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.