chapter 3 molecules of life (sections 3.4 - 3.6)
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Chapter 3 Molecules of Life (Sections 3.4 - 3.6). 3.4 Lipids. Cells use lipids as major sources of energy and as structural materials lipid Fatty, oily, or waxy organic compound All are hydrophobic (nonpolar ). Types of Lipids. - PowerPoint PPT PresentationTRANSCRIPT
Albia Dugger • Miami Dade College
Cecie StarrChristine EversLisa Starr
www.cengage.com/biology/starr
Chapter 3Molecules of Life
(Sections 3.4 - 3.6)
3.4 Lipids
• Cells use lipids as major sources of energy and as structural materials
• lipid • Fatty, oily, or waxy organic compound• All are hydrophobic (nonpolar )
Types of Lipids
• Fats and some other lipids have fatty acid tails; triglycerides have three
• Phospholipids are the main structural component of cell membranes
• Waxes are lipids that are part of water-repellent and lubricating secretions
• Steroids occur in cell membranes, and some are remodeled into other molecules
Key Terms
• fat • Lipid that consists of a glycerol molecule with one, two, or
three fatty acid tails
• triglyceride • A fat with three fatty acid tails
• fatty acid • Organic compound that consists of a chain of carbon
atoms with an acidic carboxyl group at one end • Carbon chain of saturated types has single bonds only;
that of unsaturated types has one or more double bonds
Fats and Fatty Acids
• Unsaturated fatty acids have one or more double bonds that limit their flexibility
• These bonds are termed cis or trans, depending on the way the hydrogens are arranged around them
• A cis bond kinks the tail, and a trans bond keeps it straight
Saturated and Unsaturated Fats
• Animal fats are saturated• Tend to remain solid at room temperature because their
saturated tails pack tightly together
• Most vegetable oils are unsaturated• Kinked tails do not pack tightly, so unsaturated fats are
typically liquid at room temperature
• Partially hydrogenated vegetable oils have a trans double bond that allows them to pack tightly, like saturated fats• Solid at room temperature
Fatty Acids
Fig. 3.8, p. 42
carboxyl group(head)
hydro carbon tail
B linoleic acidA stearic acid C linolenic acid
Trans and Cis
Phospholipids
• phospholipid • Lipid with a highly polar phosphate group in its hydrophilic
head, and two nonpolar, hydrophobic fatty-acid tails • Main constituent of eukaryotic cell membranes
• Opposing properties of a phospholipid molecule give rise to cell membrane structure• Two layers of lipids (lipid bilayer)• Hydrophobic tails sandwiched between hydrophilic heads
Phospholipids and Cell Membranes
• Head is hydrophilic –tails are hydrophobic
• Lipid bilayer— the structural foundation of all cell membranes
Fig. 3.10, p. 42
one layer of lipids
hydrophilic head
one layer of lipids
two hydrophobic tails
Waxes• wax • Water-repellent mixture
with long fatty-acid tails bonded to long-chain alcohols or carbon rings
• Functions:• Covers exposed surfaces
of plants• Protects and lubricates
skin and hair• Honeycomb
Steroids
• steroid • Lipid with four carbon rings and no fatty acid tails• Found in all eukaryotic cell membranes
• Cholesterol, the most common steroid in animal tissue, is remodeled into many molecules:• Bile salts (which help digest fats) and vitamin D • Steroid hormones (estrogens and testosterone)
Estrogen and Testosterone
• Estrogen and testosterone
• Steroid hormones derived from cholesterol
Steroid Functions
• Steroid hormones cause different traits to arise in males and females of many species, such as wood ducks (Aix sponsa)
Key Concepts
• Lipids• Lipids function as energy reservoirs and as waterproofing
or lubricating substances• Some are remodeled into other compounds such as
vitamins• Lipids are the main structural component of all cell
membranes
Animation: Fatty acids
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Animation 2.2: Triglyceride formation
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3.5 Proteins—Diversity in Structure and Function
• Structurally and functionally, proteins are the most diverse molecules of life
• The shape of a protein is the source of its function
• protein • Organic compound that consists of one or more chains of
amino acids (polypeptides)
Amino Acids
• Cells make thousands of different kinds of proteins from only twenty kinds of monomers (amino acids)
• amino acid • Small organic compound that is a subunit of proteins• Consists of a carboxyl group, an amine group, and a
characteristic side group (R), all typically bonded to the same carbon atom
Amino Acids
• Generalized structure of amino acids: Twenty amino acids are used in eukaryotic proteins
Fig. 3.12, p. 44
Stepped Art
Amino Acids
Building Proteins
• Protein synthesis involves covalently bonding amino acids into a chain polypeptide linked by peptide bonds
• polypeptide • Chain of amino acids linked by peptide bonds• Primary structure of a protein
• peptide bond • Bond that joins the amine group of one amino acid and the
carboxyl group of another in a protein
Polypeptide Formation
• Condensation: A peptide bond forms between the carboxyl group of the methionine and the amine group of the serine
• Additional amino acids are added to the carboxyl end
Fig. 3.13, p. 44
glutaminemethionine serine arginine
methionine
serine
methionine serine
Stepped Art
Polypeptide Formation
Animation: Peptide bond formation
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Protein Structure
• Polypeptides (primary structure) twist into loops, sheets, and coils (secondary structure) that can pack further into functional domains (tertiary structure)
• Many proteins, including most enzymes, consist of two or more polypeptides (quaternary structure)
• Fibrous proteins aggregate into much larger structures
Primary and Secondary Structure
• Primary structure (polypeptide) twists into secondary structure
Tertiary and Quaternary Structure
• Tertiary structure forms functional domains• Hemoglobin has quaternary structure (4 globin chains)
Aggregate Proteins
• Many proteins aggregate by thousands into much larger structures, such as keratin filaments that make up hair
5 Many proteins aggregate by the thousands into much larger structures, such as the keratin filaments that make up hair. Fig. 3.14.1-4, p. 45
A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain). Each type of protein has a unique primary structure.
1
glycinelysine glycine arginine
Stepped Art
2 Secondary structure arises as a polypeptide chain twists into a coil (helix) or sheet held in place by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure occur in many different proteins.
3 Tertiary structure occurs when a chain’s coils and sheets fold up into a functional domain such as a barrel or pocket. In this example, the coils of a globin chain form a pocket.
4 Some proteins have quaternary structure, in which two or more polypeptide chains associate as one molecule. Hemoglobin, shown here, consists of four globin chains (green and blue). Each globin pocket now holds a heme group (red).
Polypeptide Formation
Animation: Secondary and tertiary structure
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Combined Proteins
• Enzymes often attach sugars or lipids to proteins
• Glycoproteins allow a tissue or body to recognize its own cells
• Lipoproteins carry fats and cholesterol through the bloodstream• Low-density lipoprotein (LDL)• High-density lipoprotein (HDL)
3.6 Importance of Protein Structure
• A protein’s structure dictates its function so, if a protein unravels (denatures), it loses its function
• denature • To unravel the shape of a protein or other large biological
molecule• Caused by shifts in pH or temperature, exposure to
detergent or some salts that disrupt hydrogen bonds, and other molecular interactions responsible for protein shape
Prions
• Prion diseases, are the result of misfolded proteins• Mad cow disease (bovine spongiform encephalitis, BSE)• Creutzfeldt–Jakob disease (vCJD) in humans• Scrapie in sheep
• prion • Infectious protein• Misfolded PrPC protein
PrPC Protein Becomes a Prion
• The PrPC protein misfolds into an unknown conformation• Prions cause other PrPC proteins to misfold• Misfolded proteins aggregate into long fibers
Fig. 3.16, p. 46
?
prion protein
PrPC
protein
Conformational change
Variant Creutzfeldt–Jakob Disease
• Charlene Singh:• Diagnosed in 2001• Died in 2004
• Brain tissue shows characteristic holes and prion protein fibers radiating from several deposits
Key Concepts
• Proteins• Structurally and functionally, proteins are the most diverse
molecules of life• They include enzymes and structural materials• A protein’s function arises from and depends on its
structure
ANIMATION: Globin and hemoglobin structure
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ANIMATION: Sickle-Cell Anemia
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3.7 Nucleic Acids
• Nucleotides are small organic molecules consisting of a sugar, a phosphate group, and a nitrogen-containing base
• nucleotide • Monomer of nucleic acids; has five-carbon sugar, nitrogen-
containing base, and phosphate groups
A Nucleotide Monomer
• ATP, a nucleotide monomer of RNA, and also an essential participant in many metabolic processes
Nucleic Acids
• Nucleotides are monomers of DNA and RNA, which are nucleic acids
• nucleic acid • Single- or double-stranded chain of nucleotides joined by
sugar–phosphate bonds; for example, DNA, RNA
A Nucleic Acid
• A chain of nucleotides is a nucleic acid
• The sugar of one nucleotide is covalently bonded to the phosphate group of the next, forming a sugar–phosphate backbone
ANIMATION: Nucleotide Subunits of DNA
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DNA and RNA
• DNA (Deoxyribonucleic acid)• DNA encodes heritable information that guides the
synthesis of RNA and proteins• Consists of two nucleotide chains twisted in a double helix
• RNA (Ribonucleic acid)• RNAs interact with DNA and with one another to carry out
protein synthesis
DNA
• DNA consists of two chains of nucleotides, twisted into a double helix
• Hydrogen bonding maintains the three-dimensional structure
Other Nucleotides
• Some nucleotides have additional functions
• Example: ATP energizes many kinds of molecules by phosphate-group transfers
• ATP Adenosine triphosphate• Nucleotide that consists of an adenine base, a five-carbon
ribose sugar, and three phosphate groups
Key Concepts
• Nucleic Acids• Nucleotides are the building blocks of nucleic acids• Some have additional roles in metabolism• DNA and RNA are part of a cell’s system of storing and
retrieving heritable information
Fear of Frying (revisited)
• Trans fatty acids are rare in unprocessed foods
• Enzymes that hydrolyze cis fatty acids have difficulty breaking down trans fatty acids, a problem that may be a factor in the ill effects of trans fats on our health