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12-03: Lipids 

Lipids

  • Made of mostly Carbon and Hydrogen with a few Oxygen

    • Though they are the same elements as carbohydrates, they’re different because there are way fewer Oxygens - there is no more 1:2:1 ratio customary of carbohydrates

    • Primarily composed of non polar bonds formed between C and H

  • Hydrophobic molecules: they repel/”hate” water

    • Few polar O-H bond and more non polar C-H bonds (which share electrons equally)

    • The more C-H bonds they have, the more non polar they are

  • Used for long term energy storage, membranes, and dissolving of fat soluble vitamins (ADEK)

    Four groups:

    1. Fats

    2. Phospholipids

    3. Steroids

    4. Waxes

Fats

  • Also known as triglycerides (or triacylglycerols)

  • Made up of 1 glycerol molecule and 3 fatty acids chains

  • Lots of chemical potential energy stored in these bonds – 38 kJ/g (9cal/g)

    • More than twice the energy of carbohydrates

  • Excess (any kind of food but namely carbohydrate) consumption is converted into fat though the body can store some in glycogen

Glycerol

  • Component of triglycerides

  • Also called glycerine

  • 3 carbon molecule with 3 hydroxyls

    • It is a polyol or sugar alcohol

Fatty Acids

  • Long chains of carbons bonded to hydrogens with a carboxyl group at one end

    • Usually start counting carbons from the carboxyl end

    • Longer chains are less soluble

  • Usually even numbered, usually 16 or 18 carbons in length (with some exceptions)

Note: fat ≠ fatty acid

We can draw fatty acids in 3 ways

  1. Structural

  1. Condensed

  1. Skeletal - Line angle diagram

    The tip counts as a Carbon - every angle indicates a Carbon attached to 2 Hydrogens as seen in the structural disagram

Saturated Fatty Acids

  • Has no C=C double bonds between Carbons – there are as many Hydrogens bonded to Carbons as possible

  • Animal fats (e.g. butter made from animal (cow) milk) - higher proportion of of saturated fatty acids in their triglycerides

  • Solids at room temperature: the fatty acids can pack tighter together which makes them denser

    • When we have fats that have a high proportion of saturated fatty acids, they are linear and can pack more tightly close together and can therefore maintain a fixed shape

    • They have higher melting points

Structure of a saturated fatty acid:

Unsaturated Fatty Acids

  • Has at least 1 C=C double bond

  • Plant oils - higher proportion of unsaturated fatty acids in their triglycerides

  • Liquid at room temperature: the fatty acids are bent (at the C=C bonds) and therefore cannot pack very tightly, making them less dense

  • Can be monounsaturated (1 Carbon double bond) or polyunsaturated (more than 1 Carbon double bond)

Structure of an unsaturated fatty acid

Monounsaturated

Hydrogenation

  • Hydrogenation: the process that turns plant oils into semi solids (e.g. margarine or vegetable shortening)

    • Decrease the number of C=C bonds

  • They add hydrogen to the unsaturated fatty acids to partially saturate them. They don’t do this to all of the C=C bonds, but enough for it to become a semi-solid

  • Used to improve the shelf-life and appearance of foods

  • The product doesn’t finish off being fully saturated – there aren’t enough H’s added to fully saturate the product, it becomes partially saturated

Trans fats

  • Side effect of hydrogenation

  • H’s placement creates a trans fat when it is on the opposite side

    • Hydrogen bonds on opposite sides of the chain of C=C bonds

  • Cis fats have both H’s on the same side

Putting it all together – triglycerides

  • Fats: triglycerides that are made of glycerol and 3 fatty acids linked by ester bonds to 1 glycerol molecule

    Dehydration Synthesis:

  • 3 waters produced because we have 3 linkages (and water is a product in dehydration synthesis which causes these linkages)

  • These are all saturated fatty acids in the triglyceride molecule formed above – they can be any kind of fatty acids and can also be a mix of different fatty acids

  • Fatty acid chains can be all the same, all different, or any combination

    • Be sure to draw them in the same format/represent them in the same way

  • Triglycerides are non polar

Phospholipids

  • These are in cell membranes – phospholipid bilayer

  • Phospholipids: similar to triglycerides, however 1 of the fatty acids is replaced with a phosphate group and a choline group

Phospholipid layers

  • Since it has a polar head and non polar tail, one end is hydrophilic (loves water): the heads and one end is hydrophobic (hates water): the tails

  • Heads are polar so they will be attracted to the water - tails will orient themselves with the oil to get away from the water

    They make up most of the cell membrane 2 fatty acids (hydrophobic), glycerol, phosphate and choline (which are charged and therefore they're hydrophilic)

Liposome - 2 layers of phospholipids because there's an aqueous environment on interior & exterior which therefore attracts the heads

This is a bilayer sheet - the building blocks of the liposome


Micelle - single layer of phospholipids - tails on the inside and heads on the outside

  • Makes the soap bubbles or micellar water

    • Micelles in the water (little bubbles in solution)

    • Putting on the cotton swab - opens the micelle and then the tails face outwards and attract grease/makeup - heads are all attracted to the cotton


Steroids (Sterols)

  • Steroids: made of 4 fused hydrocarbons rings with a variety of side chain functional groups

    • Group of lipid molecules

Basic structure

Examples:

  • Cholesterol – needed for cell membranes

  • Sex hormones – estrogen and testosterone, secreted to do something, chemical messengers

Waxes

  • Waxes: fatty acids linked to alcohols (ester)

    • Fatty acids have carboxyl, alcohols have hydroxyl

  • Large molecules, no lipids form polymers

  • Examples

    • Cutin: water resistant covering made by epidermal cells of plants, conserves water and is a barrier against infection for the plants

      • Evergreen trees/pine trees – waxes around pine needles to thrive through the winter (evergreens do photosynthesis through the winter because they have enough water, water gets in through the roots)

    • Beeswax: structure for beehives

    • Earwax: a water repellent that protects the delicate ears

Where do lipids come from?

  • Made by the smooth endoplasmic reticulum within the cell

  • Able to protect the lipids from the cytoplasmic environment (filled with water)

  • It will then package the lipids into vesicles to be shipped to where they are needed in & out of the cell

Lipids

  • Made of mostly Carbon and Hydrogen with a few Oxygen

    • Though they are the same elements as carbohydrates, they’re different because there are way fewer Oxygens - there is no more 1:2:1 ratio customary of carbohydrates

    • Primarily composed of non polar bonds formed between C and H

  • Hydrophobic molecules: they repel/”hate” water

    • Few polar O-H bond and more non polar C-H bonds (which share electrons equally)

    • The more C-H bonds they have, the more non polar they are

  • Used for long term energy storage, membranes, and dissolving of fat soluble vitamins (ADEK)

    Four groups:

    1. Fats

    2. Phospholipids

    3. Steroids

    4. Waxes

Fats

  • Also known as triglycerides (or triacylglycerols)

  • Made up of 1 glycerol molecule and 3 fatty acids chains

  • Lots of chemical potential energy stored in these bonds – 38 kJ/g (9cal/g)

    • More than twice the energy of carbohydrates

  • Excess (any kind of food but namely carbohydrate) consumption is converted into fat though the body can store some in glycogen

Glycerol

  • Component of triglycerides

  • Also called glycerine

  • 3 carbon molecule with 3 hydroxyls

    • It is a polyol or sugar alcohol

Fatty Acids

  • Long chains of carbons bonded to hydrogens with a carboxyl group at one end

    • Usually start counting carbons from the carboxyl end

    • Longer chains are less soluble

  • Usually even numbered, usually 16 or 18 carbons in length (with some exceptions)

Note: fat ≠ fatty acid

We can draw fatty acids in 3 ways

  1. Structural

  1. Condensed

  1. Skeletal - Line angle diagram

    The tip counts as a Carbon - every angle indicates a Carbon attached to 2 Hydrogens as seen in the structural disagram

Saturated Fatty Acids

  • Has no C=C double bonds between Carbons – there are as many Hydrogens bonded to Carbons as possible

  • Animal fats (e.g. butter made from animal (cow) milk) - higher proportion of of saturated fatty acids in their triglycerides

  • Solids at room temperature: the fatty acids can pack tighter together which makes them denser

    • When we have fats that have a high proportion of saturated fatty acids, they are linear and can pack more tightly close together and can therefore maintain a fixed shape

    • They have higher melting points

Structure of a saturated fatty acid:

Unsaturated Fatty Acids

  • Has at least 1 C=C double bond

  • Plant oils - higher proportion of unsaturated fatty acids in their triglycerides

  • Liquid at room temperature: the fatty acids are bent (at the C=C bonds) and therefore cannot pack very tightly, making them less dense

  • Can be monounsaturated (1 Carbon double bond) or polyunsaturated (more than 1 Carbon double bond)

Structure of an unsaturated fatty acid

Monounsaturated

Hydrogenation

  • Hydrogenation: the process that turns plant oils into semi solids (e.g. margarine or vegetable shortening)

    • Decrease the number of C=C bonds

  • They add hydrogen to the unsaturated fatty acids to partially saturate them. They don’t do this to all of the C=C bonds, but enough for it to become a semi-solid

  • Used to improve the shelf-life and appearance of foods

  • The product doesn’t finish off being fully saturated – there aren’t enough H’s added to fully saturate the product, it becomes partially saturated

Trans fats

  • Side effect of hydrogenation

  • H’s placement creates a trans fat when it is on the opposite side

    • Hydrogen bonds on opposite sides of the chain of C=C bonds

  • Cis fats have both H’s on the same side

Putting it all together – triglycerides

  • Fats: triglycerides that are made of glycerol and 3 fatty acids linked by ester bonds to 1 glycerol molecule

    Dehydration Synthesis:

  • 3 waters produced because we have 3 linkages (and water is a product in dehydration synthesis which causes these linkages)

  • These are all saturated fatty acids in the triglyceride molecule formed above – they can be any kind of fatty acids and can also be a mix of different fatty acids

  • Fatty acid chains can be all the same, all different, or any combination

    • Be sure to draw them in the same format/represent them in the same way

  • Triglycerides are non polar

Phospholipids

  • These are in cell membranes – phospholipid bilayer

  • Phospholipids: similar to triglycerides, however 1 of the fatty acids is replaced with a phosphate group and a choline group

Phospholipid layers

  • Since it has a polar head and non polar tail, one end is hydrophilic (loves water): the heads and one end is hydrophobic (hates water): the tails

  • Heads are polar so they will be attracted to the water - tails will orient themselves with the oil to get away from the water

    They make up most of the cell membrane 2 fatty acids (hydrophobic), glycerol, phosphate and choline (which are charged and therefore they're hydrophilic)

Liposome - 2 layers of phospholipids because there's an aqueous environment on interior & exterior which therefore attracts the heads

This is a bilayer sheet - the building blocks of the liposome


Micelle - single layer of phospholipids - tails on the inside and heads on the outside

  • Makes the soap bubbles or micellar water

    • Micelles in the water (little bubbles in solution)

    • Putting on the cotton swab - opens the micelle and then the tails face outwards and attract grease/makeup - heads are all attracted to the cotton


Steroids (Sterols)

  • Steroids: made of 4 fused hydrocarbons rings with a variety of side chain functional groups

    • Group of lipid molecules

Basic structure

Examples:

  • Cholesterol – needed for cell membranes

  • Sex hormones – estrogen and testosterone, secreted to do something, chemical messengers

Waxes

  • Waxes: fatty acids linked to alcohols (ester)

    • Fatty acids have carboxyl, alcohols have hydroxyl

  • Large molecules, no lipids form polymers

  • Examples

    • Cutin: water resistant covering made by epidermal cells of plants, conserves water and is a barrier against infection for the plants

      • Evergreen trees/pine trees – waxes around pine needles to thrive through the winter (evergreens do photosynthesis through the winter because they have enough water, water gets in through the roots)

    • Beeswax: structure for beehives

    • Earwax: a water repellent that protects the delicate ears

Where do lipids come from?

  • Made by the smooth endoplasmic reticulum within the cell

  • Able to protect the lipids from the cytoplasmic environment (filled with water)

  • It will then package the lipids into vesicles to be shipped to where they are needed in & out of the cell