Problem 7 - Biology: Science for Life with Physiology

Question

Sister chromatids __________. A. are two different chromosomes attached to each other; B. are exact copies of one chromosome that are attached to each other; \(\mathrm{C}\). arise from the centrioles; D. are broken down by mitosis; E. are chromosomes that carry different genes

Step-by-Step Solution

Answer

Sister chromatids are exact copies of one chromosome that are attached to each other (Option B).

Step 1: Understand Sister Chromatids

Sister chromatids refer to two identical copies of a single replicated chromosome. These copies are attached to each other by a structure called the centromere. This usually happens during the S-phase of the cell cycle when the DNA is replicated.

Step 2: Analyze the Options

Review each of the provided options to find out which one correctly describes sister chromatids. - A refers to "two different chromosomes attached to each other," which is incorrect. - B refers to "exact copies of one chromosome that are attached to each other," which correctly describes sister chromatids. - C refers to "arising from the centrioles," but centrioles are involved in forming spindle fibers and not in the replication of chromosomes. - D states "broken down by mitosis," but mitosis separates sister chromatids rather than breaking them down. - E states "chromosomes that carry different genes," which applies to homologous chromosomes but not sister chromatids.

Step 3: Choose the Correct Option

Based on the analysis in Step 2, the correct description of sister chromatids is offered by option B: "are exact copies of one chromosome that are attached to each other."

Key Concepts

Cell Cycle

The cell cycle is a series of stages that a cell undergoes to grow and divide into two daughter cells. It is vital for growth, development, and repair in multicellular organisms. The cycle consists of four main stages:

• G1 phase (Gap 1): This is the stage where the cell grows and carries out normal functions. It's a period of cell growth before DNA synthesis.
• S phase (Synthesis): In this phase, DNA is replicated, resulting in sister chromatids. Each chromosome now has two identical copies attached at the centromere.
• G2 phase (Gap 2): The cell continues to grow, and proteins needed for cell division are produced. The cell prepares for mitosis.
• M phase (Mitosis): This is the stage of cell division, where sister chromatids are separated into two new cells.

These stages ensure that cell division occurs correctly, maintaining genetic consistency in the resulting daughter cells.
Understanding the cell cycle helps in comprehending how cells maintain and duplicate themselves through life processes.

DNA Replication

DNA replication is a critical process during the S phase of the cell cycle, ensuring that each new cell receives an exact copy of the genetic material. This process involves:

• Unwinding the double helix: Specialized enzymes like helicase unwind and separate the two strands of DNA.
• Synthesizing new strands: DNA polymerase adds nucleotides to each original strand, creating two new complementary strands.
• Proofreading: Enzymes check for errors and make corrections, ensuring fidelity in DNA copying.

By the end of DNA replication, each chromosome consists of two identical sister chromatids joined by a centromere. The process is remarkably precise, minimizing errors and allowing the preservation of genetic information across generations.

Centromere

The centromere is a crucial structure in chromosomes, serving as the attachment point for sister chromatids. During the S phase, when each chromosome is replicated, the centromere appears at the center, holding the sister chromatids together.

• Function in cell division: Centromeres ensure that sister chromatids are evenly distributed to each of the two daughter cells during mitosis and meiosis.
• Kinetochore formation: During cell division, the centromere is where the kinetochore forms, a structure that connects the chromosome to spindle fibers.
• Centromeres and genetic stability: They play a key role in preventing the loss of genetic information during cell division.

The centromere is essential for maintaining the structure and function of chromosomes, helping to ensure genetic stability and integrity during cell replication and division.