BIOL-102 6/2 (unit 2)

Organic Chemistry and Carbon-Based Life

• Organic refers to being carbon-based.
• All known life is carbon-based, though theories exist for non-carbon-based life.

Carbon

• Carbon has six protons and six electrons.
• It can form four bonds due to its four valence electrons.
• Smallest atom that can make the most bonds which allows for diversity of shape and function.
• Being small maximizes variability because when it get's bulky it doesn't allow much flexibility.

Carbon's Special Properties

• Four valence electrons allow it to form four covalent bonds.
• Small size compared to other elements that can form four bonds.

Silicon as an Alternative

• Silicon is theorized as another possible basis for life because:
  • It is the next smallest element that can create four covalent bonds.
  • Has the second best diversity of function and shape.
  • Theories suggest silicon-based life may exist on other planets.

Carbohydrates

• Carbohydrates are based on the presence of five carbons.

Use cases for Carbohydrates

• Energy: Provide energy, like the "sugar rush" effect.
• Structure: Example: Chitin in exoskeletons of shrimp and grass.
• Stored Energy: Starch serves as stored energy reserves.

Types of Sugars

• Sugars can be linear or, more commonly, depicted as a ring.

Monosaccharides:

• Single sugar unit.
• "Mono" means one (e.g., monocycles).

Disaccharides:

• Two sugars bonded together.
• "Di" means two (e.g., bicycle).
• Example: Lactose (glucose + galactose).
• Lactose is broken down into galactose and glucose used for energy.

Polysaccharides:

• Multiple or many sugars linked together.

• "Poly" means multiple or many.

• Example: Cellulose (wood), which is a string of glucose molecules.

• In water, sugars are usually in their ring structures; outside of water, they are more commonly in chain configurations.

ATP: The Currency of the Cell

• The way that I refer to ATP is I call it the currency of the cell.
• The reason why is because in life, almost everything that you do in life falls in one of two categories.
• It either costs money or you're doing it to hopefully make money.

Isomers

• Isomers: Molecules with the same chemical formula but different arrangements.
• Examples: Glucose, galactose, and fructose (C6H{12}O_6).
• They are hexose sugars (six carbons).
• Arrangement matters.
• Notice: Fructose is pentagon shaped (but still a hexose sugar).
• Difference: Hydroxide (OH) orientation.

Common Sugars

• Disaccharides (e.g., sucrose, lactose)
• Disaccharides listed have glucose, which is used to make ATP.

Polysaccharides (Strings of Glucose)

• Starch and cellulose are common examples.
• Both are polysaccharides made by plants.

Cellulose vs. Starch

• Cellulose: Every other glucose molecule is flipped upside down.
• Cellulose is referred to as fiber on nutritional labels.
• Cows can digest cellulose due to microorganisms in their digestive systems.
• Humans cannot effectively break down cellulose.
  • Humans are able to eat starch because, when you eat starch, you break those glucose molecules off and use them for energy.

Glycogen:

• Glycogen: Animal equivalent of starch.
• Plants store glucose as starch; animals store glucose as glycogen.
• Glycogen features side branches instead of a regular chain.

Chitin

• Chitin: Alternate flipped glucoses create a rigid structure.
• Examples: Wood and lobster shells.
• Animals use it to make exoskeletons; plants use it to make cell walls.

Food Labels

• Total carbs = Sugar + Fiber + Starch
• You can determine starch by looking at carbs and then subtracting sugar and fiber.