BIOCHEMISTRY | CARBS: SOURCES + FUNCTIONS
SHS
12
AUF-IS
UN/VERIFIED
BY: MARIANO, EMARSE | Please notify for errors/inconsistencies!
CHLOROPHYLL-CONTAINING PLANTS
→ also called Green Plants produce carbohydrates through
photosynthesis
CARBS: SOURCES + FUNCTIONS
A.
B.
C.
D.
E.
CARBOHYDRATES
I.
CLASSIFICATIONS
SOURCES OF CARBOHYDRATES
FUNCTIONS OF CARBOHYDRATES
CHIRALITY
STEREOISOMERISM
A. CARBOHYDRATES
●
“Watered carbon” or “hydrated carbon”
o consists of C, H, O
● Most abundant class of bioorganic molecules on earth
● Low abundance in human body
● 75% (by mass) of dry plant materials
1.1 CLASSIFICATIONS
MONOSACCHARIDES
→ contains a single polyhydroxy aldehyde or polyhydroxy
ketone unit
6𝐶0𝑍 + 6𝐻𝑍 𝑂 −> 𝐶6𝐻12 𝑂6 + 6𝑂2
REACTANTS
LIGHT
PRODUCTS
C. FUNCTIONS OF CARBOHYDRATES
●
Carbohydrate oxidation provides energy
●
Carbohydate storage, glycogen, provides a short term
energy reserve
●
Supplies carbon atoms for the synthesis of other biochemical
substances (proteins, lipids, and nucleic acids)
●
Carbohydrates form part of the structural framework of DNA
and RNA molecules
●
Carbohydrates linked to lipids are structural components of
cell membranes
●
Carbbohydrates linked to proteins function in a variety of cell
to cell and cell to molecule recognition process
D. CHIRALITY
HANDEDNESS
DISACCHARIDES
4.1
→ contains two monosaccharide units covalently bonded
to each other
● form of isomerism
OLIGOSACCHARIDES
● exists as mirror image/s of each other
● ISOMERS – molecules with the same molecular formula,
but atoms have distinct arrangements
→ contains 3-10 monosaccharide units covalently bonded
to each other
● all molecules have mirror images
SUPERIMPOSABLE MIRROR IMAGES
POLYSACCHARIDES
→ polymeric carbohydrate that contains 11 or more
monosaccharide units covalently bonded to each other
→ coincides at all points when laid upon each other (achiral)
B. SOURCES OF CARBOHYDRATES
2.1 PLANTS
●
Major source of carbs
●
Carbohydrate materials of plants are estimated to contain
more than half of all organic Carbon atoms
●
Dietary intake of plants = major carbohydrate source for
humans and animals
●
two-thirds (2/3) of human diet (by mass) composes of
carbohydrates
NONSUPERIMPOSABLE MIRROR IMAGES
→ left-handed and right-handed forms
→ not all points coincide when laid upon each other (chiral)
CELLULOSE
→ Structural element of plants
STARCH
→ Energy reserves of plants
TEMPLATE BY: MARIANO, E.S.
SOURCE: SIR REMEL NIEL E. TORRES
BIOCHEMISTRY | CARBS: SOURCES + FUNCTIONS
SHS
12
AUF-IS
UN/VERIFIED
BY: MARIANO, EMARSE | Please notify for errors/inconsistencies!
→ are molecules with nonsuperimposable mirror images of
each other
DIASTEREOMERS
→ are molecules that are not mirror images of each other (cistrans isomers)
4.2
●
a molecule can have multiple stereoisomer
●
2,3,4 - trihydroxybutanal has 4 stereoisomers (2 pairs of
enantiomers, and 4 pairs of diastereomers) see figure below
●
cis-trans isomers
CHIRALITY
● denoted by asterisks (*)
● handedness of a molecule with nonsuperimposable images
● an organic molecule is chiral if it has a carbon atom bonded
(single-bond) to four different atoms/molecules/groups in
a tetrahedral orientation (chiral center)
● ACHIRAL MOLECULES – do not possess handedness and
have superimposable mirror images
BROMOCHLOROIODOMETHANE
→ Trisubstituted methane molecule
→ Simplest example of a chiral molecule
→ 4 different groups are attached to the carbon atom (H, Cl,
I, Br)
→ Mirror image of the molecule is nonsuperimposable in
some points
→ Exists in 3-dimensional plane
5.1
●
●
4.3
●
●
A ring system is chiral if two halves are not equivalent
A carbon atom in a ring system can only be a chiral center
if NOT INVOLVED IN MULTIPLE BONDING (DOUBLE
BONDS)
○ 2 bonds to neighboring carbon atoms
○ 2 bonds to different substituents
4.4
●
CHIRALITY FOR RING STRUCTURES
IMPORTANCE OF CHIRALITY
Right-handed and left-handed variants of the same
molecule cause different responses in the human body,
humans can usually only use one of the two forms.
○ The human body’s response to right-handed
epinephrine is 20x greater than the lefthanded form
●
●
●
●
●
●
two types:
ENANTIOMERS
TEMPLATE BY: MARIANO, E.S.
developed by German chemist Hermann Emil Fischer
two-dimensional structural notation for showing the spatial
arrangement of groups about the chiral center in
molecules
the intersection of the vertical and horizontal lines
represent chiral centers
HORIZONTAL LINE – bonds projecting forward from the
chiral center/stereocenter
VERTICAL LINE – bonds projecting to the rear
only the chiral center is in the plane
MONOSACCHARIDE’S FISCHER PROJECTION
E. STEREOISOMERISM
●
FISCHER PROJECTION
SOURCE: SIR REMEL NIEL E. TORRES
the carbon chain is positioned vertically with the carbonyl
group (aldehyde or ketone) at or near the top
D- and L- designations is determined by the chiral carbon
farthest from the carbonyl group
BIOCHEMISTRY | CARBS: SOURCES + FUNCTIONS
SHS
12
AUF-IS
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STEP 3
●
●
●
●
●
●
in the figure above, D-glucose is a naturally occurring
enantiomer. OH group is on the right
●
L-glucose is an unnatural enantiomer, and OH group is on
the left.
5.2
●
●
●
Bond rotation on C5 or penotomy chiral carbon
We do not rotate at C6 because it is no longer a chiral
carbon
IF D-ISOMER clockwise rotation
IF L-ISOMER counterclockwise rotation
how to check if correct rotation:
○ OH group of C5 should be in position of C6
(in the same chain as the carbon chain as it
will be part of the carbon ring later on)
HAWORTH PROJECTION
represents the cyclic structure of sugars in a threedimensional perspective
developed by British carbohydrate chemist Walter
Norman Haworth
cyclic structure is due to the formation of hemiacetal or
hemiketalcompounds brought by the reaction of
aldehydes/ketones with alcohols
STEP 1
●
●
Number carbons, and draw in the first Fischer
stereochemistry
The arms come out to hug you
STEP 4
●
●
●
Turn the molecule 90 degrees clockwise so molecules on
the right side go down, molecules on the left go up. Refer to
F. Alkoxy groups on (1) Organic Molecules reviewer
STEP 2
●
●
●
Rotate the Fischer 90 degrees on its side
Note the orientation of chiral carbons!
Achiral carbons orientation can go eitherway–not much
effect
TEMPLATE BY: MARIANO, E.S.
SOURCE: SIR REMEL NIEL E. TORRES
Closure of the ring
Chemical reactions occur: OH group at C5 will perform a
nucleophilic attack on the Carbonyl carbon (C1) and will
protonate the carbonyl oxygen
BIOCHEMISTRY | CARBS: SOURCES + FUNCTIONS
SHS
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AUF-IS
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then:
●
●
●
●
●
Orientation of OH group at anomeric carbon (C1) could be
up or down (usually specified; state both if not)
Substituent of C5 which is C6 will face UPWARD if it is a Disomer
C6 will face DOWNWARD if it is an L-isomer
Orientation of substituents in either L or D-isomer changes
at all chiral centers as they are mirror images of one another
Should you wish not to show both representations, put a
squiggly line on the anomeric carbon or C1
5.3
●
●
●
HAWORTH PROJECTION OF
FRUCTOSE (polyhydroxy ketone)
In the case of Fructoses or ketoses in general, the same
conversion process occurs (steps 1-4) BUT it attacks
carbonyl carbon at C2, not C1.
C1 and C6 are not part of carbon ring; they are
substituents of C2 and C5 respectively
ORIENTATION/PLACEMENT of C1 to C2 is relative to the
orientation of OH group at C2
○ in determining alpha and beta isomer of
monosac, you are looking at the OH group
attached to anomeric carbon.
○ if OH is up, C1 substituent is down
● FRUCTOPYRANOSE: C6 OH will attack carbonyl
carbon.
This reviewer is subject to unintentional inconsistencies/errors.
Thank you for your understanding!
Do refer to other handouts/notes/references for more accuracy.
TEMPLATE BY: MARIANO, E.S.
SOURCE: SIR REMEL NIEL E. TORRES