Biochemistry Lab Midterm Exam

Nucleic acid

is an unbranched polymer

Nucleotides

monomer units of nucleic acid

DNA

stores the genetic information of an organism and transmits that information from one generation to another

RNA

translates the genetic information contained in DNA into proteins needed for all cellular function

DNA

is located in the nucleus of the cell

RNA

is located in different parts of the cell

hnRNA

in nucleus

mRNA

in cytoplasm

rRNA

in ribosome

tRNA

in cytoplasm

Breaking of the cell wall

 done by mechanical disruption through crushing or blending

Breaking of cell membrane to expose organelles

done by adding the dishwashing liquid which is an amphipathic substance

The long hydrocarbon tail of soap

breaks the lipid bilayer of cell membrane

soap’s polar head

is attracted to water

Salt

binds to the negatively charged phosphate end of the DNA chain to protect the chain as well as increases the separation of DNA from the hydrophobic layer

Filtration

 removes cellular debris from the sample

Precipitation

with cold alcohol

DNA

becomes insoluble in water in the presence of salt and alcohol (more polar)

DNA

precipitate as a white gelatinous material

Nucleotide

is composed of base, sugar and phosphate group

Glycosidic bond

joins the base and the sugar

Phosphodiester bond

joins the phosphate and sugar group

nucleotide chain

is joined together by 3 '5' phosphodiester bond/linkage

Lysis

break down

Depurination

breakdown of glycosidic bonds only if pH > 3

Products of depurination

purine base and deoxyribose with phosphate group

Total breakdown

break down of glycosidic bond with phosphodiester bond if pH < 2 plus heat

products of total breakdown

phosphate group, the purine or pyrimidine base, and deoxyribose

Further hydrolysis

breaks the nucleobases specifically the purines

Dische test

test for the deoxyribose in DNA

reagents of dische test

 diphenylamine, Sulfuric acid

positive result of dische test

 light blue to blue solution depending on the amount of DNA

THEORETICAL RESULTS SAMPLES DISCHE TEST 

HYDROLYZED (positive)

bright blue

THEORETICAL RESULTS SAMPLES DISCHE TEST 

UNHYDROLYZED (positive)

brownish blue

FEHLING'S Test

test for reducing sugar

Reagents: Fehling's A

Copper sulfate solution

reagents:  Fehling's B:

aqueous potassium sodium tartrate and sodium hydroxide

positive result of fehling’s test

brick-red precipitate

THEORETICAL RESULTS SAMPLES FEHLING'S TEST

Observations HYDROLYZED (positive) 

formation of brick-red ppt

THEORETICAL RESULTS SAMPLES FEHLING'S TEST

UNHYDROLYZED (negative)

remains blue and no formation of brick-red ppt

Bial’s Test/Bial’s Orcinol Test

test for pentoses (can only distinguish between pentose & hexose sugar)

reagents of bial’s test

Orcinol, hydrochloric acid, FeCl3

positive result of bial’s test

 Blue or green solution

THEORETICAL RESULTS SAMPLES BIAL'S TEST 

Observations HYDROLYZED (negative for ribose)

brown solution

THEORETICAL RESULTS SAMPLES BIAL'S TEST

UNHYDROLYZED (negative for ribose)

brown solution

Test for Purine Bases

 test for the presence of Adenine and Guanine

reagents of purine bases test

 Silver Nitrate and Ammonium Hydroxide

gelatinous white precipitate

positive result of purine base test

THEORETICAL RESULTS SAMPLES PURINE TEST 

Observations HYDROLYZED 

Gelatinous white precipitate

THEORETICAL RESULTS SAMPLES PURINE TEST 

UNHYDROLYZED

brown solution

Phosphate Test

test for free phosphate group

reagents of phosphate test

 Ammonium hydroxide, nitric acid, ammonium molybdate

positive result of phosphate test

yellow precipitate

THEORETICAL RESULTS SAMPLES PHOSPHATE TEST 

Observations HYDROLYZED (positive) 

Formation of yellow precipitate

THEORETICAL RESULTS SAMPLES PHOSPHATE TEST

UNHYDROLYZED (negative)

no yellow precipitate

simple

 are esters of fatty acids and alcohol

Triglycerides (Fats and Oils)

esters of fatty acids and glycerol

waxes

 esters of fatty acids and monohydric alcohol

compound

 are esters of fatty acids and alcohol that contain another functional group

phospholipids

 esters of fatty acids with glyc­erol containing an esterified phosphoric acid and a nitrogen

glycolipids

contain an amino alcohol (sphingosine or iso-sphingosine) attached with an amide linkage to a fatty acid and glycosidically to a carbohydrate (sugars, amino sugar, sialic acid)

derived

contain hydrocarbon rings

olive oil

 predominantly composed of oleic acid

coconut oil

 predominantly composed of lauric acid

lecithin

 Phosphoglycerides that contain the aminoalcoholcholine