Cell and Cellular Organelles Notes

Cell & Cellular Organelles

What is a Cell?

• A cell is the smallest, basic unit of life responsible for all life processes.
• Basic structure:
  • Cytoplasm: A fluid enclosed by a membrane.
  • Biomolecules: Proteins, nucleic acids, and lipids present in the cytoplasm.
  • Nucleus: Present in the cytoplasm.

History of Cell Theory

• Zacharias Janssen (1590):
  • Invented the first compound microscope.
• Robert Hooke (1665):
  • Used a light microscope to look at thin slices of plant tissue (cork).
  • Observed tiny chambers and coined the term 'cell'.
• Anton van Leeuwenhoek (1673):
  • First to see living microscopic organisms.
  • Termed these microorganisms 'animalcules'.
• Matthias Schleiden (1838):
  • Concluded that all living plants are made of cells.
  • Credited for developing the first two tenets of cell theory (with Schwann).
• Theodore Schwann (1839):
  • Concluded that all living animals are made of cells.
  • Credited for developing the first two tenets of cell theory (with Schleiden).
• Rudolph Virchow (1855):
  • Concluded that where a cell exists, there must have been a pre-existing cell.
  • Credited for developing the third tenet of the cell theory.

Cell Theory

• All organisms consist of one or more cells.
  • All living things, from single-celled organisms to complex multicellular organisms, are made up of cells.
• The cell is the basic unit of structure for all organisms.
  • The cell is the smallest unit of life and carries out all the functions necessary for an organism to survive and thrive.
• All cells arise only from pre-existing cells.
  • New cells are formed by the division of existing cells.
  • Essential for growth, development, and the maintenance of living organisms.

What is a Cell Organelle?

• An organelle is a membrane-enclosed intracellular compartment with specific structural and functional properties.
• List of Cell Organelles:
  1. Cell Membrane
  2. Cytoplasm
  3. Nucleus
  4. Endoplasmic Reticulum
  5. Ribosome
  6. Golgi Body
  7. Mitochondria
  8. Lysosome
  9. Plastid
  10. Vacuoles

Cell Membrane

• Present in both plant and animal cells.
• Functions as a selectively permeable membrane.
  • Permits the entry of selective materials in and out of the cell based on requirement.
• In animal cells, it provides shape and protects inner contents.

Cytoplasm

• Present in both plant and animal cells.
• Jelly-like substance within the cell membrane.
• Composed of water, organic, and inorganic compounds.
• Essential component where all cell organelles are embedded.

Nucleus

• Double-membraned organelle found in all eukaryotic cells.
• Largest organelle; control center of cellular activities and storehouse of the cell’s DNA.
• Features:
  • Nuclear membrane: Forms a wall between cytoplasm and nucleus.
  • Nucleolus: Tiny spherical bodies within the nucleus.
  • Chromosomes: Thin and thread-like structures carrying genes.
• Controls the characters and functions of cells.

Endoplasmic Reticulum (ER)

• Network of canals attached to the nucleus; the transport system of the cell.
• Two types:
  1. Rough Endoplasmic Reticulum: Involved in protein synthesizing.
  2. Smooth Endoplasmic Reticulum: Associated with the production of lipids and steroids.

Ribosomes

• Non-membrane-bound organelles found in close association with the endoplasmic reticulum.
• Either encompassed within the endoplasmic reticulum or freely traced in the cell’s cytoplasm.
• Primary function: Protein synthesis in all living cells to ensure survival.

Golgi Apparatus

• Membrane-bound organelle.
• Responsible for transporting, modifying, and packaging proteins and lipids to targeted destinations.
• Found within the cytoplasm of a cell and present in both plant and animal cells.

Mitochondria

• Powerhouses of the cell; produce energy-rich molecules for the cell.
• Double membrane-bound, sausage-shaped organelle found in all eukaryotic cells.
• Structure:
  • Double membranes divide it into two distinct aqueous compartments.
  • Inner compartment: Matrix, folded into cristae.
  • Outer membrane: Forms a continuous boundary with the cytoplasm.
• Produces energy in the form of ATP.

Lysosomes

• Organelles that digest the waste product of cells.
• Respond to foreign substances entering the cell by engulfing them.
• Found in all animal cells, but rarely found within plant cells due to the tough cell wall.

Plastids

• Large, membrane-bound organelles which contain pigments.
• Types based on pigments:
  • Chloroplast: Give plants green color due to chlorophyll.
  • Chromoplasts: Provide plants with characteristic colors (yellow, orange, red, etc.).
  • Leucoplasts: Colorless plastids which store nutrients.

Vacuoles

• Mostly defined as storage bubbles enclosed by a membrane.
• Stores food or a variety of nutrients that a cell might need to survive.
• Also stores waste products, which are eventually thrown out.
• Animal and plant cells have different sizes and numbers of vacuoles.
  • Plant cells have larger vacuoles compared to animal cells.

Similarities between Eukaryotic and Prokaryotic Cells

• Cell Membrane: Both have a cell membrane that acts as a selective barrier.
• Genetic Material: Both use deoxyribonucleic acid (DNA) for genetic information.
• Ribosomes: Both facilitate RNA translation and creation of protein.
• Cytoplasm: Fluid-like medium in which the biochemical reactions of the cell take place.

Differences between Eukaryotic and Prokaryotic Cells

• Cell arrangement:
  • Eukaryotes are often multicellular, prokaryotes are unicellular.
  • Exceptions: unicellular eukaryotes include amoebas, paramecium, yeast.
• Existence of nucleus:
  • Eukaryotic cells have a true nucleus.
  • Prokaryotic cells have no nucleus; only a "nucleoid" where the DNA is located.
• DNA Structure:
  • Eukaryotic DNA is linear and complex.
  • Prokaryotic DNA is circular and simple.
• Sexual reproduction:
  • Most eukaryotes undergo sexual reproduction.
  • Prokaryotes reproduce asexually, creating clones of themselves via binary fission.