Cell Biology Basics

• The text provides an overview of cell structure, cell theory, microscopy, and the differences between prokaryotic and eukaryotic cells, as well as the functions of life, and cell differentiation.

Cell Theory

• Cells are the basic structural unit of all living organisms
• The cell theory posits that all living organisms consist of one or more cells, cells are the basic functional unit of life, and new cells arise from pre-existing ones

Microscopy and Cell Study Skills

• Optical microscopes help see tissues, cells, and organelles
• Light is directed through a thin layer of biological material on a glass slide, then focused through lenses to allow the eye to view it through the eyepiece
• When preparing a temporary mount, slides with a liquid specimen require drops of the sample added to the slide using a pipette, and the liquid covered with a cover slip that covers the stain/tissue
• Preparing a temporary mount slide using a solid specimen requires scissors to cut a small sample of the tissue, peeling away a very thin layer of cells to be placed on the slide

Using a Microscope

• Always start with the low power objective lens
• Focus by moving the coarse focusing knob until the specimen comes into focus, then use the fine focusing knob to sharpen
• Move to higher objective lens, and only use the fine focusing knob
• The graticule has no fixed units and must be calibrated for the objective lens in use, and by using a special scale engraved on a microscope slide (a stage micrometer)
• Calculating magnification requires determining how much bigger the image is compared to the actual size
• Cell sizes are measured using micrometers (µm) or nanometers (nm) and all measurements must be in the same units

Microscope Types

• Microscopes analyze cell components
• Magnification is how much larger the image is than the real object
• Resolution is the clarity to distinguish close objects
• Optical microscopes have lower resolution using light, maximum resolution of 0.2 micrometers (μm), and magnify up to x1500, and can be used to view eukaryotic cells and their internal structures
• Electron microscopes use electrons for higher resolution (0.0002 µm), and magnify up to x1,500,000, good for small organelles
• Transmission electron microscopes (TEMS) transmit electrons through the specimen - high resolution but specimens must be very thin and non-living
• Scanning electron microscopes (SEMs) scan electrons across the surface - 3D images but lower resolution and non-living specimens
• Light microscopes are used for specimens above 200 nm, while electron microscopes are used for specimens above 0.5 nm

General Cell Structure

• The cell structure comprises the following: DNA as genetic material, cytoplasm, and a plasma membrane
• The membrane is responsible for controlling the interactions of the cell's interior with the exterior

Prokaryotic Cells

• Prokaryotes are simple, lacking a nucleus or membrane-bound organelles, with sizes ranging from 0.1µm to 5.0µm
• They includes Bacteria and Archaea
• Prokaryotic cytoplasm lacks compartments and contains 70S ribosomes and DNA in a loop
• Most have a cell wall containing murein/peptidoglycan as protection, and can be gram positive or negative
• Additional structures includes plasmids, capsules, flagella and pili

Eukaryotic Cells

• Eukaryotic cells possess complex ultrastructure with membrane-bound organelles
• Compartmentalization is advantageous, allowing higher concentrations of enzymes, separation of damaging substances, optimal conditions, and altered organelle numbers/locations
• Eukaryotic cells contain membrane bound organelles, e.g the nucleus and mitrochondria

Eukaryotic Organelles

• Nucleus: contains chromatin, separated by a double membrane
• Rough Endoplasmic Reticulum: Processes proteins made my ribosomes
• Ribosomes: site of translation which is part of protein synthesis
• Mitochondria: site of aerobic respiration surrounded by cristae, enzymes and DNA for replication.
• Golgi apparatus: Modifies proteins and lipids before packaging them for transport
• Vesicles: Membrane-bound sacs for transport
• Lysosomes: specialised vesicles that break down waste materials
• Vacuoles: In plants cells, they store water, enzymes, carbohydrates, etc
• Chloroplasts: site of photosynthesis that contains thylakoids with chlorophyll, DNA and ribosomes

Cell Wall (Plant)

• Found in plant cells outside the cell membrane for structural support
• Composed of the polysaccharide cellulose
• Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighboring plant cells
• It is freely permeable to most substances

Function of Life

• All organisms (unicellular and multicellular) share the same functions
• Metabolism is enzyme-catalyzed reactions
• Reproduction generates offspring (either sexually or asexually)
• Homeostasis maintains internal balance
• Growth is permanent increase in size
• Response to stimuli influences chances of survival
• Excretion removes metabolic wastes
• Nutrition includes acquisition of energy and nutrients

Eukaryotic Cell Structure: Animals, Fungi & Plants

• Eukaryotic cells exist in animal, plant, fungal, and protist kingdoms
• Animal Kingdom: cells do not have a cell wall, contain centrioles and store carbohydrates as glycogen
• Plant Kingdom: cells walls are composed of the polysaccharide cellulose, process many chloroplasts and possess large permanent vauloes used to stored various substance, store carbohydrates as startch
• Fungal Kingdom: cells are made up mainly of glucans, chitin and glycoproteins, non-permanent

Atypical Cell Structure

• Eukaryotic cells possess a unique or atypical structure enabling them to carry out specialised functions
• Striated muscle fibers, aseptate fungal hyphae and pholem sieve tubes a examples

Drawing Cells

• Biological drawings show specific observed features as single, clear lines
• Include a title, magnification, and scale bar, if possible

Endosymbiotic Theory

• Mitochondria structures have features in common with prokaryotes as they replicate by binary fission

Cell Differentiation

• Specialised eukaryotic cells have specific adaptations based on the functions
• Structural adaptations depends include the cell shape or cell membrane

Multicellularity

• In multicellular organisms, specialized cells of the same type group together to form tissue

Test your knowledge of fundamental cell biology concepts. Questions cover characteristics of life, homeostasis, ribosomes, waste disposal, cytoskeleton function and photosynthesis within chloroplasts. Includes questions on microscopy and data interpretation.