Ch 10 - Nitrogen and Phosphorous Containing Compounds

Question 1

What is the alpha carbon of an amino acid attached to?

Answer 1

an amino group
a carboxyl group
a hydrogen atom
an R group

Question 2

How is glycine different from all other amino acids?

Answer 2

all amino acids have a chiral stereocenter except glycine

- glycine has a hydrogen atom as an R group, making it not chiral and not optically active

Question 3

How does the stereochemistry of cysteine differ from all other amino acids?

Answer 3

• all amino acids in eukaryotes are L amino acids

- they all have S stereochemistry except cysteine which is R

Question 4

What does ampohoteric?

Answer 4

can be acids or bases (like amino acids)

Question 5

Where do amino acids get their acidic and basic characteristics from?

Answer 5

• acidic from carboxylic acids

- basic from amino groups

Question 6

How do amino acids tend to exist in neutral solution?

Answer 6

as zwitterions (dipolar ions)

Question 7

What are the nonpolar nonaromatic amino acids?

Answer 7

alanain, valine, isoleucine, leucine, glycine, proline, and methionine

Question 8

What are the aromatic amino acids?

Answer 8

tryptophan, phenylalanine, and tyrosine

Question 9

What are the polar amino acids?

Answer 9

serine, threonine, asparagine, glutamine, and cysteine

Question 10

What are the negatively charged amino acids?

Answer 10

aspartic acid and glutamic acid (contain carboxylic acids in R group)

Question 11

What are the positively charged amino acids?

Answer 11

arginine, lysine, and histidine (contain amines)

Question 12

How do nonpolar nonaromatic and aromatic amino acids relate?

Answer 12

both nonpolar nonaromatic and aromatic amino acids then to be hydrophobic and reside in the interior of proteins

Question 13

How do polar, negatively charged (acidic) and positively charged (basic) amino acids relate?

Answer 13

tend to be hydrophilic and reside on the surface of proteins, making hydrogen bonds with aqueous environment

Question 14

How do peptide bonds form?

Answer 14

by condensation reactions where water is lost and can be cleaved hydrolytically by strong acids/bases

Question 15

What does resonance of the peptide bond restrct?

Answer 15

motion about the C-N bond, which takes on partial double bond character

Question 16

What is needed to cleave a peptide bond?

Answer 16

strong acid or base

Question 17

What are polypeptides made of?

Answer 17

multiple amino acids linked by peptide bonds

- proteins are large, folded, functional polypeptides

Question 18

What are the 4 reactants in the Strecker synthesis of an amino acid?

Answer 18

an aldehyde
ammonium chloride (NH4Cl)
potassium cyanide (KCN)
- used to make the aminonitrile
- water is used to hydrolyze the aminonitrile to form the amino acid

Question 19

What are the reaction types used in Strecker synthesis?

Answer 19

• a condensation reaction (formation of an imine from a carbonyl-containing compound and ammonia, with loss of water), followed by nucleophilic addition (addition of the nitrile group), followed by hydrolysis

Question 20

Where is phosphorus found?

Answer 20

• in inorganic phosphate (Pi), a buffered mixture of hydrogen phosphate (HPO4 2-) and dihydrogen phosphate (H2PO4-)
• in the backbone of DNA, which uses phosphodiester bonds (in forming these bonds, a pyrophosphate (PPi) is released which can then be hydrolyzed to 2 inorganic phosphates)

Question 21

Why are phosphate bonds high energy?

Answer 21

because of large negative charges in adjacent phosphate groups and resonance stabilization of phosphates

Question 22

What are organic phosphates?

Answer 22

• carbon containing compounds that also have phosphate groups
• the most notable example are nucleotide triphosphates (ATP or GTP) and DNA

Question 23

What do the 3 hydrogens in phosphoric acid allow?

Answer 23

they all have unique pKa and the wide variety allows phosphoric acid to act as a buffer over a large range of pH values

Question 24

Why is rotation limited around the peptide bond?

Answer 24

because resonance gives the C-N bond partial double bond character

Question 25

Why is the C-N bond of an amide planar?

Answer 25

• because it has partial double bond characteristics due to resonance
• double bonds exist in a planar conformation and restrict movement

Question 26

What are the 4 main reactants in the Gabriel synthesis of an amino acid?

Answer 26

• begins with potassium phthalimide (nucleophile) and diethyl bromomalonate, followed by an alkyl halide (bromide is leaving group; secondary carbon electrophile)
• water is then used to hydrolyze the resulting compounds to form the amino acid
• while acids and bases are used at various times as catalysts, the are not main reactants

Question 27

What are the reaction types used in the Gabriel synthesis?

Answer 27

proceeds through 2 Sn2 reactions, hydrolysis, and decarboxylation

Question 28

What characteristics make inorganic phosphate so useful to energy transfer biologically?

Answer 28

• they have very negative charges
• when bonded to other phosphate groups in a nucleotide triphosphate, this creates repulsion with adjacent phosphate groups, increasing the energy of the bond
• they can be resonance-stabilized

Question 29

What kind of mixtures do the Strecker and Gabriel syntheses produce?

Answer 29

• they both tonain planar intermediates, which can be attacked from either side by a nucleophile
• this results in a racemic mixture of enantiomer, and the solution will be optically active

Question 30

What will likely happen to pyrophosphate in aqueous solution?

Answer 30

• pyrophosphate is unstable in aqueous solution and will degrade to form 2 equivalents of inorganic phosphates

Question 31

What would be the charge of aspartic acid at pH 7?

Answer 31

• aspartic acid is acidic because it has an extra carboxyl group
• at neutral pH, both the carboxyl groups are ionized, so there are 2 negative charges on the molecule
• only one of the negative charges are neutralized by the positive charge on the amino group, so the overall it would be negative