the structure and function of macromolecules … ap...• nucleic acids •macromolecules are large...
TRANSCRIPT
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The Structure and Function of Macromolecules Proteins & Nucleic Acids
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The FOUR Classes of Large Biomolecules
• All living things are made up of four classes of large biological molecules:
• Carbohydrates
• Lipids
• Protein
• Nucleic Acids
• Macromolecules are large molecules composed of thousands of covalently bonded atoms
• Molecular structure and function are inseparable
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Proteins Come In Many Varieties!• Proteins include a diversity of
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 3
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Enzymatic
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Enzymatic proteins
Enzyme
Example: Digestive enzymes catalyze the hydrolysis
of bonds in food molecules.
Function: Selective acceleration of chemical reactions
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Storage
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Storage proteins
OvalbuminAmino acidsfor embryo
Function: Storage of amino acids
Examples: Casein, the protein of milk, is the major
source of amino acids for baby mammals. Plants have
storage proteins in their seeds. Ovalbumin is the
protein of egg white, used as an amino acid source
for the developing embryo.
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Hormonal
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Hormonal proteins
Function: Coordination of an organism’s activities
Example: Insulin, a hormone secreted by the
pancreas, causes other tissues to take up glucose,
thus regulating blood sugar concentration
Highblood sugar
Normalblood sugar
Insulinsecreted
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Defensive
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Defensive proteins
Virus
Antibodies
Bacterium
Function: Protection against disease
Example: Antibodies inactivate and help destroy
viruses and bacteria.
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Transport
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Transport proteins
Transportprotein
Cell membrane
Function: Transport of substances
Examples: Hemoglobin, the iron-containing protein of
vertebrate blood, transports oxygen from the lungs to
other parts of the body. Other proteins transport
molecules across cell membranes.
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Receptor
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Signalingmolecules
Receptorprotein
Receptor proteins
Function: Response of cell to chemical stimuli
Example: Receptors built into the membrane of a
nerve cell detect signaling molecules released by
other nerve cells.
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Structural
60 m
Collagen
Connectivetissue
Structural proteins
Function: Support
Examples: Keratin is the protein of hair, horns,
feathers, and other skin appendages. Insects and
spiders use silk fibers to make their cocoons and webs,
respectively. Collagen and elastin proteins provide a
fibrous framework in animal connective tissues.
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More About Enzymes
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• Enzymes are a type of protein that
acts as a catalyst to speed up
chemical reactions
• Enzymes can perform their functions
repeatedly, functioning as workhorses
that carry out the processes of life
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Amino Acids: Yet Another Monomer
• Amino acids are
organic molecules
with carboxyl and
amino groups
• Amino acids differ in
their properties due
to differing side
chains, called R
groups
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Side chain (R group)
Aminogroup
Carboxylgroup
carbon
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Polypeptides• Polypeptides are unbranched
polymers built from 20 amino acids
• A protein is a biologically functional
molecule that consists of one or more
polypeptides
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Nonpolar side chains; hydrophobic
Side chain
Glycine(Gly or G)
Alanine(Ala or A)
Valine(Val or V)
Leucine(Leu or L)
Isoleucine(Ile or I)
Methionine(Met or M)
Phenylalanine(Phe or F)
Tryptophan(Trp or W)
Proline(Pro or P)
Hydrophobic: Therefore retreat from water!
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Hydrophilic: Therefore Are Attracted to Water
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Hydrophilic: But Electrically Charged!
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Peptide Bonds
• Amino acids are linked by peptide
bonds
• A polypeptide is a polymer of amino
acids
• Polypeptides range in length from a few
to more than a thousand monomers
• Each polypeptide has a unique linear
sequence of amino acids, with a carboxyl
end (C-terminus) and an amino end (N-
terminus)17
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Peptide Bonds
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Peptide Bonds
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Protein Structure & Function
• At first– just amino acids with peptide bonds
• Amino acid chain then interacts with itself (folds, coils) and the (usually aqueous environment) until it is a 3D structure
• The sequence of amino acids determines a protein’s 3D structure
• A protein’s structure determines its function
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Protein Structure: 4 Levels• Primary structure consists of its unique
sequence of amino acids
• Secondary structure, found in most
proteins, consists of coils and folds in the
polypeptide chain (backbone!)
• Tertiary structure is determined by
interactions among various side chains (R
groups)
• Quaternary structure results when a protein
consists of multiple polypeptide chains
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Primary Structure
• 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
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Secondary Structure• The coils and folds of
secondary structure
result from hydrogen
bonds between
repeating parts of the
polypeptide backbone
• Typical secondary structures are a coil called an helix and a folded structure called a pleated sheet
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Secondary Structure
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Tertiary Structure
• Tertiary structure is determined by interactions
between R groups, rather than interactions
between backbone parts
• Interactions between R groups include actual ionic
bonds and strong covalent bonds called disulfide
bridges which may reinforce the protein’s
structure.
• Intermolecular forces such as van der Waals,
hydrogen bonds, and hydrophobic interactions may
affect the protein’s structure
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Tertiary Structure
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Quaternary Structure
• 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
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Quaternary Structure
• Hemoglobin is a globular protein
consisting of four polypeptides: two
alpha and two beta chains
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Four Levels of Protein Structure Revisited
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What Determines Protein Structure?
• In addition to primary structure, physical
and chemical conditions can affect
structure
• Alterations in pH, salt concentration,
temperature, or other environmental
factors can cause a protein to unravel
• This loss of a protein’s native structure is
called denaturation
• A denatured protein is biologically
inactive
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Denature: Break Bonds or Disrupt intermolecular forces
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Nucleic Acids
• Nucleic acids store, transmit, and
help express hereditary information
• Make proteins inside cell!
• Genes are made of DNA, a nucleic
acid made of monomers called
nucleotides
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Two Types of Nucleic Acids• Two types:
– Deoxyribonucleic acid
(DNA)
– Ribonucleic acid
(RNA)
• DNA provides directions for
its own replication
• DNA directs synthesis of
messenger RNA (mRNA)
and, through mRNA, controls
protein synthesis
• Protein synthesis occurs on
ribosomes33
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Figure 5.25-1
Synthesis ofmRNA
mRNA
DNA
NUCLEUS
CYTOPLASM
1
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Figure 5.25-2
Synthesis ofmRNA
mRNA
DNA
NUCLEUS
CYTOPLASM
mRNA
Movement ofmRNA intocytoplasm
1
2
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Figure 5.25-3
Synthesis ofmRNA
mRNA
DNA
NUCLEUS
CYTOPLASM
mRNA
Ribosome
AminoacidsPolypeptide
Movement ofmRNA intocytoplasm
Synthesisof protein
1
2
3
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The Components of Nucleic Acids
• Each nucleic acid is made of
monomers called nucleotides
• Each nucleotide consists of a
nitrogenous base, a pentose sugar,
and one or more phosphate groups
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Figure 5.26ab
Sugar-phosphate backbone5 end
5C
3C
5C
3C
3 end
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
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Figure 5.26c
Nitrogenous bases
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components
Pyrimidines
Purines
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• There are two families of nitrogenous
bases
– Pyrimidines (cytosine, thymine, and
uracil) have a single six-membered
ring
– Purines (adenine and guanine) have a
six-membered ring fused to a five-
membered ring
• In DNA, the sugar is deoxyribose; in
RNA, the sugar is ribose 41
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Sugar-Phosphate Backbone
• Adjacent nucleotides are
joined by covalent bonds
that form between the —OH
group on the 3 carbon of one
nucleotide and the phosphate
on the 5 carbon on the next
• These links create a
backbone of sugar-
phosphate units
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RNA and DNA structure
• RNA molecules usually exist as single
polypeptide chains
• DNA molecules have 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
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Complimentary Base Pairing
• The nitrogenous bases in DNA pair up
and form hydrogen bonds: adenine (A)
always with thymine (T), and guanine
(G) always with cytosine (C)
• Called complementary base pairing
• In RNA, thymine is replaced by uracil
(U) so A and U pair
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Sugar-phosphatebackbones
Hydrogen bonds
Base pair joinedby hydrogen bonding
Base pair joinedby hydrogen
bonding
(b) Transfer RNA(a) DNA
5 3
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Link to 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 kinship46
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Could Prove Useful
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