export_lab final

Question 1

General structure of a triglyceride

Answer 1

Question 2

What happens to the triglyceride in the presence of the methanolic NaOH

Answer 2

fatty acid would undergo a base-catalyzed reaction with the OH group of sodium hydroxide

Question 3

Explain what happens upon treatment of boron trifluoride in methanol.

Answer 3

* The two form separate layers * Boron trifluoride is relatively non-polar, while methanol is polar * Creates separation between the two substances

Question 4

What happens in liquid-liquid extraction

Answer 4

* used to separate compounds based on their relative solubilities * carried out in water and an organic solvent * the two are immiscible

Question 5

What fractions are on the top and the bottom

Answer 5

Polar in the bottom with aqueous phase. Non-polar in the organic phase.

Question 6

What are the products of the reaction

Answer 6

FAMEs, fatty acid methyl esters

Question 7

What is the purpose of anhydrous magnesium sulfate

Answer 7

It is used in the lab as a desiccant

Question 8

Explain in layman’s terms how GC-MS works

Answer 8

* GC will separate the compound., retention time is used as the unit of measurement, individual retention times help to identify what’s present in the compound. * MS calculates fragments which vary and size, while also representing the molecular make-up of the compound.

Question 9

Which fractions contain which major lipid classes?

Answer 9

Organic layer will contain FAs that are completely hydrophobic, while the aq. layer will contain amphipathic FAs. Based on polarity can one determine what fatty acids will be found in each layer.

Question 10

Why do different lipid types come out in different solvents?

Answer 10

Fatty acids are specific to which type of solvent they will dissolve in. The principle “like dissolves like” is occurring in liquid liquid extraction.

Question 11

Why is sodium sulfate used to dry the organic solvent (chloroform)?

Answer 11

* Drying agent * A dry sample was important to obtain an optimal separation of lipids in the column chromatography portion of the lab

Question 12

Why do different lipids travel different distances on the TLC plates?

Answer 12

* Interactions with the silica * Silica (non-polar) does not react well with polar compounds, resulting in non-polar compounds traveling the least while the polar compounds move the farthest the fastest

Question 13

Why did you determine absorbance at 260 and 280 nm when determining DNA?

Answer 13

The 260 nm is related to DNA and determining the presence of nucleic acids, whereas 280 is used for proteins.

Question 14

What is the purpose of the pineapple juice?

Answer 14

* Contains bromelain * Proteolytic enzyme * Breaks bonds between proteins & nucleic acids

Question 15

Why did we not use canned pineapple juice?

Answer 15

Contamination

Question 16

What was detergent used for?

Answer 16

* breakdown of the cell membrane by dissolving lipids and proteins * create new compounds, with the proteins and lipids, in the form of precipitate

Question 17

Why is it important not to heat the banana over 70 C?

Answer 17

* unnecessary breakdown of bonds and denature the proteins past the ideal point * the yield produced if the temperature was above 70 would’ve been increased from the goal amount (polymerase chain reaction)

Question 18

What functional groups on the amino acids allow them to interact with the Dowex cation exchange resin and how does increasing the pH alter this effect?

Answer 18

basic groups

Question 19

What functional groups interact with the TLC plate silica coating?

Answer 19

(hydrophobic/hydrophilic)

Question 20

What other techniques, other than TLC, could be used to determine the amino acids in each fraction?

Answer 20

Gel electrophoresis

Question 21

Explain what an Rf value represents

Answer 21

* Larger Rf value= less polar and moves faster * Smaller Rf value= more polar, more attracted to the stationary phase.

Question 22

What happens when milk curdles naturally when it is past the printed expiration date?

Answer 22

pH is being altered and the milk becomes more acidic.

Question 23

What is the source of acid causing the curdling and how is the acid made?

Answer 23

Normally, milk is composed of free-floating small protein molecules. When curdling begins, these small proteins start to come together and bind with one another to form clumps as the pH changes.

Question 24

Which protein source contains more essential amino acids? Was this the result you expected and why?

Answer 24

Casein, yes that was to be expected. When we are in the earliest years of development, many of us drank milk. Milk is known to contain a vast amount of protein and other important nutrients to facilitate healthy growth.

Question 25

Biuret

Answer 25

peptide bonds; interaction with Cu2+ ions

Question 26

Xanthoproteic

Answer 26

phenyl groups; nitric acid test

Question 27

Sakaguchi

Answer 27

arginine

Question 28

Mechanism for the reactions involved in the xanthoproteic test with a tyrosine residue (nitration of benzene)

Answer 28