Cell Biology Quiz

Introduction to Cells

• All living things are made of cells.
• All living things begin as a single cell.
• Early cells resulting from a single cell are similar.
• Differentiation changes cell structure and function.
• Specializations allow transport of nutrients (like food and water).
• Other specializations allow cells to secrete fluids.
• Cells have varying life spans.
• Cells share common features.

Cells: History

• 1665: Robert Hooke discovered cells.
• 1670s: Marcello Malpighi and Nehemiah Grew observed and described single-celled organisms, calling them "animacules".
• 1809: Jean-Baptiste de Lamarck proposed that organisms needed cellular components to live.
• 1824: René Dutrochet stated that all plant and animal tissues are made of cells.
• 1831: Robert Brown discovered the nucleus.
• 1838: Schleiden and Schwann formulated the Cell Theory, stating all living things are composed of cells and cells form the structural base of organization.
• 1858: Rudolf Virchow proposed cells only arise from pre-existing cells.
• 1862: Louis Pasteur experimentally disproved spontaneous generation and showed fermentation involved yeast activity.
• 1897: Eduard Buchner discovered that extracts from cells contain the enzymes necessary for fermentation.

Modern Microscopes: Light Microscopes

• Increase magnification using glass or calcium fluoride crystals.
• Include compound and dissecting (stereomicroscopes).

Compound Microscopes

• Light passes through thinly sliced material.
• Can distinguish organelles 2 micrometers or larger in diameter.
• Magnification up to 1500x.

Dissecting Microscopes

• Also known as stereomicroscopes allowing 3D views of opaque objects.
• Magnification up to 30x.

Electron Microscopes

• Use beams of electrons to visualize.
• Includes transmission and scanning electron microscopes.

Transmission Electron Microscopes

• 200,000x magnification but material needs to be extremely thin.

Scanning Electron Microscope

• 10,000x magnification, allowing observation of surface details on thick objects.

Scanning Tunneling Microscopes

• Uses a probe that tunnels electrons to scan samples.
• Creates surface maps.
• Achieves atomic level resolution. (first picture of DNA segment showing its helical structure)

Eukaryotic versus Prokaryotic Cells

• Prokaryotic cells lack a nucleus (e.g., bacteria).
• Eukaryotic cells contain a nucleus (e.g., unicellular eukaryotes, fungi, plants, animals).
• Eukaryotic cells have membrane-bound organelles.

Cell Structure and Communication

• Cell wall surrounds the protoplasm (all living parts of a cell).
• Protoplasm is bound by the plasma membrane.
• Cytoplasm is the space between the plasma membrane and nucleus containing cytosol.
• Organelles are persistent structures within the cytoplasm.
• Organelles are usually, but not always, membrane-bound with specialized functions.

Anatomy of a Young Plant Cell

• Diagrams showing labeled components.

Cell Size

• Cells of higher plants range from 10 to 100 micrometers in length.
• Smaller cells have a higher surface-to-volume ratio, enabling efficient cell communication.

Cell Wall

• Main component is cellulose (long glucose chains).
• Other components include hemicellulose, pectin, and glycoproteins.
• Middle lamella is the first formed in new cell walls between adjacent cells.

Primary Cell Wall

• Flexible, laid down on either side of the middle lamella.
• Consists of a network of cellulose, hemicellulose, pectin, and glycoproteins.

Secondary Walls

• Produced inside the primary walls, by lignin inclusion.
• Cellulose microfibrils embedded in lignin for strength.

Communication Between Cells

• Fluids and dissolved substances pass through the primary walls via tiny openings called plasmodesmata.
• Plasmodesmata are cytoplasmic strands extending between cells.

Plasma Membrane

• Semipermeable outer boundary.
• Regulates substance movement in and out of the cell.
• Composed of phospholipid bilayer and proteins.
• Fluid mosaic structure.

Nucleus

• Control center of the cell.
• Contains DNA.
• Sends coded messages.
• Bound by a double membrane (nuclear envelope) with complex pores.
• Pores regulate molecules passing between nucleus and cytoplasm.

Components of the Nucleus

• Nucleoplasm: fluid medium for nuclear processes.
• Nucleolus: composed mainly of RNA.
• Chromatin strands: composed of DNA and proteins, coiling to form chromosomes.

Endoplasmic Reticulum

• Network of flattened sacs and tubes within cytoplasm.
• Facilitates cell communication and materials channeling.
• Synthesizes membranes for other organelles and modifies proteins (rough ER has ribosomes, smooth ER does not).

Ribosomes

• Consist of two subunits (RNA and proteins).
• Link amino acids to form complex proteins.
• Assembled in the nucleolus.
• Can be on the rough ER, in the cytoplasm or chloroplasts, or in other organelles.

Dictyosomes

• Stacks of flattened disks or vesicles (Golgi bodies in animal cells).
• Modify proteins with attached carbs, assemble polysaccharides, and package them into vesicles.

Function of Dictyosomes

• Modify carbohydrates attached to ER-synthesized proteins.
• Assemble and collect polysaccharides in small vesicles.
• Vesicles pinch off from dictyosome margins, migrate to membrane, and release their contents outside the cell.

Plastids

• Chloroplasts are the most conspicuous.
• Bound by two membranes, containing grana, thylakoids (site of chlorophyll and photosynthesis).
• Stroma (matrix of enzymes for photosynthesis)
• Contains circular DNA encoding photosynthesis proteins.
• Other plastids: chromoplasts (synthesize and store carotenoids), leucoplasts (colorless, store starches or oils).

Mitochondria

• Release energy from cellular respiration.
• Bound by two membranes (inner membrane forms cristae, increasing surface area for enzymes in the matrix).
• Matrix contains DNA and RNA.

Microbodies

• Small, spherical bodies containing specialized enzymes (e.g. peroxisomes in photorespiration, and glyoxysomes for fat to carbohydrate conversion).
• Bound by a single membrane.

Vacuoles

• Large fluid-filled spaces in mature cells.
• Bound by vacuolar membranes (tonoplast).
• Filled with cell sap (watery fluid containing salts, sugars, organic acids, proteins, and pigments like anthocyanins).
• Function in maintaining cell pressure and pH, storing metabolites and waste products.

The Cytoskeleton

• Network of microtubules and microfilaments.
• Involved in cell movement, architecture.
• Microtubules control cellulose addition to the cell wall, and are in flagella/cilia, spindle fibers/phragmoplast.
• Microfilaments are involved in cytoplasmic streaming.

Cellular Reproduction

• Cell cycle: a series of events when cells divide (interphase and mitosis).
• Interphase (up to 90% of cycle):
• G1: cell increases in size.
• S: DNA replication occurs.
• G2: organelles (including mitochondria) divide, and microtubules are created.

Mitosis

• Process of cellular division, producing two identical daughter cells.
• Occurs in meristems.
• Stages: prophase, metaphase, anaphase, telophase.

Chromosomes in Prophase

• Condensation of chromosomes: coiling makes them shorter and thicker.
• Structure: chromosomes made of two identical sister chromatids held together by a centromere.
• Kinetochore (protein complex) on the outer surface of each centromere.

Prophase

• Spindle fibers attach to kinetochores and anchor to opposite cell poles.
• Nuclear envelope and nucleolus disintegrate.

Metaphase

• Chromosomes line up at the cell's equator.
• Spindle fibers (collectively called the spindle) align chromosomes.
• Centromeres hold sister chromatids together.

Anaphase

• Spindle fibers shorten, pulling chromatids to opposite poles.
• Separation makes daughter chromosomes.

Telophase

• Chromosomes reach opposite poles.
• Nuclear envelope reforms around each group of chromosomes.
• Nucleoli reappear.
• Spindle fibers disappear.

Cell Plate Formation

• Phragmoplast (a complex of microtubules and ER) forms between new nuclei.
• Vesicles from dictyosomes move along microtubules and fuse to form the cell plate.
• Cell plate extends outward towards mother cell walls.

Higher Plant Cells Versus Animal Cells

• Plant cells have cell walls, a cell plate that forms during division and plasmodesmata, and chloroplasts/vacuoles.
• Animal cells lack cell walls, have plasma membranes, divide by pinching in two, do not have cell plates or plasmodesmata and have centrioles and no chloroplasts/vacuoles.