An in-depth, clearly organised, summary of Biological Molecules (the first topic in AS or A-level Biology for the AQA exam board). These are notes that got me an A* in A-level Biology in the 2023 exam year. Can be used for revision as well as understanding.
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biological molecules
carbohydrates
monomers: smaller units from which polymers: molecules made from a
larger molecules are made large number of repeating monomers
joined together
organic compounds which comprise of only C, H and O
carbohydrates are sugars that come in 2 main forms – simple and complex. This
is also referred to as simple sugars and starches.
monosaccharides:
carbohydrate monomers white crystalline solids
simplest "single sugars" same number of C as O atoms
highly soluble. dissolve in water to general formula (CH2 O )n [n
form sweet tasting solutions between 3 and 7]
e.g. glucose, fructose and galactose
hexose monosaccharides
glucose
there is alpha and beta glucose (structural isomers)
biological molecules 1
, the OH position is different, this minor structural difference has a major
effect on biological roles of alpha and beta glucose
carbons are numbered clockwise!
fructose and galactose
the other two hexose monosaccharides to learn
fructose is very soluble- main sugar in fruit/ nectar
galactose is not as soluble as glucose- important in production of
glycolipids and glycoproteins
pentose monosaccharides
pentose monosaccharides have 5 carbon atoms
ribose and deoxyribose (which has one less oxygen- deoxy*) are in RNA and
DNA
all monosaccharides and some disaccharides are reducing sugars- a sugar that
serves as a reducing agent due to its free aldehyde or ketone functional groups in
its molecular structure.
biological molecules 2
, sugars that can donate electrons (or hydrogen) to reduce (reduction is gaining
electrons) another chemical such as Benedict's reagent
disaccharides
condensation reaction: two molecules hydrolysis reaction: breaks a
chemically joining with the removal of chemical bond between two
water molecules and involves the use of a
water molecule
when they join, a glycosidic bond is formed. between the hydroxyl groups of both
the condensation reaction removes the H2 O but an O is then "left behind" as part of
polysaccharides
polymers containing monosaccharides linked with glycosidic bonds
formed by condensation reactions and mostly used as energy store and structural
components
we need to know about starch [plants], cellulose [plants] and glycogen [animals]—
all insoluble!
STARCH
made of many alpha glucose molecules
see iodine test for starch
good storage molecule as:
biological molecules 3
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