Cell Biology Quiz: Structure and Function

Cell Structure and Cell Division

• Cells are the fundamental structural and functional units of living matter
• They independently carry out life processes
• Their primary function is maintaining homeostasis in the organism

Functions of Cells

• Cells provide structural support to the body
• Cells take nutrients from food and convert them to energy
• Cells carry out specialized functions

Types of Cells

• Cells are categorized as prokaryotic and eukaryotic
• Prokaryotic cells are unicellular. Eukaryotic cells can be either unicellular or multicellular.
• Sizes of prokaryotic cells range from 0.2 to 2.0 µm in diameter whilst eukaryotic cells range from 10 to 100 µm in diameter.
• Prokaryotic cells have a simple cell wall. Eukaryotic cells have a complex cell wall.
• The nucleus is absent in prokaryotic cells but present in eukaryotic cells.
• Prokaryotic cells lack mitochondria, endoplasmic reticulum, lysosomes. Eukaryotic cells have them.
• Prokaryotic cells may lack membrane-bound organelles. Eukaryotic cells have specialized organelles.
• Prokaryotic cells reproduce asexually by binary fission. Eukaryotic cells reproduce both asexually and sexually.
• Examples of prokaryotes are bacteria. Examples of eukaryotes are plant and animal cells.

Cell Structure

• Cells contain various microscopic structures (organelles) like intermediate filaments, ribosomes, rough endoplasmic reticulum, nucleus, nucleolus, chromatin, Golgi apparatus, Golgi vesicles, cytoplasm, mitochondria, plasma membrane, microtubules, centrosome, microfilaments, lysosomes, smooth endoplasmic reticulum, secretory vesicle, peroxisome, vacuole

Cell Membrane

• Also known as plasma membrane. Forms the outer covering of the cell
• It isolates the cell and maintains the internal environment through ion and nutrient transport
• Electron micrographs show a thin, invisible structure, sometimes folded into a brush border
• The average thickness of cell membrane is approximately 7.5 nanometers
• Composition:
  • Lipids: 50-55%
  • Proteins: 40-45%
  • Carbohydrates: 5-10%
• Lipids in the cell membrane form a phospholipid bilayer
• Interspersed within this layer are integral and peripheral membrane proteins
• The membrane has two ends: a polar/hydrophilic (water-soluble) head end and a non-polar/hydrophobic (water-insoluble) tail end
• Phospholipid molecules have the hydrophilic ends facing away from each other which are in contact with aqueous solutions. Hydrophobic ends point opposite to each other

Cell Membrane Composition

• Hydrophilic head: Water-soluble, positive charge
• Hydrophobic tail: Water-insoluble, negative charge
• Protein and lipid molecules form the cell’s inner/outer layers
• The protein molecules are embedded in the polar group

Cell Membrane Functions

• The lipid layer is semi-permeable. Only fat-soluble substances (e.g., oxygen, carbon dioxide, alcohol) can pass
• Water-soluble substances (e.g., glucose, urea, electrolytes) cannot pass through the membrane

Proteins in Cell Membrane

• Integral proteins traverse the cell membrane and form channels for the passage of hydrophilic substances (e.g., water, ions, monosaccharides, amino acids).
• Peripheral proteins are located on the inner or outer surface of the bilayer.
• Peripheral protein connects with intracellular cytoskeleton and extracellular matrix to maintain connections

Role of Cholesterol

• Cholesterol contributes to the membrane's density and fluidity

Role of Carbohydrates

• Carbohydrates, as glycoproteins and glycolipids, form cell surface receptors and aid intercellular communication

Membrane Transport

• Cell membrane is selectively permeable to transport of molecules. Gases and steroids pass freely, others require specific mechanisms.

Types of Transport

• Endocytosis: Large molecules enter the cell via plasma membrane invagination.
• Exocytosis: Materials are expelled from the cell via vesicle fusion with the plasma membrane.
• Pinocytosis: Uptake of fluids and smaller molecules, mediated by pinocytic vesicles.
• Phagocytosis: A type of endocytosis where large molecules/cells (e.g., bacteria) are engulfed into a phagosome.
• Simple Diffusion: Molecules move down their concentration gradient
• Facilitated Diffusion: Molecules need a membrane protein for transport
• Active Transport: Molecules move against their concentration gradient, requiring energy (ATP)

Nucleus

• The nucleus is a membrane-bound organelle in eukaryotic cells
• It houses the cell's genetic material, DNA, in the form of chromosomes
• Chromosomes are thread-like structures of packaged DNA and proteins.
• A typical chromosome has a centromere (middle) and telomeres (ends).
• A kinetochore forms around the centromere during cell division for chromosome attachment to mitotic spindle fibers
• Histones are proteins forming nucleosomes, wrapping the DNA. DNA is supercoiled multiple times to form a chromatin fiber

Nucleoplasm

• Nucleoplasm is the fluid within the nucleus that suspends components such as DNA, RNA, associated proteins, and enzymes.
• The nucleoplasm is compartmentalized by a double-layered nuclear membrane with pores, enabling communication and transport between the nucleus and cytoplasm .

Cytoplasm

• The gel-like substance inside the cell membrane, containing proteins, ions, enzymes, and various organelles
• It contains numerous organelles with specialized metabolic functions essential for maintaining homeostasis.

Organelles

• Mitochondria: The "powerhouses" of the cell; generate ATP (energy)
• Endoplasmic Reticulum (ER): A network of membranes involved in synthesis and transport of molecules. Rough ER has ribosomes for protein synthesis. Smooth ER synthesizes lipids and detoxifies.
• Golgi Complex: Processes and packages proteins and lipids
• Lysosomes: Involved in intracellular digestion and recycling
• Peroxisomes: Involved in oxidation reactions, particularly breakdown of fatty acids and amino acids
• Centrosomes: Important in cell division; contains centrioles

Cytoskeleton

• Provides structural support and facilitates movement of organelles and cell structures
• Composed of intermediate filaments, microfilaments, and microtubules

Role of Mitochondria

• Generates energy
• The powerhouse of the cell

Role of ER

• Synthesis and transport of molecules within the cell

Role of Golgi Apparatus

• Processes the products from ER and packs them for cellular use or secretion into vesicles

Test your knowledge on cell structure and function with this quiz. Explore key concepts such as cell membrane composition, protein roles, and the importance of homeostasis. Gather a deeper understanding of cellular transport and membrane dynamics.