Chapter Summary

Cell Membrane and Associated Structures

1. The structure of the cell (plasma) membrane is described by a fluid-mosaic model.
1. The membrane is composed predominately of a double layer of phospholipids.
2. The membrane also contains proteins most of which span its entire width.
2. Some cells move by extending pseudopods; cilia and flagella protrude from the cell membrane of some specialized cells.
3. In the process of exocytosis, invaginations of the cell membrane allow the cells to take up molecules from the external environment.
1. In phagocytosis, the cell extends pseudopods, which eventually fuse together to create a food vacuole; pinocytosis involves the formation of a narrow furrow in the membrane which eventually fuses.
2. Receptor-mediated endocytosis requires the interaction of a specific molecule in the extracellular environment with a specific receptor protein in the cell membrane.
3. Exocytosis is the reverse of endocytosis and is a process that allows the cell to secrete its products.

Cytoplasm and Its Organelles

1. Microfilaments and microtubules produce a cytoskeleton, which aids movements of organelles within a cell.
2. Lysosomes contain digestive enzymes and are responsible for the elimination of structures and molecules within the cell and for digestion of the contents of the phagocytic food vacuoles.
3. Mitochondria serve as the major sites for energy production within the cell. They have an outer membrane with a smooth contour and an inner membrane with infoldings called cristae.
4. The endoplasmic reticulum is a system of membranous tubules in the cell.
1. The rough endoplasmic reticulum is covered with ribosomes and is involved in protein synthesis.
2. The smooth endoplasmic reticulum provides a site for many enzymatic reactions and, in skeletal muscles, serves to store Ca²⁺.

Cell Nucleus and Nucleic Acids

1. The cell nucleus is surrounded by a double-layered nuclear membrane. At some points, the two layers are fused by nuclear pore complexes that allow for the passage of molecules.
2. Nucleic acids include DNA, RNA, and their nucleotide subunits.
1. The DNA nucleotides contain the sugar deoxyribose, whereas the RNA nucleotides contain the sugar ribose.
2. There are four different types of DNA nucleotides, each of which contains one of four possible bases: adenine, guanine, cytosine, or thymine; in RNA, the base uracil substitutes for the base thymine.
3. DNA consists of two long polynucleotide strands twisted into a double helix. The two strands are held together by hydrogen bonds between specific bases; adenine pairs with thymine, and guanine pairs with cytosine.
4. RNA is single-stranded. Four types of RNA are produced within the nucleus: ribosomal RNA, transfer RNA, precursor messenger RNA, and messenger RNA.
3. Active euchromatin directs the synthesis of RNA; this process is called transcription.
1. The enzyme RNA polymerase causes separation of the two strands of DNA along the region of the DNA that constitutes a gene.
2. One of the two separated strands of DNA serves as a template for the production of RNA; this occurs by complementary base pairing between the DNA bases and ribonucleotide bases.

Protein Synthesis and Secretion

1. Messenger RNA leaves the nucleus and attaches to the ribosomes.
2. Each transfer RNA, with a specific base triplet in its anticodon, bonds to a specific amino acid.
1. As the mRNA moves through the ribosomes, complementary base pairing between tRNA anticodons and mRNA codons occurs.
2. As each successive tRNA molecule bonds to its complementary codon, the amino acid it carries is added to the end of a growing polypeptide chain.
3. Proteins destined for secretion are produced in ribosomes located on the rough endoplasmic reticulum and enter the cisternae of this organelle.
4. Secretory proteins move from the rough endoplasmic reticulum to the Golgi complex, which consists of a stack of membranous sac.
1. The Golgi complex modifies the proteins it contains, separates different proteins, and packages them in vesicles.
2. Secretory vesicles from the Golgi apparatus fuse with the cell membrane and release their products by exocytosis.

DNA Synthesis and Cell Division

1. Replication of DNA is semiconservative; each DNA strand serves as a template for the production of a new strand.
1. The strands of the original DNA molecule gradually separate along their entire length and, through complementary base pairing, form a new complementary strand.
2. In this way, each DNA molecule consists of one old and one new strand.
2. During the G₁ phase of the cell cycle, the DNA directs the synthesis of RNA, and hence that of proteins.
3. During the S phase of the cycle, DNA directs the synthesis of new DNA and replicates itself.
4. After a brief rest (G₂), the cell begins mitosis (the M stage of the cycle).
1. Mitosis consists of the following phases: interphase, prophase, metaphase, anaphase, and telophase.
2. In mitosis, the homologous chromosomes line up single file and are pulled by spindle fibers to opposite poles.
3. This results in the production of two daughter cells which each contain forty-six chromosomes, just like the parent cell.
5. Meiosis is a special type of cell division that results in the production of gametes in the gonads.
1. The homologous chromosomes line up side by side, so that only one of each pair is pulled to each pole.
2. This results in the production of two daughter cells that each contain only twenty-three chromosomes, which are duplicated.
3. The duplicate chromatids are separated into two new daughter cells during the second meiotic cell division.

1. describe the structure of the cell membrane and explain its functional significance.
2. state which cells in the human body transport themselves by amoeboid movement and explain how they perform this movement.
3. describe the structure of cilia and flagella, and state some of their functions.
4. explain the processes of phagocytosis, pinocytosis, receptor-mediated endocytosis, and exocytosis.
5. explain the functions of the cytoskeleton, lysosomes, mitochondria, and the endoplasmic reticulum.
6. describe the structure of the cell nucleus and explain its significance.
7. describe the structure of nucleotides and distinguish between DNA and RNA.
8. explain how DNA is constructed and what is meant by the law of complementary base pairing.
9. explain how RNA is produced according to the genetic information in DNA and distinguish between the different types of RNA.
10. describe how proteins are produced according to the information contained in messenger RNA.
11. describe the structure and function of the rough endoplasmic reticulum and Golgi complex and explain how they function in the secretion of proteins.
12. explain what is meant by the semiconservative mechanism of DNA replication.
13. describe the different stages of the cell cycle and list the events that occur in the different phases of mitosis.
14. define the terms hypertrophy and hyperplasia and explain their physiological importance.
15. describe the events that occur in meiosis; compare these to those that occur in mitosis and explain the significance of meiotic cell division in human physiology.