carbs + lipids + proteins

Question 1

features of monosaccharides (4)

Answer 1

1. linear forms have a free carbonyl group hence are all reducing sugars
2. small in size and have multiple OH groups which can form HB with water hence readily soluble in water
3. ring structures exhibit alpha and beta isomerism
4. alpha below beta above

Question 2

features of disaccharides(5)

Answer 2

1. made up of 2 monosacc joined by a glycosidic bond formed between them by condensation rxn tht involve the loss of h20
2. can be split via hydrolysis
3. same as mono
4. all are reducing sugars except sucrose
5. e.g sucrose maltose lactose

Question 3

what are polysaccharides

Answer 3

many monosaccharides joined by a glycosidic bond formed between them by condensation reactions which involve the loss of water molecules

Question 4

points of comparison between the 3 polysaccharides (7pts)
hint: Function
location
monomer
bond between monomers
orientation of monomer
structure of molecule
bonds between molecules

Answer 4

Starch vs glycogen vs cellulose
plant storage vs animal storage vs plant structural (polysacc)
stored as granules in chloroplasts vs stored in liver and muscle cells vs cell walls
2 alpha glucose vs beta glucose
alpha (1-4) within a branch and 1-6 at branch pts vs beta 1-4
same orientation vs alternate beta glucose rotated 180deg wrt to one another
helical and branched vs long str chain
no interchain HB vs interchain hb to form microfibrils

Question 5

how do the structures of starch and glycogen make them good energy storage molecules

Answer 5

helical–> allows many alpha glucose monomers to be packed per unit volume hence making them a compact energy store
most of their OH groups are involved in intramolecular hb within the helix and hence few OH groups avail for HB with water; thus insol in h20 and water potential is unaffected.
branched and thus have multiple branched ends in which hydrolytic enzymes can work on thus more glucose molecules can be released rapidly at the same time and more ATP can be generated by respiration per unit time
large molecules this no effect on WP

Question 6

how the structure of cellulose makes it a gd structural molecule

Answer 6

alternate glucose monomers are rotated 180deg wrt to each other and hence form a long str molecule with free OH grps projecting out in both directions which allow interchain HB between cellulose molecules that are parallel to each other –> forming microfibrils that have high tensile strength
few OH grps avail to HB with water as most are involved in interchain HB –> no effect on WP
meshwork of microfibrils have a porous structure and hence cell wall is freely permeable ; are strong and rigid and distributes stress in all directions to prevent lysis due to osmotic stress.
cellulases that hydrolyse cellulose are found in very few organism; thus cellulose cannot be hydrolysed by most organisms

Question 7

benedicts test for non reducing and reducing sugars

Answer 7

equal vol of sample and benedicts reagent; shake and heat in boiling water
if neg for BT then boil equal vol of sample with di HCL to hydrolyse the saccharides inside, cool and neutralise with NACO3 then redo BT

Question 8

what do lipids consist of

Answer 8

one glycerol and 3 fatty acids

Question 9

describe the formation and breakage of an ester bond

Answer 9

three non polar, hydrophobic hydrocarbon chains are joined to a glycerol backbone via the formation of 3 ester linkages. ester linkage is formed via condensation reaction 1h20 molecule removed

Question 10

describe the structures and properties of glycerol and fatty acids

Answer 10

glycerol vs fatty acids
structure: 3 polar hydrophilic OH groups which are able to form HB with water vs has charged COO- group which can interact with water
both properties are that they’re soluble in water

Question 11

desc the structures and properties of a triglyceride and a ppl

Answer 11

triglyceride consists of 3 long nonpolar hydrophobic hydrocarbon chains joined to a glycerol backbone via ester linkages.

PPL: consists of 2 long non polar, hydrophobic hydrocarbon tails joined to a glycerol backbone via ester linkages, and a hydrophilic, negatively charged

Question 11

list the emulsion test steps

Answer 11

add excess ethanol to a sample and allow to stn ofr 2 mins, add water. if emulsion is formed, lipids present

Question 12

explain how the structures and properties of a triglyceride and ppl are related to their roles in living organisms

Answer 12

triglycerides cant HB with water thus insol and doesn’t affect WP
has a high proportion of C-H bonds from which energy in the form of ATP and metabolic water can be released during oxidation, making triglycerides a suitable energy store
other roles: thermal insulation; improve buoyancy, protective layer, reservoir for fat sol vitamins ADEK
ppls are amphipathic
form bilayers as nonpolar hydrophobic hydrocarbon tails face inwards and the hydrophilic phosphate group face outwards and HB with water

Question 13

what are the properties of a phopholipid bilayer

Answer 13

has a hydrophobic core and is selectively permeable
it acts as a boundary, barrier to charged ions polar and large molecules, allows for compartmentalisation, has transient pores

Question 14

desc the structure of aas

Answer 14

carbon atom covalently bonded to hydrogen atom, r group carboxyl group and amino group

Question 14

properties of aas

Answer 14

can be hydrophobic or hydrophilic according to r groups and exist as zwitterions in solution and act as buffers

Question 15

desc formation of polypeptides

Answer 15

peptide bond formed via condensation (removal of one water molecule) results in the formation of a polymer known as a polypeptide. nucleotide sequence in DNA determines the aa sequence which determines the types and locations of R groups which determine r group interactions which determine the specific 3D conformation and thus function of the protein

Question 15

explain primary structure and the type of bonds it contains

Answer 15

number and sequence of aas in a single ppt chain; peptide bonds present

Question 16

explain secondary structure and the type of bonds it contains

Answer 16

structure formed by regular coiling or folding of a single ppt chain–> HB between carbonyl and secondary amine groups of the ppt backbone; R groups are not involved
e.g alpha helix
beta pleated sheet

Question 16

explain tertiary structure and the type of bonds it contains

Answer 16

structure formed by further extensive folding and bending of a single polypeptide chain, giving rise to a spherical globular protein with a specific 3D conformation maintained by HB IB HI and disulfide bonds. r groups r involved

Question 16

explain quaternary structure and the type of bonds it contains

Answer 16

refers tot he association of 2 or more ppt chains into a functional protein molecule; maintained by all 4 types of interactions

Question 17

properties and characteristics of alpha helix

Answer 17

made up a single ppt chain wound into a spiral structure; 3.6 aa per turn

Question 18

properties and characteristics of beta pleated sheet

Answer 18

two ofr more regions of a single ppt chain lying side by side linked tgt by HB, chains may run parallel or antiparallel, forms flat folded sheet

Question 19

structure of haemoglobin

Answer 19

quaternary structure made up of 4 ppt subunits 2 alpha globin and 2 beta globin subunits. each subunit contains a prosthetic haem group consisting of a porphyrin ring and an iron ion
each subunit is arranged so that most of the hydrophilic aas are on the external surface and vice versa
they are held tgt by intermolecular interactions between R groups except for disulfide bonds. they can move wrt to each other, allowing for a change in position that increases haemoglobins affinity for oxygen

Question 20

function of haemoglobin

Answer 20

Fe2+ binds reversibly to O2 so 1Hb can carry up to 4 o2 at a time
haemoglobin soluble in aq env and take part in chem reactions to enable the transport of oxygen
cooperative binding of oxygen

Question 21

structure of collagen

Answer 21

1 molecule consists of 3 helical ppt chains (no tertiary structure) wound around each other like a rope. each chain contains about 1k aas and contain a repeating sequence, usually a repeating tripeptide unit: glycine-X_Y where x and y are usually proline and hydroxyproline. they form a tight compact coil due to glycine, the smallest aa, allowing the r group to fit into the restricted space in the center of the triple helix.
extensive HB between aa residues of adj ppts make it insoluble; adj tropocollagen molecules r arranged in a staggered manner
covalent cross links between lysine residues at c and N ends of adj tropocollagen molecules result in the formation of fibrils

Question 22

function of collagen

Answer 22

bulky and relatively inflexible proline and hydroxyproline residues confer rigidity to the molecule, increases tensile strength and is insoluble in water; staggered arrangement minimises points of weaknesses along fibrils; has very high tensile strength making it a suitable component of connective tissue

Question 23

biuret test outline

Answer 23

add equal vol of KOH and 2 drops of copper sulphate; present means purple colouration observed