Transcript Chapter 3 - Slothnet

3
Proteins, Carbohydrates,
and Lipids
3 Proteins, Carbohydrates, and Lipids
3.1 What Kinds of Molecules
Characterize Living Things?
3.2 What Are the Chemical Structures
and Functions of Proteins?
3.3 What Are the Chemical Structures
and Functions of Carbohydrates?
3.4 What Are the Chemical Structures
and Functions of Lipids?
3 Proteins, Carbohydrates, and Lipids
Spider silk is composed of proteins.
The protein molecules in different
types of silk have different structural
characteristics and functions.
Opening Question:
Can knowledge of spider web protein
structure be put to practical use?
3.1 What Kinds of Molecules Characterize Living Things?
Molecules that make up living
organisms:
• Proteins
• Carbohydrates
• Lipids
• Nucleic acids
Most are polymers of smaller
molecules called monomers.
3.1 What Kinds of Molecules Characterize Living Things?
Proteins: combinations of 20 amino
acids.
Carbohydrates: sugar monomers
(monosaccharides) are linked to form
polysaccharides.
Nucleic acids: four kinds of nucleotide
monomers.
Lipids: noncovalent forces maintain
interactions between lipid monomers.
3.1 What Kinds of Molecules Characterize Living Things?
Macromolecules: polymers with
molecular weights >1,000.
Macromolecule function depends on
the properties of functional groups—
groups of atoms with specific
chemical properties and consistent
behavior.
A single macromolecule may contain
many different functional groups.
Figure 3.1 Some Functional Groups Important to Living Systems (Part 1)
Figure 3.1 Some Functional Groups Important to Living Systems (Part 2)
Figure 3.1 Some Functional Groups Important to Living Systems (Part 3)
3.1 What Kinds of Molecules Characterize Living Things?
Isomers: molecules with the same
chemical formula, but atoms are
arranged differently.
• Structural isomers
• cis-trans isomers
• Optical isomers
3.1 What Kinds of Molecules Characterize Living Things?
Structural isomers: differ in how their
atoms are joined together.
3.1 What Kinds of Molecules Characterize Living Things?
cis-trans isomers: different orientation
around a double bond.
3.1 What Kinds of Molecules Characterize Living Things?
Optical isomers occur when a carbon
atom has four different atoms or
groups attached to it (an asymmetric
carbon).
Some biochemical molecules that can
interact with one optical isomer are
unable to “fit” the other isomer.
Figure 3.2 Isomers (Part 2)
3.1 What Kinds of Molecules Characterize Living Things?
Biochemical unity: the four kinds of
macromolecules are present in the
same proportions in all living
organisms and have similar functions.
Organisms can obtain required
macromolecules by eating other
organisms.
Figure 3.3 Substances Found in Living Tissues
3.1 What Kinds of Molecules Characterize Living Things?
Macromolecule functions are directly
related to their three-dimensional
shapes and the sequence and
chemical properties of the monomers.
3.1 What Kinds of Molecules Characterize Living Things?
Polymers are formed in condensation
reactions.
Monomers are joined by covalent
bonds; energy must be added.
A water is removed; they are also
called dehydration reactions.
3.1 What Kinds of Molecules Characterize Living Things?
Polymers are broken down into
monomers in hydrolysis reactions
(hydro, “water”; lysis, “break”).
Hydrolysis releases energy.
Figure 3.4 Condensation and Hydrolysis of Polymers
3.2 What Are the Chemical Structures and Functions of Proteins?
Proteins have diverse functions. Only
energy storage and information
storage are not performed by proteins.
Table 3.1
3.2 What Are the Chemical Structures and Functions of Proteins?
Proteins are polymers of 20 different
amino acids.
Polypeptide chain: single, unbranched
chain of amino acids.
Proteins consist of one or more
polypeptide chains, which are folded
into specific 3-D shapes defined by
the sequence of amino acids.
3.2 What Are the Chemical Structures and Functions of Proteins?
Amino acids have carboxyl and amino
groups—they function as both acid
and base.
IN-TEXT art, p. 5
3.2 What Are the Chemical Structures and Functions of Proteins?
The α carbon atom is asymmetrical.
Amino acids exist in two isomeric
forms:
D-amino acids (dextro, right)
L-amino acids (levo, left)—this form is
found in organisms
3.2 What Are the Chemical Structures and Functions of Proteins?
The side chains or R-groups also
have functional groups.
Amino acids can be grouped based on
the side chains.
3.2 What Are the Chemical Structures and Functions of Proteins?
These hydrophilic amino acids attract ions of
opposite charges.
Table 3.2 (Part 2)
3.2 What Are the Chemical Structures and Functions of Proteins?
Hydrophilic amino acids with polar but
uncharged side chains form hydrogen
bonds.
3.2 What Are the Chemical Structures and Functions of Proteins?
Hydrophobic amino acids
Table 3.2 The Twenty Amino Acids (Part C)
3.2 What Are the Chemical Structures and Functions of Proteins?
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.
Figure 3.5 A Disulfide Bridge
3.2 What Are the Chemical Structures and Functions of Proteins?
Glycine is small and fits into tight
corners in the interior of proteins.
The proline side chain forms a ring,
which limits its hydrogen-bonding
ability and its ability to rotate about the
α carbon. It is often found where a
protein bends or loops.
3.2 What Are the Chemical Structures and Functions of Proteins?
Amino acids bond together covalently
in a condensation reaction by peptide
linkages (peptide bonds).
Figure 3.6 Formation of Peptide Linkages
3.2 What Are the Chemical Structures and Functions of Proteins?
A polypeptide chain is like a sentence:
• The “capital letter” is the amino group
of the first amino acid—the N
terminus.
• The “period” is the carboxyl group of
the last amino acid—the C terminus.
3.2 What Are the Chemical Structures and Functions of Proteins?
The primary structure of a protein is
the sequence of amino acids.
The sequence determines secondary
and tertiary structure—how the protein
is folded.
The number of different proteins that
can be made from 20 amino acids is
enormous!
Figure 3.7 The Four Levels of Protein Structure (Part 1)
3.2 What Are the Chemical Structures and Functions of Proteins?
Secondary structure:
• α helix—right-handed coil resulting
from hydrogen bonding between N–H
groups on one amino acid and C=O
groups on another.
• β pleated sheet—two or more
polypeptide chains are aligned;
hydrogen bonds form between the
chains.
Figure 3.7 The Four Levels of Protein Structure (Part 2)
Figure 3.8 Left- and Right-Handed Helices
3.2 What Are the Chemical Structures and Functions of Proteins?
Tertiary structure: Bending and
folding results in a macromolecule
with specific three-dimensional shape.
The outer surfaces present functional
groups that can interact with other
molecules.
Figure 3.7 The Four Levels of Protein Structure (D)
3.2 What Are the Chemical Structures and Functions of Proteins?
Tertiary structure is determined by
interactions between R-groups:
• Disulfide bridges
• Hydrogen bonds
• Aggregation of hydrophobic side
chains
• Ionic attractions
3.2 What Are the Chemical Structures and Functions of Proteins?
Ionic attractions form salt bridges
between positively and negatively
charged amino acids.
Figure 3.9 Three Representations of Lysozyme
Figure 3.9 Three Representations of Lysozyme
Complete descriptions of tertiary structure have
been worked out for many proteins.
3.2 What Are the Chemical Structures and Functions of Proteins?
If a protein is heated, secondary and
tertiary structure break down; the
protein is said to be denatured.
When cooled, the protein returns to
normal tertiary structure,
demonstrating that the information to
specify protein shape is in the primary
structure.
Figure 3.10 Primary Structure Specifies Tertiary Structure (Part 1)
Figure 3.10 Primary Structure Specifies Tertiary Structure (Part 2)
Working with Data 3.1: Primary Structure Specifies Tertiary
Structure
The second protein whose structure
was determined was the enzyme
ribonuclease A (RNase A).
RNase A has 124 amino acids,
including eight cysteines that form
four disulfide bridges.
Working with Data 3.1: Primary Structure Specifies Tertiary
Structure
1. The disulfide bonds were destroyed
chemically, then allowed to reform.
Protein function was assessed by
enzyme activity.
Working with Data 3.1, Figure A
Working with Data 3.1: Primary Structure Specifies Tertiary
Structure
At what time did disulfide bonds begin
to form?
At what time did enzyme activity begin
to appear?
Explain the difference between these
times.
Working with Data 3.1: Primary Structure Specifies Tertiary
Structure
2. Three-dimensional structure was
determined by UV spectroscopy.
Absorbance of UV over a range of
wavelengths was measured.
Working with Data 3.1, Figure B
Working with Data 3.1: Primary Structure Specifies Tertiary
Structure
What are the differences between the
peak absorbances of native
(untreated) and reduced (denatured)
RNase A?
What happened when reduced RNase
A was reoxidized (renatured)?
What can you conclude about the
structure of RNase A from these
experiments?
3.2 What Are the Chemical Structures and Functions of Proteins?
Quaternary structure results from the
interaction of subunits by hydrophobic
interactions, van der Waals forces,
ionic attractions, and hydrogen bonds.
Each subunit has its own unique
tertiary structure.
Figure 3.7 The Four Levels of Protein Structure (E)
Figure 3.11 Quaternary Structure of a Protein
3.2 What Are the Chemical Structures and Functions of Proteins?
Proteins bind noncovalently 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.
Figure 3.12 Noncovalent Interactions between Proteins and Other Molecules
3.2 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
• Nonpolar substances
3.2 What Are the Chemical Structures and Functions of Proteins?
Protein shape can change as a result
of:
• Interaction with other molecules—
e.g., an enzyme changes shape
when it comes into contact with a
reactant.
• Covalent modification—addition of a
chemical group to an amino acid.
Figure 3.13 Protein Structure Can Change
3.2 What Are the Chemical Structures and Functions of Proteins?
Proteins can bind to the wrong
molecules after denaturation or when
they are newly made and still
unfolded.
Chaperones are proteins that help
prevent this.
Chaperones, such as heat shock
proteins, surround a denatured protein
and allow it to refold.
Figure 3.14 Molecular Chaperones Protect Proteins from Inappropriate Binding
3.3 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
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Monosaccharides: simple sugars.
Disaccharides: two simple sugars
linked by covalent bonds.
Oligosaccharides: 3 to 20
monosaccharides.
Polysaccharides: hundreds or
thousands of monosaccharides—e.g.,
starch, glycogen, cellulose.
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
All cells use glucose
(monosaccharide) as an energy
source.
Exists as a straight chain or ring form.
Ring is more common—it is more
stable.
Ring form exists as α- or β-glucose,
which can interconvert.
Figure 3.15 From One Form of Glucose to the Other
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Monosaccharides have different
numbers of carbons:
Hexoses: six carbons—structural
isomers.
Pentoses: five carbons.
Figure 3.16 Monosaccharides Are Simple Sugars
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Monosaccharides bind together in
condensation reactions to form
glycosidic linkages.
Glycosidic linkages can be α or β.
Figure 3.17 Disaccharides Form by Glycosidic Linkages (Part 1)
Figure 3.17 Disaccharides Form by Glycosidic Linkages (Part 2)
Figure 3.17 Disaccharides Form by Glycosidic Linkages (Part 3)
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Oligosaccharides may include other
functional groups.
Often covalently bonded to proteins
and lipids on cell surfaces and act as
recognition signals.
Human blood groups get specificity
from oligosaccharide chains.
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Polysaccharides are giant polymers of
monosaccharides.
Starch: storage of glucose in plants.
Glycogen: storage of glucose in
animals.
Cellulose: very stable, good for
structural components.
Figure 3.18 Representative Polysaccharides (Part 1)
3.3 What Are the Chemical Structures and Functions of
Carbohydrates?
Carbohydrates can be modified by the
addition of functional groups:
• Sugar phosphates
• Amino sugars
• Chitin
Figure 3.19 Chemically Modified Carbohydrates (Part 1)
Figure 3.19 Chemically Modified Carbohydrates (Part 2)
Figure 3.19 Chemically Modified Carbohydrates (Part 3)
3.4 What Are the Chemical Structures and Functions of Lipids?
Lipids are nonpolar hydrocarbons;
insoluble in water.
If close together, weak but additive van
der Waals forces hold them together.
Not polymers in the strict sense
because they are not covalently
bonded.
3.4 What Are the Chemical Structures and Functions of Lipids?
Fats and oils store energy.
Phospholipids—structural role in cell
membranes.
Carotenoids and chlorophylls—capture
light energy in plants.
Steroids and modified fatty acids—
hormones and vitamins.
3.4 What Are the Chemical Structures and Functions of Lipids?
Animal fat—thermal insulation.
Lipid coating around nerves provides
electrical insulation.
Oil and wax on skin, fur, and feathers
repels water.
3.4 What Are the Chemical Structures and Functions of Lipids?
Fats and oils are triglycerides: three
fatty acids plus glycerol.
Glycerol: has three –OH groups (an
alcohol).
Fatty acid: nonpolar hydrocarbon with
a polar carboxyl group.
Carboxyls bond with hydroxyls of
glycerol in an ester linkage.
Figure 3.20 Synthesis of a Triglyceride
3.4 What Are the Chemical Structures and Functions of Lipids?
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.
Figure 3.21 Saturated and Unsaturated Fatty Acids
3.4 What Are the Chemical Structures and Functions of Lipids?
Animal fats tend to be saturated:
packed together tightly; solid at room
temperature.
Plant oils tend to be unsaturated: the
“kinks” prevent packing; liquid at room
temperature.
In-Text Art, Ch. 3, p. 57
3.4 What Are the Chemical Structures and Functions of Lipids?
Fatty acids are amphipathic: they
have opposing chemical properties.
When the carboxyl group ionizes it
forms COO– and is strongly
hydrophilic; the other end is
hydrophobic.
3.4 What Are the Chemical Structures and Functions of Lipids?
Phospholipids: fatty acids bound to
glycerol; a phosphate group replaces
one fatty acid.
• The “head” is a phosphate group—
hydrophilic
• “Tails” are fatty acid chains—
hydrophobic
• They are amphipathic
Figure 3.22 Phospholipids (Part 1)
3.4 What Are the Chemical Structures and Functions of Lipids?
In water, phospholipids line up with the
hydrophobic “tails” together and the
phosphate “heads” facing outward,
forming a bilayer.
Biological membranes have this kind of
phospholipid bilayer structure.
Figure 3.22 Phospholipids (Part 2)
3.4 What Are the Chemical Structures and Functions of Lipids?
Carotenoids: light-absorbing pigments
In-text art p. 20, (b-carotene and
vitamin A)
3.4 What Are the Chemical Structures and Functions of Lipids?
Steroids: multiple rings share carbons.
Cholesterol is important steroid in
membranes; other steroids function as
hormones.
3.4 What Are the Chemical Structures and Functions of Lipids?
Vitamins—small molecules not
synthesized by the body; must be
acquired in the diet.
Waxes—highly nonpolar and
impermeable to water.
3 Answer to Opening Question
Spider silk is very strong and is used in
applications ranging from surgical
sutures to bulletproof vests.
Silkworms and bacteria have been
genetically engineered to produce
spider silk proteins.
The silk is synthesized and stored as a
liquid precursor solution, then “spun”
out into fibers.