14. DNA Synthesis

DNA Repair

DNA Repair Mechanisms: Beautiful USMLE Lectures

The single-stranded binding proteins were malfunctioning during DNA replication.

There were one or more mutations in the RNA primer.

The proofreading mechanism of DNA polymerase was malfunctioning.

The DNA polymerase was unable to add bases to the 3′ end of the growing DNA strand.

Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these mutations?

Which statement best characterizes primary growth?
a. It does not occur in roots, only in shoots.
b. It leads to the development of cork tissue.
c. It produces the dermal, ground, and vascular tissues.
d. It produces rings of xylem, phloem, and cork tissue.

DNA Proofreading & Repair Enzymes

 These individuals are extremely sensitive to sunlight. 

 No. This is true, but it is not the only correct answer. 

 These individuals have high rates of skin cancer. 

 These individuals usually have inherited defects in the nucleotide excision repair system. 

 Cells in these individuals have difficulty repairing thymine dimers. 

 All of the listed responses are correct. 

Mutations can have serious effects.

Which of the following statements is/are correct with regard to individuals with the disorder xeroderma pigmentosum?

DNA Repair Mechanisms Base Excision Repair  - Animation

Humans possess which of the following traits? Select True or False for each trait.
T/F triploblasty
T/F parthenogenesis
T/F viviparity
T/F metamorphosis

Overview of DNA Repair Mechanisms

Mechanisms of DNA Damage and Repair

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?
a. nuclease, DNA polymerase, DNA ligase
b. telomerase, primase, DNA polymerase
c. telomerase, helicase, single-strand binding protein
d. DNA ligase, replication fork proteins, adenylyl cyclase

What happens when your DNA is damaged? - Monica Menesini

DNA replication is amazingly accurate. But an error is likely to be introduced almost every time a human cell divides.

As a result of proofreading by DNA polymerases, the overall error rate in the completed DNA molecule is approximately __________.

 No. Primase is not involved in excision repair. 

 No. Helicase and primase are involved in DNA replication, not nucleotide excision repair. 

 No. Primase is not involved in nucleotide excision repair. 

 No. Hydrolase enzymes are involved primarily in digestion. 

Review the excision of thymine dimers.

Which set of enzymes is involved in nucleotide excision repair?

 Unlike multicellular eukaryotes, bacteria lack DNA repair enzymes, so there are just more uncorrected errors at play. 

No. Bacteria such as E. coli have about 100 enzymes involved in DNA repair.

 Although the genome for each is represented as pairs of homologous chromosomes, errors in bacteria affect both homologs, but only one is affected in eukaryotes. 

 No. The bacterial genome exists as a single, circular chromosome. 

 Only errors that lead to faster-growing strains are left uncorrected in bacteria, whereas all errors are detected and repaired in multicellular eukaryotes. 

 No. Bacteria can't choose which errors to leave uncorrected, just as multicellular eukaryotes do not repair every error that occurs. 

 The third and fourth listed responses can explain this phenomenon. 

 No. Only one of the answers provides an evidence-supported explanation. 

 Because they are asexual and single-celled, all uncorrected errors of replication in bacteria are transmitted to subsequent generations. Multicellular eukaryotes typically reproduce sexually, so uncorrected errors are transmitted only if they occur in germ cells that meiotically divide to produce gametes.  

Consider the differences in how these two groups reproduce.

In a comparison between asexually reproducing bacteria and sexually reproducing multicellular eukaryotes, uncorrected errors in replication are more likely to be transmitted to subsequent generations in bacteria than in multicellular eukaryotes. Which of the following provides the best evidence-based explanation for this difference?

DNA Damage Response

You attached a birdfeeder to a tree 5 years ago at a position 6 feet above the ground. The tree has grown since at a rate of 1 foot per year. What is the current height of the birdfeeder?

 will almost certainly lead to the death of the cell 

 No. Even if the mistake is not corrected, most single base alterations have little effect on the cell. 

 cannot be repaired, and a new mutation will invariably result 

 No. Although it may lead to a new mutation, there is a chance that it will be detected and repaired. 

 will trigger the cell to destroy the new strand, and replication will begin again 

 No. Once replication has started, it will continue even if incorrect bases are incorporated. 

 is virtually impossible, as the accuracy of DNA polymerase is such that errors almost never occur 

 No. Although DNA polymerase is remarkably accurate, errors still occur. 

 can be repaired by the mismatch repair system 

Accurate replication of DNA is extremely important to the cell.

The incorporation of an incorrect base into the DNA during replication __________.

Plants experience a vast array of conditions that can alter their growth and development, including temperature and availability of water, nutrients, and light. They are also exposed to pollutants such as acid rain formed largely as a result of burning fossil fuels and volcanic eruptions. Acid rain can strip minerals and nutrients from the soil, and eat away the outer waxy layer of tissue that protects a plant. Acid rain is still a major environmental problem in certain regions. How does acid rain affect plant growth?

Develop a hypothesis on the likely effects of acid rain on primary growth in trees. Based on your hypothesis, make some predictions about the impact of acid rain on the height of tree trunks.

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Hussain Biology

1. Introduction to Biology

2. Chemistry

3. Water

4. Biomolecules

5. Cell Components

6. The Membrane

7. Energy and Metabolism

8. Respiration

9. Photosynthesis

10. Cell Signaling

11. Cell Division

12. Meiosis

13. Mendelian Genetics

15. Gene Expression

16. Regulation of Expression

17. Viruses

18. Biotechnology

19. Genomics

20. Development

21. Evolution by Natural Selection

22. Evolution of Populations

23. Speciation

24. History of Life on Earth

25. Phylogeny

26. Prokaryotes

27. Protists

28. Plants

29. Fungi

30. Overview of Animals

31. Invertebrates

32. Vertebrates

33. Plant Anatomy