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Macromolecule class #1:
Polysaccharides
•
•
•
•
•
Monomer = sugars
Sugars = small carbohydrate molecules
Carbohydrates ~= CnH2nOn
Contain one C=O group and many –OH’s
Can contain other functional groups as
well (carboxyls, amines)
• Most common sugar and monomer is
glucose
1
2
Glucose, straight chain depictions
Abbreviated
C
With
numbering
C
Remember,
always 4 bonds to carbon;
Often even if not depicted
3
anomeric
carbon
Fisher
view
Chair view
Haworth view
Handout 2-7
4
11
10
7
6
5
89
3
1 24
5
anomeric
carbon
Fisher
view
Chair view
Haworth view
Handout 2-7
6
7
6
5
89
3
1 24
7
anomeric
carbon
Fisher
view
Chair view
Haworth view
Handout 2-7
8
beta-glucose
alpha-glucose
These two distinct molecules are 2 different “isomers” of glucose.
These two are “steroisomers” differing only in 3-D structure.
Ball and stick models of glucose
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Alpha glucose
All the hydroxyls and the –CH2OH are sticking out equatorial
Except for the hydroxyl on the anomeric carbon 1
10
11
2
5
3
From Handout 2-7
12
5
3
4
1
Relationship between Haworth (flat ring) depiction and chair-form
13
Flat ring (Haworth projection) just gives the relative
positions of the H and OH at each carbon, one is
“above” the other. But it does not tell the positions of
the groups relative to the plane of the ring (up, down
Handout 2-8
or out)
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Glucose chair
http://www.scientificpsychic.com/fitness/glucosebdchair.gif
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Glucose
}
Gray = C
White = H
Red = O
C1
C6 (-CH2OH)
C5
Ring oxygen
Alpha or beta?
Chair depictions (from Googling chair + glucose)
If you could see my back . .
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Beta?
Alpha?
Chair flip
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Building a polymer from glucose
4
CH2OH
4
5
CH2OH
5
2
1
3
2
H
1
3
OH
Alpha
Beta-glucose
Beta-glucose
Polymers are built by removing a molecule of water
between them, known as dehydration, or condensation.
Dimer formation
R-OH + HO-R
→ R-O-R + HOH
This process does not happen by itself
Rather, like virtually all of the reactions in a cell, it requires the aid
of a CATALYST
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AND: Polymers are broken down by the reverse process,
ADDING a molecule of water between them, known as
HYDROLYSIS
R-O-R + HOH→ R-OH + HO-R
Here, dimer hydrolysis
This process does not happen by itself
Rather, like virtually all of the reactions in a cell, it requires the aid
of a CATALYST
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Building a polymer from glucose
4
CH2OH
4
5
CH2OH
5
2
1
3
2
H
1
3
OH
Alpha
Beta-glucose
Beta-glucose
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4
CH2OH
4
CH2OH
5
5
2
2
1
1
3
Beta-glucose
3
+
Beta-glucose
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Anomeric carbon is always one partner
Glycosidic bond
H
4
HO
CH 2OH
H
O
HO
HO
H
H
H
4
CH 2OH
H
H
H
OH
HO
HO
H
Beta-glucose residue
O
H
Beta-glucose residue
Cellobiose
Gycosidic bond here is
equatorial-to-equatorial
Beta conformation is
But not here
now locked in here
And ring is locked as a ring
(loss of an H is necessary for rxn.)
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One is forced to draw strange “elbows”
when depicting disaccharides using the
Haworth projections
(Here the C1 OH is “above” and the C4 OH is “below” (the H atom)
Whereas we just saw in actuality that they are both equatorial
in beta glucose)
Polysaccharide formation
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down
H
Tinker toys
H
Cellulose
or glycogen chain
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Cellulose
6
3
6
3
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More
glucoses
down
H
H
Cellulose
or glycogen chain
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Branching in starch
4-1
4-1
C6
4-1
4-1
4-1
6-1
4-1 4-1
4-1
4-1
4-1
Branches at carbon 6 hydroxyl
Branching  compact structure
Starch or glycogen granules,
A storage form of glucose for energy
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Cytoplasm
Nucleus
Organelles
Starch granules
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So: structure
FUNCTION
anomeric carbon
anomeric carbon
fructose
5-membered
ring works too
Handout 2-6
a-glucose
ribose
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C4
glucose
Examples of other hexoses
C2
galactose
mannose
allose
What’s different from
glucose here?
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More sugars:
Mannose C6H12O6 (different arrangement of OH’s and H’s)
Galactose C6H12O6 (different arrangement of OH’s and H’s)
Deoxyribose C5H10O5 (like ribose but one OH substituted by an H)
More disaccharides (These do not go further to become
polysaccharides):
Lactose = glucose + galactose (milk sugar)
Sucrose = fructose + glucose (table sugar, cane sugar)
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Metabolic intermediate
(Bacterial cell walls)
(Insect exoskeleton)
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Lipids
• Soluble in organic solvents (like octane, a hydrocarbon)
(so “operationally” defined)
• Heterogeneous class of structures
• Not very polymer-like (in terms of covalently bonded structures)
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A steroid
Really a small molecule
(Abbreviation convention: Always 4 bonds to carbon. Bonds to H not shown.)
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hormone
hormone
H2C
co-factor, vitamin
http://www.fas.org/irp/imint/docs/rst/Sect20/steroids.gif
Membrane component
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Fats
A fatty acid
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}
Ester (functional group,
acid + alcohol)
A trigyceride (fat)
Handout 2-9 top
Effect of fatty acid structure on physical properties
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Solid fats
cis
cis
Oils
trans
trans
cis
|
No free rotation
No free
about rotation
double bonds
about double bonds
H
|
C
C
|
X
H
||
X
|
H
|
C
|
H
|
C
||
Free rotation
Free
rotation
about
single bonds
about single bonds
- 2H
|
H
|
C
|
H
|
|
|
H
|
C
|
H
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Adipocyte (fat storage cell)
Nucleus
Fat
globule
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Handout 2-9
}
R=H: a phosphoester
(phosphoric acid + alcohol)
If R = H, “phosphatidic acid”
F.A.s can
be of
different
sizes
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[HO]
[HO]
Handout 2-9
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HO
HO
}
R=another alcohol:
A phospho-diester
HO –CH2CH2N+H3
(alcohol = ethanolamine)
Handout 2-9
44
HOH
2 fatty acid
tails each
Phosphate head
Biological membranes are phospholipid bilayers
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Incidentally, note the functional
groups we have met so far:
Hydroxyl
Amine
Amide
Carboxyl
Carbonyl
Aldehyde
Ketone
Ester: Carboxylic acid ester
Phosphoester
And:
Glycosidic bonds
C=C double bonds (cis and trans)
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PROTEINS
Amino acids (the monomer of proteins)
R
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At pH 7, ,most amino acids are zwitterions
(charged but electrically neutral)
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Equilibrium state of the carboxyl group lies far towards the ionized molecule at pH7
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+OH- ( -H+)
Net charge
+H+
50-50 charged-uncharged at ~ pH2.5 (=the pK)
50-50 charged-uncharged at ~ pH9 (=the pK)
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Numbering (lettering) amino acids
ε-amino group
ε
δ
γ
β
Alpha-carboxyl
(attached to the α-carbon)
Alpha-amino
lysine
Alpha-carbon
Shown uncharged (as on exams)
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Amino acids in 3 dimensions
See ball and stick model
• Asymmetric carbon (4 different
groups attached)
• Stereoisomers
• Rotate polarized light
• Optical isomers
• Non-superimposable
• Mirror images
• L and D forms
From Purves text
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coming out at you
going behind the screen
Mannose
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Condensation of amino acids to form a polypeptide
(must be catalyzed)
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Parts of a polypeptide chain
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Without showing the R-groups:
The backbone is monotonous.
It is the side chains that provide the variety
Handout 3-3
“Polypeptides” vs. “proteins”
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• Polypeptide = amino acids connected in a linear chain (polymer)
• Protein = a polypeptide or several associated polypeptides (discussed later)
• Often used synonymously
• Peptide (as opposed to polypeptide) is smaller, even 2 AAs (dipeptide)