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Questions and Answers
Which statement about prokaryotic cells is true?
Which statement about prokaryotic cells is true?
What is the primary role of the nucleus in a eukaryotic cell?
What is the primary role of the nucleus in a eukaryotic cell?
Which of the following distinguishes eukaryotic cells from prokaryotic cells?
Which of the following distinguishes eukaryotic cells from prokaryotic cells?
What is a key function of mitochondria within eukaryotic cells?
What is a key function of mitochondria within eukaryotic cells?
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Which component is NOT typically found in prokaryotic cells?
Which component is NOT typically found in prokaryotic cells?
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Which process is critical for the formation of new cells according to the cell theory?
Which process is critical for the formation of new cells according to the cell theory?
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In terms of cell size, how do prokaryotic cells generally compare to eukaryotic cells?
In terms of cell size, how do prokaryotic cells generally compare to eukaryotic cells?
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What defines the chromatin found in the nucleus?
What defines the chromatin found in the nucleus?
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What type of molecules are the tails of phospholipids in the lipid bilayer?
What type of molecules are the tails of phospholipids in the lipid bilayer?
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What is the primary function of integral proteins in the plasma membrane?
What is the primary function of integral proteins in the plasma membrane?
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How do carbohydrates contribute to the function of the plasma membrane?
How do carbohydrates contribute to the function of the plasma membrane?
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How does cholesterol affect the fluidity of the plasma membrane?
How does cholesterol affect the fluidity of the plasma membrane?
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What distinguishes peripheral proteins from integral proteins in the plasma membrane?
What distinguishes peripheral proteins from integral proteins in the plasma membrane?
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Where are ribosomes found within a cell?
Where are ribosomes found within a cell?
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What role does the cytoplasm play in the cell?
What role does the cytoplasm play in the cell?
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Which structure in the plasma membrane is primarily responsible for preventing water-soluble molecules from passing through?
Which structure in the plasma membrane is primarily responsible for preventing water-soluble molecules from passing through?
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What is one primary function of the rough endoplasmic reticulum?
What is one primary function of the rough endoplasmic reticulum?
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Which component of the cytoskeleton is primarily involved in cellular movement?
Which component of the cytoskeleton is primarily involved in cellular movement?
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How do microtubules contribute to cell division?
How do microtubules contribute to cell division?
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What role do lysosomes play in a cell?
What role do lysosomes play in a cell?
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Which characteristic best describes the Fluid Mosaic Model of the plasma membrane?
Which characteristic best describes the Fluid Mosaic Model of the plasma membrane?
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What is the consequence of actin filaments depolymerizing?
What is the consequence of actin filaments depolymerizing?
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Which of the following components is primarily responsible for the detoxification of drugs and storage of calcium?
Which of the following components is primarily responsible for the detoxification of drugs and storage of calcium?
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Which organelle acts as the packaging and distribution center for proteins and lipids?
Which organelle acts as the packaging and distribution center for proteins and lipids?
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Study Notes
Cell Theory:
- States that all living organisms are composed of one or more cells, the cell is the basic unit of structure and function in all living organisms, and all cells arise from pre-existing cells through the process of cell division.
- Developed in the mid-19th century by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.
- Established that the cell is the fundamental unit of life, whether the organism is unicellular (bacteria) or multicellular (humans).
Prokaryotic Cells:
- Found in organisms like bacteria and archaea.
- Lack a true nucleus; DNA is found in a region called the nucleoid.
- Generally smaller in size (1-10 µm).
- Lack membrane-bound organelles.
- Have a simple structure, containing the plasma membrane, cytoplasm, ribosomes, and sometimes flagella/pili.
- Many prokaryotes have a rigid cell wall that provides structural support and protection.
Eukaryotic Cells:
- Found in animals, plants, fungi, and protists.
- Have a true nucleus enclosed by a nuclear membrane.
- Generally larger in size (10-100 µm).
- Possess membrane-bound organelles (e.g., mitochondria, Golgi apparatus, endoplasmic reticulum).
- Highly compartmentalized, allowing for specialized functions within different organelles.
- Examples include animal cells (no cell wall), plant cells (with cell wall and chloroplasts), fungal cells (cell wall made of chitin).
Nucleus:
- The control center of the cell.
- Contains most of the cell’s genetic material (DNA), organized as chromatin.
- Surrounded by a double membrane called the nuclear envelope, which has nuclear pores for the transport of materials.
- The nucleolus, found within the nucleus, is the site of ribosomal RNA (rRNA) synthesis.
Mitochondria:
- Known as the “powerhouse of the cell,” they are responsible for producing ATP, the energy currency of the cell, through oxidative phosphorylation.
- Have their own DNA and can replicate independently of the cell.
- The double-membrane structure includes the inner membrane, which folds into cristae to increase surface area for ATP production.
Endoplasmic Reticulum (ER):
- The rough ER is studded with ribosomes; it is the site of protein synthesis and folding.
- The smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification of drugs and toxins, and calcium storage.
Golgi Apparatus:
- Acts as the packaging and distribution center of the cell. It modifies, sorts, and packages proteins and lipids for transport to various destinations (inside or outside the cell).
Lysosomes:
- Contain hydrolytic enzymes for intracellular digestion.
- Plays a key role in breaking down waste materials, old organelles, and pathogens in a process called autophagy.
Cytoskeleton:
- Composed of protein filaments, it provides structural support, maintains the cell’s shape, and aids in intracellular transport and cellular movement.
- Includes three main components: actin filaments (microfilaments), microtubules, and intermediate filaments.
Actin Filaments (Microfilaments):
- Function in cellular movement and are made of two intertwined strands of actin.
- Provide rigidity and shape to the cell.
- Can depolymerize (disassemble) and reform quickly, thus enabling a cell to change its shape and move.
Intermediate Filaments:
- Made of several strands of fibrous proteins that are wound together.
Microtubules:
- Hollow tubes made of 13 polymerized dimers of α-tubulin and β-tubulin.
- Help the cell resist compression, pull replicated chromosomes to opposite ends of a dividing cell, and are structural elements of flagella and cilia.
Plasma Membrane:
- A selectively permeable barrier that encloses the cell.
- Comprised of a phospholipid bilayer with embedded proteins, it regulates the movement of substances in and out of the cell.
- The Fluid Mosaic Model of the cell membrane was proposed by S.J. Singer and G.L. Nicolson in 1972 to describe the structure of the plasma membrane.
- The model portrays the cell membrane as a dynamic and fluid structure composed of a phospholipid bilayer with embedded proteins, where components are free to move laterally within the membrane.
Key Components of the Fluid Mosaic Model:
-
Lipid Bilayer: The fundamental structure of the plasma membrane consists of two layers of phospholipids, arranged tail-to-tail.
- Phospholipids are amphipathic molecules, meaning they have both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
- Hydrophilic heads: Composed of glycerol and a phosphate group, these face outward towards the aqueous environments inside and outside the cell.
- Hydrophobic tails: Composed of fatty acids, these face inward, away from the water, creating a barrier to most water-soluble molecules.
- The lipid bilayer is fluid because the fatty acid chains of the phospholipids are not rigid, allowing for lateral movement within the layer.
-
Proteins:
- Integral (Intrinsic) Proteins: These proteins span across the lipid bilayer (transmembrane proteins) or are deeply embedded within it. They play critical roles in transport, signal transduction, and cell communication. Examples include ion channels, transporters, and receptors.
- Peripheral (Extrinsic) Proteins: These proteins are loosely associated with the outer or inner surfaces of the membrane. They function in signaling, maintaining the cytoskeleton, and cell recognition. Peripheral proteins can be attached to integral proteins or lipid heads.
- Carbohydrates: Carbohydrate molecules are often attached to proteins or lipids on the extracellular surface of the membrane, forming glycoproteins or glycolipids. These carbohydrate structures are involved in cell recognition, immune responses, and protection.
- Cholesterol: are interspersed within the phospholipid bilayer. It helps to stabilize membrane fluidity by preventing the fatty acid chains from packing too closely together (which would make the membrane too rigid in cold conditions) and by restraining excessive movement of phospholipids (which would make the membrane too fluid in warm conditions).
Ribosomes:
- Small structures that are the sites of protein synthesis.
- Can be found floating freely in the cytoplasm or attached to the rough ER.
- Involved in translating mRNA into proteins.
Cytoplasm:
- The gel-like fluid inside the cell that surrounds the organelles.
- It is the site of many metabolic reactions, including glycolysis.
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Description
Test your knowledge on cell theory and the characteristics of prokaryotic and eukaryotic cells. This quiz covers their structures, functions, and the fundamental principles established by early cell theory proponents. Challenge yourself to see how well you understand these essential biological concepts.
