1 bio chem
TRANSCRIPT
Post-Lab Discussion
Activity 1A
Subcellular Components of the Living Cell
Activity 1B
Qualitative Tests for the Chemical Composition of
Organelles
Tests for Carbohydrates
Molisch TestBenedict's Test
Molisch Test
Positive Result: PURPLE ring betweenw/ Ribose Sol'n acid and sediment
Benedict's Test
Positive Result: BRICK RED colorationw/ Ribose Sol'n
Tests for Proteins
Biuret TestXanthoproteic Test
Biuret Test
Positive Result: PURPLE colorationw/ Ribose Sol'n
Xanthoproteic Test
Positive Result: INTENSE YELLOW colorationw/ Ribose Sol'n
Tests for Lipids
Sudan TestAcrolein Test
Sudan Test
Positive Result: RED colorationw/ Ribose Sol'n
Acrolein Test
Positive Result: BITING ODORw/ Ribose Sol'n
Results
Analysis and Conclusion
Separation
Principle: Differential Centrifugation
Tissue or cells are first disrupted to release their internal contents (homogenate).
Larger particles sediment faster than smaller ones and this provides the basis for obtaining
crude organelle fractions by differential centrifugation.
Principle: Dehydration of the carbohydrate by sulfuric acid to produce an aldehyde
Reaction:
R-CHO + (conc.) H2SO4 → R-CHO (ex. furfural) + 3 H2O
R-CHO + 2 C10H8-OH (α-naphthol) → colored product
Molisch Test
Principle: Reduction of Cu2+ ions by reducing sugars, which then can be detected by the formation of a brick red precipitate of Cu2O (Cuprous oxide)
General Reaction:
R-CHO + 2Cu2+ + 4OH- →R-COOH + Cu2O + 2H2O
Benedict's Test
Principle: Reduction of Cu2+ which thencomplexes with the N atoms on thepeptide bonds, at high pH. [Amide bond is resposible for the colour.]
Reaction:
copper(II) ions + protein (peptide bonds) → biuret complex (PURPLE)
Biuret Test
Principle: Nitration of benzene ring present inthe structure
Reaction:
G-H + HNO3 →G-NO2 (YELLOW) + H2O
Xanthoproteic Test
Principle: Ability of fat cells to selectively absorb pigments in fat-dyes such as Sudan IV
Reaction: Absorption
Sudan Test
Principle: Whenever fat is heated in the presence of dehydrating agent, fat molecule sheds glycerol in the form of the unsaturated aldehyde - acrolein
Reaction:
Glycerol + KHSO4 → C3H4O (acrolein w/ biting odor)
Acrolein Test
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