Questions and Answers
What are the principal components of protoplasm?
Water, electrolytes, proteins, lipids, carbohydrates
Water is present in most cells except fat cells.
True
What percentage of the cell is constituted by proteins?
10 to 20%
Which of the following is NOT an important ion for cellular reactions?
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What is the primary role of structural proteins in cells?
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What types of lipids are primarily found in the cell membrane?
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What are the three principal parts of a cell?
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The plasma membrane acts as a selective barrier.
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What is the primary fluid portion of the cytoplasm called?
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What do organelles within the cytosol refer to?
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Which of the following roles is NOT associated with membrane proteins?
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What is the basic structural framework of the plasma membrane?
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The head of a phospholipid is __________.
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The tail of a phospholipid is __________.
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What type of protein is embedded in the lipid bilayer and most are transmembrane?
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Study Notes
Organization of the Cell
- Protoplasm consists of water, electrolytes, proteins, lipids, and carbohydrates.
- Water is the main fluid medium, constituting 70-85% of cell concentration, facilitating chemical reactions.
- Important ions for cellular reactions: K+, Mg²+, PO₄³⁻, SO₄²⁻, HCO₃⁻, Na⁺, Cl⁻, Ca²⁺.
Proteins in the Cell
- Proteins account for 10-20% of cellular composition.
- Structural proteins form long filaments, contributing to the cytoskeleton and providing support.
- Functional proteins are engaged in catalyzing intracellular chemical reactions and have direct contact with cell fluids.
Lipids and Cell Membrane
- Lipids, comprising only 2% of total cell mass, are essential for forming cell and intracellular membranes.
- Triglycerides in fat cells account for 95% of their mass due to increased lipid content.
Principal Parts of a Cell
- Three primary components: plasma membrane, cytoplasm, and nucleus.
Plasma Membrane
- Functions as a flexible barrier, separating internal cellular environment from external surroundings.
- Acts as a selective barrier, facilitating communication between cells and their environment.
- Membrane lipids enable lipid-soluble molecule passage and restrict polar substances.
Cytoplasm
- The region between the plasma membrane and the nucleus containing the cytosol and organelles.
- Cytosol is the fluid part of the cytoplasm, including water and dissolved solutes.
- Organelles include cytoskeleton, ribosomes, endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes, and mitochondria.
Nucleus
- Houses the majority of a cell's DNA within chromosomes, which consist of single DNA molecules containing genes.
- Genes control various aspects of cellular structure and function.
Plasma Membrane Structure
- Consists primarily of a lipid bilayer; composed of 75% phospholipids, 20% cholesterol, and 5% glycolipids.
- Lipid bilayer characteristics: amphipathic nature (hydrophilic heads and hydrophobic tails) allows selective permeability.
Membrane Proteins
- Integral proteins span the lipid bilayer, significantly involved in cellular transport and communication.
- Peripheral proteins are loosely attached and play supportive roles in membrane structure and signaling.
Lipid Bilayer Composition
- Phospholipid heads are polar (hydrophilic) and tails are nonpolar (hydrophobic).
- Cholesterol interspersed among lipids stabilizes the membrane structure.
- Glycolipids present only in the extracellular-facing membrane layer, contributing to cell recognition and signaling.
Summary of Membrane Proteins
- Integral proteins are firmly embedded within the lipid bilayer, with many functioning as transmembrane proteins.
- Peripheral proteins are not embedded, providing structural support and facilitating intracellular connectivity.
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Description
This quiz covers essential concepts in cell biology, including the composition of protoplasm, the roles of proteins and lipids, and the principal parts of a cell. Evaluate your understanding of cellular structures and their functions in detail.
