Carbohydrates Flashcards
No. of monomer units in oligosaccharides
3 to 10
Solubility of monosaccharides
Freely soluble in water but insoluble in non-polar solvents
General formula of monosaccharides
(CH2O)n
Glucose is a (______) [no of carbon atoms]
Hexose
-H and -OH groups are not (__ ___ _____ ______) as the ring
In the same plane
Uses of monosaccharides (3)
1) Important energy source to produce ATP during cellular respiration
2) Building blocks for synthesis of disaccharides and polysaccharides
3) Raw material for synthesis of organic molecules (e.g. pentose in nucleotides), amino acids and fatty acids
Carbonyl group
C=O
Location of aldehyde and ketone group
Aldose: carbon atom 1
Ketose: any other C atom
Why are aldo-monosaccharides strong reducing agents?
Aldehyde groups are easily oxidised to carboxylic acids
How is the ring form of glucose created?
Oxygen on carbon no. 5 links with carbon no. 1 comprising of the carbonyl group) and transfers its H to the carbonyl oxygen to create an -OH group
Anomeric carbon
carbon bonded to 2 oxygen atoms
Hydroxyl group bonded to ______ ____ in a-glucose versus B-glucose: ____ vs ____ plane of the ring
anomeric carbon; below vs above
ABBA
alpha below beta above
How are two monosaccharides joined together?
joined via glycosidic bond in a condensation reaction
glycosidic bond [chem composition, definition]
C-O-C bond formed between anomeric carbon of one sugar unit and another carbon of another sugar unit
How is one molecule of water added for hydrolysis reaction? (2)
1) incubation with dilute acid at 100’C
2) incubation with enzyme (e.g. sucrase)
glycosidic bond in maltose vs fructose vs sucrose
a(1,4); B (1,4); a(1),B(2)
why is sucrose a non-reducing sugar?
they have no free carbonyl group as both are linked in a glycosidic bond, thus cannot participate in redox reaction
additional step required for test for non-reducing sugars
acid hydrolysis step to break sugar into reducing sugars
Benedict’s test: Under ______ conditions, copper (II) sulfate, which is a ___ ______, is reduced to insoluble ______ ____ by reducing sugars, which exists as a ____ ___ ________.
alkaline conditions; blue solution; copper (I) oxide; brick red precipitate
colour of suspension as conc. of reducing sugars increase
green to yellow to orange to brick-red
Function of starch
carbon and energy store in plant cells
How is starch stored in plant cells? (location: 2)
as starch grains within chloroplasts, or within amyloplasts (specialised plastids for starch storage)
Rough percentage composition of starch
10-30%: amylose
70-90%: amylopectin
Structure of amylose (branching, monomers, bonds)
an unbranched chain of 100s to 1000s of a-glucose residues, joined by a (1,4) glycosidic bonds
Shape of amylose
forms a compact helical structure, where there are 6 glucose units per turn
S->F in plant cells: helical structure of amylose
amylose molecules are compact, thus they take up less space and can be stored more efficiently within the plant cells
Why does sample turn blue-black in colour in presence of starch, when iodine is added?
iodine in I2/KI packs within hydrophobic core of helix to form blue-black iodine-starch complex
Structure of amylopectin (branching, monomers, bonds)
a branched chain of 1000s of a-glucose units, joined by a(1,4) and a(1,6) glycosidic bonds
branch points occur at every __ to __ residues and av. branch legnth is between __ to __ residues
12-30; 24-30
S->F: amylopectin is highly branched due to a(1,6) glycosidic bonds (2)
1) Makes it highly compact, hence starch can be stored more efficiently
2) A large number of free ends are available for hydrolysis by amylase at any one time, allowing for faster rate of hydrolysis
S->F: Starch as a large molecule
makes it insoluble, hence will not affect water potential within cells and living organisms
S->F: Starch consists of 100s to 1000s of glucose monomers
acts as a large store of carbon and energy (respiratory substrate)
S->F: glucose units linked by a(1,4) glycosidic bonds (starch)
Starch can be easily hydrolysed by enzymes, which is present in plants and most organisms
why are there few free anomeric hydroxyl grps in starch?
involved in glycosidic bond formation
S->F: Few free anomeric -OH grps
unreactive, chemically stable
How is glycogen stored in animals? (location of cells, form)
Stored mainly in liver and skeletal muscle in the form of cytoplasmic granules
Function of glycogen in liver and muscle
1) used as source of glucose to maintain blood sugar conc.
2) used as fuel source to generate ATP for muscle contraction
branch points (a(1,6) glycosidic bonds) occur every _ to _ glucose units
8 to 12
How is the structure and properties of amylopectin different from amylose?
more extensively branched, hence more compact
Iodine test for glycogen [observations]
brown solution turns red-violet in colour
Functions of protein in core of glycogen (2)
1) holds/stabilises two glycogen molecules tgt via hydrophobic interactions
2) enzyme that catalyses conversion of glucose into glycogen
Structure of glycogen (5, similar to amylopectin)
1) large molecule
2) several 100s to 1000s of glucose units
3) linked by a(1,4) glycosidic bonds
4) highly branched due to a(1,6) bonds
5) few free anomeric -OH grps as anomeric carbon is involved in glycosidic bond formation
enzyme involved in glycogen hydrolysis
glycogen phosphorylase
S->F: linked by a (1,4) bonds (glycogen)
bonds are easily hydrolysed by enzyme glycogen phosphorylase present in animals
Function of cellulose
important component of cell wall, helps to provide structural support
Monomers and bonds in cellulose
B-glucose units, B(1,4) glycosidic bonds
Orientation -> shape of cellulose
Alternate B-glucose monomers are inverted to form a long, unbranched chain
how does extensive H bonding in cellulose form?
H bonds form between protruding OH grps of parallel cellulose chains
S->F: extensive H bonds
allows for rigid cross-links between chains to form, giving cellulose high tensile strength for structural support
Describe cellulose -> microfibrils -> macrofibrils
Cross-linked cellulose chains group to form microfibrils, which associate with non-cellulose polysaccharides and are arranged in larger bundles to form macrofibrils
Properties of cell walls (2)
1) High tensile strength
2) Full permeability to water and solutes
What does high tensile strength confer?
Confer cellulose stability
Cellulose fibres laid down in diff orientations in diff layers…
allow cell wall to withstand forces exerted in all directions
S->F: cellulose is large
insoluble, hence good structural material
S->F: B-glucose are linked by B(1,4) glycosidic bonds
they have diff molecular shape from a(1,4) glycosidic bonds, thus amylase cannot hydrolyse them. few organisms produce cellulase, hence cellulose is stable
S->F: cellulose provides high tensile strength for structural support (3)
1) Alternate B-glucose units linked by B (1,4) glycosidic bonds are inverted, allowing cellulose to form long, unbranched straight chains
2) Extensive hydrogen bonds between parallel chains
3) Parallel cellulose chains are grouped in microfibrils, which eventually cluster into macrofibrils
