Cell Structures and Microscopes

Assignments and Practice Quizzes

• Assignment due next week (26th), includes this week's and next week's lessons (Wednesday).
• Practice quizzes available, start with the chemistry unit.
  • Covers cell structures, microscopes, and cell transport (Wednesday).
• Assignment may require drawing/labeling; can be done on paper and submitted as a picture.
• Alternatively, use Word to create a key for labeling.

Review Questions: Biomolecules

• Proteins:
  • What is the difference between protein structures and their functions?
  • How does the R group make proteins different (the R group is the unique part of each protein)?
• Organic Molecules:
  • What elements are present in an organic molecule?
  • What is the difference between organic and inorganic molecules?
• Enzymes:
  • What is the role of enzymes in the body?
• Lipids:
  • What are the differences between unsaturated and saturated fatty acids?
    • Unsaturated fatty acids are liquid at room temperature.
    • Saturated fatty acids are solid at room temperature due to double bonds between carbons.

Cells and Organization

• Biological level of organization (from the first presentation):
  • Atoms combine to form molecules.
  • Molecules combine to form cells.
  • Organelles are the smallest parts within a cell (analogous to organs in a body).
• Topics to be covered:
  • Differences between eukaryotic and prokaryotic cells.
  • Cytoskeletons.

Cell Theory and Microscopes

• Before microscopes, scientists classified organisms based on what they could see with the naked eye.
• Cell Theory (developed starting in 1830s by Schleiden, Schwann, and others):
  • All organisms are composed of cells.
  • Cells come from pre-existing cells (multiply asexually, making identical copies).
  • Cells are the basic unit and structure of all organisms (stated by a German physician).
• Microscopes enabled the discovery of cells.
• Comparison of cell sizes:
  • Atoms are too small to be seen with lab microscopes.
  • Viruses are also generally too small to be seen with standard microscopes.
  • Chloroplasts can be seen in some labs.
  • Cells are visible with light microscopes.
  • Frog eggs are visible to the human eye.
  • Cell sizes range from 1 millimeter to 1 micrometer in diameter.
• Smaller cells are more efficient due to a large surface area to volume ratio, facilitating the transport of molecules (e.g., $CO<em>2$, $O</em>2$) in and out.
• The nucleus is the control center; shorter distance to the cell membrane is beneficial.

Surface Area to Volume Ratio

• Important for cell efficiency.
• The surface area is the outside of the cell; the volume is the inside.
• As a cell grows larger, both volume and surface area enlarge.
• Example: Comparing centimeter cubes of different sizes.
  • A 4 cm cube has a lower surface area to volume ratio compared to a 1 cm cube.
  • A 1 cm cube is more beneficial to the cell (ratio of 6:1).

Light Microscopes

• Also known as compound light microscopes.
• Use lenses to focus light through the specimen.
• Magnification:
  • Multiply the eyepiece magnification by the lens magnification.
  • Example: If the eyepiece is 10x and the lens is 40x, the total magnification is 400x.
• Components:
  • Eyepiece (to look through).
  • Lenses (various magnifications, e.g., 10x, 40x, 100x).
  • Stage (where the specimen is placed).
  • Stage adjustment knob.
  • Clips to hold the specimen slide.
  • Light source (adjustable).
• Procedure:
  • Lower the stage before use.
  • Clip the specimen slide onto the stage.
  • Start with the lowest power lens (e.g., 4x).
  • Adjust the light.
  • Then switch to higher power lenses.

Electron Microscopes

• Electrons are passed through the specimen and focused using magnetic lenses.
• Images are displayed on a TV screen.
• Magnification can be 500,000 times better than the human eye.
• Scanning Electron Microscopes:
  • Specimen is coated with a thin layer of metal.
  • Electron beam scans the outside, creating a 3D image.
  • The image is then photographed.

Microscopy Advancements

• Early microscopes were simple magnifying glasses.
• The invention of electricity enabled the use of light in microscopes, improving visibility.
• Comparison of images:
  • Electron microscopes provide more details than light microscopes.
  • Transmission electron microscopes show more internal details.
  • Scanning electron microscopes provide 3D surface images.
• Observing cells:
  • Example: Cells from the inside of the mouth can be viewed under different magnifications and contrasts.

Prokaryotic Cells

• Primitive cells.
• Lack membrane-bound organelles, including a nucleus.
• Examples: Bacteria and Archaea.
• Structures:
  • Plasma membrane.
  • Cell wall.
  • Capsule (for protection).
  • Flagella (for movement).
  • Various shapes (e.g., bacillus).
• Cell walls are made of polysaccharides (many sugars/carbohydrates).
• Plasma membrane structure is similar to that of eukaryotic cells.
• Nucleoid: Region where DNA is located (no nucleus).
• Ribosomes: Present in all cells.
• Cytoplasm: Gel-like structure inside the cell.
• Fimbriae: Structures used to pass DNA from cell to cell.

Eukaryotic Cells

• Have a nucleus and membrane-bound organelles.
• Two types: Plant and animal cells.
• Endosymbiotic theory: Explains the origin of eukaryotic cells (theory may evolve with new discoveries).

Animal Cells

• Lack a rigid cell wall (cell membrane only).
• The cell membrane appears to pinch off, dividing the cell.
• Do have ribosomes.

Plant Cells

• Have a distinct, almost geometrical shape due to the cell wall.
• Structures:
  • Cell membrane and cell wall.
  • Ribosomes.
  • Large central vacuole.
  • Chloroplasts (only in plant cells).

Cell Differentiation and Specialization

• Cells multiply and become specialized.
• The nucleus sends signals for cell specialization.
• Examples: Liver cells, nerve cells, etc.
• Malfunctions in cells can lead to severe disorders.
• Example: Cytoskeleton abnormalities can cause deformities.
• Vesicles move around using the cytoskeleton, which provides structural support and transport pathways.
• Cell walls are present in plant cells, fungi, and many protists, made of polysaccharides.

Nucleus

• Control center of the cell.
• Nuclear envelope surrounds the nucleus.
• Nuclear pores allow RNA to exit but not DNA.
• Chromatin (made of chromosomes) contains genetic information.
• Chromosomes are packed DNA wrapped around proteins and are visible during cell division.

Ribosomes

• Present in all cells.
• Involved in protein synthesis, transcription, and translation.

Endomembrane System

• Intracellular membranes that restrict some enzymes.
• Components:
  • Nuclear envelope.
  • Endoplasmic reticulum (ER).
  • Golgi apparatus.
  • Vesicles

Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes attached, involved in modifying and processing proteins (protein synthesis).
• Smooth ER: No ribosomes, synthesizes lipids, involved in testosterone production in males.
• Liver cells are abundant in smooth ER, detoxifying drugs (e.g., Advil, Tylenol).

Golgi Apparatus

• Modifies proteins and lipids with signal sequences.
• Receives vesicles from the ER containing proteins and lipids.
• Transfers and exports proteins and lipids.
• Vesicles move to the plasma membrane and release contents.
• Located away from the nucleus, unlike the ER.

Lysosomes

• Produced by the Golgi apparatus.
• Contain enzymes.
• Not typically found in plants.
• Dysfunctional lysosomes can cause Tay-Sachs disease (gene therapy is being developed to replace the missing enzyme).

Peroxisomes

• Similar to lysosomes, contain enzymes.
• Catalyze reactions that produce hydrogen peroxide ($H<em>2O</em>2$).
• Break down hydrogen peroxide into water ($H<em>2O$) and oxygen ($O</em>2$) using catalase.
• Lack of peroxisomes leads to toxic levels of hydrogen peroxide.

Vacuoles

• In plants, store water (90% of the plant's volume) and nutrients.

Chloroplasts

• Important in respiration and photosynthesis.
• Absorb light from the sun to produce glucose (carbohydrate) and release oxygen ($O_2$) into the atmosphere.
• Found only in plants, not in animal cells.
• Photosynthesis starts by absorbing light; produces glucose which is a carbohydrate.

Mitochondria

• Cellular respiration occurs, producing ATP (energy molecule).
• These two processes (chloroplasts and mitochondria) work together.
• Chloroplasts: Stacks of thylakoids; the energy from the sun strikes the membrane of the thylakoid and goes through photosystems I and II and the electron transport chain.

Mitochondria Structure

• Double membrane.
• Produce most of the cell's ATP.

Cytoskeleton

• Maintains the shape of the cell.
• Different types of cytoskeletons depending on the organism.
• Various filaments support the nuclear envelope and connect cells via cell junctions.
• Microtubules interact with other molecules to cause the movement of organelles.

Centrioles

• Involved in cell division.
• Cylinders with filaments are released during cell division.

Cilia and Flagella

• Some eukaryotic cells have cilia and flagella.
• Cilia:
  • Filter like structures in the upper respiratory tract.
• Flagella:
  • Found in sperm cells for movement.
• Flagella structure: Little tail forming a lot of microtubules.