Important words and concepts
from Chapter 5, Campbell & Reece, 2002 (1/14/2005):
by Stephen T. Abedon (abedon.1@osu.edu) for Biology 113 at the Ohio State University
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Course-external links are in brackets Click [index] to access site index Click here to access text’s website Vocabulary words are found below |
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(1) Chapter title: The Structure and Function of Macromolecules
(a)
This chapter considers the larger biologically important organic
molecules known as carbohydrates, lipids, proteins, and nucleic acids.
(b)
“Understanding the architecture of a particular macromolecule helps
explain how that molecule works . . . In molecular biology, as in the study of
life at all levels, form and function are inseparable.”
(c)
[structure and function of
macromolecules (Google Search)] [index]
(d)
Found at this site are additional pages of possibly related interest
including: [carbohydrates] [glucose
model] [lipids] [proteins] [nucleic
acids] [biomolecules links] [index]
BIOLOGICAL POLYMERS
(2) Polymer (monomer,
subunit)
(a)
Many macromolecules consist of polymers
(b)
A polymer is a large molecule built up from smaller building block
molecules
(c)
Monomers (a.k.a., subunits) are the building block molecules
(d)
“The inherent differences between human siblings reflect variations in
polymers, particularly DNA and proteins. Molecular
differences between unrelated individuals are more extensive, and between
species greater still . . . The molecular logic of life is simple but elegant:
Small molecules common to all organisms are ordered into unique macromolecules
. . . For each class (of compound) we will see that the macromolecules have
emergent properties not found in their individual monomers.”
(e)
[polymer, monomer, subunit, polymer subunit (Google Search)] [index]
(3) Polymerization (condensation reaction, dehydration reaction, dehydration synthesis)
(a)
Polymerization is the linking together of monomers to form polymers
(b)
Polymerization in biological systems typical occurs via dehydration
synthesis
(c)
A condensation reaction occurs via the loss of a small molecule,
usually from two different substances, resulting in the formation of a bond
(d)
Dehydration reaction is synonymous with condensation reaction
except that dehydration reaction is limited to those condensations in
which the small molecule is water
(e)
Dehydration synthesis is synonymous with dehydration reaction
(f)
See Figure 5.2a, The
synthesis and breakdown of polymers
(g)
Energy is expended to polymerize—so all condensation/dehydration reactions
require an input of energy in order to move forward!!! Energy is expended to
make polymers!
(h)
In biological systems, enzymes are
required to polymerize—without enzymes, no polymerization; so enzymes are
required to make polymers!
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FAQ: What reactions or
bonds take place because of dehydration synthesis? The most important
thing to understand about dehydration synthesis is why it is named what it is
(i.e., dehydration synthesis or condensation reaction). That is, these are
reactions in which a water molecule is removed from two reactants. As a
consequence of the removal of the water, what is left of the two reactants
(their residues) are bonded together, hence the use of the term synthesis:
Dehydration synthesis = removal of water to achieve synthesis. Since water is removed, there
have to be the ingredients of water present on the two reactants to remove.
These are H-O-H. More specifically, there will exist a hydroxyl group plus a
hydrogen that typically is bonded to an electronegative atom (i.e., O or N).
That is, -OH and H-. Remove -OH and H- and you have all the ingredients for
water. Left behind are a pair of elections which are responsible for creating
the bond between what is left of the two reactants. For example: C-OH + HO-C can react to give
you C-O-C + H-O-H. Note
that only one of the carbons need be bound to an -OH (though at least one
must). The other carbon could be bound to an -NH: C-OH
+ HN-C can react to give you C-N-C + H-O-H. In
addition, the carbons are not limited in what else may be bonded to them nor
the types of bonds (though the octet rule must always be adhered to, i.e.,
carbon can only have four bonds around it). Consequently, you can have
dehydration synthesis between, for example, carboxyl groups and amino or
hydroxyl groups: O=C-OH
+ HO-C gives you O=C-O-C + H-O-H This
is how fatty acids (the carboxyl group) bind to glycerol (which supplies the
hydroxyl group). O=C-OH
+ HN-C gives you O=C-N-C + H-O-H This
is a peptide bond linking two amino acid residues. In
general, dehydration synthesis is how polymerization occurs in biological
systems. Also, don't let the repeated use of carbon in the above examples
throw you. Dehydration synthesis can occur between two non-carbon containing
molecules (or ions). An example of such a reaction is the binding of two
phosphates together, e.g., as in the reaction ADP + Pi --> ATP + HOH. |
(i)
(j)
[polymerization, condensation reaction,
dehydration reaction,
dehydration synthesis
(Google Search)] [polymerization reactions (All About Chemistry: Polymers and Polymerization)]
[index]
(a)
The reaction known as hydrolysis represents the opposite of condensation reaction (specifically, the opposite of dehydration reaction/synthesis)
(b)
See Figure 5.2b, The
synthesis and breakdown of polymers
(c)
Hydrolysis acts to convert polymers to monomers
(d)
Hydrolysis liberates energy—polymers
contain energy put there by dehydration synthesis; thus, some of the energy
required to polymerize is returned upon hydrolysis (not
all, however, due to the second law of thermodynamics)
(e)
Hydrolysis plays a very important role in the liberation of usable
energy within cells (see ATP hydrolysis in next
chapter)
(f)
Enzymes are employed in biological systems to
effect most hydrolysis reactions
(g)
Example: Digestion of food involves numerous hydrolysis reactions
(h)
[hydrolysis (Google Search)] [dehydration reaction
(nice animation of dehydration synthesis and hydrolysis) (BSC Software)] [index]
CARBOHYDRATES
(a)
The carbohydrates are a class of carbon-based biomolecules that include
the sugars
plus polymers
whose monomers
are sugars
(b)
Carbohydrates may be classified by how many monomers are present, e.g.,
monosaccharide (1 subunit), disaccharide (2
subunits), and polysaccharide (>2 subunits)
(c)
Carbohydrates are also classified in terms of what kind of sugars the
monomers consist of as well as by how the monomers are put together (the kinds
of bonds and the atoms involved in the bonds)
(d)
[carbohydrates, carbohydrate chemistry
(Google Search)] [carbon-based compounds,
functional groups, carbohydrates (Biology at Clermont College)] [index]
(6) Monosaccharides (aldose,
ketose)
(a)
A monosaccharide is carbohydrate that consists of only a
single monomer
(b)
The molecular formula of monosaccharides is (CH2O)n
(c)
See Figure 5.3, The
structure and classification of some monosaccharides
(d)
The number of carbons (n in the formula above) varies
between monosaccharide types, but for every carbon in a monosaccharide, there
is also one water-molecule equivalent (count
the carbon, hydrogen, and oxygen atoms in the various sugars shown in Figure
5.3)
(e)
All carbons in a monosaccharide are bonded to a hydroxyl group (-OH) except for one which is
bonded to a carbonyl group (=O) (note that this statement is true only
for the linear form of monosaccharides) (compare Glucose, Galactose, and Fructose as shown in Figure 5.3)
(f)
An aldose is a monosaccharide whose carbonyl group is found on an end carbon, i.e., aldoses are aldehyde sugars
(g)
A ketose is a monosaccharide whose carbonyl group is
found on a middle carbon, i.e., ketoses are ketone sugars
(h)
The spatial arrangement of hydroxyl groups
(-OH) around carbons varies between monosaccharides (compare Glucose and Galactose—but not
Fructose, as shown in Figure 5.3)
(i)
[monosaccharide, aldose, ketose (Google Search)] [monosaccharide browser (edit space-filling
models of linear monosaccharides – a little clumsy, i.e., there ought to be a
button that allows you to switch directly between D and L isomers, but
otherwise a lot of fun) (Jon Maber)] [index]
(a)
Most common monosaccharides form rings in aqueous
solutions
(b)
See Figure 5.4, Linear and
ring forms of glucose
(c)
Note how in this figure glucose is drawn without most of the carbons
explicitly shown; this presentation convention allows you to see how some hydroxyl groups are found above the ring while
others are found below the ring; switching –OH positions creates a different
molecule (and does not occur spontaneously, except for the –OH formed upon
interconversion of linear and ring forms; switching –OH positions would create
a different sugar, i.e., involves a chemical reaction)
(d)
(remind me to show you a
model of glucose to prove to you that the above statement is indeed true)
(e)
Note how the ring and linear forms of a sugar interconvert;
this interconversion goes on naturally in biological systems even without the
help of enzymes, but is frozen in place upon the
formation of sugar polymers such as dissacharides
(f)
(a)
Glucose is the most common monosaccharide
(b)
Glucose is a hexose meaning that it has six carbons (i.e., its
molecular formula is C6H12O6) (ribose, by
contrast, is a pentose—it has five carbons)
(c)
Glucose is an aldose
(d)
See Figure 5.3, The
structure and classification of some monosaccharides
(e)
beta-D-glucose: 
;
alpha-D-glucose: 
, with
numbering:
(f)
See Figure 5.4, Linear and
ring forms of glucose
(g)
[glucose, glucose chemistry, glucose monosaccharide,
hexose, dextrose (Google Search)] [glucose, amylose, glycogen, cellulose, amylopectin
(Molecules of Life)]
[index]
(9) Disaccharide (glycosidic linkage, maltose, lactose, sucrose)
(a)
A disaccharide is formed upon the formation of a glycosidic linkage (a
type of bond) between monosaccharides
(b)
This glycosidic linkage forms via a dehydration reaction:
(c)
(d)
Examples of disaccharides include:
(i)
Maltose = glucose + glucose (starch
breakdown product)
(ii)
Lactose = glucose + galactose (hydrolyzed by
ß-galactocidase, an type of enzyme)
(iii)
Sucrose = glucose + fructose (glucose + fruit sugar =
“plant sugar”)
(e)
See Figure 5.5, Examples of
disaccharides
(f)
[disaccharide, glycosidic linkage,
maltose, lactose, lactose –tolerance
–intolerance -milk, lactose chemistry, sucrose (Google Search)] [index]
(a)
Sugars include both the monosaccharides and
the disaccharides, i.e., these small carbohydrate
molecules we call sugars
(b)
[sugar, sugar chemistry (Google Search)] [sugars and sweeteners (Food Resource)] [index]
(a)
Polysaccharides are polymers of monosaccharides
(>2)
(b)
Most (all?) macromolecular carbohydrates are
polysaccharides
(c)
Polysaccharides typically serve as
(i)
carbon and energy storage molecules (starch, glycogen)
or
(ii)
as structural material (e.g., in plants, insects, and fungi).
(d)
[polysaccharide (Google Search)] [index]
(12) Starch (amylose, amylopectin, glycogen)
(a)
Starch is a polysaccharide that consists entirely of glucose monomers
(b)
Starch serves as a glucose storage molecule
(c)
Glucose can be removed from starch
by hydrolysis
as it is needed
(d)
Starch is a low-osmolarity carbohydrate storage form (osmolarity is
function of particle number, not size)
(e)
In starch, the glucose monomers are linked (minimally) by 1-4 linkages
(this means that the number 1 carbon of one glucose is linked by a glycosidic linkage to the number 4 carbon of a second
glucose—note the labeled carbons in Figure
5.4)
(f)
See Figure 5.5a, Examples of
disaccharides
(g)
There are a number of different kinds of starch that play similar jobs
in different organisms
(i)
Amylose = unbranched starch (only 1-4 linkages)
(ii)
Amylopectin = branched starch (found in plants)
(iii)
Glycogen = heavily branched starch (found in animals)
(h)
Branches are 1-6 linkages (i.e., glycosidic linkage
between a number 1 carbon and a number 6 carbon) and branched starches contain
both 1-4 and 1-6 linkages, creating a very large, “fluffy” molecule
(i)
See Figure 5.6, Storage
polysaccharides
(j)
[starch, starch chemistry, amylose, amylopectin, glycogen (Google Search)] [glucose, amylose, glycogen, cellulose, amylopectin
(Molecules of Life)]
[starch general information, images, and links (Food Resource)] [index]
(a)
Cellulose is a structural polysaccharide
(e.g., cell walls, wood, etc.)
(b)
Cellulose contrasts with amylose in that amylose contains only
alpha 1-4 linkages while cellulose is a linear polymer of glucose
connected only by beta 1-4 linkages
(c)
Note, in Figure 5.7, the
very subtle distinction between the alpha and the beta configurations of
glucose; these two forms of glucose are interconvertible as the ring
forms of glucose open and close (form and then convert back to the
linear form), but not interconvertable once glucose has been incorporated into
a polysaccharide such as starch or cellulose
(d)
See Figure 5.7, Starch and
cellulose structures compared
(e)
See Figure 5.8, The
arrangement of cellulose in plant cell walls
(f)
Thus, an only subtle difference between amylose and cellulose results
in one being a stiff, structural material (cellulose) and the other a flexible,
energy-storage material (amylose); this idea that subtle chemical and
structural differences can make a big difference in the function (or lack
thereof) of biomolecules is an oft repeated theme when studying the molecules
of life
(g)
The following is a portion of the polymer cellulose—note the b-1,4 linkages between the glusose residues: 
(h)