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Organic Molecules
Organic Molecules: Building Blocks of Life
Carbohydrate Structure
Lipid Structure
Protein Structure
Nucleic Acid Structure
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Organic Molecules: The Building Blocks of Life
Organic Molecules
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Notes:
• The carbon atom is the most versatile of all atoms for building
molecules. This is due in part to carbon’s tetravalence, or tendancy
to make four covalent bonds with other atoms. Carbon atoms bond
together to form straight chains, branched chains, or rings – making
for an incredible variety of carbon skeletons as the basis for
organic molecules.
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Narration
The molecules that make up living things are all
based on carbon. Carbon atoms have four bonding
sites. They can bond with hydrogen, in this case,
forming the molecule CH4, methane gas. Carbon
atoms can also bond with each other, like this.
Carbon chains can be combined. An OH from one
and an H from another are removed, forming H2O.
This is called a condensation reaction. Condensation reactions can assemble building block molecules into long chains of repeating units called
polymers. Four kinds of biologically produced
polymers play major roles in life: carbohydrates,
lipids, proteins and nucleic acids.
In a condensation reaction, two molecules become covalently
bonded together and a small molecule is lost, usually water. When
this covalent bond forms between two monomers, one monomer
contributes an OH group and the other a hydrogen, forming H20. To
make a polymer, the condensation reaction occurs over and over
as each monomer is added to the chain. Condensation reactions
are catalyzed by enzymes, and they require energy from the cell.
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• All molecules containing more than one carbon atom are termed
organic. Oxygen and hydrogen are found in most organic molecules
and nitrogen is also common. Hydrocarbons are organic molecules made only of carbon and hydrogen, such as ethane, or the
tail portion of fatty acids. The C-C and C-H bonds in hydrocarbons
are non-polar, meaning that electrons are distributed evenly between the two atoms of the bond.
• Functional groups add even greater variation to organic molecules. Examples of these are amino, carboxyl, hydroxyl or
phosphate groups. Combinations of these bonded to various
carbon skeletons form the main organic molecules of life.
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Carbohydrate Structure
Organic Molecules
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Sugars are simple carbohydrates. They can be
monosaccharides, either straight chains or rings of
six carbons; or disaccharides—double sugars.
Starch, a polysaccharide, is a complex carbohydrate, made from many sugar molecules.
When an animal eats a starch—its digestive enzymes render the polymer back to its building
block sugars, ready for absorption.
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Notes:
Carbohydrates include sugars and their polymers. The simplest carbohydrates are monosaccharides, or single sugars. Disaccharides are
double sugars formed from two monosaccharides joined by a condensation reaction. Polysaccharides are macromolecule polymers formed
from a few to a few thousand monosaccharides joined together.
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Monosaccharides occur in two forms, either as an aldose or a ketose,
depending on the location of the carbonyl group (C=0). Sugars are
also classified according to the length of the cabon skeleton, which
ranges from three to seven carbon atoms, and by the spatial arrangement of their parts. For example, glucose and fructose have the same
molecular formula (C 6H 12O6) but differ in the position of the carboxyl
group. Monosaccharides are a major food source for cells. Sugar
molecules also act as raw material for building other organic molecules, such as amino acids.
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Disaccharides, such as maltose, lactose and sucrose, are two-unit
polymers of monosaccarides joined with a glycosidic linkage. Sucrose, table sugar, is a disaccharide common in nature. It is used by
plants to transport food energy from leaves to roots.
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Polysaccharides are divided into two groups, storage polysaccharides and structural polysaccharides . In plants and animals, starch
and glycogen are storage polysaccharides. Cellulose and chitin are
strucutral polysaccharides. Polysaccharides are usually made from
glucose (or modified-glucose) monomers. Hydrolysis of storage
polysaccharides releases glucose, a major cellular fuel source.
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Lipid Structure
Organic Molecules
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Notes:
• There are three groups of lipids: fats, phospholipids and
steroids. Fats are made of glycerol and fatty acids. Fatty acids
have hydrocarbon chain ‘tails’ consisting of 16 or 18 carbons with
a carboxyl group ‘head’. A triglyceride (a fat) results when three
fatty acids bond to a glycerol with ester linkages.
• Plasma membranes rely on the mix of hydrophobic and hydrophilic properties of phospholipids to maintain stability and
flexibility. Steroids, including cholesterol, have a carbon skeleton made of four interconnected rings with a variety of functional
groups attached to the rings. Cholesterol is a key starting molecule for the biochemical synthesis of most other steroids.
Narration
Lipids are made of short carbon chains called fatty
acids. The plasma membrane is a double layer of
phospholipids composed of two fatty acids attached to a phosphate containing “head”. These
“heads” are “hydrophilic (attracted to water) so in
water they orient like this—heads pointing out. The
tails are hydrophobic and so point in. This orientation to water is responsible for the typical bilayer
configuration of all cell membranes. Another lipid
configuration has three fatty acids combined with a
glycerol—a triglyceride—the energy storing fat
produced by animals. A third type of lipid, cholesterol, is found in membranes and is used by cells
for synthesizing certain steroid hormones.
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• The major function of fats is energy storage. Since fats store
twice as much energy as carbohydrates, they represent a much
more efficient storage molecule. In general, animals store energy
as fats, while plants, being non-motile, are able to survive by
storing energy as starch. Animals store fats in adipose cells,
which swell and shrink as fat reserves go up and down.
• Fatty acids can be saturated or unsaturated. A saturated fatty
acid has no double bonds between carbon atoms in the hydrocarbon tails. An unsaturated fatty acid can have one or more double
bonds between carbon atoms in the tails. A fatty acid will have a
kink wherever a double bond occurs.
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Organic Molecules
Protein Structure
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Fats and carbohydrates are basically chains
of similar building block molecules. Proteins
are also polymers, but are made from 20
different amino acid building blocks. Condensation reactions can fit amino acids
together in any combination.
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Notes:
Based on combining twenty amino acid building blocks, nature has
formed millions of different kinds of proteins. Proteins are used for
structural support, storage, transport of substances, signalling within
an organism, movement and defence. Some proteins are enzymes
that accelerate chemical reactions, thereby regulating an organism’s
metabolism and other biochemical activities.
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Every amino acid has a central carbon atom bonded to four things:
1) a hydrogen atom, 2) a carboxyl group 3) an amino group, and
4) a side group, or ‘R group’. The twenty amino acids in proteins
differ from each other only at the side (R) group. Physical and
chemical properties of the side group determine characteristics of
the amino acid. For example, side groups can be polar, non-polar
or electrically charged.
Amino Acid Table
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Amino acid building blocks inside a protein are called peptides, and
a chain of peptides is a polypeptide. Condensation reactions
between amino acids create peptide bonds. The peptide bond links
the carboxyl group of one amino acid to the amino group of its
neighbor.
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Proteins are usually made from two or more polypeptide chains.
They have four levels of structure: primary structure is the amino
acid sequence in a polypeptide; secondary structure results from
simple folding and coiling of the polypeptide units; tertiary structure
involves further folding; and quarternary structure results from
linking (2-many) polypeptides together. The result is a unique conformation for each protein that contributes to its individual function.
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Nucleic Acid Structure
Organic Molecules
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Notes:
• Nucleic acids are polymers made of nucleotide building blocks.
Two types of nucleic acids, deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA) are essential for the cell. DNA stores
the genetic code, while several types of RNA are involved with
the transfer of genetic information and building of proteins.
Extensions:
• Nucleotides consists of three parts: a phosphate group, a
pentose sugar and a nitrogenous base. In DNA, the sugar is
deoxyribose. In RNA, the sugar is ribose.
Narration
Nucleic acids are polymers made from four kinds
of building block nucleotides. DNA is an extremely long molecule composed of two strands
wound in a double helix. Each strand is made up
of a chain of nucleotides. Nucleotides have a
common structure – a phosphate group, a sugar
and a nitrogenous base unit. There are four kinds
of nitrogenous bases – thymine, guanine, cytosine
and adenine.
• There are two families of nitrogenous bases, pyrimidines and
purines. Pyrimidines have a six-membered ring. Pyrimidines
include: cytosine (C) (in DNA and RNA), thymine (T)(only in
DNA), and uracil (U)(only in RNA). The purines adenine (A)
and guanine (G) are larger with a six-membered ring attached to
a five-membered ring.
• In DNA, covalent bonds join the phosphate group of one nucleotide to the sugar of its neighbor. This results in an alternating
phosphate-sugar backbone. Each strand of DNA has a unique
sequence of bases attached to this phosphate-sugar backbone.
• Two complementary DNA strands form a double helix, and this
is the normal form of DNA in the cell. Genes, the unit of inheritance, are made of DNA. The coding capabilities of DNA result
from the arrangement of base sequences on the DNA strands.
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