BIOL 130 Lecture 5: BIOL 130 – Week Two Notes Cont'd (Cellular Chemistry - LEC 5,6)

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1 Aug 2016
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BIOL 130 – Week Two Notes Cont’d
What are carbohydrates?
-Carbohydrates = a group of molecules that contain carbon, hydrogen, and
oxygen in a 1:2:1 ratio
oAKA “Carbin-Hydrates” (CHOs)
oGeneral formula = (CH2O)n
Ex. Glucose = C6H12O6  (CH2O)6
But sucrose is C12H22O11 ???
-Types:
oMono saccharides - simple sugars
oMonomer = monosaccharide
oDimer = disaccharide
oTrimer = trisaccharide …. oligosaccharide
oOligo saccharides - (oligo = few) small chains
oAttached to proteins - glycoproteins
oAttached to lipids  glycolipids
oPoly saccharides  very long sugar chains
-How to differentiate between oligo saccharides and poly saccharides:
oSmall polymers = oligosaccharide
oBig polymers = polysaccharide
oDistinction b/w 2 is quite cloudy though
What are the typical structural features of sugar monomers?
-Carbonyl group (either ketone or aldehyde)
-Lots of -OH groups
-Vary in length of carbon skeleton (C3, C5, C6, …)
oWhat would you call a 4 carbon sugar??
-Isomeric forms (glucose, fructose, galactose)
oIdentical chemical groups arranged differently
-Monosaccharides often form rings in
solution
What are the 2 types of isomers?
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-Structural Isomer =
identical groups but
bonded to different
carbons
-Stereo (Optical) Isomer
= identical groups bonded
to the same carbons but
in different orientations
-There are 16 different hexose structures possible, all with the formula:
C6H12O6
Does the arrangement of hydroxyl groups make a big difference in biological
function?
-Just simply arranging molecules differently completely changes how said
molecules can be used by the cell
-As fuel:
oGlucose = the main source of chemical energy for cellular respiration
oGalactose must first be converted to glucose before it can be used as
fuel
-As sweeteners:
oGlucose + Fructose = Sucrose (table sugar)
oGlucose + Galactose = Lactose (milk sugar)
Lactose is not as sweet, a lot of people have difficulty using it as
a food source, causes intestinal damage
What is an anomeric carbon and anomer?
-Anomeric Carbon = stereocentre; Carbon on which OH is bonded to
-Direction on which bond occurs determines linkage:
oWhen OH comes in to bond from the top  Alpha glucose with OH
pointed down
oWhen OH comes in to bond from the bottom  Beta glucose with OH
pointed up
-Anomer = cyclic monosaccharide or glycoside
How are disaccharides formed through condensation reactions?
-Monomers are linked when C1 of one monosaccharide binds to a C on
another – often C4
-Geometry of bond different depending on:
oWhether OH group of C1 is in α or β position
oWhich C of other sugar is involved in linkage
-Geometry at C1 position (anomeric carbon) determines the type of bonds
we’ll make - Important because 2 glucose rings are now in same planes*
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oAlpha 1,4 linkages just line-up parallel to each other to form bonds
oBeta 1,4 linkages require flipping of ring structures by 180 degrees to
form bonds
-Abilities to form bonds affect our use for these molecules + our ability to
break them down
How is polymerization used to build
polysaccharides and what
polysaccharides are made?
-Both are storage forms for energy
-It’s a reversible system – can be
broken to release energy
(glucose) or converted to it
-Starch – plants; Glycogen – animals
-Both consist of α-glucose monomers linked by α-1,4 bonds
-Both coil into a helix (due to geometry of linkages)
-Starch is mixture of unbranched amylose (α-1,4 ) and branched amylopectin
(α-1,4 and α-1,6 )
-Glycogen is highly branched (α-1,4 and α-1,6 )
What is Cellulose?
-Cellulose = a structural
polysaccharide in plants;
polymer of β-glucose, joined by β-1,4 linkages (really just a difference of
geometry b/w alpha and beta)
-Each glucose is flipped relative to adjacent ones
-Allows for H-bonding between adjacent strands
-Extremely stable + resistent to outside forces
-Most abundant organic molecule on earth
What is Chitin?
-Chitin = a structural polysaccharide in
animals; a component of cell walls of fungi, exoskeletons of arthropods
(insects, crustaceans), radulas of molluscs, beaks of cephalopods
-Second most abundant organic molecule on earth
-But rather than glucose, monomer is N-acetylglucosamine
-Like cellulose, also strengthened by H-bonding between strands
What is Peptidoglycan?
-Peptidoglycan = a structural
polysaccharide in bacteria; a
component of bacterial cell
-The most complex CHO so far!
-2 different alternating monomers linked by β-1,4 bonds
-Chain of amino acids attached to one of the sugars
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