Cell Biology Chapter Quiz

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

• Course offered by Dr. Michael Cardinal-Aucoin during Winter 2025 at York University.
• Course code is Biol 1000.

The Eukaryotic Cell

• Eukaryotic cells have internal membranes forming compartments called organelles, specialized for specific functions.
• Plant, animal, and protist cells share most of the same organelles.
• Organelles include:
  • Nucleus
  • Endomembrane system (endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles)
  • Mitochondria
  • Chloroplasts
  • Peroxisomes
  • Cytoskeleton

Eukaryotes

• Eukaryotic cells possess internal membranes dividing the cell into compartments called organelles, each specialised for a specific task.
• Plant, animal, and protist cells have similar organelles.
• Organelles vary in size.

Nucleus

• Nucleus (most prominent organelle) stores the cell's DNA.
• Nuclear envelope: a double membrane boundary of the nucleus
• Nuclear pores: allow molecules to enter/exit the nucleus.
• Nucleolus: a structure within the nucleus where ribosomal RNA (rRNA) is made.
• Chromatin: DNA organized with proteins (e.g., histones).
• Chromosomes: During cell division, chromatin condenses.

Nucleus (continued)

• DNA in a single cell stretches 6.5 kilometers if laid out end-to-end
• DNA is organized into chromatin, a complex of DNA and proteins.
• During cell division, chromatin condenses to form chromosomes.

Nuclear Pore

• Nuclear pores: multi-protein complexes controlling material traffic into and out of the nucleus.
• Molecules like proteins and building blocks of DNA and RNA travel through nuclear pores.

Ribosomes

• Ribosomes are found in both prokaryotes and eukaryotes.
• Eukaryotic ribosomes are manufactured in the nucleolus.
• Ribosomes are complexes of rRNA and proteins, making polypeptides (proteins).
• Ribosomes can be free in the cytosol or attached to the endoplasmic reticulum.

Protein Synthesis

• Free ribosomes synthesize proteins for use inside the cell.
• Ribosomes bound to the rough endoplasmic reticulum synthesize proteins destined for secretion or for insertion into membranes.

How proteins end up where they should

• Proteins destined for certain organelles have signal peptides (signal sequences) to direct them.
• These signal sequences direct the protein to specific organelles.

Proteins destined for nucleus

• Proteins destined for the nucleus contain a nuclear localization signal (NLS).
• This signal helps direct them towards the nucleus.

Endomembrane System

• Contains various interconnected organelles involved in protein and lipid synthesis, modification, sorting, and transport.
• Nuclear envelope, Endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, plasma membrane
• Endomembranes are interconnected but not continuous.

Endomembrane System (continued)

• The endomembrane system communicates through physical connections or via transfer vesicles (small membrane-bound sacs).
• The endomembrane system consists of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles, along with the plasma membrane.

Endoplasmic Reticulum (ER)

• The ER, an extensive network of membranes, is continuous with the nuclear envelope.
• It is a major site for protein and lipid synthesis.
• Two types of ER:
  • Rough ER: studded with ribosomes, processing proteins (e.g., proteins secreted from the cell or proteins to be inserted into membranes).
  • Smooth ER: lacks ribosomes, involved in processes like lipid synthesis, carbohydrate metabolism, etc., detoxification.

Golgi Apparatus

• The Golgi apparatus receives proteins and lipids from the ER, modifies them, sorts them, and packages them into vesicles for delivery to other organelles or secretion.
• It resembles flattened membrane sacs called cisternae, surrounded by vesicles.
• It is a sorting station for proteins.

Lysosomes

• Lysosomes are vesicles containing hydrolytic enzymes, breaking down macromolecules: proteins, nucleic acids, lipids, and complex carbohydrates.
• Lysosomes maintain an acidic pH, optimal for the hydrolytic enzymes.
• Lysosomes are found only in animal cells.

Vacuoles

• Vacuoles are large vesicles that perform various roles, including storing nutrients.
• Plant cells typically contain a central vacuole that helps maintain turgor pressure.
• Digestive vacuoles analogous to animal lysosomes, degrade macromolecules.
• Contractile vacuoles assist in regulating water balance (found in some protists).

Mitochondria

• Mitochondria are sites of cellular respiration, extracting energy from sugars, fats, and other fuels to produce ATP.
• They are double-membraned organelles.
• They have inner membrane in folds (cristae).
• Some cells have many mitochondria; others have few (based on function).
• The mitochondria have their own DNA and ribosomes.

Chloroplasts

• Chloroplasts capture light energy to make sugars through photosynthesis.
• Also double-membraned
• Internal membranes in stacks (grana)
• Thylakoid membranes contain pigments.
• Innermost space (stroma) contains enzymes for photosynthesis.

Origins of Mitochondria and Chloroplasts (Endosymbiosis Theory)

• Mitochondria and chloroplasts evolved from engulfed prokaryotic bacteria, respectively, aerobic bacteria and cyanobacteria, forming symbiotic relationships.
• Evidence for this theory includes similar size to bacteria.
• The engulfed bacteria have their own DNA and ribosomes.

Peroxisomes

• Peroxisomes are small metabolic compartments involved in various functions, including fatty acid breakdown and detoxification.
• Peroxisomes produce hydrogen peroxide as a byproduct.
• The hydrogen peroxide is broken down into water and oxygen using the enzyme catalase.