Basic Biological Molecules #1

Chapter 2: Pg. 39-60

How many bonds on a carbon?

4

What are hydrocarbons made of?

Hydrogen and carbon

What are functional groups?

Certain groups that work as a unit and are responsible for giving organic molecules their:

* Physical properties
* Chemical reactivity
* Solubility in solution.

Name some functional groups

* Hydroxyl
* Amino
* Methyl
* Carbonyl
* Carboxy
* Sulfhydryl

Chemical properties of functional groups/How do these affect the properties of the parent molecule?

If you have a parent molecule, different compounds can be created depending on which functional group is used

How does ethane change when a hydroxyl group is added?

* Hydrocarbon ethane is CH3CH3
* It is toxic and a flammable gas
* If you take out one of the hydrogens and add a hydroxyl group (OH) to it, then, you have CH3CH2OH which is ethanol
* Ethanol is palatable

How does ethane change when a carboxyl group is added?

Substitute a carboxyl group (COOH) and the molecule becomes acetic acid

What are carbohydrates?

* Large simple sugar molecules made of sugar building blocks
* Function is to mainly store chemical energy and act as durable building materials for construction

What is the formula for carbohydrates/sugars?

(CH2O)n

What is a 3-carbon sugar?

Triose

What is n in the carbohydrate formula?

* The sugars that are important for cellular metabolism have n values that range from 3-7
* N is the number of carbons

What is a 4-carbon sugar?

Tetrose

What is a 6-carbon sugar?

Hexose

What is a 5-carbon sugar?

Pentose

What is a 7-carbon sugar?

Heptose

How are carbohydrates classified?

* Number of carbons
* Ketose/aldose
* Straight chain vs ring form

What is a ketose?

* When looking at the structure of a simple sugar, you can see that there is a backbone made of carbon atoms with single bonds and each carbon atom is linked to a hydroxyl group
* The exception is when there is a carbonyl group located at an internal position which forms a ketone group
* The sugar is ketose and the monosaccharide example is fructose

What is aldose?

* An aldehyde group forms when the carbonyl is located at one end of the sugar
* The molecule is called an aldose and the monosaccharide example is glucose

What is a stereoisomer?

* When you have two possible configurations that can’t be superimposed on one another; the two molecules are then called stereoisomers
* They have the same chemical reactivities; however, their structures are mirror images (right and left hands)

In terms of glucose, what is the difference between the D and L forms?

* The D form is when the hydroxyl (OH) group on the asymmetric carbon projects to the right
* The L form is when the hydroxyl group projects to the left
* Look at the chiral carbon farthest from the carbonyl group

Why is it important for the cell to know the difference between D and L forms?

* When you have living cells, they can detect which is the D form and which is the L form of a sugar
* Usually, the cell only uses one of the stereoisomers

In terms of glucose, what is the difference between the alpha and beta rings?

* Not like the precursor in the open chain, the C of the ring has 4 different groups and will have a new center of asymmentry and can be found within the sugar molecule
* Due to the extra asymmetric carbon atom, each pyranose (six-membered ring) exists as alpha and beta stereoisomers
* When the OH group on the first carbon projects below the plane of the ring, it is an alpha-pyranose
* When the hydroxyl projects upward on the first carbon, it is a beta-pyranose

Why is it important for the cell to know the difference between alpha and beta rings?

* The differences between the alpha and beta forms are important because biological consequences could result
* Ex: The compact shape of glycogen and starch molecules as well as the extended conformation of cellulose

Why do we care about stereoisomers?

* The shape of the key matters; it functions differently if the shape is different
* Ex: changing the hydroxyl group from the left to the right
* Changes in formation (conformational changes) affect function

What is sucrose?

* Disaccharides that can be joined to one another by covalent glycosidic bonds to make larger molecules
* Also known as table sugar
* Major component of plant sap which carries chemical energy from one section of the plant to another part

Is sucrose a sugar?

Yes

What is the composition of sucrose?

Sucrose is a disaccharide made up of glucose and fructose monosaccharides

What kind of bonds does sucrose have?

Covalent glycosidic bonds (alpha 1,2 linkage)

What is lactose?

* Lactose is in the milk of most mammals
* It gives fuel for baby mammals to grow and develop
* When consumed, lactose is hydrolyzed by the enzyme, lactase, which is found in the plasma membranes of the cells that line the intestine
* Several people lose this enzyme after childhood and can’t consume dairy afterward

Is lactose a sugar?

Yes

What is the composition of lactose?

Lactose is a disaccharide made up of glucose and galactose monosaccharides

What kind of bonds does lactose have?

Glucose \[4\] and galactose \[1\] beta 1,4 linkage

What are some examples of common monosaccharides?

* Fructose
* Glucose
* Galactose

What does maltose, sucrose, and lactose have in common?

Dehydration synthesis

What is glycogen?

* Glycogen is a branched polymer and has only one type of monomer which is glucose
* Most of a glycogen molecule’s sugar units are joined together by alpha 1-4 glycosidic bonds
* There are branch points that have a sugar joined to three neighboring units instead of two as in the unbranched segments of the polymer
* The additional neighbor which forms the branch is linked by an alpha 1-6 glycosidic bond
* Glycogen is a storehouse of surplus chemical energy for most animals and can fuel about 30 minutes of moderate activity

Is glycogen a polysaccharide?

Yes

What is starch?

* Starch is the bank where most plants find their chemical energy
* Starch is a mixture of two different polymers: amylose (an unbranched helical molecule with sugars joined by alpha 1-4 linkage) and amylopectin (different form of glycogen as it is less branches and has an irregular pattern; alpha 1-6 linkage)
* Starch is stored as densely packed granules that can be enclosed in membrane-bound organelles in the plant cell
* Starch is synthesized in animals, but they have an enzyme that can hydrolyze it

What two monomers make up starch?

Amylose and amylopectin

What type of bonds does glycogen have?

1-4 and 1-6 glycosidic bonds

What is cellulose?

* Cellulose makes up cotton and linens and is a major component of cell walls
* They are durable because they are long and unbranched molecules that have side-by-side aggregates to form molecular cables that resist pulling forces.
* It is made up of only glucose monomers and it is joined by beta (1-4) linkages unliked glycogen and starch.

Is cellulose a polysaccharide?

Yes

What type of bonds does cellulose have?

Beta 1-4 linkages

What is the composition of cellulose?

Only glucose monomers

Why can our cells digest glycogen and starch, but not cellulose?

* Our cells can digest glycogen and starch, but not cellulose because we lack the enzyme to degrade it.
* Some animals like sheep and termites can harbor bacteria and protozoa which synthesize the cellulase enzyme.
* Cellulose is a major component of dietary fiber that human enzymes can’t digest.

What is chitin?

* Chitin is an unbranched polymer of N-acetyl glucosamine.
* It has an acetyl group instead of a hydroxyl group (like glucose) bonded to the second carbon of the ring.
* It is important for the structural material (outer coverings of insects/crustaceans) associated with invertebrates.

What kind of bonds does chitin have?

Beta 1-4 linkage

What is the composition of chitin?

Unbranched polymer of N-acetyl glucosamine.

Is chitin a polysaccharide?

Yes

Why is chitin important?

It is important for the structural material (outer coverings of insects/crustaceans) associated with invertebrates.

What are glycosaminoglycans?

* Another polysaccharide group is glycosaminoglycans (GAGs)
* They have the structure ABAB and A and B are different sugars.
* Most GAGs are found in the spaces surrounding cells, unlike heparin.

Are glycosaminoglycans polysacchardies? (ABAB)

Yes

Why are glycosaminoglycans important?

* An example is heparin which is secreted by the lungs and tissues when there is an injury.
* It stops blood flow and prevents blood clots that prevent blood from going to the heart and lungs.
* Heparin activates an inhibitor (antithrombin) of an important enzyme (thrombin).

Why are chitin and glycosaminoglycans important?

Polysaccharide in the connective tissue between cells

What are lipids?

* Lipids comprise a diverse group of nonpolar biological molecules
* They share common properties like dissolving in organic solvents (chloroform/benzene) and an inability to dissolve in water (explaining many of their varied biological functions)
* Important lipids of a cell include fats, steroids, and phospholipids.

What are the important lipids in the cell?

* Fats
* Steroids
* Phospholipids

What are the components of a fat molecule?

* Fats are made up of a glycerol molecule linked by ester bonds to three fatty acids (long unbranched hydrocarbon chains with a single carboxyl group at one end)
* The composite molecule is called a triglyceride

What does amphipathic mean?

Has both hydrophobic and hydrophilic regions

What makes fatty acids amphipathic?

* The hydrocarbon chain (C-H) is hydrophobic and the carboxyl group (OH) (head) has a negative pH and is hydrophilic.
* Since it has both hydrophobic and hydrophilic regions, it is amphipathic.

Why is it important that fatty acids are ampipathic?

It can interact with both water and hydrophobic things (grease)

What are saturated fats?

* Fatty acids that lack double bonds like stearic acid are saturated
* Without double bonds=saturated with hydrogens

What are unsaturated fats?

* Then, if they have double bonds they are unsaturated
* Double bonds=fewer hydrogens

Why is it important that some fats are saturated and some are unsaturated?

* Naturally occurring fatty acids with double bonds are in the cis configuration and make kinks in the chain.


*  If the fatty acid chain has more double bonds, it is harder to pack together and lower the temperature at which they melt.

What are omega-3 fatty acids?

* Fatty acids with a double bond in the #3 position
* Linoleic acid, EPA, DHA
* Cardiovascular health

Why are fats used to store energy in the cell more than carbohydrates?

* Fats are rich in chemical energy and a gram of fat contains twice as much energy as a carbohydrate.
* Fats are stored up as fat droplets so they take up less space (no water).

How is a phospholipid different from a fat in terms of its structure and properties?

* A phospholipid is similar in that it has only two fatty acid chains instead of three and is called a diacylglycerol. The third hydroxyl group of the glycerol backbone is covalently bonded to a phosphate group which is covalently bonded to a small polar group.
* Unlike fat molecules, phospholipids have two ends that have different properties. The end that has the phosphate group is hydrophilic (polar) and the other end made of the two fatty acid tails is hydrophobic. This is because phospholipids mainly function in cell membranes and the cell membrane properties are dependent on phospholipid components.

Why is it important for a phospholipid to be different from a fat in terms of its structure and properties?

This is because phospholipids mainly function in cell membranes and the cell membrane properties are dependent on phospholipid components.