Cell Biology: Flagella and Cilia Movement

Cell Structure

• Cell: the fundamental unit of any living organism
• Metabolism: all of the chemical reactions that occur within a cell
• DNA (Deoxyribonucleic acid): genetic material that makes up the genes of the chromosomes

Cell Categories

• Eukaryotic cells: contain a true nucleus and a complex system of membrane-bound organelles (algae, protozoa, fungi, plants, animals, humans)
• Prokaryotic cells: lack a true nucleus and other membrane-bound organelles (bacteria and archaea)

Eukaryotic Cell Structure

• Nucleus:
  • The “command center” of the cell
  • Composed of nucleoplasm, chromosomes, and a nuclear membrane
• Cell membrane:
  • Encloses the cell
  • Composed of large molecules of proteins and phospholipids
  • Regulates the passage of nutrients, waste products, and secretions into and out of the cell
  • Has selective permeability
• Cytoplasm:
  • A semifluid, gelatinous, nutrient matrix
  • Contains storage granules and a variety of organelles
  • Where most metabolic reactions occur
• Endoplasmic reticulum (ER):
  • A highly convoluted system of membranes arranged to form a transport network in the cytoplasm
  • Rough ER has ribosomes attached to it, whereas smooth ER does not
  • Rough ER – involved in secretion and membrane protein synthesis; site of glycosylation of proteins
  • Smooth ER – synthesizes lipids, phospholipids, and steroids
• Ribosomes:
  • Consist of ribosomal RNA and protein
  • Sites of protein synthesis
• Golgi complex:
  • Connects or communicates with ER
  • Completes the transformation of newly synthesized proteins and packages them for storage or export
  • A stack of flattened, membranous sacs
• Lysosomes and peroxisomes:
  • Originate in the Golgi complex
  • Lysosomes contain lysozyme and other digestive enzymes
  • Found in ALL eukaryotic cells
  • Break down worn-out parts of the cell or the whole cell
  • Peroxisomes are membrane-bound vesicles where H2O2 is generated and broken down
  • Found in MOST eukaryotic cells
  • Break down long chain fatty acids so they can be utilized by the mitochondria
• Mitochondria:
  • The “powerhouses” of the cell
  • ATP molecules are produced within mitochondria by cellular respiration
  • Energy is released from glucose and other nutrients
  • Number of mitochondria varies depending on the activities of the cell
• Plastids:
  • Membrane-bound structures containing photosynthetic pigments
  • Sites of photosynthesis
  • Light energy → chemical energy
  • Chloroplasts are a type of plastid; they contain chlorophyll
• Cytoskeleton:
  • A system of fibers throughout the cytoplasm
  • Three types of fibers: microtubules, microfilaments, and intermediate filaments
  • Microtubules and microfilaments are essential for a variety of activities
  • Strengthen, support, and stiffen the cell; gives the cells its shape; cell division, contraction, and motility
• Cell wall:
  • Some eukaryotic cells contain cell walls – an external structure to provide shape, protection, and rigidity
  • Simpler in structure than prokaryotic cell walls
  • Chitin found in cell walls of fungi; cellulose in cell walls of algae and plants
• Flagella and cilia:
  • Some eukaryotic cells (e.g., spermatozoa and certain protozoa) possess long, thin, whiplike organelles of locomotion called flagella
  • Flagellated cells may possess one or more flagella
  • Some cells move by means of cilia, which are shorter, thinner, and more numerous than flagella, and described as being “hair-like”
  • Movement occurs by cilia beating with a coordinated, rhythmic movement
  • Cilia can be found on some species of protozoa and certain types of cells in our bodies (e.g., ciliated epithelial cells in the respiratory tract)

Prokaryotic Cells

• About 10 times smaller than eukaryotic cells
• Simple compared to eukaryotic cells
• Reproduce by binary fission
• Bacteria and archaea
• The cytoplasm is not filled with internal membranes
• The cytoplasm of prokaryotic cells is surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer
• LACK membrane-bound organelles
• Cell membrane:
  • Similar in structure and function to the eukaryotic cell membrane
  • Selectively permeable
  • Flexible and thin, cannot be seen with a compound microscope
  • Many enzymes are attached to the cell membrane where metabolic reactions take place
• Chromosome:
  • Prokaryotic chromosome usually consists of a single, long, supercoiled, circular DNA molecule and serves as the control center of the cell
  • Suspended in the cytoplasm
  • Plasmids are small, circular molecules of DNA that are not part of the chromosome (extra-chromosomal)
  • Capable of self-replication
  • Can give the cell an advantage
• Cytoplasm:
  • A semifluid that consists of water, enzymes, waste products, nutrients, proteins, carbohydrates, and lipids – materials required for metabolic functions
• Cytoplasmic particles:
  • Most are ribosomes, some of which occur in clusters
  • Prokaryotic ribosomes are smaller than eukaryotic ribosomes
  • Granules present in some bacteria
  • Consist of starch, lipids, sulfur, iron, or other stored substances
• Bacterial cell wall:
  • A rigid exterior that defines the shape of bacterial cells and gives protection
  • Chemically complex
  • Not present in all bacteria
  • Main constituent of most bacterial cell walls is peptidoglycan (found only in bacteria)
  • Gram-positive bacteria have a thick layer of peptidoglycan; Gram-negative bacteria have a much thinner layer