Post on 29-Mar-2018
BiologicalMolecules
Chapter 3
Topoisomerase protein bound to DNA
Carbon in Biological Molecules
• Organic molecules– Derived from living organisms– Contain a carbon backbone
• Inorganic molecules– CO2, CO, and all molecules without carbon
Carbon
• Carbon is versatile and can form up to4 covalent bonds.
• Because it can make so many differentbonds, Carbon is present in nearlyevery structure in a cell.
6 CCarbon12.01
Carbon
• Most organic molecules have a carbonbackbone.– A chain of carbon atoms bonded together.
• Branching off of the backbone are a variety offunctional groups.– Small molecules with a specific function that
determine the chemical nature of the largermolecule.
6 CCarbon12.01
Organic Molecules oftencontain Functional Groups
C6H12O6
• A modular approach: small organicmolecules, subunits, are combined toform larger molecules.
• Monomers, “one part”, single subunits.– Example: sugars
• Polymers, “many parts”, long chains ofmany subunits.– Example: starches
Synthesis of Organic Molecules Dehydration Synthesis• “To form by removing water.”
1. A hydrogen ion (H+) is removed from onesubunit.
2. A hydroxyl group (OH-) is removed from thea second subunit.
3. The two subunits can now covalently bondand the H+ and OH- can form water.
Hydrolysis
• “To break apart with water”
• Water is ionized and the H+ and OH-
bind to each new subunit.
• The major way our digestive systembreaks down food.
Types ofBiologicalMolecules
CarbohydratesLipids
ProteinsNucleic Acids
RNA Polymerase protein synthesizingRNA strand from a template DNA helix.
C6H12O6 =
“Chemical Structure”
“Space-Filling Model”
“Ball and Stick Model”
=“Chemical Formula”
Carbohydrates• Molecules composed of carbon, hydrogen,
and oxygen in a ratio of ~1:2:1 --> (CH2O)n
• Monosaccharide: composed of one sugar.– Glucose, fructose, galactose
glucose
• Disaccharide: composed of two sugars.– Short-term energy storage.– Created by dehydration synthesis of two
monosaccharides.– Examples: sucrose, maltose, lactose
• Polysaccharide: composed of many sugars.– Long-term storage– Structural materials– Starches, glycogen, cellulose
• Polysaccharide: composed of many sugars.– Long-term storage– Structural materials– Starches, glycogen, cellulose
Lipids
• Composed almost entirely of carbon andhydrogen.
• Hydrophobic and insoluble in water.
• 3 classes of lipids:– Oils, fats, and waxes– Phospholipids– Steroids, and other “fused-ring” compounds
Oils, Fats, and Waxes
• Formed bydehydration ofglycerol andfatty acid subunits.– Fatty acids are long
strands of CH2 with acarboxylic acidfunctional group(-COOH) on the end.
Oils, Fats, and Waxes•Saturated fatty acids:all excess bonds occupied byhydrogen atoms.
•Usually solid at roomtemperature.
•Unsaturated fatty acids:double-bonded carbon atoms,resulting in fewer hydrogenatoms.
•Liquid at room temperature.
Trans Fats• Chemically modified
unsaturated fats byhydrogenation.– Example: partially-
hydrogenated soybeanoil.
• Keeps oils solid atroom temperature
• Difficult to metabolize.
C
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Saturated Fat (butter, lard)
C
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cis-Unsaturated Fat (oils)
C
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trans-Unsaturated Fat (margarine)
C
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Phospholipids• Makes up the plasma membrane
surrounding cells.• Consists of
– Phosphate-nitrogen “head” (hydrophilic)– 2 fatty acid “tails” (hydrophobic).
Cell Membrane:a Phospholipid Bilayer
Hydrophilic “Head”
Hydrophobic “Tail”
Phospholipid
Lipid Bilayer
The hydrophobicinterior of themembrane inhibitswater movement,preventing leaks.
Steroids• 4 carbon rings fused together with
functional groups.• Formed by a similar biochemical
pathway as other lipids.• All are synthesized from cholesterol.
– Cholesterol comesfrom animalderived foods.
– Most animalssynthesize all theyneed.
Cholesterol• Aids in keeping the membrane fluid and protects
neurons in the brain.• Non-polar.• Carried through the bloodstream on lipoproteins.
– High-density lipoproteins (HDL) = "good" cholesterol.– Low-density lipoproteins (LDL) = "bad" cholesterol.
• LDL is ~100x largerthan HDL.
• LDL can be depositedin arteries formingplaques.
Proteins
• Composed of chains ofamino acids.
• Many different functions:– Enzymes guide chemical
reactions.– Structural proteins:
collagen, keratin.– Movement: actin and
myosin.– Defense: antibodies.
ATP Synthase
Collagen
Actin
Myosin
AntibodyProtein crystal structures from the RCSB Protein Data Bank
Amino Acids
• All amino acids share the same generalstructure:– Amino group (NH2)– Carboxylic group (COOH)– Variable group (R)
• 20 different amino acids, each with adifferent ‘R’ group.
The Twenty Amino Acids
Protein Synthesis
• Proteins are synthesized by a dehydrationreaction between two amino acids.
• Short amino acid chains are called peptides.• Longer amino acid chains (>50 aa) are called
polypeptides.
Proteins have 4 Levels of Structure1. Primary structure: sequence of amino acids.2. Secondary structure: helix or ß-sheet held together
by hydrogen bonds.3. Tertiary structure: complex 3-dimensional shape
of the polypeptide.4. Quaternary structure: individual polypeptides
subunits can link to form a larger protein.
Keratin andHair Texture
• Disulfide bondsbetween amino acids(cysteine) in keratinresult in curly, wavy, orstraight hair.
Curly Hair
Nucleic Acids• Long chains of nucleotide subunits.
– Nucleotides consist of a 5-carbon sugar, aphosphate group, and a nitrogen-containingbase (the variable group).
• Nucleotides are covalently linked via theirphosphate groups to form nucleic acids.
Two Main Typesof Nucleotides
• Ribose nucleotides(subunit of RNA)– Ribonucleic acid (RNA) is
copied from DNA and isinvolved in protein synthesis.
• Deoxyribose nucleotides(subunit of DNA)– Deoxyribonucleic acid (DNA)
contains the genetic materialof all living organisms.
DNA
• Linked deoxyribosenucleotides form asingle-stranded DNA(ssDNA) molecule.
• Two ssDNA chainsbind with hydrogenbonds between thenitrogen-containingbases to form ahelical structure.
• Other nucleotides:– Cyclic AMP (adenosine monophosphate)
– Intracellular messenger.– Adenosine triphosphate, ATP
– Energy currency of all cells.– NAD+ and FAD
– Electron carriers.
Homework
Chapter 3
Thinking Through the Concepts, Review Question #5
Applying the Concepts #1