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Importance of Carbohydrates Widely distributed in nature Key intermediates of metabolism (sugars) Found in the structural components of plants (cellulose) Important in manufacturing materials of industrial products: Paper, lumber, fibers Key component in food sources Sugars, flour, vegetable fiber
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Chapters 25-7 Biomolecules Importance of Carbohydrates
Widely distributed in nature Key intermediates of metabolism
(sugars) Found in the structural components of plants (cellulose)
Important in manufacturing materials of industrial products: Paper,
lumber, fibers Key component in food sources Sugars, flour,
vegetable fiber Chemical Formula and Name
Term carbohydrate comes from the historical belief that glucose was
a hydrate of carbon Carbohydrate generally refers to
polyhydroxylated aldehydes and ketones Classification of
Carbohydrates
Simple sugars(monosaccharides) cannot be converted into smaller
sugars by hydrolysis Complex carbohydrates consist of two or more
simple sugars connected by acetal bonds Classification of
carbohydrates Naturally Occurring D Sugars
D sugars occur naturally and have the hydroxyl group at the bottom
of the chirality center pointing to the right L sugars are the
mirror image of corresponding D sugars and have the opposite
configuration from the D sugar at all chirality centers D, L sugars
Anomers Anomers are produced when an open-chain monosacchride
cyclizes to a pyranose form Cyclization of the open-chain
monosacchride results in generation of a new chirality center at
the former carbonyl atom The hemiacetal carbon is called the
anomeric center Cyclic structures of monosaccharides: Anomers
Glucose in its Cyclic Pyranose Forms
Cyclic structures of monosaccharides: Anomers Glycoprotein
Formation
Reactions of monosaccharides The Eight Essential
Monosaccharides
Cells need eight monosaccharides for proper functioning It is more
energetically efficient to obtain these from environment than
through biosynthesis They include L-fucose, D-galactose, D-glucose,
D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine,
D-xylose, and N-acetyl-D-neuraminic acid The eight essential
monosaccharides The Eight Essential Monosaccharides Maltose and
Cellobiose
Disaccharides Lactose Disaccharide that occurs naturally in
milk
Contains two different monosaccharides joined by a -glycosidic bond
Disaccharides Sucrose Also known as table sugar
Yields 1 equivalent of glucose and 1 equivalent of fructose on
hydrolysis Disaccharides Polysaccharides and Their Synthesis
Polysacchrides are complex carbohydrates in which many simple
sugars are linked Cellulose and starch are the two most widely
occurring polysaccharides Polysaccharides and their synthesis
Cellulose Comprises thousands of D-glucopyranosyl
14--glucopyranosides as in cellobiose Cellulose molecules form a
large aggregate structures held together by hydrogen bonds Main
component of wood and plant fiber Polysaccharides and their
synthesis Starch and Glycogen Digested into glucose Components of
starch
Starch comprises monosaccharide units linked by 14--glycoside bonds
Digested into glucose Components of starch Amylose, which comprises
20% of starch Polysaccharides and their synthesis Starch and
Glycogen Amylopectin, which comprises 80% of starch
Polysaccharides and their synthesis Glycogen Polysaccharide that
serves the same energy storage function in animals that starch
serves in plants Highly branched and larger than amylopectin-up to
100,000 glucose units Polysaccharides and their synthesis
Biomolecules Amino acids contain a basic amino group and an acidic
carboxyl group They are joined as amides between the NH2 of one
amino acid and the CO2H to the next amino acid Chains with fewer
than 50 units are called peptides A protein comprises of large
chains that have structural or catalytic functions in biology
Structures of Amino Acids
Amino acids occur primarily in the form of a dipolar ion,
orzwitterion, in an aqueous solution Since amino acid zwitterions
are internal salts, most properties are associated with salts Amino
acids are amphiprotic Structures of amino acids Common Amino Acids
20 amino acids form amides in proteins
All are -amino acids - Amino and carboxyl are connected to the same
C They differ by the other substituent attached to the carbon,
called the side chain Structures of amino acids The 20 Common Amino
Acids in Proteins
Structures of amino acids The 20 Common Amino Acids in
Proteins
Structures of amino acids The 20 Common Amino Acids in
Proteins
Structures of amino acids The 20 Common Amino Acids in
Proteins
Structures of amino acids Chirality of Amino Acids
The carbons of the amino acids are centers of chirality Glycine is
achiral The stereochemical attributes of naturally occurring -amino
acids are similar to that of L sugars -amino acids are also called
L amino acids Structures of amino acids Classification Based on
Side Chains
Common amino acids can be classified as: Neutral - Fifteen amino
acids Acidic - Two amino acids Aspartic and glutamic acid Basic -
Three amino acids Lysine, arginine, and histidine Cysteine and
tyrosine possess weakly acidic chains that can be protonated in a
basic solution Classified as neutral amino acids Structures of
amino acids Essential Amino Acids Humans can synthesize only 11 of
the 20 amino acids Called non-essential amino acids Rest are
obtained from food Found in plants and microorganisms Called
essential amino acids Structures of amino acids Isoelectric Point
(pI) of Amino Acids
It is the pH at which the amino acid is balanced between anionic
and cationic forms Exists primarily as the neutral, dipolar
zwitterion Amino acids and the Henderson-Hasselbalch equation:
Isoelectric points Peptides and Proteins Proteins and peptides are
amino acid polymers in which the individual amino acid units,
called residues, are linked together by amide bonds or peptide
bonds Peptides and proteins Peptides and Proteins The long
repetitive sequence of NCHCO atoms that make up a continuous chain
is called the proteins backbone Peptides are always written with
the N-terminal amino acid (the one with the free NH2 group) on the
left and the C-terminal amino acid (the one with the free CO2H
group) on the right Alanylserine is abbreviated Ala-Ser or A-S, and
serylalanine is abbreviated Ser-Ala or S-A Peptides and proteins
Peptide Linkages Amino acids in peptides are linked together by
amide bonds Amide nitrogen interacts with the carbonyl group,
causing delocalization of its unshared electron pair Peptides and
proteins Peptide Linkages Disulfide linkages in peptides occur
between two cysteine residues Peptides and proteins Protein
Structure Classified as fibrous or globular
Fibrous proteins comprise polypeptide chains arranged side by side
in long filaments Tough and insoluble in water Globular proteins
are coiled into compact, roughly spherical shapes Soluble in water
and are capable of motion within the cells Protein structure
Protein Structure The primary structure of a protein is simply the
amino acid sequence. The secondary structure of a protein describes
how segments of the peptide backbone orient into a regular pattern.
The tertiary structure describes how the entire protein molecule
coils into an overall three-dimensional shape. The quaternary
structure describes how different protein molecules come together
to yield large aggregate structures Protein structure -Helix
Right-handed coil of the protein backbone
Each spiral contains 3.6 amino acid residues Protein structure
-Pleated Sheet -pleated sheet contains a fully extended peptide
chain Protein structure Tertiary Proteins Structure of tertiary
proteins is influenced by
Hydrophilic interactions of the polar side chains Hydrophobic
interactions of the nonpolar side chains Formation of disulphide
bridges between cysteine residues Formation of hydrogen bonds
between nearby amino acid residues Salt bridges Protein structure
Denaturation of Proteins
The tertiary structure of a globular protein is the result of weak
intramolecular attractions that can be disrupted by a change in
temperature or pH, causing the protein to become denatured Protein
structure Enzymes and Coenzymes An enzyme is a protein that acts as
a catalyst for a biological reaction. Increases the rate of
reaction by decreasing the activation energy Most enzymes are
specific for substrates while enzymes involved in digestion, such
as papain, attack many substrates Enzymes and coenzymes Enzymes and
Coenzymes Factors that contribute to the accelerating action of
enzymes: Ability to adjust their shape Wrapping action Ability to
lower the rate-limiting transition state Enzymes and coenzymes
Energy Diagrams for Uncatalyzed and Enzyme-Catalyzed
Processes
Enzymes and coenzymes Classification of Enzymes
Enzymes and coenzymes Enzymes and Coenzymes Most enzymes contain a
non-protein component called a cofactor It is either an inorganic
ion or a small organic molecule called a coenzyme Coenzymes are
reactants that undergo a chemical change during the reaction and
require an additional step to revert to their initial state Derived
from vitamins Enzymes and coenzymes Lipids Natural molecules that
can be preferentially extracted using nonpolar organic solvents
Includes fats, oils, waxes, vitamins and hormones, some components
of membrane Classified based on hydrolysis Fats and waxes Waxes,
Fats, and Oils Waxes contain various esters formed from long-chain
(C16-C36) carboxylic acids and long-chain alcohols (C24-C36)
Triacontyl hexadecanoate is found in beeswax Waxes, Fats, and Oils
Triacylglycerol Triesters of glycerol with three long-chain
carboxylic acids called fatty acids Waxes, Fats, and Oils
Structures of Some Common Fatty Acids
Waxes, Fats, and Oils Fatty Acids When hydrolysed with NaOH, a fat
or oil yields glycerol and three fatty acids Fatty acids contain an
even number of carbon atoms and are unbranched Of the 100 different
known fatty acids, 40 are common Palmitic acid (C16) and stearic
acid (C18) are the most common saturated fatty acids Oleic (C18)
and linoleic (C18) acids are the most common unsaturated fatty
acids Waxes, Fats, and Oils Fatty Acids Monosaturated fatty acids
have one double bond
Oleic acid Polyunsaturated fatty acids have more than one double
bond Linoleic, linolenic, and arachinodic acid Humans require
linoleic and linolenic acid Deprivation leads to stunted growth and
skin lesions in infants Linolenic acid has shown to lower blood
tryglyceride levels Waxes, Fats, and Oils Unsaturated and
Polyunsaturated Fatty Acids
Waxes, Fats, and Oils Double Bonds in Fatty Acids
Melting points of unsaturated fatty acids are generally lower than
those of saturated fatty acids Number of double bonds influences
the melting point of oil Catalytic hydrogenation reduces the number
of double bonds Reaction is carried at a high temperature using a
nickel catalyst Remaining double bonds undergo cis-trans
isomerization, resulting in trans unsaturated fatty acids Waxes,
Fats, and Oils Soap Mixture of sodium or potassium salts of
long-chain fatty acids produced by alkaline hydrolysis
(saponification) of animal fat with alkali Soap Cleansing Action of
Soap
Carboxylate end of the long-chain molecule is ionic and therefore
is hydrophilic Hydrocarbon tail is nonpolar and dissolves in grease
and oil Soaps enable grease to be dissolved into water Soap
Phospholipids Phospholipids are diesters of H3PO4, phosphoric
acid
Classified into glycerophospholipids and sphingomyelins
Glycerophospholipids
Based on phosphatidic acid, which contains a glycerol backbone
linked by ester bonds to two fatty acids and phosphoric acid
Phospholipids Phosphoglyceride Membranes
Phosphoglycerides are the major lipid component of cell membranes
Their nonpolar tails aggregate in the center of a lipid bilayer
Phospholipids Steroids Molecules derived from the triterpenoid
lanosterol
Has four fused rings A, B, C, and D, beginning at the lower left
Steroids Steroids Two cyclohexane rings can be joined in either a
cis or trans manner Steroids Steroid Conformations
Steroids Male Sex Hormones Testosterone and androsterone are the
two most important male sex hormones, or androgens Have a
significant influence on the development of secondary sex
characteristics and muscle growth Steroids Female Sex Hormones
Estrone and estradiol are two most important female sex hormones,
or estrogens Progesterone is the most important progestin; it that
functions during pregnancy Steroids