Lactate dehydrogenase, an enzyme involved in glycolysis,...

Lactate dehydrogenase, an enzyme involved in glycolysis, from several species are compared using a Southern blot technique in the figure on the left: (A) yeast; (B) snail; (C) mouse; (D) rat; and (E) human (after K. Webster, Journal of Experimental Biology 2003). A. Justify the claim that these data provide evidence that supports glycolysis as a conserved core property. There are three forms of lactate dehydrogenase whose roles vary within an organism: LDH-A, -B, and -C. The question arises as to the origins of each. The cladogram on the right (after S. Tsuji et al., Proc Natl Acad Sci 1994) displays a proposed relatedness of variations in LDHs over many species. B. Based on these data, describe the differences between the likely evolutionary sequences of LDH-A, -B, and -C in the African frog and in humans. C. Evaluate the claim that in both species (African frog and human), LDH-C is the most recently evolved form of the enzyme.

Lactate dehydrogenase, an enzyme involved in glycolysis, from several species are compared using a Southern blot technique in the figure on the left: (A) yeast; (B) snail; (C) mouse; (D) rat; and (E) human (after K. Webster, Journal of Experimental Biology 2003).
A. Justify the claim that these data provide evidence that supports glycolysis as a conserved core property.
There are three forms of lactate dehydrogenase whose roles vary within an organism: LDH-A, -B, and -C. The question arises as to the origins of each. The cladogram on the right (after S. Tsuji et al., Proc Natl Acad Sci 1994) displays a proposed relatedness of variations in LDHs over many species.
B. Based on these data, describe the differences between the likely evolutionary sequences of LDH-A, -B, and -C in the African frog and in humans.
C. Evaluate the claim that in both species (African frog and human), LDH-C is the most recently evolved form of the enzyme.

Key Concepts

Conservation of Core Metabolic Pathways

This concept refers to the idea that essential biochemical processes, such as glycolysis, are preserved across diverse species through evolution. Because these pathways are fundamental for cellular energy production and survival, the underlying enzymes tend to have highly conserved sequences and functions. The conservation of these pathways across organisms highlights their critical role, and evidence from comparative studies supports that glycolysis is a core property maintained over evolutionary time.

Southern Blot Analysis

Southern blotting is a molecular biology technique used to detect specific DNA sequences within a complex mixture. It involves transferring DNA fragments from a gel onto a membrane and then probing with a labeled complementary sequence. In comparative studies, this method can reveal the presence and similarity of gene sequences among different species, providing evidence for sequence conservation and evolutionary relationships.

Gene Duplication and Evolution of Isoenzymes

Gene duplication is an evolutionary mechanism that results in copies of genes within the genome, which may then diverge and acquire new or specialized functions. The appearance of multiple isoenzymes, such as different forms of lactate dehydrogenase, is often a result of such duplication events. Over time, these duplicated genes may evolve distinct roles in different tissues or under varying physiological conditions, reflecting both conservation of a core function and the diversification necessary for specialized roles.

Phylogenetic Analysis and Cladograms

Phylogenetic analysis uses genetic information to reconstruct evolutionary relationships among genes or species, often visualized in the form of cladograms. These diagrams depict the divergence and common ancestry of various forms, helping to map out the evolutionary sequence of gene variants. By analyzing the relationships and branching patterns, researchers can infer the relative age of specific isoenzymes and evaluate hypotheses about their evolutionary origins, such as determining which variant arose most recently.

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