Cell Theory & Prokaryotic/Eukaryotic Cells

• The lecture covers Cell Structure and Function, specifically Chapter 4 for Biology by Mader and Windelspecht.

The Cell Theory

• All organisms consist of one or more cells.
• Cells represent the basic organizational units of all living organisms.
• All cells come from pre-existing cells through cell division; cells are self-reproducing.

Cell Size

• Ranges from 1 mm to 1 micrometer.
• A large surface area of plasma membrane is needed for adequate material exchange.
• Surface-area-to-volume ratio is key; cells necessity to be small.
• Larger cells have decreased relative surface area, reducing transport efficiency.
• Smaller cells have a larger surface area relative to their volume, which enhances molecule exchange.

Types & Parts

• Two primary cell types exist: prokaryotic and eukaryotic.
• All cells share 3 main parts: plasma membrane, nucleoid/nucleus, and cytoplasm.

Prokaryotic Cells

• Have a simple internal structure.
• Lack membrane-bound organelles.
• A cell envelope surrounds them.
• Contain a single, circular DNA strand in a nucleoid region, not a nucleus.
• Enzymes catalyzing reactions are bound to the cell membrane.
• Structurally similar but biochemically distinct, classified into Eubacteria and Archaea.

Bacteria

• There are 3 different shapes: bacillus, coccus and spirillum.
• Some cause diseases like Tuberculosis, Tetanus, and Gonorrhea.
• Critical for decomposition.
• Used in manufacturing products and drugs, such as insulin.
• Cyanobacteria, or blue-green algae, have thylakoids and can perform photosynthesis.

Cell Envelope include:

• Plasma membrane: A phospholipid bilayer with embedded peripheral proteins
  • Internal pouches (mesosomes) increase surface area.
• Cell Wall: Maintains cell shape, strengthened by peptidoglycan.
• Glycocalyx: A polysaccharide layer on the cell exterior Well-organized or removable capsule

Prokaryotic Cytoplasm and Appendages

• Cytoplasm contains water, inorganic and organic molecules, and enzymes.
• The plasma membrane bounds.
• Nucleoid: Contains a coiled DNA molecule.
• Plasmids: Small circular DNA rings.
• Appendages: structures extending from the cell.
• Flagella provide motility, functioning like propellers
• Filament, hook, and basal body structures.
• Fimbriae are bristle-like fibers for surface attachment.
• Conjugation pili are rigid structures for DNA transfer between cells.

Eukaryotic Cells

• Characterized by a membrane-bound nucleus housing DNA.
• Contain specialized organelles that perform specific functions and isolate reactions.
• The plasma membrane, composed of a phospholipid bilayer, separates cell contents and regulates material passage.
• Distinguished from prokaryotic cells by the nucleus and specialized organelles.

Origin of Eukaryotic Cells

• Fossil records suggest prokaryotes were the first cells.
• Eukaryotes are biochemically more related to archaea than bacteria.
• Nucleus is believed to have evolved through plasma membrane invagination.
• Invagination also explains the origins of the endoplasmic reticulum and the Golgi apparatus.
• Energy organelles could have originated when larger cells engulfed smaller prokaryotic cells.
• Endosymbiotic theory explains the above.

Eukaryotic Organelles classes:

• Endomembrane system: organelles that communicate via membrane channels and vesicles.
• Energy-related organelles: mitochondria and chloroplasts.
  • They are independent, self-sufficient with their own DNA, and divide on their own.

Eukaryotic Cell Structures and Functions

• Cell Wall: Protection and support (outer layer of cellulose or chitin).
• Cytoskeleton: Structural support and cell movement (network of protein filaments).
• Flagella (cilia): Motility (cellular extensions with a 9 + 2 microtubule arrangement).
• Plasma Membrane: Regulates passage, cell recognition (lipid bilayer with embedded proteins).
• Endoplasmic Reticulum: Compartments, protein/lipid synthesis (internal membrane network).
• Nucleus: Control center, directs synthesis/reproduction (double membrane bound).
• Golgi Apparatus: Modifies and packages proteins for export from the cell and forms secretory vesicles.
• Lysosomes: Vesicles that contain digestive enzymes that break down worn-out organelles and debris and plays a role in cell death.
• Microbodies: Vesicles that Isolate particular chemical activities.
• Mitochondria: Performs oxidative metabolism.
• Cholorplasts: Photosynthesis
• Chromosomes contain hereditary information (long DNA threads complexed with protein).
• Nucleolus: Assembles ribosomes (site of rRNA synthesis).
• Ribosomes: Protein synthesis (small assemblies of RNA and protein).

Nucleus

• Command center of the cell.
• Separated from the cytoplasm by a nuclear envelope

Nuclear envelope

• Consists of a phospholipid bilayer.
• Contains chromatin (DNA and proteins) in a semifluid nucleoplasm.
• Contains nucleolus: the site for ribosome synthesis, composed of rRNA.
• Nuclear pores import cytoplasm proteins and export mRNA and ribosomal subunits

Ribosomes

• Occur as single ribosomes or in groups (polyribosomes).
• Can be found freely in the cytoplasm or attached to the ER membrane.
• Composed of two subunits—one large (30 nm) and one small (20 nm)—both made of proteins and rRNA, synthesized in the nucleolus.
• The site of protein synthesis is where the DNA-mRNA-protein sequence occurs.
• May be located on the endoplasmic reticulum (making it rough) or freely in the cytoplasm, either singly or in groups, called polyribosomes.
• Information for the gene is copied into mRNA, which is exported into the cytoplasm.
• Proteins synthesized by cytoplasmic ribosomes stay in cytoplasm; those made by attached ribosomes stay in ER.

Function of Ribosomes

• mRNA is copied from a gene, exits via a nuclear pore, and a ribosome attaches to begin protein and peptide synthesis
• Signal recognition particle (SRP) binds, halting synthesis temporarily.
• SRP binds to a receptor, a channel opens, and synthesis resumes.
• The polypeptide is fed into ER.
• An enzyme removes the signal peptide.
• Ribosomal subunits and mRNA detach, leaving the polypeptide to fold in the ER.

The Endomembrane System

• A continuous system of membrane channels and vesicles from the nuclear envelope.
• Compartmentalizes the cell
• Enzymatic reactions are restricted to specific compartments.
• Consists of: nuclear envelope, endoplasmic reticulum, Golgi apparatus, and vesicles.
• Transport materials are transported between organelles of the system

Endoplasmic Reticulum or ER

• Rough ER synthesizes and modifies proteins and adds sugar to create glycoproteins
• Smooth ER synthesizes lipids, detoxifies drugs, stores materials, and forms transport vesicles.

Golgi Apparatus

• Consists of flattened, curved saccules and looks like a stack of pancakes.
• Modifies proteins and lipids with "signal" sequences.
• Receives ER vesicles on the cis (inner) face then modifies and packages them for export from the trans (outer) face.
• From the trans face , vesicles either transport materials within the face, are exported through exocytosis, return to the ER , or merge with the plasma membrane.

Lysosomes

• Membrane-bound vesicles formed by the Golgi apparatus.
• Contain powerful digestive enzymes that break down large molecules and are highly acidic.
• Perform Digestion of large molecules
• Perform Recycling of cellular resources (dead mitochondria)
• Tay-Sachs disease results from a defect in lysosomal enzymes.

Peroxisomes

• Membrane-bound vesicles contain enzymes synthesized by free ribosomes.
• Common in cells that synthesize and break down lipids.
• Contain enzymes that oxidize fatty acids: RH₂ + O₂ → R + H₂O₂
• In plants, seeds use peroxisomes to oxidize fatty acids into molecules that can be converted to sugars and are Needed for seed germination

Vacuoles

• Present in animal (few, fat cells) and protist (for water regulation) cells.
• Plant cells contain a large central vacuole (90% of cell volume) which contain cell sap.
  • Functions include storage of water, sugar, salts, pigments, and wastes.
  • Development of turgor pressure to provide support.
• Store toxic chemicals to deter herbivores.
  • Fuses with organelles break down (~lysosomes).

Energy-Related Organelles

• Chloroplasts is found in plants, algae, and cyanobacteria
  • Contain multiple copies of DNA.
  • Disc-like thylakoids form stacked grana.
  • Suspended in semi-fluid stroma.
  • Chlorophyll is located in the thylakoid membrane, and carbohydrate-synthesizing enzymes are located in the fluid stroma.
• Mitochondria
  • Power house of the cell that produces most of the ATP
  • converts chemical energy of CHO into ATP by the process called cellular respiration.
  • Contain outer and inner membranes (cristae).
  • Present in eukaryotic cells.
• Matrix contains DNA and ribosomes
• Smaller than chloroplasts
• Depending on the cell's metabolic activity the number of them varies
• About the size of bacteria

The Cytoskeleton

• The internal skeleton supports cell shape, holds organelles in place, and allows cell movement.
• Allows cell division Assembles when Phosphatases removes PO4 from proteins Disassemble when kinases adds PO4 to proteins
• Composed of;
• Actin filaments, or thin filaments, support the microvilli shape of intestinal shape
• Essential for internal traffic
• Assist cytoplasmic streaming
• Help pseudopods of amoeboid function Consist of twisted pearl necklace; a key component of muscle contraction with myosin
• Intermediate Filaments:
  • Support nuclear envelope
  • Create the support for cell to cell junction.
  • Support the plasma membrane
  • Provide great mechanical strength.
• Microtubules
  • Hollow cylinders formed by tubulin dimers, controlled by MTOC
  • Allow for organelle movement, interacting with motor molecules like kinesin and dynein.
  • The spindle distributes chromosomes during cell division.
• Centrioles
  • Short, hollow cylinders made of 27 microtubules, in pairs in animal cells near the centrosome, for microtubule assemble and separate chromosomes during cell division.
• Cilia and Flagella
  • Hair-like structures that aid in cell movement (9 + 2 microtubule arrangement).
  • Cilia are shorter and move in coordinated waves, while flagella move in a whiplike motion.

These questions cover cell theory, contrasting it with spontaneous generation, and exploring its implications for newly discovered organisms. It also covers prokaryotic cells (cell wall function, conjugation pili) and surface area to volume ratio.