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Chapter 5
The Structure and Function of Large Biological Molecules Important Topics: Polymer and monomers of biological molecule Dehydration and hydrolysis reactions Types of carbohydrates, structure, function and examples Types of Lipids, structure, function and examples Types of Proteins, structure, function and examples Types of nucleic acids, structure, function and examples
Alcohol dehydrogenase , a protein that breaks down alcohol in the body, is shown here as a molecular model. This protein affects how well that person tolerates drinking alcohol. Proteins are one class or large molecules, or macromolecules.
Why this chapter matters
Hemoglobin is a protein that transports oxygen to our cells. Cell uses the oxygen to break down sugar and release energy This energy allows cell to carry out activities required for it to survive.
Figure 5.1a Macromolecules are polymers that are made of monomers
- Polymer : Large molecule that consists of identical subunits ( monomers ).
- Monomers : small identical subunits that make the polymer
- Biological molecules that are polymers are
- Carbohydrates
- Proteins
- Nucleic acids
Figure 5.2b Hydrolysis: breaking down a polymer
- Polymers are disassembled to monomers by hydrolysis , a reaction that is essentially the reverse of the dehydration reaction
- Enzymes are specialized macromolecules that speed up chemical reactions such as those that make or break down polymers
- Digestive enzymes can break a polymer like protein into amino acids by hydrolysis
Hydrolysis adds a water molecule, breaking a bond.
1 2 3 4
(^1 2 )
Dehydration reaction: synthesizing a polymer A dehydration reaction occurs when two monomers bond together through the loss of a water molecule
Short polymer (^) Unlinked monomer
Dehydration removes a water molecule, forming a new bond.
Longer polymer
1 2 3 4
1 2 3
Figure 5.
CONCEPT 5.2: Carbohydrates serve as fuel and building material
Carbohydrates: Sugar & its Polymer Three types of Carbohydrates:
- Monosaccharides (Single sugars)
- Disaccharides (Two sugars)
- Polysaccharides (Many sugars)
Monosaccharides: Single sugar
- Molecular formula of CH 2 O
- Ex. Glucose, Galactose, Fructose, Ribose etc
Many sugars form a ring structure in
aqueous solution
Fig. 5-
(a) Linear and ring forms (b) Abbreviated ring structure
Figure 5.
Many sugars form a ring structure in
aqueous solution
Disaccharides: Two sugars
Table sugar- Sucrose=Glucose + Fructose Malt sugar - Maltose=Glucose + Glucose Milk sugar- Lactose=Glucose + Galactose
- A disaccharide is formed when a dehydration reaction joins two monosaccharides
- This covalent bond between two monosaccharides is called a glycosidic linkage
Lumen learning
Polysaccharides: many sugars
- Are polymers of sugars
- Have storage and structural roles in organisms
Types of polysaccharides:
1.Storage Polysaccharide
- Starch in plants ,
- Glycogen in animals 2.Structural Polysaccharide
- Cellulose in plants ,
- Chitin in animals
Figure 5.UN
Summary of Key Concepts: Carbohydrates
- Consist of mostly hydrophobic molecules,
do not mix with water
- Large molecules that do not form polymers
- Three types of lipids are:
- Fats
- Phospholipids and
- Steroids
CONCEPT 5.3: Lipids are a group of
hydrophobic molecules
The synthesis and structure of a fat, or triacylglycerol
What are fats or triglycerides?
- Fats are constructed from two types of smaller molecules: glycerol and fatty acids
- 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
- In a fat, three fatty acids are joined to glycerol by an ester linkage , creating a triacylglycerol , or triglyceride
Function of Fats
- Storage of energy
- Fat is stored in Adipose tissue
- Adipose tissue protects vital organs such
as kidney and insulates the body
Saturated Fats:
- contain saturated fatty acids that have maximum number of hydrogen atoms possible with no double bonds
- Solid at room temperature
- Ex. Animal fats, butter margarine Unsaturated Fats or oils:
- Contain unsaturated fatty acids that have one or more double bonds
- Liquid at room temperature
- Ex. Plant and fish fats
Saturated and unsaturated fats
Figure 5.
Saturated and unsaturated fats and fatty acids
- A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
- Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen
- Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds
- These trans fats may contribute more than saturated fats to cardiovascular disease
- Certain unsaturated fatty acids are not synthesized in the human body
- These essential fatty acids include the omega-3 fatty acids , required for normal growth, and thought to provide protection against cardiovascular disease
Omega 3 Fatty Acids Which of the following best explains why fats, instead of carbohydrates, are used for long-term energy storage in animals?
A. Fats contain more energy, gram for gram, because they are amphipathic. B. Carbohydrates contain less energy than fats do because the larger number of O–H bonds in carbohydrates have lower free energy than the C–H bonds in fats. C. Fats are easier to store because they are nonpolar. D. Our ancestors ate more fats than carbohydrates, so we adapted to the storage of fats.
Figure 5.
The structure of a phospholipid
The structure of phospholipids results in a
bilayer arrangement found in cell
membranes
Figure 5.
Peptide bond
New peptide bond forming Side chains
Back- bone
Amino end (N-terminus)
Peptide bond Carboxyl end (C-terminus)
- Amino acids are linked by peptide bonds
- A polypeptide is a polymer of amino acids
- Each polypeptide has a unique sequence
of amino acids, with a carboxyl end (C-
terminus) and an amino end (N-terminus)
Polypeptides (Amino Acid Polymers)
Protein structure and function
- A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape
- The sequence of amino acids determines a protein’s 3D structure
- A protein’s specific structure determines its function
Four Levels of Protein Structure
- Primary structure-unique sequence of amino acids
- Secondary structure-consists of coils and folds in the polypeptide chain
- Tertiary structure-determined by interactions among various side chains (R groups)
- Quaternary structure- consists of multiple polypeptide chains
Figure 5.20a
the sequence of amino acids in a protein
Primary structure Amino acids
Amino end
Carboxyl end
Primary structure of transthyretin
Secondary structure
Hydrogen bond
helix
pleated sheet strand, shown as a flat arrow pointing toward the carboxyl end
Hydrogen bond
Figure 5.20c
Secondary structure of proteins
- Is the folding or coiling of the polypeptide into a repeating configuration as a result of hydrogen bonds
- Typical secondary structures are a coil called the helix and a folded structure called a pleated sheet
Figure 5.18d Exploring levels of protein structure: Tertiary stabilization
- Results from interactions between amino acids and R groups
- These interaction includes: hydrogen bonds, ionic bonds, hydrophobic interactions and van dar waal’s interactions
- Strong covalent bonds called disulfide bridges may reinforce the protein’s structure
Figure 5.18b Exploring levels of protein structure: Secondary through quaternary structure
Quaternary structure is the overall protein structure that results from the aggregation of two or more polypeptide subunits
Quaternary Structure of Proteins
- Collagen is a fibrous protein consisting of three polypeptides coiled like a rope
- Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains
A single amino acid substitution in a protein causes sickle-cell disease
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
Gene expression: DNA → RNA → protein What is the roles of nucleic acids?
- DNA or gene stores information for the synthesis of specific proteins
- Each gene along a DNA molecule directs synthesis of a messenger RNA (mRNA)
- The information to make proteins is passed on from DNA to mRNA
- The flow of genetic information can be summarized as DNA → RNA → protein - This process is called gene expression
- Protein synthesis occurs in ribosomes
Figure 5. Components of nucleic acids
The Components of Nucleic Acids
- Nucleic acids are polymers called
polynucleotides
- Each polynucleotide is made of monomers
called nucleotides
- Each nucleotide consists of a
nitrogenous base , a pentose sugar , and
one or more phosphate groups
- Nucleoside = nitrogenous base + sugar
- Nucleotides are linked by phosphodiester
bonds
- Phosphodiester bond : A covalent bond
between sugar of one nucleotide and the
phosphate on the next nucleotide
The Components of Nucleic Acids
- Two types of Nitrogenous bases
- Pyrimidines : Cytosine (C ), Thymine (T) in DNA, Uracil (U) in RNA
- have a single six-membered ring
- Purines : Adenine (A) and Guanine (G)
- Have a six-membered ring fused to a five- membered ring
- In DNA, the sugar is deoxyribose ; in RNA, the sugar is ribose
Figure 16.
3.4 nm
1 nm
0.34 nm
Hydrogen bond
(a) Key features of DNA structure Space-filling model (b) Partial chemical structure (c)
3 end 5 end
3 end
5 end
T
T
A
A
G
G
C
C
C C C C C C C C
C
G G G G
G G
G G G
T
T T
T T T
A
A A
A A A
Structure of DNA: Double Helix 2 strands are held together due to hydrogen bonds between complementary bases
Figure 5.
Sugar-phosphate backbones Hydrogen bonds
Base pair joined by hydrogen bonding
Base pair joined by hydrogen bonding
(a) DNA (b) Transfer RNA
5 3
3 5
- 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
The Structures of DNA and RNA Molecules
- RNA , in contrast to DNA, is single-stranded
- Complementary pairing can also occur between two RNA molecules or between parts of the same molecule
- In RNA, thymine is replaced by uracil (U), so A and U pair
- While DNA always exists as a double helix, RNA molecules are more variable in form - Only certain bases in DNA pair up and
form hydrogen bonds: adenine (A) always
with thymine (T), and guanine (G) always
with cytosine (C)
- This is called complementary base
pairing
- Complementary Bases: Bases that form
pairs due to hydrogen bonds between
them
