DNA Structure and Replication

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Questions and Answers

Describe the roles of both helicase and ligase in DNA replication, and explain why both are essential for the process to occur efficiently and accurately.

Helicase unwinds the DNA double helix, creating a replication fork, while ligase joins Okazaki fragments on the lagging strand to create a continuous strand. Without helicase, DNA strands would not separate for replication. Without ligase, the lagging strand would consist of many fragments.

Explain the significance of complementary base pairing in DNA structure and replication. How does this principle ensure the accurate transmission of genetic information?

Complementary base pairing (A with T, and G with C) ensures that each strand of DNA can serve as a template for creating a new, identical strand during replication. This system helps maintain the fidelity of genetic information from one generation to the next.

Compare and contrast the structures of chromatin, chromosomes, and sister chromatids. How does each relate to the packaging and organization of DNA within a cell?

Chromatin is the loosely packed form of DNA found during interphase. A chromosome is a tightly coiled structure of DNA, and sister chromatids are two identical copies of a single chromosome connected by a centromere. This structure allows for efficient organization and segregation of DNA during cell division.

Describe the semi-conservative nature of DNA replication and explain the experimental evidence that supports this model.

<p>Semi-conservative replication results in two DNA molecules, each containing one original strand and one newly synthesized strand. The Meselson-Stahl experiment using isotopes of nitrogen provided evidence for this model.</p> Signup and view all the answers

Outline the major events that occur during each phase of the cell cycle (Interphase, Mitosis, Cytokinesis) and explain why each phase is critical for successful cell division.

<p>Interphase: cell growth and DNA replication; Mitosis: chromosome segregation; Cytokinesis: cell division into two daughter cells. All phases are essential to duplicate and distribute genetic material accurately, ensuring daughter cells are viable.</p> Signup and view all the answers

Explain the importance of DNA replication and the potential consequences if this process did not occur accurately or efficiently. How does it relate to genetic disorders?

<p>DNA replication ensures genetic information is passed accurately to daughter cells. Errors can lead to mutations, potentially causing genetic disorders or cancer, also the cell can die.</p> Signup and view all the answers

Describe the role of the centromere and kinetochore during mitosis. What would happen if the kinetochore did not properly attach to the mitotic spindle?

<p>The centromere is the region where sister chromatids are attached, and the kinetochore is the protein structure on the centromere where microtubules attach. If the kinetochore doesn't attach, chromosomes may not separate correctly, resulting in daughter cells with an abnormal number of chromosomes.</p> Signup and view all the answers

Apoptosis is a programmed cell death. Describe the significance of apoptosis in the context of normal development and maintenance of healthy tissues.

<p>Apoptosis removes damaged or unnecessary cells during development, preventing tumors and maintaining tissue homeostasis. It's a controlled process that ensures cells die without causing inflammation or damage to surrounding tissues.</p> Signup and view all the answers

Explain how the antiparallel nature of DNA strands affects the process of DNA replication. Why is one strand synthesized continuously while the other is synthesized in fragments?

<p>DNA polymerase can only add nucleotides to the 3' end of a strand, replication occurs continuously on the leading strand (3' to 5' template) and discontinuously on the lagging strand (5' to 3' template), forming Okazaki fragments.</p> Signup and view all the answers

Compare and contrast mitosis and cytokinesis. Explain how each process contributes to cell division.

<p>Mitosis is the division of the nucleus and genetic material, while cytokinesis is the division of the cytoplasm. Mitosis ensures each daughter cell receives a complete set of chromosomes, and cytokinesis physically separates the two new cells.</p> Signup and view all the answers

Flashcards

Double helix

The twisted ladder shape of DNA, composed of two strands of nucleotides.

Chromosome

A structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Chromatin

A complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.

Nucleotide

A building block of DNA and RNA, consisting of a sugar, phosphate group, and nitrogenous base.

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Primase

Enzyme that synthesizes short RNA sequences called primers, needed to start DNA replication.

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Replication fork

The structure formed when DNA is being replicated, creating a Y-shape.

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Ligase

Enzyme that joins Okazaki fragments and seals gaps in the DNA strand during replication.

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Semi-conservative

The process where one strand of DNA acts as a template for a new strand, resulting in two DNA molecules, each with one original and one new strand.

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Interphase

The period of the cell cycle during which the cell grows, replicates its DNA, and prepares for cell division.

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Mitosis

The process of cell division that results in two identical daughter cells.

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Study Notes

DNA Structure

  • DNA structure enables it to store and transmit genetic information.
  • All living things must have DNA.
  • The basic unit of DNA is a nucleotide.
  • Hydrogen bonds are between nitrogenous bases, and phosphodiester bonds are between the sugar-phosphate backbone.
  • Complementary base pairing occurs between adenine (A) with thymine (T), and guanine (G) with cytosine (C).
  • Chromosome: A tightly packed structure of DNA visible during cell division.
  • Chromatin: The complex of DNA and proteins that make up chromosomes.
  • Sister chromatid: Two identical copies of a single chromosome that are connected by a centromere.
  • Homologous chromosome: Chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location.

DNA Replication

  • DNA needs to copy itself for cell division to ensure each daughter cell has the correct genetic information.
  • DNA replication is the process of making an identical copy of a DNA molecule.
  • DNA replication is necessary for cell division, growth, and repair.
  • Helicase unwinds the double helix, primase synthesizes RNA primers, DNA polymerase adds nucleotides to the new DNA strand, and ligase joins DNA fragments.
  • DNA replication is a semi-conservative process because each new DNA molecule consists of one original strand and one newly synthesized strand.

Cell Cycle

  • The cell cycle is a repeating series of growth, DNA replication, and division.
  • The cell cycle is important for growth, development, and repair in organisms.
  • The phases of the cell cycle include interphase (G1, S, G2), prophase, metaphase, anaphase, telophase, and cytokinesis.
  • Interphase: The cell grows and prepares for division; DNA replicates during the S phase.
  • Prophase: Chromosomes condense and become visible.
  • Metaphase: Chromosomes line up along the metaphase plate.
  • Anaphase: Sister chromatids separate and move to opposite poles of the cell.
  • Telophase: Chromosomes arrive at the poles, and the nuclear envelope reforms.
  • Cytokinesis: The cytoplasm divides, resulting in two daughter cells.
  • The cell spends most of its time in interphase.
  • During interphase, DNA is in the form of chromatin; during mitosis, it condenses into chromosomes.
  • The cell cycle may look different for different types of cells based on the needs of the organism

Mitosis

  • Mitosis is cell division to create two genetically identical cells, which is essential for growth, repair, and asexual reproduction.
  • The stages of mitosis are prophase, metaphase, anaphase, and telophase.
  • Prophase: Chromosomes condense, nuclear envelope breaks down, spindle fibers form.
  • Metaphase: Chromosomes line up at the metaphase plate.
  • Anaphase: Sister chromatids separate and move to opposite poles.
  • Telophase: Chromosomes arrive at poles, nuclear envelope reforms, chromosomes decondense.
  • Cells need to divide for growth, repair, and replacement of damaged or old cells.

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