Understanding Microscopes

Microscopes

• Magnification is the number of times an image is larger than the real size of an object.
• Magnification = image size / actual size
• Resolution is the ability to distinguish between two separate points. A light microscope has a resolution of 200nm, while an electron microscope has a resolution of 0.5nm.
• Light microscopes have a maximum magnification of x1500, while electron microscopes have a maximum magnification of x500,000.
• Electron microscopes produce electron micrographs, while light microscopes produce photomicrographs.
• Electron microscopes are better than light microscopes because they have a higher resolution, which is important when looking at very small structures like cell membranes (7nm) and ribosomes (22nm).

Types of Electron microscopes

• Transmission electron microscope (TEM) allows for viewing internal structures; it has a resolution of 0.5nm.
• Scanning electron microscope (SEM) allows for a 3-D appearance, but can't be used by students. It's resolution is between 3nm and 20nm.

Cell Structures

• Animal cells: Nucleus, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria can be observed.
• Plant cells: Cell wall, nucleus, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, vacuoles, mitochondria, chloroplasts can be observed.

Nucleus

• Largest organelle, spherical, surrounded by a double membrane (nuclear envelope) with nuclear pores.
• Contains chromatin (DNA and histone proteins), and a nucleolus (dark and spherical, making ribosomes).
• The outer membrane has ribosomes attached to it. Chromatin can be heterochromatin (dark) or euchromatin (light).
• The nucleus controls the production of proteins.
• The nucleolus makes ribosomes.

Endoplasmic Reticulum

• Rough endoplasmic reticulum (RER): Flattened fluid-filled sacs (cisternae) with 80S ribosomes attached, continuous with outer nuclear membrane, and throughout the cytoplasm.
• Functions: Post-translational modification of proteins, transport proteins to the Golgi apparatus.
• Smooth endoplasmic reticulum (SER): Tubular, fluid-filled sacs (no ribosomes attached), more irregular than RER, throughout the cytoplasm.
• Functions: Synthesis of lipids, cholesterol, and steroid hormones like sex hormones, transportation to the Golgi apparatus, breaking down toxic substances in the liver.

Golgi Apparatus

• Membranous organelle (flattened fluid-filled sacs called cisternae, arranged in a stack).
• Functions: Processing, chemical modification, and glycosylation of proteins; packaging into secretory vesicles and lysosomes.

Ribosomes

• Non-membranous organelles, 20-25nm.
• Two subunits: large and small, made of rRNA and protein, 70S and 80S ribosomes.
• Function: polypeptide synthesis.

Lysosomes

• Spherical membranous organelles containing hydrolytic enzymes.
• Functions: Phagocytosis (engulfing of bacteria), Autophagy (digestion of the parent cell) such as worn-out organelles (mitochondria), and digestion of materials.
• Release of digestive enzymes inside the cell.

Mitochondria

• Double membranous organelles, 2.5-5µm long x 0.1µm width.
• Inner membrane is folded into cristae.
• Functions: Aerobic respiration and ATP production.

Chloroplasts

• Double membranous organelles.
• Inner membrane consists of fluid filled sacs with chlorophyll pigments and ATP synthase.
• The grana are stacks of thylakoids.
• The lamellae are the skeleton maintaining the distance between thylakoids.
• Functions: Photosynthesis, formation of organic molecules, and formation of ATP.

Cilia and Flagella

• Beat or whip to move substances across cell surfaces, or propel the cell.
• Structure: 9 pairs of microtubules arranged around a center of 2 microtubules.
• Protein building blocks or dynein, which enables the movements, are located between the microtubules.
• Function: movement/assist in movement.

Microvilli

• Finger-like extensions on the cell membrane.
• Increase cell surface area, especially in cells specializing in absorption, such as epithelial cells in the small intestine.
• Composed of many bundles of actin filaments.
• Functions: Increased surface area for absorption.

Cell Walls

• Rigid outer layers that surrounds some cells, giving support and/or protection.
• Plant cell walls are primarily made of cellulose, which gives them strength.
• Cell walls also contain hemicellulose and pectin, giving them a slightly elastic structure.
• Importance: Supports plant cells; important in maintaining the cell shape. The middle lamella and primary wall are the first walls for support, while the secondary cell wall is the second layer of strength.

Carbohydrates

• A class of compounds primarily comprising carbon, hydrogen, and oxygen.
• Monosaccharides are the simplest carbohydrates, including glucose, fructose, and galactose.
• Disaccharides are formed from two monosaccharides linked together (e.g., sucrose).
• Polysaccharides are long chains of monosaccharides (e.g., starch, glycogen, cellulose, chitin).
• The chemical formula is (CH₂O)n.

Lipids

• Fats, oils, steroids, phospholipids, waxy substance
• Glycerol + 3 Fatty Acids
• Properties vary according to the number of carbon atoms (long chains of carbon atoms) in hydrocarbon chain.
• Saturated fatty acids have no double bonds and are usually solid at room temperature (e.g., fat).
• Unsaturated fatty acids have one or more double bonds and are typically liquid at room temperature (e.g. oil).

Phospholipids

• Glycerol + 2 Fatty Acids + Phosphate group.
• Hydrophilic heads (polar), hydrophobic tails (non-polar)
• Phospholipids make up the cell membrane.

Steroids

• Cholesterol and other examples
• Four fused carbon rings.
• Crucial structural components in the cell membrane and also precursors to various hormones.

Proteins

• Polymers of amino acids.
• 20 different types of amino acids.
• Four levels of structure: primary, secondary, tertiary, and quaternary structure
• Primary structure: Sequence of amino acids.
• Secondary structure: Folding into β-sheets or α-helices.
• Tertiary structure: Three-dimensional shape.
• Quaternary structure: Multiple polypeptide chains.
• Crucial structural and functional components in the cell.
• Enzymes are globular proteins.

Water

• Properties: Cohesion, adhesion, high specific heat, high latent heat of vaporization, and a solvent, density, and freezing point.
• Importance in biological systems: Transportation, maintaining cell structures, reaction rates, and the interactions of biologically relevant molecules.

Enzyme Regulation

• Factors affecting enzyme activity: Temperature (denaturation), pH, substrate concentration, enzyme concentration, inhibitors.
• Enzyme inhibitors: Competitive inhibitors: Bind to the active site preventing substrate binding. Noncompetitive inhibitors: Bind to a different site that changes the enzyme shape.
• Cell Regulation: The cell controls reactions with these specific components.

Cytosis

• Active process, requiring ATP.
• Endocytosis: Taking substances into the cell (Pinocytosis: takes in fluids/Phagocytosis: engulfing solid particles).
• Exocytosis: Releasing substances from the cell, such as a secretory product.

This quiz covers the fundamental concepts of microscopes, including magnification and resolution. You will learn about the differences between light and electron microscopes, their respective capabilities, and types. Test your knowledge on how these tools are used in observing tiny structures.