The Structure and Function of Large Biological Molecules
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Transcript of The Structure and Function of Large Biological Molecules
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The Structure and Function of Large Biological Molecules
Chapter 5
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The Molecules of Life• Living things made up of 4 classes of large
biological molecules (macromolecules) : 1. Carbohydrates2. Lipids3. Proteins4. Nucleic acids
• Molecular structure and function are linked• Unique, emergent properties
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Macromolecules are polymers, built from monomers
• polymer -long molecule of many building blocks
• monomers - single unit
Sucrose
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The Diversity of Polymers
• Each cell has thousands of different macromolecules –built from monomers
• Macromolecules vary among cells, among species, and between species
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Carbohydrates serve as fuel and building material
• Carbohydrates = sugars and sugar polymers
–Monosaccharides = single sugars• Ex. glucose (C6H12O6)• major fuel for cells • raw material for building molecules
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• Sugars often form rings (in aqueous solution)
(a) Linear and ring forms (b) Abbreviated ring structure
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• Disaccharide = two sugars
• Ex. lactose, sucrose, maltose
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Polysaccharides
• Polysaccharides - polymers of sugars = starch– storage and structural roles
• The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
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Storage Polysaccharides
• Starch– plants store starch– Glucose polymer
• Glycogen – Animals store glycogen (glucose polymer)– Humans in liver and muscle cells
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(b) Glycogen: an animal polysaccharide
Starch
GlycogenAmylose
Chloroplast
(a) Starch: a plant polysaccharide
Amylopectin
MitochondriaGlycogen granules
0.5 µm
1 µm
Amylose - unbranchedAmylopectin - branched
Glycogen is more branched than starch
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Structural Polysaccharides• Cellulose =component of tough wall of plant cells
• polymer of glucose (glycosidic linkages differ from starch)
• The difference is based on two ring forms for glucose:
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• Enzymes digest cellulose in some animals– Cows, termites, have symbiotic relationships with
microbes that digest cellulose• In humans, cellulose is indigestible fiber
Mastigophoran, anaerobic, methane
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• Chitin in the exoskeleton of arthropods and in fungi
The structureof the chitinmonomer.
(a) (b) (c)Chitin forms theexoskeleton ofarthropods.
Chitin is used to makea strong and flexiblesurgical thread.
Cicada exoskeleton
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Lipids are hydrophobic
• Lipids - fats, phospholipids, steroids
Triglyceride = 3 fatty acids joined glycerol
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Saturated fats maximum number of
H possible (no double bonds)
Solid at room T (animal fats)
Unsaturated fats one or more double
bonds Liquid at room T
(plant, fish oils)
(a)
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• Coronary artery disease associated with diet rich in saturated fats
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• Hydrogenation – process of converting unsaturated fats to
saturated fats by adding hydrogen– Extends shelf life, prevents oil separation– Ex. margarine, peanut butter
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• The good news:• Fats store energy (adipose cells)• Cell membranes need lipid• Lipid cushions and insulates
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Steroids
• Steroids – – Ex. estrogen, testosterone
• Cholesterol– Steroid in animal cell membranes– Synthesized in the liver
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Proteins
• Proteins = more than 50% of dry mass of cells
• Protein functions – structural support –collagen
– pigment - melanin
– transport - hemoglobin
– cellular communications– movement– defense against foreign substances-antibodies
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• Enzymes – All are proteins– catalyst speeds up chemical reactions– reusable – specific to each reaction– essential to life– Heat or chemicals may denature
– animation
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Polypeptides
• Polypeptides – polymers built from set of 20 amino acid building
blocks– may be a few or thousands long
• protein – one or more polypeptides– has a function
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Peptide
Protein
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Protein Structure and Function
• proteins consists of one or more polypeptides twisted, folded, and coiled into unique shape
A ribbon model of lysozyme(a) (b)A space-filling model of lysozyme
GrooveGroove
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• sequence of aa determines a 3D structure• structure determines function
Antibody proteinProtein from flu virus
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Four Levels of Protein Structure
• Primary structure =unique sequence of amino acids
25
20
15
10
51
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• Secondary structure = coils and folds– helix and pleated sheet– H-bonds
β pleated sheet
α helix
Example: spider silk
Strong as steelStretchy
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• Tertiary structure determined by interactions between amino acids– hydrogen bonds– ionic bonds– hydrophobic interactions– disulfide bridges (covalent bonds)
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Tertiary structure
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• Quaternary structure two or more polypeptide chains may form one macromolecule
• ex. hemoglobin• activity
α Chains
β ChainsHemoglobin
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A patient with sickle cell disease
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Denaturation of proteins
• Denaturation – Loss of protein structure biologically inactive– pH, heat, chemicals
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The Roles of Nucleic Acids
Deoxyribonucleic acid (DNA)replicates prior to cell divisioncontains codes for proteins (genes)
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Nucleic acids hold a code
• Gene – unit of inheritance– code for protein primary structure– composed of DNA
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The Structure of Nucleic Acids
• Nucleotides
G,A,T,C building blocks (monomers)– Pyrimidines (cytosine,
thymine, and uracil) – Purines (adenine and
guanine) (c) Nucleoside components: nitrogenous bases
Purines
Guanine (G)Adenine (A)
Cytosine (C)Thymine (T, in DNA)
Uracil (U, in RNA)
Nitrogenous basesPyrimidines
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Ribose (in RNA)Deoxyribose (in DNA)
Sugars
(c) Nucleoside components: sugars
•Nucleotides contain sugar•DNA deoxyribose•RNA ribose (ribonucleic acid)
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DNA Polymers
Sugar phosphate backbone
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The DNA Double Helix
• A DNA molecule has 2 strands that form double helix
• hydrogen bonds between:– adenine (A) thymine (T) – guanine (G) cytosine (C)
• DNA replication– Before a cell divides
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DNA, Proteins and Evolution
• DNA is inherited– Cell to cell– Parent to offspring
• Closely related species more similar in DNA sequence than more distantly related species– Human/human 99.1 %– Human/chimp 98.5%
• Molecular biology used to assess evolutionary relatedness