Outline of Sugar Types Found in Cells - Part 1 · ©1998 by Alberts, Bray, Johnson, Lewis, Raff,...
Transcript of Outline of Sugar Types Found in Cells - Part 1 · ©1998 by Alberts, Bray, Johnson, Lewis, Raff,...
©1998 by Alberts, Bray, Johnson, Lewis, Raff, Roberts, Walter. http://www.essentialcellbiology.com Published by Garland Publishing, a member of the Taylor & Francis Group.
Outline of Sugar Types Found in Cells - Part 1
Monosaccharides usually have the general formula (CH2O) n , where n can be 3, 4, 5, 6, 7, or 8, and have two or more hydroxyl groups. They either contain an aldehyde group ( ) and are called aldoses or a ketone group ( ) and are called ketoses.
MONOSACCHARIDES
Note that each carbon atom has a number.
Many monosaccharides differ only in the spatial arrangement of atoms—that is, they are isomers. For example, glucose, galactose, and mannose have the same formula (C6H12O6) but differ in the arrangement of groups around one or two carbon atoms.
These small differences make only minor changes in the chemical properties of the sugars. But they are recognized by enzymes and other proteins and therefore can have important biological effects.
RING FORMATION ISOMERS
C
C
H
HHO
OH
CH OH
CH OH
CH
H
OH
C
H
H
HO
OH
CH OH
CH OH
CH
H
OH
CH OH
CH OH
CH OH
CH
H
OH
CH OH
CH
H
OH
3-carbon (TRIOSES) 5-carbon (PENTOSES) 6-carbon (HEXOSES)
ALD
OS
ES
KE
TO
SE
S
C
OH
C
OHC
OH
glyceraldehyde ribose glucose
fructose
H
H
OH
CH OH
CH OH
CH
H
OH
ribulose
H
H
OH
CH
H
OH
dihydroxyacetone
O
C
C
O
C
C
O
C
C
CH
CH2OH
CH2OH
OH
CH OH
CHO H
CH
H
H
HH
H
H H
HH
H
HO
OH
OH
OH
OH
OH
OHOH
CO
O
CH2OH
CH
CH2OH
OH
CH OH
CH OH
1
2
3
4
4
4
5
5
6
3
3
2
2
1
CH2OH
HH
H
H
H
HOOH
OH
OH
O
1
5
1
2
3
4
5
6
glucose
CH2OH
H
H
H
H
H
HOOH
OH
OH
O
mannose
CH2OH
HH
H
H
H
HO
OH
OH
OHgalactose
O
O
CO
C OH
glucose
ribose
In aqueous solution, the aldehyde or ketone group of a sugarmolecule tends to react with a hydroxyl group of the samemolecule, thereby closing the molecule into a ring.
HC
O
©1998 by Alberts, Bray, Johnson, Lewis, Raff, Roberts, Walter. http://www.essentialcellbiology.com Published by Garland Publishing, a member of the Taylor & Francis Group.
Outline of Sugar Types Found in Cells - Part 2
CH2OH
HO
O
OH
OH
CH2OH
OH
CH2OH
NH
HOCH2
HO
CH2OH
HO
O
OH
OH
O H CH2OH
OH
HOCH2
HO
HO
+
O
CH2OH
O CH2OH
O
OH
O
HO
OH
HO
O OH
NH
OO
HO
CH3
O
In many cases a sugar sequence is nonrepetitive. Many different molecules are possible. Such complex oligosaccharides are usually linked to proteins or to lipids, as is this oligosaccharide, which is part of a cell-surface moleculethat defines a particular blood group.
COMPLEX OLIGOSACCHARIDES
OLIGOSACCHARIDES AND POLYSACCHARIDESLarge linear and branched molecules can be made from simple repeating units.Short chains are called oligosaccharides, while long chains are calledpolysaccharides. Glycogen, for example, is a polysaccharide made entirely ofglucose units joined together.
branch points glycogen
sucrose
a glucose b fructoseDISACCHARIDES The carbon that carries the aldehyde or the ketone can react with any hydroxyl group on a second sugar molecule to form a disaccharide. Three common disaccharides are
maltose (glucose + glucose) lactose (galactose + glucose) sucrose (glucose + fructose)
The reaction forming sucrose is shown here.
a AND b LINKS SUGAR DERIVATIVESThe hydroxyl group on the carbon that carries the aldehyde or ketone can rapidly change from one position to the other. These two positions are called a and b .
As soon as one sugar is linked to another, the a or b form is frozen.
The hydroxyl groups of a simple monosaccharide can be replaced by other groups. For example,
C O
CH3
C O
CH3
OHO
OH
O
b hydroxyl a hydroxyl
C
O
OH
OH
OH
HO
OH
CH2OH
CH2OHNH2
H
O
OH
OH
HO
O
OH
OH
HO
CH3
O
NH
C
Hglucosamine
N-acetylglucosamineglucuronic acid
O
H2O
O
O
O
P
ATP ADP
CH2OH
O
OH
OH
OHHO
glucose
CH2O
H+
O
OH
OH
OHHO
glucose 6-phosphate
+ + +
hexokinase
P
P
CH2O
O
OH
OH
OHHO
glucose 6-phosphate fructose 6-phosphate
(ring form) (ring form)
(open-chain form)
1
1
2
2
3
4
56
6
O H
C
CH OH
CHO H
CH OH
CH OH
CH2O
3
4
5
P
P
(open-chain form)
1
1
2
2
6
C
CHO H
CH OH
CH OH
CH2O
CH2OH
3
34 4
5
5
phosphoglucoseisomerase OH2C CH2OHO
HO
OH
OH
6
ATP+ ADP H++ +phosphofructokinaseP OH2C CH2OHO
HO
OH
OH
P POH2C CH2OO
HO
OH
OH
Glucose is phosphorylated by ATP to form a sugar phosphate. The negative charge of the phosphate prevents passage of the sugarphosphate through the plasma membrane, trapping glucose inside the cell.
Step 1
The six-carbon sugar is cleaved to produce two three-carbon molecules. Only the glyceraldehyde3-phosphate can proceed immediately through glycolysis.
Step 4
The other product of step 4, dihydroxyacetone phosphate, is isomerized to form glyceraldehyde 3-phosphate.
Step 5
A readily reversible rearrangement of the chemical structure (isomerization) moves the carbonyl oxygen from carbon 1 to carbon 2, forming a ketose from an aldose sugar. (See Panel 2–3, pp. 70–71.)
Step 2
The new hydroxyl group on carbon 1 is phosphorylated by ATP, in preparation for the formation of two three-carbon sugar phosphates. The entry of sugars into glycolysis is controlled at this step, through regulation of the enzyme phosphofructokinase.
Step 3
fructose 6-phosphate fructose 1,6-bisphosphate
+
(ring form)
OH
C
CH OH
aldolase
P
P
(open-chain form)
C
CHO H
CH OH
CH OH
CH2O
CH2O
O
P
C
CHO H
H
CH2O
PCH2O
O
P POH2C CH2OO
HO
OH
OH
fructose 1,6-bisphosphatedihydroxyacetone
phosphateglyceraldehyde
3-phosphate
O
P
C
CH2O
CH2OH triose phosphate isomerase
OH
C
CH OH
PCH2O
glyceraldehyde3-phosphate
dihydroxyacetonephosphate
O
For each step, the part of the molecule that undergoes a change is shadowed in blue,and the name of the enzyme that catalyzes the reaction is in a yellow box.
Panel 13–1 Details of the 10 steps of glycolysis
+ +ADP
enolase
phosphoglycerate mutase
+
O O–
C
CH OH
PCH2O
3-phosphoglycerate
O O–
C
CH O P
CH2OH
2-phosphoglycerate
O O–
C
CH O P
CH2OH
2-phosphoglycerate
O O–
C
C O P
CH2
H2O
phosphoenolpyruvate
O O–
C
C O P
CH2
phosphoenolpyruvate
O O–
C
C O
CH3
pyruvate
O O–
C
C O
CH3
O O–
C
C O
CH3
ATP+ ADP
phosphoglycerate kinaseO O
C
CH OH
P
P
CH2O
1,3-bisphosphoglycerate
+
O O–
C
CH OH
PCH2O
3-phosphoglycerate
The two molecules of glyceraldehyde 3-phosphate are oxidized. The energy-generation phase of glycolysis begins, as NADH and a new high-energy anhydride linkage to phosphate are formed (see Figure 13–5).
Step 6
H+
+ ++
glyceraldehyde 3-phosphatedehydrogenaseO H
C
CH OH
PCH2O
glyceraldehyde3-phosphate
O O
C
CH OH
P
P
CH2O
1,3-bisphosphoglycerate
NADH
NADH
H++
The transfer to ADP of the high-energy phosphate group that was generated in step 6 forms ATP.
Step 7
The remaining phosphate ester linkage in 3-phosphoglycerate, which has a relatively low free energy of hydrolysis, is moved from carbon 3 to carbon 2 to form 2-phosphoglycerate.
Step 8
The removal of water from 2-phosphoglycerate creates a high-energy enol phosphate linkage.
Step 9
The transfer to ADP of the high-energy phosphate group that was generated in step 9 forms ATP, completing glycolysis.
Step 10
NET RESULT OF GLYCOLYSIS
ATP
ATP
+pyruvate kinase
CH2OH
O
OH
OH
OHHO
glucosetwo molecules
of pyruvate
ATP
ATP
NADH ATP
ATP
ATP
In addition to the pyruvate, the net products aretwo molecules of ATP and two molecules of NADH.
1
2
3
PiNAD+
P
ATP ADP
CH2OH
O
OH
OH
OHHO
glucose
CH2O
H+
O
OH
OH
OHHO
glucose 6-phosphate
+ + +
hexokinase
P
P
CH2O
O
OH
OH
OHHO
glucose 6-phosphate fructose 6-phosphate
(ring form) (ring form)
(open-chain form)
1
1
2
2
3
4
56
6
O H
C
CH OH
CHO H
CH OH
CH OH
CH2O
3
4
5
P
P
(open-chain form)
1
1
2
2
6
C
CHO H
CH OH
CH OH
CH2O
CH2OH
3
34 4
5
5
phosphoglucoseisomerase OH2C CH2OHO
HO
OH
OH
6
ATP+ ADP H++ +phosphofructokinaseP OH2C CH2OHO
HO
OH
OH
P POH2C CH2OO
HO
OH
OH
Glucose is phosphorylated by ATP to form a sugar phosphate. The negative charge of the phosphate prevents passage of the sugarphosphate through the plasma membrane, trapping glucose inside the cell.
Step 1
The six-carbon sugar is cleaved to produce two three-carbon molecules. Only the glyceraldehyde3-phosphate can proceed immediately through glycolysis.
Step 4
The other product of step 4, dihydroxyacetone phosphate, is isomerized to form glyceraldehyde 3-phosphate.
Step 5
A readily reversible rearrangement of the chemical structure (isomerization) moves the carbonyl oxygen from carbon 1 to carbon 2, forming a ketose from an aldose sugar. (See Panel 2–3, pp. 70–71.)
Step 2
The new hydroxyl group on carbon 1 is phosphorylated by ATP, in preparation for the formation of two three-carbon sugar phosphates. The entry of sugars into glycolysis is controlled at this step, through regulation of the enzyme phosphofructokinase.
Step 3
fructose 6-phosphate fructose 1,6-bisphosphate
+
(ring form)
OH
C
CH OH
aldolase
P
P
(open-chain form)
C
CHO H
CH OH
CH OH
CH2O
CH2O
O
P
C
CHO H
H
CH2O
PCH2O
O
P POH2C CH2OO
HO
OH
OH
fructose 1,6-bisphosphatedihydroxyacetone
phosphateglyceraldehyde
3-phosphate
O
P
C
CH2O
CH2OH triose phosphate isomerase
OH
C
CH OH
PCH2O
glyceraldehyde3-phosphate
dihydroxyacetonephosphate
O
For each step, the part of the molecule that undergoes a change is shadowed in blue,and the name of the enzyme that catalyzes the reaction is in a yellow box.
Panel 13–1 Details of the 10 steps of glycolysis
+ +ADP
enolase
phosphoglycerate mutase
+
O O–
C
CH OH
PCH2O
3-phosphoglycerate
O O–
C
CH O P
CH2OH
2-phosphoglycerate
O O–
C
CH O P
CH2OH
2-phosphoglycerate
O O–
C
C O P
CH2
H2O
phosphoenolpyruvate
O O–
C
C O P
CH2
phosphoenolpyruvate
O O–
C
C O
CH3
pyruvate
O O–
C
C O
CH3
O O–
C
C O
CH3
ATP+ ADP
phosphoglycerate kinaseO O
C
CH OH
P
P
CH2O
1,3-bisphosphoglycerate
+
O O–
C
CH OH
PCH2O
3-phosphoglycerate
The two molecules of glyceraldehyde 3-phosphate are oxidized. The energy-generation phase of glycolysis begins, as NADH and a new high-energy anhydride linkage to phosphate are formed (see Figure 13–5).
Step 6
H+
+ ++
glyceraldehyde 3-phosphatedehydrogenaseO H
C
CH OH
PCH2O
glyceraldehyde3-phosphate
O O
C
CH OH
P
P
CH2O
1,3-bisphosphoglycerate
NADH
NADH
H++
The transfer to ADP of the high-energy phosphate group that was generated in step 6 forms ATP.
Step 7
The remaining phosphate ester linkage in 3-phosphoglycerate, which has a relatively low free energy of hydrolysis, is moved from carbon 3 to carbon 2 to form 2-phosphoglycerate.
Step 8
The removal of water from 2-phosphoglycerate creates a high-energy enol phosphate linkage.
Step 9
The transfer to ADP of the high-energy phosphate group that was generated in step 9 forms ATP, completing glycolysis.
Step 10
NET RESULT OF GLYCOLYSIS
ATP
ATP
+pyruvate kinase
CH2OH
O
OH
OH
OHHO
glucosetwo molecules
of pyruvate
ATP
ATP
NADH ATP
ATP
ATP
In addition to the pyruvate, the net products aretwo molecules of ATP and two molecules of NADH.
1
2
3
PiNAD+
After the enzyme removes a proton from the CH3 group on acetyl CoA, the negatively charged CH2
– forms a bond to a carbonyl carbon of oxaloacetate. The subsequent loss by hydrolysis of the coenzyme A (CoA) drives the reaction strongly forward.
Step 1
An isomerization reaction, in which water is first removed and then added back, moves the hydroxyl group from one carbon atom to its neighbor.
Step 2
COO–
COO–
COO–HO
H H
H H
C
C
C
COO–
COO–
COO–
HO
H H
H
H
C
C
C
COO–
COO–
COO–
H H
H
C
C
C
citrate cis-aconitateintermediate
isocitrate
aconitase
H2O
H2O
H2O
H2O
acetyl CoA S-citryl-CoAintermediate
citrateoxaloacetate
COO–
COO–
O OCC S CoA
citratesynthase
CH3 CH2
H2OO C S CoA
CH2
COO–
COO–CHO
CH2
HS H+CoA
CH2
COO–
COO–
COO–
CHO
CH2
+ + +
Details of the eight steps are shown below. For each step, the part of the molecule that undergoes a change is shadowed in blue,and the name of the enzyme that catalyzes the reaction is in a yellow box.
CH2
COO–
COO–
COO–
CHO
CH2
H2O
H2O
H2O
CH2
CO2
CO2
CO2
COO–
COO–
COO–
HC
CHHO
CH2
COO–
COO–
C O
CH2
CH2
COO–
COO–
CH2
CH
COO–
COO–
CH
H OHC
COO–
COO–
CH2
COO–
C O
CH2
S CoA
O
CH3 S CoA
acetyl CoA
HS CoA
HS CoA
HS CoA
HS CoA
CH2
OC
COO–
COO–
CH2
O
O
C
COO–
COO–
COO–
CH2
CH3 C
next cycle
Pi
GTPGDP
+
Step 1 Step 2
Step 3
Step 4Step 6
Step 7
Step 8
Step 5
citrate (6C) isocitrate (6C)
succinyl CoA (4C)succinate (4C)
fumarate (4C)
malate (4C)
oxaloacetate (4C)
oxaloacetate (4C)
pyruvate
α-ketoglutarate (5C)+ H+
NADH
+ H+NADH
+ H+NADH
NAD+
NAD+
NAD+
+ H+NADHNAD+
FADH2
FAD
(2C)
CITRIC ACID CYCLE
The complete citric acid cycle. The two carbons from acetyl CoA that enter this turn of the cycle (shadowed in red ) will be converted to CO2 in subsequent turns of the cycle: it is the two carbons shadowed in blue that are converted to CO2 in this cycle.
C
Panel 13–2 The complete citric acid cycle
In the first of four oxidation steps in the cycle, the carbon carrying the hydroxyl group is converted to a carbonyl group. The immediate product is unstable, losing CO2 while still bound to the enzyme.
Step 3
The a-ketoglutarate dehydrogenase complex closely resembles the large enzyme complex that converts pyruvate to acetyl CoA (pyruvate dehydrogenase). It likewise catalyzes an oxidation that produces NADH, CO2, and a high-energy thioester bond to coenzyme A (CoA).
Step 4
A phosphate molecule from solution displaces the CoA, forming a high-energy phosphate linkage to succinate. This phosphate is then passed to GDP to form GTP. (In bacteria and plants, ATP is formed instead.)
Step 5
In the third oxidation step in the cycle, FAD removes two hydrogen atoms from succinate.
Step 6
The addition of water to fumarate places a hydroxyl group next to a carbonyl carbon.
Step 7
In the last of four oxidation steps in the cycle, the carbon carrying the hydroxyl group is converted to a carbonyl group, regenerating the oxaloacetate needed for step 1.
Step 8
COO–
COO–
HO
H H
H
H
C
C
C
isocitrate
isocitratedehydrogenase
CO2
COO–
COO–
COO–
H H
H
O
C
C
C
oxalosuccinateintermediate
COO–
NADHNAD+ + H+ H+
COO–
COO–
H H
H H
O
C
C
C
a-ketoglutarate
succinate dehydrogenase
FADH2FAD
COO–
COO–
H H
H H
C
C
succinate
COO–
COO–
H
H
C
C
fumarate
fumaraseCOO–
COO–
HO H
H H
C
C
malate
COO–
COO–
H
H
C
C
fumarate
H2O
a-ketoglutarate dehydrogenase complex
CO2
NADHNAD+ + H+
COO–
COO–
H H
H H
O
C
C
C
a-ketoglutarate
COO–
H H
H H
O
C
C
C
succinyl-CoA
HS CoA
S CoA
+
H2O
COO–
H H
H H
O
C
C
C
succinyl-CoA
S CoA
COO–
COO–
H H
H H
C
C
succinate
HS CoA+
succinyl-CoA synthetase
Pi GTPGDP
malate dehydrogenase
NADHNAD+ + H+
COO–
COO–
HO H
H H
C
C
malate
COO–
COO–
OC
oxaloacetate
CH2
After the enzyme removes a proton from the CH3 group on acetyl CoA, the negatively charged CH2
– forms a bond to a carbonyl carbon of oxaloacetate. The subsequent loss by hydrolysis of the coenzyme A (CoA) drives the reaction strongly forward.
Step 1
An isomerization reaction, in which water is first removed and then added back, moves the hydroxyl group from one carbon atom to its neighbor.
Step 2
COO–
COO–
COO–HO
H H
H H
C
C
C
COO–
COO–
COO–
HO
H H
H
H
C
C
C
COO–
COO–
COO–
H H
H
C
C
C
citrate cis-aconitateintermediate
isocitrate
aconitase
H2O
H2O
H2O
H2O
acetyl CoA S-citryl-CoAintermediate
citrateoxaloacetate
COO–
COO–
O OCC S CoA
citratesynthase
CH3 CH2
H2OO C S CoA
CH2
COO–
COO–CHO
CH2
HS H+CoA
CH2
COO–
COO–
COO–
CHO
CH2
+ + +
Details of the eight steps are shown below. For each step, the part of the molecule that undergoes a change is shadowed in blue,and the name of the enzyme that catalyzes the reaction is in a yellow box.
CH2
COO–
COO–
COO–
CHO
CH2
H2O
H2O
H2O
CH2
CO2
CO2
CO2
COO–
COO–
COO–
HC
CHHO
CH2
COO–
COO–
C O
CH2
CH2
COO–
COO–
CH2
CH
COO–
COO–
CH
H OHC
COO–
COO–
CH2
COO–
C O
CH2
S CoA
O
CH3 S CoA
acetyl CoA
HS CoA
HS CoA
HS CoA
HS CoA
CH2
OC
COO–
COO–
CH2
O
O
C
COO–
COO–
COO–
CH2
CH3 C
next cycle
Pi
GTPGDP
+
Step 1 Step 2
Step 3
Step 4Step 6
Step 7
Step 8
Step 5
citrate (6C) isocitrate (6C)
succinyl CoA (4C)succinate (4C)
fumarate (4C)
malate (4C)
oxaloacetate (4C)
oxaloacetate (4C)
pyruvate
α-ketoglutarate (5C)+ H+
NADH
+ H+NADH
+ H+NADH
NAD+
NAD+
NAD+
+ H+NADHNAD+
FADH2
FAD
(2C)
CITRIC ACID CYCLE
The complete citric acid cycle. The two carbons from acetyl CoA that enter this turn of the cycle (shadowed in red ) will be converted to CO2 in subsequent turns of the cycle: it is the two carbons shadowed in blue that are converted to CO2 in this cycle.
C
Panel 13–2 The complete citric acid cycle
In the first of four oxidation steps in the cycle, the carbon carrying the hydroxyl group is converted to a carbonyl group. The immediate product is unstable, losing CO2 while still bound to the enzyme.
Step 3
The a-ketoglutarate dehydrogenase complex closely resembles the large enzyme complex that converts pyruvate to acetyl CoA (pyruvate dehydrogenase). It likewise catalyzes an oxidation that produces NADH, CO2, and a high-energy thioester bond to coenzyme A (CoA).
Step 4
A phosphate molecule from solution displaces the CoA, forming a high-energy phosphate linkage to succinate. This phosphate is then passed to GDP to form GTP. (In bacteria and plants, ATP is formed instead.)
Step 5
In the third oxidation step in the cycle, FAD removes two hydrogen atoms from succinate.
Step 6
The addition of water to fumarate places a hydroxyl group next to a carbonyl carbon.
Step 7
In the last of four oxidation steps in the cycle, the carbon carrying the hydroxyl group is converted to a carbonyl group, regenerating the oxaloacetate needed for step 1.
Step 8
COO–
COO–
HO
H H
H
H
C
C
C
isocitrate
isocitratedehydrogenase
CO2
COO–
COO–
COO–
H H
H
O
C
C
C
oxalosuccinateintermediate
COO–
NADHNAD+ + H+ H+
COO–
COO–
H H
H H
O
C
C
C
a-ketoglutarate
succinate dehydrogenase
FADH2FAD
COO–
COO–
H H
H H
C
C
succinate
COO–
COO–
H
H
C
C
fumarate
fumaraseCOO–
COO–
HO H
H H
C
C
malate
COO–
COO–
H
H
C
C
fumarate
H2O
a-ketoglutarate dehydrogenase complex
CO2
NADHNAD+ + H+
COO–
COO–
H H
H H
O
C
C
C
a-ketoglutarate
COO–
H H
H H
O
C
C
C
succinyl-CoA
HS CoA
S CoA
+
H2O
COO–
H H
H H
O
C
C
C
succinyl-CoA
S CoA
COO–
COO–
H H
H H
C
C
succinate
HS CoA+
succinyl-CoA synthetase
Pi GTPGDP
malate dehydrogenase
NADHNAD+ + H+
COO–
COO–
HO H
H H
C
C
malate
COO–
COO–
OC
oxaloacetate
CH2