Introduction to Cell Biology

Introduction to Cell Biology

• Cell biology is the study of cell structure and function, focusing on the concept that the cell is the fundamental unit of life.
• The term “cell” was first introduced by Robert Hooke in 1667 while examining thin slices of cork with a microscope.
• Hooke observed "cells" which actually were the walls of dead plant cells.

Cell Theory

• There are three main principles of Cell Theory:
  • Cells are the basic unit of structure and organization for all living organisms.
  • All living organisms are composed of cells.
  • Cells arise from pre-existing cells.

Parts of the Cell

• Protoplasm is the living matter of the cell.
• Protoplasm is made up of three main parts:
  • Cell membrane: Also known as the plasma membrane, it surrounds the cytoplasm of a cell and acts as a semi-permeable barrier, controlling the entry and exit of substances.
  • Nucleus: Considered the "control center" of the cell, it controls cell activities like growth, DNA replication, repair, and cell division. It is bound by a double-layered membrane.
  • Cytoplasm: The part of the protoplasm located between the cell membrane and the nucleus, containing the organelles.

Nucleus

• Parts of the Nucleus:
  • Nuclear envelope: a double-layered membrane separating the nucleus from the cytoplasm.
  • Nucleoplasm: the dense material within the nucleus, containing DNA and proteins.
  • Nucleolus: the large structure in the nucleus of eukaryotic cells, responsible for ribosome production.
  • Chromatin: a complex of DNA and proteins called "histones" that form chromosomes within the nucleus of eukaryotic cells.
  • Nuclear pore: channels in the nuclear envelope that regulate the transport of molecules between the nucleus and cytoplasm.

Cytoplasm

• Cytoplasm is a gel-like substance composed of water, dissolved substances, and organelles.

Organelles

• Organelles are specialized structures within the cytoplasm that perform specific functions:
  • Cell wall: a rigid organelle providing support, protection, and shape for the cell. Present in plants, fungi, and bacteria.
  • Endoplasmic Reticulum (ER): a network of membranous tubules within the cytoplasm, continuous with the nuclear envelope.
    • Rough ER: contains ribosomes attached to its surface, responsible for protein synthesis.
    • Smooth ER: lacks ribosomes, involved in lipid synthesis.
  • Mitochondrion: considered the "powerhouse" of the cell, responsible for converting oxygen and nutrients into ATP (energy).
  • Vacuole: a space within a cell, lined with a membrane and filled with fluid; functions as a storage tank for food, water, and waste.
  • Lysosomes: organelles containing hydrolytic enzymes enclosed in a membrane, responsible for digestion of food and cellular debris.
    • Involved in cell protection and breakdown of the cell during cell death.
  • Peroxisomes: small organelles containing enzymes involved in nutrient absorption and alcohol digestion.
  • Chloroplast: organelles found in plant cells and some eukaryotic algae that conduct photosynthesis. Contain chlorophyll, which absorbs sunlight and uses it to produce food.
  • Golgi apparatus: a complex of vesicles and folded membranes; function as the "post office" of the cell, packaging and secreting materials.
  • Centrioles: minute cylindrical organelles near the nucleus in animal cells, involved in the development of spindle fibers during cell division.

Ribosomes

• Ribosomes are NOT considered organelles because they lack a membrane covering.
• They are molecular machines found in all living cells, responsible for protein synthesis.
• Ribosomes can be found in the cytoplasm and on the surface of the rough ER.

Cytoskeleton

• The cytoskeleton is a network of fibers that provides support, shape, and organization to the cell.
• It is present in all types of cells and consists of three main components:
  • Microfilaments: thin fibers made of actin protein.
  • Microtubules: thicker fibers made of tubulin protein.
  • Intermediate filaments: fibers made of various proteins.

Cell Movement

• Cell motility is essential for many physiological processes, including cell migration, cell regeneration, and tissue development.
• Three main types of locomotive structures contribute to cell movement:
  • Cilia: hair-like filaments found on the surface of tissue cells, responsible for movement.
  • Flagella: whip-like structures that allow cells to move.
  • Pseudopodia: cytoplasm-filled projections of the cell membrane used for movement.

Types of Cells

• There are two main types of cells:
  • Eukaryotic cells: contain a true nucleus bound by a membrane.
  • Prokaryotic cells: lack a true nucleus, with DNA free in the cytoplasm.
  • Both types of cells have ribosomes, a cell membrane, DNA, and a cytoskeleton. Eukaryotic cells may also have a cell wall depending on their type.

Comparison of Eukaryotic and Prokaryotic Cells

• Eukaryotic Cells:
  • Size: Larger than 10 micrometres.
  • DNA: Linear DNA enclosed within a nuclear envelope.
  • Organelles: With organelles.
  • Cell wall: Made up of cellulose or chitin (plants & fungi).
• Prokaryotic Cells:
  • Size: Smaller than 10 micrometres.
  • DNA: Circular DNA located in the cytoplasm.
  • Organelles: Without organelles.
  • Cell wall: Made up of peptidoglycan.

Animal and Plant Cells

• Both animal and plant cells are eukaryotic:
  • Share features like a cell membrane, Golgi apparatus, cytoplasm, nucleus, DNA, mitochondria, rough ER, smooth ER, lysosomes, peroxisomes, and ribosomes.
• Differences between animal and plant cells:
  • Size: Plant cells are larger than animal cells.
  • Shape: Plant cells have a fixed rectangular shape, while animal cells are more fluid and lack a defined shape.
  • Cell wall: Plant cells have a cell wall; animal cells lack a cell wall.
  • Vacuole: Plant cells have a large central vacuole; animal cells may have small vacuoles.
  • Chloroplast: Plant cells contain chloroplasts; animal cells do not.
  • Centrioles: Present in animal cells, absent in plant cells.
  • Food storage: Animal cells store glycogen as their primary food source; plant cells store starch.

Review of Animal Cell

• Key components:
  • Cell membrane
  • Mitochondrion
  • Lysosomes
  • Golgi Apparatus
  • Vesicles
  • Vacuole
  • Centrioles
  • Nucleus
  • Rough ER
  • Cytoplasm
  • Smooth ER
  • Nuclear envelope
  • Nuclear pore
  • Nucleolus
  • Nucleoplasm

Review of Plant Cell

• Key components:
  • Cell Wall
  • Cell membrane
  • Chloroplast
  • Vacuole
  • Lysosomes
  • Mitochondrion
  • Cytoplasm
  • Rough ER
  • Smooth ER
  • Golgi apparatus