Download Document

Chapter 5
The Structure and
Function of
Macromolecules
1
Carbon Chemistry
• Organic chemistry is the study of carbon
compounds
• Carbon atoms can form diverse molecules by
bonding to four other atoms
• Carbon compounds range from simple
molecules to complex ones
• Carbon has four valence electrons and may
form single, double, triple, or quadruple
bonds
2
Isomers
• Isomers are molecules with the same molecular
formula but different structures and properties
• Three types of isomers are
– Structural
H
– Geometric
H C H
H C H
H H H H H
H
H
– Enantiomers
H C C C C C H
H C C C H
(a) Structural isomers
H H H
H H H H H
(b) Geometric isomers
X
H
C C
X
H
H
X
CO2H
(c) Enantiomers
H
C
CH3
C
C
X
H
CO2H
NH2 NH2
C
CH3
H
3
Figure 4.7 A-C
• Enantiomers Are important in the
pharmaceutical industry
Figure 4.8
L-Dopa
D-Dopa
(effective against
Parkinson’s disease)
(biologically
inactive)
4
• Pararhodopsin (inactive) and
rhodopsin (active) – made by
rods in the retina
• Conversion between the two is
done by an enzyme complex that
requires Vitamin A
5
The Molecules of Life
• Overview:
– Another level in the hierarchy
of biological organization is
reached when small organic
molecules are joined together
– Atom ---> molecule ---
compound
6
Macromolecules
– Are large molecules composed of smaller
molecules
– Are complex in their structures
Figure 5.1
7
Macromolecules
•Most macromolecules are polymers,
built from monomers
• Four classes of life’s organic
molecules are polymers
– Carbohydrates
– Proteins
– Nucleic acids
– Lipids
8
• A polymer
– Is a long molecule consisting of
many similar building blocks called
monomers
– Specific monomers make up each
macromolecule
– E.g. amino acids are the monomers
for proteins
9
The Synthesis and Breakdown of
Polymers
• Monomers form larger molecules by
condensation reactions called dehydration
synthesis
HO
1
2
3
H
Unlinked monomer
Short polymer
Dehydration removes a water
molecule, forming a new bond
HO
1
2
H
HO
3
H 2O
4
H
Longer polymer
Figure 5.2A (a) Dehydration reaction in the synthesis of a polymer
10
The Synthesis and Breakdown of
Polymers
• Polymers can disassemble by
– Hydrolysis (addition of water molecules)
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
H
H
H 2O
HO
H
Figure 5.2B (b) Hydrolysis of a polymer
11
• Although organisms share
the same limited number of
monomer types, each
organism is unique based on
the arrangement of
monomers into polymers
• An immense variety of
polymers can be built from a
small set of monomers
12
Carbohydrates
• Serve as fuel and building
material
• Include both sugars and
their polymers (starch,
cellulose, etc.)
• 1:2:1 ratio of C:H:O
13
Sugars
• Monosaccharides
– Are the simplest sugars
– Can be used for fuel
– Can be converted into other
organic molecules
– Can be combined into polymers
14
Types of Monosaccharides
Triose – formula ______ ex. glyceraldehyde
and dihydroxyacetone
Tetrose – formula
Pentose- formula ____ Ex.
ribose
Hexose – formula ____ ex.
glucose, dextrose, fructose,
galactose
Heptose – formula ____
15
• Examples of monosaccharides
Triose sugars Pentose sugars
(C3H6O3)
(C5H10O5)
Aldoses
H
C
O
H
O
C
H
O
C
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
C
OH
HO
C
H
C
OH
H
H
C
OH
H
Glyceraldehyde
H
H
H
H
C
OH
H
HO
C
H
C
OH
HO
C
H
H
C
OH
H
C
OH
H
C
OH
H
C
OH
H
H
Glucose
Galactose
H
C OH
C
O
H
C OH
C
O
O
C OH
H
C OH
HO
H
H
C OH
H
C OH
Dihydroxyacetone H C OH
H
C OH
H
C OH
H
H
O
H
H
C OH
C
Ketoses
H
C
Ribose
Figure 5.3
Hexose sugars
(C6H12O6)
Ribulose
C H
H
Fructose
16
• Monosaccharides
– May be linear
– Can form rings
H
H
HO
H
H
H
O
1C
2
6CH
C
OH
C
H
C
OH
3
4
5
C
6
C
OH
OH
2OH
5C
H
4C
OH 3
H
OH
C
H
6CH
O
H
2C
OH
H
1C
H
O
H
4C
OH
2OH
5C
H
OH
3C
H
CH2OH
O
H
H
1C
2C
OH
OH
6
H
5
4
HO
H
OH
3
H
O
H
1
2
OH
OH
H
Figure 5.4 (a) Linear and ring forms. Chemical equilibrium between the linear and ring
structures greatly favors the formation of rings. To form the glucose ring,
carbon 1 bonds to the oxygen attached to carbon 5.
17
What is the difference between
alpha and beta glucose?
Top of page 73 in your book
18
• Disaccharides
– Consist of two
monosaccharides
– Are joined by a bond called a
glycosidic linkage
– These bonds are numbered.
The numbers come from what
two carbons the bond forms
between
19
• Example: In sucrose, glucose and
fructose are bonded together by a 1-2
glycosidic linkage. The 1 C on the
glucose molecule and the 2 C on the
fructose molecule.
Extremely important that
you know the numbers.
20
(a) Dehydration reaction
in the synthesis of
maltose. The bonding
of two glucose units
H
forms maltose. The
glycosidic link joins
the number 1 carbon
of one glucose to the HO
number 4 carbon of
the second glucose.
Joining the glucose
monomers in a
different way would
result in a different
disaccharide.
H
(b) Dehydration reaction
H
in the synthesis of
O
sucrose. Sucrose is
a disaccharide formed
from glucose and fructose.
Notice that fructose,
though a hexose like
glucose, forms a
five-sided ring.
CH2OH
CH2OH
O
H
OH H
H
H
H
OH
HO
H
OH
H 2O
H
O
H
Glucose
CH2OH
H
O
H
HO
H 2O
O
H
H
OHOH
H
HO
H
O
H
H
OH
O
H
CH2OH
H
1–4
1 glycosidic
linkage
HO
OH
H
Fructose
H
O
H
H
O
H
H
OH
OH
Maltose
H
H
4
O
CH2OH
O
H
OH
Glucose
Glucose
CH2O
H
O
H
O
H
H
H
OH
CH2OH
CH2OH
H
HO
H
O
H
O
H
OH
H
1–2
H
glycosidic
1
linkage
O
CH2OH
O
2
H HO
H
CH2OH
OH H
Sucrose
Figure 5.5
21
Maltose is glu + glu with a 1 – 4 glycosidic
linkage. Maltose is the sugar in beer,
found in germinating grain and some in
corn syrup. If you turn the second
glucose molecule around so that the
bond is a 1 – 1 glycosidic linkage, you
don’t get maltose. You get trehalose
which is the sugar found in
insects’ blood (also used in some
hair care products).
22
Polysaccharides
• Polysaccharides
– Are polymers of sugars
– Serve many roles in organisms
23
Storage Polysaccharides
Chloroplast
Starch
• Starch
– Is a polymer
consisting
entirely of
glucose
monomers
– Is the major
storage form of
glucose in plants
1 m
Amylose
Amylopectin
Figure 5.6(a) Starch: a plant polysaccharide
24
• Glycogen
– Consists of glucose monomers
– Is the major storage form of glucose in
animals in liver
Mitochondria Giycogen
granules
0.5 m
Glycogen
Figure 5.6(b) Glycogen: an animal polysaccharide
25
• Glucagon – made by the alpha cells in
the islet of Langerhans in the pancreas
breaks glycogen down and makes it
glucose again (glycogenolysis)
Insulin is made by beta cells of
the islet of Langerhans
They are antagonistic hormones.
26
Structural Polysaccharides
• Cellulose
– Is a polymer of glucose
27
– Has different glycosidic linkages than
starch
H
4
H
O
CH2O
H
O
HO
H H
H
O
H
H
H
O
H
 glucose
O
C
H
H
O
H
C
H
C
H
C
O
H
H
O
H
O
H
O
H
C
C
CH2O
H
O
H
O
H
H
H
4
H
O
O
H
H
O
H
1
H
 glucose
(a)  and  glucose ring structures
H
O
CH2O
H
O
O
H
1
O
4
CH2O
H
O
O
H
1
O
4
CH2O
H
O
O
H
1
O
4
CH2O
H
O
O
H
H
O
Figure 5.7 A–C
O
H
1
O
4
O
H
O
CH2O
H
O
O
H
O
O
H
O
O
O
H
H
H
(b) Starch: 1– 4 linkage of  glucose monomers
CH2O
H
O
O
H
1
O
H
O
O
H
O
O
CH2O
CH2O
O
O
H
H
H
H
(c) Cellulose: 1– 4 linkage of  glucose monomers
O
H
28
– Is a major component of the tough walls
that enclose plant cells
Cell walls
Cellulose microfibrils
in a plant cell wall
Microfibril
About 80 cellulose
molecules associate
to form a microfibril, the
main architectural unit
of the plant cell wall.
0.5 m
Plant cells
Parallel cellulose molecules are
held together by hydrogen
bonds between hydroxyl
groups attached to carbon
atoms 3 and 6.
Figure 5.8
OH CH2OH
OH
CH2OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH
CH2OH
2
H
CH2OH
OH CH2OH
OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH
CH
2
2OH
H
CH2OH
OH
OH CH2OH
O O
O O
OH
OH
OH O
O OH
O O
O
O CH OH
OH CH2OH
2
H
 Glucose
monomer
Cellulose
molecules
A cellulose molecule
is an unbranched 
glucose polymer.
29
• Cellulose is difficult to digest
– Cows have microbes in their stomachs to
facilitate this process
Figure 5.9
30
• Chitin, another important structural
polysaccharide
– Is found in the exoskeleton of arthropods
– Can be used as surgical thread
CH2O
H
O OH
H
H
OH H
OH
H
H
NH
C
O
CH3
(b) Chitin forms the exoskeleton
(a) The structure of the
of arthropods. This cicada
chitin monomer.
is molting, shedding its old
exoskeleton and emerging
Figure 5.10 A–C
in adult form.
(c) Chitin is used to make a
strong and flexible surgical
thread that decomposes after
the wound or incision heals.
31
Nucleic Acids
• Nucleic acids store and transmit
hereditary information
• Genes
– Are the units of inheritance
– Program the amino acid sequence of
polypeptides
– Are made of nucleotide sequences
on DNA
32
The Roles of Nucleic Acids
• There are two types of nucleic acids
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
33
Deoxyribonucleic Acid
• DNA
– Stores information for the synthesis
of specific proteins
– Found in the nucleus of cells
34
DNA Functions
– Directs RNA synthesis (transcription)
– Directs protein synthesis through RNA
DNA
(translation)
1 Synthesis of
mRNA in the nucleus
NUCLEUS
2 Movement of
mRNA into cytoplasm
via nuclear pore
mRNA
CYTOPLASM
mRNA
Ribosome
3 Synthesis
of protein
Figure 5.25
Polypeptide
Amino
acids
35
The Structure of Nucleic
Acids
5’ end
• Nucleic acids
– Exist as polymers called
polynucleotides
5’C
O
3’C
O
O
5’C
O
3’C
(a) Polynucleotide,
or nucleic acid
Figure 5.26
OH
3’ end
36
• Each polynucleotide
– Consists of monomers called nucleotides
– Sugar + phosphate + nitrogen base
Nucleoside
Nitrogenous
base
O

O
P
5’C
O
CH2
O
O
Phosphate
group
Figure 5.26
3’C
Pentose
sugar
(b) Nucleotide
37
Nucleotide Monomers
• Nucleotide monomers
Nitrogenous bases
Pyrimidines
NH2
O
O
C
C
CH
C
3
N
CH
C
CH HN
HN
CH
C
CH
C
C
CH
N
N
O
N
O
O
H
H
H
Cytosine Thymine (in DNA)Uracil
(in RNA)
RNA)
Uracil (in
U
C
U
T
– Are made up of
nucleosides (sugar +
base) and phosphate
groups
Purines
O
NH2
N C C
N C C
NH
N
HC
HC
C
CH
N C
N
NH2
N
N
H
H
Adenine
Guanine
A
G
5”
Pentose sugars
HOCH2 O
4’
OH
H H
1’
5”
HOCH2 O OH
4’
H H
1’
H
H
H 3’ 2’ H
3’ 2’
OH H
OH OH
Deoxyribose (in DNA) Ribose (in RNA)
Figure 5.26
(c) Nucleoside components
38
Nucleotide Polymers
• Nucleotide polymers
– Are made up of nucleotides linked by
the–OH group on the 3´ carbon of one
nucleotide and the phosphate on the 5´
carbon on the next
39
Gene
• The sequence of bases along a
nucleotide polymer
– Is unique for each gene
40
The DNA Double Helix
• Cellular DNA molecules
– Have two polynucleotides that spiral around
an imaginary axis
– Form a double helix
41
• The DNA double helix
– Consists of two antiparallel nucleotide
strands
5’ end
3’ end
Sugar-phosphate
backbone
Base pair (joined by
hydrogen bonding)
Old strands
A
3’
end
Nucleotide
about to be
added to a
new strand
5’ end
3’ end
Figure 5.27
5’ end
New
strands
3’ end
42
A,T,C,G
• The nitrogenous bases in DNA
– Form hydrogen bonds in a complementary
fashion (A with T only, and C with G only)
43
DNA and Proteins as Tape
Measures of Evolution
• Molecular comparisons
– Help biologists sort out the
evolutionary connections among
species
44
45