The Nucleus and Nucleic Acids

Objectives

When you have completed this section, you should be able to

• describe the structure of the cell nucleus;
• describe how DNA is organized in the nucleus;
• compare the molecular structures of DNA and RNA; and
• compare the functions of DNA and RNA.

Think About It

What would be the base sequence of the DNA strand across from ATTGACTCG? If a DNA molecule were known to be 20% adenine, predict its percentage of cytosine and explain your answer.

Key Point Review

1. What is the difference between DNA and chromatin?

2. What are the three components of a nucleotide? Which component varies from one nucleotide to another?

3. What two factors govern the pattern of base pairing in DNA?

4. Summarize the differences between RNA and DNA.

Protein Synthesis and Secretion

Objectives

When you have completed this section, you should be able to

• explain what is meant by the genetic code and describe the way in which DNA codes for protein structure;
• describe the events of genetic transcription and translation, and explain the importance of these processes;
• explain what happens to a protein after its amino acid sequence has been synthesized; and
• explain how DNA, which codes only for proteins, indirectly regulates the synthesis of other classes of biomolecules.

Key Point Review

5. Define genetic code and codon.

6. Describe the roles of RNA polymerase and SnRNPs in mRNA synthesis.

7. Describe the roles of ribosomes and tRNA in translation.

8. Why are chaperones important in determining tertiary protein structure?

9. What roles do the rough ER and Golgi complex play in the production and secretion of proteins?

DNA Replication and the Cell Cycle

Objectives

When you have completed this section, you should be able to

• describe how DNA is replicated;
• discuss the consequences of replication errors;
• describe the life history of a cell, including the events of mitosis;
• explain how the timing of cell division is regulated;
• describe some of the genetic and environmental causes of cancer; and
• explain why untreated cancer is fatal.

Key Point Review

10. Describe the roles of DNA helicase, DNA polymerase, and DNA ligase.

11. Why is DNA replication called semiconservative?

12. Define mutation. Why are some mutations harmless and others harmful?

13. List the four stages of the cell cycle and describe the main events of each.

14. Describe the structure of a chromosome at metaphase.

15. Explain how an oncogene may cause cancer and how a tumor suppressor gene may prevent cancer.

Chromosomes and Heredity

Objectives

When you have completed this section, you should be able to

• describe the structure and paired arrangement of human chromosomes;
• define allele and discuss the various ways in which alleles interact to affect the traits of the individual; and
• discuss the interaction of heredity and environment in producing individual traits.

Think About It

When a karyotype is needed, why does a cytogeneticist use cells at metaphase instead of interphase?

Think About It

Would it be possible for an albino woman to have children with normal pigmentation? Use a Punnett square and one or more hypothetical genotypes for the father to demonstrate your point.

Think About It

Why couldn't one person have all three of these alleles?

Key Point Review

16. Define these terms: homologous chromosomes, locus, gene, and allele.

17. Why must a carrier of a genetic disease be heterozygous?

18. Distinguish between multiple gene inheritance and pleiotropy.

19. Give at least three reasons why a person's genotype cannot necessarily be inferred from the phenotype.

20. Explain why some traits occur mainly in males, even though they can be inherited only from their mothers.

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