Eukaryotic Cells: Structure and Function

Eukaryotic Cells Overview

• Membrane-bound organelles, including a nucleus, mitochondria, and endoplasmic reticulum are found within eukaryotic cells.
• Protozoa, fungi, plants, and animals are some of the organisms with eukaryotic cells.
• Eukaryota is the biological domain to which these organisms are assigned.
• Eukaryotic cells are more complex and larger than the prokaryotic cells.
• The domains Archaea and Bacteria house prokaryotic cells.

Eukaryotic Cell Parts

• The plasma membrane also referred to as cell membrane separates the inside of a cell.
• The semi-permeable plasma membrane is important for cell growth, secretion, and division.
• The plasma membrane in eukaryotes has proteins, carbohydrates, and two phospholipid layers (lipids with a phosphate group).
• Polar, hydrophilic heads are oriented towards the outside and inside of the cell.
• These polar heads interact with the aqueous environment that is both external and internal to a cell.
• Non-polar, hydrophobic tails are tucked between the heads, shielded from the aqueous surroundings.
• The cell wall provides a rigid structure outside the plasma membrane in plants and fungi being absent in animal cells.
• Plants cell walls contain cellulose, hemicellulose, proteins, and pectin.
• Fungi cell walls contain cellulose, galactans, mannans, and calcium carbonate.
• The middle lamella is the cell wall's outermost layer, made of calcium pectates, which binds cells.
• The primary wall is the middle layer, consisting of cellulose and hemicellulose and is found in young, proliferating cells where growth occurs.
• Cytoplasm includes the matrix in which various cellular components are located, and cytosol is the cytoplasm's fluid component.
• Eukaryotic cytoplasm has microfilaments, intermediate filaments, and microtubules, which create a complex internal structure, also known as the cytoskeleton

Ribosomes & Organelles

• Involved in protein synthesis and polypeptides are ribosomes.
• A membrane does not enclose ribosomes.
• Ribosomes, also known as "protein factories," are where protein synthesis primarily takes place.
• Eukaryotic ribosomes are 80S, made of a large 60S subunit of rRNA and a smaller 40S subunit with one rRNA molecule.
• Organelles are structures with specific functions, such as the nucleus, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes, and centrosomes.
• Not all the organelles are in all cells.

Nucleus Information

• A double membrane structure contains DNA in the nucleus.
• The nucleus is the main organelle.
• The nucleus is present in all eukaryotic cells, except human RBCs and plant sieve cells.
• In photosynthetic organisms, DNA is also present in mitochondria and chloroplasts.

Endoplasmic Reticulum

• A network of small, tubular structures creates two sections within eukaryotic cells: luminal space (inside ER) and extraluminal space (cytoplasm).
• Smooth endoplasmic reticulum (SER) lacks ribosomes for lipid synthesis, whereas, rough endoplasmic reticulum (RER) has ribosomes for protein synthesis.

Golgi Apparatus

• Disc-shaped structures make up the Golgi, known as cisternae.
• The Golgi is in nearly all eukaryotic cells, with the exceptions of plant sieve cells and human red blood cells.
• Vesicles transport secreted material to the cis face (or forming face), which is oriented toward the plasma membrane.
• The trans face (or maturing face), which is oriented towards the nucleus, releases the received substance into the cell.
• An important site for packaging material within the cell.

Mitochondria, Lysosomes, Peroxisomes & Centrosomes

• The "powerhouses of the cell," produce ATP.
• Mitochondria possess DNA, RNA, and protein synthesis machinery.
• The inner mitochondrial membrane folds into cristae, whereas the outer mitochondrial membrane remains smooth.
• Golgi complexes produce membrane-enclosed spheres called lysosomes.
• Lysosomes have hydrolytic enzymes that are suited for the acidic pH (less than 7)
• The main function of lysosomes is to digest lipids, proteins, carbohydrates, and nucleic acids.
• Peroxisomes oxidize organic compounds via enzymes
• They are structurally comparable to, but smaller than lysosomes.
• Near the nucleus, centrosomes consist of the pericentriolar area and centrioles.
• The mitotic spindle is organized by the pericentriolar material, which is essential for cell division and microtubule production in cells that aren't dividing.

Cytoskeleton, Cilia and Flagella

• A filamentous network, the cytoskeleton, is responsible for cell structure and motility.
• Cilia and flagella structures differ in length and quantity per cell.
• Cilia provide rowing motions and cover an entire cell's surface, while flagella provide up and down movements and are at one end of a cell.

Fungi

• Fungi are heterotrophic eukaryotes with roles in nutrient cycling, reproducing sexually and asexually.
• Associations between fungi, bacteria, and plants are symbiotic.
• Certain fungi are responsible for diseases affecting animals and plants.
• Leather, plastics, jams, and pickles are just a few of the unlikely materials that fungi can inhabit, causing deterioration and spoilage.
• The scientific study of fungi is known as mycology.
• Polysaccharide chitin is in fungal cell walls, but not in other microorganisms.
• Septate hyphae can be divided into cells, whereas aseptate hyphae have multinucleated cytoplasm.

Fungi Classification

• Fungi are divided into three groups based on their life cycles, fruiting body structure, and spore arrangement: single-celled microscopic yeasts, macroscopic filamentous fungi (mushrooms), and multicellular filamentous molds.
• Moulds consist of hyphae, which grow at the tips, branch out, and interweave to form mycelium and secrete digestive enzymes.
• Yeasts are single-celled eukaryotes without mycelia observed through a microscope.
• Species of of yeast can reproduce by budding and are useful in cancer genetics research.
• Spores are present in all fungi.
• Fungi reproduce sexually or asexually.
• Sporangiospores and conidia are the types of asexual spores.
• Five phyla of fungi include Chytridiomycota, Zygomycota, Glomeromycota, Ascomycota, and Basidiomycota.

Fungal Infections

• Mycoses is the term for fungal infections, which may be subcutaneous, superficial, cutaneous, or systemic.
• Cutaneous mycoses target the living skin layers (dermis); superficial mycoses attack nails, hair, and the outermost skin layers (epidermis).
• Subcutaneous and systemic mycoses are more severe and affect the dermis and underlying tissues.
• Common fungal infections include athlete's foot (tinea pedis), jock itch (tinea cruris), ringworm, yeast infections, and onychomycosis.

Algae Classification and Nutritution

• Algae are aquatic photosynthesizers and range in size from microscopic unicellular species (diatoms, desmids, dinoflagellates) to large multicellular species (kelp).
• The average algal cell is composed of cytoplasm, a cell wall, a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies.
• Auxotrophs are algae that require B12 complex vitamins and fatty acids while algae can photosynthesize, and certain species are heterotrophic.
• Osmotrophy involves absorbing dissolved substances.
• Phagotrophy involves engulfing bacteria.

Algae Reproduction

• Spores can be produced during asexual reproduction and vegetative methods include mitosis and fragmentation.
• Gametes produced by meiosis unite during sexual reproduction.
• Algae can reproduce vegetatively/asexually and sexually.
• Algae are classified as cyanobacteria (prokaryotic) or eukaryotic.
• Cyanobacteria (blue-green algae) are gram-negative bacteria capable of nitrogen fixation.
• Eukaryotic algae are a polyphyletic group not from a single common ancestor.
• Protothecosis is caused by Prototheca, a chloroplast-lacking green alga, causing skin lesions and is rarely caused by Chlorella.
• Phycotoxins are substances created by some algae the are poisonous to animals.
• Soil is the habitat for Prototheca and causes subcutaneous lesions and spreads via the lymphatic system, especially in those who are immunosuppressed.