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Organic Molecules: Lipids
• Hydrophobic organic molecules
• More calories per gram than carbohydrates.
• Four primary types:– fatty acids– triglycerides– phospholipids– steroids
Fats are macromolecules constructed from:
• Glycerol, a three-carbon alcohol.
• Fatty acids *Composed of a carboxyl group at one end and
an attached hydrocarbon chain (“tail”).
* Carboxyl group (“head”) has properties of an
acid.
* Hydrocarbon chain – long carbon skeleton.
Non-polar C-H bonds make the chain
hydrophobic and not water soluble.
Fatty Acids
• Chain of usually 4 to 24 carbon atoms
• Carboxyl (acid) group on one end and a methyl group on the other
• Polymers of two-carbon acetyl groups
Fatty Acids• Saturated fatty acid - carbon atoms saturated
with hydrogen • Unsaturated fatty acid - contains C=C bonds
that could bond more hydrogen
Triglyceride Synthesis (2)
• Triglycerides are called neutral fats– fatty acids bond with their carboxyl ends, therefore no
longer acidic
Triglycerides
• Hydrolysis of fats occurs by lipase enzyme
• Triglycerides at room temperature– liquids called oils, often polyunsaturated fats from
plants– solids called fats, saturated fats from animals
• Function - energy storage– also insulation and shock absorption for organs
Phospholipids
• Composed of a hydrophilic “head” attached to two fatty acids.
• Third fatty acid is replaced with a negatively charged phosphate group.
• Can have small variable molecules (usually polar or charged) attached to phosphate.
Phospholipids• Cluster in water as their hydrophobic tails
turn away from water (micelle formation).
• Major constituents of cell membranes.
Steroids• Cholesterol
– other steroids derive from cholesterol• cortisol, progesterone, estrogens, testosterone and
bile acids
– is an important component of cell membranes – produced only by animals
• 85% naturally produced by our body • only 15% derived from our diet
Cholesterol
• All steroids have this 4 ringed structure with variations in the functional groups and location of double bonds
Cholesterol – LDL vs. HDL
• LDL: “Bad” cholesterol– Low-density Lipoprotein
– Builds up as plaques in arteries causing heart attacks
– Hydrogenated oils & trans fatty acids are sources
• HDL: “Good” cholesterol– High-density Lipoprotein
– Removes LDL cholesterol
back to the liver
Organic Molecules: Proteins• Polymer of amino acids
• 20 amino acids– identical except for -R
group attached to central carbon
– amino acid properties determined by -R group
• The amino acids in a protein determine its structure and function
Amino Acids• Nonpolar -R
groups are hydrophobic
• Polar -R groups are hydrophilic
• Proteins contain many amino acids and are often amphiphilic
• -R groups determine shape of protein
Peptides
• A polymer of 2 or more amino acids• Named for the number of amino acids they
contain– dipeptides have 2, tripeptides have 3– oligopeptides have fewer than 10 to 15 – polypeptides have more than 15– proteins have more than 100
• Dehydration synthesis creates a peptide bond that joins amino acids
• Secondary structure– α helix (coiled), β-pleated sheet (folded) shapes held
together by hydrogen bonds between nearby groups
• Tertiary structure– interaction of large segments to each other and
surrounding water
• Quaternary structure– two or more separate polypeptide chains interacting
Protein Structure• Primary structure
– determined by amino acid sequence
Primary Structure of Insulin
• Composed of two polypeptide chains joined by disulfide bridges
• Frederick Sanger determined amino acid sequence (early 1950s).
• Contain a non-amino acid moiety called a prosthetic group
• Hemoglobin has 4 polypeptide chains, each chain has a complex iron containing ring called a heme moiety
Conjugated Proteins
Sickle Cell Anemia
• Caused by one different amino acid in hemoglobin
• Genetic• Pain in joints• No cure at present• Strangely Sickle Cell
raises resistance to Malaria
Protein Conformation and Denaturation
• Conformation - overall 3-D shape is crucial to function– important property of proteins is the ability to
change their conformation• opening and closing of cell membrane pores
• Denaturation– drastic conformational change that destroys
protein function• occurs with extreme heat or pH• often permanent
Enzymes• Function as catalysts
– promote rapid reaction rates
• Substrate - the substance an enzyme acts upon
• Naming convention– enzymes now named for their substrate with -ase
as the suffix• amylase enzyme digests starch (amylose)
• Lower activation energy – energy needed to get reaction started is lowered
• enzymes facilitate molecular interaction
• Active sites– area on enzyme that attracts and binds a substrate
• Enzyme-substrate complex– temporarily changes a substrate’s conformation, promoting
reactions to occur
• Reusability of enzymes– enzymes are unchanged by reactions and repeat process
• Enzyme-substrate specificity– active site is specific for a particular substrate
• Effects of temperature and pH– change reaction rate by altering enzyme shape– optimum: temp = body temp, pH = location of enzyme
Enzyme Structure and Action
Metabolic Pathways• Chain of reactions, each catalyzed by an
enzyme • A B C D
– A is initial reactant, B+C are intermediates and D is the end product
, , represent enzymes
• Regulation of metabolic pathways– activation or deactivation of the enzymes in a
pathway regulates that pathway• end product D may inhibit or enzymes
Protein Functions• Structure
– collagen, keratin
• Communication– some hormones, cell receptors
• ligand - molecule that reversibly binds to a protein
• Membrane Transport– form channels, carriers (for solute
across membranes)
• Catalysis– enzymes are proteins
Protein Functions 2
• Recognition and protection– glycoprotein antigens, antibodies and clotting
proteins
• Movement– muscle contraction– cilia and flagella– spindle fibers
• Cell adhesion– proteins bind cells together
Nucleic Acids• The primary structure of proteins is
determined by genes – hereditary units that consist of DNA, a type of nucleic acid.
• There are two types of nucleic acid: 1. Deoxyribonucleic acid (DNA)
*Contains coded info that programs all cell activity.
*Contains directions for its own replication. *Copied and passed on from one generation to another. *In eukaryotic cells, it is found primarily in the nucleus.
Nucleic Acids
The second type of nucleic acid is:
2. Ribonucleic acid (RNA)
*Functions in the actual synthesis of proteins
coded for by DNA.
*Ribosomes – sites of protein synthesis.
*Messenger RNA (mRNA) – carries encoded
genetic message from nucleus to cytoplasm.
*Flow of genetic info: DNA →RNA →Protein
2. A phosphate group attached to the number 5 carbon of the sugar; and
3. A nitrogenous base at C1
*There are two families of nitrogenous bases:
1. Pyrimidines
2. Purines
DNA
DNA is a polymer of nucleotides
joined by linkages between the
phosphate of one nucleotide
and the sugar of the next.
Variable nitrogenous bases
are added to this sugar-
phosphate backbone.
Watson and Crick – 3D Structure of DNA (1953)
• Two nucleotide chains wound as a double helix.• S-P backbones on outside of helix.• N bases paired in the interior of the helix and are
held together by H-bonds.• Base-pairing rules: guanine (G)-cytosine (C) and
thymine (T)-adenine (A).• Two strands of DNA are complementary – serve
as templates.• Most DNA molecules are long – thousands to
millions of base pairs each.
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