Download Ch 3 organic molecules

Chapter 5
The Structure and Function of
Large Biological Molecules
What do you know about…
• Carbohydrates?
• Lipids?
• Proteins?
• Nucleic Acids?
Concept 5.2: Carbohydrates serve as fuel and
building material
• Carbohydrates include sugars and the
polymers of sugars
• The simplest carbohydrates are
monosaccharides, or single sugars
• Carbohydrate macromolecules are
polysaccharides, polymers composed of many
repeating single sugars (monomers)
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose
Sugars
• Monosaccharides – empiracle formula
(simplest form) =
• Monosaccharides are classified by
– The location of the carbonyl group (as aldose
or ketose)
– The number of carbons in the carbon skeleton
• Though often drawn as linear skeletons, in
aqueous solutions many sugars form rings
• Monosaccharides serve as a major fuel for
cells and as raw material for building molecules
(a) Linear and ring forms
(b) Abbreviated ring structure
• Monosaccharides join to form disaccharides
and polysaccharides
– RXN =
– Requires enzymes
– glycosidic linkage
1–4
glycosidic
linkage
Glucose
Glucose
(a) Dehydration reaction in the synthesis of maltose
Maltose
Polysaccharides can be broken down, or digested
in the opposite reaction…
• Digestion
– use H2O to breakdown polymers
• reverse of dehydration synthesis
• cleave off one monomer at a time
• H2O is split into H+ and OH–
HO
– H+ & OH– attach to ends HO
– requires enzymes
– releases energy
H2O
enzyme
H
H HO
H
Polysaccharides
Polymers of sugars
costs little energy to build
easily reversible = release energy
differ in position of glycosidic
linkages
Function:
energy storage
starch (plants)
glycogen (animals)
in liver & muscles
structure
cellulose (plants)
chitin (arthropods & fungi)
Why does the structure matter? How does it
work?
slow release
starch
(plant)
fast release
glycogen
(animal
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
 Glucose
(b) Starch: 1–4 linkage of
 glucose monomers
 Glucose
(b) Cellulose: 1–4 linkage of
 glucose monomers
The key – different enzymes do the job! Specific to
the alpha & beta linkage forms
• Cellulose – undigestable roughage
Most abundant organic
compound on Earth
herbivores have
evolved a mechanism
to digest cellulose
most carnivores have
not
what do they eat?
How is this related to
corn fuels??
How can herbivores digest cellulose so
well?
BACTERIA live in their digestive systems & help
digest cellulose-rich (grass) meals
Caprophage
Concept 5.3: Lipids are a diverse group of
hydrophobic molecules
• Lipids are the one class of large
biological molecules that do not form
polymers
• The unifying feature of lipids is
having little or no affinity for water
– Hydro …?
• The most biologically important lipids
are fats, phospholipids, and steroids
Fats
-
Fats are
constructed from
two types of
smaller
molecules:
glycerol and
fatty acids
-
Glycerol
-
Fatty acids
Fatty acid
(palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
• Fatty acids vary in length and number and
locations of double bonds
• Saturated fats vs. Unsaturated fats
Properties of saturated vs. unsaturated fats?
Fats can be hydrogenated to make them saturated
• A diet rich in
saturated fats may
contribute to
cardiovascular
disease through
plaque deposits atheriosclerosis
Adding hydrogens
• Hydrogenating vegetable oils also creates
unsaturated fats with trans double bonds
• These trans fats may contribute more than
saturated fats to cardiovascular disease
Why fat?
• Energy
• Storage – plants and animals
• Adipose tissue also cushions vital organs and
insulates the body
No fat?
• two fatty acids
and a
phosphate
group are
attached to
glycerol
Hydrophobic tails
• Component of
cell
membrane
Hydrophilic head
Phospholipids
Choline
Phosphate
Glycerol
Hydrophilic
head
Fatty acids
Hydrophobic
tails
• When phospholipids are added to water, they
self-assemble into a bilayer, with the
hydrophobic tails pointing toward the interior
Steroids
• Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings
• Cholesterol, an important steroid, is a
component in animal cell membranes
Proteins have many structures, resulting in a wide
range of functions
• Proteins account for more than 50% of the dry
mass of most cells
• Protein functions include:
–
structural support, storage, transport, cellular
communications, movement, and defense
against foreign substances
Polypeptides = proteins
• Amino acids are the monomers
Amino
group
Carboxyl
group
Amino Acid Polymers
Peptide
bond
• Polypeptides
range in length
from a few to more
than a thousand
monomers
(a)
• Each polypeptide
has a unique linear
sequence of amino
acids
Side chains
Peptide
bond
Backbone
(b)
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
Fig. 5-17
Nonpolar
Glycine
(Gly or G)
Structure =
function
Valine
(Val or V)
Alanine
(Ala or A)
Methionine
(Met or M)
Leucine
(Leu or L)
Trypotphan
(Trp or W)
Phenylalanine
(Phe or F)
Isoleucine
(Ile or I)
Proline
(Pro or P)
Polar
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
Asparagine Glutamine
(Asn or N) (Gln or Q)
Electrically
charged
Acidic
Aspartic acid Glutamic acid
(Glu or E)
(Asp or D)
Basic
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)
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 three-dimensional structure
• A protein’s structure determines its function
• Primary
structure, the
sequence of
amino acids in a
protein, is like the
order of letters in
a long word
Primary Structure
1
5
+H
3N
Amino end
10
Amino acid
subunits
15
• Primary structure
is determined by
inherited genetic
information of
DNA
20
25
Protein Folding in the Cell
• It is hard to predict a protein’s structure from its
primary structure
• Chaperonins are protein molecules that assist
the proper folding of other proteins
Polypeptide
Correctly
folded
protein
Cap
Hollow
cylinder
Chaperonin
(fully assembled)
Steps of Chaperonin 2
Action:
1 An unfolded polypeptide enters the
cylinder from one end.
The cap attaches, causing the 3 The cap comes
cylinder to change shape in
off, and the properly
such a way that it creates a
folded protein is
hydrophilic environment for
released.
the folding of the polypeptide.
• The coils and folds of secondary structure result from
hydrogen bonds between the polypeptide backbone
• Typical secondary structures are a coil called an  helix and
a folded structure called a  pleated sheet
 pleated sheet
Examples of
amino acid
subunits
 helix
Secondary Structure
•
Tertiary structure is
determined by
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
Hydrophobic
interactions &
van der Waals
interactions
Hydrogen
bond
Disulfide bridge
Ionic bond
Polypeptide
backbone
• Quaternary
structure
results when
two or more
polypeptide
chains form one
macromolecule
Polypeptide
chain
 Chains
• 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
Iron
Heme
 Chains
Hemoglobin
Collagen
Denaturation
• Alterations in pH, salt concentration,
temperature, or other environmental factors
can cause a protein to unravel – lose its
PRIMARY structure
• A denatured protein is biologically inactive
• Enzymes act as a catalyst to speed up
chemical reactions
• Enzymes can perform their
functions repeatedly
Substrate
(sucrose)
Glucose
OH
Fructose
HO
Enzyme
(sucrase)
H2O
Concept 5.5: Nucleic acids store and transmit
hereditary information
• The amino acid
sequence of a
polypeptide is
programmed by a unit of
inheritance called a gene
• DNA codes for RNA,
which makes proteins
5' end
5'C
Nucleotide = nucleoside + PO4
3'C
Nucleoside
Nitrogenous
base
5'C
Phosphate
group
5'C
3'C
(b) Nucleotide
3' end
(a) Polynucleotide, or nucleic acid
3'C
Sugar
(pentose)
Nitrogenous bases
Pyrimidines
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Purines
Adenine (A)
Guanine (G)
(c) Nucleoside components: nitrogenous bases
The DNA Double Helix
• A DNA molecule has two polynucleotides spiraling
around an imaginary axis, forming a double helix
• In the DNA double helix, the two backbones run in
opposite 5 → 3 directions from each other, an
arrangement referred to as antiparallel
• One DNA molecule includes many genes
• The nitrogenous bases in DNA pair up and form
hydrogen bonds: adenine (A) always with thymine
(T), and guanine (G) always with cytosine (C)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Joining nucleotides
Covalent phosphodiestser bonds form between
the sugar-phosphate units
(-OH of 3’ carbon and PO4 of 5’)
Weak hydrogen bonds form between
the Nitrogenous bases
Fig. 5-28
5' end
3' end
Sugar-phosphate
backbones
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
3' end
5' end
New
strands
5' end
3' end
5' end
3' end
DNA and Proteins as Tape Measures of Evolution
• The linear sequences
of nucleotides in DNA
molecules are passed
from parents to
offspring
• Two closely related
species are more
similar in DNA than
are more distantly
related species
• Molecular biology can
be used to assess
evolutionary kinship