Transcript Amino Acids - HCC Learning Web

Chapter 3
The Molecules of Life
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
Ice cream and lactose molecule
Biology and Society: Got Lactose?
• Lactose is the main sugar found in milk.
• Some adults exhibit lactose intolerance, the inability to
properly digest lactose.
– Instead of lactose being broken down and absorbed in the
small intestine
– Lactose is broken down by bacteria in the large intestine
producing gas and discomfort.
• There is no treatment for the underlying cause of lactose
intolerance.
• Affected people must
– Avoid lactose-containing foods or
– Take the enzyme lactase when eating dairy products
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Organic Compounds
• A cell is mostly water.
• The rest of the cell consists mainly of carbon-based
molecules.
• Organic compounds are carbon-based molecules.
• Carbon forms large, complex, and diverse molecules
necessary for life’s functions.
• Cells are surrounded by cell membrane or plasma
membrane
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Organic Compounds
• Among all atoms, carbon is a versatile
– Bonding ability
– It has four electrons in an outer shell that can hold
eight.
– Carbon can share its electrons with other atoms to form
up to four covalent bonds.
• Carbon can use its bonds to attach to other carbons
– As it does so, a huge diversity of carbon skeletons can
be formed
carbon skeletons can be linear, branched, or even take a
shape of one or more rings
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Variations in carbon skeletons
Double bond
Carbon skeletons vary in length
Carbon skeletons may be unbranched or branched
Carbon skeletons may have double
bonds, which can vary in location
Carbon skeletons may
be arranged in rings
Hydrocarbons
The simplest organic compounds are hydrocarbons,
which are organic molecules containing only carbon and
hydrogen atoms.
The simplest hydrocarbon is Methane, consisting of a
single carbon atom bonded to four hydrogen atoms
Methane, the simplest hydrocarbon
Structural formula
Ball-and-stick model
Space-filling model
Figure 3.2
Hydrocarbons as fuels
• Larger hydrocarbons form fuels for engines.
• Hydrocarbons of fat molecules fuel our bodies.
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Functional groups
• Each type of organic molecule has a unique three-D shape.
• The shapes of organic molecules relate to their functions.
– Many vital process in the living organisms rely on the ability of
molecules to recognize each other
• The unique properties of an organic compound depend on
– Its carbon skeleton
– The atoms attached to the skeleton
• The groups of atoms that usually participate in chemical
reactions are called functional groups.
• Two common examples are
– Hydroxyl groups (-OH) and
– Carboxyl groups (-COOH)
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Functional groups
• If one attaches atoms other than hydrogen and carbon to a
hydrocarbon skeleton, new molecular properties emerge
• These additional atoms are called functional groups
Hydroxyl group
Carbonyl group
Found in alcohols and sugars
Found in sugars
Amino group
Found in amino acids, urea in urine
(from protein breakdown)
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Carboxyl group
Found in amino acids,
fatty acids and some vitamins
Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are
gigantic, earning the name macromolecules.
• Three categories of macromolecules are
– Carbohydrates
– Proteins
– Nucleic acids
• Most macromolecules are polymers.
• Polymers are made by stringing together many smaller
molecules called monomers (one unit).
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Giant Molecules from Smaller Building Blocks
Organisms synthesize macromolecules
• Dehydration reaction
– links two monomers together and
– removes a molecule of water
Organisms also have to break down macromolecules.
Digestion breaks down macromolecules to make monomers
available to your cells.
• Hydrolysis
– Breaks bonds between monomers
– Adds a molecule of water
– Reverses the dehydration reaction
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Synthesis and digestion of polymers
Short polymer
Monomer
Dehydration
reaction
Hydrolysis
Longer polymer
a Building a polymer chain
b Breaking a polymer chain
Which group of large biological molecules is not
synthesized via dehydration reactions?
a) polysaccharides
b) lipids
c) proteins
d) nucleic acids
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Carbohydrates
• Carbohydrates are sugars or sugar polymers.
• They include
– small sugar molecules in soft drinks
– long starch molecules in pasta and potatoes
• Different types includes
– Monosaccharides- glucose, fructose
– Disaccharides - sucrose, maltose
– Polysaccharides - starch
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Monosaccharides
• Monosaccharides are simple sugars that cannot be
broken down by hydrolysis into smaller sugars.
• Common examples are
– Glucose in sports drinks
– Fructose found in fruit
– Both glucose and fructose are found in honey.
• Glucose and fructose are isomers, molecules that have
the same molecular formula but different structures.
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Monosaccharides (simple sugars)
Glucose
Fructose
C6H12O6
C6H12O6
Isomers
Monosaccharides
• Monosaccharides are the main fuels for cellular work.
• In aqueous solutions, many monosaccharides form rings.
The ring structure of glucose
b Abbreviated
ring structure
a Linear and ring structures
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Disaccharides
• A disaccharide is
– a double sugar
Glucose
Galactose
– constructed from
two
monosaccharides
– Formed by a
dehydration
reaction
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Lactose
Disaccharides
Other disaccharides include
– Maltose in beer, malted milk
shakes, and malted milk ball candy
– Sucrose in table sugar, consists
of glucose and fructose
Sucrose is
– The main carbohydrate in plant sap, nourishes all the parts
– Extracted from sugarcane and bulbous roots of sugar beets
– Rarely used as a sweetener in processed foods
High-fructose corn syrup is made by a commercial process that
converts
– natural glucose in corn syrup to much sweeter fructose.
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High-fructose corn syrup
processed to extract
Starch
broken down into
Glucose
converted to sweeter
Fructose
added to foods as
high-fructose corn syrup
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Figure 3.8
• The United States is one
of the world’s leading
markets for sweeteners.
– The average American
consumes
– about 45 kg of sugar
(about 100 lbs.) per year
– mainly as sucrose and
high-fructose corn syrup
Polysaccharides
• Polysaccharides are complex carbohydrates
– Made of long chains of sugar units and polymers of
monosaccharides
– They can be straight or branched
– The manner in which the monomers are connected
may change
– Different types of polysaccharides may be
characteristics of different types of organisms
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Starch granules
in potato tuber cells
Glycogen granules
in muscle
tissue
(a) Starch
Glucose
monomer
(b) Glycogen
Cellulose microfibrils
in a plant cell wall
Cellulose
molecules
Figure 3.9
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(c) Cellulose
Hydrogen bonds
Polysaccharides
• Starch is
– a familiar example of a polysaccharide
– used by plant cells to store energy
• Potatoes and grains are major sources of starch in the human diet.
• Cellulose
– is the most abundant organic compound on Earth
– forms cable-like fibrils in the tough walls that enclose plants
– cannot be broken apart by most animals because glucose
monomers are linked in a different orientation
– We use lumber as building material
• Glycogen is
– used by animals cells to store energy (liver and muscle cells)
– converted to glucose when it is needed
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(a) Starch
Glucose
monomer
(b) Glycogen
(c) Cellulose
Hydrogen bonds
Figure 3.9d
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Polysaccharides
• Monosaccharides and disaccharides dissolve readily in
water.
• Cellulose does not dissolve readily in water.
• Almost all carbohydrates are hydrophilic, or “waterloving,” adhering water to their surface.
– The hydrophilic quality of cellulose makes the bath
towel so water absorbent
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Which polysaccharide is the storage form of
energy in animals
a) cellulose
b) chitin
c) starch
d) glucose
e) glycogen
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Lipids
• Lipids are neither macromolecules nor polymers
– hydrophobic, unable to mix with water
– Two main types are fats and steroids
Oil (hydrophobic = afraid of water)
Vinegar (hydrophilic= water loving)
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Fats
• A typical fat, or triglyceride, consists of a glycerol molecule
joined with three fatty acid molecules via a dehydration reaction.
Fatty acid
The synthesis and structure of a fat, or triglyceride
Glycerol
(a) A dehydration reaction linking a fatty acid to glycerol
Animation: Fats
(b) A fat molecule with a glycerol “head” and three
energy-rich hydrocarbon fatty acid “tails”
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Fats
• If the carbon skeleton of a fatty acid has
– fewer than the maximum number of hydrogens, it is unsaturated
–
have a double bond between at lest two carbon in hydrocarbon chain
– the maximum number of hydrogens, then it is saturated
• A saturated fat has no double bonds, and all three of its fatty
acids are saturated.
• Most animal fats have a high proportion of saturated fatty acids
– Can easily stack, tending to be solid at room temperature
– Contribute to atherosclerosis, a condition in which lipidcontaining plaques build up within the walls of blood vessels
• Most plant oils tend to be low in saturated fatty acids
-are made with polyunsaturated fatty acids which are
liquid at room temperature.
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Fats
• Hydrogenation
–
–
–
–
converts unsaturated fats to saturated fats
adds hydrogen atoms artificially
makes liquid fats solid at room temperature
creates trans fat, a type of unsaturated fat that is even less healthy
than saturated fats
• Fats perform essential functions in the human body including
– Energy storage – fats provide long term storage of molecules that
can deliver energy when needed
– Cushioning- many pressure-sensitive areas of the human body has
fat as padding
– Insulation – fat layers provides protection against heat loss around
the sensitive body core
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TYPES OF FATS
Saturated Fats
Unsaturated Fats
Margarine
INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED
COTTONSEED OIL, PARTIALLY HYDROGENATED
COTTONSEED OIL AND SOYBEAN OILS, MONO AND
DIGLYCERIDES, TBHO AND CITRIC ACID
Plant oils
Trans fats
ANTIOXIDANTS
Omega-3 fats
Figure 3.12
Steroids
• Steroids are very different from fats in structure and
function.
– The carbon skeleton is bent to form four fused rings.
– Steroids vary in the functional groups attached to
this core set of rings.
• Cholesterol is
– A key component of cell membranes
– The “base steroid” from which your body produces
other steroids, such as estrogen and testosterone
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Examples of steroids
Cholesterol
Testosterone
A type of estrogen
Steroids
• Synthetic anabolic steroids
–
–
–
–
Resemble testosterone and mimic some of its effects
Can cause serious physical and mental problems
May be prescribed to treat diseases such as cancer and AIDS, and
Are abused by athletes to enhance performance
THG
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Ball player Canseco admitted to using steriods. Track star
Marion Jones also admitted, resulting in stripping her of 5
Olympic medals.
Proteins
• Proteins
– Are polymers constructed from amino acid monomers
– account for more than 50% of the dry weight of
most cells
– Perform most of the tasks the body needs to function
– Form enzymes, chemicals that change the rate of a
chemical reaction without being changed in the process
• All proteins are constructed from a common set of 20
kinds of amino acids.
• Each amino acid consists of a central carbon atom
bonded to four covalent partners in which three of those
attachment groups are common to all amino acids.
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The Monomers of Proteins: Amino Acids
• All proteins are macromolecules constructed from a
common set of 20 kinds of amino acids.
• Each amino acid consists of a central carbon atom
bonded to four covalent partners.
• Three of those attachment groups are common to all
amino acids:
– a carboxyl group (-COOH),
– an amino group (-NH2), and
– a hydrogen atom.
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Carboxyl
group
Amino
group
Side
group
a The general structure of an amino acid
Hydrophobic
side group
Hydrophilic
side group
Leucine
Serine
b Examples of amino acids with hydrophobic and hydrophilic
side groups
Proteins as Polymers
Cells link amino acids together
-
by dehydration reactions,
-
forming peptide bonds
(between atom and nitrogen
atom of two amino acids)
and
-
Carboxyl
group
Amino
group
Side
group
Side
group
Amino acid
Amino acid
Dehydration reaction
creating long chains of
amino acids called
polypeptides.
Side
group
Side
group
Peptide bond
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MAJOR TYPES OF PROTEINS
Structural Proteins
(provide support)
Storage Proteins
(provide amino
acids for growth)
Contractile
Proteins
(help movement)
Transport Proteins
(help transport
substances)
Figure 3.15
Enzymes
(help chemical
reactions)
Proteins as Polymers
• Your body has tens of thousands of different kinds of
protein.
• Proteins differ in their composition, order and arrangement
of amino acids
• The specific sequence of amino acids in a protein is its
primary structure.
• A slight change in the primary structure of a protein affects
its ability to function.
• The substitution of one amino acid for another in
hemoglobin causes sickle-cell disease.
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SEM
A single amino acid substitution in a protein causes sickle-cell
disease
1
6 7. . . 146
5
2
3 4
Normal hemoglobin
1
5
SEM
Normal red blood cell
a Normal hemoglobin
Sickled red blood cell
b Sickle-cell hemoglobin
6
2
3 4
Sickle-cell hemoglobin
7. . . 146
Protein Shape
• A functional protein consists of one or more
polypeptide chains, precisely folded and coiled into a
molecule of unique shape.
• Proteins consisting of
– One polypeptide have three levels of structure
– More than one polypeptide chain have a fourth,
quaternary structure
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a Primary structure
- the amino acid sequence of the protein
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Figure 3.20-1
Amino
acids
b Secondary structure
a Primary
structure
Pleated sheet
Alpha helix
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Figure 3.20-2
Amino
acids
b Secondary structure
c Tertiary
structure
a Primary
structure
Pleated sheet
Polypeptide
Alpha helix
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Figure 3.20-3
The four levels of protein structure
Amino
acids
b Secondary structure
c Tertiary
structure
d Quaternary
structure
a Primary
structure
Pleated sheet
Protein with
four polypeptides
Polypeptide
Alpha helix
Protein Shape
• A protein’s three-dimensional shape
– Recognizes and binds to another molecule
– Enables the protein to carry out its specific function in a cell
Target
Protein
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A computer model showing an
enzyme closely related to
human lactase binding with
lactose
What Determines Protein Shape?
• A protein’s shape is sensitive to the surrounding
environment.
• Unfavorable temperature and pH changes can cause
denaturation of a protein, in which it unravels and loses
its shape.
• High fevers (above 104º F) in humans can cause some
proteins to denature.
• Misfolded proteins are associated with
– Alzheimer’s disease
– Mad cow disease
– Parkinson’s disease
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Nucleic Acids
• Nucleic acids are
– macromolecules that provide the directions for building proteins
– Include DNA (deoxyribonucleic acid) and
RNA (ribonucleic acid)
– genetic material that organisms inherit from their parents
• The monomers of nucleic acids are called nucleotide
• DNA resides in cells in long fibers called chromosomes.
• A gene is a specific stretch of DNA that programs the
amino acid sequence of a polypeptide.
• The chemical code of DNA must be translated from
“nucleic acid language” to “protein language.”
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Building a protein
Gene
DNA
Nucleic acids
RNA
Amino acid
Protein
Nucleic Acids
Nucleic acids are polymers of nucleotides.
Each nucleotide has three parts:
• A five-carbon sugar
Nitrogenous base
• A phosphate group
A, G, C, or T
• A nitrogenous base
Thymine T
Phosphate
group
Phosphate
Base
Sugar
deoxyribose
a Atomic structure
Sugar
b Symbol used in this book
Nucleic Acids
Adenine A
Thymine T
Adenine A
Guanine G
Each DNA nucleotide has
one of the following bases:
1. Adenine (A)
2. Guanine (G)
3. Thymine (T)
4. Cytosine (C)
Cytosine C
Guanine G
Thymine T
Space-filling model of DNA
Cytosine C
Figure 3.24
The structure of DNA
Dehydration reactions
• Link nucleotide monomers into long chains
called polynucleotides
• Form covalent bonds between the sugar of
one nucleotide and the phosphate of the next
• Form a sugar-phosphate backbone
• Nitrogenous bases hang off the sugarphosphate backbone.
This is analogous
to how our muscles are
Supported by the vertebrae
and discs in our own
backbone.
Sugar-phosphate
backbone
Base
Nucleotide
pair
Hydrogen
bond
Bases
a DNA strand
polynucleotide
b Double helix
(2 polynucleotide strands
The structure of DNA
• Two strands of DNA join together to form a double
helix.
• Bases along one DNA strand hydrogen-bond to bases
along the other strand.
• The functional groups hanging off the base determine
which bases pair up:
– A only pairs with T.
– G can only pair with C.
• RNA, ribonucleic acid, is different from DNA.
– RNA is usually single-stranded but DNA usually exists as a
double helix.
– RNA uses the sugar ribose and the base uracil (U) instead
of thymine (T).
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An RNA nucleotide
Nitrogenous base
A, G, C, or U
Uracil U
Phosphate group
Sugar ribose
The Process of Science:
Does Lactose Intolerance Have a Genetic Basis?
• Observation: Most lactose-intolerant people have a
normal version of the lactase gene.
• Question: Is there a genetic basis for lactose intolerance?
• Hypothesis: Lactose-intolerant people have a mutation but
not within the lactase gene.
• Prediction: A mutation would be found nearby the lactase
gene.
• Experiment: Genes of 196 lactose-intolerant people were
examined.
• Results: A 100% correlation between lactose intolerance
and one mutation was found.
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A genetic cause of lactose intolerance
DNA
Lactase gene
14,000 nucleotides
Human cell
Chromosome 2
Section of
DNA in 46
one DNA molecule chromosome 2
chromosomes
C at this site causes
lactose intolerance
T at this site causes
lactose tolerance
Evolution Connection:
Evolution and Lactose Intolerance in Humans
• Most people are lactose-intolerant as adults:
– African Americans and Native Americans — 80%
– Asian Americans — 90%
– But only 10% of Americans of northern European descent
are lactose-intolerant
• Lactose tolerance appears to have evolved in northern
European cultures that relied upon dairy products.
• Ethnic groups in East Africa that rely upon dairy
products are also lactose tolerant but due to different
mutations.
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Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose
Dietary energy;
storage; plant
structure
Disaccharides:
lactose, sucrose
Polysaccharides:
starch, cellulose
Monosaccharide
Figure UN3-2a
Lipids
Functions
Long-term
energy storage fats;
Hormones steroids
Components
Fatty acid
Glycerol
Examples
Fats triglycerides;
Steroids testosterone,
estrogen
Components of
a triglyceride
Figure UN3-2b
Proteins
Functions
Components
Amino
group
Enzymes, structure,
storage, contraction,
transport, and others
Examples
Carboxyl
group
Lactase an enzyme
hemoglobin
a transport protein
Side
group
Amino acid
Figure UN3-2c
Nucleic acids
Functions
Components
Examples
Phosphate
Base
Information
storage
DNA, RNA
Sugar
Nucleotide
Figure UN3-2d
Figure 3.UN02
Large biological
molecules
Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose;
Disaccharides:
lactose, sucrose;
Polysaccharides:
starch, cellulose
Dietary energy;
storage; plant
structure
Monosaccharide
Lipids
Proteins
Long-term
energy storage
(fats);
hormones
(steroids)
Enzymes,
structure,
storage,
contraction,
transport, etc.
Components of
a triglyceride
Side
group
Fats (triglycerides);
steroids
(testosterone,
estrogen)
Lactase
(an enzyme);
hemoglobin
(a transport protein)
Amino acid
Nucleic acids
Information
storage
T
Nucleotide
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DNA, RNA
Diversity among Biological Macromolecules
Which type of biological polymer is the storage form of
genetic information in the cell?
a) polysaccharides
b) polypeptides
c) DNA
d) RNA
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Subunits
Amino acids are the subunits of ____________
a) proteins
b) starch
c) nucleic acids
d) fatty acids
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