The Survey of the Natural Sciences usually includes biology questions related to cells and molecules. We’ll explore some important concepts to know.
Generalized Eukaryotic Cell
Each eukaryotic cell has a nucleus and other membrane-bound organelles.
A eukaryotic cell:
- Contains rod-shaped chromosomes
- Has vesicles to transport waste
- Has vacuoles for storage and support
- Contains a centrosome (microtubule organizing center or MTOC) if it is an animal cell; plant cells do not have MTOCs
- Has lysosomes if it is an animal cell; plant cells do not have lysosomes
- Has a central vacuole and chloroplasts if it is a plant cell; animal cells do not have central vacuoles and chloroplasts
Use the diagram below to review the parts of an animal eukaryotic cell:
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 which 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 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 (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
Unlike eukaryotic cells, prokaryotic cells (like those which make up bacteria) do not have organelles. However, prokaryotic cells do contain ribosomes and they have plasma membranes.
Cellular metabolism refers to the biochemical reactions, which are catalyzed by proteins called enzymes. Biochemical reactions take place in all cells belonging to living organisms. There are two main types of cellular metabolism: catabolism and anabolism, which have opposite purposes.
Catabolism degrades molecules, typically through oxidation, in which electrons are removed from the molecules. The process of catabolism generally takes place to allow energy to be gathered from the molecules. You may recall that processes that release energy are exergonic.
Anabolism usually requires cells to expend energy (instead of gathering energy) by transferring electrons to molecules. Reactions that require the expenditure of energy are endergonic. Anabolic processes build tissue by synthesizing the four classes of macromolecules: polysaccharides, proteins, lipids, and nucleic acids.
- Polysaccharides: stored as carbohydrates, such as glycogen
- Proteins: form an array of cell functions and are made up of amino acids
- Lipids: hydrophobic molecules composed mainly of hydrocarbon bonds
- Nucleic acids: Transmit and express the genetic information (DNA and RNA)