Transcript 05LecturePresentationintro to carbs

Overview: The Molecules of Life
4 Classes of organic molecules make
up living things:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
Overview: The Molecules of Life
•
Cells use a limited number of building blocks
(40 to 50) to build thousands of different
organic molecules.
•
Most of the molecules are very large macromolecules – 1000s of covalently
connected atoms.
•
Cells build macromolecules from smaller
building blocks
•
Emergent properties and correlation of
structure to function are common themes in
this chapter.
Concept 5.1: Macromolecules are polymers, built
from monomers
• A polymer - long molecule consisting of many
similar small building blocks called monomers
• Three of the four classes of life’s organic
molecules are polymers:
– Carbohydrates
– Proteins
– Nucleic acids
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Did you really understand that polymer/monomer
stuff?
• Let’s think of some analogies that will help us
visualize the relationship between polymers
and monomers:
POLYMERS AND MONOMERS ARE LIKE. . .
The chemical reaction which makes or breaks
down a polymer is basically the same for all
organic compounds.
MAKE
• Condensation reaction or dehydration
reaction - two monomers covalently bond
together & one molecule of water is formed
• Enzymes speed up the dehydration process
Animation: Polymers
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Fig. 5-2a
HO
1
2
3
H
Short polymer
HO
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
HO
1
2
H
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
BREAK
• Polymers are disassembled to monomers by
hydrolysis, essentially the reverse of
dehydration reaction
• A molecule of water is required for each bond
that is broken
• Enzymes speed up the hydrolysis process
Animation: Polymers
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Fig. 5-2b
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
(b) Hydrolysis of a polymer
H
H
H2O
HO
H
Fig. 5-2
HO
1
2
3
H
Short polymer
HO
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
HO
2
1
H
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
(b) Hydrolysis of a polymer
H
H
H2O
HO
H
TEST YOURSELF
Suppose you eat a serving of green beans. What reactions
must occur for the amino acid monomers in the protein of the
beans to be converted to proteins in your body?
These reactions would occur too slowly at cellular
temperatures to keep you alive. Name the molecules that
speed up chemical reactions such as condensation and
hydrolysis.
Concept 5.2: Carbohydrates serve as fuel and
building material
• Carbohydrates are sugars and polymers of
sugars such as starch and cellulose; most
sugar names end in -ose
• Composed of C, H, O; ratio of H to O is 2:1
• Classified by number of monomers they
contain :
– Monosaccharide – one monomer
– Disaccharide – two monomers
– Polysaccharide – many monomers
SIMPLE SUGARS: MONOSACCHARIDES
• molecular formula is usually multiple of CH2O
• Glucose (C6H12O6) is most common
monosaccharide.
• Monosaccharides are classified by
1. location of carbonyl group (aldose or ketose)
2. number of carbons in carbon skeleton
3. multiple hydroxyl groups
4. there may be chiral carbons
Fig. 5-3
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose
Fig. 5-3a
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Fig. 5-3b
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Dihydroxyacetone
Ribulose
Fructose
NOTE: glucose, fructose, and galactose are isomers:
C6H12O6
Glucose and galactose:
Glucose and fructose:
Fructose and galactose:
Fig. 5-3
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose
Fig. 5-4
• Though often drawn as linear skeletons, in
aqueous solutions many sugars form rings
• Note that the closing of the ring involves the
carbonyl group
(a) Linear and ring forms
(b) Abbreviated ring structure
Fig. 5-4a
(a) Linear and ring forms
Fig. 5-4b
•Carbons are numbered clockwise
from the oxygen in the ring.
(b) Abbreviated ring structure
• Monosaccharides are major nutrients for cells:
(1) source of energy
(2) carbon skeletons for building other organic
molecules
• Glucose – “blood sugar”; the major fuel used
by most cells; common building block for
structural sugars
• Fructose - fruit sugar
• Galactose - a monomer found in milk sugar
DOUBLE SUGARS: DISACCHARIDES
• Disaccharides - dehydration reaction joins two
monosaccharides
• The new covalent bond between the two
monosaccharides is called a
glycosidic linkage
Animation: Disaccharides
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-5
1–4
glycosidic
linkage
Glucose
Glucose
Maltose
(a) Dehydration reaction in the synthesis of maltose
1–2
glycosidic
linkage
Glucose
Fructose
(b) Dehydration reaction in the synthesis of sucrose
Sucrose
COMMON DISSACHARIDES
• Sucrose – glucose + fructose; produced by
plants; table sugar is generally produced from
sugar cane or sugar beets
• Lactose – glucose + galactose; milk sugar;
lactose intolerant individuals produce little to
none of enzyme needed to break the glycosidic
linkage between glucose and galactose
• Maltose – glucose + glucose; malt sugar;
found in germinating seeds and produced
during beer brewing
Note on plants and sugars
• Plants produce the sugar glucose as a
product of photosynthesis
• Plants transport sugar in their sap as
sucrose.
• Plants store sugar in polymers of glucose
called starch.
CAN YOU DETERMINE THE MOLECULAR
FORMULAS FOR SUCROSE, MALTOSE,
AND LACTOSE?
SUGAR POLYMERS: POLYSACCHARIDES
• Polysaccharides, polymers of sugars, have
storage and structural roles
• The structure and function of a polysaccharide
are determined by its sugar monomers and the
positions of glycosidic linkages
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Storage Polysaccharides: STARCH
• Starch, storage polysaccharide of plants,
consists entirely of glucose monomers
• Plants store surplus starch as granules within
chloroplasts and other plastids
• Plant “banks” glucose while conditions for
photosynthesis are good, then makes
“withdrawals” by hydrolyzing starch when
glucose is needed.
Storage Polysaccharides: STARCH
• Most animals produce the enzymes needed to
break down starch
• The major sources of starch in our diet come
from potato tubers and grains like rice, wheat,
and corn
Storage Polysaccharides: GLYCOGEN
• Glycogen is a storage polysaccharide in
animals
• Humans and other vertebrates store glycogen
mainly in liver and muscle cells
• When blood sugar drops glycogen is
hydrolyzed to glucose and is transported into
the blood.
• Humans have only about a 24 hour supply of
glycogen
Fig. 5-6
Chloroplast
Mitochondria Glycogen granules
Starch
0.5 µm
1 µm
Glycogen
Amylose
Amylopectin
(a) Starch: a plant polysaccharide
(b) Glycogen: an animal polysaccharide
If both starch and glycogen are polymers of
glucose, how do they differ?
• STARCH: glucose monomers joined by 1-4
linkage – carbon 1 on one monomer is joined
to carbon 4 on the next monomer
– Angle of the bonds creates a helical (sprial)
molecule
– Amylose, the simplest starch, has not
branches; amylopectin is branched
• GLYCOGEN – extensively branched
Structural Polysaccharides: CELLULOSE
• Cellulose is a major component of the tough
wall of plant cells; it is the most abundant
organic compound on Earth!
• Like starch, cellulose is a polymer of glucose,
but the glycosidic linkages differ
• The difference is based on two ring forms for
glucose: alpha () and beta ()
Animation: Polysaccharides
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Fig. 5-7
(a) α and β glucose
ring structures
α Glucose
(b) Starch: 1–4 linkage of
α glucose monomers
β Glucose
(b) Cellulose: 1–4 linkage of
β glucose monomers
Fig. 5-7a
α Glucose
(a) α and β glucose ring structures
β Glucose
Fig. 5-7bc
(b) Starch: 1–4 linkage of α glucose monomers
(c) Cellulose: 1–4 linkage of β glucose monomers
• Polymers with  glucose are helical
• Polymers with  glucose are straight
• In straight structures, H atoms on one
strand can hydrogen bond with OH groups
on other strands
• Parallel cellulose molecules held together
this way are grouped into microfibrils, which
form strong building materials for plants
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Fig. 5-8
Cell walls
Cellulose
microfibrils
in a plant
cell wall
Microfibril
10 µm
0.5 µm
Cellulose
molecules
b Glucose
monomer
SO WHY CAN’T WE END HUNGER BY EATING
CELLULOSE??! A POLYMER OF GLUCOSE! MOST
ABUNDANT ORGANIC COMPOUND ON THE PLANET!
• Enzymes that digest starch by hydrolyzing 
linkages can’t hydrolyze  linkages in cellulose
• NO ANIMAL CAN MAKE THE ENZYME TO
HYDROLYZE  LINKAGES
• Cellulose in human food passes through the
digestive tract as insoluble fiber; abrades lining
of digestive tract which stimulates mucus
production and eases passage of feces
through the tract; IF you don’t get enough fiber
in your diet, you may become constipated!
• Fungi, some bacteria, and some protists do
produce the enzymes to digest cellulose; their
role as decomposers is critical to the recycling
of matter in the biosphere
• Many herbivores, from cows to termites, have
symbiotic relationships with these microbes
Speculate! Does Checkers or Gus have gut flora
that break down cellulose?
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-9
What would happen if a cow was given enough antibiotics
to kill all the prokaryotes in its gut? Please ask me about
what happens to the grass the cow eats!!!!!!!
Chitin, a structural polysaccharide
• Found in the exoskeleton of arthropods and the
cell walls of fungi
• Structurally similar to cellulose but has a
nitrogen containing group attached to glucose
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-10
(a) The structure
of the chitin
monomer.
(b) Chitin forms the
exoskeleton of
arthropods.
(c) Chitin is used to make
a strong and flexible
surgical thread.