Recent questions tagged cell-structure

Description : What is the general nature of cells?

Last Answer : All animals, plants, and microorganisms are composed of cells. Cells range in volume from a few attoliters among bacteria to milliliters for the giant nerve cells of squid; typical cells ... are distinguished not only by their different structures but also by their different metabolic activities. 

Description : What type of experiments can we carry out that might shed light on the origin of life?

Last Answer : A landmark experiment that was designed to provide some answers to this question was conducted by Stanley Miller and Harold Urey, working at the University of Chicago (see Fig. 1-1) ... building blocks are known to arise under very plausible and readily reproduced physical and chemical conditions 

Description : What does a typical animal cell look like? 

Last Answer : There is no such thing as a typical animal cell, since cells vary in overall size, shape, and contents of the various subcellular organelles. 

Description : How may cells be disrupted in order to obtain subcellular organelles by centrifugal fractionation?

Last Answer : There are several ways of disrupting cells: 1. Osmotic lysis. The plasma membranes of cells are water-permeable but are impermeable to large molecules and some ions. Thus if cells are placed ... cause microcavitation in the sample, and this disrupts the cell membranes, usually in a few seconds.

Description : There is an inherited disease in which a person’s lysosomes lack the enzyme β-glucosidase What are the clinical and biochemical consequences of this deficiency?

Last Answer : The disease is called Gaucher disease, and it is the most common of the sphingolipidoses; its incidence in the general population is ∼1:2500. This class of disease results from defective hydrolysis of ... may show signs of mental deterioration if much of the lipid accumulates in the brain as well. 

Description : How many red blood cells are there in an average 70- kg person?

Last Answer : There are ∼2.6 × 1013, or 26 trillion. The total blood volume is ∼5.5 L, and ~40% of that is red blood cells;i.e., there are ~2.2 L of red cells. Since each cell has a volume of ∼86 × 10−15 L , the result follows from dividing 2.2 L by this number. 

Description : How many red blood cells are produced in an average 70-kg person every second?

Last Answer : The number is 2.5 million! The average life span of a human red cell is 120 days; therefore the number produced per second is simply given by the 26 trillion (average cells in 70kg person), divided by 120 days and expressed in seconds. 

Description : PAS staining of microscope sections of red blood cells gives a pink stain on only one side of the cell membrane. Which side is it, the extracellular or the intracellular side? 

Last Answer : Extracellular. All glycoprotein and glycolipids of the plasma membrane of red and all other cells are on theoutside of the cell. No oligosaccharides are present on the inner face of the cell membrane. 

Description : A commonly used test of the viability of cells in tissue culture is whether or not they exclude a supravital dye such as toluidine blue. If the cells exclude the dye, they are considered to be viable. What is the biochemical basis of this test? 

Last Answer : The membranes of all living cells are selectively permeable to ions and other chemical species. This selectivity is in many cases linked to the supply of ATP, and one feature of cell death is a low ... of ATP. In this state, the cell no longer excludes foreign compounds, such as toluidine dye. 

Description : Microsomes are small spherical membranous vesicles with attached ribosomes. They sediment, during differential sedimentation, only in the late stages of a preparation when very high centrifugal velocities are used. They don’t appear in electronmicrographs of a cell. From where do they arise?

Last Answer : Fragments of endoplasmic reticulum are transformed from lipid bilayer sheets, with attached ribosomes, into spherical vesicles. This is a result of the homogenization used in preparing the samples and also the tendency of lipid bilayers to spontaneously reseal. 

Description : There are two forms of the enzyme carbamyl phosphate synthetase, one in the mitochondrial matrix and the other in the cytoplasm. What might be the consequence and role of this compartmentation of enzymes?

Last Answer : It enables separate control over the rates of urea and pyrimidine synthesis  

Description : (a) From what primary source is the DNA in your mitochondria, your mother or your father? (b) Speculate onpossible inheritance patterns if there were a defect in one or the other parent’s mitochondria.

Last Answer : (a) Mother. (b) If a defect exists in a mitochondrial gene, all progeny from that female will carry the defect. Several well-defined diseases resulting from such a defect have been described. 

Description : Given that mitochondria do not have the same aggressive autolytic capacity as lysosomes, what might be the significance of having such a complex membranous structure? After all, the ... reticulum and the plasma membrane could potentially support those enzymes found in mitochondrial membranes.

Last Answer : In fact, bacteria do not have mitochondria, but some types do have membranous intrusions into the cytoplasm called mesosomes. These are similar in function to the inner membrane of ... advantage) control of the various metabolic processes that are now distributed between distinct compartments. 

Description : In some sufferers of Down syndrome, the somatic cell nuclei do not contain three chromosomes number 21.There is a chromosomal defect relating to chromosome number 21; what might it be? 

Last Answer : A fragment, usually the short arm, of chromosome 21 is translocated onto another chromosome; thus, there are three copies of a fragment of the short arm in any one cell. This is a relatively rare occurrence.