Lecture 4 - Organic Molecules - Learning Objectives: Chapter 2.5

Question 1

Describe the basic structure of an amino acid.

Answer 1

- Amino acids are the monomers of proteins
Each has:
- Amino group
- alpha carbon
- Carboxyl group
- R group (side chain)

Question 2

Describe how amino acids link together via peptide bonds to form proteins

Answer 2

Carbon of the carboxyl group of one amino acid is linked to the nitrogen in the adjacent amino acid by a covalent peptide bond

Question 3

Identify and Define the three components of a nucleic acid.

Answer 3

- Nucleotides are the monomers of nucleic acids
Each has:
- 5-carbon sugar
- Nitrogenous Base
One or more phosphate groups.

Question 4

Describe the difference between a deoxyribonucleotide and a ribonucleotide.

Answer 4

In DNA the 5-carbon sugar is deoxyribose.

In RNA, it is ribose.

Question 5

Identify the five nitrogen-containing bases of nucleic acids and differentiate between the two
classes (purines and pyrimidines).

Answer 5

Purine:

• adenine
• guanine

Pyrimidine:

• Thymine
• Cytosine
• Uracil (replaces Thymine in RNA)

Question 6

Describe the process of nucleotide joining.

Answer 6

• Joined by phosphodiester bonds.
• The 5’ phosphate group of one nucleotide binds the 3’ OH group on the sugar of another nucleotide.
• results in loss of water.

Question 7

Describe the structure of DNA.

Answer 7

• Double helix (two strands).
• Sugar-phosphate backbones wrap around outside.
• Complementary base- pairing on the inside
  (A-T and G-C)

Question 8

Define a carbohydrate and identify/describe the two main classes of sugars.

Answer 8

Simple carbohydrates are monosaccharides:

• exist as linear or cyclical structures
• composed of carbon, hydrogen, oxygen
• contain 5 or 6 carbons

Two main sugars are:

• aldose, contains aldehyde group (H-C- -O) at end of chain.
• Ketose, contains ketone group (C- -O) within chain

Question 9

Define Mono-, Di-, and Polysaccharides.

Answer 9

Monosaccharides: One sugar
v Disaccharides: Two sugars linked together
v Polysaccharides: Many sugars linked together

Question 10

Describe the cyclization process of ketose and aldose sugars.

Answer 10

Aldose:
The carbon in the aldehyde (-COH) of an aldose forms a covalent bond with the oxygen of the -OH of another carbon in the same molecule.
????????

Question 11

Describe the process of glycosidic bond formation.

Answer 11

Covalent bond between 1’ Carbon of one simple sugar and soome other Carbon of the same molecule.

Question 12

Identify the major difference between lipids and the other three classes of biomolecules.

Answer 12

Lipids are NOT defined by chemical structure, they are defined by their hydrophobic nature.

Question 13

• Describe and compare the three types of lipids

Answer 13

I. Fatty Acids (Triacylglycerol): long carbon chains attached to a carboxyl group.

II. Steroids: carbon rings

III. Phospholipids: glycerol
backbone + 2 fatty acid chains
+ phosphate head group

Question 14

Describe the formation of a triacylglycerol.

Answer 14

Structure: glycerol’s 3 hydroxyl (–OH) groups covalently bind to the
carboxyl group (-COOH) of three fatty acids.

Question 15

Compare saturated vs unsaturated fats.

Answer 15

Saturated Fats:
made up of fatty acids that do not contain C=C bonds
- saturated with hydrogen atoms.

Unsaturated Fats:
made up of fatty acids that contain C = C bonds
- kinks caused by double bonds reduce tightness of packing and lower melting temp.

Question 16

Define Van der Waals forces and describe their role in lipid structure.

Answer 16

Fatty acids are uncharged: hydrocarbon chains contain no polar covalent bonds
……however……
- The constant motion of electrons leads to regions of slight charges: attract/repel molecules.
Forces are weaker than hydrogen bonds: many act together to
stabilize molecules.

Question 17

Describe the structure and function of a phospholipid.

Answer 17

Function: major component of the cell membrane

Structure: glycerol attached to two fatty acids and a phosphate containing
head group.