2.3 Carbohydrates and Lipids

Question 1

Why is C important?

Answer 1

organic compounds contain C
each C forms 4 covalent bonds, allowing a great diversity of compounds to exist
additional groups added to the C-C molecule gives the organic compound its properties
covalent bonds are strong so molecules are stable

Question 2

What is the Theory of Vitalism?

Answer 2

it was once thopught that living organisms were composed of organic molecules that could only be produced by a vital force
this theory was falsified by discoveries in biochemistry and the structure of DNA
the chemical synthesis of Urea also falsified this theory:
- found in human urine
- in 1828 Fredrich Wohler synthesised it artificially
- using silver isocyanate and ammonium chloride

Question 3

What is metabolism?

Answer 3

web of all enzyme catalysed reactions in a cell or organism

Question 4

What is anabolism?

Answer 4

synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions
e.g. sugar from CO2

Question 5

What is catabolism?

Answer 5

the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
e.g. respiration

Question 6

What are carbohydrates?

Answer 6

made of C, H and O
(CH2O)n
used to store energy

Question 7

Monosaccharides

Answer 7

are monomers (single sugar)
also known as reducing sugars 
are small enough to pass through a cell membrane
e.g. glucose (C6H12O6) - photosynthesis and respiration, ribose (C5H10O5) - component of RNA, fructose - made by plants found in fruits, galactose - breakdown of lactose, deoxyribose

Question 8

Forms of glucose

Answer 8

D glucose - living things
L glucose - not in living things

alpha D glucose - makes up starch and glycogen polymers
beta D glucose - makes up cellulose polymer

Question 9

Disaccharides

Answer 9

produced by combining monosaccharides

sucrose: table sugar - glucose and fructose - condensation reaction in plants
lactose: milk sugar - glucose and galactose
maltose: malt sugar - two glucose

Question 10

relationship between mono and disaccharides

Answer 10

condensation reaction joins two monosaccharides to form a disaccharide by removing a water molecule and forming a glycosidic bond
hydrolysis reaction splits a disaccharide by providing a water molecule and breaking the glycosidic bond to form two monosaccharides

Question 11

Polysaccharides

Answer 11

many sugar units

e.g. starch, glycogen, cellulose

Question 12

Starch

Answer 12

can be long branched (amylopectin) or unbranched (amylose)
chains of alpha D glucose
the way that plants store their carbohydrates
if amylose: helical chains, circle type ring
if amylopectin: branches every approx 20 subunits

Question 13

Glycogen

Answer 13

long branched
chains of alpha D glucose
the way that animals store their glucose
insoluble so large amounts can be stores
very very long chains

Question 14

Cellulose

Answer 14

unbranched 
beta D glucose
plant cell walls
humans and most vertebrates are unable to digest cellulose because enzymes that break down the linkages are not found in vertebrates
linear chains

Question 15

What are lipids?

Answer 15

C compounds
mostly or entirely hydrophobic
fats and waxes are solid at room temp
insoluble in water
important energy storage compounds - greatest energy per gram of all food types
3 main types: triglycerides, phospholipids and steroids

Question 16

Triglyerides

Answer 16

most common
three fatty acids + glycerol
formed during a condensation reaction between three fatty acids and one glycerol

Question 17

Type of fatty acids

Answer 17

saturated: max number of H atoms, animal origin, single covalent bonds
unsaturated: one or more double bonds, plant origin

mono-unsaturated: one double bond
poly-unsaturated: two or more double bonds
cis unsaturated: H atoms bonded to the same side of the double bond
trans unsaturated: H atoms bonded to opposite sides (coronary heart disease)

Question 18

Phospholipids

Answer 18

two fatty acids + one glycerol
phosphate group rather than third fatty acid
partly hydrophobic - amphipathic

Question 19

Steroids

Answer 19

17 C atoms in 4 rings

e. g. cholesterol, testosterone, estrogen, cortisol and Vitamin D
* Vit D has one broken ring

Question 20

Energy storage (carb vs lipid)

Answer 20

carbs: 100 g = 1760 kJ (but 1g of glycogen is associated with 2g water)
protein: 100g = 1510 kJ
lipid: 100g = 4000 kJ

lipid energy per gram is double
lipids can be stored and utilised without water and so, therefore, is 6x more effective than carbs