Cell Theory and Structure Quiz

Cell Theory

• Cells are the basic units of organization and function in all organisms.
• All cells come from other cells.
• All living cells have a common origin, owing to basic similarities in their structures and molecules.

Cell Size

• Most cell components are measured in nanometers (nm).
• Everything entering or leaving a cell passes through the plasma membrane.
• The ratio of surface area to volume is critical for cell size.
• Some variations in cell shape increase the surface area to volume ratio (e.g., microvilli).

Cell Movement and Structure

• Amoebas and white blood cells change shape as they move.
• Sperm cells have long, whip-like tails (flagella) for locomotion.
• Nerve cells have long, thin extensions to transmit messages over great distances.
• Rectangular epithelial cells stack to form sheet-like tissues.

Cell Study Methods

• Robert Hooke first described cells in 1665 using a microscope he made.
• Antonie van Leeuwenhoek discovered bacteria, protists, blood cells, and sperm cells using small lenses.
• Microscopes in the late 19th century allowed biologists to study cells in more detail.

Light Microscopes

• Light microscopes use a tube with glass lenses to magnify images.
• Magnification is the ratio of the size of the magnified image to the actual size of the object.
• Light microscopes have magnification up to a maximum of 2000x, dependent on lens quality and wavelength.
• Resolving power refers to the smallest distance between two points that can be distinguished as separate.
• Different types of light microscopes, with different optical systems, help study living cells: bright-field, dark-field, phase contrast, differential-interference-contrast, fluorescence, and confocal.

Electron Microscopes

• Electron microscopes study the ultrastructure of cells.
• Some electron microscopes have resolving powers less than 1 nm.
• An electron beam, focused by electromagnets, is used to create images.
• Two types: transmission electron microscope and scanning electron microscope.

Cell Fractionation

• Cell fractionation separates cell parts to study them in detail.
• Cells are broken apart and spun in a centrifuge, separating the extract into a pellet and a supernatant.
• The supernatant can be centrifuged multiple times (differential centrifugation) to separate further components.
• Pellets of separated parts can be resuspended or further purified by density gradient centrifugation.

Prokaryotic Cells

• Bacteria and Archaea are prokaryotic cells.
• Prokaryotic cells lack membrane-bound organelles.
• Prokaryotic DNA is located in a nucleoid region.
• Most have cell walls outside the plasma membrane.
• Many have prokaryotic flagella for movement.
• The interior contains ribosomes and storage granules.

Eukaryotic Cells

• Eukaryotic cells have membrane-bound organelles.
• DNA is located in the nucleus.
• Cytoplasm is the area outside the nucleus.
• The cytoskeleton provides structure and facilitates movement.
• Some organelles (e.g., ribosomes) are present in all types of cells, while others are specific to particular cell types.

Organelles (membranous)

• Endoplasmic reticulum (ER): A network of membranes; smooth ER synthesizes lipids and breaks down toxins; rough ER synthesizes proteins.
• Golgi complex: Processes, sorts, and modifies proteins.
• Lysosomes: Small sacs of digestive enzymes that break down wastes, bacteria, and damaged organelles.
• Vacuoles: Large, membrane-enclosed sacs that store water, nutrients, or wastes. Plant vacuoles play a significant role in growth and development.
• Peroxisomes: Contain enzymes that transfer hydrogen from other compounds to oxygen, break down fatty acids, produce cholesterol and phospholipids, and help detoxify some substances.

Organelles (energy converting)

• Mitochondria: Convert chemical energy in some foods to ATP through aerobic respiration. Have a double membrane with folds (cristae) that increase surface area for reactions. Mitochondrial DNA contributes to genetic diseases.
• Chloroplasts: Convert light energy to chemical energy through photosynthesis, enclosed in membranes. Important in plants and some algae. Store starch in cells of plants.

Cytoskeleton

• The cytoskeleton gives eukaryotic cells their shape and allows for movement.
• It's a network of fibers: microtubules (hollow rods), microfilaments (flexible, solid fibers), and intermediate filaments (tough, flexible fibers).
• Microtubules are involved in cell division, intracellular transport, and form cilia/flagella.
• Microfilaments generate movement and are important in muscle cells.
• Intermediate filaments are important for cell shape.

Cell Coverings

• Many animal cells secrete an extracellular matrix composed of carbohydrates and fibrous proteins.
• Collagen is a main fibrous protein in the ECM, organized by fibronectins.
• Integrins in the cell plasma membrane attach to fibronectins.
• Many cells have a glycocalyx (surface coating), aiding cellular recognition and interactions.
• Bacterial, archaeal, fungal, and plant cells are often enclosed by cell walls; animal cells do not usually have a cell wall. Plant cell walls contain cellulose.

Nucleus

• The nucleus is the control center of the cell.
• It has a double membrane (nuclear envelope).
• Pores regulate material movement.
• The nuclear lamina helps organize nuclear contents and regulates the cell cycle.
• Chromatin is DNA and associated proteins.
• The nucleolus is a region within the nucleus where ribosomal RNA (rRNA) is produced, part of ribosome assembly.
• DNA replication occurs during cell division, copying DNA and passing it on to daughter cells.