The cell - cell diversity

Cellular Structures and Organelles

• Peroxisomes are enclosed by a single membrane and contain enzymes responsible for various metabolic reactions.
  • Contain catalase, providing defense against hydrogen peroxide and other cellular toxins like uric acid.
  • Break down fatty acids, an essential part of energy production.
• Mitochondria:
  • Have a double membrane structure with folded inner membrane (cristae).
  • Matrix contains enzymes that break down carbohydrates.
  • Cristae house protein complexes that produce ATP (cellular respiration).
• Chloroplasts:
  • Have a double membrane structure with folded inner membrane (cristae).
  • Matrix contains enzymes that break down carbohydrates.
  • Cristae house protein complexes that produce ATP (cellular respiration).
• Vacuoles and Vesicles:
  • Vacuoles (large) and vesicles (small) are membranous sacs for storing substances.
  • Found in plants, they store nutrients, water, plant pigments, and toxins.
  • Vesicles bud from one membrane and fuse with another, carrying membrane components and soluble proteins.

Plastids

• Three types of plastids in plant cells:
  • Chloroplasts
  • Chromoplasts: synthesize and store pigments
  • Leucoplasts: store food such as starches, proteins, and lipids

Cytoskeleton

• Network of filaments and tubules that extends from the nucleus to the plasma membrane.
• Supports organelles and provides a structural framework for the cell.
• Consists of:
  • Actin filaments: bundles or mesh-like networks, involved in cell shape and movement.
  • Microtubules: small hollow cylinders made of tubulin, maintaining cell shape and serving as tracks for organelle movement.
  • Intermediate filaments: ropelike assemblies of fibrous polypeptides, supporting plasma membrane and nuclear envelope.

Plant Cell Wall

• Composed of three layers:
  • Primary cell wall: thin, accommodates cellular growth.
  • Secondary cell wall: begins after growth phase, hardens or thickens primary cell wall.
  • Middle lamella: pectin-rich layer, forming the outermost layer between adjacent plant cells.

Fungal Cell Walls

• Contain chitin, a structurally important component.

Archaea

• Three classifications:
  • Methanogens: produce methane as a metabolic byproduct in anaerobic conditions.
  • Halophiles: found in high-salt environments, such as the Great Salt Lake or salty soil.
  • Thermophiles: live in hot environments, such as hot springs and hydrothermal vents.

Eukaryotes

Cyto-architecture

• Nucleus:
  • Surrounded by a double membrane (nuclear envelope).
  • Communicates with cytosol via nuclear pores.
  • Contains the main genome, DNA, and RNA synthesis.
• Endoplasmic Reticulum (ER):
  • System of interconnected sacs and tubes of membrane.
  • Synthesizes lipids and proteins, extends across the cell.

Flagella and Motility

• Flagella:
  • Composed of the protein flagellin.
  • Motor proteins are buried within the basal body of the plasma membrane.
  • Flow of hydrogen ions through the complex promotes promotive force, allowing bacteria to swim (chemotaxis).
• Fimbriae:
  • Shorter than flagella.
  • Single or in pairs.
  • Adhere to another bacterium during DNA transfer.

Golgi Apparatus

• Receives proteins and lipids from ER, involved in post-translational modification of proteins.
• Organizes and packages proteins for secretion or delivery to other areas within the cell.
• Transport of proteins via:
  • Exocytotic vesicles: involved in packaging and delivery of proteins destined for extracellular release.
  • Secretory vesicles: similar to exocytotic vesicles, but with variations.
  • Lysosomal vesicles: contains proteins and ribosomes destined for the lysosome, ready for degradation.

Golgi Apparatus

• Located in the cytoplasm of eukaryotic cells, composed of stacked curved saccules of membrane-enclosed vesicles
• Receives proteins and lipids from the endoplasmic reticulum (ER) for post-translational modification
• Organizes and packages proteins for secretion or delivery to other areas within the cell
• Proteins are transported via three main ways:

Exocytotic Vesicles

• Involved in the packaging and delivery of proteins destined for extracellular release
• Vesicles bud off the Golgi apparatus and move to the plasma membrane, fusing and releasing contents into the extracellular space

Secretory Vesicles

• Similar to exocytotic vesicles, but with variations
• Proteins are packaged, but stored prior to release, which is mediated by cell signaling pathways

Lysosomal Vesicles

• Contains proteins and ribosomes destined for lysosomes, ready for degradation
• Lysosomes and endosomes:

Lysosomes

• Spherical organelles produced by the Golgi apparatus, containing hydrolytic enzymes for intracellular digestion

Endosomes

• Sort ingested molecules, recycle some back to the plasma membrane

Peroxisomes

• Enclosed by a single membrane, containing enzymes for various metabolic reactions
• Contain catalase, providing defense against hydrogen peroxide (a marker of oxidative stress)
• Break down fatty acids, an important part of energy production

Archea

• Classified into three groups:

Methanogens

• Produce methane as a metabolic byproduct in anaerobic conditions

Halophiles

• Found in high-salt environments, such as the Great Salt Lake or soil with high salt concentrations

Thermophiles

• Found in hot environments, such as hot springs and hydrothermal vents

Eukaryotes

Cyto-architecture

Nucleus

• Surrounded by a double membrane (nuclear envelope)
• Communicates with the cytosol via nuclear pores
• Contains the main genome, DNA, and RNA synthesis, chromatin, and ribosomal subunits

Endoplasmic Reticulum (ER)

• A system of interconnected sacs and tubes of membrane extending across the cell
• Site of lipid and protein synthesis

Rough ER

• Ribosomes synthesize proteins, delivering them into the ER lumen

Smooth ER

• No ribosomes, highly developed for functions like steroid hormone synthesis and sequestering Ca2+ from the cytosol

Mitochondria and Chloroplasts

Peroxisomes

• Contain enzymes for various metabolic reactions
• Provide defense against hydrogen peroxide and other cellular toxins
• Break down fatty acids, an important part of energy production

Mitochondria

• Found in most eukaryotic cells
• Folded membrane within an outer membrane, with cristae housing protein complexes that produce ATP (cellular respiration)

Chloroplasts

• Found in most eukaryotic cells
• Folded membrane within an outer membrane, with cristae housing protein complexes that produce ATP (cellular respiration)

Vacuoles and Vesicles

• Membranous sacs that store substances, with vacuoles being larger and vesicles being smaller

Cell Diversity

Prokaryotes

• Lack a nucleus and most organelles, found in bacteria and archaea

Eukaryotes

• Have a nucleus and membrane-bound organelles, found in fungi, protozoa, plants, and animals

Origin of Life

• Believed to have originated from a common ancestor
• Evolved into prokaryotes (eubacteria and archaea) and eukaryotes
• Eukaryotes acquired mitochondria and later, chloroplasts in plants
• Similarities in mitochondria and chloroplasts across eukaryotes suggest a common origin