Biologically Important Molecules

Question 1

What are the biologically important molecules?

Answer 1

Proteins, carbohydrates, lipids, nucleus acids

Question 2

What is a Quaternary [4] Structure?

Answer 2

It is the highest level of protein structure, which describes interactions between polypeptide subunits. [A subunit is a single polypeptide chain that is part of a large complex containing many subunits–multisubunit complex].
The arrangement of these subunits is what we mean by quaternary structure.
The interaction between the subunits is what determines the function of proteins.

Question 3

What forces stabilize Quaternary [4] Structure?

Answer 3

The same forces that stabilize secondary and tertiary structure, non-covalent interactions (the hydrogen bonds, Van der Waals interaction).
Covalent bonds may also be involved in this structure when it has disulfide bonds holding the subunits together, this is the case in antibodies (large protein molecule). But, peptide bonds are NOT in this structure because that is what defines Sequence [1] structure

Question 4

What is the difference between a disulfide bridge involved in quaternary structure and one involved in tertiary structure?

Answer 4

Quaternary disulfides are bonds that form between chains that aren’t linked by peptide bonds. (chains different polypeptides together making it more complex)
Tertiary disulfides are bonds that from between residues in the same polypeptide.

Question 5

What of the following may be considered an example of tertiary protein structure?
I. van der Waals interactions between two Phe R-groups located far apart on a polypeptide
II. Hydrogen bonds between backbone amino and carboxyl
III. Covalent disulfide bonds between cysteine residues located far apart on a polypeptide

Answer 5

I. and III. are correct

Question 6

What is a Carbohydrate?

Answer 6

serves as the principle energy source for cellular metabolism due to carbohydrates being able to be broken down into CO2 through a process called oxidation (also known as burning or combustion).
Understanding the nomenclature, structure, and chemistry of carbohydrates is the key to understanding cellular metabolism.

Question 7

What is glucose as a polymer?

Answer 7

in the form of the polymer cellulose, the building block of wood and cotton.

Question 8

What is a monosaccharide?

Answer 8

A single carbohydrate. (the monomer) Also known as a single sugar.
General Formula: C(n)H(2n)O(n)

Question 9

Name some metabolically important monosaccharides.

Answer 9

Fructose
Glucose
Ribose

Question 10

What is a disaccharide?

Answer 10

When two monosaccharides bond together, however many form polysaccharides

Question 11

What is the bond between two sugar molecules called?

Answer 11

Glycosidic linkage

a covalent bond is formed between them, formed in a dehydration reaction the requires enzymatic catalysis.

Question 12

What is sucrose?

Answer 12

When fructose and glucose bond, forming a disaccharide.

Question 13

What is lactose?

Answer 13

When galactose and glucose bond, forming a disaccaride

Question 14

How are Glycosidic linkages named?

Answer 14

Named according to which carbon in each sugar comprises the linkage. The configuration (alpha or beta) of the linkage is also specified.
For example, lactose (milk sugar) is a disaccharide joined in a galactose-beta-1,4-glucose linkage.

Question 15

What is the difference between an alpha and beta glycosidic bond?

Answer 15

If the anomeric carbon of glucose is pointing down, that means it is an alpha-1,2
For example, Sucrose: Glc-alpha-1,2-Fru

Question 16

Name the most common disaccharides and their linkage names.

Answer 16

lactose: Gal-beta-1,4-Glc
sucrose: Glc-alpha-1,2-Fru
maltose: Glc-alpha-1,4-Glc
cellobiose: Glc-beta-1,4-Glc
- these all build important macromolecules

Question 17

What is glycogen?

Answer 17

serves as an energy storage carbohydrate in animals and is composed of thousands of glucose units joined in alpha-1,4 linkages, alpha-1,6 branches are also present

Question 18

What is starch?

Answer 18

It is the same as glycogen but the branches are a little different and it serves the same purpose in plants

Question 19

What is cellulose?

Answer 19

It is a polymer of cellobiose, but cellobiose is unable to exist freely in nature. It exists in its polymerized, cellular form.
The beta-glycosidic bonds allow the polymer to assume a long, straight, fibrous shape. Wood and cotton are made of cellulose

Question 20

What is Hydrolysis of polysaccharides?

Answer 20

Hydrolysis of polysaccharides into monosaccharides is favored thermodynamically.
It is essential in order for these sugars to enter metabolic pathways (glycolysis) and be used for energy by the cell.
But, this hydrolysis does not occur at a significant rate without enzymatic catalysis, different enzymes catalyze the hydrolysis of different linkages.
These enzymes are named after the sugar they catalyze the hydrolysis for. Ex. maltose by maltase. (highly specific to its linkage)

Question 21

Why can’t we eat cotton?

Answer 21

We don’t have the enzymes that can help break down (hydrolyze) the Beta-linkages found in cellulose

Question 22

How can we digest lactose since usually mammals can’t digest Beta-linkages?

Answer 22

We have an enzyme called lactase, which can digest lactose. Usually children have lactase so they can digest mother’s milk, but over time adults still have this enzyme. Those who don’t are either lactose malabsorbers or lactose intolerant

Question 23

Which requires net energy input: polysaccharide synthesis or hydrolysis?

Answer 23

Because hydrolysis of polysaccharide is favor thermodynamically, energy input is required to drive the reaction towards polysaccharide synthesis. (Because more energy is needed for synthesis)

Question 24

It the activation energy of polysaccharide hydrolysis were so low that no enzyme was required for the reaction to occur, would this make polysaccharides better for energy storage?

Answer 24

No, because then polysaccharides would hydrolyze spontaneously (they would be unstable). The high activation energy of polysaccharide hydrolysis allows us to use enzymes as gatekeepers, when we need energy from glucose, we open the gate of glycogen hydrolysis.

Question 25

What is a lipid?

Answer 25

are oily or fatty substances that play three physiological roles

1) in adipose cells, triglycerides (fats) store energy
2) in cellular membranes, phospholipids constitute a barrier between intracellular and extracellular environments.
3) cholesterol is a special lipid that serves as  the building block for the hydrophobic steroid hormones

Question 26

What is the main characteristic of lipids?

Answer 26

Hydrophobicity, water-fearing. Very important because this means that lipids do not dissolve in water. Carbon-carbon bonds and carbon-hydrogen bonds are nonpolar, meaning they do not dissolve in water due to not being polar (water is extremely polar). So, any substances with these two elements will not dissolve in water.

Question 27

What is a synonym for hydrophobic?

Answer 27

Lipophilic, lipid-loving

Question 28

What is a synonym for hydrophilic?

Answer 28

Lipophobic

Question 29

What are fatty acids composed of?

Answer 29

Of long unsubstituted alkanes that end in a carboxylic acid. The chain is typically 14 to 18 carbons long because they are synthesized two carbons at a time from acetate, only even-numbered fatty acids are made in human cells.

Question 30

What is a saturated fatty acid?

Answer 30

A fatty acid with no carbon-carbon double bonds is saturated with hydrogen because every carbon atom in the chain is covalently bound to the maximum number of hydrogens.

Question 31

What is an unsaturated fatty acid?

Answer 31

A fatty acid that has one or more double bonds in the tail. These double bonds are almost always (Z) (or cis).

Question 32

How does the shape of an unsaturated fatty acid differ from that of a saturated fatty acid?

Answer 32

An unsaturated fatty acid is bent, or “kinked,” at the cis double bond.

Question 33

If fatty acids are mixed into water, how are they likely to associate with each other?

Answer 33

The long hydrophobic chains will interact with each other to minimize contact with water, exposing the charged carboxyl group to the aqueous environment.

Question 34

How do free fatty acids interact in an aqueous solution?

Answer 34

They form a structure called a micelle (with the tails on the inside and heads on the outside). The force that drives the tails into the center of the micelle is called the hydrophobic interaction.

Question 35

What is the hydrophobic interaction (present in micelle)?

Answer 35

it results from the fact that water molecules must from an orderly solvation shell around each hydrophobic substance. The reason is H2O has a dipole that “likes” to be able to share its charges with other polar molecules.

A solvation shell allows for the most water-water interaction and the least water-lipid interaction. The problem is that forming this shell is an increase in order and thus resulting in decrease in entropy (ΔS < 0), which is unfavorable according to the second law of thermodynamics.

Question 36

Since it is not thermodynamically favorable, how does a fatty acid micelle from?

Answer 36

water forms a shell around the spherical micelle with the result being that water interacts with polar carboxylic acid head groups while hydrophobic lipid tails hide inside the sphere.

Question 37

How does soap help to remove grease from your hands?

Answer 37

Grease is hydrophobic. It dose not wash off easily in water because it is not soluble in water. Scrubbing your hands with soap causes micelles to from around the grease particles.

Question 38

What is a triacylglycerol (triglyceride)?

Answer 38

(the storage from of the fatty acid is fat) This is the technical name for fat.
Composed of three fatty acids esterified (replacing Hydrogen with an alkyl or other organic group) to a glycerol molecule. Glycerol is a three-carbon triol with the formula HOCH2-CHOH-CH2OH.
It has three hydroxyl groups that can be esterified to fatty acid. It is necessary to store fatty acids in the relatively inert from of fat because free fatty acids are reactive chemicals.

Question 39

Triacylglycerol undergo reactions typical of?

Answer 39

esters

such as base-catalyzed hydrolysis

Question 40

What does amphipathic mean? Give an example of a substance that is this.

Answer 40

substance have both hydrophilic and hydrophobic regions.
Example: Soap, the sodium salts of fatty acids, produced by base-catalyzed hydrolysis of triglycerides from animal fat into fatty acid salts (soaps). this reaction is called Saponification.

Question 41

What is Saponification?

Answer 41

Reaction produced by base-catalyzed hydrolysis of triglycerides from animal fat into fatty acid salts. (This creates soap, sodium salts of fatty acids)

Question 42

What are Lipases?

Answer 42

are enzymes that hydrolyzes fats.

Question 43

What are Triacylglycerols stored in?

Answer 43

fat cells as an energy source

Question 44

Are fats a more efficient energy source than carbohydrates? And why?

Answer 44

They are more efficient for two reasons:
1. Packing: their hydrophobicity allows fats to pack together much more closely than carbohydrates. (carbohydrates carry a great amount of water-of-solvation–water molecules hydrogen bonded to their hydroxyl groups) The amount of carbon per unit area or unit weight is much greater in a fat droplet than in dissolved sugar.

2. Energy Content: All packing considerations aside, fat molecules store much more energy than carbohydrates. Regardless of what you dissolve it in, a fat has more energy carbon-for-carbon than a carbohydrate. The reason is that fats are much more reduced (energy metabolism stats with the oxidation of foods to release energy, since carbohydrates are more oxidized in the beginning, oxidizing them releases less energy)

Question 45

What are membrane lipids?

Answer 45

they are phospholipids derived from diacylglycerol phosphate or DG-P.

Question 46

What is phosphatidyl choline?

Answer 46

a phospholipid formed by the esterification of a choline molecule [HO(CH2)2N+(CH3)3] to phosphate group of DG-P.

Question 47

What are phospholipids?

Answer 47

Detergents, substances that efficiently solubilize oils while remaining highly water-soluble. They are like soaps but stronger.

Question 48

How do phospholipids minimize interactions with water?

Answer 48

by forming an orderly structure, called a lipid bilayer.
Hydrophobic interactions drive the formation of this layer. Once formed it is stabilized by the van der Waals forces between the long tails.

Question 49

Would a saturated or an unsaturated fatty acid residue have more van der Waals interactions with neighboring alkyl chains in a bilayer membrane?

Answer 49

The bent shape of the unsaturated fatty acid means that it doesn’t fit in as well and has less contact with neighboring groups to from van der Waals interactions. Phospholipids composed of saturated fatty acids make the membrane more solid.

Question 50

What did double bonds do in phospholipid acids?

Answer 50

Double bonds mean it is an unsaturated fatty acid.

• they tend to increase membrane fluidity. Unsaturation prevents the membrane from solidifying by disrupting the ordderly packing of the hydrophobic lipid tails
• the right amount of fluidity is essential for function.
• decreasing the length of fatty acid tails also increases fluidity.
• steroid cholesterol is the third modulator of membrane fluidity.

Question 51

How does the steroid, cholesterol, affect fluidity?

Answer 51

It is a modulator of fluidity of the membrane.

• if the temperature decreases, fluidity increases in the same way as kinks in fatty acid tails, thus known as membrane antifreeze.
• At high temperatures, cholesterol attenuates (reduces) membrane fluidity.
• Cholesterol keeps fluidity at an optimum level.

Question 52

What are the structural determinants of membrane fluidity?

Answer 52

degree of saturation, tail length, and amount of cholesterol.