Cell Structure and Size Quiz

Chapter 6: A Tour of the Cell

• All organisms are made of cells, which are the simplest collection of matter that can be alive.
• Cells are related by descent from earlier cells.
• Cells can differ, but they share common features.

Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells

• Cells are usually too small to be seen by the naked eye.

Microscopy

• Microscopes are used to visualize cells.
• In a light microscope (LM), visible light passes through a specimen and then through glass lenses.
• Lenses refract (bend) the light so that the image is magnified.
• Three key parameters of microscopy are:
  • Magnification: the ratio of an object's image size to its real size.
  • Resolution: the clarity of the image. It is the minimum distance of two distinguishable points.
  • Contrast: visible differences in brightness between parts of the sample.
• Light microscopes can effectively magnify to about 1,000 times the size of the actual specimen.
• Techniques enhance contrast and enable cell components to be stained or labelled.
• The resolution of standard light microscopy is too low to study organelles in eukaryotic cells.

Electron Microscopy

• Two basic types of electron microscopes (EMs) study subcellular structures:
  • Scanning electron microscopes (SEMs): focus a beam of electrons onto the surface of a specimen, producing 3-D images.
  • Transmission electron microscopes (TEMs): focus a beam of electrons through a specimen. They are used to study the internal structure of cells.

Recent Advances in Light Microscopy

• Labeling individual cells with fluorescent markers improves detail.
• Confocal and deconvolution microscopy provide sharper 3D images of tissues and cells.
• New techniques for labelling cells improve resolution.
• Super-resolution microscopy distinguishes structures as small as 10-20nm across.

Cell Fractionation

• Cell fractionation takes cells apart and separates the major organelles from one another.
• Centrifuges fractionate cells into their component parts.
• Cell fractionation helps scientists determine the functions of organelles.
• Biochemistry and cytology help correlate cell function with structure.

Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions

• The basic structural and functional unit of every organism is one of two types: prokaryotic or eukaryotic.
• Only bacteria and archaea consist of prokaryotic cells.
• Protists, fungi, animals, and plants consist of eukaryotic cells.

Comparing Prokaryotic and Eukaryotic Cells

• Basic features of all cells include: a plasma membrane, cytosol, chromosomes, and ribosomes.

• Prokaryotic cells are characterized by:

  • No nucleus
  • DNA in an unbound region called the nucleoid
  • No membrane-bound organelles
  • Cytoplasm bound by the plasma membrane.

• Eukaryotic cells are characterized by:

  • DNA in a nucleus that is bounded by a double membrane
  • Membrane-bound organelles
  • Cytoplasm in the region between the plasma membrane and nucleus.

• Eukaryotic cells are generally larger than prokaryotic cells.

The Nucleus: Information Central

• The nucleus contains most of the cell's genes and is usually the most conspicuous organelle.
• The nuclear envelope encloses the nucleus, separating it from the cytoplasm.
• The nuclear envelope is a double membrane; each membrane consists of a lipid bilayer.
• Pores regulate the entry and exit of molecules from the nucleus.
• The nuclear lamina maintains the shape of the nucleus.
• In the nucleus, DNA is organized into discrete units called chromosomes.
• Each chromosome contains one DNA molecule associated with proteins, called chromatin.
• Chromatin condenses to form discrete chromosomes as a cell divides.
• The nucleolus is the site of rRNA synthesis, located within the nucleus.

Ribosomes: Protein Factories

• Ribosomes are complexes made of ribosomal RNA and protein.
• Ribosomes carry out protein synthesis in two locations:
  • In the cytosol (free ribosomes)
  • On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)

Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell

• The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane.
• These components are either continuous or connected via transfer by vesicles.

The Endoplasmic Reticulum: Biosynthetic Factory

• The endoplasmic reticulum accounts for more than half of the total membrane in many eukaryotic cells.
• The ER membrane is continuous with the nuclear envelope.
• Two regions of ER exist:
  • Smooth ER, which lacks ribosomes.
  • Rough ER, whose surface is studded with ribosomes.

Functions of Smooth ER

• Synthesizes lipids
• Metabolizes carbohydrates.
• Detoxifies drugs and poisons.
• Stores calcium ions.

Functions of Rough ER

• Has bound ribosomes, which secrete glycoproteins (proteins bonded to carbohydrates).
• Distributes transport vesicles, secretory proteins.
• Is a membrane factory for the cell.

The Golgi Apparatus: Shipping and Receiving Center

• The Golgi apparatus consists of flattened membranous sacs called cisternae.
• Modifies products of the ER
• Manufactures certain macromolecules
• Sorts and packages materials into transport vesicles.

Lysosomes: Digestive Compartments

• A lysosome is a membranous sac of hydrolytic enzymes.
• Lysosomal enzymes work best in the acidic environment inside the lysosome.
• Hydrolytic enzymes and lysosomal membranes are made by the rough ER and transferred to the Golgi for further processing.
• Lysosomes use enzymes to recycle the cell's own organelles and macromolecules in autophagy.

Vacuoles: Diverse Maintenance Compartments

• Vacuoles are large vesicles derived from the ER and Golgi.
• Vacuoles perform a variety of functions in different kinds of cells:
  • Food vacuoles are formed by phagocytosis
  • Contractile vacuoles, found in freshwater protists, pump out excess water.
  • Central vacuoles, found in many mature plant cells, hold organic compounds and water.

Concept 6.5: Mitochondria and chloroplasts change energy from one form to another

• Mitochondria are the sites of cellular respiration and use oxygen.
• Chloroplasts are found in plants and algae and are the sites of photosynthesis.
• Peroxisomes are oxidative organelles.

Mitochondria: Chemical Energy Conversion

• Mitochondria are found in nearly all eukaryotic cells.
• They have a smooth outer membrane and an inner membrane folded into cristae.
• The inner membrane creates two compartments: intermembrane space and mitochondrial matrix.
• Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix.
• Cristae increase the surface area for enzymes synthesizing ATP.

Test your knowledge on cellular structures and their sizes with this quiz. Questions cover topics such as microscopy techniques, ribosome measurements, and mitochondrial components. Perfect for biology students studying cellular biology or related fields.