Transcript Amino acids - Zanichelli online per la scuola

David Sadava, David M. Hillis,
H. Craig Heller, May R. Berenbaum
La nuova
biologia.blu
Le cellule e i viventi
Chemistry’s Life
What Kinds of Molecules Characterize Living Things?
Isomers: molecules with the same chemical formula,
but atoms are arranged differently.
Functional groups— groups of atoms with specific
chemical properties and consistent behavior.
Some Functional Groups Important to Living Systems (part 1)
A single macromolecule may contain many different
functional groups.
Some Functional Groups Important to Living Systems (part 2)
What Kinds of Molecules Characterize Living Things?
Molecules that make up living organisms:
• Proteins
• Carbohydrates
• Lipids
• Nucleic acids
Condensation and Hydrolysis of Polymers
Most are polymers of smaller molecules called monomers.
Macromolecules: polymers with molecular weights >1,000 Da.
Polymers are formed in
condensation reactions.
Polymers are broken down into
monomers in hydrolysis
reactions.
Hydrolysis releases energy.
What Are the Chemical Structures and Functions of Carbohydrates?
Carbohydrates have the general formula CmH2nOn.
They are:
• sources of stored energy
• used to transport stored energy
• carbon skeletons for many other molecules
Monosaccharides Are Simple Sugars
What Are the Chemical Structures and Functions of Carbohydrates?
Monosaccharides bind together in
condensation reactions to form glycosidic
linkages.
Disaccharides: two simple sugars linked
by covalent bonds.
Oligosaccharides: three to twenty
monosaccharides.
Disaccharides Form by Glycosidic Linkages
What Are the Chemical Structures and Functions of Carbohydrates?
Polysaccharides are giant polymers of
monosaccharides.
Cellulose: very stable,
good for structural
components.
Starch: storage of
glucose in plants.
Glycogen: storage of
glucose in animals.
What Are the Chemical Structures and Functions of Lipids?
Lipids are non-polar hydrocarbons; insoluble in water.
Fats and oils are triglycerides: three fatty acids plus
glycerol.
Carboxyls bond with hydroxyls of glycerol in an ester
linkage.
Glycerol: has three –OH groups (an alcohol).
Fatty acid: nonpolar hydrocarbon with a polar carboxyl
group.
They are amphipathic, and they can be
saturated or unsaturated.
Saturated and Unsaturated Fatty Acids
Saturated fatty acid: no double bonds between carbons
(it is saturated with H atoms).
Unsaturated fatty acid: one or more double bonds
in carbon chain.
Synthesis of a Triglyceride
What Are the Chemical Structures and Functions of Lipids?
Phospholipids: fatty acids bound to glycerol; a
phosphate group replaces one fatty acid.
What Are the Chemical Structures and Functions of Lipids?
In water, phospholipids form a bilayer.
What Are the Chemical Structures and Functions of Lipids?
Carotenoids: light-absorbing pigments
Steroids: multiple rings share carbons.
Vitamins—small molecules not synthesized by the
body; must be acquired in the diet.
Waxes—highly nonpolar and impermeable to water.
What Are the Chemical Structures and Functions of Proteins?
Proteins are polymers of 20 different amino acids.
Amino acids have carboxyl and amino
groups—they function as both acid and base.
What Are the Chemical Structures and Functions of Proteins?
These hydrophilic amino acids attract ions of opposite
charges.
The Twenty Amino Acids
The Twenty Amino Acids
Hydrophilic amino acids
with polar but uncharged
side chains form
hydrogen bonds.
Hydrophobic amino acids
The Twenty Amino Acids
The terminal —SH group of cysteine can react with
another cysteine side chain to form a disulfide
bridge, or disulfide bond (—S—S—).
These are important in protein folding.
What Are the Chemical Structures and Functions of Proteins?
Amino acids bond
together covalently in
a condensation
reaction by peptide
linkages (peptide
bonds).
The Four Levels of Protein Structure
Quaternary Structure of a Protein
What Are the Chemical Structures and Functions of Proteins?
Conditions that affect secondary and tertiary structure:
• High temperature
• pH changes
• High concentrations of polar molecules
• Non-polar
If a protein is heated, is said
to be denatured.
What Are the Chemical Structures and Functions of Proteins?
Proteins bind non-covalently with specific molecules.
Specificity is determined by:
•Shape — there must be a general “fit” between the
3-D shapes of the protein and the
other molecule.
•Chemistry — R groups on
the surface interact with
other molecules via ionic,
hydrophobic, or hydrogen bonds.
What Are the Chemical Structures and Functions of Nucleic Acids?
Nucleic acids are
polymers specialized
for the storage,
transmission, and
use of genetic
information.
What Are the Chemical Structures and Functions of Nucleic Acids?
RNA contains the sugar ribose.
DNA contains deoxyribose.
What Are the Chemical Structures and Functions of Nucleic Acids?
Complementary base pairing: purines pair
with pyrimidines by hydrogen bonds.
RNA and DNA
What Physical Principles Underlie Biological Energy Transformations?
Metabolism: the sum total of all chemical
reactions occurring in a biological system at a
given time.
Metabolic reactions involve energy changes.
Two types of metabolism:
• Anabolic reactions: complex molecules are
made from simple molecules, and energy input
is required.
• Catabolic reactions: complex molecules are
broken down to simpler ones, and energy is
released.
What Is the Role of ATP in Biochemical Energetics?
ATP (adenosine
triphosphate) captures
and transfers free
energy.
ATP releases a large
amount of energy when
hydrolyzed.
ATP can phosphorylate,
or donate phosphate
groups, to other
molecules.
What Are Enzymes?
Enzymes and ribozymes are highly specific.
Reactants are called substrates.
Substrate molecules bind to the active site of the
enzyme.
The three-dimensional shape of the enzyme determines
the specificity.
E + S ES  E + P
How and Where Did the Small Molecules of Life Originate?
Francesco Redi first disproved
spontaneous generation in 1668.
About 4 billion years ago,
chemical conditions, including
the presence of water,
became just right for life.
Two of the theories on the origin of
life:
1. Life came from outside Earth
2. Life arose on Earth through
chemical evolution.
Adapted from
Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014
Inc. All rights reserved