• Carbohydrates contain carbon, hydrogen and oxygen, usually with the general formula CnH2nOn
Glucose
• A monosaccharide with the formula C6H12O6 Monosaccharides are small
soluble carbohydrate
• A hexose monosaccharide (six carbon atoms) in a ring structure
monomers. They also include
• Soluble in water → easily transported
fructose and galactose.
• Main energy source for animals and plants
→ chemical bonds store lots of energy
• Two isomers: α-glucose and β-glucose → H and OH groups on carbon 1 inverted in β-glucose
Displayed formula: Skeletal formula:
K0H glucose B-glucose
C11-2OH
a-
B-glucose
a-
glucose carbon
I
numbers
µ " "
-5C "
\ [
µ -0 c-
Hit H
, _ OH
[
4 '
OH HI '
H , OH HO
H GH H
'
OH
Glycosidic bonds and condensation/hydrolysis reactions
• Condensation reaction: two molecules join to form a new chemical bond and a water molecule is
eliminated
• Condensation reactions form glycosidic bonds between monosaccharides to create disaccharides and
polysaccharides
• Hydrolysis reaction: a water molecule is used and the chemical bond is broken (reverse of a
condensation reaction → breaks glycosidic bonds)
"
fHzOH FH20 polysaccharide with glycosidic bonds
"
'
÷
" " .
"
, '
o OH - ◦ -
↑ ↑
↓H'
H20 inserted H20 inserted
it
'
OH
FH20
"
f. HZOH FH20 µ ✓
hydrolysis reaction
,
q
H c- ° c- ◦
, /
, ,HH , / "
"
to
I 1
no "
OH
to OH
monoofaccharidesT.IO µ OH
GH glycosidic f GH
bond
Disaccharides
• Two monosaccharides joined together with a glycosidic bond in a condensation reaction
• Maltose = glucose + glucose
• Sucrose = glucose + fructose Monosaccharides and
• Lactose = glucose + galactose disaccharides are sugars.
Polysaccharides
• Large polymers of monosaccharides joined with glycosidic bonds
• Starch and glycogen are large energy storage molecules which cannot leave cells
Starch Iodine test for starch
• Glucose storage in plants → hydrolysed when glucose is needed 1) Add iodine in potassium iodide
• Insoluble in water → does not affect the water potential of solution to sample.
cells so water is not drawn in by osmosis 2) If starch is present: goes from
• Amylose → unbranched α-glucose polysaccharide (1,4 glycosidic browny-orange to blue-black.
bonds)
→ helical structure so is compact amylose -
amylopectin
-
• Amylopectin → branched α-glucose polysaccharide (1,4 and 1,6
I
/
'
glycosidic bonds) ii. ÷ .
-
-
-
,
_
-
→ branches mean enzymes can easily access more /
I
✗
glucose
-
glycosidic bonds = faster glucose release 1
-
↓
I
-
.
-
.
,
_
Glycogen Cellulose
• Excess glucose storage in animals • Found in plant cell walls to give strength
→ easily hydrolysed when glucose is needed • Unbranched long and straight β-glucose polymers
• Insoluble in water → does not affect the (1,4 glycosidic bonds)
water potential of cells so water is not drawn • Chains linked with many hydrogen bonds to form
in by osmosis strong rigid microfibrils
• Highly branched α-glucose polysaccharide (1,4
hydrogen
- -
-
-
and 1,6 glycosidic bonds) → more ends so B- glucose i t ' " " -
bonds
→
. .
glucose can be released quickly by enzymes, i. i. i. i.
"
Using a colorimeter
• A more accurate and quantitative way to measure glucose concentration after the Benedict’s test
(judging colour is subjective and more affected by human error)
• When the precipitate is filtered out of the solution, the solution left is the Benedict’s reagent
→ more glucose = more precipitate = the less blue the remaining solution will be
• A colourimeter measures absorbance of light → lower absorbance = more blue colour lost = more glucose
• Zero the colorimeter to distilled water to make sure values are comparable
• Can use a serial dilution of a known concentration of glucose to produce a calibration curve
In this case we are diluting the glucose Carrying out the Benedict’s test on all tubes
solution by a factor of two each time. and a negative control (distilled water) will
produce a calibration curve.
transfer transfer transfer
transfer } }
} 5cm
}
5cm 5cm
5cm
negative
A) mix mix
o6☒←
+
control
mix mix
✗
%"
to get to get target
§
05 -
✗
-
IM 05M 025M 012514
> calibration
04 -
× curve
-
- -
§ 03 -
Wvu
v
•
v v -
002 -
>
Of ↑ in ✗
10cm [ ↑
£ °"
2M
glucose }
-
5cm distilled water
solution
in each tube ◦
to start to 65 to I5 2IO
concentration ( M)
glucose
Make sure to mix Now we can measure the absorbance of a
well at each stage. glucose solution with an unknown concentration
and use the calibration curve to find the
concentration. This is called interpolation.
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