Download hydrogen bonds - Orientamento In Rete

PROGETTO ORIENTAMENTO
IN RETE
CORSO DI
BIOLOGIA
In Inglese
UD 1
Prof.ssa LONGO
1
Organic Molecules
Organic molecules are molecules
composed of carbon and
hydrogen, and often containing
other elements such as
phosphorus, sulfur, oxygen and
nitrogen
Elements of Life
Carbon
Hydrogen
Phosphorus
Sulfur
Oxygen
Nitrogen
Six elements
make up 96%
of your mass!
Carbohydrates
There are two types of carbohydrates:
 The simple sugars
 Glucose, sucrose, fructose (and many others)
 The complex carbohydrates.
 Carbohydrates that are made of long chains of
sugars
 Starches, cellulose, glycogen
Simple Sugars
 All carbohydrates
are made up of units
of sugar (also called
saccharide units).
 Carbohydrates that
contain only one
sugar unit are called
monosaccharides.
Glucose
Fructose
Simple Sugars
 Disaccharides have two sugar units bonded
together.
 For example, common table sugar is sucrose
(below), a disaccharide that consists of a
glucose unit bonded to a fructose unit.
Complex Carbohydrates
 Complex carbohydrates are polymers of
the simple sugars.
 In other words, the complex
carbohydrates are long chains of simple
sugar units bonded together.
 For this reason the complex
carbohydrates are often referred to as
polysaccharides.
Complex Carbohydrates
Starch (below) is a polymer of the monosaccharide
glucose (n is the number of repeating glucose
units and ranges in the 1,000's).
Starches and cellulose are complex carbohydrates
used by plants for energy storage and structural
integrity.
Complex Carbohydrates
Glycogen, another polymer of glucose, is a
polysaccharide used by animals to store energy.
Both starch and glycogen are polymers of
glucose.
Starch is a long, straight chain of glucose units,
whereas glycogen is a branched chain of glucose
units.
Structure of Glycogen
Proteins
o Proteins are polymers of
amino acids.
o Amino acids all have the
general structure:
o The R in the diagram
represents a functional
group that varies depending
on the specific amino acid
in question.
Twenty amino
acids in
human
metabolism
Proteins
When 2 amino acids bond
together, water is
released as the carboxyl
end of one amino acid
bonds to the amine end of
the adjacent one forming
a peptide bond, as
illustrated at the left.
Because water is lost, the process is called:
 Condensation synthesis, or…
 Condensation polymerization
Proteins
When many amino acids bond together to create long
chains, the structure is called a protein (it is also
called a polypeptide because it contains many peptide
bonds).
Proteins
 Proteins are large molecules that may
consist of hundreds, or even thousands
of amino acids.
 Proteins are important in cell structure,
as enzymes, which speed up reactions in
the body, and as antibodies which fight
infection
Fats
Fats are a sub-group of compounds
known as lipids that are found in the
body and have the general property of
being hydrophobic (meaning they are
insoluble in water).
Other lipids include waxes, and steroids,
such as cholesterol.
Fats
Fats are also known as triglycerides, molecules
made from the combination of one molecule of
glycerol with three fatty acids.
“R” is a
long
chain of
carbon
and
hydrogen
Glycerol
Fatty
acids
Triglyceride
Fats
Fats are concentrated forms of
energy storage
 9 calories per gram
 Fats are components of cell
membranes

Properties of Water
• Polar molecule
• Cohesion and
adhesion
• High specific
heat
• Density –
greatest at 4oC
• Universal solvent
Polarity of Water
• In a water molecule two hydrogen atoms
form single polar covalent bonds with an
oxygen atom. Gives water more structure
than other liquids
– Because oxygen is more electronegative, the
region around oxygen has a partial negative
charge.
– The region near the two hydrogen atoms has
a partial positive charge.
• A water molecule is a polar molecule with
opposite ends of the molecule with
opposite charges.
• Water has a variety of unusual properties
because of attractions between these
polar molecules.
– The slightly negative regions of one molecule
are attracted to the slightly positive regions of
nearby molecules, forming a hydrogen bond.
– Each water molecule
can form hydrogen
bonds with up to
four neighbors.
Fig. 3.1
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
HYDROGEN BONDS
• Hold water molecules
together
• Each water molecule
can form a maximum
of 4 hydrogen bonds
• The hydrogen bonds
joining water
molecules are weak,
about 1/20th as strong
as covalent bonds.
• They form, break, and
reform with great
frequency
• Extraordinary Properties
that are a result of
hydrogen bonds.
– Cohesive behavior
– Resists changes in
temperature
– High heat of vaporization
– Expands when it freezes
– Versatile solvent
Organisms Depend on Cohesion
Hydrogen bonds hold the substance together, a
phenomenon called cohesion
• Cohesion is responsible for the
transport of the water column in
plants
• Cohesion among water molecules
plays a key role in the transport of
water against gravity in plants
• Adhesion, clinging
of one substance to
another, contributes
too, as water adheres
to the wall of the
vessels.
• Surface tension, a measure of the force
necessary to stretch or break the surface
of a liquid, is related to cohesion.
– Water has a greater surface tension than
most other liquids because hydrogen bonds
among surface water molecules resist
stretching or breaking the surface.
– Water behaves as if
covered by an invisible
film.
– Some animals can stand,
walk, or run on water
without breaking the
Fig. 3.3
Copyright ©surface.
2002 Pearson Education, Inc., publishing as Benjamin Cummings
– When water reaches 0oC, water becomes locked
into a crystalline lattice with each molecule
bonded to to the maximum of four partners.
– As ice starts to melt, some of the hydrogen bonds
break and some water molecules can slip closer
together than they can while in the ice state.
– Ice is about 10% less dense than water at 4oC.
Fig. 3.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Solvent for Life
• Solution
– Solute
– solvent
• Aqueous solution
• Hydrophilic
– Ionic compounds
dissolve in water
– Polar molecules
(generally) are water
soluble
• Hydrophobic
– Nonpolar
compounds
Vocabulary
• Catalyst: A substance that speeds up a
chemical reaction without itself being
changed
• Enzyme: A biological catalyst that is
usually a protein
• Substrate: The reactant(s) upon which
an enzyme has its action
• Product: A substance that results from
a chemical reaction
Catalysts Lower Activation Energy
Enzyme-Substrate Interaction
Enzyme Inhibition
Enzymes are…
• Essential to all forms of life
• Not “used up” by the reaction that
they catalyze
• Specific to the reaction that they
catalyze