Intro to Cells and Cell Theory

• Cells are the fundamental unit of life and have self-replicating structures.
• Robert Hooke first observed and named cells in 1665 from a slice of cork.
• Some organisms are unicellular; others are multicellular.
• Cell diameters range from 2-120μm.

Cell Theory

• Proposed in 1839 by Matthais Schleiden and Theodor Schwann.
• All living things consist of cells.
• Cells are the smallest working unit of all living things.
• All cells originate from pre-existing cells through cell division.

Definition of a Cell

• A cell is the smallest unit capable of performing life functions.

Examples of Cells

• Bacteria
• Amoeba Proteus
• Nerve Cell
• Plant Stem
• Red Blood Cell

Types of Cells

• Prokaryotic
• Eukaryotic

Prokaryotic Cells

• Lack structures surrounded by membranes.
• Have few internal structures.
• Are one-celled organisms like bacteria.

Eukaryotic Cells

• Contain organelles surrounded by membranes.
• Includes of most living organisms.

Constituents of a Cell

• Protoplasm is the collective term for the different substances that make up a cell.
• Protoplasm is composed of water, carbohydrates, lipids, proteins, and electrolytes.
• Water makes up 70-80% of a cell.
• The electrolyte components are Sodium(Na+), Potassium(K+), Magnesium(Mg2+), Calcium(Ca2+), Phosphate, Chloride (Cl-), and Bicarbonate (HCO3 - ).

Subcellular Structures

• Major structures present in a cell are the cell membrane, cytoplasm with its organelles, and the nucleus.

Cell Membrane

• A thin, pliable, elastic outermost structure that envelops the cell.
• It consists of a bilipid layer with embedded integral and peripheral proteins.

Functions of Cell Membrane

• Protection as the outermost boundary of cell organelles.
• Digestion through taking in food and excreting waste.
• Selective permeability to non-polar (like gases, lipids, steroid hormones, alcohols) and polar molecules (like H₂O, soluble ions, glucose, urea).
• Non-polar molecules dissolve and move more rapidly across the membrane.
• Polar molecules penetrate the membrane more slowly.
• Chemical and physical properties of the membrane control the passage of ions in and out of the cell and help maintain components in intracellular fluid (ICF) and extracellular fluid (ECF).
• Cells links adjacent cells together to form tissues via junctional composes
• Insulating properties; acts as a dielectric material of a charged condenser and has a high insulating value.

Cell Wall

• Most commonly found in plant cells and bacteria.
• Supports and protects cells.

Nucleus

• The control center that directs cell activities.
• Separated from the cytoplasm by the nuclear membrane.
• Contains genetic material, DNA.

Nuclear Membrane

• Surrounds the nucleus.
• Is made of two layers.
• Allows material to enter and leave the nucleus through openings.

Chromosomes

• Located in the nucleus.
• Made of DNA.
• Contain instructions for traits and characteristics.

Nucleolus

• Is located inside the nucleus.
• Contains RNA used to build proteins.

Cytoplasm

• A thick, gel-like mixture.
• Is surrounded by the cell membrane.

Cytosol

• The aqueous part of the cytoplasm outside the organelles.
• It accounts for approximately 70% of the total cell volume.
• Consists mainly of cytoskeleton filaments, organic molecules, salt, and water.
• Contains distinctive proteins.

Endoplasmic Reticulum

• Moves materials around in a cell.
• Is a network of tubular and flat vesicular structures in the cytoplasm.
• An extensive network of closed, flattened membrane-bounded sacs called cisternae.
• Space inside the tubules is filled with Endoplasmic Matrix.
• A smooth has no ribosomes, while rough has ribosomes embedded in its surface.

Ribosomes

• Each cell contains thousands of ribosomes.
• Ribosomes make proteins.
• They are found on the endoplasmic reticulum and floating throughout the cell.

Mitochondria

• First observed by Kolliker in 1850 as granular structures in the striated muscles.
• The powerhouse of the cell.
• Has a length of 5-12μm and a diameter of 0.5-1μm.
• It produces energy through breaking down fats and carbohydrates.
• Controls the water level and other materials in the cell.
• Recycles and decomposes proteins, fats, and carbohydrates.
• The components consists of an outer membrane, inner membrane, intermediate space, cristae(infoldings of the inner membrane), and matrix which is the space enclosed by the inner membrane.
• Functions as a power generating unit, and maintains concentration of calcium ions, is involved in energy transduction, and is responsible for thermogenesis.
• Contains large numbers of integral membrane proteins called Porins, allowing molecules of 5000 daltons or less to pass through the outermost membrane.
• Contains enzymes concerned with 'citric acid cycle' and 'respiratory chain oxidation' in the interior matrix .
• It is involved in the major metabolic pathways like oxidation of carbohydrates, lipids, and amino acids and part of biosynthetic pathways involving urea and heme synthesis in inner matrix.
• The inner membrane contains ATPase and other enzymes concerned with the synthesis and metabolism of ATP, including enzymes of the Electron Transport Chain.
• The ultimate purpose of these mechanisms is oxidative phosphorylation and synthesis of ATP.
• Contains some protein synthesized by Mitochondrial DNA.

Golgi Bodies

• Acts as a protein 'packaging plant'.
• Moves materials within the cell.
• Moves materials out of the cell.

Lysosome

• Acts as a ‘digestive plant’ for proteins, fats, and carbohydrates.
• Transports undigested material to the cell membrane for removal.
• If it explodes, the cell breaks down.

Vacuoles

• Membrane-bound sacs.
• Vacuoles are used for storage, digestion, and waste removal.
• Contain water solution.
• Help plants maintain their shape.

Chloroplast

• Usually found in plant cells.
• Contains green chlorophyll.
• Where photosynthesis occurs.