Cell Biology Basics Quiz

Cytology and Histology

• Cytology and histology are the study of cells and tissues, respectively.

Cell Theory: History

• Cells were not discovered until the invention of the microscope in the 17th century.
• Robert Hooke (1665) observed cells and named them "cellulae" (Latin for "small rooms").
• Anton van Leeuwenhoek (Dutch microscopist) observed living cells, calling them "animalcules".
• Matthias Schleiden (1838) stated that all plants are composed of cells.
• Theodor Schwann (1839) reported that all animal tissues are composed of cells.

Cell Theory: Principles

• All organisms are composed of one or more cells.
• Cells are the basic units of organization of all organisms.
• Cells arise only by division of a previously existing cell.

Cell as a Living Being

• Cells can absorb, process, and utilize food.
• Cells can excrete waste.
• Cells can secrete substances.
• Cells can reproduce
• Cells can repair themselves.

Cell as a Unit

• A structural unit: support for biological activities.
• A reproduction unit: development or repairing of organs.
• An information unit: contains hereditary information.
• A unit of function: ensures the realization of the biological activities necessary for life.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells (bacteria, archaebacteria):
  • Small (1 to 10 µm)
  • All unicellular
  • Genetic material (DNA) not enclosed in a membrane (nucleoid)
  • No internal membrane system
  • Cell division mainly by binary fission
• Eukaryotic cells:
  • Larger (10 to 100 µm)
  • Uni or multi cellular
  • Genetic material (DNA) enclosed in a membrane (nucleus)
  • Contain numerous membrane-bounded organelles
  • Cell division by mitosis

Prokaryotic Cell Division

• Binary fission:
  • Replication of DNA
  • Segregation of DNA
  • Cell splitting into two identical daughter cells.

Mitosis

• A type of cell division that results in two identical daughter cells in eukaryotic cells.

Cellular Features Shared by All Cells

• Nucleoid/Nucleus: Contains DNA, the genetic material.
• Cytoplasm: Semifluid matrix containing sugars, amino acids, and proteins.
• Ribosomes: Synthesize proteins.
• Plasma Membrane: Encloses the cell and separates its contents from the surroundings, a phospholipid bilayer with embedded proteins.

Prokaryotic Cells: Simple Organization

• Prokaryotes lack a nucleus and membrane-bounded organelles.
• They have a nucleoid region containing a single, circular DNA molecule.
• Many have plasmids, small, extrachromosomal DNA molecules.
• Exhibit three basic shapes: cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped).

Prokaryotic Cell Walls: Peptidoglycan

• Peptidoglycan is a unique polymer found in bacterial cell walls determining their shape.
• Cell walls protect the cell, maintain its shape, and prevent excessive water uptake or loss.
• Antibiotics target the peptidoglycan synthesis in bacteria for treatment of bacterial infections.

Gram-positive vs. Gram-negative Bacteria

• Gram-positive bacteria: Thicker peptidoglycan layer, stains purple with Gram stain.
• Gram-negative bacteria: Thinner peptidoglycan layer, stains pink with Gram stain, usually located outside the cell wall (outer membrane).
• Outer membrane resistant to antibiotics.

S-layer, Capsule, Flagella, and Pili

• S-layer: Additional glycoprotein layer outside peptidoglycan, providing protection or adhesion.
• Capsule: Gelatinous layer surrounding the cell wall, found in many pathogenic bacteria enhance adhesion and protect the cell
• Flagella: Long, whip-like appendages for motility.
• Pili: Short, hair-like appendages for attachment or genetic exchange (conjunction).

Bacterial Conjugation

• Process where bacteria exchange genetic material through pili.

Cell Division: Binary Fission

• Asexual reproduction mode in bacteria.
• Duplication of DNA.
• The cell wall constricts, creating two new cells.

Archaea

• Archaea have unusual membrane lipids and their DNA structure and the cell wall is differently composed compared to bacteria.
• Peptidoglycan is absent.

Eukaryotic Cells

• More complex than prokaryotic cells.
• Cells have compartmentalization (organelles) and a membrane system.

Eukaryotic Cell Organization

• Cells are organized into two main parts:
  1. Nucleus: the control center of the cell.
  2. Cytoplasm: the region outside the nucleus, where most cellular processes occur

The Nucleus

• Spherical shape.
• Located in the central region of the cell.
• Contains DNA (genetic material) that synthesizes nearly all the proteins of eukaryotic cells.
• Nucleus exhibits nucleolus, which plays a role in ribosome components synthesis
• Nuclear envelope: Double membrane surrounding the nucleus, perforated with pores allowing substances to move in and out of the nucleus.
• The network of fibers within the nuclear envelope is called the nuclear lamina.

The Nuclear Envelope

• Double phospholipid bilayer membrane.
• Perforated with pores.
• Controls the passage of proteins and RNA-protein complexes which transport materials between the nucleus and the cytoplasm.
• Continuous with the endoplasmic reticulum.
• Nucleus shape is due to the nuclear lamina, involved in deconstruction/reconstruction during cell division.
• Nuclear pores are complex structures (orthogonal radial symmetry), consisting of multiple proteins which helps control the passage of substances.
• Exchange in both directions between the cytoplasm and the nucleoplasm using active or passive transport.

Nucleolus

• Dark-staining region in the nucleus.
• Where ribosome subunits are assembled.

Chromatin: DNA Packaging

• DNA is packaged with proteins (histones) forming chromatin.
• Two forms: Heterochromatin (generally not active) and Euchromatin (active).
• In non-dividing cells: DNA is a thin network of threads called chromatin.
• When cell prepares to divide, Chromatin forms distinct structures called chromosomes.

Primary Structure of DNA

• A nucleotide polymer.
• Composed of a phosphate group, deoxyribose sugar, and nitrogenous bases (A, T, C, G).

Secondary Structure of DNA

• Double helix.
• Two complementary strands held together by hydrogen bonds.
• A–T (2 hydrogen bonds); C–G (3 hydrogen bonds).
• Antiparallel.

Structure of Chromatin

• Composed of DNA wrapped around histones (proteins).
• Two forms: hetero- and euchromatin.
• Levels of chromatin condensation.

Ribosomes

• Complex molecular assemblies.
• Composed of rRNA and proteins.
• The cell's protein synthesis machinery.
• Found free in cytoplasm or attached to endoplasmic reticulum.

Ribosomes: Protein Synthesis

• Synthesize proteins for the cytoplasm, nucleus, mitochondria, other organelles, to endomembrane system, etc.
• Need mRNA and tRNA to function effectively.
• Ribosome subunits join to make a functional ribosome (when actively synthesizing proteins).

mRNA

• The genetic information from DNA is transferred to the cytoplasm to the protein synthesis machinery in the form of mRNA.
• mRNA is a matrix on which amino acids for a specific protein are polymerized.

Transcription

• Takes place in the nucleus.
• One DNA strand acts as a template.
• Uses RNA polymerase.
• Synthesizes an RNA strand following the complement rule.

Translation

• mRNA migrates into cytoplasm and attaches to a ribosome.
• mRNA is read codon by codon.
• Codons correspond to amino acids.
• tRNA carries specific amino acids to the ribosome.
• Amino acids are linked to create a protein molecule.

Expression of Genetic Information

• DNA triplets (codons) correspond to mRNA codons.
• mRNA codons correspond to specific anti-codons on tRNA.
• Anti-codons correspond to specific amino acids.

The Endomembrane System

• Internal membranes in eukaryotic cells that divide the cell into compartments.
• Includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles.
• Channels for molecular passage.
• Surfaces for lipid and protein synthesis

Endoplasmic Reticulum (ER)

• Largest internal membrane in eukaryotic cells.
• Two types:
  • Rough ER (RER): Studded with ribosomes, synthesizes and modifies proteins, and plays a role in protein folding and quality control.
  • Smooth ER (SER): Synthesizes lipids, metabolizes carbohydrates, stores calcium ions, and plays a role in detoxification.

Golgi Apparatus

• Stacked, membranous sacs (cisternae) in eukaryotic cells.
• Processes, packages, and distributes molecules (proteins and lipids) synthesized in the ER.
• 3 zones: Cis, medial, and Trans face.

Lysosomes

• Membrane-bound vesicles in eukaryotic cells.
• Contain enzymes that break down macromolecules (proteins, nucleic acids, carbohydrates, lipids).
• Involved in recycling of cellular components and destroying harmful substances.

Peroxisomes

• Membrane-bound organelles in eukaryotic cells.
• Contain enzymes that carry out oxidation reactions.
• Involved in several biological functions, including detoxification of harmful substances and breakdown of fatty acids.

Mitochondria

• Sausage-shaped organelles involved in cellular respiration.
• Produce ATP (adenosine triphosphate), the cell's energy currency.
• Contain their own DNA and ribosomes, but depend on the nucleus for many of their proteins.

The Cytoskeleton

• Network of protein fibers throughout the cytoplasm of eukaryotic cells, maintaining cell shape and movement/transport of intracellular components.
• Three types of fibers:
  • Actin filaments (microfilaments) for mobility, maintaining and changing cell shape during cell division.
  • Microtubules for structure/organization and mobility.
  • Intermediate filaments for cell strength.

Centrosomes and Centrioles

• Centrosome is the microtubule organizing center (MTOC).
• Centrioles occur in pairs, near the nucleus, involved in cell division.

Intermediate Filaments

• Tough, stable fibers that maintain cell morphology and shape.
• More durable than actin filaments or microtubules.
• Constituted by proteins (e.g., vimentin, keratin)

Test your knowledge on key concepts in cell biology with this quiz. Questions cover cell theory, the differences between prokaryotic and eukaryotic cells, and specific structures within cells. Perfect for students studying biology at any level!