STRUCTURE & FUNCTION OF LARGE BIOLOGICAL MOLECULES (MACROMOLECULES)
1 Macromolecules – Are large molecules composed of a large number of repeated subunits – Are...
Transcript of 1 Macromolecules – Are large molecules composed of a large number of repeated subunits – Are...
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Macromolecules
– Are large molecules composed of a large number of repeated subunits
– Are complex in their structures
Figure 5.1
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MacromoleculesMacromolecule Subunit
Complex Carbohydrates(e.g. starch)
Simple sugar (e.g. glucose)
Lipid (triglycerides) Glycerol and fatty acids
Protein Amino Acids
Nucleic Acids (DNA or RNA) Nucleotides
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• A polymer– Is a long molecule consisting of many similar
smaller building blocks called monomers– Specific monomers make up each
macromolecule– E.g. amino acids are the monomers for proteins
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The Synthesis and Breakdown of Macromolecules
• Monomers form larger molecules by condensation reactions called dehydration synthesis
(a) Dehydration reaction in the synthesis of a polymer
HO H1 2 3 HO
HO H1 2 3 4
H
H2O
Short polymer Unlinked monomer
Longer polymer
Dehydration removes a watermolecule, forming a new bond
Figure 5.2A
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Condensation Reactions
• Requires energy because new bonds are being formed
• Are also called a anabolic reactions because smaller molecules join together to form larger molecules
small LARGE
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The Synthesis and Breakdown of Macromolecules
• Polymers can disassemble by– Hydrolysis (addition of water molecules to lyse or
“break apart” the macromolecule)
(b) Hydrolysis of a polymer
HO 1 2 3 H
HO H1 2 3 4
H2O
HHO
Hydrolysis adds a watermolecule, breaking a bond
Figure 5.2B
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Hydrolysis
• Releases energy because bonds are being broken
• Are also called a Catabolic reactions because larger molecules are being broken down into smaller subunits
LARGE small
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• An immense variety of polymers can be built from a small set of monomers
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Question 1
• How many molecules of water are needed to completely hydrolyze a polymer that is 10 monomers long?
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Question 2
• After you eat a slice of apple, which reactions must occur for the amino acid monomers in the protein of the apple to be converted into proteins in your body?
Amino acids are incorporated into proteins in your body by dehydration reactions
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CARBOHYDRATES
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Carbohydrates
• Serve as fuel and building material
• Include both sugars and their polymers (starch, cellulose, etc.)
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Sugars
• Monosaccharides– Are the simplest sugars– Contain a single chain of carbon atoms
with hydroxyl groups– They also contain carbonyl (aldehyde
or keytone) groups– Can be combined into polymers
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• Examples of monosaccharidesTriose sugars
(C3H6O3)Pentose sugars
(C5H10O5)Hexose sugars
(C6H12O6)
H C OH
H C OH
H C OH
H C OH
H C OH
H C OH
HO C H
H C OH
H C OH
H C OH
H C OH
HO C H
HO C H
H C OH
H C OH
H C OH
H C OH
H C OH
H C OH
H C OH
H C OH
H C OH
C OC O
H C OH
H C OH
H C OH
HO C H
H C OH
C O
H
H
H
H H H
H
H H H H
H
H H
C C C COOOO
Aldo
ses
Glyceraldehyde
RiboseGlucose Galactose
Dihydroxyacetone
Ribulose
Keto
ses
FructoseFigure 5.3
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• Monosaccharides– May be linear– Can form rings
H
H C OH
HO C H
H C OH
H C OH
H C
O
C
H
1
2
3
4
5
6
H
OH
4C
6CH2OH 6CH2OH
5C
HOH
C
H OH
H
2 C
1C
H
O
H
OH
4C
5C
3 C
H
HOH
OH
H
2C
1 C
OH
H
CH2OH
H
H
OHHO
H
OH
OH
H5
3 2
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.
OH3
O H OO
6
1
Figure 5.4
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α glucose vs. β glucose
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• Oligosaccharides – contain two or three monosaccarides attached by covalent bonds called glycosidic linkages
– Disaccharides• Consist of two monosaccharides• Are joined by a single glycosidic linkage
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Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide.
Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring.
(a)
(b)
H
HO
H
HOH H
OH
O H
OH
CH2OH
H
HO
H
HOH H
OH
O H
OH
CH2OH
H
O
H
HOH H
OH
O H
OH
CH2OH
H
H2O
H2O
H
H
O
H
HOH
OH
OH
CH2OH
CH2OH HO
OHH
CH2OH
HOH H
H
HO
OHH
CH2OH
HOH H
O
O H
OHH
CH2OH
HOH H
O
HOH
CH2OH
H HO
O
CH2OH
H
H
OH
O
O
1 2
1 41– 4
glycosidiclinkage
1–2glycosidic
linkage
Glucose
Glucose Glucose
Fructose
Maltose
Sucrose
OH
H
H
Figure 5.5
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Polysaccharides
• Polysaccharides– Are polymers of sugars with several hundred to
several thousand monosaccharide subunits held together by glycosidic linkages
– Serve many roles in organisms
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Storage Polysaccharides
• Starch– Is a polymer
consisting entirely of glucose monomers
– Is the major storage form of glucose in plants
Chloroplast Starch
Amylose Amylopectin
1 m
(a) Starch: a plant polysaccharideFigure 5.6
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Two types of Starch
• Amylose– Straight chain polymer of α (alpha) glucose– Has 1-4 glycosidic linkages
• Amylopectin– Branched chains of α glucose and β glucose– Has 1-4 glycosidic linkages in the main chains and
1-6 glycosidic linkages at the branch points
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Glucose Storage in Animals
• Glycogen– Consists of glucose monomers– Similar to Amylopectin (has 1-4 and 1-6
glycosidic linkages), but there are more branches in glycogen
– Stored in muscle and liver
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MitochondriaGiycogen granules
0.5 m
(b) Glycogen: an animal polysaccharide
Glycogen
Figure 5.6
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Structural Polysaccharides• Cellulose– Is a polymer of glucose– Has different glycosidic linkages than starch– The main structural polysaccharide in plants and plant cell
walls
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– Cellulose is a straight chain polymer of β glucose with 1-4 glycosidic linkages
(c) Cellulose: 1– 4 linkage of glucose monomers
H O
O
CH2OH
HOH H
H
OH
OHH
H
HO
4
C
C
C
C
C
C
H
H
H
HO
OH
H
OH
OH
OH
H
O
CH2OH
HH
H
OH
OHH
H
HO4 OH
CH2OHO
OH
OH
HO41
O
CH2OH
O
OH
OH
O
CH2OH
O
OH
OH
CH2OH
O
OH
OH
O O
CH2OHO
OH
OH
HO 4O
1
OH
O
OH OHO
CH2OHO
OH
O OH
O
OH
OH
(a) and glucose ring structures
(b) Starch: 1– 4 linkage of glucose monomers
1
glucose glucose
CH2OH CH2OH
1 4 41 1
Figure 5.7 A–C
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Plant cells
0.5 m
Cell walls
Cellulose microfibrils in a plant cell wall
Microfibril
CH2OH
CH2OH
OH
OHO
OOHO
CH2OHO
OOH
OCH2OH OH
OH OHO
O
CH2OH
OO
OH
CH2OH
OO
OHO
O
CH2OHOH
CH2OHOHOOH OH OH OH
O
OH OH
CH2OH
CH2OH
OHO
OH CH2OH
OO
OH CH2OH
OH
Glucose monomer
O
O
O
O
O
O
Parallel cellulose molecules areheld together by hydrogenbonds between hydroxyl
groups attached to carbonatoms 3 and 6.
About 80 cellulosemolecules associate
to form a microfibril, themain architectural unitof the plant cell wall.
A cellulose moleculeis an unbranched glucose polymer.
OH
OH
O
OOH
Cellulosemolecules
Figure 5.8
– Unlike amylose and amylopectin (starches), cellulose molecules are neither coiled nor branched
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• Cellulose is difficult to digest– However, it does contribute to “roughage” in the
diet fibre– Cows have microbes in their stomachs to facilitate
this process
Figure 5.9
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• Chitin, another important structural polysaccharide– Is found in the exoskeleton of arthropods– Can be used as surgical thread
(a) The structure of the chitin monomer.
OCH2OH
OHHH OH
H
NH
CCH3
O
H
H
(b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emergingin adult form.
(c) Chitin is used to make a strong and flexible surgical
thread that decomposes after the wound or incision heals.
OH
Figure 5.10 A–C
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LIPIDS
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Lipids
• Lipids are hydrophobic molecules• Mostly C-H (non-polar)• are the one class of large biological molecules
that do not consist of polymers• Uses: structure of cell membranes, energy
source
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Lipids
• Fats• Phospholipids• Steroids
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Fats– Are constructed from two types of smaller
molecules:• single glycerol and • three fatty acids
Fatty Acid
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Glycerol
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ESTER LINKAGE
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• Saturated fatty acids– Have the maximum number of hydrogen
atoms possible– Have no double bonds– Are solid at room temperature (e.g. animal
fats)
(a) Saturated fat and fatty acid
Stearic acid
Figure 5.12
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• Unsaturated fatty acids– Have one or more double bonds, causing a bend in its
structure– Are liquids at room temperature (e.g. vegetable fats)
(b) Unsaturated fat and fatty acidcis double bondcauses bending
Oleic acid
Figure 5.12
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Unsaturated Fats• Monounsaturated fats (MUFA)– Have one double bond in their fatty acids
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•Polyunsaturated fats (PUFA)
Have more than one double bond in their fatty acid chains
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Phospholipids– Have only two fatty acids– Have a phosphate group instead of a third
fatty acid
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• Phospholipid structure–Consists of a hydrophilic “head” and
hydrophobic “tails”CH2
O
PO O
O
CH2CHCH2
OO
C O C O
Phosphate
Glycerol
(a) Structural formula (b) Space-filling model
Fatty acids
(c) Phospholipid symbol
Hyd
rop
hob
i c t
ails
Hydrophilichead
Hydrophobictails
–
Hyd
rop
hi li c
head
CH2 Choline+
Figure 5.13
N(CH3)3
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Micelles
• When phospholipids are added to water, they form micelles
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Phospholipid Bilayer
– Results in a phospholipid bilayer arrangement found in cell membranes
Hydrophilichead
WATER
WATER
Hydrophobictail
Figure 5.14
Water and other polar and ionic materials cannot pass through the membrane except by the help of proteins in the membrane
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Steroids
• Steroids– Are lipids that have a carbon skeleton consisting
of four fused rings– Contain many different functional groups
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• One steroid, cholesterol– Is found in cell membranes– Is a precursor for some hormones
HO
CH3
CH3
H3C CH3
CH3
Figure 5.15
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NUCLEIC ACIDS
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Nucleic Acids
• Nucleic acids store and transmit hereditary information
• There are two types of nucleic acids– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)
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• DNA– Stores information for the synthesis of specific proteins– Found in the nucleus of cells
• RNA– Reads information in DNA– Transports information to protein building structures within cell
Function of DNA and RNA
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The Structure of Nucleic Acids
• Nucleic acids (also called Polynucleotides)– Are polymers made up of
individual nucleotide monomers
(a) Polynucleotide, or nucleic acid
3’C
5’ end
5’C
3’C
5’C
3’ endOH
Figure 5.26
O
O
O
O
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• Each Nucleotide contains– Sugar + phosphate + nitrogen base
Nitrogenousbase
Nucleoside
O
O
O
O P CH2
5’C
3’CPhosphate
group Pentosesugar
(b) NucleotideFigure 5.26
O
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Nucleotide Monomers(c) Nucleoside components
Figure 5.26
CH
CH
Uracil (in RNA)U
Ribose (in RNA)
Nitrogenous bases Pyrimidines
CN
NC
OH
NH2
CH
CHO
CN
H
CH
HNC
O
CCH3
N
HNC
C
HO
O
CytosineC
Thymine (in DNA)T
NHC
N C
CN
C
CH
N
NH2 O
N
HC
NHH
CC
N
NH
CNH2
AdenineA
GuanineG
OHOCH2
H
H H
OH
H
OHOCH2
H
H H
OH
H
Pentose sugars
Deoxyribose (in DNA) Ribose (in RNA)
OHOH
CH
CH
Uracil (in RNA)U
4’
5”
3’
OH H2’
1’
5”
4’
3’ 2’
1’
Pyrimidines (single ring)
Purines (double ring)
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Nucleotide Polymers
• nucleotides linked by the–OH group on the 3´ carbon of one nucleotide and the phosphate on the 5´ carbon on the next
• Phosphodiester bond
3’C
5’ end
5’C
3’C
5’C
3’ endOH
Figure 5.26
O
O
O
O
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Gene
• The sequence of bases along a nucleotide polymer– Is unique for each gene
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The DNA Double Helix• Have two polynucleotides that
spiral around each other• held together by hydrogen
bonds between nitrogenous bases– A (adenine) will always bond with
T (thymine – DNA only), or U (uracil – RNA only) 2 hydrogen bonds
– C (cytosine) will always bond with G (guanine) 3 hydrogen bonds
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• The DNA double helix– Consists of two antiparallel nucleotide strands
3’ end
Sugar-phosphatebackbone
Base pair (joined byhydrogen bonding)
Old strands
Nucleotideabout to be added to a new strand
A
3’ end
3’ end
5’ end
Newstrands
3’ end
5’ end
5’ end
Figure 5.27