3.5 Lipids

What are lipids known as?

fats and oils

What elements are lipids made out of?

carbon, hydrogen and oxygen

Lipids that are solid at room temperature?

fats

Lipids that are liquid at room temperature?

oils

3 different types of lipid?

triglycerides, phospholipids and cholesterol

Why are all lipids non-polar molecules?

the electrons in the outer orbital that form bonds are more evenly distributed than in polar molecules

What do lipids being non-polar mean about their charge?

there are no positive or negative areas within the molecule

Why are all lipids non-soluble in water?

they are hydrophobic (due to being non-polar)

hydrophobic?

repel water molecules

What type of molecule are lipids?

macromolecules

What are macromolecules?

large complex molecules

What are macromolecules built from?

repeating units, or known as monomers

Triglycerides: what elements are they made out of?

Carbon, hydrogen, oxygen

Triglycerides: what are they made from combining?

one glycerol molecule with three fatty acids

Triglycerides: What group of molecules is glycerol a member of?

alcohols

Triglycerides: What group of molecules do fatty acids belong to?

carboxylic acids

Triglycerides: Fatty acid structure?

a carboxyl group with a hydrocarbon chain attached

Triglycerides: carboxyl group chemical formula?

–COOH

What do the molecules glycerol and fatty acids contain?

hydroxyl (OH) groups

What molecules do these hydroxyl groups interacting form?

three water molecules

What bonds do these hydroxyl groups interacting form?

ester bonds

What are bonds ester bonds?

bonds between the fatty acids and the glycerol molecule

What is the reaction that forms ester bonds called?

Esterification

What type of reaction is esterification an example of?

condensation reaction (produces 3 water molecules)

How are triglycerides synthesised?

by the formation of the ester bond between each fatty acid and the glycerol molecule

diagram of triglyceride?

…

How many water molecules are produced during esterification (and diagram of process)?

3

How do you break down triglycerides/each ester bond?

three water molecules need to be added to reverse the reaction that formed the triglyceride

What is this reaction an example of?

a hydrolysis reaction

What are the two types of fatty acids?

Saturated and unsaturated.

What are saturated fatty acids?

no double bonds present between their carbon atoms

Why are these fatty acids called 'saturated'?

Because the carbon atoms form the maximum number of bonds with the hydrogen atoms (they are saturated with hydrogen atoms)

What are unsaturated fatty acids?

Fatty acids with at least one double bonds between carbon atoms

Monosaturated?

just one double bond

Polysaturated?

two or more double bonds

What does the presence of double bonds cause the molecule to do?

kink or bend

Diagram of a saturated hydrocarbon chain?

…

Diagram of an unsaturated hydrocarbon chain?

…

What does the kink or bends caused by double bonds make saturated fatty acids unable to do?

can't pack so closely together

What do unsaturated fatty acids not being able to pack so closely together cause their state to be at room temperature?

liquid (not solids) - therefore described as oil at room temp rather than fats

What type of triglycerides do plants contain?

unsaturated triglycerides

What do these unsaturated triglycerides normally occur as in plants?

oils

Which type of triglyceride tends to be more healthy?

unsaturated (oils) are more healthy than saturated (solid - fats)

What does some evidence show an excess of saturated fats can lead to (however evidence remains inconclusive)?

coronary heart disease

What does an excess of any type of fat lead to?

obesity - also puts a strain on the heart

What are phospholipids?

modified triglycerides

What elements do phospholipids contain?

phosphorus as well as carbon, hydrogen and oxygen

Where are phospholipids found?

cell membranes (eukaryotes and prokaryotes)

What is one of the fatty acid chains replaced with in a triglyceride to make a phospholipid?

a phosphate group (meaning there are only 2 fatty acid chains in a phospholipid)

What makes phosphate ions soluble in water?

they have extra electrons - negatively charged

Phospholipid structure diagram?

…

What part of the phospholipid are the fatty acid chains?

non-polar tails

What part of the phospholipid is the phosphate group?

the charged heads

Hydrophobic?

repelled by water

Hydrophilic?

will interact with and are attracted to water

What part of the phospholipid is hydrophobic?

non-polar tails

What part of the phospholipid is hydrophilic?

the Phosphate head

What part of the phospholipid is hydrophilic?

the charged Phosphate head

What do the non-polar tails mix readily with?

fat

Why do phospholipids behave in an interesting way when they interact with water?

due to their dual hydrophobic/hydrophilic structure

Why are phospholipids called surfactants (surface active agents)?

they form a layer on the surface of the water

When forming a layer on the surface of water where are the phosphate heads positioned?

in the water (hydrophilic)

When forming a layer on the surface of water where are the fatty acid tails positioned?

sticking out of the water (hydrophobic)

a bilayer?

two-layered sheet formation

What are the hydrophobic tails protected from the water by?

the hydrophilic heads (on the outside)

Why does the phospholipid bilayer act as a good barrier?

the centre of the bilayer (tails) are hydrophobic so water-soluble can't easily pass through it

As a result of this bilayer arrangement what do phospholipids play an important role in?

cell membranes

What do they separate the aqueous cytosol in cells from?

an aqueous environment

What are macromolecules?

very large molecules, also known as polymers, which are built from repeating smaller units called monomers

Examples of macromolecules/polymers?

triglyceride and phospholipid

What are sterols known as?

steroid alcohols

What are sterols?

complex alcohol molecules (another type of lipid found in cells)

Example of a sterol?

Cholesterol

Polar?

has a slightly negatively charged region and has a slightly positive charged region

Structure of cholesterol?

a four carbon ring structure attached to hydrocarbon tail

What does the carbon ring structure have attached to it?

a hydroxyl (OH) group at one end

Elements present in cholesterol?

carbon, hydrogen, and oxygen

What part of cholesterol is polar?

the hydroxyl group

What part of cholesterol is hydrophilic?

the hydroxyl group (because it is polar)

What part of cholesterol is hydrophobic?

the rest of the molecule (apart from the hydroxyl group)

Where is cholesterol primarily made in the body?

Liver and intestines

What does cholesterol have an important role in?

the formation of cell membranes

Where is cholesterol positioned within the cell membrane?

between the phospholipid - with the hydroxyl group at the periphery of the membrane

Periphery?

outer edge

Why does cholesterol size and shape allow it to fit in between the phospholipid molecules in the membrane?

small size and flattened shape

What causes cholesterol to pack more closely together with the phospholipids in the membrane?

cholesterol binds with the hydrophobic tails of the phospholipids

What is the function of cholesterol in membranes (that them packing closely together allows them to be able to do)?

strengthen cell membranes (adds stability) and regulates their fluidity

Regulating cell membrane temperature: low temperatures?

keeps membranes fluid at low temperatures

Regulating cell membrane temperature: high temperatures?

stopping them becoming too fluid at high temperatures

3 examples of things manufactured using cholesterol?

Vitamin D, steroid hormones and bile

Roles of lipids: membranes?

membrane formation and the creation of hydrophobic barriers

Roles of lipids: what are key in the production of?

hormones

Roles of lipids: electrical insulation?

electrical insulation necessary for impulse transmission

Roles of lipids: waterproofing - examples?

in birds' feathers and on plant leaves

What do triglycerides in particular have an important role in?

long-term energy storage

Where are they stored?

under the skin and around vital organs

What do lipids provide under the skin and in these vital organs: thermal insulation?

thermal insulation to reduce heat loss (e.g. in penguins)

What do lipids provide under the skin and in these vital organs: cushioning?

cushioning to protect vital organs (e.g. heart and kidneys)

What do lipids provide under the skin and in these vital organs: buoyancy?

buoyancy for aquatic animals like whales