Cell Biology Quiz: Eukaryotic Cells

Biology 1 - Cells, Molecular Biology, and Genetics (Biol 1000)

• Course offered by Dr. Michael Cardinal-Aucoin in Winter 2025 at York University
• Course focuses on cells, molecular biology, and genetics.

The Eukaryotic Cell

• Eukaryotic cells have internal membranes forming compartments called organelles.
• Each organelle is specialized for a particular task.
• Plant, animal, and protist cells generally share the same organelles.
• Organelles include: nucleus, endomembrane system (endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles), mitochondria, chloroplasts, peroxisomes, and cytoskeleton.

Eukaryotes

• Eukaryotic cells have internal membranes that divide the cell into compartments (organelles) to help perform specific functions.
• Plant, animal and protist cells have similar organelles.

Nucleus

• Stores the DNA.
• The nuclear envelope encloses the nucleus with an inner and outer membrane.
• Nuclear pores in the envelope allow molecules to move in and out of the nucleus.
• The nucleolus is a dense region where rRNA (ribosomal RNA) is synthesized. Ribosomes are assembled here.
• DNA in the nucleus is organized into chromatin, which is DNA associated with proteins (like histones).
• During cell divison, chromatin condenses to form chromosomes (distinct units).

Nuclear Pore

• Controls traffic into and out of the nucleus.
• Multi-protein structure.
• Allows molecules like proteins and building blocks of DNA and RNA to enter or exit.

Ribosomes

• Present in both prokaryotes and eukaryotes.
• In eukaryotes, ribosomes are assembled in the nucleolus.
• Made up of proteins and rRNA.
• Some are free in the cytosol, others are bound to the endoplasmic reticulum membrane.
• Sites of protein synthesis; amino acids are assembled into proteins.

Protein Synthesis

• Proteins synthesized by free and bound ribosomes have different fates.
• Free ribosomes make proteins for use within the cytosol.
• Bound ribosomes make proteins that are destined for secretion or for use within organelles like the endoplasmic reticulum or Golgi.
• Proteins have signal sequences that direct them to the correct location.

Endomembrane System

• Composed of internal membranes that communicate via direct connections or via vesicles.
• Key components include nuclear envelope, endoplasmic reticulum (rough ER and smooth ER), Golgi apparatus, lysosomes, vacuoles, and plasma membrane.

Endoplasmic Reticulum (ER)

• A network of membranes, continuous with the nuclear envelope.
• Accounts for more than half the total membrane in eukaryotic cells.
• Two distinct regions differ in structure and function: rough ER and smooth ER.
  • Rough ER: studded with ribosomes; synthesizes proteins destined for secretion or for use within other organelles; synthesizes membrane components.
  • Smooth ER: lacks ribosomes; synthesizes lipids, metabolizes carbohydrates, detoxes drugs and poisons; stores calcium ions.
• The ER is involved in protein synthesis, lipid synthesis, and calcium storage.

Golgi Apparatus

• Looks like flattened membrane sacs (cisternae) and vesicles surrounding the cisternae.
• Not physically connected to the ER.
• Modifies, sorts, and packages proteins and lipids.
• Acts as a sorting station for proteins and lipids.

Lysosomes

• Specialized vesicles derived from the Golgi body.
• Filled with hydrolytic enzymes that break down damaged or unneeded macromolecules.
• Keeps pH around 5; optimal for enzymes to function.
• Important to cellular digestion, and recycling.

Vacuoles

• Large vesicles derived from the ER and Golgi.
• Perform diverse functions, including storing nutrients, acting as lysosomes in some plants, and maintaining turgor pressure in plant cells.

Mitochondria

• Sites of cellular respiration.
• Enclosed by two membranes; outer is smooth, inner is folded into cristae.
• Inner membrane divides the mitochondrion into intermembrane space and mitochondrial matrix, where enzymes, mitochondrial DNA and ribosomes are found.
• Critical for producing ATP, the cell's energy currency.

Chloroplasts

• Capture sunlight energy to produce sugars via photosynthesis.
• In plants and some other eukaryotes.
• Enclosed by a double membrane, contains thylakoid membrane with grana and stroma space.

Origins of Mitochondria and Chloroplasts (Endosymbiosis Theory)

• Mitochondria and chloroplasts evolved from free-living prokaryotic organisms.
• These organisms were engulfed by a larger cell and developed a symbiotic relationship, becoming organelles inside of the cell.
• Evidence supports this theory, including their double membranes, their having free ribosomes and circular DNA.

Peroxisomes

• Specialized metabolic compartments bounded by a single membrane. Perform reactions to break down fatty acids and reduce reactive oxygen species.
• Contain enzymes (catalase) to break down hydrogen peroxide (H2O2), which is a byproduct of these processes.

Other Topics

• Specific pages were given to the endomembrane system and its component parts, like insulin and secretion, in more detail.
• The functions and structures of plant and animal cells were outlined in diagram/image pages.