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The Structure and Function of Large Biological Molecules - Coggle Diagram
The Structure and Function of Large Biological Molecules
Macromolecules are polymers, built from monomers
Large polymers are known as macromolecules for their huge size
A polymer is a long molecule consisting of many similar building blocks
The repeating units that serve as building blocks are called monomers
Carbohydrates, proteins, and nucleic acids are polymers
The Synthesis and Breakdown of Polymers
Enzymes are specialized macromolecules that speed up chemical reactions such as those that make or break down polymers
A dehydration reaction occurs when two monomers bond together through the loss of a
water molecule
Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction
The Diversity of Polymers
A cell has thousands of different macromolecules
Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species
A huge variety of polymers can be built from a small set of monomers
CONCEPT 5.2: Carbohydrates serve as fuel and building material
Carbohydrates include sugars and polymers of sugars
The simplest carbohydrates are monosaccharides, or simple sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
Sugars
Monosaccharides have molecular formulas
that are usually multiples of CH₂O
Glucose (C₆H₁₂O₆) is the most common monosaccharide
Monosaccharides are classified by
The location of the carbonyl group (as aldose
or ketose)
The number of carbons in the carbon skeleton
Polysaccharides
Polysaccharides, the polymers of sugars, have storage and structural roles
The architecture and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages
Storage Polysaccharides
Starch, a storage polysaccharide of plants, consists of glucose monomers
Plants store surplus starch as granules within chloroplasts and other plastids
The simplest form of starch is amylose
Glycogen is a storage polysaccharide in animals
Glycogen is stored mainly in liver and muscle cells
Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases
Structural Polysaccharides
The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ
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The difference is based on two ring forms for glucose: alpha (α) and beta (β)
CONCEPT 5.3: Lipids are a diverse group of hydrophobic molecules
Lipids are the one class of large biological molecules that does not include true polymers
The unifying feature of lipids is that they mix poorly, if at all, with water
Lipids consist mostly of hydrocarbon regions
The most biologically important lipids are fats, phospholipids, and steroids
Fats
Fats are constructed from two types of smaller molecules: glycerol and fatty acids
Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats
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In a fat, three fatty acids are joined to glycerol
by an ester linkage, creating a triacylglycerol,
or triglyceride
The fatty acids in a fat can be all the same or of
two or three different kinds
Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon
A fatty acid consists of a carboxyl group attached to a long carbon skeleton
CONCEPT 5.4: Proteins include a diversity
Proteins account for more than 50% of the dry mass of most cells
Some proteins speed up chemical reactions
Enzymes are proteins that act as catalysts to speed up chemical reactions
Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life
Amino Acids (Monomers)
Amino acids are organic molecules with amino and carboxyl groups
Amino acids differ in their properties due to differing side chains, called R groups
Polypeptides (Amino Acid Polymers)
Amino acids are linked by covalent bonds called peptide bonds
A polypeptide is a polymer of amino acids
Polypeptides range in length from a few to more than 1,000 monomers
Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus)
Other protein functions include defense, storage, transport, cellular communication, movement, and structural support
Proteins are all constructed from the same set of 20 amino acids
Polypeptides are unbranched polymers built from these amino acids
The bond between amino acids is a peptide bond
A protein is a biologically functional molecule that consists of one or more polypeptides
Protein Structure and Function
The specific activities of proteins result from their intricate three-dimensional architecture
A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape
The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s structure determines how it works
The function of a protein usually depends on
its ability to recognize and bind to some other molecule
Four Levels of Protein Structure
The primary structure of a protein is its unique sequence of amino acids
Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain
The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
Typical secondary structures are a coil called an
α helix and a folded structure called a β pleated sheet
Tertiary structure is determined by interactions among various side chains (R groups)
Tertiary structure, the overall shape of a polypeptide, results from interactions between
R groups, rather than interactions between backbone constituents
These interactions include hydrogen bonds,
ionic bonds, hydrophobic interactions, and
van der Waals interactions
Strong covalent bonds called disulfide bridges may reinforce the protein’s structure
Quaternary structure results when a protein consists of multiple polypeptide chains
The primary structure of a protein is its sequence of amino acids
Primary structure is like the order of letters in a long word
Primary structure is determined by inherited genetic information
Quaternary structure results when two or more polypeptide chains form one macromolecule
Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
Hemoglobin is a globular protein consisting of
four polypeptides: two α and two β subunits
of structures, resulting in a wide range
of functions
Sickle-Cell Disease: A Change in Primary Structure
A slight change in primary structure can affect a protein’s structure and ability to function
Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
The abnormal hemoglobin molecules cause the red blood cells to aggregate into chains and to deform into a sickle shape
CONCEPT 5.5: Nucleic acids store, transmit, and help express hereditary information
The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
Genes consist of DNA, a nucleic acid made of monomers called nucleotides
The Roles of Nucleic Acids
Each gene along a DNA molecule directs synthesis of a messenger RNA (mRNA)
The mRNA molecule interacts with the cell’s protein-synthesizing machinery to direct production of a polypeptide
The flow of genetic information can be summarized as DNA → RNA → protein
The Components of Nucleic Acids
Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
Nucleoside = nitrogenous base + sugar
There are two families of nitrogenous bases
Pyrimidines (cytosine, thymine, and uracil)
have a single six-membered ring
Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring
In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose
Nucleotide = nucleoside + phosphate group
Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups
Nucleotide Polymers
Nucleotides are linked together by a phosphodiester linkage to build a polynucleotide
A phosphodiester linkage consists of a phosphate group that links the sugars of two nucleotides
These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
The sequence of bases along a DNA or mRNA polymer is unique for each gene
The portion of a nucleotide without the phosphate group is called a nucleoside
The Structures of DNA and RNA Molecules
DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helix
The backbones run in opposite 5′ → 3′ directions from each other, an arrangement referred to as antiparallel
One DNA molecule includes many genes
