A-Level Biology AQA

3.1.3 - Lipids

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Triglyceride structure

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Description and Tags

Biology

A-Level Biology

AQA

10th

14 Terms

Triglyceride structure

1 glycerol + 3 fatty acid

<p><strong>1 glycerol</strong> + <strong>3 fatty acid</strong></p>

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Fatty acid molecules

Have ‘tails’ made of hydrocarbons
Tails ‘hydrophobic’ (repel water)
- → lipids insoluble in water
All fatty acids have same basic structure, but hydrocarbon tail varies

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Basic structure of fatty acid

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What bond forms between glycerol + fatty acid?

Ester bond

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What reaction occurs during formation of triglycerides?

Condensation reaction

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Formation of triglycerides

Ester bond forms between each fatty acid and the gycerol molecule
- Each time, water molecule is released
3x condensation reactions

<ul><li><p><strong>Ester bond</strong> forms between each fatty acid and the gycerol molecule</p><ul><li><p>Each time, <strong>water </strong>molecule is <strong>released</strong></p></li></ul></li><li><p><strong>3x condensation reactions</strong></p></li></ul><p></p>

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Saturated fatty acid

No double bonds between C atoms (in hydrocarbon tail/R group)

<p><strong>No double bonds</strong> between <strong>C atoms</strong> (in <strong>hydrocarbon tail/R group</strong>)</p>

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Unsaturated fatty acid

1+ double bond between C atoms

→ causes kinks in chain

<p><strong>1+ double bond</strong> between <strong>C atoms</strong></p><p>→ causes <strong>kinks </strong>in chain</p>

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Phospholipids

Found in cell membrane
1 fatty acid replaced by phosphate group
Phosphate group hydrophilic (attracts water)

<ul><li><p>Found in<strong> cell membrane</strong></p></li><li><p>1 fatty acid replaced by<strong> phosphate group</strong></p></li><li><p>Phosphate group <strong>hydrophilic</strong> (attracts water)</p></li></ul><p></p>

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Structure + function of triglycerides

Energy storage molecules

Long hydrocarbon tails contains lots of chemical energy
- → lots of energy released when they’re broken down
- Lipids have 2x energy per gram than carbohydrates
Insoluble
- → don’t affect water potential and cause water to enter by osmosis
- Triglycerides stay together as insoluble droplets in cells
  - → fatty acid tails hydrophobic so face inwards, shielded from water

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Structure + function of phospholipids

Make up bilayer of cell membranes (which control what enters/leaves cell)

Hydrophilic heads + hydrophobic tails
- → form double layer with heads facing out towards water
Centre of bilayer hydrophobic
- → water-soluble substances can’t pass through easily
  - → membrane is barrier to those substances

<p>Make up <strong>bilayer </strong>of <strong>cell membranes </strong>(which <strong>control</strong> what <strong>enters/leaves </strong>cell)</p><ul><li><p><strong>Hydrophilic heads</strong> + <strong>hydrophobic tails</strong></p><ul><li><p>→ form <strong>double layer </strong>with heads facing <strong>out </strong>towards water</p></li></ul></li><li><p><strong>Centre </strong>of bilayer <strong>hydrophobic</strong></p><ul><li><p>→ water-soluble substances <strong>can’t </strong>pass through easily</p><ul><li><p>→ membrane is<strong> barrier</strong> to those substances</p></li></ul></li></ul></li></ul><p></p>

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Name of test for lipids

Emulsion test

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Test for lipids

Shake test substance with ethanol for 1min so it dissolves, then pour solution into water
Any lipid shows up as milky emulsion
More lipid = more noticeable milky colour