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[Year 2] Human Metabolism And Clinical Biochemistry > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

Which parts of the lipid are hydrophillic and hydrophobic?

A

Head of the lipid - Polar and so hydrophillic

Tail of the lipid - non polar and so hydrophobic

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2
Q

What is meant by an unsaturated and a saturated fat?

A

Saturated - no double bonds (stearic acid)

Unsaturated - Has double bond(s) (linoleic acid) has a cis double bond (if trans bond turns into a trans fat)

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3
Q

How are triglycerides formed?

A

Through dehydration synthesis, from fatty acids and glycerol

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4
Q

Why are phospholipids important?

A

They are integral to the cell membrane and lipoproteins

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5
Q

What can cholesterol be metabolised to?

A
  • Steroid hormones
  • Bile acids
  • Vitamin D
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6
Q

How are cholesterol esters formed and where are they stored?

A
  • Formed when there is an excess of cholesterol through an enzymatic reaction of cholesterols polar head turning it from a hydroxyl group to an ester group
  • Stored as cytosolic lipid droplets
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7
Q

What is the reaction needed to change cholesterol esters back to cholesterol?

A

Cholesteryl ester —-> cholesterol

  • using cholesterol esterase and water
  • as well as cholesterol it produces fatty acids
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8
Q

What are the main sources of cholesterol?

A
  • food such as eggs, meat and cheese

- the liver

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9
Q

How are lipids that are insoluble in an aqueous environment transported through the human body?

A
  • Through the macromolecular complex called a lipoprotein
  • They have an inner hydrophobic core made up of esterified cholesterol and triglyclerides
  • They have an outer hydrophillic core that consists of unesterified cholesterol (because of its OH group), phospholipids and apolipoprotein
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10
Q

What are the types of different lipoproteins?

A
  • Chylomicrons
  • Very low density lipoproteins (VLDL)
  • Low density lipoproteins (LDL)
  • High density lipoproteins (HDL)
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11
Q

What are the key facts about chylomicrons?

A
  • They are the largest type of lipoprotein
  • They form in the intestine from dietary lipids, they then enter the bloodstream
  • Their outer core consists of phospholipids, cholesterol and apolipoproteins
  • Their inner core consists of triacylglycerols and cholesteryl esters
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12
Q

What are the key facts about low density lipoproteins (LDL)?

A
  • Consists mainly of cholesterol, which it delivers to peripheral tissues
  • LDL receptors on the peripheral cells/ tissues bind to the LDL via apoprotein B100 (ApoB100)
  • The LDL is internalised and the cholesterol is released into the cell
  • This is the BAD cholesterol
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13
Q

What are the key facts about High density lipoprotein (HDL)?

A
  • HDL is the smallest lipoprotein
  • It mainly consists of apoproteins
  • HDL collects excess cholesterol from peripheral tissue and returns it to the liver
  • HDL is also produced by the liver
  • This is the GOOD cholesterol
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14
Q

What are the highest percentage composition components of each of the lipoproteins?

A
  • Chylomicron - triglycerides (98%)
  • LDL - cholesterol (60%)
  • HDL - Protein (50%)
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15
Q

What are the lipid metabolic pathways?

A

The exogenous pathway and the endogenous lipid metabolism

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16
Q

What happens during the exogenous metabolism?

A
  • liver produces bile acids and cholesterol and they are combined with the dietary lipids that then all transported to the small intestine
  • form the small intestine the chylomicrons are produced
  • the chylomicrons are then transported in the blood through the capillaries transporting different products to muscle and adipose cells
  • a chylomicron remnant emerges from the capillaries and binds back with the liver where it is metabolised
17
Q

What happens during endogenous lipid metabolism?

A
  • liver produced VLDL which travels through the capillaries and after supplying tissue with products emerges as IDL
  • IDL can bind specifically to the liver to be metabolised or it can be made into LDL
  • the LDL can then travel and bind to specific receptors on peripheral tissues or it can bind to the liver to be metabolised
18
Q

What are the functions of all the lipoproteins?

A

Chylomicrons - Transport dietary lipids to the liver and other tissues
VLDL - Gets produced by the liver and as they circulate in the tissues they give up their triacylegylcerol and become LDLs which are taken up by tissues
HDL - Transport cholesterol from the tissues back to the liver

19
Q

What is the LDL metabolism?

A
  • When the LDL docks with an LDL receptor it makes the lipoprotein-receptor complex which then undergoes endocytosis
  • Once inside the cell the LDL gets degraded and cholesterol enters the cytoplasm
  • Excessive accumulation of this cholesterol can lead to atherosclerosis
20
Q

What is the HDL metabolism?

A
  • Essential for removing excess cholesterol from cells
  • Transporter moves cholesterol from the cytosolic leaflet to the extracellular leaflet where it can diffuse into the HDL
  • Defects in the genes of the transporter causes tangier disease characterised by accumulations of cholesterol in tissues and a high risk of heart attack
21
Q

How are triglycerides digested?

A
  • They are first emulsified [The breaking down of large fat globules to small ones]
  • They then undergo enzymatic hydrolysis via lipase enzymes
22
Q

What happens during emulsification?

A
  • The fat droplet gets a ‘soapy layer’ that consists of bile salts and phosphatidyl choline (lecithin) and a pancreatic lipase starts to digest the fat droplet
  • The digestion of the fat droplet causes micelle formation (lots of smaller fat droplets)
23
Q

What are the different lipases that are involved in the enzymatic hydrolysis of lipids in the human body?

A
  • Lingual lipase
  • Gastric lipase
  • Pancreatic lipase
  • Intestinal lipase
24
Q

What is the major site of lipid digestion?

A

The small intestine

25
Q

Which lipase is the most active in the lipid metabolism?

A

Pancreatic lipase

26
Q

What does pancreatic lipase actually do?

A

It hydrolysed the fatty acids in positions 1 and 3 of the triacylglyerol producing a monoglyceride and free fatty acids

27
Q

Why are fatty acids so important to us as humans?

A
  • They can go on to produce membrane lipids that are a key part of the phospholipid bilayer of a cells membrane
  • They can also undergo Beta oxidation with the production of FADH2 and NADH to make Acetyl CoA which can then enter into the citric acid cycle, eventually producing ATP
28
Q

Where are drugs mostly metabolised?

A

In the liver

29
Q

What often happens during the drug metabolism?

A
  • Metabolism often increases the drugs polarity which facilitates its excretion via the kidneys
  • The toxicity of the drug reduces (not always though)
30
Q

Where do all of the reactions that make up the drug metabolism happen?

A

They occur in the Hepatic Microsomal Enzyme System (MES)

31
Q

What are the 2 routes a drug can take when getting metabolised by the liver?

A

It can be broken down into reactive metabolites (these can lead to the covalent modification of cellular macromolecules leading to toxicity)or stable metabolites (these just get excreted)

32
Q

What is a cytochrome P450?

A

The Cytochrome P450s are a family of enzymes containing heme as a cofactor that function as monooxgenases

33
Q

What is the role of cytochrome P450?

A
  • Helps during the synthesis of steroid hormones, cholesterol and vitamin D
  • Drug metabolism
  • Electron transport chain
34
Q

What happens if the Cytochrome P450 enzymes become inhibited?

A

There will be too much of the drug accumulating in the body that could become lethal, the drug will find it very hard to be metabolised and excreted

[Year 2] Human Metabolism And Clinical Biochemistry (7 decks)

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