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Carbon and Life Part 3 VoiceThread Transcript

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.

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