Cell Biology Nucleus Functions Quiz
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Questions and Answers

What is the primary function of the nuclear lamina?

  • To synthesize proteins
  • To regulate transcription of mRNA
  • To store DNA and RNA
  • To provide structural support to the nuclear envelope (correct)

Which of the following correctly describes the nuclear envelope?

  • Formed by a network of protein filaments
  • Contains a space that is 10-20nm wide
  • Is continuous with the endoplasmic reticulum (correct)
  • A single-layered membrane surrounding the nucleus

How do genetic mutations related to the nuclear lamina affect individuals?

  • They can lead to enhanced cell division
  • They improve the structural integrity of the nucleus
  • They enhance the transcription of mRNA
  • They may cause progeria syndrome (correct)

What is the significance of nuclear pores in the cell nucleus?

<p>They allow the transport of RNA and proteins between the nucleus and cytoplasm (D)</p> Signup and view all the answers

What is a characteristic of the chromatin found within the nucleus?

<p>It plays a key role in DNA replication and storage (A)</p> Signup and view all the answers

What is the primary function of the nuclear pore complex?

<p>To allow the transport of water-soluble molecules across the nuclear envelope (D)</p> Signup and view all the answers

Which of the following molecules can pass through the nuclear pore complex?

<p>Signal molecules (D)</p> Signup and view all the answers

What is the diameter of the channel in the central zone of the nuclear pore complex?

<p>9 nm (A)</p> Signup and view all the answers

What is the substance surrounding the chromosomes and nucleoli in the nucleus called?

<p>Nucleoplasm (A)</p> Signup and view all the answers

Which component is NOT typically found dissolved in the nucleoplasm?

<p>Ribosomes (A)</p> Signup and view all the answers

What characteristic distinguishes integral membrane proteins from peripheral proteins?

<p>Integral proteins are permanently attached to the membrane. (D)</p> Signup and view all the answers

Which mechanism explains the movement of water and charged inorganic ions across membranes?

<p>Carriers or special channels through the bilayer. (D)</p> Signup and view all the answers

What is a key function of the nucleus in eukaryotic cells?

<p>It controls genetic information in the cell. (B)</p> Signup and view all the answers

Which type of integral membrane protein spans the entire plasma membrane and can act as a transporter?

<p>Integral transmembrane proteins. (B)</p> Signup and view all the answers

What makes the inner face of the plasma membrane more fluid compared to the outer layer?

<p>Higher amount of unsaturated fatty acids. (C)</p> Signup and view all the answers

Which type of cells in the human body lack a nucleus?

<p>Red blood cells and platelets. (A)</p> Signup and view all the answers

Which of these proteins typically associate temporarily with biological membranes?

<p>Peripheral proteins. (D)</p> Signup and view all the answers

Which structural arrangement can integral transmembrane proteins possess?

<p>A b-barrel configuration. (D)</p> Signup and view all the answers

What is the role of nucleolar organizer regions (NORs)?

<p>They are crucial for the formation of the nucleolus. (D)</p> Signup and view all the answers

What happens to the nucleolus during cell division?

<p>It disappears and reappears post-division. (C)</p> Signup and view all the answers

Which statement accurately describes ribosomes?

<p>They contain roughly equal amounts of RNA and proteins. (D)</p> Signup and view all the answers

How many pairs of autosomes does a human karyotype contain?

<p>22 pairs of autosomes. (D)</p> Signup and view all the answers

The size of the nucleolus reflects what aspect of a cell?

<p>The activity level of the cell. (D)</p> Signup and view all the answers

What structure is formed from DNA coiled around histone proteins?

<p>Nucleosome (B)</p> Signup and view all the answers

Which form of chromatin is primarily involved in gene transcription?

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

Which of the following accurately describes heterochromatin?

<p>It is tightly packed and not transcribed. (D)</p> Signup and view all the answers

How many chromosomes do humans possess?

<p>46 chromosomes (C)</p> Signup and view all the answers

What is the approximate diameter of the finest chromatin fibers?

<p>2 nm (C)</p> Signup and view all the answers

What is the primary role of heterochromatin in chromosomes?

<p>Protects the integrity of chromosomes (B)</p> Signup and view all the answers

During which phase of the cell cycle can chromatin fibers be observed more distinctly?

<p>Interphase (A)</p> Signup and view all the answers

What are the basic components of a nucleosome?

<p>DNA and histones (B)</p> Signup and view all the answers

What characterizes the lipid bilayer in the plasma membrane?

<p>It contains hydrophobic tails facing inwards. (C)</p> Signup and view all the answers

Which component is NOT part of the fluid mosaic model?

<p>Static arrangement of all molecules (A)</p> Signup and view all the answers

What differentiates integral proteins from peripheral proteins in the plasma membrane?

<p>Integral proteins are firmly associated with the membrane. (A)</p> Signup and view all the answers

What role do the proteins associated with the lipid bilayer play?

<p>They function in transport and signaling. (B)</p> Signup and view all the answers

What structure surrounds the nucleus and contains nuclear pores?

<p>Nuclear envelope (A)</p> Signup and view all the answers

What type of chromatin is generally more active in gene expression?

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

Which eukaryotic organelle is responsible for housing the genetic material in a cell?

<p>Nucleus (B)</p> Signup and view all the answers

What is the primary component of the eukaryotic plasma membrane?

<p>Phospholipids (D)</p> Signup and view all the answers

What features are unique to eukaryotic cells compared to prokaryotic cells?

<p>Containment of organelles within membranes (A)</p> Signup and view all the answers

How does the glycocalyx benefit the cell?

<p>By protecting and aiding in cell recognition (A)</p> Signup and view all the answers

Flashcards

Outer Layer of Cell Membrane

The outer layer of a cell membrane composed of phospholipids. It is arranged with hydrophilic heads facing outwards and hydrophobic tails facing inwards. The outer layer is more solid and viscous due to the presence of saturated fatty acids.

Inner Layer of Cell Membrane

The inner layer of a cell membrane composed of phospholipids. It has a more fluid consistency due to the presence of unsaturated fatty acids, allowing for greater flexibility and movement.

Integral Transmembrane Protein

A type of membrane protein that spans the entirety of the cell membrane. It is usually folded into an alpha-helix or beta-barrel structure.

Integral Membrane Proteins

Proteins that are permanently attached to the cell membrane and cannot be easily removed. Integral proteins act as anchors, transporters, channels, enzymes, and receptors.

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Peripheral Proteins

Proteins that are temporarily associated with integral membrane proteins or the peripheral regions of the lipid bilayer. They may associate and dissociate with the membrane.

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Nucleus

A type of cell found in eukaryotes that contains genetic material (DNA) and controls cellular processes. It is the control center of the cell.

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Prokaryotes

Organisms, such as bacteria and archaea, that do not possess a nucleus. Their DNA is located in the cytoplasm.

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Eukaryotes

Organisms, such as animals and plants, that have a nucleus where their DNA is located. They are distinguished by having a well-defined nucleus.

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What is the plasma membrane made of?

The plasma membrane, a thin layer surrounding every living cell, is composed of a lipid bilayer, a double layer of phospholipids.

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Why do phospholipids arrange into a bilayer?

Phospholipids are amphipathic molecules - they have both hydrophobic (water-fearing) tails and hydrophilic (water-loving) heads. This allows them to self-assemble into a bilayer structure, with the hydrophobic tails facing inwards and the hydrophilic heads facing outwards.

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What is the fluid mosaic model?

The fluid mosaic model describes the plasma membrane as a flexible and dynamic structure. It's like a mosaic, with various proteins embedded within the lipid bilayer, free to move around.

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What's the difference between integral and peripheral membrane proteins?

Integral membrane proteins are permanently embedded within the lipid bilayer, while peripheral membrane proteins associate only with the surface of the membrane.

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What are the functions of membrane proteins?

Membrane proteins perform various crucial functions like transporting molecules across the membrane, acting as receptors for signals, providing structural support, and participating in cell-to-cell communication.

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Describe the structure of the nucleus.

The nucleus, the control center of the cell, is surrounded by a double-layered nuclear envelope, which is perforated with nuclear pores that regulate the passage of molecules into and out of the nucleus.

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What's the difference between euchromatin and heterochromatin?

Euchromatin is a less condensed form of chromatin, allowing for active gene expression. Heterochromatin, on the other hand, is tightly packed and transcriptionally inactive.

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Why does each organism have a specific number of chromosomes?

Each species has a specific number of chromosomes, which contain DNA and carry genetic information. This number is characteristic for that species.

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What is the function of the nucleus?

The nucleus acts as the control center of the cell, housing DNA, the blueprint for life. It directs the cell's activities by regulating gene expression.

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What is the function of the plasma membrane?

The plasma membrane, also called the cell membrane, acts as a selective barrier, controlling what enters and exits the cell. This ensures the cell maintains its internal environment and functions properly.

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Nuclear Envelope

A double-layered membrane surrounding the nucleus, separating it from the cytoplasm. It has a perinuclear space between the membranes, allowing for selective transport of materials.

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Nuclear Lamina

A protein meshwork located adjacent to the inner nuclear membrane, providing structural support for the nucleus. It helps maintain nuclear shape and assists in positioning nuclear pores.

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Nuclear Pores

Tiny openings in the nuclear envelope that allow for the selective transport of molecules between the nucleus and the cytoplasm.

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Nucleoplasm

The substance within the nucleus containing DNA in the form of chromatin, which is the genetic material.

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Nuclear pore central zone

The central part of the nuclear pore complex that functions as a channel for the transport of molecules between the nucleus and cytoplasm.

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Nuclear pore cytoplasmic face

The portion of the nuclear pore complex facing the cytoplasm.

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Nuclear pore nuclear face

The portion of the nuclear pore complex facing the nucleus.

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Nuclear matrix

A fibrous network found within the nucleoplasm.

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Ribosomal RNA (rRNA)

A type of RNA that is a key component of ribosomes, cellular structures where protein synthesis takes place.

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Nucleolar Organizer Regions (NORs)

Regions on specific chromosomes where the formation of the nucleolus is initiated.

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Ribosomes

Ribosomes are fundamental cellular structures responsible for the synthesis of proteins, essential for various cell functions.

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Nucleolus Size and Cell Activity

The size of the nucleolus directly corresponds to the cell's level of activity in protein synthesis.

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Chromatin

The complex of DNA and proteins that make up chromosomes. It exists in two forms: euchromatin and heterochromatin.

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Euchromatin

The less condensed form of chromatin, allowing for active gene transcription.

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Heterochromatin

The tightly packed form of chromatin, which is inactive for gene transcription.

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Nucleosome

The basic unit of chromatin; consists of a segment of DNA wrapped around a histone octamer.

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Histone Octamer

A protein complex with eight subunits, acting as a scaffold for DNA coiling in chromatin.

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Chromatid

The condensed, duplicated chromosome visible during cell division, consisting of two identical chromatids.

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Centromere

The region where sister chromatids attach during cell division, ensuring equal distribution of genetic material.

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Study Notes

Cell Ultrastructure: Nucleus & Plasma Membrane

  • The lecture covers the fundamentals of human biology, focusing on the nucleus and plasma membrane.
  • The date of the lecture is October 2nd, 2024, and the lecturer is Adrian Dervan PhD.
  • The course code is FUNBIO 4.
  • Learning outcomes include describing the fluid mosaic model of the plasma membrane, differences between integral and peripheral proteins, and how these function in semipermeable membranes.
  • The structure of the nucleus including the nuclear envelope, pores, and karyoplasm will be examined.
  • Differentiation between euchromatic and heterochromatic nuclei and the characteristic chromosome number of each organism will be explained.

Cell Membranes - Plasma & Nuclear Membrane

  • Animal and plant cells are eukaryotic.
  • Eukaryotic cells contain a nucleus and other organelles enclosed by membranes.
  • Organelles like the nucleus, plasma membrane, lysosomes, and mitochondria are needed for cell function.

Plasma Membrane

  • Under the electron microscope (EM), the plasma membrane appears as a three-layered structure between 7.5-10 nm in diameter.
  • All living cells have a plasma membrane.
  • The plasma membrane is a lipid bilayer, primarily composed of phospholipids.
  • Phospholipids have hydrophilic heads and hydrophobic tails, allowing them to form a bilayer in water.
  • Detergent molecules are roughly cone-shaped and associate in water as spherical structures.
  • The outer face of the membrane has more saturated fatty acids and cholesterol, making it more solid.
  • The inner face has more unsaturated fatty acids, making it more fluid.

Plasma Membrane - Fluid Mosaic Model

  • Biological membranes can be considered a two-dimensional liquid.
  • The model, proposed by Singer & Nicolson (1972), consists of phospholipid molecules and embedded or associated proteins & lipids.
  • Many cells are surrounded by a cell coat or glycocalyx, formed by carbohydrate side chains of proteins and lipids.
  • The membrane protects the cell and may help keep other cells at a distance.
  • Membranes enable cells to recognize one another and communicate.

Membrane Proteins

  • Two main classes: integral and peripheral proteins.
  • Integral proteins: transmembrane (spanning the membrane) or integral monotopic (embedded in one side).
  • Peripheral proteins: attached to integral proteins or peripheral regions of the lipid bilayer.
  • Proteins are involved in anchoring, transport, enzymes, and cell signaling.

The Nucleus

  • All cells except mammalian red blood cells (RBCs) and platelets have a nucleus.
  • The nucleus is the control center of the cell.
  • Functions include controlling genetic information, heredity characteristics, protein synthesis, cell division/growth, DNA/RNA/ribosome storage and regulation of mRNA-to-protein transcription and ribosome production.

The Nucleus - Structure

  • The nucleus has a nuclear envelope, chromatin, nucleolus, nuclear pores, and nucleoplasm.
  • The nuclear envelope is a double-layered membrane with pores, isolating nuclear material from the cytoplasm.
  • A perinuclear space (20-40nm wide) lies between the two membranes.
  • The outer membrane is continuous with the endoplasmic reticulum within the cytoplasm.
  • The nuclear lamina is present at the inner face of the nuclear envelope.
  • Provides structural support for the nucleus and aids in positioning nuclear pores.

The Nucleus - Nuclear Pore

  • The nuclear pore complex has thousands of pores occupying 10-30% of the nuclear envelope's surface.
  • The structure is ring-like, octagonal, and over 50nm in diameter (1nm = 1.0 x 10-9 meters).
  • The complex includes protein subunits arranged in a central zone and on the cytoplasmic and nuclear faces.
  • The nuclear pore complex regulates the passage of molecules (water-soluble) in and out of the nucleus.

The Nucleus - Nucleoplasm

  • The nucleoplasm is the highly viscous liquid that fills the nucleus, surrounding the chromosomes.
  • It houses many substances like nucleotides and enzymes.
  • The nuclear matrix, a network of fibers, is also found within the nucleoplasm and is similar to the cell cytoskeleton. Chromatin packing is not fully known.

Chromatin Fibers

  • During interphase (when the cell is not dividing), chromatin forms a collection of threads and fibres visible with an electron microscope.
  • The finest chromatin fibrils are approximately 2nm in diameter (comparable to the dimensions of the DNA molecule).
  • Chromatin is either euchromatin (lightly packed, DNA transcribed) or heterochromatin (tightly packed, DNA not transcribed, found at the nuclear periphery).

Chromatin Packing

  • Chromatin coiling levels lead to chromosome formation.
  • Nucleosomes are basic units consisting of DNA double helix coiled around histone protein units; these units repeat along chromatin.

Number of Chromosomes in Species

  • Different species have different numbers of chromosomes. Humans have 46 chromosomes (22 pairs of autosomes and 2 sex chromosomes).

Nucleolus

  • Nucleoli (singular: nucleolus) are in the nucleoplasm, 1 to 4 per cell, often dense, basophilic, and disappear during cell division, reappearing afterwards.
  • The nucleolus organizer regions (NORs), chromosomal regions, are crucial for nucleolus formation.
  • The size of the nucleolus reflects the cell's activity level.

Nucleolus: Function

  • Nucleoli are associated with specific chromosome regions that transcribe rRNA, functioning in ribosome formation.
  • rRNA is also found in other cytoplasmic organelles.
  • Ribosomes (composed of rRNA and proteins) are involved in protein synthesis.

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Cell Structure: Nucleus & Plasma Membrane PDF

Description

Test your knowledge on the structure and function of the cell nucleus, including the nuclear lamina, nuclear envelope, and nuclear pore complex. This quiz covers key concepts related to genetic mutations and the distinct features of chromatin. Get ready to explore vital cellular mechanisms and their significance!

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