2.3 carbohydrates and lipids

Question 1

outline the structural organization of carbohydrates (monomer —> polymer)

Answer 1

monosaccharides are joined together by condensation reactions to form polysaccharides (water produced)

the covalent bond connecting the monosaccharides together is called a glycosidic linkage

polysaccharides can be digested into smaller oligosaccharides via hydrolysis reactions (water is required)

Question 2

list three examples of monosaccharides, disaccharides and polysaccharides

Answer 2

monosaccharides: glucose, galactose, fructose

disaccharides: lactose, sucrose, maltose

polysaccharides: cellulose, glycogen, starch

Question 3

list 3 functions for carbohydrates within cells

Answer 3

short term energy source (glycogen and starch)

structural component (cellulose in plant cell walls)

cell recognition and signaling (glycoproteins in plasma membranes)

Question 4

complete the following table comparing different polysaccharides of glucose

Answer 4

cellulose:
monomer- b glucose
bonding- 1-4 linkage
shape- linear (sheets)
function- structural component of plant cell walls

amylose:
monomer- a glucose
bonding- 1-4
shape- linear (helical)
function- short term energy storage in plants (type of starch)

amylopectin:
monomer- a glucose
bonding- 1-4 AND 1-6
shape- less branched (per ~20 units)
function- short term energy storage in plants (type of starch)

glycogen:
monomer- a glucose
bonding- 1-4 and 1-6
shape- more branched (~per 10 units)
function- short term energy storage in animal cells

Question 5

identify the main classes of lipids

Answer 5

simple lipids
esters of fatty acids:

triglycerides, waxes

compound lipids
esters of fatty acids and other groups:

phospholipids, sphingolipids

derived lipids
composed of hydrocarbon ring:

steroids, cholesterol

Question 6

list five different functions of lipids

Answer 6

storage of energy (triglycerides)
hormonal role (steroids)
insulation (sphingolipids)
protection of organs (triglycerides waxes)
structural component (phospholipids)

SHIPS

Question 7

compare the use of carbohydrates and lipids (triglycerides) as energy sources

Answer 7

storage: t= long-term storage; c= short-term energy storage

osmotic effect: t= have less effect on osmotic pressure (they are hydrophobic/not a solute)

digestion: c= are easier to digest (more readily consumed and can be digested anaerobically)

ATP yield: lipid digestion has a higher ATP yield (~twice as much energy per gram)

solubility: t= are insoluble in water and hence harder to transport

Question 8

explain why carbohydrates and lipids are used preferentially to proteins as an energy source

Answer 8

proteins digestion produces nitrogenous wastes (due to presence of an amine group)

nitrogenous wastes are toxic to cells (must be removed via excretion by the kidneys)

Question 9

differentiate between saturated and unsaturated fatty acids

Answer 9

saturated fatty acids do not have double bonds (possess maximum amount of hydrogen atoms)

unsaturated fatty acids possess double bonds (may be monounsaturated or polyunsaturated)

Question 10

contrast cis and trans isomers

Answer 10

cis:

-H atoms on the same side of double bond
-double bond creates kink in fatty acids chain
-are loosely packed and usually liquid
-occurs commonly in nature
-generally considered good for health

trans:

-H atoms on opposite sides of the double bond
-double bond does not create kink in chain
-are tightly packed and usually solid
-occurs in processed foods
-generally considered bad for health

Question 11

identify the role of high density and low density lipoproteins

Answer 11

low density proteins transport cholesterol from the liver to the rest of the body

high density lipoproteins scavenge excess cholesterol and return it to the liver for disposal

Question 12

outline the effect of different type of fatty acids on lipoprotein levels

Answer 12

cis fatty acids raise levels of HDL (high density lipoproteins) —> lowers blood cholesterol

saturated fatty acids raise level of LDL (raises blood cholesterol)

trans fats raise levels of LDL and lower level of HDL (significantly raise blood cholesterol)

cis fatty acids are generally considered good for health, saturated and trans fats are considered bad for health

Question 13

describe the health implications associated with high levels of blood cholesterol

Answer 13

high cholesterol levels lead to hardening and narrowing of the arteries (atherosclerosis)

the cholesterol forms fat deposits in the arterial lining, leading to the development of plaques

if a plaque ruptures, blood clotting will cause the vessels to become blocked

if coronary arteries become blocked, coronary heart disease will result (including heart attacks)

Question 14

discuss the evidence for and against health risks associated with diets rich in lipids

Answer 14

for:
-a positive correlation exists between intake of saturated fats and incidence of CHD
-intervention studies demonstrate that lowering intake of saturated fats reduces onset of CHD
-in patients who have died from CHD, fatty deposits with high levels of trans fats were found in arteries

against:
-certain populations have high fat intakes but low rates of CHD (maasai tribe in africa)
-genetic factors play a significant role (blood cholesterol levels only show a weak association to diet)
-results from intervention studies are influenced by cohort size and composition, as well as study duration

Question 15

BMI formula

Answer 15

kg (m2) -1

65/ (1.75 x 1.75)

kg divide by height in m x m