Carbohydrates Flashcards
what are the functions of carbohydrates?
-storage
-energy source
-structural
-inter-cellular communication
what is the general formula of carbohydrates?
(CH2O)n
what structure do larger monosaccharides have?
form ring structures
what are six and five member rings called?
-five: furanoses
-six: pyranoses
how can you differentiate between aldoses and ketoses?
-if oxygen is on an aldehyde, it is an aldose
-if oxygen is on an a ketone, it is a ketose
which stereoisomers do carbohydrates form
Form D- and L- stereoisomers
which stereoisomer is naturally found?
D-stereoisomer
what other shape can sugars be found (apart from rings) and why?
can form chair conformation because of the spread of electrons
two different anomers can exist, why and what is the importance of this
why = depends on orientation of OH group on anomeric carbon (carbon 1)
important because the orientation of OH group determines the shape of the molecule when sugars bind to each other
which 2 anomers exist?
OH group can be across from each other (equatorial)
or
OH group can be down from each other (axial)
how is a glycosidic bond formed?
when two monosaccharides join together in a condensation reaction
what does a glycosidic bond being beta or alpha depend on?
the orientation of the OH group
which other chemical groups can carbohydrates contain?
-phosphate
-amino
-acetyl
how can other chemical groups affect carbohydrates?
-changes properties e.g. charge
describe glucosaminoglycans
-unbranched polysaccharide made up of repeating disaccharide units that contain a hexosamine and uronic acid
-highly polar and attract water
how do disaccharides differ?
-types of monosaccharide
-nature of bond
what is an oligosaccharide?
-more than two but less than a lot (maybe 6) monosaccharides
describe O-linked glycosylation
-attachment of sugar molecule to oxygen atom of certain amino acids
-this is a post-translational modification
-clustered in proteins
-has protective role e.g. mucin
describe N-linked glycosylation
-attachment of oligosaccharide to nitrogen atom of certain amino acids
-spread through protein
-more variable
-has effect on protein folding, activity and cellular location
what is mucin?
a glycoprotein constituent of mucus
what is the difference between homopolysaccharides and heteropolysaccharides?
-homopolysaccharides are made up of the same monosaccharides
-heteropolysaccharides are made up of different monosaccharides
what is cellulose?
-linear chains of glucose joined by beta 1-4 glycosidic bonds
-main component of plant cell walls
-strong bc lots of H bonds form between the straight chain glucose
-forms more complex structures w other polysaccharides
describe chitin
-main structural component of exoskeletons of insects, crustaceans, spiders
-present in cell wall of fungi, algae and in capsule of some bacteria
-structurally different from cellulose bc formed from chains of N-acetyl-D-glucosamine
-stronger than cellulose
describe starch
-stores energy in plants as food reserve
-forms insoluble granules in cytoplasm
-made of a-amylose and amylopectin
describe a-amylose
-linear homopolysaccharide
-glucose monomers linked by alpha 1-4 linkages
-forms spiral structure (helical conformation) bc bonds are in different places compared to cellulose - this makes it more compact
Describe amylopectin
-branched bc of occasional 1-6 linkages
-can contain up to million glucose monomers
Describe glycogen
-present in all tissue but prevalent in liver and muscle
-structurally similar to amylopectin but more branched
-degraded to glucose by glycogen phosphorylase and debranching enzyme
Describe glycoproteins
short carbohydrate chains covalently linked to serine, threonine or asparagine
-often branched
-circulating proteins
how is glycogen degraded to glucose?
-glycogen phosphorylase removes glucose molecules at end of chains
-debranching enzymes act as transferase by removing glucose molecules near branch points and also cleave branch points
what are examples of glycoproteins?
-hormones
-antibodies
-extracellular matrix
-enzymes
-components of bacterial cell wall
What 2 ways can carbohydrate groups in glycoproteins be linked
N-linked glycosylation tends to be quite variable and has important effects on protein folding, activity and cellular location
O-linked glycosylation often occurs in clusters on proteins with a protective role ie mucin
what are the functions of salivary mucins?
-Have between 2 and 7 sugar units attached
-formation of mucus
-lubrication
-modulation of oral bacteria
what are the two forms of salivary mucins?
high or low molecular weight mucins
describe glycolipids
-Cerebrosides and gangliosides
-present in all eukaryotic cell membranes
-involved in intercellular communications
-contain the same oligosaccharides as glycoproteins
-act as cell recognition factors
-important feature of bacterial cell wall - causes strong immune reaction in humans
-glycolipids determine blood group
GlycoRNA?
Paper published last year describes existence of glycosylated RNA
Found on plasma membrane
As yet, function unknown
describe digestion of carbohydrates
-begins in the mouth
-saliva contains a-amylase which hydrolyses alpha 1-4 linkages except outermost bonds
-along w chewing, this reduces polysaccharides to oligosaccharides of eight or less monomers
-further digested by pancreatic a-amylase and other glycosidases
-some bacteria break up complex carbs that body cannot do itself
Digestion overview
describe the relationship bw carbohydrate intake and oral health
-high carbohydrate intake is linked to oral health (caries, gum disease (diabetes predisposes)
-bacteria in mouth that can cause gum disease uses glycoproteins and glycolipids as food source
describe Glycocalyx
-The glycoproteins and glycolipids on the cell surface form the glycocalyx
-This forms a thick protective barrier
-In bacteria, the glycocalyx can form a layer on which bacteria can adhere to objects such as replacement joints and teeth
