Download Organic Molecules

Organic Molecules
(Figure 2-14; Table 2-4)
• “Organic” describes compounds that contain C–C or
C–H bonds
• Carbohydrates
– Organic compounds containing carbon, hydrogen, and
oxygen
– Commonly called sugars and starches
• Monosaccharides
– Simple sugars with short carbon chains; those with six carbons
are hexoses (e.g., glucose), whereas those with five are
pentoses (e.g., ribose, deoxyribose) (Figure 2-15)
• Disaccharides and polysaccharides
– Two (di-) or more (poly-) simple sugars that are bonded
together through a synthesis reaction (Figure 2-16)
Organic Molecules
• Proteins (Table 2-5)
– Most abundant organic compounds
– Chainlike polymers
– Amino acids—building blocks of proteins
(Figures 2-17 to 2-19)
• Essential amino acids
– Eight amino acids that cannot be produced by the
human body
• Nonessential amino acids
– 12 amino acids can be produced from molecules
available in the human body
Organic Molecules
• Amino acids consist of:
– Carbon atom
– Amino group
– Carboxyl group
– Hydrogen atom
– Side chain
Organic Molecules
• Levels of protein structure (Figure 2-20)
– Protein molecules are highly organized and show a
definite relationship between structure and function
– There are four levels of protein organization:
• Primary structure—refers to the number, kind, and sequence
of amino acids that make up the polypeptide chain
• Secondary structure—polypeptide is coiled or bent into
pleated sheets stabilized by hydrogen bonds
• Tertiary structure—a secondary structure can be further
twisted, resulting in a globular shape; the coils touch in many
places and are “welded” by covalent and hydrogen bonds
• Quaternary structure—highest level of organization occurring
when protein contains more than one polypeptide chain
Organic Molecules
• Structural proteins form the structures of the body
• Functional proteins cause chemical changes in
the molecules
– Shape of a protein’s molecules determines its function
• Denatured proteins have lost their shape and therefore their
function Proteins can be denatured by changes in pH,
temperature, radiation, and other chemicals
• If the chemical environment is restored, proteins may be
renatured and function normally
Organic Molecules
• Lipids (Table 2-6)
– Water-insoluble organic molecules that are
critically important biological compounds
– Major roles:
• Energy source
• Structural role
• Integral parts of cell membranes
Organic Molecules
• Lipids (cont.)
– Triglycerides, or fats (Figures 2-22 and 2-23)
• Most abundant lipids and most concentrated
source of energy
• The building blocks of triglycerides are glycerol
(the same for each fat molecule) and fatty acids
(different for each fat, they determine its chemical
nature)
– Types of fatty acids—saturated fatty acid (all available
bonds are filled) and unsaturated fatty acid (has one or
more double bonds)
– Triglycerides are formed by a dehydration synthesis
Organic Molecules
• Lipids (cont.)
– Phospholipids (Figure 2-25)
• Fat compounds similar to triglyceride
• One end of the phospholipid is water-soluble
(hydrophilic); the other end is fat-soluble
(hydrophobic)
• Phospholipids can join two different chemical
environments
• Phospholipids may form double layers called
bilayers that make up cell membranes
Organic Molecules
• Lipids (cont.)
– Steroids (Figure 2-26)
• Main component is steroid nucleus
• Involved in many structural and functional roles
Organic Molecules
• Lipids (cont.)
– Prostaglandins
• Commonly called
“tissue hormones”;
produced by cell
membranes throughout
the body
• Effects are many and
varied; however, they
are released in
response to a specific
stimulus and are then
inactivated
Organic Molecules
• Nucleic Acids
– DNA (deoxyribonucleic acid)
• Composed of deoxyribonucleotides; that is,
structural units composed of the pentose sugar
(deoxyribose), phosphate group, and nitrogenous
base (cytosine, thymine, guanine, or adenine)
• DNA molecule consists of two long chains of
deoxyribonucleotides coiled into double-helix
shape (Figure 2-27)
• Alternating deoxyribose and phosphate units form
backbone of the chains
Organic Molecules
• DNA (cont.)
– Base pairs hold the two chains of DNA
molecule together
– Specific sequence of more than 100 million
base pairs constitute one human DNA
molecule; all DNA molecules in one individual
are identical and different from those in all
other individuals
– DNA functions as the molecule of heredity
Organic Molecules
• Nucleic acids
– RNA (ribonucleic acid)
• Composed of the pentose sugar (ribose),
phosphate group, and a nitrogenous base
• Nitrogenous bases for RNA are adenine, uracil,
guanine, or cytosine (uracil replaces thymine)
• Some RNA molecules are temporary copies of
segments (genes) of the DNA code and are
involved in synthesizing proteins
• Some RNA molecules are regulatory, acting as
enzymes (ribozymes) or silencing gene expression
(RNA interference)
Organic Molecules
• Nucleic acids and related molecules
(cont.)
– NAD and FAD (Figure 2-31)
• Used as coenzymes to transfer energy-carrying
molecules from one chemical pathway to another
– cAMP (cyclic AMP)
• Made from ATP by removing two phosphate
groups to form a monophosphate
• Used as an intracellular signal
Organic Molecules
• Combined forms (cont.)
– Examples:
• Adenosine triphosphate (ATP)—two extra
phosphate groups to a nucleotide
• Lipoproteins—lipid and protein groups combined
into a single molecule
• Glycoproteins—carbohydrate (glyco, “sweet”) and
protein
Metabolism
• Catabolism
– Larger molecules  smaller chemical units
– Usually hydrolysis
– Release energy
+ H2O
Hydrolysis
Large Molecule
Small Molecules
Metabolism
• Anabolism
– Smaller subunits  Larger molecules
– Dehydration synthesis
– Requires energy (ATP)
+ H2O
Dehydration Synthesis
Small Molecules
Large Molecule
Metabolism
• Adenosine Triphosphate (Figure 2-29)
– Pentose sugar (ribose)
– Nitrogen-containing molecule (adenine)
– Three phosphate groups
– High-energy bonds
Organic Molecules
• Nucleotides (cont.)
– ATP (cont.)
• High-energy bonds present between phosphate groups
• Cleavage of high-energy bonds releases energy during
catabolic reactions
• Energy stored in ATP is used to do the body’s work
• ATP often called the energy currency of cells
• ATP is split into adenosine diphosphate (ADP) and an
inorganic phosphate group by a special enzyme
• If ATP is depleted during prolonged exercise, creatine
phosphate (CP) or ADP can be used for energy