Biological Chemistry > Lipids > Flashcards

Lipids Flashcards

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1
Q

Give some examples of Lipids ?

A
  • Fully saturated stearic acid
  • Cholesterol
  • Sphingolipids: 3 different fatty acids attached to ceramide backbone
  • Glycerolphospholipids: 3 different fatty acids attached to glycerol backbone
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2
Q

Explain the main biological functions of lipids ?

A
  1. Storage of energy
    - reduced compounds: lots of available energy
    - hydrophobic nature: good packing
  2. Insulation from environment
    - low thermal conductivity
    - high heat capacity (can “absorb” heat)
    - mechanical protection (can absorb shocks)
  3. Water repellant
    - hydrophobic nature: keeps surface of the organism dry
    - prevents excessive wetting (birds)
    - prevents loss of water via evaporation
  4. Buoyancy control and acoustics in marine mammals
    - increased density while diving deep helps sinking (just a hypothesis)
    - spermaceti organ may focus sound energy: sound stun gun?
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3
Q

Explain some more of the main biological functions of lipids ?

A
  1. Membrane structure
    - main structure of cell membranes & anchors for membrane proteins
  2. Cofactors for enzymes
    - vitamin K: blood clot formation
    - coenzyme Q: ATP synthesis in mitochondria
  3. Signalling molecules
    - paracrine hormones (act locally)
    - steroid hormones (act body-wide)
    - growth factors
    - vitamins A and D (hormone precursors)
  4. Pigments
    - colour of tomatoes, carrots, pumpkins, some birds
  5. Antioxidants
    - Vitamin E
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4
Q

Lipids that contain fatty acids (complex lipids). Give examples of kinds of lipids ?

A

Storage lipids: Triacylglycerols

Membrane lipids: Phospholipids & Glycolipids

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5
Q

Name some derived Lipids that do not contain fatty acids ?

A

Cholesterol, vitamins, pigments

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6
Q

Classification of Lipids ?

A
  1. Membrane lipids e.g. Fatty Acids – hydrocarbon chain (4-36 carbons) with carboxylic acid group: can be branched/unbranched, saturated, mono/polyunsaturated. E.g. membrane lipids

Complex/storage lipids (contain fatty acids):

  1. Triglycerides & Waxes: simple lipids from fatty acids esterified with alcohol
  2. Phospholipids (Sphingolipids & glycolipids): compound lipids from fatty acids esterified with alcohol & additional groups
  3. Derived Lipids (do not contain fatty acids): derived by hydrolysis e.g. cholesterol, vitamins, pigments.
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7
Q

In a fatty acid, the carboxyl group behaves as ?

A

As an acid, is hydrophilic and chemically active

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8
Q

Long hydrocarbon chain is ?

A

Hydrophobic & not very reactive

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9
Q

The commonest fatty acids in mammalian metabolism are:

A 
Palmitic (16:0) (26% of human fat) 
Stearic acid (18:0) (45% of human fat)
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10
Q

Almost all natural fatty acids have ?

A

An even number of carbons

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11
Q

What is the general formula?

A

General formula CH3(CH2)nCOOH, where n is usually an even number of length 14 - 24 carbon atoms

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12
Q

Most natural fatty acids ?

A

They are unbranched

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13
Q

Long hydrocarbon chain may be ?

A

Saturated or unsaturated & terminates in a carboxyl group (1COOH)

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14
Q

Properties of Saturated Fatty Acids ?

A
  • Contain only single C–C bonds
  • Closely packed
  • Strong attractions between chains
  • High melting points
  • Solids at room temperature
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15
Q

Properties of Unsaturated Fatty Acids ?

A
  • Contain one or more double C=C bonds
  • Nonlinear chains do not allow molecules to pack closely
  • Few interactions between chains
  • Low melting points
  • Liquids at room temperature
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16
Q

Give examples of a saturated and unsaturated fatty acid ?

A

Stearic Acid – A Saturated Fatty acid

Oleic Acid – Unsaturated Fatty acid (monosaturated omega 9 fatty acid)

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17
Q

Cis-double bond restricts ?

A

Rotation & introduces a rigid bend in hydrocarbon tail

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18
Q

What is the omega end and the alpha end ?

A

Omega end = methyl group

Alpha end = carboxyl group

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19
Q

Fatty acids are found in ?

A

Cell membranes where tightness of packing their hydrocarbon chains affects fluidity (not flexibility) of membrane

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20
Q

Saturated hydrocarbon chains pack ?

A

Tightly together in membranes stabilised by van der Waals. Structurally a zig-zag configuration. C-C bond forms 109° bond angle with free rotation

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21
Q

Unsaturated hydrocarbon chains (e.g. oleic) have ?

A

1+ double bonds along their length creating rigid kinks, impairing ability to pack

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22
Q

Explain simple short hand nomenclature ?

A
  • specifies carbon chain length (4-36)

- number of double bonds in chain separated by a colon

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23
Q

What is delta numbering ?

A

Delta numbering position of the double bond(s) D in relation to carbonyl group

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24
Q

What is Omega numbering ?

A

Omega numbering position of double bond(s) w in relation to terminal methyl

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25
C18:1 (Δ9) = oleic acid, an omega 9 fatty acid. What is the full name ?
Full name: Cis-9-Octadecenoic acid
26
How do you number Polyunsaturated fatty acids ?
Carbons are numbered in opposite direction, assigning 1 to the methyl carbon designated
27
The double bonds are susceptible to ?
The double bonds are very susceptible to PEROXIDATION to form hydroperoxides [ ROOH ] - these can oxidise membrane proteins
28
What combats this process of peroxidation ?
Antioxidants, such as the vitamins C and E, Q10 (ubiquinone) and glutathione (GSH)
29
Omega 3 & omega 6 act as?
Competing substrates for the same enzyme
30
Mammals cannot synthesise so ?
Must obtain from diet
31
What is the Optimal ratio of omega-6:omega-3 ?
It is between is between 1:1 and 1:4
32
Presence of double bond in FAs prevents ?
Free rotation & creates two configurations
33
Double bonds in natural unsaturated fatty acids are?
They are commonly in cis configuration, which kinks the chain
34
Explain cis configuration ?
If hydrogen atoms attached to the carbon atoms of a double bond are positioned on the same side of the double bond
35
Explain trans configuration ?
If hydrogen atoms attached to the carbon atoms of a double bond are positioned on a different side of the double bond
36
Trans fatty acids are rare?
From hydrogenated fats
37
Branched chain fatty acids (BCFA) are usually ?
Saturated fatty acids with 1+ methyl branches on the carbon chain
38
BCFAs are mostly found ?
In bacteria
39
BCFAs are found in the ?
In the vernix caseosa of human infants & play a role in fostering the development of the human intestinal microbiota
40
Lanolin is another example of?
An animal material containing BCFA
41
Solubility & melting points are largely determined by ?
The length & degree of unsaturation
42
Longer FA with few double bonds =
Low solubility
43
Unsaturated cis fatty acids have ?
A lower melting point
44
Saturated FA are ?
Waxy and stable (higher melting point)
45
Solubility decreases as ?
The chain length increases
46
Melting point decreases as ?
- decreases as the chain length decreases | - decreases as the number of double bonds increases
47
Catabolism (breakdown) of fatty acids (generate energy) by ? produces ? and where ?
Beta Oxidation. - produces acetyl-CoA - produces reducing power (NADH, FADH2) takes place in the mitochondria
48
Anabolism (synthesis) of fatty acids (create biologically important molecules e.g. triglycerides, phospholipids, hormones, ketones) synthesised by ? requires ? and where ?
- Synthesised by acetyl-CoA and malonyl-CoA - requires reducing power from NADPH - takes place in cytosol in animals, chloroplast in plants
49
Fatty acids are built in several passes, processing ?
One acetate unit at a time
50
Explain fatty acid synthesis ?
- Fatty acid synthesis is the creation of fatty acids from Acetyl-CoA and NADPH - Each acetate is coming from activated malonate (malonyl-CoA) - Overall goal is to attached acetate from Malonyl-CoA to growing chain & then reduce it
51
Where does Fatty acid synthesis occur ?
Fatty acid synthesis occurs in cell compartments where NADPH levels are high e.g. cytosol in vertebrates, or in plants the chloroplast
52
Sources of NADPH are ?
Either pentose phosphate pathway or malic enzyme, or in plants via photosynthesis
53
Beta oxidation is the catabolic process by ?
Which fatty acids are broken down in the mitochondria to acetyl CoA with the release of energy (ATP) dissipating CO2 & H2O
54
Once inside the cell, CoA ligase catalyses the reaction between ?
A fatty acid molecule with ATP to give a fatty acyl-CoA molecule which enters the citric acid cycle of each turn of the cycle
55
What kind of structure do Phospholipids have ?
Phospholipids* have an amphipathic structure: polar, hydrophilic head & two non-polar, hydrophobic tails§
56
How can the various forms of Phospholipids be diversified ?
Diversification via: - modifying backbone - changing fatty acids - modifying head groups Different organisms & tissues have different membrane lipid compositions
57
What are the three components of phospholipid ?
A) Phosphorylated head group B) Three carbon glycerol backbone C) Two hydrocarbon fatty acid chains
58
Similar in structure to TAGs except ?
One of the alcohols of glycerol is esterified by phosphate instead of a fatty acid (= phosphatidic acid PA)
59
The phosphate group can then be esterified by ?
A second alcohol to form phosphoacylglycerol
60
The phospholipids comprise two groups based upon a backbone of ?
Glycerol or Sphingosine
61
The phosphate group in both structures are ?
The phosphate group is charged at physiological pH
Biological Chemistry
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