Transcript the_structure_and_function_of_macromolecules

Macromolecules –
Structure and Function
Within cells, small organic molecules (monomers)
are joined together to form larger molecules
(polymers).
 Macromolecules are large molecules composed of
thousands of covalently connected atoms.
 Three of the four classes of life’s organic
molecules are polymers:

▪ Carbohydrates
▪ Proteins
▪ Nucleic acids

An immense variety of polymers can be built
from a small set of monomers.
Monomers form larger
molecules by
condensation reactions
called dehydration
reactions.
 Polymers are
disassembled to
monomers by hydrolysis,
a reaction that is the
reverse of the
dehydration reaction.

Short polymer
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
Longer polymer
Dehydration reaction in the synthesis of a polymer
Hydrolysis adds a water
molecule, breaking a bond
Hydrolysis of a polymer
Carbohydrates include sugars and the polymers
of sugars.
 The simplest carbohydrates are single sugars, or
monosaccharides.
• Monosaccharides have molecular formulas that
are usually multiples of CH2O.
• Glucose is the most common monosaccharide.
 Carbohydrate macromolecules are
polysaccharides, polymers composed of many
sugar building blocks.

Triose sugars
(C3H6O3)
Pentose sugars
(C5H10O5)
Hexose sugars
(C5H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose


Monosaccharides serve as a major fuel for
cells and as raw material for building
molecules.
Though often drawn as a linear skeleton,
in aqueous solutions they form rings.
Linear and
ring forms
Abbreviated ring
structure


A disaccharide is formed when a dehydration
reaction joins two monosaccharides.
This covalent bond is called a glycosidic
linkage.
Dehydration
reaction in the
synthesis of maltose
1–4
glycosidic
linkage
Glucose
Glucose
Dehydration
reaction in the
synthesis of sucrose
Maltose
1–2
glycosidic
linkage
Glucose
Fructose
Sucrose


Polysaccharides, the polymers of sugars,
have storage and structural roles.
The structure and function of a
polysaccharide are determined by its sugar
monomers and the positions of glycosidic
linkages.
• Storage polysaccharides: starch & glycogen
• Structural polysaccharides: cellulose & chitin

Starch, a storage polysaccharide of plants,
consists entirely of glucose monomers.
• Plants store surplus starch as granules within
chloroplasts and other plastids.

Glycogen is a storage polysaccharide in
animals.
• Humans and other vertebrates store glycogen
mainly in liver and muscle cells.
Starch & Glycogen
Chloroplast
Starch
Mitochondria Glycogen granules
0.5 µm
1 µm
Amylose
Amylopectin
Starch: a plant polysaccharide
Glycogen
Glycogen: an animal 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.
 The difference is based
on two ring forms for
glucose:

a Glucose
b Glucose
a and b glucose ring structures
Starch: 1–4 linkage of a glucose monomers.
alpha () and beta ()
Cellulose: 1–4 linkage of b glucose monomers.
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
0.5 µm
Plant cells
Cellulose
molecules
 Glucose
monomer
Enzymes that digest starch by hydrolyzing alpha
linkages can’t hydrolyze beta linkages in
cellulose.
 Cellulose in human food passes through the
digestive tract as insoluble fiber.
 Some microbes use enzymes to digest cellulose.
 Many herbivores, from cows to termites, have
symbiotic relationships with these microbes.

Chitin, another structural polysaccharide, is found in
the exoskeleton of arthropods.
 Chitin also provides structural support for the cell
walls of many fungi.
 Chitin can be used as surgical thread.


A.
B.
C.
D.
Which of these polysaccharide/function
pairs are INCORRECTLY matched:
starch/storage in plants
chitin/structure in plants fungi/arthropods
glycogen/storage in animals
cellulose/structure in plants



Lipids are the one class of large biological
molecules that do not form polymers.
All lipids have little or no affinity for
water.
The most biologically important lipids are
fats, phospholipids, and steroids.
When lipids are mixed with water, the water
molecules bond to each other and exclude
the lipid molecules. What causes lipids to
be hydrophobic?
A.
B.
C.
D.
They are extremely polar molecules.
They consist mostly of water molecules.
They consist mostly of hydrocarbons which
form polar covalent bonds.
They consist mostly of hydrocarbons which
form nonpolar covalent bonds.




The major function of fats is energy storage.
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.
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
Animation: Fats
•
In a fat, three fatty acids are joined to
glycerol by an ester linkage, creating a
triacylglycerol, or triglyceride.
Ester linkage
Fat molecule (triacylglycerol)
Fatty acids vary in length (number of carbons)
and in the number and locations of double bonds.
 Saturated fatty acids have the maximum number
of hydrogen atoms possible and no double bonds
(straight chains – solids at room temperature).
 Unsaturated fatty acids have one or more double
bonds (bent chains – liquids at room
temperature).

Oleic acid
Stearic acid
cis double bond
causes bending
Saturated fat and fatty acid.
Unsaturated fat and fatty acid.


Trans fats are unsaturated, but the
hydrogens around the double bonds are
arranged in such a way that the fatty
acid chains are still straight.
Trans fats are
known to raise
bad cholesterol
and lower good
cholesterol.
Which of the following statements about
fats is FALSE?
Most animal fats are saturated fats.
B. Saturated fats are liquids at room
temperature.
C. Plant fats and fish fats are usually
unsaturated.
D. A diet rich in saturated fats may contribute to
cardiovascular disease through plaque
deposits.
A.


In a phospholipid, two fatty acids and a phosphate
group are attached to glycerol.
The two fatty acid tails are hydrophobic and the
phosphate group forms a hydrophilic head.
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Structural formula
Space-filling model
Phospholipid symbol
When phospholipids are added to water, they
self-assemble into a bilayer, with the
hydrophobic tails pointing toward the interior.
 Phospholipid bilayers are the major component
of all cell membranes.

Hydrophilic
head
Hydrophobic
tails
WATER
WATER
Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings.
 Cholesterol, an important steroid, is a
component in animal cell membranes.
 Although essential in animals, high levels of
cholesterol in the blood may contribute to
cardiovascular disease.

Which of the following statements about
proteins/polypeptides is FALSE?
Polypeptides are polymers of amino acids.
All proteins consist of more than one
polypeptide.
C. Amino acids in a polypeptide are linked by
peptide bonds.
D. Each polypeptide has a unique linear sequence
of amino acids.
A.
B.
Enzymes are a type of protein that acts as a
catalyst, speeding up chemical reactions.
 Enzymes can perform their functions repeatedly,
functioning as workhorses that carry out the
processes of life.

Substrate
(sucrose)
Glucose
Enzyme
(sucrase)
Fructose
Amino acids are organic
molecules with
carboxyl and amino
groups.
 Amino acids differ in
their properties due to
differing side chains,
called R groups.
 Cells use 20 amino
acids to make
thousands of proteins.

 carbon
Amino
group
Carboxyl
group
Glycine (Gly)
Alanine (Ala)
Valine (Val)
Leucine (Leu)
Isoleucine (Ile)
Nonpolar
Methionine (Met)
Phenylalanine (Phe)
Tryptophan (Trp)
Proline (Pro)
Polar
Serine (Ser)
Threonine (Thr)
Cysteine (Cys)
Tyrosine (Tyr)
Acidic
Asparagine (Asn) Glutamine (Gln)
Basic
Electrically
charged
Aspartic acid (Asp) Glutamic acid (Glu)
Lysine (Lys)
Arginine (Arg)
Histidine (His)
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 conformation, which
determines its function.

Both ribbon
models and
space-filling
models can be
used to depict
a protein’s
conformation.
Groove
A ribbon model
Groove
A space-filling model
Primary structure is a protein’s unique sequence of
amino acids.
 Secondary structure, found in most proteins,
consists of coils and folds in the polypeptide chain.
 Tertiary structure is determined by interactions
among various side chains (R groups).
 Quaternary structure results when a protein
consists of multiple polypeptide chains.

 pleated sheet
+H
3N
Amino end
Amino acid
subunits
 helix
Amino end
Amino acid
subunits
Primary structure,
the sequence of
amino acids in a
protein, is like the
order of letters in a
long word.
 Primary structure is
determined by
inherited genetic
information.

Carboxyl end
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
alpha helix and a folded structure called a beta
pleated sheet.

 pleated sheet
Amino acid
subunits
 helix



Tertiary structure is
determined by interactions
between R groups, rather
than interactions between
backbone constituents.
These interactions between
R groups include hydrogen
bonds, ionic bonds,
hydrophobic interactions,
and van der Waals
interactions.
Strong covalent bonds
called disulfide bridges
may reinforce the protein’s
conformation.
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Ionic bond
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 alpha and two beta chains.

 Chains
Polypeptide
chain
Iron
Heme
Polypeptide chain
Collagen
 Chains
Hemoglobin
Which of these factors can affect protein
conformation?
A. temperature
B. alternations in pH
C. salt concentration
D. all of the above
The loss of a protein’s
native conformation is
called denaturation.
Denaturation
Normal protein
Denatured protein
Renaturation