Biological molecules - Carbohydrates Flashcards
what elements do carbohydrates contain
C, H and O
what is the general formula for carbohydrates
(CH2O)n
what are the functions of carbohydrates
source of energy e.g glucose
store of energy e.g starch and glycogen
structural units e.g cellulose (plants) chitin (insects)
components of nucleic acids, glycolipids
describe the structure of carbohydrates
carbohydrates can be monomers or polymers, meaning that they can be single molecules or larger molecules made of the same repeating units
how are carbohydrates classified
monosaccharides, disaccharides and polysaccharides
what are the properties of monosaccharides
sweet, soluble in water, form crystals
describe the structure of monosaccharides
can be straight chain or ring form
triose sugars contain 3 carbons
pentose sugars contain 5 carbons (e.g ribose, deoxyribose)
hexose sugars contain 6 carbons (e.g alpha glucose, beta glucose, galactose)
describe the structural difference between alpha and beta glucose
alpha glucose has a hydrogen above the hydroxyl group on carbon 1, whereas beta glucose has the hydrogen below the hydroxyl group on carbon 1
what are the uses of glucose in living organisms
reactant in respiration, source of energy, used to make larger molecules e.g glycogen
describe the differences between the structure of alpha glucose and ribose
alpha glucose is a hexose sugar whereas ribose is a pentose sugar
ribose has 10 hydrogen atoms whereas alpha glucose has 12
glucose has 4 hydroxyl groups and ribose has 3
what are disaccharides
two monosaccharides joined together by a glycosidic bond
what are the properties of disaccharides
sweet, soluble in water, form crystals
what is formed from two alpha glucose molecules
maltose
what is formed from glucose and fructose
sucrose
what is formed from glucose and galactose
lactose
which reaction is involved in the formation of disaccharides
condensation reactions
describe the formation of disaccharides
two hydroxyl groups interact between the monosaccharides - two hydrogen and 1 oxygen are removed and join to form water
a covalent bond called a glycosidic bond forms between carbon 1 and 4 on the glucose molecules.
which reaction is involved in the breakdown of disaccharides
hydrolysis reaction
describe the breakdown of disaccharides
the reaction needs water and is catalysed by enzymes
what are polysaccharides
polysaccharides are polymers - they are made of many repeating units of monosaccharides that have undergone condensation reactions to join them together.
how is the polymerisation of polysaccharides carried out in organisms
by enzymes
give the properties of polysaccharides
not sweet, insoluble in water, can’t be crystallised
where is starch found
in plants (starch granules)
how is starch formed
many alpha glucose molecules join by glycosidic bonds during condensation reactions to form two different polysaccharides
what are the two polysaccharides that make up starch
amylose and amylopectin
describe the structure of amylose
formed when alpha glucose molecules are joined by 1.4 glycosidic bonds and forms a coiled structure
how is the coiled structure of amylose maintained
by hydrogen bonds
describe the structure of amylopectin
formed when alpha glucose molecules are joined by 1.4 glycosidic bonds and forms a coiled structure, but there are also branches formed by 1.6 glycosidic bonds
what are the three properties of starch
insoluble in water, branched, compact
why is it important that starch is insoluble
it does not affect the water potential of cells. glucose would lower the water potential and cause water to enter the cells by osmosis.
less likely to be lost from cells
why is it important that starch is branched
enzymes can be used to remove glucose molecules (hydrolysis reaction). the branched structure of amylopectin means that lots of glucose can be removed quickly for respiration
why is it important that starch is compact
being compact means starch does not take up a lot of space, making it a good energy storage molecule
where is glycogen found
in animals (glycogen granules)
describe the structure of glycogen
many alpha glucose molecules join by 1,4 glycosidic bonds with 1,6 glycosidic bonds forming branches
how is glycogen different in structure to amylopectin
shorter 1,4 glycosidic chains, more 1.6 glycosidic bonds so more branched and more compact. this means it is easier to remove glucose molecules in glycogen
what are the three properties of glycogen
insoluble in water, branched, compact
why is it important that glycogen is insoluble
does not affect the water potential of cells
less likely to be lost from cells
why is it important that glycogen is branched
enzymes can be used to remove glucose molecules (hydrolysis reaction). the very branched structure of glycogen means that lots of glucose can be released quickly for respiration
why is it important that glycogen is compact
being compact means it does not take up a lot of space, making it a good energy storage molecule
where is cellulose found
in plants (cell wall)
describe the structure of cellulose
cellulose is made of long, unbranched chains of beta glucose molecules joined by 1,4 glycosidic bonds. The cellulose chains are held together by hydrogen bonds, forming strong fibres called microfibrils
how are the chains of beta glucose formed in cellulose
to form the glycosidic bond, alternate beta glucose molecules are rotated through 180 degrees forming straight chains.
how are the microfibrils formed in cellulose
the straight chains of beta glucose molecules have lots of hydroxyl groups projecting from carbon2. These form hydrogen bonds with adjacent cellulose molecules, forming microfibrils.
what to microfibrils join to form
macrofibrils, which join to form fibres, which criss-cross in the cell wall giving extra strength
what are the functions of cellulose
cell walls and fibre
why do microfibrils and macrofibrils have a very high tensile strength
because of the glycosidic bonds and hydrogen bonds between chains.
why is the high tensile strength of micro and macro fibrils important in the cell wall
it prevents plant cells from bursting when they are turgid
why else is cellulose useful in the cell wall
fibres run in all directions, giving extra strength to the cell wall.
spaces between fibres mean the cell wall is fully permeable, allowing water and mineral ions to pass in and out of plant cells.
why are turgid plant cells important
they help to support the structure of the whole plant
why is cellulose important for fibre
cellulose forms the fibre in our diets needed to help maintain a healthy digestive system
what makes cellulose good for cell walls
very strong and insoluble
