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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 3
The Molecules of Cells
Modules 3.11 – 3.20
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PROTEINS
3.11 Proteins are essential to the structures and
activities of life
• Proteins are involved in
– cellular structure
– movement
– defense
– transport
– communication
• Mammalian hair is composed of structural
proteins
• Enzymes regulate chemical reactions
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Figure 3.11
Hair color -eumelanin and
phaeomelanin
Two gene pairs-Four gene pairs??
Phaeomelanin colors hair red.
Nored/red
 Eumelanin- determines the darkness of the
hair color.
Low brown eumelanin results in blonde hair
Higher brown eumelanin results in brown.
Brown/blonde
 High black eumelanin results in black hair
Low black eumelanin results in gray hair
Black/grey
Most noticeable in red-heads, all humans
have varying concentrations of phaeomelanin.
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• Brown/blonde Not Red/red
• Phaeomelanin is more chemically stable than
black eumelanin. But less chemically stable
than brown eumelanin. So it breaks down
more slowly when oxidized. Brown-Red-Black
(most stable to least stable)
• Bleach will cause darker hair to turn reddishbrown during the artificial coloring process. As
the phaeomelanin continues to break down, the
hair will gradually become orange, later yellow,
and then white.
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Muscle contraction –actin and myosin
http://www.sci.sdsu.edu/movies/a
ctin_myosin.html
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Enzymes - proteins that catalyze chemical and biochemical reactions within living cell
and outside. This group of proteins probably is the biggest and most important group of
the proteins.
•Hormones - proteins that are responsible for the regulation of many processes in
organisms. Hormones are usually quite small and can be classifies as peptides (2-100
aa.) Best known protein hormones are: insulin, growth factors, etc.
•Transport proteins - These proteins are transporting or store some other chemical
compounds and ions. Some of them are well known: cytochrome C - electron transport;
hemoglobin and myoglobin - oxygen transport
•Immunoglobulin or Antibodies - proteins that involved into immune response of the
organism to neutralize large foreign molecules, which can be a part of an infection. ie.
antibodies
•Structural proteins - These proteins maintain the structure of other biological
components, like cells and tissues. Collagen, elastin, α-keratin, fibrin - these proteins are
involved into formation of the whole organism body.
•Motor proteins. These proteins can convert chemical energy into mechanical energy.
actin and myosin are responsible for muscular motion.
•Receptors These proteins are responsible for signal detection and translation into other
type of signal.
•Signalling proteins - This group of proteins is involved into signaling transduction
process.
•Storage proteins. These proteins contain energy, which can be released during
metabolism processes in the organism. Egg ovalbumin and milk casein are such proteins.
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3.12 Proteins are made from just 20 kinds of amino
acids
• Proteins are the most structurally and
functionally diverse of life’s molecules
– Their diversity is based on different
arrangements of amino acids
– Proteins may be composed of one polypeptide
chain or several.
– Protein folding of the chain is essential to
protein function.
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• The monomer of a polypeptide is an amino
acid. Each amino acid contains:
– an amino group
– a carboxyl group
– an R group, which distinguishes each of the 20
different amino acids
Figure 3.12A
Amino
group
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Carboxyl (acid)
group
• Each amino acid has specific properties
Leucine (Leu)
Serine (Ser)
HYDROPHOBIC
Figure 3.12B
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Cysteine (Cys)
HYDROPHILIC
(*) Essential only in certain cases.
• An essential amino acid is
an amino acid that cannot be
synthesized de novo by the
organism (usually referring
to humans), and therefore
must be supplied in the diet.
• Eight amino acids are
generally regarded as
essential for humans:
phenylalanine, valine,
threonine, tryptophan,
isoleucine, methionine,
leucine, and lysine
• PVT. TIM HALL (histidine
and arginine in children )
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20 amino acids
Essential
Nonessential
Isoleucine
Alanine
Leucine
Asparagine
Lysine
Aspartate
Methionine
Cysteine*
Phenylalanine
Glutamate
Threonine
Glutamine*
Tryptophan
Glycine*
Valine
Proline*
Serine*
Tyrosine*
Arginine*
Histidine*
Amino acids can be linked by peptide bonds to form polypeptides.
• Cells link amino acids together by dehydration
synthesis
• The bonds between amino acid monomers are
called peptide bonds
Carboxyl
group
Amino
group
PEPTIDE
BOND
Dehydration
synthesis
Amino acid
Amino acid
Figure 3.13
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Dipeptide
3.14 Overview: A protein’s specific shape
determines its function
• A protein, such as lysozyme, consists of polypeptide chains
folded into a unique shape
– The shape determines the protein’s function
– A protein loses its specific function when its polypeptides
unravel. Milk curdles and egg white solidifies when their
proteins are unraveled. Mad Cow Disease is caused by a
malformed protein.
Figure 3.14A
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Figure 3.14B
3.15 A protein’s primary structure is its amino
acid sequence
3.16 Secondary structure is polypeptide coiling or
folding produced by hydrogen bonding
Primary
structure
Amino acid
Secondary
structure
Hydrogen
bond
Pleated sheet
Alpha helix
Figure 3.15, 16
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3.17 Tertiary structure is the overall shape of a
polypeptide and due to R group interactions
3.18 Quaternary structure is the relationship
among multiple polypeptides of a protein
Tertiary
structure
Polypeptide
(single subunit
of transthyretin)
Quaternary
structure
Transthyretin, with four
identical polypeptide subunits.
Transthyretin carries thyroid
hormone through the blood.
Figure 3.17, 18
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3.19 Talking About Science: Linus Pauling
contributed to our understanding of the
chemistry of life
• Pauling made important contributions to our
understanding of protein structure and
function. He is often considered one of the
founders of molecular biology.
Figure 3.19
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NUCLEIC ACIDS
3.20 Nucleic acids are information-rich polymers of
nucleotides
• Nucleic acids such and DNA and RNA serve as
the blueprints for proteins
• They ultimately control the life of a cell
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• The monomers of nucleic acids are nucleotides
– Each nucleotide is composed of a sugar,
phosphate, and nitrogenous base
Nitrogenous
base (A)
Phosphate
group
Figure 3.20A
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Sugar
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Pyrimidines
Adenine (A)
Guanine (G)
Purines
Figure 10.2B
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Note the designation of the Carbons as 1-5.
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DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
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Figure 10.2A
• DNA consists of two
polynucleotides twisted
around each other in a
double helix. The sugar is
deoxyribose. The bases are
adenine, thymine, guanine,
and cytosine.
– The sequence of the
four kinds of
nitrogenous bases in
DNA carries genetic
information
Base
pair
Nitrogenous
base (A)
Figure 3.20C
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DNA is Antiparallel
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RNA is single stranded and the sugar is ribose.
The bases are
adenine , uracil,
guanine and
cytosine.
DNA
RNA
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The Bases of RNA
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In most organisms, stretches of a DNA
molecule, called genes, program the amino acid
sequences of proteins. Retroviruses use RNA as
their genetic material. The Dogma is not always
correct.
The Central Dogma. Dogma (the plural is either dogmata
or dogmas, Greek δόγμα, plural δόγματα) is the established belief
or doctrine held by a religion, ideology or any kind of organization,
thought to be authoritative and not to be disputed or doubted. Wiki
– DNA information is transcribed into RNA, a
single-stranded nucleic acid
– RNA is then translated into the primary
structure of proteins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings