CARBOHYDRATE SYNTHESIS

INTRODUCTION

Structurally, carbohydrates are defined as polyhydroxyl aldehydes or ketones and their derivatives (Lehninger, 1970; Campbell & Farrell, 2009). The empirical formula (CH2O)n is attributed to several carbohydrates which suggests that these compounds are hydrates of carbon, however, further studies have shown that this notion is not applicable to all carbohydrates. Carbohydrates are classified into three types: (1) monosaccharide, or simple sugars, consisting of one polyhydroxyl aldehyde or ketone unit; (2) disaccharides, composed of two polyhydroxyl aldehyde or ketone unit; and (3) polysaccharides, contain many monosaccharide units.

Carbohydrates, such as sugars and starches, are the most abundant class of naturally-occurring organic compounds. Autotrophic organisms such as plants manufacture carbohydrates during photosynthesis. In contrast, heterotrophic organisms, who lack this ability consume carbohydrate directly via ingestion of plants, or indirectly, through consumption of meat, milk, and eggs.

In photosynthetic organisms, biosynthesis of carbohydrates, involves the conversion of hexoses generated from carbon dioxide and water into starch, cellulose, and other polysaccharides (Lehninger,1970). Specifically, the central pathway utilized involves the conversion of glucose or glucose-6-phosphate to pyruvate, which is catalyzed by various glycolytic enzymes, in either aerobic or anaerobic conditions (Campbell & Farrell, 2009; Lehninger, 1970; Garrett & Grisham, 2010). Moreover, several feeder pathways converge into the central pathway which leads from non-carbohydrate precursors, e.g. the intermediates of the tricarboxylic acid being transformed into precursors of glucose (Lehninger,1970).

In this experiment, differences in the carbohydrate production of monocot and dicot leaves will be observed and confirmed with the use of Benedict’s test and iodine test. Moreover, carbohydrate production in variegated leaves of Sanchezia speciosa was also observed and confirmed using the aforementioned qualitative tests.

METHODOLOGY

Carbohydrate Production in relation to species

Leaves of Bambuseae sp. and Pachystachys lutea were collected and cut into approximately 1 cm2 pieces, then, 0.5 grams of each leaf sample was weighed. The weighed samples were then boiled separately for 10 minutes in 250 mL beakers which contained 50 mL water. The boiled leaves were then removed from each container and set aside, while Benedict’s test was performed on the two water extracts. Results of the test were then recorded.

On the other hand, 2-3 pieces of the boiled leaves were placed in test tubes containing about 5 mL of 95% ethanol. The test tubes were then placed in a water bath approximately 70 °C until the leaves were bleached. The bleached leaves were placed in a watch glass, cooled, and then bathed in iodine solution. Excess iodine solution was removed and results were recorded.

Carbohydrate Production in variegated leaves

Variegated leaves of Sanchezia speciosa were collected and cleaned. Afterwards, the green and non-green portions were separated—each portion was cut into small pieces and 0.5 grams of each leaf portion was weighed. The two portions were boiled separately in 250 mL beakers which contained 50mL water for 10 minutes. Tests for reducing sugars and starch were conducted for the water extracts and boiled leaves, respectively.

Works CitedCampbell, M. K. & Farrell, S. O., 2009. Biochemistry. California: Thomson Brooks/Cole.

Garrett, R. H. & Grisham, C. M., 2010. Biochemistry. Massachusetts: Brooks/Cole.

Lehninger, A. L., 1970. Biochemistry. New York: Worth Publishers, Inc..