Structural Biochemistry/Cellular Bases

Molecular Organization

The Cell and Its Organelles

The cell is the most fundamental unit of living organisms, providing both structure and function. Different cells may take on different shapes, sizes, and functions, but all have the same fundamental properties. Within the cell are various organelles, which give the cell structure and function. The amounts and types of organelles found vary from cell to cell.^[1]

There are two major types of cells: prokaryotes and eukaryotes. A prokaryotic cell, such as a bacteria cell, is one which lacks a "true" nucleus and membrane-bound organelles. The genetic information of a prokaryote is localized in the nucleoid region within the cytoplasm. On the other hand, eukaryotic cells store their genetic information in a membrane-enclosed nucleus. The larger of the two types, eukaryotes further differ from prokaryotes in that they contain membranous organelles, such as the mitochondria and the endoplasmic reticulum.

Two common types of eukaryotic cells are animal and plant cells. Plant cells have cell walls, which give them their rigid structure. Unique to plant cells, chloroplasts allows them to photosynthesize. These two structures are not found in animal cells. The absence of a cell wall enables animals cells to adopt a variety of shapes. A lysosome, which contains digestive enzymes, is found exclusively in animal cells. Another difference between animal and plant cells is the size of their vacuoles. Animal cells have several small vacuoles throughout the cytoplasm while plant cells contain just one large central vacuole.

Cell Size

The size of a cell is limited by diffusion. Though larger cells are able to contain more biochemicals, a smaller size that maximizes the surface area-to-volume ratio is most ideal. Simple geometry tells us that the area-to-volume ratio is given by 3/r, which is inversely proportional to the radius. Molecules, such as oxygen, that are required by the cell to function need to be able to reach all parts of the cell efficiently. Thus, a greater diffusion rate is promoted by a smaller cell size.^[2]

Cell Movement

One of the most traveled cells are blood cells. Red blood cells move passively as the bloodstream carries them. White blood cells protect people from viruses and bacteria so their movement needs to be quick to the site of infection. The feeling of pain is what happens when white blood cells move to the focused site. The white blood cells move like amoebae, where they move by stretching parts of themselves and the entire cell moves towards where said part was stretched. This process is repeated over and over again. ^[3]

Cell Theory

The Cell Theory is that all living things are composed of cells and that all cells originate from pre-existing cells. Cells are relatively small because it reassures a big surface to volume ratio, which is need to facilitate a fast exchange of material with the extracellular environment.

Supramolecular Complexes

Supramolecular complexes compose the organelles. These include chromosomes, plasma membrane, and the cell wall.

Macromolecules

Supramolecular complexes are composed of macromolecules, such as DNA, protein, and cellulose. Macromolecules are the rather large in size molecules in chemistry. The weak, non-covalent forces between macromolecules provide stability and structure to the supramolecular complex. The four major macromolecules are nucleic acids, proteins, sugars, and lipids. Macromolecules needs assistance, such as salts or ions, when dissolving. In the case of proteins, they will denature when the concentration is out of their range of concentration. Since they are so big, they will also effect the rate of equilibrium when there is a very high concentration of macromolecules.

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Monomeric Units

Macromolecules can be further subdivided into their respective monomeric units. DNA is composed of nucleotide units, while protein is composed of amino acids. Carbohydrates are made of sugar subunits, and lipids are made of fatty acid subunits.

The Structural Hierarchy

Supramolecular complex	Macromolecules	Monomeric Units
Chromosome	DNA	Nucleotides
Plasma membrane	Protein	Amino Acid
Cell Wall	Cellulose	Sugars

References

↑ Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)
↑ Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)
↑ Inside the Cell
↑ Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)

[1] Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)

[2] Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)

[cell-3] Inside the Cell

[4] Nelson, David L. (2004). Principles of Biochemistry (4th Ed. ed.). W. H. Freeman. ISBN 0716743396. {{cite book}}: |edition= has extra text (help)

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