Lipids,proteins, and nucleic acids

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Transcript Lipids,proteins, and nucleic acids

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
* 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 (1)
• Three fatty acids bonded to glycerol by
dehydration synthesis
Triglyceride Synthesis (2)
• Triglycerides are called neutral fats
– fatty acids bond with their carboxyl ends, therefore no
longer acidic
• Hydrolysis of fats occurs by lipase enzyme
• Triglycerides at room temperature
– liquids called oils, often polyunsaturated fats from
– solids called fats, saturated fats from animals
• Function - energy storage
– also insulation and shock absorption for organs
• 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.
A Phospholipid - Lecithin
• Cluster in water as their hydrophobic tails
turn away from water (micelle formation).
• Major constituents of cell membranes.
• 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
• 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
– amino acid properties
determined by -R group
• The amino acids in a
protein determine its
structure and function
Amino Acids
• Nonpolar -R
groups are
• Polar -R groups
are hydrophilic
• Proteins contain
many amino acids
and are often
• -R groups
determine shape
of protein
• A polymer of 2 or more amino acids
• Named for the number of amino acids they
– 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
Dipeptide Synthesis
Protein Structure
• Primary structure
– determined by amino acid sequence
• 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
Primary Structure of Insulin
• Composed of two
polypeptide chains
joined by disulfide
• Frederick Sanger
determined amino
acid sequence
(early 1950s).
Conjugated Proteins
• 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
Sickle Cell Anemia
• Caused by one
different amino acid in
• Genetic
• Pain in joints
• No cure at present
• Strangely Sickle Cell
raises resistance to
Protein Conformation and
• Conformation - overall 3-D shape is crucial to
– 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
• Function as catalysts
– promote rapid reaction rates
• Substrate - the substance an enzyme acts
• 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
Enzymes and Activation Energy
Enzyme Structure and Action
• 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
Enzymatic Reaction Steps
Metabolic Pathways
• Chain of reactions, each catalyzed by an
 
– 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
• 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
*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
Nucleic acids are made from
Each nucleotide consists of:
1. A five carbon sugar;
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 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 sugarphosphate 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.
Model of DNA