Ch 3 Test Yourself Flashcards
3.1
1. What are the basic cellular functions that define life?
The basic processes of life include having a metabolism and the ability to grow, develop, reproduce, adapt, respire, become influenced by outside stimuli, maintain a stable internal environment, and convert food into usable energy.
3.1
2. Describe the series of events that scientists think led to the formation of the first cells on earth.
The first cells are thought to have evolved in the massive oceans of our primitive Earth about 3 billion years ago. Jolted by the fierce electrical energy from frequent lightning storms and by the intense, unabated radiation from the sun, the three molecules (methane gas [CH4], water [H2O], and ammonia [NH3]) that made up the primitive atmosphere were forced to collide and split apart. The first organic molecules, similar to amino acids, are thought to have formed in this environment. Clustering into heavy droplets, these molecules are believed to have been washed by driving rains from the atmosphere into the warm, shallow seas below. There, proteins, lipids, and carbohydrates evolved and arranged themselves over time into sophisticated, organized structures - - the first cells.
3.1
3. What is the difference between a prokaryote and a eukaryote?
Prokaryotes do not contain nuclei. Eukaryotic cells have a distinct nucleus in which the DNA has combined with protein to form chromosomes. These, in turn, are surrounded by a protective nuclear envelope.
3.1
4. Why are cells not the size of watermelons?
Smaller cells have smaller nutritional requirements than large cells but have a proportionately larger surface through which they can absorb the substances they need. Thus, smaller cells are able to complete their metabolic functions more rapidly and efficiently than large cells. If cells were the size of watermelons, they would not be able to take in nutrients fast enough to feed themselves and would die. A second limiting factor in cell size is related to the governing capability of the nucleus. A single nucleus can control the metabolic activity of a small cell better than it could a large one. Also, the more active a cell is, the greater its metabolic needs. Therefore, it is not surprising that very large cells or cells that are more active, such as cardiac and skeletal muscle cells, have two or more nuclei.
3.2
1. Name three structures that all mammalian cells possess.
The cell membrane, the cytoplasm (which includes cytosol and organelles), and the nucleus.
3.2
2. Which part of the lipid layer bilayer is hydrophobic and which part is hydrophilic?
The hydrophilic heads of the phospholipid bilayer are attracted to the aqueous environments found in the extracellular and intracellular spaces. The lipid tails, on the other hand, are hydrophobic and are repelled by these aqueous compartments. Therefore, they are turned inward and face one another inside the bilayer.
3.2
3. What types of protein are found in the cell membrane?
The cell membrane contains structural and globular proteins. Globular proteins include integral and peripheral proteins.
3.2
4. Where are these proteins located and what are their functions?
Integral and peripheral proteins are types of globular proteins. Some integral proteins are located within the bilayer, spanning it. These forms selective passageways and pores that permit only particular substances to enter or exit the cell. Some integral proteins are membrane receptors that act as binding sites on the cell’s surface. Peripheral proteins are bound to the inside and outside surfaces of the cell membrane and sometimes act as enzymes to catalyze specific chemical reactions. They may also be involved in the mechanics of changing the cell’s shape. Glycoproteins, in addition to glycolipids, are the principle components of the “sugar coating” that covers the surface of some cells. This coating is called the glycocalyx.
3.2
5. What are the molecule components of rafts and what role do rafts play in the life of a cell?
Rafts are composed of densely packed phospholipids, cholesterol, and protein. These dense regions are stiff and form rigid, raftlike structures within the otherwise fluid phospholipid bilayer of the cell membrane.
3.2
6. What is the glycocalyx and what important role does it play in cellular interaction?
The glycocalyx is a “sugar coating” on the outside of the cell; it is made of glycoprotein and glycolipid molecules. Similar to the stripes on zebras or the fingerprints on human hands, each glycocalyx is unique. It provides improved cell-to-cell adhesion and represents an important biologic marker for intercellular recognition and for the interactions between the cell and antibodies and the cell and viruses.
3.2
7. What are CAMs and what do they do?
CAM refers to cell adhesion molecules, which are sticky glycoproteins (part of the glycocalyx) that cover the surfaces of almost all cells in mammals and allow them to bond to extracellular molecules and to each other. These molecules are also important in helping cells move past one another and in signaling circulating cells, such as white blood cells, to areas of inflammation or infection.
3.2
8. What are membrane receptors and ligands and what role do they play in the health of the cell?
Membrane receptors are integral proteins and glycoproteins that act as binding sites on the cell surface. Some of them play a vital role in cell-to-cell recognition, a process called contact signaling. This is particularly important during cell-mediated immune responses and helps bacteria and viruses find preferred “target” cells. Membrane receptors are also involved in a process called chemical signaling. Hormones, neurotransmitters, and other chemical messengers called ligands bind to specific binding sites on cell surfaces. Once bound to the cell membrane, ligands can bring about a change in the cell’s activity. Some ligands act as enzymes to activate or inactivate a particular cellular activity.
3.2
8. How does obesity affect cell membrane receptors for insulin?
Obesity can affect cell membrane receptors for insulin by causing a decrease in the number of insulin receptors on the cell surface, leading to reduced insulin binding and impaired insulin signaling, ultimately resulting in insulin resistance; this happens due to a combination of factors including increased inflammation, altered cell membrane composition, and excessive fatty acid accumulation within the cells, which disrupt the normal function of the insulin receptor complex.
3.2
9. What are caveolae and what role do they play in the cell membrane?
Caveolae are minute invaginations of the cell membrane, like tiny dimples. Caveolae often pinch off entirely from the cell membrane, forming vesicles. These vesicles can form singly or in clusters (like tiny rosettes). Caveolae are formed only from rafts in the cell membrane that contain the protein caveolin.
3.2
10. How are cilia and flagella different?
*Cilia occur in large numbers on the exposed surface of some cells. They are shorter than flagella and measure only about 10 um long. They move synchronously, one after the other, creating waves of motion that propel fluid, mucus, and debris across the cell surface. Cilia are best known for their important functions (1) in the upper respiratory tract, where they propel bacteria and mucus away from the lungs, and (2) in the oviduct, where their beating motion pulls the ovulated egg away from the ovary and into the opening of the oviduct.
*Flagella generally occur singly and are significantly longer than cilia. They are typically attached to individual cells and propel the cell forward by undulating. Flagella move cells through fluid, whereas cilia move fluid across cell surfaces. The tail of a sperm cell is an example of a flagellum.
