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Molecular biochemistry > Lipids > Flashcards

Lipids Flashcards

1
Q

What is a lipid?

A

A biomolecule that is soluble in nonpolar solvents

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2
Q

What is a fatty acid?

A

Monocarboxylic acid with long unbranched hydrocarbon chain

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3
Q

Most animal fatty acids have … numbers of carbon atoms

A

Even

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4
Q

What are fats?

A

Triglycerides: 3FA chains esterified to one glycerol molecule

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5
Q

What are sources of fatty acid?

A

Diet: triglycerides absorbed across intestinal epithelium and transported in blood by chylomicrons to liver and adipose tissue (hydrolysed to free fatty acids)

De Novo synthesis in liver: carried by VLDL to other tissue (often stored in adipose)

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6
Q

How is digested FA carried to liver?

A

Chylomicrons

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7
Q

How are newly synthesised FA carried from the liver to tissue?

A

VLDL

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8
Q

What are essential fatty acids, why are they essential?

A

Linoleic and Linolenic acid (can’t be made in the body)

Body can’t introduce C=C beyond C9

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9
Q

What is the structure of a phospholipid, how is it made?

A

Diacylglycerol molecule (2 FA, one glycerol via ester linkages)

Headgroup attached to 3rd position via phosphodiester bond and an alcohol

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10
Q

How many water molecules to make a phospholipid?

A

4

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11
Q

What are the roles of phospholipid?

A

Component of cell membrane lipid bilayer

Component of pulmonary surfactant (maintain lung structure)

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12
Q

What are different classes of phospholipid, how do they arise?

A

Dictated by their head group:

No head group apart from glycerol –> phosphatidylglycerol

Serine head group –> phosphatidylserine

Ethanolamine head group –> phosphatidylethonalamine

Choline –> phosphatidylcholine

Inositol –> phosphpatidylinositol (forms PIP2)

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13
Q

What is the name of a phospholipid with Serine head group?

A

Phosphatidylserine

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14
Q

What is the name of a phospholipid with no head group apart from glycerol?

A

Phosphatidylglycerol

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15
Q

What is the name of a phospholipid with choline head group?

A

Phosphatidylcholine

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16
Q

What is the name of a phospholipid with Inositol head group?

A

Phosphpatidylinositol (forms PIP2)

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17
Q

What is structure of cholesterol what’s it made from?

A

27C 4 ring, acetyl CoA

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18
Q

What are the roles of cholesterol (5)?

A

Component of plasma membrane - decrease fluidity

Precursor of steroid hormones

Precursor of bile salts

Precursor of vitamin D

Component of lipoproteins (e.g. Chylomicrons, VLDL, HDL)

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19
Q

What do lipoproteins do?

A

Transport triglycerides and cholesterol in blood between tissues of body

20
Q

Why is LDL considered bad?

A

Depositis cholesterol in plaques which can block blood vessels

21
Q

What are the roles of lipids (3)?

A

1) Energy source: higher specific energy than glycogen or protein, lower hydration level than glycogen
2) Structural role (1:component of bilayer membrane e.g. phospholipids, 2: stabilise fat water interfaces)
3) Signalling molecule (extracellular: steroid hormones and eicosanoids e.g. prostaglandis) (Intracellular: second messengers from PIP2 breakdown e.g. IP3 and DAG)

22
Q

How do lipids stabilise water fat interfaces?

A

Bile salts in intestine emulsify dietary lipids

Pulmonary surfactant (mixture of phospholipid and protein) reduce surface tension at interface of alveolar lining fluid and air in lung - prevent alveolar collapse

23
Q

Describe role of cholesterol in membrane?

A

Inserts into hydrophobic portion so sterically inhibit fatty acyl chains movement so membrane less fluid

24
Q

Describe structure of plasma membrane bilayer in terms of phospholipids , what’s the significance of the tails?

A

Polar headgroups facing aqueous environment

Hydrophobic tails point inwards - diffusion barrier to prevent ions/hydrophilic molecules crossing

25
Q

What carbon is the alpha carbon on a fatty acid?

A

The carbon next to the carboxyl group is labeled as carbon alpha

26
Q

What carbon is the beta carbon on a fatty acid?

A

The carbon 2 away from the carboxyl, next to alpha

27
Q

What carbon is the omega carbon on a fatty acid?

A

The last carbon in the FA, most distant from alpha

28
Q

How can middle carbons/ double bonds in the chain be named?

A

omega - X

where X is the number of places away from omega

29
Q

Why are omega 3 FA named as such?

A

Last double bond in the chain is 3 positions away from the omega carbon.

30
Q

How can ester bonds be hydrolysed, what is produced?

A

The addition of NaOH or KOH, producing glycerol and 3 Na+/K+ fatty acid salts which is soap.

31
Q

How are phospholipids degraded?

A

Specific phospholipase enzyme.

Phospholipases A1 & A2 remove acyl fatty acid chains (turnover)

Phospholipase C removes phosphorylated head group (e.g changes PIP2 into inositol phosphate IP3)

32
Q

What makes sphingolipids structurally different?

A

Contain the C-18 amino alcohol called sphingosine (rather than glycerol).

This amide group is attached via an amide linkage to the C2 carbon.

33
Q

How is sphingosine attached to the FA chain? Which carbon?

A

Attached via an amide linkage to the C2 carbon.

34
Q

Is cholesterol polar or non-polar, what determines this?

A

Non-polar

The hydroxyl group is esterified in cholesterol esters, leading to a highly non-polar structure.

35
Q

Part of large complexes by which triglycerides and phospholipids are transported around the body.

A

Apolipoproteins

Proteins that bind lipids (oil-soluble substances such as fat and cholesterol) to form lipoproteins

36
Q

Are FA amphiphilic?

A

Yes

37
Q

Do FA have detergent like properties?

A

yes

38
Q

Which particles acquire cholesterol from peripheral cells (reverse transport of cholesterol)?

A

HDL

39
Q

What is an essential enzyme for cholesterol synthesis?

A

HMG-CoA reductase is important in the synthesis of cholesterol

40
Q

How do statins work?

A

Inhibit HMG-CoA reductase

41
Q

In phospholipids unsaturated FA tails, what conformation are the double bonds usually in?

A

Cis (for packing)

42
Q

Is cholesterol planar?

A

Yes

43
Q

An example of a glycolipid is…

A

Ganglioside

44
Q

Fatty acids in triacylglycerols (triglycerides) stored in adipose tissue are

A

Always saturated

45
Q

In glycerol phospholipids…

A

Fatty acids at position 2 are usually unsaturated

46
Q

What is specific about the fatty acids in glycerol phospholipids?

A

The ones at position 2 are usually unsaturated

Molecular biochemistry (5 decks)

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