Biology Cell Introduction

The Cell

• All living organisms, including humans, are made up of cells.
• 70-75% of the cell's weight is composed of water, while organic compounds account for 25-30% of the cell's weight.
• Inorganic compounds make up the rest of the cell's weight.

History/Background

• Robert Hooke was the first person to use the term "cell" to describe the small empty chambers in the structure of cork.
• Matthias Schleiden concluded that all plant tissues are composed of cells.
• Theodor Schwann concluded that all animal tissues are composed of cells.
• Rudolf Virchow proposed the theory of biogenesis, stating that cells can only arise from pre-existing cells.

Cell Theory

• The cell is the basic unit of life.
• The activities of the cell depend on the collective activities of its cells.
• The structure of the cell determines its function.

Parts of a Eukaryotic Cell

• Plasma Membrane

  • A phospholipid bilayer containing cholesterol, proteins, and some carbohydrates.
  • Forms a selectively permeable boundary of the cell.
  • Regulates material movement into and out of the cell.
  • Enables cell communication.

• Nucleus

  • Contains DNA that serves as the genetic material for directing protein synthesis.
  • Enclosed within a double membrane called the nuclear envelope.
  • Nucleolus consists of RNA and proteins that function in ribosomal assembly.

• Cytoplasm

  • Can be seen between the plasma membrane and the nucleus.
  • Organelles are membrane-bound structures that carry out specific metabolic activities of the cell.
  • Cytosol provides support for organelles and serves as the viscous fluid medium.

• Mitochondria

  • Double membrane-bound organelles containing a circular strand of DNA.
  • Responsible for building up energy in the form of ATP.

• Endoplasmic Reticulum (ER)

  • Rough ER: has ribosomes attached on the cytoplasmic surfaces.
  • Smooth ER: has no ribosomes and produces lipids, cholesterol, and hormones.

• Golgi Apparatus

  • Modifies, packages, and sorts materials from the ER in transport vesicles.
  • Vesicles transport cellular material.

• Peroxisomes

  • Smaller, spherical membrane-bound organelles that detoxify specific harmful substances.

• Lysosome

  • Spherical shaped membrane-bound organelles that digest microbes or materials by the cell.

• Cytoskeleton

  • Organized network of protein filaments that maintains structural support and organization of the cell.
  • Microfilaments maintain cell shape, intermediate filaments give mechanical support to structures like the nucleus and plasma membrane, and microtubules provide structural support.

Prokaryotic Cell

• Lack a membrane-bound nucleus.
• DNA is condensed within the cytosol to form a nucleoid.
• Have no subcellular organelles, only infoldings of the plasma membrane called mesosomes.

Cell Membrane Transport

• Passive Transport Process

  • Diffusion: movement of a substance from an area of higher concentration to an area of lower concentration.
  • Facilitated diffusion: requires a channel or protein carrier.
  • Osmosis: diffusion of water across a selectively permeable membrane.

• Active Transport Process

  • Uses energy (ATP) provided by the cell.

Cell Life Cycle

• Interphase

  • Longer phase of the cell cycle.
  • DNA replication occurs.

• Mitosis

  • Prophase: two chromatids joined at the centromeres.
  • Metaphase: chromosomes aligned at the center.
  • Anaphase: chromatids separated at the centromeres to opposite poles.
  • Telophase: chromosomes uncoil, and nuclear envelope reforms.

Cellular Structure and Function

• Cells are the basic unit of life, and all living organisms, including humans, are made up of cells.
• There are two major classes of cells: Eukaryotes and Prokaryotes.
• Eukaryotes have DNA found in the nucleus of the cell, contain membrane-bound organelles, and undergo mitosis.
• Prokaryotes lack membrane-bound organelles, do not have DNA enclosed within a membrane, and undergo binary fission.

Mitochondria

• Mitochondria are double membrane-bound organelles containing a circular strand of DNA.
• The outer membrane is highly permeable due to the presence of a pore-forming protein called porin.
• The intermembrane space contains many proteins that participate in oxidative phosphorylation.
• The inner membrane has multiple folds projecting inwards, called cristae, where energy is built up in the form of ATP.

Endoplasmic Reticulum (ER)

• ER is a network of protein filaments responsible for modifying, packaging, and sorting materials.
• There are two types of ER: Rough ER and Smooth ER.
• Rough ER has ribosomes attached to its surface, responsible for protein synthesis.
• Smooth ER lacks ribosomes, produces lipids, cholesterol, and hormones, and breaks down toxins.

Golgi Apparatus

• The Golgi Apparatus is a series of elongated, flattened sac-like membranous structures.
• It modifies, transports, and packages materials, and stores proteins produced by attached ribosomes.

Lysosomes

• Lysosomes are spherical-shaped membrane-bound organelles formed from the Golgi apparatus.
• They contain digestive enzymes and are responsible for digesting microbes or materials ingested by the cell.

Cytoskeleton

• The cytoskeleton is an organized network of protein filaments providing structural support and organization to the cell.
• Microfilaments maintain cell shape, intermediate filaments provide mechanical support, and microtubules regulate material movement into and out of the cell.

Nucleus

• The nucleus is enclosed within a double membrane called the nuclear envelope.
• It contains the DNA that serves as the genetic material for directing protein synthesis.
• The nucleolus is a region within the nucleus where RNA and proteins are found, functioning in ribosomal assembly.

Cytoplasm

• Cytoplasm is the fluid medium between the plasma membrane and the nucleus where organelles are embedded.
• It provides support for organelles and serves as the viscous fluid medium for cellular metabolic activities.

Plasma Membrane

• The plasma membrane is a phospholipid bilayer containing cholesterol, proteins, and some carbohydrates.
• It forms a selectively permeable boundary of the cell and acts as a physical barrier to enclose cell contents.

Peroxisomes

• Peroxisomes are smaller, spherical membrane-bound organelles formed from the endoplasmic reticulum.
• They detoxify specific harmful substances.