Cell Structure Part IV: The Nucleus

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Questions and Answers

Which of the following accurately describes the nucleus's function?

  • Directs all the metabolic activities and plays a role in heredity. (correct)
  • Involves only the reproduction of cells.
  • Serves as the primary site for protein synthesis.
  • Functions exclusively during cell division.

What characterizes the appearance of an open face nucleus?

  • It is irregularly shaped and always multiple in number.
  • It is typically found in resting cells like lymphocytes.
  • It appears dark-stained and lacks visible details.
  • It appears pale-stained with visible details, active in function. (correct)

What forms the nuclear envelope?

  • A single membrane with nuclear pores.
  • Two membranes, outer and inner, with nuclear pores interrupting it. (correct)
  • A thick wall made of protein.
  • Multiple overlapping membranes without pores.

Which type of chromatin represents the part that is active in gene expression?

<p>Euchromatin (C)</p> Signup and view all the answers

What are nuclear pores responsible for?

<p>They allow for controlled exchange of materials between the nucleus and cytoplasm. (A)</p> Signup and view all the answers

Which statement correctly describes the nucleolus?

<p>It plays a crucial role in ribosome production. (C)</p> Signup and view all the answers

What is the composition of chromatin?

<p>Nucleoprotein, which is DNA conjugated with histone protein. (A)</p> Signup and view all the answers

What is the nature of the nuclear sap?

<p>It serves as a suspension medium for the nuclear components. (A)</p> Signup and view all the answers

What is the appearance of the nucleolus at the electron microscopy (E.M) level?

<p>An irregular spongy mass (A)</p> Signup and view all the answers

Which chromosomes contain the Nucleolar Organizer Genes that are essential for rRNA transcription?

<p>13, 14, 15, 21, 22 (D)</p> Signup and view all the answers

What is NOT a function of the nucleolus?

<p>Directing protein synthesis (D)</p> Signup and view all the answers

Which component does NOT contribute to the structure of nuclear sap?

<p>Mitochondrial DNA (C)</p> Signup and view all the answers

What is the correct sequence of stages in interphase?

<p>G1, S, G2 (C)</p> Signup and view all the answers

What forms as a result of S-stage during the cell cycle?

<p>A pair of S-chromosomes (D)</p> Signup and view all the answers

What is the primary role of nuclear sap in the cell?

<p>To facilitate the movement of RNA (C)</p> Signup and view all the answers

Which statement about the cell cycle is accurate?

<p>Interphase consists of three stages. (A)</p> Signup and view all the answers

Flashcards

What is the main function of the nucleus?

The nucleus is the control center of the cell, directing all metabolic activities and playing a vital role in heredity and cell division.

What is the nuclear envelope?

The nuclear envelope is a double membrane that encloses the nucleus, separating it from the cytoplasm. It is composed of an outer and inner membrane and is punctured by nuclear pores.

What is chromatin?

Chromatin is the complex of DNA and proteins that makes up chromosomes. It appears as basophilic granules under a light microscope.

What is heterochromatin?

Heterochromatin is a condensed, inactive form of chromatin. Its genes are mostly inactive.

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What is euchromatin?

Euchromatin is a relaxed, active form of chromatin. Its genes are usually active.

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What is the nucleolus?

The nucleolus is a dense, spherical structure inside the nucleus where ribosomal RNA is produced. It appears as a basophilic region under a light microscope.

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What is the nuclear sap?

The nuclear sap is the fluid inside the nucleus that contains dissolved enzymes, nucleotides, and other molecules.

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What is interphase?

Interphase is the period of the cell cycle when the cell is not dividing. It consists of three phases: G1, S, and G2.

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Where is rRNA synthesized?

Ribosomal RNA (rRNA) is synthesized around "nucleolar organizer genes", which are located on specific chromosomes. These genes contain the DNA sequence for rRNA.

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How does the nucleolus appear under a light microscope?

The nucleolus appears as a dark, basophilic mass under a light microscope. This is because it contains a high concentration of RNA, which stains intensely with basic dyes.

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What is the structure of the nucleolus under an electron microscope?

The nucleolus is not enclosed by a membrane and has a spongy, irregular structure. It's also surrounded by heterochromatin, which is condensed chromatin.

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What is the function of the nucleolus?

The nucleolus is involved in the synthesis and processing of rRNA, which is then combined with proteins to form ribosomal subunits. These subunits leave the nucleus and move to the cytoplasm, where they assemble into mature ribosomes.

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What is nuclear sap?

Nuclear sap is a clear, semiliquid solution that fills the nucleus. It's also known as nucleoplasm.

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What are the components of nuclear sap?

Nuclear sap contains important molecules including proteins, enzymes, and nucleotides. These molecules are essential for DNA and RNA synthesis.

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What is the function of nuclear sap?

Nuclear sap acts as a medium for molecules like rRNA, mRNA, and tRNA to move around the nucleus. This movement is crucial for gene expression and protein synthesis.

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Study Notes

Cell Structure (Part IV)

  • The nucleus is the master organelle within the cell, directing metabolic activities and playing a crucial role in heredity and cell division.
  • The nucleus's structure includes:
    • Nuclear Envelope
    • Chromatin
    • Nucleolus
    • Nuclear sap

Learning Outcomes

  • Students will be able to describe the characteristics of the nucleus and its components.
  • Students will be able to describe the nuclear envelope in both light microscopy (LM) and electron microscopy (EM) views.
  • Students will be able to describe chromatin in both LM and EM views, and categorize the types.
  • Students will be able to describe the nucleolus in both LM and EM views.
  • Students will be able to define and describe the structure of nuclear sap
  • Students will be able to define and describe the stages of interphase in the cell cycle.

Nucleus (Detailed)

  • The nucleus is the control center of the cell.
  • It directs all metabolic activities and plays a role in heredity and cell division.
  • Nucleus appearance through light microscopy (LM):
    • Can be single or multiple
    • Can be round, oval, flat or irregular in shape
    • Position can be central, eccentric, or peripheral.
  • Nucleus appearance through electron microscopy (EM):
    • Composed of 2 membranes (outer and inner) with pores to permit the exchange of material with the cytoplasm.

Nuclear Envelope

  • A membrane enclosing the nucleus, separating it from the surrounding cytoplasm.
  • Light microscopy view (LM): A single basophilic line surrounding the nucleus, with chromatin attached to its inner surface.
  • Electron microscopy view (EM): Composed of two membranes.
  • Pores interrupt the envelope; these are closed with diaphragms.

Chromatin

  • Basophilic material forming chromosomes.
  • Composed of nucleoprotein (DNA + histone protein).
  • Light microscopy view (LM): Basophilic granules called chromatin granules.
  • Electron microscopy view (EM): Two types:
    • Heterochromatin (condensed chromatin)- inactive
    • Euchromatin (extended chromatin)- active in protein synthesis

Nucleolus

  • One or more rounded basophilic bodies present within the interphase nucleus.
  • Light microscopy view (LM): Rounded basophilic mass within the nucleus.
  • Electron microscopy view (EM): Irregular spongy mass; not membrane-bound.
  • Surrounded by aggregations of DNA heterochromatin known as nucleolus-associated chromatin
  • Contains nucleolar organizers genes on specific chromosomes (13, 14, 15, 21, 22).

Nuclear Sap

  • Semifluid clear solution where chromatin and nucleoli are suspended.
  • Structure: Proteins, nucleoproteins, and enzymes coordinating DNA and RNA synthesis.
  • Function: Medium for ribonucleic acids (rRNA, mRNA, and tRNA) movement toward nuclear pores

Cell Cycle and Interphase

  • A series of stages where cells divide and produce new cells.
  • Interphase: The period between two cellular divisions.
  • Stages of interphase:
    • G1 (Gap 1): Rapid growth and metabolic activity
    • S (Synthesis): DNA replication
    • G2 (Gap 2): Growth and final preparations for cell division.

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