Carbohydrate activity for AP Biology
Obtain an organic molecule kit.
There should be 6 black (carbon), 6 red (oxygen), one or two blue (nitrogen or
phosphorous), and a bunch of white (hydrogen). There should also be numerous gray
sticks to connect them. Please record exactly the number that you have of each of the
balls.
Create a glucose ring structure without help
Without looking into iPad yet, make a glucose molecule out of six carbons and one
oxygen. Once the ring structure is complete, each remaining carbon should have an –H
and –OH on the two remaining holes. The number 5 carbon should only have a hydrogen
as its oxygen is the one in the ring itself.
Check for position of –OH and –H relative to structure using iPad
Now open iPad to any diagram of glucose that you want. Make sure it is the α-glucose
and not the β-glucose version (yet). Notice how the –OH’s and the –H’s are not all on
the same side of the structure. When viewing a two dimensional diagram, the –OH and –
H facing up are up and those facing down are down when laying the molecule flat on the
table. (The bottom of the two dimensional structure on the screen is facing you when flat
on the table.)
Now see how an alpha-glucose is different from a beta-glucose. What is the significant
difference(s)?
The main difference between α-glucose and β-glucose are in the types of molecules they
make.
When linking an α-glucose to another α-glucose then the molecules all face up (carbon 6
is up) which makes starch and glycogen.
When linking an β-glucose to another α β-glucose then the molecules alternate face up
and face down (carbon 6 is up then down) which makes cellulose.
Making starch and/or glycogen
Make all of your molecules α-glucose and combine them through condensation synthesis
to make one long chain. Carbon 1 must ALWAYS be to the right when combining two
glucose molecules and they will link to the 4 carbon of the next molecule. These bonds
are always a 1-4 glycosidic linkages when joining two glucose molecules.Notice how all
of the carbon 6’s of the glucose are facing upward on the table?
Take your glucose out of the starch and replace the –OH or –H that you removed from it.
Making cellulose
Now convert all of your α-glucose into β-glucose. Do the same thing with other groups
and combine the molecules. Carbon 1 must ALWAYS be to the right when combining
two glucose molecules. These bonds are always a 1-4 glycosidic linkages when joining
two glucose molecules.
Notice how the only way to join them is to flip every other one of the molecules over to
keep the strand straight.
This is why it is impossible for animals to digest cellulose fibers because we have no
enzymes to digest β-glycosidic bonds.
Take your glucose out of the starch and replace the –OH or –H that you removed from it.
Making Fructose
Take your glucose molecule and break the bond between the oxygen in the ring and
carbon 1. Remove the hydrogen from carbon 2 and place it on the open hole of carbon 1.
Connect the oxygen to carbon 2. Open your iPad and find the structure of fructose. Does
your structure look EXACTLY like the fructose in the diagram? If not, what would you
have to change to make it match exactly. Make that change if you have to.
Making Sucrose
Pair up with another group. One group return the molecule to its original glucose
structure. You will now do condensation synthesis to join the two molecules except this
time you will form a 1-2 glycosidic linkage. You will have to turn the fructose around
and face the table when you join them together. Notice how the carbon 1 is sticking up
between the two sugar monomers when you form the dimer.
Take your glucose/fructose out of the sucrose molecule and replace the –OH or –H that
you removed from it. Take apart your molecule and put it back into the kit that it came
from. Please check the number of each atom in the kit to assure me that there are none
missing in your or another groups kit.