carbohydrates Flashcards
functions of carbohydrates
energy store
- starch in plants
- glycogen in animals
structural
- cellulose in plants
- chitin in insects
cell recognition
- cell surfaces carbohydrates
metabolism
- metabolic intermediates
- energy substrates
sizes of carbohydrates
monosaccharides
- single sugars
- basic units of carbohydrates
oligosaccharides
- 2-10 residues
- name changes depending on how many eg di or try
polysaccharides
- more than 20 residues
- macromolecules with long chains
- made of one or many monosaccharides
monosaccharides
simplist carbohydrates - building blocks
cannot be easily broken down
classifying according to:
- number of carbon atoms in structure
- whether they have an aldehyde (aldose) or ketone (ketose)
structure of a monosaccharide
aldoses
all have aldehyde group on first carbon -CHO
CH2OH on lowest carbon
in same group have same general formula with different arrangements of OH groups
glucose, mannose and galactose
structure of glucose
structure of mannose
structure of galactose
ketoses
all have ketone group on second carbon C=O
CH2OH on first and last carbon
within group have same general formula with different arrangement of OH groups
names end in -ulose
eg fructose
structure of fructose
what is an epimer?
different compounds with the same molecular formula that differ by configuration at only one carbon
important as biological system can differentiate between them
eg glucose and galactose
have same atoms joined to same atoms
except configuration at carbon 4
= c4 epimer of glucose
hemiactal
where intramolecular (within some molecule) monosaccharides react with themselves
hydroxyl OH reacts with a carbonyl C=O
internal hemiactal
occurs in monosaccharides with 5 or more carbons
results in a ring structure
forms a new chiral (asymmetric) carbon
carbon atom bound with 4 different groups bonded to it
special as bonded to 2 oxygen atoms
called anomeric carbon
common monosaccharides
glucose
fructose
ribose
galactose
glucose
aldose (aldahexose)
monomer to create cellulose
central to cell metabolism
found in monosaccharide form in plants, fruit and blood
structure
fructose
ketose (ketohexose)
monomer to create sucrose
found in leaves, fruit and honey
anomeric carbon of ketone is c2 not c1
structure
ribose
aldapentose
component of ribonucleic acid
reduced form (deoxyribose) used in DNA
structure
galactose
component of lactose
makes galactans - structural cell wall polysaccharide in plants
component of antigens on blood cells that create blood groups
how are monosaccharides joined?
hydroxyl OH on carbon 1 reacts with the hydroxyl on carbon 4 of another molecule
2 hydrogens and an oxygen released in a condensation reaction = water
covalent bond forms between oxygen on anomeric carbon and carbon 4 of another
= glycosidic bond
what is a disaccharide?
two monosaccharides joined by a glycosidic bond
alpha or beta depending on arrangement of OH on anomeric carbon
eg maltose, lactose and sucrose
maltose
2 glucose molecules
formed during breakdown of starch
alpha 1,4 bond
structure
lactose
galactose and glucose joined by beta 1,4 bond
beta bond harder to degrade than alpha = harder to breakdown
structure
sucrose
fructose and glucose joined
both anomeric carbon of fructose and glucose involved
glycosidic bond described differently depending on which molecule you start with
if start with glucose = alpha 1,2
if start with fructose = beta 2,1
structure
reducing sugars
a sugar that can be oxidised and therefore acts as a reducing agent
if only one anomeric carbon involved in bond, free anomeric is not trapped in ring structure
free to reform a straight chain
means carbonyl carbon on straight chain is free to be oxidised
if oxidised then acts as a reducing agent and reduces other molecules
eg maltose
what determines whether a sugar is reducing or non-reducing?
which carbons are involved in the bond
only one anomeric involved means second glucose isn’t trapped
can reform a straight chain
not in ring structure
non-reducing sugars
eg sucrose
fructose is a ketose (anomeric carbon is carbon 2)
means anomeric carbon of both glucose and fructose is used in the glycosidic bond
so both locked I bring and no straight chains form
sugar derivates
as well as monosaccharides, there are derivates
include amino sugars, acidic sugars and deoxy sugars
deoxy sugars
formed when a hydrogen replaces one of the hydroxyl groups
eg ribose and deoxyribose
acidic sugars
formed when a carboxylic acid group replaces the CH2OH at carbon 6
creates a uronic acid
eg glucuronic acid for glucose
amino sugars
formed when hydroxyl group is replaced by an amino group
further modification of amino group by acetic acid forms an amide
eg amino sugar of glucose = glucosamine
amide modification is N-acetyl-glucosamine
polysaccharides
polymers of monosaccharides
two types based on presence of basic sugar units
can be straight or have side chains
functions include storage and structural
homo/hetero polysaccharides
homo = one monosaccharide unit repeated
hetero = more than one monosaccharide unit
properties of a storage polysaccharide
energy stores
- many monosaccharides in one, broken down and used in metabolism
alpha links readily degraded by enzymes
- means they can be broken down easily
highly branched
- rapid release of monosaccharides
- more monosaccharides sotred within
- more ends made for quicker enzyme action
less dense energy store than triacylglycerol
- due to associated water weight whereas triacyglycerol is hydrophobic
glycogen
storage polysaccharide in animals
stored in liver and muscle cells
structure similar to amylopectin
but more alpha 1,6 branches every 10-12 glucose molecules
more branches = more glucose per molecule
many branches = many non-reducing ends
so more easily broken down by enzymes
inulin
storage polyacchiade in root and tubers of some plants
polymer of fructose, and usually glucose at one end
joined by an alpha 1,2 bond
non-reducing sugar
both anomeric carbons used in glycosidic bonds, cant open up
not digested in human gut
regulate osmosis and stabilise membranes
industrial applications of inulin
food industry
- honey
- isolated frucrans = dietary fibre
oligofructans = sweeteners in reduced calories foods
properties of structural polysaccharides
provide structural integrity in plant, agal and fungal cell walls
form skeleton of arthropods
contain beta links between sugars
not as easily broken down by enzymes
alternate monosaccharide units invert to give long straight chains
hydrogen bonding between chains increases strength
viscous polysaccharides contain substituted monosaccharides which are charged a physiological pH
starch
energy storage polysaccharide in plants
present in starch granules of chloroplasts
two components - amuse and amylopectin
amylose
glucose polymer with alpha 1,4 bonds
one long chain with one reducing sugar end (locked in ring) and one non-reducing (straight chain) end
angle of glycosidic bonds cause coils and form a helix
- two helical forms: single or double
not soluble in cold water (only hot)
amylopectin
glucose polymer with alpha 1,4 linked backbone
branches joined by alpha 1,6 bonds every 15-25 glucose units
branches = more glucose molecules per chain
one reducing end and many non-reducing ends
- useful for quicker enzyme action for metabolism
industrial applications of starch
food industry
- thickener and stabilisers
pharmaceutical industry
- filler in drug tablets due to large polymeric structure
cosmetics
- foundation and toothpaste
paper
- provide strength and smoothness
glue
- swells and gelatinises
biofuels
cellulose
structural polysaccharide in plant cell walls
glucose polymer joined by beta 1,4 bonds
alternate monosaccharide unit invert to create long straight chains
- important for structural integrity
several chains align to form microfibrils
- hydrogen bonds between chains
- arrange in random directions to give strength to cell walls, no shear plane
chitin
structural polysaccharide in insects and crustacean exoskeletons
beta 1,4 linked N-acetyl glucosamine
base unit is a sugar derivative
hydroxyl group at carbon 2 of glucose replaced by amide group
peptidoglycan
chains of heteropolysaccharide composed of alternating N-acetyl glucosamine and N-acetyl muramic acid
linked by beta 1,4 bonds
used in bacterial cell walls
held by tetra-peptide chains attached to NAM
- cross links to another chain
- forms strong structure for cell wall
peptide chains on N-acetyl muramic acids residues in adjacent molecules are linked by further short peptide chains
what determines blood groups?
short polysaccharide chains attached to cel membrane protein
terminal 3 or 4 sugars determine the blood group sugars
galactose
N-acetylglucosamine
N-acetylgalactosamine
fructose
blood group types
type O = no terminal sugar
type A = alpha 1,3 linked GalNac
type B = alpha 1,3 linked galactose
why must the correct blood group be given?
must not give blood cells with surface antigens that will react with recipients plasma antibodies
A or AB can receive A
B or AB can receive B
O can only receive O
AB can receive any
O = universal donors
AB = universal recipients
