Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

6. Enzymes and Enzyme Kinetics

Enzymes

Biochemistry

6. Enzymes and Enzyme Kinetics

Enzymes

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Multiple Choice

Which molecule catalyzes covalent bond formation between fragments of DNA?

Topoisomerase

DNA polymerase

Helicase

DNA ligase

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Verified step by step guidance

Step 1: Understand the role of DNA ligase in the context of DNA replication and repair. DNA ligase is an enzyme that catalyzes the formation of covalent bonds between the 3'-hydroxyl group of one DNA fragment and the 5'-phosphate group of another, sealing nicks in the DNA backbone.

Step 2: Compare the functions of the other enzymes listed in the problem. Topoisomerase relieves supercoiling in DNA, DNA polymerase synthesizes new DNA strands by adding nucleotides, and helicase unwinds the DNA double helix. None of these enzymes are responsible for covalent bond formation between DNA fragments.

Step 3: Recognize that DNA ligase is specifically involved in processes like DNA replication (joining Okazaki fragments on the lagging strand) and DNA repair (sealing breaks in the DNA backbone). This is a key distinguishing feature of DNA ligase.

Step 4: Recall the chemical mechanism of DNA ligase. It uses ATP or NAD+ as a cofactor to activate the phosphate group at the nick site, facilitating the formation of a phosphodiester bond between DNA fragments.

Step 5: Confirm that DNA ligase is the correct answer based on its unique role in catalyzing covalent bond formation between DNA fragments, which is not performed by the other enzymes listed.