Carbohydrates Flashcards
the general functions of carbohydrates
- storage molecules
- main source of energy
- (polysaccharides) insoluble in water
- has a carbonyl functional group
- multiple hydroxyl groups
- forms supporting structures
- general formula (CH2O)n
- either an aldose or ketose w aldehyde or ketone group
Glucose
alpha
HCOH
beta
OHCH
Types of monosaccharides
triose 3C
glyceraldehyde
first sugar formed in respiration or photosynthesis used as a respiratory substrate or to form starch
pentose 5C
Ribose
deoxyribose
component of RNA/DNA
hexose 6C
Glucose
sugar formed from photosynthesis and respiration used as a substrate in ATP production in respiration
used to make other organic compounds like fatty acids and amino acids as its carbon skeleton can be rearranged
Fructose
monomer used in production of sucrose
isomer of glucose
galactose
monomer used in production of lactose necessary for lactating mammals.
isomer of glucose
Physical properties of monosaccharides
- soluble
- crystalline structures
- sweet
chemical properties of monosaccharides
- reducing sugars
monosaccharides have a free aldehyde or ketone group that can donate e- to cu2+ of benedicts solution reducing copper ions to Cu solid. Hence solution turns from blue to red
formation of disaccharides
condensation
formed from monosaccharides
formed through condensation reactions involving the formation of glycosidic bonds between the monomers
e.g.
maltose
an alpha 1,4 glycosidic bond is formed between to alpha glucose monomers with the loss of water to form maltose
lactose
between two beta glucose beta 1,4 glycosidic bond is formed with the loss of water
sucrose
between two alpha glucose, alpha 1,2 glycosidic bond is formed with the loss of water
formation of monosaccharides
Hydrolysis
by cleaving the glycosidic bond between monomers in a disaccharide with the gain of a water molecule
using an acid at high temperature–> used to test for non reducing sugars/ hydrolytic enzymes
Physical properties of disaccharides
- Soluble —> can be moved around in great concentrations with efficiency, great transport sugars (sucrose in plants)
- Crystalline structures
- Sweet
Chemical properties of disaccharides
Reducing sugars except of sucrose in which the aldehyde group of glucose and ketone group of fructose are involved in glycosidic bonding hence not free, unable to donate electron to reduce copper ions to copper
Polysaccharides
Starch
Cellulose
Glycogen
How polysaccharides are formed
when may monomers (usually hexoses) undergo condensation reaction and form numerous glycosidic bonds.
General properties
- Insoluble in water
- they fold into compact molecules allowing for the packing of many monomers
- folded for branched
- exert no osmotic pressure will not interfere with chemical interactions in the cell
- large cannot diffuse out of a membrane
Amylose
polymer
made up of many alpha glucose residues
alpha glucose residues linked together by alpha 1,4 glycosidic bonds
not branched but helical structure
stabilised by hydrogen bonds between helices
soluble only in high temperatures due to breakage of the H bonds
Not able to form cross links as the hydroxyl groups on C2 projecting into the interior of helix
Amylopectin
-highly branched
-made up of many alpha glucose residues
-alpha glucose residues linked together by alpha 1,4 -glycosidic bonds and alpha 1,6 at branch points
-adj glucose residues involved in hydrogen bonding between OH groups these OH groups project into the middle of the helix
-has reduced solubility due to OH groups of residues involved in H bonds with adj residues. Less sites available for water molecules to form H bonds with amylopectin
compact helical structure stabilised by hydrogen bonds
Starch Structure
Above: refer to amylose and amylopectin
Polymer containing amylose helices entangled in branches of amylopectin
large molecule folded into a compact structure
Starch functions
- has numerous branches, branch point for hydrolytic enzymes to act on and hydrolyse starch to glucose. Hence starch can hydrolysed easily
- large but compact. Packs many glucose residues per unit volume.
- Insoluble in water/ exerts no osmotic pressure as it does not participate in H bonds with water and also due to branching
- Large and is not able to diffuse out the cell membrane
- Storage molecule
- Accumulates forming starch grains in chloroplasts
Glycogen structure
more highly branched than amylopectin and starch
large but compact
Glycogen functions
- energy storage molecule
- accumulates to form glycogen granules in liver and muscles
- Highly branched so it can be more easily hydrolysed by enzymes to give glucose when required due to presence of numerous branch points means degradative enzymes can act simultaneously to increase yield of glucose (efficient)
- Glucose removed one by one from non reducing end when glycogen is used as energy source
- one mol. one red. end many non reducing ends
Cellulose structure
- composed of beta glucose residues
- linked together by beta 1,4 glycosidic bonds
- not branched
- straight linear chains of glucose residues run parallel to each other
- adjacent glucose residues rotated 180 degrees with respect to each other
- Intra chain H bonds occur between the hydroxyl and O of adj molecule
- Interchain H bond between OH projecting outwards from each chain and O of parallel chain, this crosslinking binds chains rigidly together
- Cellulose chains associate in groups to form bundles -microfibrils
- Microfibrils arrange in larger bundles to form macrofibrils
- Macrofibrils of successive layers are interwoven in a gel like matrix to form the cell wall increasing the tensile strength
- meshwork of macrofibrils that form the cell wall is porous
- cellulose fibres form a meshwork helps to distribute stress in all directions
Cellulose function
cellulose is a major component of the cell wall
- cell wall has great tensile strength
- it is freely permeable
- highly rigid + strong
