Cell Biology Quiz: Fundamentals and Functions

Cytology: The Study of Cells

• Cytology is the study of cells
• Body fluids account for 42 liters in the human body
• Intracellular fluids (ICF) account for 28 liters
• Extracellular fluids (ECF) include plasma (3 liters), lymph, and interstitial fluid (11 liters)
• Intracellular materials include fibers and crystals

Cells: Structural and Functional Units of Life

• Cells are the building blocks of life, produced by the division of preexisting cells
• Cells perform all vital functions
• Cells form intercellular materials and fluids
• Cells are adapted to wide ranges of sizes and shapes
• There are approximately 30-40 trillion cells, 200 types
• Cell surfaces include basal, lateral, and apical surfaces

General Functions

• Cells provide covering and lining
• Cells perform storage
• Cells facilitate movement
• Cells connect tissues
• Cells defend against pathogens
• Cells facilitate communication
• Cells participate in reproduction

Cellular Diversity: Size

• A micrometer (µm) is one-millionth of a meter (10⁻⁶)
• Cells range in diameter from 10-15 micrometers
• Some cells, like neurons, can be larger than 1 meter in length
• Red blood cells (RBCs) have an average diameter of 8 µm
• Ova, or egg cells have an average diameter of 140 µm

Cellular Diversity: Cell Shapes

• Cells exhibit diverse shapes
• Examples of cell shapes include squamous, cuboidal, columnar, polygonal, stellate, spheroid, discoid, fusiform (spindle-shaped), and fibrous

Basic Plasma Membrane Components

• A cell is enclosed by a plasma membrane.
• The membrane is a boundary between the extracellular fluid (ECF) and intracellular fluid (ICF).
• It is 6-10 nm thick.
• It is selectively permeable.
• Phospholipids comprise a bilayer, with water-loving heads and water-repelling tails.
• Proteins are embedded, acting as receptors, enzymes, transport channels, and cell identity markers.
• Glycoproteins (sugary proteins) are on the outside surface.

Plasma Membrane Composition

• The plasma membrane consists primarily of:
  • Phospholipids (75%)
  • Cholesterol (20%)
  • Glycolipids (5-10%)
• Proteins include:
  • Transmembrane/Integral proteins
  • Peripheral proteins
  • Glycoproteins

Functions of Membrane Proteins

• Receptor proteins: bind to chemical messengers
• Enzyme proteins: catalyze specific reactions
• Channel proteins: passageways for ions/molecules
• Transport/Carrier proteins: actively transport molecules
• Cell-identity markers: glycoproteins signaling cell origin
• Cell-adhesion proteins (CAMs): cells adhere to one another

Major Types of Membrane Transport

• Passive Transport: Moves materials down a concentration gradient (no energy needed).
  • Simple Diffusion: Movement of nonpolar molecules, water, and ions
  • Facilitated Diffusion: Assisted by membrane protein
• Active Transport: Moves materials against a concentration gradient (energy needed).
  • Primary Active Transport: Uses ATP directly
  • Secondary Active Transport: Uses electrochemical gradient established by primary active transport

Glycocalyx

• A fuzzy, sugary coat on top of proteins and lipids on the cell surface.
• Function: protects cell, recognizes as part of the body, and binds tissues.

Surface Extensions of Plasma Membrane

• Microvilli: absorption, increase surface area, microfilaments
• Cilia: movement of materials over cell surface, microtubules
• Flagella: propulsion of sperm cells, microtubules

Cell Junctions

• Tight junctions: interlocked proteins prevent passage of water and solutes
• Desmosomes: very strong, offers resistance to stretching and twisting.
• Gap junctions: connexons allow diffusion of ions, small molecules, and electrical impulses

Nucleus

• The largest organelle in the cell
• A control center for the cell, acting as a 'brain'.
• Contains the instructions to regulate production of other cell parts (100,000 different proteins)
• Has various shapes depending on other cells.
• Uninucleate, multinucleate, or anucleate
• Contains the following components:
  • Nuclear envelope
  • Nuclear pores
  • Nucleoplasm
  • Chromosomes
  • Nucleolus

Cytoplasm

• Cytosol (ICF): intracellular fluid
• Organelles
• Cytoskeleton
• Inclusions

Cytosol/ICF

• Composed primarily of water (75-90%)
• Proteins (15-20%), mostly enzymes
• Carbohydrates, lipids, amino acids
• Ions (e.g., K+, Na+, Ca++, Cl−)

Cytoskeleton

• Organized proteins forming filaments and tubules.
• Functions: Support, shape, organizes organelles, move materials, and participate in cell division

Inclusions

• Non-essential to cell survival
• Stored cellular products, pigments (melanin), fat droplets, glycogen
• Foreign bodies (dust particles, viruses, intracellular bacteria)

Organelles: Membrane-Bound

• Mitochondria: aerobic respiration, ATP
• Endoplasmic Reticulum (ER): protein synthesis (rough ER) and lipid synthesis/detoxification (smooth ER)
• Peroxisomes: Oxidize substances and break down fatty acids
• Lysosomes: digestive enzymes, breakdown material, and cell waste.
• Golgi apparatus: modifies proteins, packaging, and transports materials

Organelles: Non-membrane Bound

• Ribosomes: protein synthesis
• Centrioles: participate in cell division

Endoplasmic Reticulum (ER)

• Rough ER (RER) has ribosomes, produces proteins
• Smooth ER (SER) lacks ribosomes, synthesizes lipids, detoxifies materials (e.g., alcohol, drugs).

Golgi Complex/Apparatus

• Stacks of cisternae (flattened sacs).
• Modifies, package, sorts, and transports proteins and other materials.
• Involved in secretion.
• Vesicles from the Golgi can become lysosomes

Lysosomes

• Contain digestive enzymes
• Involved in disease defense (endocytosis)
• Waste cleanup
• Cell death (autophagy, autolysis)

Peroxisomes

• Oxidize organic molecules for detoxification.
• Convert hydrogen peroxide (H₂O₂) to water (H₂O) and oxygen (O₂)
• Break down fatty acids

Mitochondria

• Site of aerobic respiration (generating ATP)
• Contain outer and inner membranes (cristae)
• Have their own DNA (mtDNA)
• Abundant in tissues that need high energy (muscle, sperm).

Ribosomes

• Composed of two subunits.
• Sites of protein synthesis
• Found free in the cytosol or bound to RER.

Centrioles

• Cylindrical structures composed of microtubules organized in groups of three.
• Participate in cell division.
• Not found in some cells (RBCs, skeletal muscle cells.)

The Cell Cycle

• Interphase (G₁: growth, S: DNA replication, G₂: growth & preparation)
• Mitosis (Prophase, Metaphase, Anaphase, Telophase)

Mitosis

• Phases: Prophase (chromosomes condense, nuclear envelope breaks down), Metaphase (chromosomes align at the cell's center), Anaphase (sister chromatids separate), Telophase (chromosomes decondense, nuclear envelope reforms).

Early and Late Prophase

• Chromatin condenses into chromosomes
• Nuclear envelope breaks down
• Nucleolus disappears
• Mitotic apparatus forms to connect to chromosomes

Chromosomes

• Organized structures of DNA (with proteins)
• Consists of two identical chromatids held together at the centromere.

Anatomy of Chromosomes

• Single chromosome: single strand of DNA
• Duplicated chromosome: two identical strands of DNA held together at the centromere.
• Parts: Chromatid, centromere, telomeres, short arm, long arm

Metaphase: M for Middle

• Chromosomes line up along the center of the cell

Anaphase: A for Apart

• Sister chromatids separate and move to opposite ends of the cell

Telophase: T for Two

• Chromosomes begin to decondense
• Nuclear envelope reforms
• Nucleolus reforms
• Mitotic apparatus disassembles

Cytokinesis

• Division of the cytoplasm.
• Begins in anaphase and ends with two identical daughter cells.

Meiosis: Reproductive Cell Division

• Two successive stages of nuclear division
• Produces haploid gametes (reproductive cells) from diploid cells
• Meiosis I: Homologous chromosomes pair and undergo crossing-over
• Meiosis II: Sister chromatids separate, creating four haploid cells

Aging and Cells

• Progressive alteration of homeostatic mechanisms
• Changes in structure and function
• Increased vulnerability to stress and disease
• Genetically programmed cessation of division, shortened telomeres, free radical buildup, intensified immune response.