Carbohydrates - polysaccharides Flashcards
what is a polysaccharide
polymers containing many monosaccharides linked by glycosidic bonds
they are polymers of monosaccharides
what are polysaccharides mainly used as
energy stores and structural components
name the energy stores
starch (plants) and glycogen (animals)
name the structural component
cellulose
what is alpha glucose
important molecule as it is the substrate for respiration which occurs in the mitochondria
how does alpha glucose provide energy
enzymes break apart alpha glucose molecules which generate energy in the form of ATP which is utilised by the rest of the body
what is the equation for respiration
glucose + oxygen —-> carbon dioxide + water
how can you create a store of energy
if you join lots of glucose molecules together into polysaccharides you can create a source of energy
how do plants store energy
as starch in chloroplasts
how do animals store energy
as glycogen in cells of muscles and livers
how are glycogen and starch compact
they do not occupy a large amount of space as they both occur in dense granules within the cell
how can glucose be used for respiration
polysaccharides hold glucose molecules in chains so they can be easily snipped from the ends of the chains by hydrolysis when required for respiration
which chains of glucose are branched and which are unbranched
amylose is unbranched whereas amylopectin is branched
are branched or unbranched chains more compact.
branched chains are more compact
what do branched chains allow
they offer the chance for lots of glucose molecules to be snipped off by hydrolysis at the same time, when lots of energy is required quickly
why is it important to have alpha glucose as a respiratory substrate
excess amount of glucose in body fluids are very dangerous for cell structure
what is glucose a product of
photosynthesis
what is glucose a substrate of
respiration
are polysaccharides more or less soluble in water than monosaccharides
less soluble
why are polysaccharides less soluble
because of their sieze and also because regions which could hydrogen bond with water are hidden away inside the molecule
what would happen if glucose molecules dissolved in the cytoplasm
the water potential would reduce and excess water would diffuse in disrupting normal workings of cells
is starch soluble in water
no, it is insoluble in water
why is it important that starch doesnt doesnt dissolve in water
so it doesn’t affect osmosis
how much of starch does amylose and amylopectin make up
20% amylose and 80% amylopectin
what is amylose
long unbranched chain of alpha glucose that has a compact coiled structure. it is good for storage
what is amylopectin
long branched chain of alpha glucose. glucose can be released quickly as it is easier for enzymes to get to the branches
how does alpha glucose form amylose
condensation
how does amylose break down into alpha glucose
hydrolysis
what is the monomer for amylose and amylopectin
alpha glucose
what type of bonding does amylose have
1-4 glycosidic bonding
describe the formation of amylose
as it forms it coils making it compact (due to the bond angles, this is stablisied with hydrogen bonds. it isnt branched so it has few break off points.
what makes amylose less soluble
hydroxyl groups on carbon 2 are situated on the inside of the coil making the molecule less soluble and allowing hydrogen bonds to form to maintain the coils structure
what is the monomer for amylopectin
alpha glucose
what type of bonding does amylopectin have
1-4 and 1-6 glycosidic bonding
describe the formation of amylopectin
as it forms, its branched structures give more break off points (due to the bonding). it coild together into a spiral shape held together with hydrogen bonds but with branches emerging from the spirals
how do animals store carbohydrates
glycogen
what structure is glycogen similar to
amylopectin as it has many alpha 1-6 glycosidic bonds that produce an even more branched structure.
how is glycogen stored
as small granules in the muscles and liver
what is the difference between starch and glycogen
less dense and more soluble than starch and broken down more rapidly. it indicates higher metabolic requirements of animals compared with plants
how are the bonds like in glycogen
1,4 glycosidic bonds between carbon 1 and 4 and branches formed by glycosidic bonds between carbon 1 and 6
why does glycogen have less tendency to coil
1-4 bonded chains tend to be smaller than in amylopectin making it less likely to coil
why does glycogen have more branches
it makes it more compact so makes it easier to remove monomer units as there are more ends
describe cellulose
found in plants to form the cell walls. it is a tough, insoluble and fibrous substance.
what is cellulose made of
from long chains of 15000 beta glucose molecules bonded together through condensation reactions to form glycosidic bonds.
what is different about the structure and bonding of cellulose
its made from beta glucose. the 2nd beta glucose is rotated by 180 degrees. this is so the hydroxyl groups are more closer and bond together. the removal of water forms a glycosidic bond.
why are cellulose chains straight
they lie side by side as a result of the bonding. the hydrogen and hydroxyl groups on carbon 1 are inverted in beta glucose. this means that every other beta glucose molecule chain is rotated by 180 degrees. this and the beta 1-4 glycosidic bonding help prevent the chain from spiralling.
how are hydrogen bonds formed in cellulose chains
they form between rotated beta glucose molecules in each chain giving it additional strenght. the hydroxyl group on carbon 2 sticks out, enabling hydrogen bonds to be formed between chains.
how are macrofibrils formed from microfibrils
when 60 to 70 cellulose chains are bound together they form microfibrils which are 10-30nm in diameter. these bundle into macrofibrils containing 400 microfibrils which are embedded into pectin to form cell walls. macrofibrils run in all directions criss crossing the wall for extra strength
why is cellulose an excellent material for plant cell walls
microfibrils and macrofibrils have very high tensile strength because of the strength of the glycosidic bonds but also because of hydrogen bonds between chains.
why is it difficult to digest cellulose
the glycosidic bonds between glucose molecules are less easy to break. most animals dont have an enzyme to catalyse the reaction
what make the cell wall fully permeable
because plants do not have a rigid skeleton, each cell needs to have strenght to support the whole plant. there is space between macrofibrils for water and mineral ions to pass on their way into and out of cells
what prevents the cell wall from bursting when turgid
the walls high tensile strength prevents plant cells from bursting when turgid. turgid cells press against each other supporting the plant and protecting the cell membrane
what are bacteria cell walls made of
peptigoglycan. this is made from long polysaccharide hains that lie in parallel, cross linked by short peptide chains.
