Cell Structure and Function Quiz

Cell Structure and Function

• Cells are the basic units of structure and function in all living things.
• Robert Hooke observed and named cells in 1665.
• The cell theory was proposed by Schleiden and Schwann in 1839.
  • All living things are made up of cells.
  • Cells are the smallest working unit of living things.
  • All cells come from pre-existing cells through cell division.
• Some organisms are unicellular (consist of 1 cell), while others are multicellular (aggregates of specialized cells).

Cell Theory

• All living things are composed of cells.
• Cells are the basic unit of all organisms.
• All cells arise from pre-existing cells.

How We Study Cells

• Microscopes are used to visualize cells.
• Cell fractionation is used to separate organelles for study.
• Most cells are between 1-100 µm in diameter.
• Light microscopes can be used to visualize most cells.
• Electron microscopes can provide higher resolution of cellular structures.

Light Microscope (LM)

• Visible light passes through a specimen and lenses to magnify the image.
• Magnification and resolving power are key features.
• Magnification of LM is ~1,000x
• Resolution of LM is about 2 microns.

Electron Microscope (EM)

• A beam of electrons is used to visualize specimens.
• Theoretically, resolution can reach 0.1 nanometers.
• Practical limit is closer to 2 nanometers.
• Two types: Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM).

Transmission Electron Microscope (TEM)

• Used to study internal ultrastructure of cells.
• Thin sections of preserved cells are stained with heavy metals to enhance the image.
• 2-dimensional micrographs.

Scanning Electron Microscope (SEM)

• Used to study the external surface of cells.
• The sample surface is covered with a thin gold film.
• High resolution images of the surface.
• 3-dimensional images.

Cell Fractionation

• Used to separate cell components (organelles) for study.
• Disrupted cells are centrifuged at different speeds and durations to fractionate components of various sizes.
• Different pellets are collected at each speed to isolate specific components.

The Nucleus and Its Envelope

• The nucleus contains most of the genes in a eukaryotic cell.
• Some genes are located in mitochondria and chloroplasts.
• The nucleus averages about 5 microns in diameter.
• The nucleus is enclosed by a nuclear envelope, a double membrane.
• Nuclear pores allow large molecules to pass through.
• The nuclear side of the envelope is lined by the nuclear lamina, a network of intermediate filaments that maintain the shape of the nucleus.

Level of Chromatin Packing

• In the nucleus, DNA and associated proteins are organized into chromatin.
• In a normal cell, chromatin appears as a diffuse mass.
• During cell division, chromatin coils up to form chromosomes.

Nucleolus

• Region in the nucleus, containing rRNA and proteins to form ribosomal subunits.
• rRNA synthesis happens here and subunits leave to combine in cytoplasm to form ribosomes.

Ribosomes

• Particles composed of proteins and rRNA (ribosomal RNA).
• Function in protein synthesis.
• Prokaryotic ribosomes = 70S; Eukaryotic ribosomes = 80S.
• Free ribosomes synthesize proteins that function in the cytosol.
• Bound ribosomes synthesize proteins that are destined for membranes or secretion.

The Endomembrane System

• A group of membranes in eukaryotic cells interconnected through direct physical contact or transfer vesicles.
  • Examples include the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and plasma membrane.

Endoplasmic Reticulum (ER)

• A network of membranes throughout the cytoplasm.
• Cisternae = fluid-filled spaces within the ER.
• Interconnected, continuous with the nuclear envelope.
  • rough ER has ribosomes; smooth ER does not.

Smooth ER

• Lipid synthesis (oils, phospholipids, steroids).
• Glycogen metabolism in liver cells.
• Detoxification of drugs and poisons.
• Calcium storage for muscle contraction

Rough ER

• Proteins synthesis (secretory, membrane, or organelle proteins)
• Ribosomes on the rough ER attach newly formed protein to the ER.
• The protein is threaded into the cisternal space, folds into its native conformation, and then glycosylation attaches oligosaccharides for targeting.
• Proteins are wrapped in transport vesicles that bud from the ER.

Golgi Apparatus

• Flattened membranous sacs (cisternae)
• Unlike ER cisternae, Golgi cisternae are not physically connected.
• Sorting, modifying, and packaging proteins (and lipids) for secretion or destined for another location within cell.
  • Proteins and lipids are processed (glycosylation and phosphorylation).
  • Some polysaccharides are synthesized in Golgi.

Lysosomes

• Contain hydrolytic enzymes to digest macromolecules.
• Lysosomal enzymes & membranes are made by rough ER and processed through Golgi.
• These are acidic and protect the cell from leakage of enzymes in the event their compartment breaks.
• Involved in intracellular digestion (phagocytosis & autophagy).

Vacuoles

• Membrane-bound sacs.
• Diverse functions: food vacuoles, contractile vacuoles (in protists), and central vacuoles (in plants).

Mitochondria

• Sites of cellular respiration (produce ATP from sugar & other organic fuel).
• Enclosed by double membrane: outer, inner (folded into cristae).
• Matrix contains circular DNA, ribosomes, and enzymes for metabolic pathways.
• Intermembrane space hosts components of the electron transport chain.

Chloroplast

• Sites of photosynthesis
• Enclosed by double membrane; inner membrane forms thylakoids stacked into grana.
• Stroma = fluid-filled area surrounding the thylakoids.
  • Contains DNA, ribosomes, enzymes for carbohydrate synthesis.

Microbodies

• Single-membrane-bound cytoplasmic particles.
• Contain enzymes for various metabolic reactions.

Peroxisomes

• Contain enzymes that catalyze reactions involving hydrogen peroxide (H2O2).
• Break down fatty acids.
• Contain the enzyme catalase to convert H2O2 to water.

Cytoskeleton

• Network of fibers in the cytoplasm that gives a cell its shape and structural support, and organizes cell components and for movement.

Microtubules

• Hollow tubes composed of tubulin dimers.
• Involved in cell shape, organization, intracellular transport of organelles.
  • Cell division (spindle fibers), cilia, and flagella

Centrosomes and Centrioles

• Centrosomes (microtubule-organizing centers) are near the nucleus.
• Centrioles are contained in animal cells and composed of 9 sets of triplets of microtubules in a ring.
  • They assist in organizing microtubule assembly and cell division.

Cilia and Flagella

• Hair-like structures (cilia) or whip-like structures (flagella) involved in locomotion or moving fluids.
• Made of microtubules arranged in a "9+2" pattern.
• Anchored in the cell by basal bodies (identical to centrioles).

Microfilaments (or Actin Filaments)

• Twisted double chain of actin subunits.
• Important in cell shape (bearing tension), and cell movement (like crawling, cytoplasmic streaming, muscle contraction).

Intermediate Filaments

• Rope-like fibers.
  • Involved in cell shape (supporting & resisting), anchors structures.
  • Examples are keratins (in skin, hair), lamins (nuclear lamina), neurofilaments, and vimentins.

Test your knowledge on cell structure and the fundamental principles of cell theory. This quiz covers key concepts such as unicellular and multicellular organisms, the history of cell discovery, and methods used to study cells. Dive into the fascinating world of microscopic life!