Download 2. Biomolecules-Carbs and Lipids

Chapter 5
The Structure and Function of
Macromolecules
PowerPoint lectures are originally from Campbell / Reece
Media Manager and Instructor Resources for BIOLOGY,
7th & 8th Edition by N. A. Campbell & J. B. Reece
Copyright 2005 & 2008 Pearson Education, Inc. Publishing
as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: The Molecules of Life
• All living things are made up of four classes
of large biological molecules: carbohydrates,
lipids, proteins, and nucleic acids
• Macromolecules are large molecules
composed of thousands of covalently
connected atoms
• Molecular structure and function are
inseparable
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2011 Pearson
Education, Inc.
The Molecules of Life
• The four classes of macromolecules that are
important to life are:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Most macromolecules are polymers, built from
monomers
• Three of the four classes of life’s organic
molecules are polymers:
– Carbohydrates
– Proteins
– Nucleic acids
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Macromecules are made of monomers
• Carbohydrates, Proteins, and Nucleic Acids are all
polymers made from building blocks. Building blocks can
be called monomers
monomer
Macromolecule Type
Carbohydrate
Protein
Nucleic Acid
(DNA and RNA)
Name of
Monomer
monosaccharide
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Amino acid
nucleotides
The Synthesis of Polymers by DEHYDRATION
REACTIONS
• Monomers form larger
molecules called polymers
by condensation reactions
called dehydration
reactions.
• A dehydration reaction
occurs when two monomers
bond together through the
loss of a water molecule
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HO
1
2
3
H
Short polymer
HO
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
HO
1
2
H
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
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The Breakdown of Polymers by HYDOLYSIS
REACTIONS
• Polymers are disassembled to monomers
by hydrolysis, a reaction that is essentially
the reverse of the dehydration reaction.
• In hydrolysis, bonds are broken by the
addition of water molecules.
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Fig. 5-2b
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
(b) Hydrolysis of a polymer
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H
H
H2O
HO
H
Concept 5.2: Carbohydrates serve as fuel and
building material
• Carbohydrates include single (simple) sugars and
their polymers
• Carbohydrates may be classified as:
– Monosaccharides (the simplest)
– Disaccharides
– Polysaccharides
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Monosaccharides
• Monosaccharides have molecular formulas that
are usually multiples of CH2O
(CH2O)n
where n ranges from 1-7
• Glucose (C6H12O6) is the most common
monosaccharide.
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Monosaccharides
• Monosaccharides have two
functional groups:
1- One carbonyl group that is either:
– An aldehyde group OR
– a ketone group
2- Many hydroxyl groups.
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Monosaccharides
• Monosaccharides are classified by:
– The specific type of the carbonyl group:
• Aldoses
• ketoses
– and the number of carbons in the carbon skeleton:
• Trioses (3 Carbons)
• Tetroses (4 Carbons)
• Pentoses (5 Carbons)
• Hexoses (6 Carbons)
• Heptoses (7 Carbons)
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LE 5-3
Triose sugars
(C3H6O3)
Pentose sugars
(C5H10O5)
Hexose sugars
(C5H12O6)
Glyceraldehyde
Ribose
Galactose
Glucose
Dihydroxyacetone
Ribulose
Fructose
Monosaccharides
• Functions of monosaccharides:
– major fuel (source of energy) for cells and
– raw material for building other molecules such
as fatty acids and amino acids.
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Monosaccharides
• Though often drawn as a linear skeleton, in
aqueous solutions they form rings
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alpha and Beta Forms of Glucose
• There are two interconvertible forms of glucose
that differ in the placement of the hydroxyl
group attached to the number 1 carbon in the
ring form of glucose.
• These forms are α-glucose and β-glucose.
α-Glucose
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β-Glucose
Disaccharides
• A disaccharide is formed when a dehydration reaction joins
two monosaccharides
• The covalent bond joining two monosaccharides 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
• Polymers of monosaccharides
• Based on their function, there are two types of
polysaccharides:
– Storage polysaccharides.
– Structural polysaccharides.
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Storage Polysaccharides
• Store glucose and are hydrolyzed as needed to
provide sugar for cells.
• Examples on storage polysaccharides:
– Starch in Plants
– Glycogen in animals
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Figure 5.6b
Mitochondria
Glycogen granules
0.5 m
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Starch (A Storage Polysaccharides in Plants)
• Starch is a carbohydrate polymer consists
entirely of α-glucose monomers.
• Starch is a storage polysaccharide in plants.
• Two types of starch:
– Amylose is the unbranched polymer.
– Amylopectin is the branched polymer.
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LE 5-6a
Chloroplast
Starch
1 µm
Amylose
Amylopectin
Starch: a plant polysaccharide
Glycogen (A Storage Polysaccharides in Animals)
• Glycogen is a storage polysaccharide in
animals
• Humans and other vertebrates store
glycogen mainly in liver and muscle cells
Glycogen: an animal polysaccharide
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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
• The difference is based on two ring forms for
glucose: alpha () and beta ()
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2011 Pearson
Education, Inc.
Figure 5.8
Cellulose
microfibrils in a
plant cell wall
Cell wall
Microfibril
10 m
0.5 m
Cellulose
molecules
 Glucose
monomer
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Cellulose Digestion
• Enzymes that digest starch by hydrolyzing alpha
linkages can’t hydrolyze beta linkages in cellulose
• Humans can’t digest 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
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Chitin (A Structural Polysaccharides)
• Chitin 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
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Figure 5.9b
Chitin is used to make a strong and flexible surgical
thread that decomposes after the wound or incision
heals.
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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 (Hydrophobic)
• Lipids are hydrophobic becausethey consist
mostly of hydrocarbons, which form nonpolar
covalent bonds
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2011 Pearson
Education, Inc.
Lipids
• The most biologically important lipids are:
– fats
– Phospholipids
– steroids
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Fats
• Fats are constructed from one glycerol
and three fatty acid molecules
• 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 hydrocarbon skeleton
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Figure 5.10
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
Ester linkage
(b) Fat molecule (triacylglycerol)
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Fatty Acids
• 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
• Unsaturated fatty acids
have one or more double
bonds
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Alpha linolenic acid (ALA) An Omega-3
f.a. and the parent of other omega-3 f.as
Fats (Saturated fats)
• Fats made from saturated fatty acids are called
saturated fats
• Most animal fats are saturated
• Saturated fats are solid at room temperature
• A diet rich in saturated fats may contribute to
cardiovascular disease through plaque deposits
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Fats (Unsaturated fats)
• Fats made from unsaturated fatty acids are called
unsaturated fats
• Plant fats and fish fats are usually unsaturated
• Plant fats and fish fats are liquid at room
temperature and are called oils
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Fats
• Fats separate from water because water
molecules form hydrogen bonds with each
other and exclude the fats
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Trans Fatty Acids
• 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
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Major Functions of Fats
• 1- Good source of energy. One gram of fat
stores more than twice as much energy as one
gram of a polysaccharide, such as starch.
• 2- Adipose tissue (the tissue that stores fats in
the body) also functions to cushion vital organs
such as the kidneys, and a layer of fat beneath
the skin insulates the body. The subcutaneous
layer is especially thick in whales, seals, and
most other marine mammals.
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Phospholipids
• In a phospholipid, two fatty acids and a phosphate
group are attached to glycerol
• The two fatty acid tails are hydrophobic, but the
phosphate group and its attachments form a
hydrophilic head
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Hydrophobic tails
Hydrophilic head
Figure 5.12
Choline
Phosphate
Glycerol
Fatty acids
Hydrophilic
head
Hydrophobic
tails
(a) Structural formula
(b) Space-filling model
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(c) Phospholipid symbol
Phospholipids in water (a micelle formation)
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Phospholipids in water (a bilayer formation)
The structure of phospholipids in water results also in a
bilayer arrangement found in cell membranes
Hydrophilic
head
WATER
WATER
Hydrophobic
tails
Phospholipids are the major component of all cell membranes
Steroids
• Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings
• Different steroids are created by varying functional
groups attached to the rings.
Estradiol
Female lion
Male lion
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Testosterone
Cholerterol (A Steroid)
• Cholesterol, an important
steroid, is a component
in animal cell
membranes
• Although cholesterol is
essential in animals, high
levels in the blood may
contribute to
cardiovascular disease
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Lipid Summary
Type of Lipid
Structure of Lipid
Made out of one glycerol
molecule (blue part below)
with three fatty acids
attached (black parts
below).
Triglycerides
These are entirely
hydrophobic. The "tri"
prefix of the name comes
from having three fatty
acids.
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Function of Lipid
These are the "fats" and
also the "oils." They are
used for long-term sugar
storage or for insulation of a
multicellular organism.
Lipid summary cont’d
Type of Lipid
Structure of Lipid
Phospholipids have the special
property of having both
hydrophobic and hydrophilic
parts, although they are still
mostly hydrophobic. A molecule
that is both hydrophilic and
hydrophobic is called amphipathic.
Phospholipids
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Function of Lipid
Phospholipids help to make up the
basis of cellular membranes-- you
will learn much more about these
when we study membranes.
Lipid summary cont’d
Type of Lipid
Steroids (a sterol derivative)
Structure of Lipid
They are entirely hydrophobic, and
have their own special structure that
does NOT include fatty acids.
These molecules are all ringed
structures, with 4 carbon rings.
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Function of Lipid
This group includes cholesterol,
estrogen, testosterone, progesterone,
and cortisone. Most steroids are used
as hormones.
Lipids, Nutrition, and Health
Functions of Fats
• Used to build cells and parts of the cell (e.g. brain cells, nerve
tissues, cell membrane)
• Stored in the body in adipose tissue
– Adipose tissue are called fat depots
• Surround vital organs (e.g. heart, kidney, spleen) to serve as
protective cushion
• Stored under the skin for insulation
• Fat reserves are converted to glycerol and fatty acids ( 9 kcal
per gram)
– Glycerol is burned for energy or converted to glucose
The human adipocyte
• Compose adipose tissue
• For storage and synthesis of
triacylglycerides, insulation, energy
storage (higher energy content than
glycogen)
• White fat cells: lipid droplet with
peripheral cytoplasm and nucleus; semiliquid fat with some sterol derivatives
• Brown fat cells: lipid droplets scattered,
high mitochondria content
www.cnrs.fr, www.vulgaris-medical.com
Fats Transport
• Some important blood
lipoproteins
– Group of proteins with a
triglyceride or cholesterol
– Very-low density lipoprotein
(VLDL)
• Transport new triglycerides
from liver to adipose tissue
– Low density lipoprotein
(LDL)
• Transport cholesterol from
liver to cells
– High density lipoprotein
(HDL)
• Transport cholesterol from
tissues to liver
Atherosclerosis: Not just a simple
clogging problem!
From: http://www.nia.nih.gov/NR/rdonlyres/C3B176CB-3173-4F89-8FDA2774FB751108/4227/pic_atherosclerosis.jpg
Cholesterol biosynthesis
From: http://banon.cshl.edu/cgi-bin/eventbrowser?DB=gk_current&FOCUS_SPECIES=Homo%20sapiens&ID=191273&
Lowering cholesterol synthesis
• Use hypolipidemic drugs (eg. Statins)
• STATINS are HMG-CoA inhibitors
– Eg. Lovastatin
Table from: http://en.wikipedia.org/wiki/Statin
Crisco and Olestra (by P&G)
1911: Shortening
“To eat, or not to eat - fat is the question.”
- from the Introduction of Mary Enig, Know your Fats: The
Complete Primer for Understanding the Nutrition of Fats, Oils,
and Cholesterol, Bethesda Press, USA, 2000.
Olestra
• 1998, Proctor and Gamble introduced a new
fat/oil substitute called Olestra (brand name
Olean®
• material replaces fats in snack foods such as
potato chips
• claimed that food using Olestra in place of
digestible fats provide less calories since the
Olestra is not digested and passes through the
body unchanged
• Some side effects include abdominal cramping
and loose stools
Olestra
How does Olestra work?
http://www.cnn.com/HEALTH/9802/10/fakefat.olestra/olestra.large.jpg
Olean®
Olean®
http://static.howstuffworks.com/gif/question526-fat-chips.jpg
http://static.howstuffworks.com/gif/question526-olestra-chips.jpg
Carnitine Craze
• Responsible for fatty
acid transport from
cyosol to
mitochondria where
the FA is
metabolised
• Naturally
synthesized from Lys
and Met (L-isomer)
in liver and kidneys
Image from http://en.wikipedia.org/wiki/Image:AcylCoA_from_cytosol_to_the_mitochondrial_matrix.gif
Carnitine Craze
•
•
•
•
•
Highest amount in meat, dairy, nuts
Healthy individuals, including strict
vegetarians, generally synthesize enough Lcarnitine to prevent deficiency.
The roles of L-carnitine supplementation as
an adjunct to standard medical therapy in
myocardial infarction, heart failure, angina
pectoris, Alzheimer's disease, and HIV
infection require further research.
Although recent studies in rats suggest acetylL-carnitine supplementation may be
beneficial in preventing age-related declines
in energy metabolism and memory, it is not
known whether acetyl-L-carnitine
supplementation will help prevent such agerelated declines in humans.
There is little evidence that L-carnitine
supplementation improves athletic
performance in healthy people.
Info from: http://en.wikipedia.org/wiki/Carnitine, The Linus
Pauling Institute (Oregon State University).
http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/