Water and Lipids

Question 1

What is water?

Answer 1

• It is the medium in which all metabolic reactions take place in cells
• Between 70% to 95% of the mass of a cell is water
• As 71% of the Earth’s surface is covered in water it is a major habitat for organisms.

Question 2

What makes it a polar molecule?

Answer 2

The sharing of the electrons is uneven between the oxygen and hydrogen atoms

The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms.

This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole

When a molecule has one end that is negatively charged and one end that is positively charged it is also a polar molecule

Water is a polar molecule

Question 3

What are the properties of water?

Answer 3

An excellent solvent.
Acts as a transport medium.
High specific heat capacity.
High latent heat of vaporisation.
Less dense when a solid (floats and acts as a habitat for polar bears/penguins).
High surface tension and cohesion.
Acts as a reagent in many chemical reactions.

Question 4

What is the role of water being a solvent in living organisms and why.

Answer 4

• Allows chemical reactions to occur within cells.
• Transport medium e.g.
  Metabolites can be
  transported efficiently.
• Process allows prokaryotic
  cells to exchange
  substances like nutrients
  and products via diffusion.
  Reason: the polarity of water.

Question 5

Define specific heat capacity

Answer 5

The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C

Question 6

Why does water have such a high specific heat capacity.

Answer 6

The high specific heat capacity is due to the many hydrogen bonds present in water. It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly

Question 7

Advantages of water’s specific heat capacity in living organisms?

Answer 7

Provides suitable stable habitats in aquatic environments.

Is able to maintain a constant temperature as water is able to absorb a lot of heat.

This is vital in maintaining temperatures that are optimal for enzyme activity in all types of cells.

Water in blood plasma is also vital in transferring heat around the body.

As blood passes through more active (‘warmer’) regions of the body, heat energy is absorbed.

Water in tissue fluid also plays an important regulatory role in maintaining a constant body temperature

Question 8

What is the latent heat of vaporisation?

Answer 8

In order to change state (from liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate

This is an advantage for living organisms as only a little water is required to evaporate for the organism to lose a great amount of heat

Question 9

What’s the benefit of the latent heat of vaporisation of water to living organisms?

Answer 9

This provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin.

Question 10

What is cohesion and adhesion?

Answer 10

Cohesion is when water molecules stick to each-other.
Adhesion is when water molecules adhere to other surfaces.

Question 11

Function of lipids?

Answer 11

Fats - Storage of energy.
- Protection of internal
organs.
- Insulation.
(Brown fat) - when it metabolises, it releases heat.

• Water storage.
• Coconut oils - good for your
  hair.
• Vital for your cells.
• Reserve of energy.
• Buoyancy.
• Source of metabolic water
• Waterproofing
• Vitamin storage.
• Hormone production.

Question 12

What are they made up of?

Answer 12

Elements: Carbon, Hydrogen, Oxygen

Question 13

What is a monomer and a polymer?

Answer 13

Monomer: single small molecule that may combine with other monomers to form a polymer (E.g. Monosaccharides, nucleotides, amino acids).

Polymer: large molecule built from many single monomers joined together by covalent bonds to form a chain/branched chain.

Question 14

What is condensation polymerisation?

Answer 14

Involves the removal of water molecule to form a covalent bond.
Leads to a larger molecule being formed by bonding together smaller molecules.
It is an ‘anabolic reaction’.

Question 15

What is hydrolysis?

Answer 15

Breaking Bonds - A molecule of water is added causing the breaking of a covalent bond.
Smaller molecules are formed by the splitting of a larger molecule.
It is a ‘catabolic reaction’.

Question 16

What are the different types of bonds

Answer 16

Glyosidic bonds - formed between monosaccharide subunits and disaccharides and polysaccharides.

Peptide bond - found
between the amino acids
that join to form dipeptides
and polypeptides.

Ester bonds – found
between glycerol and fatty
acids.
Phosphodiester bonds –
found between successive
sugar molecules in a
polynucleotide

Question 17

What are lipids?

Answer 17

Substances like fats, oils and wax.

They dissolve in non-polar
substances but not in water.

The are a source of energy.

Electrical and organ
insulation.

Question 18

What is the structure of a lipid?

Answer 18

CH3 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - COOH

Question 19

Esterification and breakdown of triglyceride.

Answer 19

Ester bond links fatty acid to the glycerol.

Carboxylic acid (fatty acid) functional group (-COOH) and hydroxyl (glycerol) functional group (-OH) are involved.

3 hydroxyl groups from 3 fatty acids, 3 hydrogens are lost —> 3 molecules of water are lost.

Lipids can be hydrolysed to 3 fatty acids and glycerol.

Condensation reaction: Fatty acid + Glycerol —> Ester + Water

Question 20

Fatty acid notes.

Answer 20

General formula of fatty acid:
-RCOOH.

Triglycerides are mostly
insoluble in water.

Some are soluble in certain
solvents like
ether/chloroform.

Fatty acids are non-polar
(hydrophobic). This is due to
no uneven distribution of
electrical charge within the
molecule.

Fats don’t affect cell water
potential.

Question 21

Saturated vs Unsaturated fatty acids

Answer 21

Fatty acids can be either.

Saturated fatty acids have C-C (animal fats).

Unsaturated fatty acids have one or more C=C (plant oils).

You can have, Saturated, Monosaturated or Polysaturated lipids.

Question 22

Fatty acid properties

Answer 22

Unsaturated fats melt at lower temps. than saturated fats.

Double bond causes “kinking” (The cis double bond causes a bend or a “kink” that prevents the fatty acids from packing tightly, keeping them liquid at room temperature).

This keeps lipid molecules far apart, preventing them from packing uniformly.

Question 23

What are phospholipids?

Answer 23

A phospholipid is a triglyceride - one fatty acid is replaced with a polar phosphate group.

They form 90% of the cell membrane structure.

Question 24

What is Cholesterol?

Answer 24

Cholesterol is a derived lipid, found mostly in cell membranes.

It has hydrocarbon rings, a chain, and a hydroxyl group.

Question 25

Function of cholesterol?

Answer 25

Strengthens the cell membrane and reduce its fluidity.

Question 26

Comparing Lipid Molecules.

Answer 26

Triglyceride - Glycerol + 3 fatty acids; Compact energy store ; Insoluble in water ; Thermal and electrical insulation; Waterproofing. Phospholipid; Glycerol + 2 fatty acids + phosphate group ; Molecule is part hydrophobic and part hydrophilic ; ideal for cell surface membrane structure; Glycolipids are involved in cell signalling. Cholesterol: Four-carbon-based ring structures joined together; forms a small thin molecule that fits into the lipid bilayer giving strength and stability; used to form steroid hormones.

Question 27

Properties of triglycerides.

Answer 27

They are fats and oils. Made up of fatty acid and glycerol molecules. Function: - Energy storage. - Insulation. - Buoyancy. - Protection.

Question 28

Triglycerides - energy storage

Answer 28

The long hydrocarbon chains contain little oxygen. When they are oxidised during respiration, the C-H bonds break and release energy used to produce ATP and large no. of water molecules during cellular respiration. They don't cause osmotic water uptake since they are hydrophobic, so more energy can be stored in cells.

Question 29

Triglycerides - Insulation

Answer 29

Part of the composition of the myelin sheath. Myelin sheath provides insulation and increases speed of transmission of nerve impulses. Compose part of the adipose tissue layer below skin to prevent heat loss.

Question 30

Triglycerides - Buoyancy

Answer 30

Low density of fat tissue increases ability of animals to float more easily.

Question 31

Triglycerides - Protection

Answer 31

Adipose tissue in mammals contain stored triglycerides - helps protect organs from damage risks.

Question 32

Phospholipids

Answer 32

Formed from the monomer glycerol and fatty acids. Only 2 fatty acids are bonded to the glycerol molecule and one is replaced with a phosphate ion. Phosphate is soluble in water (hydrophilic) since it is polar. Fatty acid 'tails' are non-polar, so insoluble in water (hydrophobic). Phospholipids are amphipathic (contain both hydrophilic and hydrophobic parts). Due to this, they form monolayers or bilayers in water.

Question 33

Phospholipids (continued)

Answer 33

Main component of cell membranes in both eukaryotic and prokaryotic organisms. A hydrophobic core is created when phospholipid bilayer forms due to presence of fatty acid tails. The core acts as a barrier to water-soluble materials. They can be less fluid or more fluid depending on weather they are saturated or less saturated respectively. Control protein orientation. Allow movement within the layer but holds proteins within the membrane.

Question 34

Cholesterol

Answer 34

Lipid molecule found in the cell membrane of eukaryotic cells is cholesterol Just like phospholipid molecules, cholesterol molecules have hydrophobic and hydrophilic regions Their chemical structure allows them to exist in the bilayer of the membrane Molecules of cholesterol are synthesised in the liver and transported via the blood Cholesterol affects the fluidity and permeability of the cell membrane It increases the rigidity of the membrane (makes the membrane less flexible) It acts as a barrier. This prevents water-soluble substances from diffusing across the membrane Molecules of cholesterol are used to produce steroid-based hormones.

Question 35

What are Lipids?

Answer 35

Lipids are macromolecules that contain carbon, hydrogen and oxygen atoms. Unlike carbohydrates, lipids contain a lower proportion of oxygen Lipids are non-polar and hydrophobic (insoluble in water) Lipids play an important role in energy yield, energy storage, insulation and hormonal communication

Question 36

What are Triglycerides?

Answer 36

Triglycerides are non-polar, hydrophobic molecules Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom) Fatty acids contain a methyl group at one end of a hydrocarbon chain known as the R group and at the other is a carboxyl group The shorthand chemical formula for a fatty acid is RCOOH

Question 37

How do fatty acids vary?

Answer 37

Length of the hydrocarbon chain (R group) The fatty acid chain (R group) may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil) Unsaturated fatty acids can be mono or poly-unsaturated

Question 38

Difference between cis-fatty acids and trans-fatty acids

Answer 38

If H atoms are on same sides of the double bond, they are called cis-fatty acids. They are also metabolised by enzymes. If H atoms are on opp. sides of the double bond, they are called trans-fatty acids. They can't be metabolised.

Question 39

Ester bond

Answer 39

Triglycerides contain three ester bonds between the fatty acids and the glycerol molecule An ester bond forms when a hydroxyl (-OH) group from the glycerol bonds with the carboxyl (-COOH) group of the fatty acid An H from glycerol combines with an OH from the fatty acid to make water The formation of an ester bond is a condensation reaction

Question 40

What is a hydrolysis reaction?

Answer 40

Three fatty acids join to one glycerol molecule to form a triglyceride Therefore for one triglyceride to form, three water molecules are released The ester bonds can break during breakdown of the triglyceride molecule (e.g. during digestion) This process is a hydrolysis reaction and three water molecules are taken in the reverse reaction to the condensation