L1.7 LIPIDS

Question 1

Explain how length and saturation of hydrocarbon chains affect the fluidity of lipids.

Answer 1

Membrane fluidity is affected by fatty acids. More specifically, whether the fatty acids are saturated or unsaturated has an effect on membrane fluidity. Saturated fatty acids have no double bonds in the hydrocarbon chain, and the maximum amount of hydrogen. The absence of double bonds decreases fluidity, making the membrane very strong and stacked tightly. Unsaturated fatty acids have at least one double bond, creating a “kink” in the chain. The double bond increases fluidity. Membrane fluidity is also affected by cholesterol. Cholesterol can make the cell membrane fluid as well as rigid.

Question 2

Predict whether a fatty acid is likely to be in a solid or liquid physical state at room temperature

Answer 2

Unsaturated fats have one or more double bonds inside their fatty acid chains. The two carbons on the hydrocarbon molecules each have triple or double bonds, and hydrogens cannot saturate them. This makes the entire molecular structure weaker, so the substance stays liquid at room temperature Long, saturated fatty acids are most likely to be solid at room temperatures;

Question 3

List the three most important types of lipids found in cells and describe their general structure
and function.

Answer 3

FATS (also called TRIGLYCERIDES or TRIACYLGLYCEROLS) are nonpolar molecules
composed of three fatty acids linked to glycerol

STERIODS are a class of lipids with a characteristic nonpolar four-ring
hydrocarbon structure

PHOSPHOLIPIDS are the most common lipid found in biological membranes

Question 4

Explain why phospholipids spontaneously form bilayers in water.

Answer 4

ecause their fatty acid tails are poorly soluble in water, phospholipids spontaneously form bilayers in aqueous solutions, with the hydrophobic tails buried in the interior of the membrane and the polar head groups exposed on both sides, in contact with water

Question 5

Predict whether a given molecule would be permeable across a selectively permeable
membrane.

Answer 5

The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot. Water can pass through between the lipids.

The cell membrane is a barrier between the interior of the cell and the outside world. The ability of a molecule to travel across a membrane depends on its concentration, charge and size. In general, molecules diffuse across membranes from areas of high concentration to low concentration. Cell membranes prevent charged molecules from entering the cell unless the cell maintains an electrical potential. However, small molecules may be able to slip through the membrane regardless of their charge.

Question 6

Amphipathic

Answer 6

(“dual-sympathy”) is a term used to describe compounds that contain both hydrophilic and hydrophobic elements.

Question 7

bilayer

Answer 7

aka phospholipid ____; a thin polar membrane made of two layers of lipid molecules; usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains

Question 8

cholesterol

Answer 8

a component of animal cell membranes that reduces membrane fluidity and permeability to some solutes (particularly in mammalian membranes)

It interacts with the fatty acid tails of phospholipids to moderate the properties of the membrane:

1. functions to immobilize the outer surface of the membrane, reducing fluidity
2. makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross
3. functions to separate phospholipid tails and so prevent crystallization of the membrane
4. helps secure peripheral proteins by forming high-density lipid rafts capable of anchoring the protein

Question 9

ester linkage

Answer 9

the type of linkage that holds glycerol and fatty acids together to form triglycerides

Question 10

fat

Answer 10

(also called TRIGLYCERIDES or TRIACYLGLYCEROLS) are nonpolar molecules
composed of three fatty acids linked to glycerol

Question 11

fatty acid

Answer 11

are key building blocks of important lipids found in organisms

Question 12

glycerol

Answer 12

e glycerol head is hydrophilic, or “water-loving.”

Question 13

head group

Answer 13

gives a molecule its polar and hydrophilic character making it water-soluble.

Question 14

hydrocarbon

Answer 14

a compound of hydrogen and carbon

Question 15

hydrocarbon tail

Answer 15

hydrocarbon chain that makes up fatty acids makes the tail end of the molecule hydrophobic, or water-resistant,

Question 16

lipid

Answer 16

are carbon-containing compounds that are largely nonpolar and hydrophobic

Question 17

micelle

Answer 17

are lipid molecules that arrange themselves in a spherical form in aqueous solutions. The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic regions (polar head groups) as well as hydrophobic regions (the long hydrophobic chain).

Question 18

phospholipids

Answer 18

e the most common lipid found in biological membranes

Question 19

saturated

Answer 19

Fatty acids that possess no double bonds are saturated (have maximum number of H atoms)

Saturated fatty acids are linear in structure, originate from animal sources (i.e. fats) and are typically solid at room temperatures

Question 20

Selective permeability

Answer 20

a property of cellular membranes that only allows certain molecules to enter or exit the cell.

Question 21

Steroid

Answer 21

are a class of lipids with a characteristic nonpolar four-ring
hydrocarbon structure

Question 22

Unsaturated

Answer 22

Fatty acids with double bonds are unsaturated – either monounsaturated (1 double bond) or polyunsaturated (>1 double bond)

Unsaturated fatty acids are bent in structure, originate from plant sources (i.e. oils) and are typically liquid at room temperatures

Question 23

Differentiate between saturated and unsaturated fatty acids.

Answer 23

Saturated fatty acids lack double bonds between the individual carbon atoms, while in unsaturated fatty acids there is at least one double bond in the fatty acid chain. Saturated fats tend to be solid at room temperature and from animal sources, while unsaturated fats are usually liquid and from plant sources.

Question 24

Differentiate between trans and cis unsaturated fats, and determine their relative melting
temperatures.

Answer 24

A trans double bond creates a straight chain, whereas a cis double bond results in a chain
that is bent

Question 25

Predict whether a given molecule would be water- or fat-soluble.

Answer 25

Water-soluble molecules have many polar groups and are hence soluble in polar solvents such as water. Fat-soluble molecules are predominantly nonpolar and hence are soluble in nonpolar solvents

Question 26

Compare and contrast lipids with the other three macromolecules (proteins, nucleic acids and
carbohydrates) in terms of structure and function.

Answer 26

commonalties: They all contain the element carbon. They contain simpler units that are linked together making larger molecules.
Differences: they have different monomers of monosaccharaides, amino acids, nucleotides,

Similarities:

Complex carbohydrates (e.g. polysaccharides) and lipids both contain a lot of chemical energy and can be used for energy storage
Complex carbohydrates and lipids are both insoluble in water - they are not easily transported
Carbohydrates and lipids both burn cleaner than proteins (they do not yield nitrogenous wastes)

Differences:

Lipid molecules contain more energy per gram than carbohydrates (about twice as much)
Carbohydrates are more readily digested than lipids and release their energy more rapidly
Monosaccharides and disaccharides are water soluble and easier to transport to and from storage sites than lipids
Animals tend to use carbohydrates primarily for short-term energy storage, while lipids are used more for long-term energy storage
Carbohydrates are stored as glycogen in animals while lipids are stored as fats (in plants carbohydrates are stored as cellulose and lipids as oils)
Lipids have less effect on osmotic pressure within a cell than complex carbohydrates

Question 27

list the roles of lipids

Answer 27

Structure: Phospholipids are a main component of cell membranes

Hormonal signalling: Steroids are involved in hormonal signalling (e.g. estrogen, progesterone, testosterone)

Insulation: Fats in animals can serve as heat insulators while sphingolipids in the myelin sheath (of neurons) can serve as electrical insulators

Protection: Triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury

Storage of energy: Triglycerides can be used as a long-term energy storage source