Cell Structure: Biology Week 2

• Cell Structure is Week 2 of Biology

Cell Theory

• A basic biology principle evolved from 300 years of evidence.
• The cell theory states:
  • All organisms consist of cells.
  • Cells come from pre-existing cells (biogenesis).
  • The cell is the smallest unit of living organization.

Common Features of Cells

• Plant, animal, and bacterial cells share cytoplasm, a cell membrane, DNA, and ribosomes.

Cell Size

• The size of plant cells, animal cells, human red blood cells, and bacteria vary significantly.

Prokaryotic vs Eukaryotic Cells

• Prokaryotic cells do not have membrane bound organelles whereas Eukaryotic cells have several specialised membrane-bound organelles

Comparison of Prokaryotic and Eukaryotic Cells

• Prokaryotic cells are smaller than eukaryotic cells
• Prokaryotic cell have a large surface area to volume ratio, eukaryotic cells have a smaller ratio
• Prokaryotic cells lack membrane-bound organelles, while eukaryotic cells have many
• Prokaryotic chromosomal DNA is in a single-stranded loop, eukaryotic DNA is linear and thread-like
• Prokaryote DNA exists in the nucleoid region of the cytoplasm, and eukaryote DNA is located in the membrane bound Nucleus
• Small ribosomes are scattered in the cytoplasm of prokaryotes, while eukaryotes contain many of the ribosomes, either attached to the endoplasmic reticulum, or free in the cytoplasm
• The phospholipid bilayer of prokaryotic cells encloses cytoplasm in bacteria and can fuse into a monolayer; eukaryotic cells have a bilayer of phospholipid molecules that encloses the cytoplasm
• Prokaryotic cell walls consist of protein-carbohydrate compound called murein while eukaryotic cells contain; chitin in fungi and cellulose in plants
• Prokaryotic and eukaryotic cells may use the flagella to provide means to move consisting of three protein fibrils coiled in a helix in prokaryotes and a highly organised array of microtubules in eukaryotes.

Classification of Living Things

• Living things are classified into three domains based on cell type
• The six kingdoms are bacteria, archaea, protista, plantae, fungi, and animalia
• Bacteria and archaea have prokaryotic cells, while protista, plantae, fungi and animalia have eukaryotic cells.

Bacteria

• Bacteria have been confirmed as the first organism on Earth from 3.5 billion-year-old fossil evidence
• Bacteria metabolisms:
  • Aerobic or anaerobic.
  • Generate energy by photosynthesis or chemosynthesis.
• Roles of bacteria include:
  • Ecosystems: breakdown plant and animal remains and waste.
  • Food industry: cheese and yogurt production.
  • Medicine: antibiotics, drugs, and even human insulin production.
  • Pollution control: breakdown of oils and plastics.

Archaea

• Extremophiles are prokaryotes that thrive in extreme conditions such as:
  • High temperatures (thermophiles).
  • Low temperatures.
  • Higher atmosphere.
  • Very alkaline environments.
  • Very acidic environments (acidophiles).
  • Very salty environments (halophiles).
  • Little to no oxygen.
  • Areas without light.

Eukaryotic Cell Function Matrix

Synthesis and Processing of Proteins and Lipids: Nucleus

• Contains genetic material: linear chromosomes composed of DNA and proteins.
• Chromosomes are not clearly visible except during cell division.
• Contains a nucleolus: ribosome assembly site.
• Surrounded by a double-layered nuclear membrane dotted with nuclear pores.

Synthesis and Processing of Proteins and Lipids: Ribosomes

• Site of protein synthesis.
• Formed from proteins and ribosomal RNA (rRNA).
• Can be free-floating or bound to the rough ER.
• Proteins produced in free ribosomes function in the cytoplasm.
• Proteins produced in ribosomes bound to the rough ER are secreted out of cells, packaged into organelles, or inserted into the cell membrane.

Synthesis and Processing of Proteins and Lipids: Endoplasmic Reticulum

• Rough ER
  • Has ribosomes attached.
  • Proteins pass into the ER cavity after being made, containing enzymes.
  • Enzymes add sugar molecules to the protein.
  • Proteins then move into the Golgi apparatus for export from the cell.
  • Abundant in secreting cells, such as pancreatic cells.
• Smooth ER
  • Contains enzymes involved in synthesizing molecules other than protein e.g., phospholipids and steroids.
  • Abundant in steroid-secreting cells in the testes, ovaries, kidneys, and adrenal glands.

Synthesis and Processing of Proteins and Lipids: Golgi Apparatus

• Vesicles form to transport proteins when proteins formed in the rough ER reach the Golgi apparatus, for transport proteins from one cisternae to the next.
• Proteins are modified for cell use or transport out.
• Vesicles budding from the Golgi transport proteins:
  • Out of the cell by exocytosis.
  • Into the cell membrane.
  • Into lysosomes.

Synthesis and Processing of Proteins and Lipids: Lysosomes

• Digest unwanted matter with specialized vesicles.
• Recycling units for cells
• Specific to animal cells.
• Lysosomes fuse with vesicles containing unwanted matter such as damaged organelles or foreign matter.
• Digested unwanted matter by enzymes in lysosomes
• Small molecules used by the cell diffuses into the cytoplasm
• Lysosomes contains retained or released matter from the cell via exocytosis

Energy Transformations: Mitochondria

• Site of cellular respiration to produce ATP.
• Bounded by a double membrane.
• Cristae increases surface area for aerobic respiration.
• Active cells contain many mitochondria (e.g., heart muscle cells).
• Composed of mitochondrial DNA (mtDNA) showing evidence for endosymbiosis is present.

Energy Transformations: Chloroplasts

• Site of photosynthesis.
  • Trap light energy turns water into hydrogen and oxygen.
  • Combined hydrogen with CO2 to form glucose.
• Oxygen released into the atmosphere.
• Found in plants and many protists.
• The three membranes composed consist of inner membrane, outer membrane, and thylakoid system.
• Contains compartments with different enzymes due to the formation of membranes.

Storage and Cell Structure: Vacuoles

• Membrane-bound storage sacs.
• Contain water, food, and waste.
• Animal cells contain many small, temporary vacuoles.
• Plant cells contain a single permanent vacuole surrounded by a tonoplast membrane.
  • Creates turgor pressure.

Storage and Cell Structure: Cell Wall

• Found in plants, fungi, and some prokaryotes.
• Surrounds the plasma membrane.
• Composed mostly of cellulose in plants.
• Composed of chitin in fungi.

Storage and Cell Structure: Cytoskeleton

• Fiber types consists of Microfilaments, Microtubules, and Intermediate filaments.
• Supports cell structure.
• Allows cell movement.
• Aids in the transport of organelles and vesicles within the cell.

Storage and Cell Structure: Centrioles

• Consists of Cylindrical structures built from microtubules.
• Common eukaryotic cells are present, many plants do not have present
• Involved in cell division and formation of cilia and flagella.

Storage and Cell Structure: Cilia and Flagella

• Hair-like structures on the surface of cells.
• Provide motility.
• Cilia are only in eukaryotes.
• Flagella can be either prokaryotes and eukaryotes.

Organelle Functions

Compartmentalization in Eukaryotic Cells - Benefits

• Concentrating enzymes and reactants in organelles is possible.
• The right conditions (e.g., optimal pH) are maintained for enzymes and reactants to work.
• Allows multiple processes to occur at the same time, in the same cell.
• Reduces the cell's exposure to environmental damage.

Summary Points

• Prokaryotic and eukaryotic cells are the two basic types of cells.

• Prokaryotes consist of Archaea and Bacteria that lack organelles

• Eukaryotes have 4 kingdoms: Protista, Fungi, Plantae and Animalia.

• Prokaryotes have a simple cell structure with a nucleoid lacking a membrane, scattered ribosomes, and DNA mainly as a single-stranded loop.

• Eukaryotes contain a complex cell structure and cytoplasm, a membrane-bound nucleus, many organelles, and DNA mainly in chromosomes.

• Archaea live in very harsh environments due to their unique cell membrane structure.

• Eukaryotic cell compartmentalization:

  • Enzymes and reactants are concentrated inside specific organelles.
  • Correct environment to function.
  • Incompatible chem reactions occur at the same time.
  • Reduces the cell's vulnerability to environmental changes.

Organelle Summary in Eukaryotic Cells

• Main structure in a plant cell consists of the nucleus, tonoplast, vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum, ribosomes, plastids, mitochondria, and cell wall.
• Main structure in an animal cell consists of the nucleus, ribosomes, Golgi apparatus, rough and smooth endoplasmic reticulum, vacuoles, mitochondria, lysosomes, vesicles, and centrioles.