Lipids Flashcards
1
Q
Explain the structure of fatty acids.
A
- They are carboxylic acids that contain 4-28 carbons (carboxyl group)
- Short chain (less than 6), medium-chain (6-12), long chains (13-21) and very long chain (over 22)
- Most naturally occurring fatty acids contain straight chain (no branching), even number of carbons
2
Q
What does it mean for a hydrocarbon chain to be saturated and unsaturated?
A
- Saturated: only carbon-carbon single bonds
- Unsaturated: one or more carbon-carbon double binds
- Monounsaturated (one double bond), polyunsaturated (many double bonds)
3
Q
Why are fatty acids not soluble in water?
A
- The long non-polar hydrocarbon chain results in a molecule that has great non-polar characteristics
- The carboxyl group is highly polar and can form hydrogen bonds, yet the non-polar chain has greater characteristics
4
Q
What type of bonding exists between fatty acids?
A
- Intermolecular forces, depends on the length of the chain and whether it is saturated or unsaturated
- Longer chains have stronger London dispersion forces, high melting points
- Saturated fatty acids are very straight, allow better contact between fatty acid chains, increases strength of London dispersion forces
- Unsaturated fatty acids have a kink (bend), weaker London dispersion forces and lower melting point
5
Q
What are triglycerides?
A
- Fatty acids that are bonded together with a glycerol through a condensation reaction
- 1 glycerol bonds to 3 fatty acids since it contains three hydroxyl groups (can form 3 water molecules)
- Reaction between fatty acids (carboxylic acids) and an alcohol result in an ester, ester linkage
- Reverse reaction is hydrolysis (addition of H2O)
6
Q
Explain the melting points of triglycerides.
A
- Triglycerides a.k.a fats/oils
- Difference between them is their state at room temperature
- Fats are solid at r.t.p (usually from animal sources), oils are liquid at r.t.p, usually from plants
7
Q
What makes triglycerides non-linear? Explain the melting points of saturated and unsaturated.
A
- Carbon-carbon double bonds cause kinks, chain is not linear
- Weaker London dispersion forces between triglycerides, lower melting point, likely to be liquid at r.t.p
- Saturated, more linear, more surface area between triglycerides, increases strength of forces, higher melting point
8
Q
What is the iodine number?
A
- Quantitative measurement of unsaturated for fats
- Mass of iodine that is absorbed by 100g of a chemical substance
- The more sites of unsaturated result in a greater iodine number (addition reaction with halogens)
- Iodine is slowly added to a sample of a lipid until no further colour change is observed, yellow-brown remains (it turns colourless before)
- When it becomes yellow-brown, there are no more double bonds present
- Method used to indicate number of double bonds present
9
Q
Which lipids have more unsaturation?
A
- Vegetable oils have more unsaturation than fats from animal sources
- Vegetable oils iodine number: 80-200
- Animal fats iodine number: 40-70, higher melting point, high degree of saturation, low iodine number
10
Q
How do you calculate the iodine number?
A
- Expressed as a percentage of mass of the iodine reacted by the mass of lipid reacted
11
Q
What are phospholipids?
A
- Other form of lipid
- Derived from triglycerides and perform function for the cell by forming a protective layer around the cell (cell membrane)
- The structure is similar to triglycerides, except that the glycerol is bonded to 2 fatty acids and one phosphate group (PO4 3-)
- Phosphate group contains ionic and non-polar function groups
12
Q
What characteristics do phospholipids have?
A
- Phosphate group results in water solubility, has ion-dipole attraction between negative phosphate group and polar water molecules
- Hydrophilic heads (water soluble) and hydrophobic tails (water insoluble)
- The phosphate heads form ion-dipole attraction with water molecules and the fatty acid tails avoid water
- Form phospholipid bilayer in aqueous environments
13
Q
What role do phospholipids play in solubility, the cell membrane and compartmentalisation?
A
- Phospholipid bilayer can form around hydrophobic (non-polar) vitamins, allows them to be dissolved and transported in bloodstream
- In the cell membrane consists of a bilayer and proteins and cholesterol, forms protective layer
- The cell contains inside and outside water, the tails form the inside
- Cell membrane is selectively permeable, some substances can cross, some cannot
- Phospholipid bilayer forms around organelles, allows compartmentalisation within the cell
14
Q
What type of reactions do phospholipids undergo?
A
- Condensation reactions involving glycerol
- Hydrolysis in acidic or basic media, releasing fatty acid chains
- Hydrolysis involving enzymes (catabolic)
15
Q
What are steroids? Explain the structure.
A
- Chemical substances naturally produced in the body, act as structural components in cell membranes or as hormones
- Contains steroidal backbone which is made of four fused rings: three cyclohexane rings and one cylcopentane (17 carbons)
- The backbone is non-polar, yet the presence of polar functional groups help increase the polarity and water solubility
- Most steroids are water insoluble, carrier proteins used that bind to the steroid to better increase its solubility
16
Q
What is cholesterol?
A
- Type of steroid, adds rigidity to phospholipid bilayer
- Has four fused rings, very non-polar (hydrophobic)
- Hydroxyl functional group is attracted to charged phosphate head, rest of cholesterol is non-polar
17
Q
What are steroids used for?
A
- Medical conditions can result in lower levels of steroids, prescribed to have normal levels
- Also used for non-medical reasons, enhanced growth or athletic performance
- Increases levels of cholesterol in bloodstream due to steroids, increase risk of CHD and stroke
18
Q
How are steroids used for enhanced athletic performance?
A
- Testosterone used with other drugs, growth and development of male characteristics
- Increased levels of testosterone can improve strength and endurance
- Can lead to hair loss and decreased fertility
19
Q
Why must fats be consumed through the diet?
A
- Allows body to obtain energy and recycle nutrients into lipids
- Form structural components within the body
- Used to produce steroids for growth and development or build new cell membranes to replace old ones
- Over-consumption can lead to health effects
20
Q
Why are lipids good sources of energy?
A
- Lipids can be used as an energy source for organisms reacting in a combustion reaction
- Converts three fatty acids from triglycerides to CO2 and H2O, releases energy
- Lipids are more reduced than carbohydrates, they have more hydrogen and less O2 and produce more energy when oxidised, more bonds made, exothermic (mexo)
- Fatty acids require more oxygen to oxidise to make CO2 (fatty acids have O2 oly from carboxyl)
- Lipids yield more energy per gram when oxidised, compared to carbohydrates, lipids almost double the amount as carbs
21
Q
What negative effect can triglycerides (saturated) have on health?
A
- Excess energy obtained from fats, stored for later use, too much can interfere with metabolic pathways
- Saturated fatty acids have a linear structure, greater surface area for London dispersion forces
- Hence saturated fats are solid at room temperature, excess intake can increase cholesterol levels in blood
22
Q
What type of unsaturated fatty acids exist and what effect do they have on health?
A
- Naturally occur in cis form, synthetic produced as trans fats
- Trans fats are more linear than cis fats, hence trans fats resemble saturated fats in structure and function
- High consumption of trans fats result in higher blood cholesterol levels, increased risk for heart disease
23
Q
What are lipoproteins and what are the two types?
A
- Lipoproteins carry cholesterol through aqueous bloodstream since cholesterol is non-polar
- Lipoproteins make it more soluble
- High density and low density
24
Q
What do high density lipoproteins (HDL) do?
A
- Travel through the bloodstream, absorb excess cholesterol and transport it to the liver for removal
- HDL is ‘good’ cholesterol, composed of more protein and less triglycerides
25
Q
What do low density lipoproteins (LDL) do?
A
- Travel through the bloodstream, deposit cholesterol in the walls of blood vessels
- ‘bad’ cholesterol, composed of less protein and more triglycerides
- Can cause buildup known as plaque
- Plaque can form blockage in blood flow, result in heart attack or stroke
26
Q
What is rancidity?
A
- If fats are not consumed right away, they can react with oxygen becoming rancid (spoil)
- Distinct rancid odours and flavours
- Hydrolytic rancidity and Oxidative rancidity
27
Q
What is hdrolytic rancidity?
A
- Process of hydrolysis, turns triglycerides back into glycerol and three fatty acids
- One of the fatty acids produces butanoic acid
- Unpleasant odour
- Certain enzymes, increased temperature and presence of water can increase the rate of rancidity
- Use of refrigerator reduces rate of oxidation
- Diary products become rancid quickly
27
Q
What is hdrolytic rancidity?
A
- Process of hydrolysis, turns triglycerides back into glycerol and three fatty acids
- One of the fatty acids produces butanoic acid
- Unpleasant odour
- Certain enzymes, increased temperature and presence of water can increase the rate of rancidity
- Use of refrigerator reduces rate of oxidation
- Diary products become rancid quickly
28
Q
What is oxidative rancidity?
A
- When oxygen reacts with carbon-carbon double bonds of unsaturated fats, catalysed by light
- Variety of compounds produced, ketones and aldehydes, unpleasant aroma
- Oxidative rancidity occurs more frequent when substance is exposed to light and greater exposure to oxygen
- E.g. fish (unsaturated fats)
- Unsaturated more susceptible to oxidative rancidity
29
Q
What roles do lipids have in the body?
A
- Energy storage, release more energy when oxidised
- Insulation and protection of organs, stored in adipose tissue
- Steroid hormones, e.g. progesterone, testosterone, anabolic steroids
- Cell membranes
30
Q
What is hydrogenation and when does it usually occur?
A
- Unsaturated fats are hydrogenated to saturated fats with a higher melting point by adding hydrogen under pressure in the presence of a heated nickel catalyst
- Happens in cis-unsaturated fatty acids
- Yet partial hydrogenation may occur, turned into trans-isomers, promote formation of LDL cholesterol, increase risk of heart disease
