When you take the Survey of the Natural Sciences, you should expect to answer biology questions related to cells and molecules. In this section, we’ll explore some important concepts to know.
Generalized Eukaryotic Cell
Every eukaryotic cell has a nucleus, as well as other organelles that are bound by membranes.
Here are some other features of eukaryotic cells to be familiar with:
- They contain rod-shaped chromosomes.
- Vesicles transport waste.
- The vacuoles are used for storage and provide support.
- Animal cells have a centrosome (microtubule organizing center or MTOC), but plant cells do not.
- Animal cells also have lysosomes, while plant cells do not.
- Unlike an animal cell, a plant cell has a cell wall, a large central vacuole, and chloroplasts.
Use the following diagram of an animal eukaryotic cell to review its parts:
Centriole: involved in the production of spindle fibers during cell division
Plasma membrane: protects the interior of the cell from the exterior environment. The plasma membrane is selectively permeable and it regulates the movement of ions and nutrients in and out of the cell based upon their sizes and/or charges.
Vesicles: consist of fluid and encased in a lipid bilayer. They are involved in transport and enzyme storage.
Golgi apparatus: sorts lipids and proteins. The Golgi apparatus also modifies proteins and packages them for secretion while transporting lipids and synthesizing lysosomes.
Lysosome: contains enzymes that are used for digestion and the removal of waste, such as old organelles and endocytosed pathogens, like bacteria and viruses
Nucleus: stores and replicates deoxyribonucleic acid (DNA) and preserves chromosomes, enclosed in a protective double membrane. The nucleus also regulates the cell’s growth, metabolism, and reproduction.
Endoplasmic reticulum (smooth): synthesizes lipids and steroid hormones, detoxifies of metabolic byproducts, does not have membrane-bound ribosomes
Endoplasmic reticulum (rough): has ribosomes attached to its membrane, synthesizes proteins through translation
Ribosomes: site of protein synthesis (aka translation); may be free-floating in the cytoplasm or attached to rough endoplasmic reticulum
Cytoplasm: the “jelly-like” liquid in which the cell’s organelles are suspended; helps facilitate cell signaling, communication, and transport
Mitochondrion: responsible for ATP (adenosine triphosphate) production and regulates cell metabolism. Many are found within the cell and referred to collectively as “mitochondria.”
Cytoskeleton: made up of microfilaments, supports the plasma membrane and gives the cell structure
Note that unlike eukaryotic cells, prokaryotic cells (such as those which make up bacteria) do not have organelles, including nuclei. However, they do contain ribosomes and have a plasma membrane.
The synthesization of proteins is a very important cell function. Use the table below to review the major steps of this process. As you read, remember mRNA is messenger RNA, and tRNA is transfer RNA.
Protein synthesis is made possible by translation, the process in which the mRNA is decoded to specify the sequence of the amino acids in a polypeptide.
The codons found in RNA are adenine (A), cytosine (C), guanine (G), and uracil (U). Adenine and uracil pair (A-U) and cytosine and guanine pair (C-G).
Cellular metabolism refers to the biochemical reactions that occur within the cells of living organisms. Biochemical reactions are catalyzed by enzymes, a type of protein. There are two main types of metabolism, catabolism, and anabolism.
Catabolism degrades molecules, usually by the process of oxidation, in which electrons are removed from the molecules. It generally allows energy to be gathered from the molecules. Processes that release energy are exergonic.
Anabolism, on the other hand, usually requires cells to expend energy by transferring electrons to molecules. Reactions that cause cells to expend energy are endergonic.
Anabolic processes build tissue by synthesizing the four classes of macromolecules needed to maintain cells: carbohydrates, proteins, lipids, and nucleic acids.