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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
Macromolecules are polymers, built from monomers
• polymer -long molecule of many building blocks
• monomers - single unit
Sucrose
The Diversity of Polymers
• Each cell has thousands of different macromolecules –built from monomers
• Macromolecules vary among cells, among species, and between species
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
• Sugars often form rings (in aqueous solution)
(a) Linear and ring forms (b) Abbreviated ring structure
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
Storage Polysaccharides
• Starch– plants store starch– Glucose polymer
• Glycogen – Animals store glycogen (glucose polymer)– Humans in liver and muscle cells
(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
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:
• 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
• 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
Lipids are hydrophobic
• Lipids - fats, phospholipids, steroids
Triglyceride = 3 fatty acids joined glycerol
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)
• Hydrogenation – process of converting unsaturated fats to
saturated fats by adding hydrogen
– Extends shelf life, prevents oil separation
– Ex. margarine, peanut butter
• The good news:• Fats store energy (adipose cells)• Cell membranes need lipid• Lipid cushions and insulates
Steroids
• Steroids – – Ex. estrogen, testosterone
• Cholesterol– Steroid in animal cell membranes– Synthesized in the liver
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
• Enzymes – All are proteins– catalyst speeds up chemical reactions– reusable – specific to each reaction– essential to life– Heat or chemicals may denature
– animation
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
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
• sequence of aa determines a 3D structure• structure determines function
Antibody proteinProtein from flu virus
• Secondary structure = coils and folds– helix and pleated sheet– H-bonds
β pleated sheet
α helix
Example: spider silk
Strong as steelStretchy
• Tertiary structure determined by interactions between amino acids– hydrogen bonds– ionic bonds– hydrophobic interactions– disulfide bridges (covalent bonds)
• Quaternary structure two or more polypeptide chains may form one macromolecule
• ex. hemoglobin• activity
α Chains
β ChainsHemoglobin
Denaturation of proteins
• Denaturation – Loss of protein structure biologically inactive– pH, heat, chemicals
The Roles of Nucleic Acids
Deoxyribonucleic acid (DNA)replicates prior to cell divisioncontains codes for proteins (genes)
Nucleic acids hold a code
• Gene – unit of inheritance– code for protein primary structure– composed of DNA
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
Ribose (in RNA)Deoxyribose (in DNA)
Sugars
(c) Nucleoside components: sugars
•Nucleotides contain sugar
•DNA deoxyribose
•RNA ribose (ribonucleic acid)
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