Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

8. DNA Replication

Overview of DNA Replication

Genetics

8. DNA Replication

Overview of DNA Replication

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1:22 minutes

Problem 17

Textbook Question

Outline the current model for DNA synthesis.

Verified step by step guidance

Understand that DNA synthesis, also known as DNA replication, is a semi-conservative process where each of the two strands of the original DNA molecule serves as a template for the formation of a new complementary strand.

Recognize the role of enzymes: Helicase unwinds the double helix, creating a replication fork, while single-strand binding proteins stabilize the unwound strands.

Learn how primase synthesizes a short RNA primer to provide a starting point for DNA polymerase, which adds nucleotides to the growing DNA strand in the 5' to 3' direction.

Distinguish between the leading strand (synthesized continuously) and the lagging strand (synthesized discontinuously in short fragments called Okazaki fragments). DNA ligase later joins these fragments.

Understand the proofreading and error correction mechanisms: DNA polymerase has exonuclease activity that removes mismatched nucleotides, ensuring high fidelity during replication.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

DNA Replication

DNA replication is the biological process by which a cell duplicates its DNA, ensuring that each daughter cell receives an identical copy of the genetic material. This process involves unwinding the double helix structure of DNA, followed by the synthesis of new complementary strands using existing strands as templates.

Enzymes Involved in DNA Synthesis

Several key enzymes play crucial roles in DNA synthesis, including DNA helicase, which unwinds the DNA strands, and DNA polymerase, which synthesizes new DNA strands by adding nucleotides complementary to the template strand. Other enzymes, such as primase and ligase, assist in starting the synthesis and joining Okazaki fragments on the lagging strand.

Leading and Lagging Strands

During DNA replication, the two strands are synthesized differently: the leading strand is synthesized continuously in the direction of the replication fork, while the lagging strand is synthesized in short segments called Okazaki fragments, which are later joined together. This difference arises due to the antiparallel nature of DNA strands and the unidirectional activity of DNA polymerase.

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Related Practice

Textbook Question

Distinguish between

(a) unidirectional and bidirectional synthesis, and

(b) continuous and discontinuous synthesis of DNA.

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Textbook Question

Diagram a replication fork in bacterial DNA and label the following structures or molecules.

a. DNA pol III

b. Helicase

c. RNA primer

d. Origin of replication

e. leading strand (label its polarity)

f. DNA pol I

g. Topoisomerase

h. SSB protein

i. Lagging strand (label its polarity)

j. Primase

k. Okazaki fragment

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Textbook Question

List the proteins that unwind DNA during in vivo DNA synthesis. How do they function?

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Textbook Question

Define and indicate the significance of

(a) Okazaki fragments,

(b) DNA ligase, and

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Textbook Question

Why is DNA synthesis expected to be more complex in eukaryotes than in bacteria? How is DNA synthesis similar in the two types of organisms?

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Textbook Question

Suppose that E. coli synthesizes DNA at a rate of 100,000 nucleotides per minute and takes 40 minutes to replicate its chromosome.

(a) How many base pairs are present in the entire E. coli chromosome?

(b) What is the physical length of the chromosome in its helical configuration—that is, what is the circumference of the chromosome if it were opened into a circle?

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Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Supercoiled strands remain after replication, which is never completed.

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Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Synthesis is very slow.

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