Question

1. Cystinuria is a disease characterized by the abnormal production of painful kidney stones. The stone formation does not appear to be related to patient dehydration. These stones are produced because certain amino acids tend to build up and crystallize outside the transport cells. Can your group think of any reason why a cell might fail to reabsorb organic molecules?
2. Epulos, a bacterium growing in the gut of tropical surgeonfish can reach the size of 500 micrometers. How does this compare to other bacteria and what problems does this present the Epulos? What are some ways that a cell this size could alter its structure to survive?
3. Many biologists speculate that the first major steps in the evolution of a eukaryotic cell from a prokaryotic ancestor would be the loss of a cell wall and the development of an extensive cytoskeleton. Why do you suppose these steps are so important? Specifically discuss what these steps allowed a eukaryotic ancestor.

Answer 1

* Solutes along with salts and other aminoacids get reabsorbed from urine in the proximal tubule. Salts don't need any transporters for their reabsorption.The other amino acids that are not reabsorbed do not create crystals in urine.



* epulos are a group of Gram-positive bacteria that have a symbiotic relationship with surgeonfish.They are still the largest known heterotrophic bacteria. In addition to their large size, Epulopiscium, commonly referred to as "epulos," are morphologically diverse and extremely polyploid.

Ways can form epulos

Epulos also have unique reproductive strategies in which certain

1 cells can form intracellular offspring,
2 similar to microbial sporulation; furthermore,
3 several epulo morphologies exhibit sporulation.

While the bacteria have not been successfully grown in the lab, scientists have gained a better understanding of Epulopiscium spp

*This major theme in the origin of eukaryotes is known as endosymbiosis.

steps allowed a eukaryotic ancestor.

1 Time scale of evolution. The scale indicates the approximate times at which some of the major events in the evolution of cells are thought to have occurred.

2 Water vapor was refluxed through an atmosphere consisting of CH4, NH3, and H2, into which electric sparks were discharged. Analysis of the reaction products revealed the formation of a variety of organic molecules, including the amino acids alanine, aspartic acid, glutamic acid, and glycine.

3 Self-replication of RNA. Complementary pairing between nucleotides (adenine [A] with uracil [U] and guanine [G] with cytosine [C]) allows one strand of RNA to serve as a template for the synthesis of a new strand with the complementary sequence.

4 The first cell is thought to have arisen by the enclosure of self-replicating RNA and associated molecules in a membrane composed of phospholipids. Each phospholipid molecule has two long hydrophobic tails attached to a hydrophilic head group. The hydrophobic tails are buried in the lipid bilayer; the hydrophilic heads are exposed to water on both sides of the membrane.

5 Glycolysis is the anaerobic breakdown of glucose to lactic acid. Photosynthesis utilizes energy from sunlight to drive the synthesis of glucose from CO2 and H2O, with the release of O2 as a by-product. The O2 released by photosynthesis is used in oxidative metabolism, in which glucose is broken down to CO2 and H2O, releasing much more energy than is obtained from glycolysis.

6 Electron micrograph of E. coli. The cell is surrounded by a cell wall, within which is the plasma membrane. DNA is located in the nucleoid

7 Both animal and plant cells are surrounded by a plasma membrane and contain a nucleus, a cytoskeleton, and many cytoplasmic organelles in common. Plant cells are also surrounded by a cell wall and contain chloroplasts and large vacuoles

8 Present-day cells evolved from a common prokaryotic ancestor along three lines of descent, giving rise to archaebacteria, eubacteria, and eukaryotes. Mitochondria and chloroplasts originated from the endosymbiotic association of aerobic bacteria and cyanobacteria, respectively, with the ancestors of eukaryotes.