B1.1 Carbohydrates and lipids

Question 1

Describe the condensation reaction

Answer 1

• Combines 2 molecules, releasing a water molecule
• Many repeated condensation reactions btwn monomers produce polymers (e.g. monosaccharide to polysaccharides)

Question 2

state/describe monosaccharides

Answer 2

• quite soluble
• Made of carbon, hydrogen, oxygen

[Glucose, Galactose, Fructose] - Hexoses (6-carbon atoms), isomers of C6H12O6

[Ribose, Deoxyribose] - Pentoses (5-carbon atoms), C5H10O5 and C5H10O4 respectively

Question 3

state/describe disaccharides

Answer 3

(2 monosaccharides joined by condensation reaction), soluble

• sucrose (glucose+fructose)
• maltose (glucose+glucose)
• lactose (glucose+galactose)

Question 4

state/describe polysaccharides

Answer 4

Polymers of monosaccharides, low solubility
ENERGY STORAGE MOLECULES

Starches (found in plants, for short-term storage):
- Amylose (unbranched)
- Amylopectin (branched)

Fibres (indigestible by humans):
- Cellulose (insoluble)
- Pectins (soluble)

Glycogen (storage form of glucose in animals)
- highly branched polymer of glucose w many side branches
- Stored in liver and muscles

Question 5

Describe the structure of amino acids

Answer 5

• each central C atom has attached to it:
• a hydrogen atom
• a r group (1 of 20)
• amino group (NH2)
• a carboxylic acid group (COOH)

amino acid > dipeptide > polypeptide

Question 6

structure of nucleic acids

Answer 6

phosphate + ribose sugar + nitrogenous base

nucleic acid (monomer)> polynucleic acid (polymer)

Question 7

Describe hydrolysis reactions

Answer 7

The addition of a water molecule to break down a large molecule. Water is split into O and OH groups which are incorporated to produce monomers.

e.g. the breaking down of macromolecules to their monomers by a series of hydrolysis reactions

Question 8

Properties and uses of glucose

Answer 8

• soluble
• relatively small
• transportable in blood, dissolved in plasma
• chemically very stable (like most carbohydrates) = useful for food storage. However, this would cause osmotic problem in cells if stored in large quantities and is hence converted to glycogen/starch
• glucose yields energy when oxidised = used as a substrate in respiration

Question 9

Starch in plant cells (structure, properties)

Answer 9

• Starch is a mixture of unbranched amylose (1, 4 glycosidic bonds) and branched amylopectin (shorter chains of linked 1, 4 a-glucose units, but with branch points of 1,6 glycosidic bonds along the chains.)
• The bonds btwn glucose molecules bring the molecules together as a helix
• the whole starch molecule is stabilised by countless Hydrogen bonds btwn parts of component glucose molecules.
• Glycogen is a polymer of alpha-glucose (chemically very similar to amylopectin, although larger and more highly branched)

Question 10

Practice drawing a-glucose, b-glucose, galactose

Answer 10

good luck

Question 11

How are energy stores built/mobilised?

Answer 11

Build: a-glucose molecules are added by condensation
Mobilised: a-glucose molecules are removed by hydrolysis

Question 12

Structure of cellulose (fibre)

Answer 12

• a polymer of glucose that forms microfibrils
• Indigestible by most animals (enzymes that digest starch by hydrolysing a-glucose linkages are unable to hydrolyse b-glucose linkages)
• ALTERNATING ORIENTATION of b-glucose monomers, resulting in STRAIGHT CHAINS that can be grouped into bundles and CROSS-LINKED with HYDROGEN BONDS

Question 13

Glycoproteins for cell recognition example

Answer 13

ABO antigens in red blood cells - play a role in blood transfusion

Remember -
- RECEIVING blood, as long as the RBC has the antigen it can receive blood from that blood type, and O can always be received. E.g. AB can receive blood from A, B, AB, O

• DONATING blood, as long as ONE antigen is present in both blood types can donate. O can donate to everyone. e.g. B can donate to B, AB.

Question 14

Properties and types of lipids

Answer 14

• only soluble in non-polar solvents
• sparingly soluble in polar solvents
• hydrophobic = does not dissolve in water. This is as lipids consist mostly of hydrocarbons, which form non-polar covalent bonds
• Triglycerides (fats [solid at 20c] and oils [liquid at 20c])
• Steroids [liquid at 20c]
• Waxes
• Phospholipids

Question 15

Formation of triglycerides

Answer 15

Condensation reaction between glycerol backbone and 3 fatty acids

Question 16

Formation of phospholipids

Answer 16

Condensation reaction btwn glycerol backbone and 2 fatty acids. Phosphate group attached in place of the third fatty acid.

Fatty acids are non-polar hydrophobic, phosphate group is polar hydrophilic

Question 17

structure of fatty acids + Diff btwn unsaturated and saturated fatty acids

Answer 17

All fatty acids consist of a carboxyl (COOH) group, the hydrocarbon chain, and the methyl group (CH3).

Unsaturated fatty acids have one or more double bonds btwn carbons (e.g. oil)

Saturated fatty acids have no double bonds btwn carbon atoms (e.g. butter)

Question 18

How does unsaturated vs saturated affect melting point in triglycerides?

Answer 18

Triglycerides with unsaturated fatty acids have lower melting points than triglycerides with saturated fatty acids

Unsaturated fatty acids have bends in their hydrocarbon tails = reduce density and lowers melting points. Oils generally have shorter fatty acid tails

Saturated fatty acids with saturated bonds = more densely packed, increases melting point. Fats generally have longer fatty acid tails.

Plants usually have unsaturated fatty acids, animals usually have saturated fatty acids

Question 19

Difference btwn monounsaturated and polyunsaturated fatty acids

Answer 19

poly = 2 or more h bonds
mono = 1 h bond

Question 20

Where are triglycerides found and what are their properties?

Answer 20

In animals, triglycerides are found in adipose tissue

• chemically very stable = v little energy lost over time
• immiscible in water = oil droplets formed in the cytoplasm, does not have an osmotic effect
• good insulators of heat = thermal insulator to conserve body heat
• release x2 energy compared to carbohydrates = energy stored in 1/2 the body mass

Question 21

Examples of non-polar steroids passing through phospholipids bilayer (2) and why

Answer 21

Oestradiol and testosterone

The hydrophobic properties of these enzymes enable them to be soluble in the fatty acid layers of the membranes.

Question 22

Identifying steroids

Answer 22

4 carbon rings attached to one another NOT 4-carbon rings

Question 23

Structure/properties of waxes

Answer 23

Long chain fatty acid bound to long chain alcohol

• high melting point
• waterproof
• resistant to degradation