DNA Structure and Replication Crash Course Biology #10 Worksheet Answers
This document provides answers to the worksheet accompanying Crash Course Biology #10 on DNA structure and replication. Remember that understanding the why behind the answers is crucial for true comprehension. These answers are intended as a guide, and your specific worksheet might have slightly different phrasing.
Section 1: DNA Structure
1. What are the three components of a nucleotide?
- Answer: A nucleotide consists of a phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base (adenine, guanine, cytosine, or thymine).
2. Which bases pair together in DNA?
- Answer: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
3. Describe the overall structure of a DNA molecule.
- Answer: DNA is a double helix, resembling a twisted ladder. The sides of the ladder are formed by alternating sugar and phosphate groups, while the rungs are formed by the paired nitrogenous bases. The two strands run antiparallel to each other (one 5' to 3', the other 3' to 5').
4. What type of bonds hold the bases together? What type of bonds hold the sugar-phosphate backbone together?
- Answer: Hydrogen bonds hold the bases together (two between A and T, three between G and C). Phosphodiester bonds hold the sugar-phosphate backbone together.
Section 2: DNA Replication
1. What is the central dogma of molecular biology?
- Answer: The central dogma describes the flow of genetic information: DNA → RNA → Protein.
2. What does it mean that DNA replication is semi-conservative?
- Answer: Semi-conservative replication means that each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.
3. What is the role of DNA polymerase in DNA replication?
- Answer: DNA polymerase is the enzyme that adds nucleotides to the growing DNA strand, synthesizing new DNA. It also has a proofreading function to correct errors.
4. What are Okazaki fragments and why are they necessary?
- Answer: Okazaki fragments are short, newly synthesized DNA fragments formed on the lagging strand during replication. They are necessary because DNA polymerase can only synthesize DNA in the 5' to 3' direction, and the lagging strand runs in the opposite direction.
5. What is the role of DNA ligase?
- Answer: DNA ligase joins the Okazaki fragments together to form a continuous lagging strand.
6. What are some of the proteins involved in DNA replication and what are their functions (e.g., helicase, primase, single-stranded binding proteins)?
- Answer:
- Helicase: Unwinds the DNA double helix.
- Primase: Synthesizes RNA primers, providing a starting point for DNA polymerase.
- Single-stranded binding proteins (SSBs): Prevent the separated DNA strands from reannealing.
- Topoisomerase: Relieves torsional strain ahead of the replication fork.
Important Note:
This is a general answer key. The specific questions and therefore the answers on your worksheet might vary slightly. Refer to your lecture notes and textbook for a deeper understanding of the concepts. Always focus on grasping the underlying principles rather than memorizing answers.
