Slide 1
Carbohydrates are commonly referred to as sugars. The
monomers of carbohydrates are the monosaccharides or simple sugars.
Examples of monosaccharides are glucose and fructose.
Slide2
Simple sugars join together to make more complex disaccharides -
sugars made of two monosaccharides. An example is sucrose which is table
sugar or lactose - the sugar found in dairy products.
Slide 3
Polysaccharides are long chains of monosaccharides. For
example the starches are long chains of glucose monomers. The difference
between the different types of starches shown on this image is the way the
glucose units are linked together.
Starches are polysaccharides that are mainly used for energy storage. Plants store energy as starches - when you eat a potato or a carrot you are eating the plants energy stores that it could use later to fuel cellular metabolism.
Glycogen is an animal starch that is mainly stored in the liver and muscle cells. Endurance athletes "hit the wall" when their glycogen stores are depleted. For marathon runners this is usually around the 20 mile mark - part of marathon training is to train the body to use glycogen efficiently. Carboloading (or eating lots of carbohydrates) before an event is one way to help avoid glycogen depletion.
Slide 4
Structural polysaccharides help provide structural support to
cells and organisms. Plant cells have strong cell walls made of
cellulose which is a long chain of repeating glucose units.
The fungi and some animals use a structural polysaccharide known as chitin to provide structural support. Animals like this fiddler crab have a hard exoskeleton made of chitin - this exoskeleton provides strong support for muscles as well as protection against drying out and being damaged by predators.
Slide 5
The lipids are commonly referred to as fats. One important
distinction between the lipids and the other macromolecules is that the lipids
are not polymers. All of the other macromolecules are polymers.
The lipids are structurally diverse but they all share the characteristic that
they are hydrophobic or repelled by water.
Slide 6
The dietary fats or triacylglycerols are comprised of a glycerol
bonded to three fatty acid chains. A fatty acid is a long chain of
carbons and hydrogens. This is a very energy rich molecule - the fats
are an excellent source of calories.
Slide 7
The dietary fats can be described as being either saturated or
unsaturated. Saturated fats tend to be solid at room temperature like
butter or lard. The saturated fats are defined as having only single
bonds between the carbons of the hydrocarbons. This means the fatty
acids are saturated with carbon atoms. The linear structure of these
fatty acids allow them to pack tightly and are usually solid at room
temperature.
The unsaturated fats have at least one double bond between two carbon atoms in the fatty acid chains. The result is a kink in the structure of the fatty acid - the chains can't pack as tightly and the unsaturated fats tend to be liquid at room temperature. Vegetable oils and fish oils are examples of unsaturated fats.
Slide 8
The phospholipids are strcuturally similar to the dietary fats in
that there is glycerol attached to two fatty acid chains. The
phospholipids are the main component of cell membranes. They have a
hydrophilic water-loving head region and a hydrophobic water-repelling tail
region.
Slide 9
When phospholipids are placed in water the hydrophobic and
hydrophilic regions interact with the water to make a bilayer. The
hydrophilic heads align themselves so they are in contact with the water while
the hydrophobic tails align themselves so that they are buried inside the
bilayer and away from the water. This bilayer is the main component of
our cell membranes and it regulates the movement of other essential molecules
in and out of the cell. Hydrophobic - hydrophilic interactions are very
important in biology - we will see more examples of these interactions as we
move through the course.
Slide 10
The final group of lipids are the steroids. Structurally
they are very different from the dietary fats and phospholipids. The
steroids are characterized by a fused ring structure and the sex hormones are
an example of steroids. We can look at the structures of testosterone
and estrogen to illustrate an important point in biology. Subtle changes
in structure can lead to very different functions or chemical behaviors.
Estrogen and testosterone are structurally very similar but they have very
different effects on an organism.
Slide 11
We can see an example of these different effects by observing a
bird that has a condition known as bilateral gynandromorphy. The two
outer birds are normal - the one on the left is a male evening grosbeak and
the one on the right is a female. The one in the middle is both male and
female - male on the left half and female on the right half. This
condition results from a mistake in mitosis in early embryonic
development. This mistake causes the sex chromosomes to distribute
abnormally. The left side of the bird is male and thus more sensitive to
testosterone. The right side of the bird is female and thus more
sensitive to estrogen. The dramatically different sides of this bird are
due to the dramatically different behaviors of estrogen and testosterone.
Slide 12
This phenomenon has been observed not only in birds but in
insects like this butterfly and crustaceans like this crab.