lipids

Question 1

lipids are made up of which elements?

Answer 1

carbon, hydrogen and oxygen, with much less oxygen than hydrogen.

Question 2

what are lipids insoluble and soluble in?

Answer 2

insoluble in water (i.e. hydrophobic, non-polar), but soluble in organic or non-polar solvents

Question 3

what are the three classes of lipids?

Answer 3

• simple lipids
• compound lipids (lipid joined to a non-lipid component)
• steroids and sterols

Question 4

what falls under simple lipids?

Answer 4

• fats and oils
• waxes

Question 5

fats and oils are formed from

Answer 5

fatty acids that are joined to a glycerol molecule

Question 6

at room temperature, fats are in ___ state whereas oils are in ___ state

Answer 6

fats - solid, oils - liquid

Question 7

waxes are formed from

Answer 7

fatty acids that are joined to high-molecular weight alcohols

Question 8

what falls under compound lipids?

Answer 8

• phospholipids
• glycolipids
• lipoproteins

Question 9

phospholipids are formed from

Answer 9

joining fattty acids and one phosphate group to a glycerol molecule

Question 10

what is the non-lipid component in phospholipids

Answer 10

phosphate group

Question 11

glycolipids are formed from

Answer 11

joining fatty acids to carbohydrate

Question 12

non lipid component in glycolipids

Answer 12

carbohydrate

Question 13

where can glycolipids be found

Answer 13

at cell membranes

Question 14

carbohydrate moiety in glycolipids is important for

Answer 14

cell-to-cell recognition and adhesion

Question 15

lipoproteins consist of

Answer 15

proteins and lipids chemically combined together

Question 16

steroids are lipids characterised by

Answer 16

a carbon skeleton consisting of 4 interconnected rings

Question 17

most abundant group of steroids

Answer 17

sterols

Question 18

sterols are made up of

Answer 18

an -OH group and hydrocarbon chain

Question 19

a fatty acid is

Answer 19

a molecule containing a long chain of hydrogen and carbon atoms called a hydrocarbon chain, with a carboxyl group (-COOH) at one end

Question 20

general formula of fatty acids

Answer 20

R-COOH, where -COOH is called the carboxyl group and R is the (uncharged and hydrophobic) hydrocarbon chain (usually long).

Question 21

fatty acids that have shorter hydrocarbon chains have a lower/higher molecular weight, and therefore have lower/higher melting points

Answer 21

lower, lower

Question 22

saturated fatty acids have an absence/presence of C=C bonds

Answer 22

absence

Question 23

unsaturated fatty acids have an absence/presence of C=C bonds

Answer 23

presence

Question 24

in unsaturated fatty acids, the C=C bonds cause

Answer 24

a kink (bend) in the hydrocarbon chain

Question 25

the kinks in unsaturated fatty acids result in

Answer 25

loose packing of the fatty acids, and therefore lower melting points

Question 26

saturated hydrocarbon tails are not kinked, and thus,

Answer 26

pack more tightly, therefore have higher melting points

Question 27

glycerol is

Answer 27

an organic compounds with three hydroxyl groups

Question 28

glycerol is soluble/insoluble in water

Answer 28

soluble

Question 29

describe the formation of fats (monoglycerides, diglycerides and triglycerides)

Answer 29

1. Each hydroxyl group (-OH) of glycerol is able to react with the carboxyl group of a fatty acid (-COOH) in a condensation reaction, resulting in the formation of an ester bond. 2. A monoglyceride is formed by joining one fatty acid molecule to a glycerol molecule. 3. A diglyceride is formed by joining two fatty acid molecules to a glycerol molecule. 4. Since glycerol has 3 hydroxyl groups, a total of 3 molecules of fatty acids can react with 1 molecule of glycerol to yield 1 molecule of triglyceride with the removal of 3 molecules of water in 3 condensation reactions, resulting in the formation of 3 ester bonds.

Question 30

properties of triglycerides

Answer 30

1. Triglycerides can exist in different physical states at room temperature. Saturated fats are often solid (e.g., butter), while unsaturated fats are typically liquid (e.g., vegetable oil). 2. The melting point of triglycerides varies based on the fatty acid composition. Saturated fats with straight chains have higher melting points than unsaturated fats with kinks in their chains. 3. Triglycerides are generally insoluble in water due to their hydrophobic nature. They are soluble in nonpolar solvents, such as ether or chloroform. --> Stored as droplets inside cells because they do not affect water potential in cells (will not cause swelling of cells). --> Fats are prevented from diffusing out of cells since they are insoluble. 4.Triglycerides have lower densities than water, which is why oils float on water. This property is influenced by both the fatty acid composition and the physical state.

Question 31

functions of triglycerides

Answer 31

1. compact energy source 2. help regulate body temperature by providing thermal insulation 3. less dense than water, so gives buoyancy to aquatic animals 4. stored in adipose tissue which provides cushioning around organs, offering protection and support 5. releases twice as much water as do carbohydrates when oxidised during respiration, important for animals that live in dry, hot desert where water is scarce

Question 32

elaborate on how triglycerides function as a compact energy source .

Answer 32

One gram of triglyceride yields about twice as much energy as one gram of carbohydrates when oxidised. The energy released is used to make ATP. In other words, triglycerides have about half the mass of carbohydrates for an equivalent amount of energy stored. It is therefore a light weight energy source for animals that move by speed or flight and for seeds dispersed by wind or insects. When energy is needed, triglycerides are hydrolysed to release fatty acids and glycerol. Fatty acids can then be oxidized to produce ATP, serving as a significant energy source.

Question 33

what is the simplest phospholipid

Answer 33

phosphatidic acid

Question 34

how is phosphatidic acid/phospholipid formed

Answer 34

One molecule of phosphoric acid reacts with one of three hydroxyl groups of glycerol by a condensation reaction. The other two hydroxyl groups react with fatty acids as in the formation of a triglyceride.

Question 35

properties of phospholipids

Answer 35

1. The amphipathic nature of phospholipids is crucial for their role in forming cell membranes. Phospholipids are able to form a bilayer – a stable structure that is not easily disrupted. 2. The fluidity of phospholipid bilayers is influenced by factors such as temperature and the degree of saturation of the fatty acid tails. Unsaturated fatty acids introduce kinks, increasing fluidity.

Question 36

state the function of phospholipids

Answer 36

major component in cell membrane

Question 37

describe how phospholipids function as a major component in cell membrane

Answer 37

As cell surface membrane, they form a lipid bilayer that surrounds cells, providing a barrier between the internal and external environments. As membranes of cellular organelles, such as the endoplasmic reticulum, Golgi apparatus, and mitochondria, phospholipids contribute to the organelles’ structural integrity. The amphipathic nature of phospholipids contributes to the selective permeability (NOT partially permeable) of cell membranes. The hydrophobic core prevents the free passage of polar molecules and ions, regulating the entry and exit of substances. The individual phospholipid molecules in the bilayer are free to move, which confers to cell membrane its flexibility and fluidity. This allows cell growth, exocytosis and endocytosis.

Question 38

cholesterol consists of

Answer 38

four interconnected hydrocarbon rings with a hydroxyl group at one end

Question 39

cholesterol serves as a precursor for

Answer 39

the synthesis of various steroid hormones, bile acids, and vitamin D

Question 40

properties of cholesterol

Answer 40

1. The amphipathic nature of cholesterols is crucial for their role in regulating the fluidity and stability of cell membranes. Cholesterol aligns itself with phospholipids, where the hydrophobic rings interact with the fatty acid tails of phospholipids, while the hydroxyl group faces outward, interacting with the hydrophilic head groups of phospholipids and the surrounding aqueous environment. 2. Cholesterol can form crystalline structures in cell membranes, influencing their fluidity and permeability.

Question 41

functions of cholesterol

Answer 41

1. Function to maintain membrane fluidity and stability by interacting with phospholipids. At low temperatures, cholesterol prevents phospholipids from packing too closely, preventing the membrane from becoming too rigid and solidifying. At high temperatures, cholesterol reduces the lateral movement of phospholipids, preventing the membrane from becoming too fluid. 2. Cholesterol regulates the permeability of cell membranes to ions and small molecules by affecting the activity of ion channels embedded in the cell membrane.