Carbohydrates Flashcards
carbohydrates roles
energy storage/ transport (metabolic energy)
cell-cell communication/ adhesion
host-pathogen/symbiont interactions
structural components
DNA/RNA components
carbohydrates elemental composition
C,H,O,S/N
2+ hydroxyl groups
2 simplest carbs
glyceraldehyde
dihydroxyacetone
aldose number of asymmetric carbons
aldoses have 1 more asymmetric carbons than ketoses
chiral centre
4 different groups
different 3D conformation
C1
aldehyde carbon
C2
carbonyl group in ketoses
aldehyde + alcohol
hemiacetal
pyranose
6C ring due to similarity to pyran
why do aldose sugar rings form
alcohol is part of same molecule as aldehyde/ ketone
aldose sugar rings in solution
dominate as more energetically favorable than open-chain form
ketone + alcohol
hemiketal
non-planar chair configurations
axial (opposite directions on adjacent carbons)
equatorial (less crowded)
anomers
sugar isomers with 2 anomeric carbons
additional chiral crabon for ring-formation aldoses
C1
alpha anomer
C1/C5 have same stereochemistry
beta anomer
C1/C5 have different stereochemistry
anomeric C in ketones
C2
glucose assymetric carbons and variations
2 stereoisomers D/lL
4 asymmetric carbons
what form is glucose most commonly found in?
D form
dextrorotatory
rotate plane of polarised light to the right
laevorotatory
rotate plane of polarised light to left
epimers
when only asymmetric C2,3 or 4 are in a different configuration to glucose
cylization of open-chain form of glucose
C5 hydroxyl group attacks oxygen atom of C1 aldehyde group to form intramolecular hemiacetal
2 anomers alpha/ beta
ketohexose cyclization
C2 keto group reacts w C6/5 hydroxyl group to form intramolecular hemiketal
glycosidic bond
bond formation between hemiacetal group of sugar and oxygen of hydroxyl group via loss of water in condensation reaction
1-4, glycosidic linkage
N/ S glycoside formation
sugars can join w other hydroxyl containing molecules (O-glycosides)/ -NHR/-SH
Alpha glycosidic bond
bond on C1 opposite configuration to C5 same sugar
C1 axial in D sugar
maltose
2* alpha glucopyranose
starch digestion product
beta glycosidic bond
bond on C1 in same configuration to C5 of same sugar
equatorial in D sugar
lactose
galactopyranosyl/ glucopyranose
milk sugar
lactase enzyme breakdown
sucrose
alpha glucopyranosyl/ Beta fructofranose
transport form of carbs in plants
sucrase breakdown
reducing end
terminal sugar in which C1 is unattached/ aldehyde can form
non-reducing sugar
terminal sugar in which C1 is involved in glycosidic bond
reducing sugar
any sugar capable of acting as reducing agent due to free eldehyde or ketone group
alpha glucans
a 1,4 linkage kinked, causing polysaccharide twisting into helical structure
therefore more compact, storage molecule, degraded quickly when needed
glycogen/ starch
polysaccharides of D-glucose linked by alpha 1,4- glycosidic and a 1,6 branching
cellulose
beta 1,4 linked glucose planar chains cross-linked by H bonds
crystalline microfibrils
cellulosic biofuels
hydrolysis of cellulose to glucose via enzymes converting glucose to ethanol in microbial fermentation
cellulosic biofuel pros
no net CO2 release
use of agricultural waste
high availability
cellulosic biofuel cons
recalcitrant to enzyme digestion due to structure
expensive/ inefficient
gram neg bacteria peptidoglycan
1/ 2 layers
e.g. E coli
gram pos bacteria peptidoglycan
40+ layers
e.g. staph. aureus
tetrapeptide
4 amino acids joined by peptide bonds
cross-linked by short peptides
membrane-associated transpeptidases
produce links
e.g. e.coli (direct link)
s. aureus (pentapeptide bridge) < pentaglycine bridge
penicillin mechanism of cross-links
inhibtion of cross-linkage transpeptidase via substrate mimicking> slotting into transpeptidase substrate
lysozyme mechanism
targets cell wall sugar backbone
glycoconjugates
carbohydrates covalently linked to other molecules (e.g. proteins/lipids)
glycoproteins
eukaryotic proteins with carbohydrates attached
N-linked
joined to amide of asparigines (N)
usually on secreted proteins#
complex oligosaccharide structures
N-glycosylation functions
protein folding
stability
cell recognition
O-linked
joined to hydroxyl of serine/threonine
commonly N acetyl glucosamine
cytoplasmic
phosphorylation reciprocal
mucins
O-linked glycoproteins
mucus component
cover epithelial surface for lubrication/ protection
proteoglycans
proteins attached mostly by O-linkage to polysaccharides (GAGs)
proteoglycans functions
joint lubricant
ECM structure
ECM adhesion mediation
bind cell proliferation factors
GAG
glucosaminoglycan
disaccharide repeats of amino sugar and uronic acid sugars
sulfated
bind much water to form hydrated gel
complex carb synthesis
glycosyltransferases catalyze glycosidic bond formation and trasnfer activated sugar nucleotides to molecule
blood group A
produce GTA that put GalNAc on
blood group B
produce GTB that put a Gal on
blood group O
GT’s non-functional
Blood group AB
produce both GTA/GTB
Sars-Cov-2 viral infection
surface spike proteins bind to human ACE2 receptors on host cell surface
antibodies bind to spike proteins, blocking interaction between virus and ACE2
Glycans on spike limit/ reduce atibody-binding
spike proteins
heavily glycosylated
involve different kinds of N-glycans
RBD’S
RBD
receptor binding domains
up/ down state
needs to be up to bind to ACE2
N-glycan types
high mannose
complex
hybrid
specific N-glycans stabilise RBD up state
