When answering these questions DO NOT exceed the space provided. If your answers

Question

When answering these questions DO NOT exceed the space provided. If your answers can space then you are likely being excessively verbose. Succinctnes important aspect of scientific communication not fit into the s when expressing ideas is an BLOOD SMEAR Consider the staining reaction of the erythrocytes in the blood smea 1. What SPECIFIC characteristics of the hae r. moalobin composition can you CONCLUDE from the Cytoplasmic staining reaction? Specific means 'not general', which means drilling deeply into the connection between observation and conclusion. CRITICAL THINKING HINT: consider how stains work and how the haemoglobin molecule is constructed (THEORY) (2 marks). Consider the staining reaction of the leukocytes. 2. Explain WHY the nucleus exhibits this particular staining reaction. Again, drill deeply! CRITICAL THINKING HINT: The nucleus is composed largely of DNA and protein (FACT) consider how stains work (THEORY) and how these molecules are constructed (THEORY) (3 marks).

Explanation / Answer

Question 1

Negatively charged anionic dyes such as eosin-Y are used in cytoplasmic staining reactions. These dyes are acidic and so, they bind to basic proteins in the cytoplasm. Erythrocytes are full of hemoglobin. Each of these proteins have in them an Fe3+ ion complexed to porphyrin ring and they also have many positively charged amino acids (arginine and lysine). These positively charged proteins bind to eosin-Y and this causes the RBCs to be stained pink-red.

Question 2

Positively charged basic dyes such as azure B bind strongly to DNA because the two strands of DNA contain a large number of negatively charged phosphate groups. Since leukocytes have nuclei where DNA synthesis is one of the major activities, the content of DNA in usually high. Thus, basic dyes are used to stain the nuclei of leukocytes blue.

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