind to the GI tract preventing them from being reabsorbed into the hepatic-portal circulation and promoting their loss in faeces
20
Q

Describe two mechanisms by which tissues can obtain lipids from lipoproteins

A

1) Lipoprotein lipase - Removes core TAGs from lipoproteins to produce fatty acids and glycerol, found attached to inner surface of capillaries in adipose tissue
2) Receptor mediated endocytosis - LDL binds to LDL receptors on surface membrane and complex is taken up in cell

21
Q

How are superoxide radicals produced in the cell?

A

0.1-2% of electrons are leaked from the electron transport chain before they reach the end of the chain and prematurely reduce oxygen in the mitochondria

22
Q

List 3 reactive oxygen species

A

1) Hydroxyl radical
2) Nitric oxide
3) Peroxynitrite (formed from nitric oxide and oxygen reacting together

23
Q

Which ROS has an important role in inflammation/

A

Peroxynitrite

24
Q

Outline cellular defences against ROS

A
  • Superoxide dismutase + catalase
  • NADPH and glutathione
  • Antioxidant vitamins
  • Flavonoids and vitamins
25
Q

How is superoxide dismutase used as a cellular defence against ROS?

A
  • SOD catalyses the reaction of superoxide radicals together to form water + hydrogen peroxide
  • However hydrogen peroxide os a ROS
  • Catalase rapidly breaks hydrogen peroxide down to water and oxygen
26
Q

The reaction of unsaturated lipids with ROS forms ______ ______. This damage to cell membranes is thought to be involved in the early stage of cardiovascular disease.

A

lipid peroxides

27
Q

What is hyperlipoproteinaemia?

A

Any condition in which, after a 12 hour fast, the plasma cholesterol and/or plasma triglycerides are raised

28
Q

List signs or symptoms of very high blood cholesterol

A
  • Corneal arcus
  • Xanthelasma and/or tendon xanthoma
  • Accelerated development of atherosclerotic diseases
29
Q

Outline two pathways by which tissues can obtain the cholesterol they need

A

1) Direct synthesis of cholesterol from acetyl CoA within tissues
2) Receptor mediated endocytosis of LDL particles

30
Q

What cells are capable of oxidative burst?

A

Neutrophils and monocytes

31
Q

Name two enzymes involved in defences against ROS

A

Superoxide dismutase

Catalase

32
Q

What is oxidative stress?

A
  • Occurs when the production of ROS is excessive and anti-oxidant levels are low
  • Underlies pathology of atherosclerosis, Parkinson’s and Alzheimers’s
33
Q

What are the potential problems of a low-fat diet?

A

Need fats for cellular components such as lipid membranes as well as signalling molecules

34
Q

Name two anti-oxidant vitamnins

A

Vitamin E

Vitamin C

35
Q

Briefly explain how a respiratory burst is produced by monocytes and neutrophils

A
  • Produced by a membrane-bound enzyme complex termed NADPH oxidase
  • It transfers electrons from NADPH across the membrane to couple these to molecular oxygen to generate superoxide radicals

Semester 1 (37 decks)

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