Cell Structures and Functions

• Study notes on cells, their structures, and functions

Introduction to Cytology

• Cells are the basic structural and functional units of living organisms
• Most cells range in size from 1 to 100 µm and are visible only with a microscope
• A light microscope can magnify objects up to approximately 1,000 times their actual size
• Modern techniques improve contrast and allow for the staining and identification of cell components
• Subcellular structures, including membrane-bound organelles, are too small to be seen with light microscopes

Electron Microscopy

• Used for examining subcellular structures
• Two main types of electron microscopy exist

Scanning Electron Microscopy (SEM)

• Suitable for detailed examination of surfaces
• Provides images with a three-dimensional appearance

Transmission Electron Microscopy (TEM)

• Used to study the internal structure of materials using an electron beam

Cell Size and Scale

• 1 Centimeter (cm) = 10^-2 Meter (m)
• 1 Millimeter (mm) = 10^-3 Meter
• 1 Micrometer (µm) = 10^-3 Millimeter = 10^-6 Meter
• 1 Nanometer (nm) = 10^-3 Micrometer = 10^-9 Meter

Cell Size Examples

• Most eukaryotic cells (plant and animal cells) typically range from 10 to 100 μm
• Certain cells can reach extreme sizes, such as the frog egg cell (1 mm), the African ostrich egg (15 cm), and human nerve cells (over 1 meter long)
• Most prokaryotic cells (bacteria) range from 1 to 5 μm
• Thiomargarita namibiensis, a sulfur bacterium, can reach a diameter of up to 0.75 mm
• Mycoplasmas range from 0.1 to 1.0 μm

Common Cell Features

• All cells possess a cell (or plasma) membrane:
• Separates the cell from the external environment
• Functions as a selective barrier, controlling the passage of oxygen, nutrients, and waste products
• Cytoplasm:
• Includes all cellular contents within the plasma membrane, excluding the nucleus

Cytosol

• A gel-like fluid enclosed by the cell membrane
• Many biochemical processes take place within the cytosol
• The cytosol contributes to the overall cytoplasm outside the organelles

Chromosomes

• Carry hereditary information in the form of DNA

Ribosomes

• Large protein/RNA complexes visible under an electron microscope
• Function as sites of protein synthesis

Prokaryotic and Eukaryotic Cells

• Living organisms are classified into two groups based on cell structure: prokaryotes and eukaryotes
• Eukaryotic cells are compartmentalized, with most of the genetic material (DNA) enclosed within a nucleus bounded by two membranes
• Prokaryotic cells lack a distinct nuclear compartment; the DNA is concentrated in a non-membrane-bound region called the nucleoid

Domains of Life

• The three fundamental domains are Bacteria, Archaea, and Eukaryota
• Bacteria and Archaea are prokaryotic domains
• Eukaryotes include protists, fungi, plants, and animals
• Eukaryotic cells contain additional membranes that enclose individual organelles, which perform specific functions within the cell

Prokaryotic Cells (Prokaryotes)

• Lack a cell nucleus
• Nuclear area is called the nucleoid
• The genome of most prokaryotes consists of a single, circular, double-stranded DNA molecule, known as the bacterial chromosome
• Some prokaryotes have additional DNA molecules called plasmids
• Plasmids are small, circular DNA molecules carrying genetic information, such as antibiotic or toxin resistance
• Plasmids can be transferred between bacteria through conjugation
• Cytoplasmic membrane
• A thin, flexible barrier surrounding the cell and separating the cytoplasm from the environment
• Consists of a lipid bilayer with embedded proteins
• Cell Wall
• A rigid wall surrounding the cytoplasmic membrane
• Gives the cell shape and stability
• Made of a peptidoglycan layer composed of polysaccharide chains cross-linked by amino acids

Cell Wall Function

• Protects the cell from virus entry of bacteriophages
• Prevents the cell from bursting due to osmotic pressure
• The chemical structure and genetic material are similar to Prokayotes and Eukaryotes

Schleimschicht

• Protects from dehydration outside the cell

Fimbrien

• Attach other solids, nutrients and bacteria
• Larger outside cell membrane and allows for movement

Eukaryotic Cells

• In addition to the plasma membrane, eukaryotes have a complex system of internal membranes
• Divide the cell into compartments called organelles
• Create separate spaces for different metabolic processes and specialized tasks
• This organization links structure to function

Membranous Organelles

• Zellkern (nucleus)
• Only highly differentiated and specialized cells have membraneous organelles
• Endomembrane System
• Surrounds parts of other organelles
• Mitochondrien
• Organelles that generate energy
• Chloroplasten -Found in Plant and Green Alge
• Peroxisomen
• Found in the liver and kidneys

Ribosomen

• Also in Prokayotes in different Forms and functions

Cytoskelett

• Varied cytoskeletel components

The Cell Nucleus

• Surrounded by two closely spaced membranes interspersed with nuclear pores
• Facilitate communication between the nuclear interior and the cytosol
• Contains the nucleolus, which concentrates genes for the creation of a certain RNA
• Generates RNA of ribosomes which have proteins

Endomembrane System

• Consists of the rough ER, smooth ER and Golgi apparatus

Lysosomen

• Membrane-bound, digest molecuels
• Neutral Ph value
• Breaks down uneccessary nutrients

Vacuolen

• Varying depending on cell type
• Functions to isolate the vacuole and reintroduce it into the cell

Ribosomen

• Build proteins
• In cell's cytosol

Mitochondrien

• Organelles of cell metabolism with a matrix

ZelleZell Komunikation

• Communication of animals happens in cells
• Transferred through water