1 Macromolecule class #1: Polysaccharides Monomer = sugars Sugars = small carbohydrate molecules...
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Transcript of 1 Macromolecule class #1: Polysaccharides Monomer = sugars Sugars = small carbohydrate molecules...
1Macromolecule 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
2
Glucose, straight chain depictions
With numbering
C C
Remember, always 4 bonds to carbon; Often even if not depicted
Abbreviated
3
anomeric carbon
Handout 2-7Haworth view
Fisher view
Chair view
4
1 234567891011
5
anomeric carbon
Handout 2-7Haworth view
Fisher view
Chair view
6
1 23456789
7
anomeric carbon
Handout 2-7Haworth view
Fisher view
Chair view
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.
9Ball and stick models of glucose
10Alpha glucoseAll the hydroxyls and the –CH2OH are sticking out equatorialExcept for the hydroxyl on the anomeric carbon 1
11
From Handout 2-7
2
5
3
12
From Handout 2-7
4
1
5
3
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 or out)
Relationship between Haworth (flat ring) depiction and chair-form
Handout 2-8
14
Glucose chair
http://www.scientificpsychic.com/fitness/glucosebdchair.gif
15
Glucose
}Gray = CWhite = HRed = O
Ring oxygen
C6 (-CH2OH)
C5
C1
hydr
oxyl
Alpha or beta?
16Chair depictions (from Googling chair + glucose)
Beta?
Alpha? Chair flip
If you could see my back . .
17
CHOH2
12
3
45
B eta-g lucose
Building a polymer from glucose
CHOH2
12
3
45
B eta-g lucose
OH
H
Alpha
18Polymers are built by removing a molecule of water
between them, known as dehydration, or condensation.
R-OH + HO-R
→ R-O-R + HOHThis process does not happen by itself
Rather, like virtually all of the reactions in a cell, it requires the aid of a CATALYST
Dimer formation
19AND: 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-RHere, 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
20
CHOH2
12
3
45
B eta-g lucose
Building a polymer from glucose
CHOH2
12
3
45
B eta-g lucose
OH
H
Alpha
21
CHOH2
12
3
45
B eta-g lucose
CHOH2
12
3
45
B eta-g lucose+
22
O
H
H
H
CH OH2HO
HO HO
HH
4
O
H
H
H
CH OH2
HOOH
HO
HH
4
Beta-glucose residueBeta-glucose residue
Cellobiose
Glycosidic bond
Anomeric carbon is always one partner
Beta conformation is now locked in hereAnd ring is locked as a ring(loss of an H is necessary for rxn.)
But not hereGycosidic bond here isequatorial-to-equatorial
23
One is forced to draw strange “elbows” when depicting disaccharides using theHaworth 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)
24
or glycogen chain
down
out
H
H
Cellulose
Tinker toys
Polysaccharide formation
25
Cellulose
3
6
3
6
26
or glycogen chain
down
out
H
H
Cellulose
More glucoses
27
4-1
4-1
4-1
4-1
4-14-1
6-14-1 4-1
4-14-1
Branches at carbon 6 hydroxylBranching compact structureStarch or glycogen granules, A storage form of glucose for energy
Branching in starch
C6
28NucleusCytoplasm
Organelles
Starch granules
29So: structure FUNCTION
30anomeric carbon
anomeric carbon
a-glucosefructose ribose
Handout 2-6
5-membered ring works too
31
C2
glucose galactose mannose
C4
What’s different from glucose here?
Examples of other hexoses
allose
32More 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)
33
(Insect exoskeleton)
(Bacterial cell walls)Metabolic intermediate
34
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)
35A steroid
(Abbreviation convention: Always 4 bonds to carbon. Bonds to H not shown.)
Really a small molecule
36
hormone hormone
co-factor, vitamin Membrane component
http://www.fas.org/irp/imint/docs/rst/Sect20/steroids.gif
H2C
37
A fatty acid
Fats
38
A trigyceride (fat)
Ester (functional group, acid + alcohol)}
Handout 2-9 top
39
trans
cis
cis
C C| |
HH
HH| |
| || C C| |
HH|| ||
- 2H
X
Free rotation about single bonds
No free rotationabout double bonds
cis
Solid fats
Oils
Effect of fatty acid structure on physical properties
Free rotation about single bonds
No free rotation about double bonds
C C|
|H
H
||
|
|
X
trans
40
Fatglobule
Nucleus
Adipocyte (fat storage cell)
41
R=H: a phosphoester(phosphoric acid + alcohol)
If R = H, “phosphatidic acid”
}Handout 2-9
F.A.s can be of different sizes
42
[HO]
[HO]
Handout 2-9
43
R=another alcohol:A phospho-diester
}HO
HO
Handout 2-9
HO –CH2CH2N+H3
(alcohol = ethanolamine)
44HOH
HOH
Phosphate head
2 fatty acid tails each
Biological membranes are phospholipid bilayers
45
Incidentally, note the functional groups we have met so far:
HydroxylAmineAmideCarboxylCarbonylAldehydeKetoneEster: Carboxylic acid ester
Phosphoester
And:
Glycosidic bondsC=C double bonds (cis and trans)
46
Amino acids (the monomer of proteins)
PROTEINS
R
47
At pH 7, ,most amino acids are zwitterions(charged but electrically neutral)
48
Equilibrium state of the carboxyl group lies far towards the ionized molecule at pH7
49
+OH- ( -H+)
+H+
Net charge
50-50 charged-uncharged at ~ pH9 (=the pK)50-50 charged-uncharged at ~ pH2.5 (=the pK)
50
Numbering (lettering) amino acids
Alpha-carbon
Alpha-carboxyl (attached to the α-carbon)Alpha-amino
β
γδ
ε
ε-amino group
lysine
51Shown uncharged (as on exams)
52
53Amino 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
54
Mannose
coming out at you
going behind the screen
55
Condensation of amino acids to form a polypeptide(must be catalyzed)
56
Parts of a polypeptide chain
57
Without showing the R-groups:
The backbone is monotonous.It is the side chains that provide the varietyHandout 3-3
58“Polypeptides” vs. “proteins”
• 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)