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Living Cells

Question 1

All living cells, both prokaryotic and eukaryotic, have the following cell structures: plasma membrane, cytosol, ribosomes, and at least one chromosome. Choose any one of these. Describe its basic structure (including molecular composition) as well as the function. Explain why a cell could not exist without the function(s) performed by this cell structure.


I have chosen ribosomes for analysis. A ribosome consists of ribosomal proteins and ribonucleic acid (RNA). The role of ribosomes is to translate the genetic information stored in the DNA into the sequences of amino acids (Weinstein, 1995). Structurally, a ribosome consists of two subunits (larger and smaller subunit), which are marked in accordance with their ability to sediment on a special gel. For eukaryotic cells, these are 60S and 40S subunits, and for prokaryotic cells, ribosomes consist of 50S and 30S subunits (Solomon & Berg & Martin, 2004).

Ribosomes are responsible for synthesizing proteins in the cell. Proteins perform a variety of functions in the cells, e.g. structural support of cells, movement, protection from viruses etc. To create proteins, the cell generates mRNA in the nucleus, and the connection between ribosome subunits starts the process of protein synthesis.

Question 2

Cells can be categorized as either prokaryotic or eukaryotic. Only bacterial cells are prokaryotic. For question two, answer any one of the following comparison questions. Be sure to compare both molecular (physical) structure and function in each answer.

Compare the bacterial flagellum (prokaryotic) to an animal cell flagellum (eukaryotic)? How do they differ; how are they similar?


Flagellum is an organelle specializing in motion; it can be considered a molecular motor of the cell (Weinstein, 1995). Although flagella of prokaryotic and eukaryotic cells perform the same functions, they have different structure, form and propulsion mechanism.

On the molecular level prokaryotic flagellum consists of protein flagellin; this structure bends to the outer membrane using the “hook”. Movement is performed by the Mot complex made of protein (analogue of a rotary engine) located at the anchor point at the outer membrane of the cell (Solomon & Berg & Martin, 2004).

The structure of eukaryotic flagella is significantly more complex. The base of the flagella is formed by 9 groups of microtubules (3 microtubules in each group), which surround 2 single microtubules in the center (Weinstein, 1995). The “fundament” of flagella is the basal body, kinetosome or blepharoplast (Karp, 2009). The movement is performed due to ATP hydrolysis performed by the dynein “arms” stretching between 9 microtubules to the central structure.

Question 3

Choose any one of the following eukaryotic cell structures for a short essay (I have chosen Lysosome). Describe its basic structure (including molecular composition) as well as the function. Why is the function important to keeping the cell alive?


Lysosomes are organelles with a membrane filled with enzymes. Goldi apparatus is responsible for making the lysosomes, and enzymes contained in the lysosomes are created by the endoplasmic reticulum (Karp, 2009). Key enzymes found in the lysosomes are lipase, amylase, proteases, nucleases and phosphoric acid monoesters (Karp, 2009).

The role of lysosomes is to degrade garbage and worn out organelles in the cells. In addition to this, lysosomes handle the products of endocytosis mediated by receptors, e.g. receptor, ligand and associated membrane (Weinstein, 1995). Thus, lysosomes are vital for the cell’s disposal processes, digestive processes, self-reparation and autolysis.


Weinstein, P. (1995). Introductory biology. Pascal Press.
Solomon, E.P. & Berg, L.R. & Martin, D.W. (2004). Biology. Cengage Learning.
Karp, G. (2009). Cell and Molecular Biology: Concepts and Experiments. John Wiley and Sons.