Mastering A&P Homework No. 3

Mastering A&P Homework No. 3 1. 2. 3. Which of the following would NOT diffuse through the plasma membrane by means of simple diffusion?  Glucose - Glucose, a small polar solute, uses a membrane transporter (a protein carrier) to cross the plasma membrane via facilitated diffusion. In simple diffusion, small nonpolar and lipid-soluble substances (including gases) diffuse directly through the lipid bilayer. 4. This figure illustrates which of the following descriptions?  the use of a sodium concentration gradient to power the pumping of glucose into the cell - The sodium ion gradient is generated by the Na+-K+ pump at the left. Diffusion of sodium ions through the Na+-glucose symport (shown at the right) provides the energy necessary to actively transport glucose into the cell. Such a mechanism is used by intestinal cells (to absorb nutrients) and kidney cells (to recover glucose from urine prior to excretion). 5. By which mechanism would a steroid molecule diffuse into the cell?  A - Steroid molecules are nonpolar fat-soluble molecules, which would be expected to diffuse directly across the phospholipid bilayer. Such solutes do not require a membrane protein to facilitate transport. 6. Which of the following is a difference between primary and secondary active transport?  In primary active transport, the transport protein gets phosphorylated; in secondary active transport, the transport protein is not phosphorylated. - In primary active transport, energy comes directly from the hydrolysis of ATP and the subsequent phosphorylation of the primary active transporter. In secondary active transport, the solute (usually Na+) concentration gradient produced by primary active transport provides the (kinetic) energy to move other solutes, such as ions and glucose, against their concentration gradients. For example, glucose can be transported against its concentration gradient through a Na+-glucose symporter as Na+ moves down its concentration gradient (a gradient produced by the Na+-K+ pump). 7. What is a membrane potential?  a voltage or electrical charge across the plasma membrane - The membrane potential is the electrical potential energy (measured in millivolts) resulting from the separation of oppositely charged particles (ions) across the plasma membrane. At rest, membrane potentials are typically negative, ranging from -50 to -100 mV, with more anions (than cations) concentrated along the internal surface of the membrane, and more cations (than anions) concentrated along the external surface. 8. What major function occurs on the specific membranes indicated by A?  synthesis of secreted proteins - Structure A is the rough endoplasmic reticulum (ER). The figure illustrates how proteins are synthesized on ribosomes bound to the rough ER, sorted in the Golgi, and delivered to the plasma membrane for secretion or packaged into lysosomes. 9. Which cell component helps to maintain the structural integrity of the cell?  Cytoskeleton - The cytoskeleton acts as the cell's "bones," "muscles," and "ligaments" by supporting cellular structures and providing the machinery to generate various cell movements. 10. 11.Which of the following statements best explains why the leading and lagging strands are synthesized using two different mechanisms?  The DNA is replicated in one direction, but DNA polymerase must work in opposite directions on each parent strand. - In the figure, the DNA of the chromosome is being replicated from right to left. Because the "old" DNA of the parental template consists of antiparallel strands, the new DNA is polymerized in two different directions. 12. The region of molecule B that encodes a polypeptide is 24 nucleotides in length. Consider another such molecule with a coding region of 300 nucleotides. What is a reasonable estimate for the length of the corresponding polypeptide that will be produced during protein synthesis?  100 Amino acids - Each amino acid corresponds to a codon of 3 nucleotides. Therefore, a coding region of 300 nucleotides contains 100 codons and will produce a polypeptide of 100 amino acids in length. 13. A: During which phase of the cell cycle does DNA duplication, or replication, take place?  Interphase - Yes! DNA replicates during interphase. This process provides each new daughter cell with a full complement of genetic material. B: When a double helix of DNA is replicated, two complete helices are formed. Together, these helices are called sister __________.  Chromatids - Yes! Each new daughter cell receives one of the sister chromatids. After the chromatids separate, each is considered a new chromosome. At the end of cell division, each new cell contains 23 pairs of chromosomes. C: During which phase of mitosis do sister chromatids line up at the center of the cell?  Metaphase - Yes! Spindle microtubules from both poles of the cell attach to the sister chromatids and pull them in both directions. During metaphase, the sister chromatids are forced to the center of the cell. D: During which phase of mitosis do the sister chromatids move apart?  Metaphase - Yes! During anaphase, the centromeres split and the spindle microtubules pull the sister chromatids to opposite poles of the cell. The single chromatids are now considered chromosomes. E: During which phase of mitosis do nuclear envelopes and the nucleoli reappear?  Telophase - Yes! Telophase begins when the chromosomes stop moving. Nuclear envelopes form, and nucleoli reappear. Ultimately, the cell divides in two by a process known as cytokinesis. F: During which phase of mitosis do the nuclear envelope and nucleoli disappear?  Prophase - Yes! Prophase is the first phase of mitosis. During this phase, the sister chromatids condense, the nuclear envelope and nucleoli disappear, and the spindle apparatus forms. E. What is the name of the process by which the cytoplasm divides in two?  Cytokinesis - Yes! During cytokinesis, a ring of actin and myosin filaments contract to form a cleavage furrow and the cell divides in two.