Macromolecules of Life:
Carbohydrates and Lipids
January 28, 2004

Readings: Starr, Chapter 3 pages 34-35, 38-41. Don't forget This Week's WarmUp and Good For
Trans Fats 101: What are some of the health effects of partially hydrogenated oils like margerine and shortening?

The object of opening the mind, as of opening the mouth, is to shut it again on something solid.
- Gilbert Keith Chesterton, 1864-1936

I. Living matter is made of cells, but what are cells made of?

Cells are made of molecules based on based on 4 main chemical elements: carbon, nitrogen, oxygen, and hydrogen (plus lots of other elements) and the many compounds that can be made from combining these elements.

Cells put the chemical "building blocks" C, O, H, and N (and others) together to make useful molecules for food and energy that allow them to perform the 5 functions of life.

Enzymatic reactions inside cells join together small organic molecules (monomers; building blocks) to form large molecules (polymers) by a process called dehydration synthesis, to make Macromolecules:

The 4 main macromolecules in cells made largely from C, O, H, and N are Carbohydrates, Lipids, Proteins, and Nucleic Acids.

For each of these 4 macromolecules, I would like you to know:

1. What the monomer (basic building block) is
2. What types of polymers result
3. What the functions of each macromolecule are in cells.

II. Carbohydrates (sugars, starches, cellulose)

• Made from joining H2O and CO2 by plants during photosynthesis (we will discuss this on February 12)
• Monomer: Simple sugars: CH2O (ratio of one carbon and one oxygen to every 2 hydrogens)
• Bread, cereal, potatoes, fruits, vegetables, and pasta = are made mostly of carbohydrates (sugars and starches).
• Three main functions: energy for cells, structural support, cell-cell communication

1. A. Monosaccharides (simple sugars; monomers) = energy for cells

• Glucose: grape sugar, corn sugar, dextrose
• Fructose: honey
• Galactose: part of milk sugar (lactose)

This is a molecule of glucose. We will discuss on February 17 about how glucose, our body's main fuel, is broken down during cellular respiration to result in energy for our cells.

1. B . Disaccharides (double sugars) or oligosaccharides (short-sugars) = energy for cells

• Maltose = glucose - glucose (brewing beer)
• Lactose = glucose - galactose (milk sugar)
• Sucrose = glucose - fructose (table sugar)

2. Polysaccharides (long chains of sugar polymers) - these sugar polymers are not "sweet" although they are made up of repeating glucose monomers!

• Starch (plants), glycogen (animals): storage polymers

Function: Energy storage
Examples: Potatoes - pure starch! Pasta, bread, crackers - ground up wheat starch
Structure: 1-4 linkage of a-glucose

Note: animal cells can't make sugars "from scratch", but can polymerize plant sugars into glycogen , a related storage polymer.

• Once we have eaten, monosaccharides, disaccharides and starches are converted to the monomer glucose, our bodys preferred fuel, and circulate through the blood (reserves are stored in our bodies as glycogen).
• Disorders of blood glucose (diabetes, hypoglycemia) are very serious!
• Why is it better to eat "complex carbohydrates" (poly-saccharides) over "simple" or "refined carbohydrates" (mono- and disaccharides)?

• Cellulose (plants), chitin (insects, fungi): structural polymers

Function: Structural support
Examples: Cellulose: Paper, wood, cotton, the chewy stuff in celery.... Chitin: The crunchy exoskeleton of insects and shrimp, the soft spongy material that makes up a mushroom.
Structure: 1-4 linkage of b-glucose

Note: These structural polymers are almost indigestable...which is a good thing since they function as structural support! Some animals (like cows) and insects (like termites) have special bacteria in their intestines that can break the 1-4 linkage of b-glucose...but we cannot break this bond!

 

3. Glyco-proteins and Glyco-lipids: Cell-cell communication

Function: Cell-cell commnication, Cell recognition: "Self" vs. "non-self" immune response, cell adhesion (cells sticking together).
Examples: The ABO blood groups in humans are the result of red blood cells coated with specific O-type, A-type and/or B-type glycoproteins ("sugar-proteins") and glycolipids ("sugar-lipids"); the immune response to pathogenic bacteria is often stimulated by the glycoproteins on the surface of the bacteria, organ transplant rejection, etc!
Structure: A few of the most common sugars in cell-cell communication are Galactose, Glucose, Mannose, Sialic Acid, N-acetyglucosamine, and many others! (You do not need to know the names of these sugars). Sugars come in so many three-dimensional shapes, and connect to each other and to proteins and lipids in so many ways that an almost infinite number of possible combinations is possible - allowing cells to precisely differentiate between "self" and "non-self".

Note: Over 60% of all proteins (and many lipids) in cells are bound to sugar molecules, including antibodies, some hormones, and many other cellular enzymes, and plasma membrane lipids.

Just checking: What questions do you have about Carbohydrates? Make sure you understand their basic structure and their 3 main functions!!!

III. Lipids - Fats, oils, phospholipids, and steroids - All are hydrophobic (water-hating)! 3 main types:

1. Triacylglycerols (fats and oils)

• Structure: Made from 1 glycerol + 3 fatty acid tails = tri-acylglycerol
• Example: Fats: Butter, lard Oils: Corn oil, olive oil, margerine
• Note: Vary in length and location of double bonds in tail (we will talk about the significance of these bonds in "nutrition" below.)

TWO major functions of fats and oils:

A. Energy storage. Fats are a more compact fuel than starch.

• Fat contains twice the energy-rich (C-H) bonds as glucose
• Fat stores twice as much energy as glucose
• Fat produces twice as many calories (9 kcal/gm vs 4 kcal/gm) when burned
• Unfortunately, you need to put twice as much energy to burn off a pound of excess fat than you do of glycogen...

B. Cushions and insulates the body and nerves. Each and every one of your nerves is wrapped in a lipid-rich layer called the myelin sheath.

2. Diacylglycerides (phospholipids): lipid bilayers (the plasma membrane of every cell and the membranes within eukaryotic cells)

• Structure - similar to a triacylglycerol, but has only 2 fatty acid tails, and in addition has a phosphate group = (1 glycerol, 2 fatty acids, and a -PO4)

• The -PO4 makes the glycerol "head" water soluble, or hydrophilic.
• The long hydrocarbon tail is hydrophobic.

• Function: Due to this "amphipathic" nature (both water-loving and water-hating regions in a single molecule), phospholipids self assemble into bilayers that shield the tail from water = forming membranes (phospholipid bilayers!).

3. Steroids: (cholesterol, steroid hormones)

• Structure: Considered to be a "cousin" of fats - and are made from lipids. Have no fatty acids in their structure, but are very hydrophobic , see Fig 3.10b in your book
• Functions of Chloesterol:
  • (1) Help to maintain membrane fluidity, pliability and resilience in membranes of animals, which have high amounts or rigid, saturated fatty acids.
  • (2) Sex hormones (testosterone, estrogen and progesterone) are all made from cholesterol
• Cholesterol gets a 'bad rap" in our diet, but has CRUCIAL roles in the functioning of our cells - we couldn't live without cholesterol!!!
• However, too much cholestereol in the diet is known to be a factor in atherosclerosis and heart disease.
• Cholesterol circulates in the bloodstream bound to carrier 'lipo-proteins'. High Density Lipoprotein (HDL - the "Good" kind) carries blood cholesterol to the liver where is can be eliminated from the body. Low Density Lipoprotein (LDL - the "Bad" kind) deposits blood cholesterol in the artery walls, where it can lead to constriction of blood vessels, heart disease, heart attacks, etc.

IV. Fats and Nutrition: Confused about dietary fat and health? There is a LOT of conflicting information on fats, oils, butter vs. margerine, olive oil vs. fish oil..it's enough to make your head swim!!! Here is a summary about the differences between fats and some of the possible health effects of each fat. A good article about fats can be found here from the American Heart Association

Saturated (fats): no double bonds; saturated with hydrogens.	Solid at room temperature - animal fats (bacon, lard, butter, palm oil, coconut oil). These fats raise total blood cholesterol level, HDL and LDL, and have been shown to increase the risk of coronary heart disease.
MonoUnsaturated (oils): a double bond ("kink") forms (loss of 2 hydrogens).	Liquids at room temperature - olive oil, canola oil, peanut oil. These are the GOOD fats - they lower total blood cholesterol by raising HDL (good) cholesterol and lowering LDL (bad) cholesterol levels.
PolyUnsaturated (oils): more than one double bond ("kink") forms (loss of more than 2 hydrogens).	Liquids at room temperature - corn oil, soybean oil, Omega-3 and -6 fish oils. These are also the GOOD fats - they lower total blood cholesterol by lowering both HDL (good) and LDL (bad) cholesterol.
Hydrogenated oils (margarine, crisco) - hydrogens are added synthetically to plant oils to create trans-fatty saturated acids.	Solids at room temperature - these oils are factory-made by adding hydrogens to liquid vegetable oil, creating a solid shortening or margarine. Evidence has been accumulating for over 10 years that these 'trans-fats' have adverse effects on health - Are thought to raise both LDL (bad) cholesterol and lower HDL (good) cholesterol levels. and can be even worse that saturated animal fat in the development of coronary heart disease. Starting in 2006, all food labels will be required to list the amount of trans-fats, and numerous food companies like Kraft Nabisco are taking big steps to reduce the amounts of trans-fats in your foods.

*Note: these categories describe the most prominent fat found; for instance, corn oil has MORE polyunsatuated fat than monounsaturated fat, so it is considered to be polyunsaturated; butter is mostly saturated fat but also contains some unsaturated fat, etc)

Objectives:

For each of the macromolecules discussed today and Monday, make sure you understand in each case:

1. What the monomer is
2. What types of polymers result
3. What the functions of each macromolecule are in cells.

You may want to make one big chart with room for this information as well as for simple sketches.

For today, specifically:

1. Compare and contrast the difference between monosaccharides and disacharides. Make sure you can list a yummy example of each.
2. Compare and contrast the polysaccharides starch and cellulose. How are they alike - and what is their ONE crucial difference? Give examples of foods we eat that contain these macromolecules.
3. How do sugars help our body tell which cells are 'self' and which cells are foreign?
4. Compare and contrast TRI-acylglycerols and DI-acyl glycerols - what is the function of each? How are their structures similar and different? Where are BOTH of these types of molecules made in cells?
5. What is cholesterol and what role does it play in our body's normal functioning?
6. Compare and contrast saturated fat, mono-and poly-unsaturated fat, and trans fat in terms of where they come from and their effects on blood cholesterol.
7. What is Olestra?