Prokaryotic Cells

• Cell structure refers to the organization of different components within a cell
• These components are called organelles
• Organelles perform specific functions required for the cell to function correctly
• Cell structures can be studied using microscopy techniques
• Electron microscopy provides higher resolution compared to light microscopy
• All cells have some common structures, such as the plasma membrane, cytoplasm, and genetic material
• Cells are broadly classified into two types: prokaryotic and eukaryotic

Prokaryotic Cells

• Prokaryotic cells are generally smaller and simpler in structure compared to eukaryotic cells
• They lack a membrane-bound nucleus
• The genetic material (DNA) is located in a region called the nucleoid
• Prokaryotic cells do not have other membrane-bound organelles
• The cell wall provides support and protection
• The cell wall is composed of peptidoglycan in bacteria
• Some prokaryotes have a capsule outside the cell wall for protection and attachment
• Ribosomes are present for protein synthesis, but they are smaller than those in eukaryotes
• Some prokaryotes have flagella for movement
• Pili are small, hair-like structures involved in attachment and genetic material transfer
• Examples of prokaryotic cells include bacteria and archaea

Eukaryotic Cells

• Eukaryotic cells are larger and more complex than prokaryotic cells
• They possess a membrane-bound nucleus that houses the genetic material (DNA)
• Eukaryotic cells contain various membrane-bound organelles, each with specific functions
• Examples of eukaryotic cells include animal cells, plant cells, fungi, and protists

Nucleus

• The nucleus is the control center of the cell, containing the cell's DNA
• It is surrounded by a double membrane called the nuclear envelope
• Nuclear pores in the envelope regulate the movement of substances between the nucleus and cytoplasm
• The nucleolus is a structure within the nucleus where ribosomes are assembled
• Chromatin, composed of DNA and proteins, is found within the nucleus and condenses into chromosomes during cell division

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is an extensive network of membranes involved in protein and lipid synthesis
• There are two types of ER: rough ER (RER) and smooth ER (SER)
• RER has ribosomes attached to its surface and is involved in protein synthesis and modification
• SER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids synthesized in the ER
• It consists of flattened membrane-bound sacs called cisternae
• Vesicles transport molecules between the ER and the Golgi, and between different Golgi compartments
• Proteins and lipids are modified, sorted, and packaged into vesicles for transport to other destinations

Lysosomes

• Lysosomes are organelles containing enzymes that break down cellular waste and debris
• They digest old or damaged organelles, as well as engulfed foreign materials
• Lysosomes play a crucial role in cellular recycling

Mitochondria

• Mitochondria are the powerhouses of the cell, responsible for generating ATP (adenosine triphosphate) through cellular respiration
• They have a double membrane structure, with an inner membrane folded into cristae to increase surface area
• Mitochondria contain their own DNA and ribosomes

Chloroplasts

• Chloroplasts are found in plant cells and algae and are responsible for photosynthesis
• They contain chlorophyll, a pigment that captures light energy
• Like mitochondria, chloroplasts have a double membrane and their own DNA and ribosomes

Cytoskeleton

• The cytoskeleton is a network of protein fibers that provides structural support and facilitates cell movement
• It consists of three main types of fibers: microfilaments, intermediate filaments, and microtubules
• Microfilaments are composed of actin and are involved in cell shape, movement, and muscle contraction
• Intermediate filaments provide structural support and stability
• Microtubules are composed of tubulin and are involved in cell division, intracellular transport, and the formation of cilia and flagella

Cell Membrane

• The cell membrane, also known as the plasma membrane, surrounds the cell and separates its contents from the external environment
• It is composed of a phospholipid bilayer with embedded proteins and cholesterol
• The cell membrane regulates the movement of substances into and out of the cell
• Proteins in the membrane can act as channels, carriers, receptors, or enzymes

Cell Wall

• The cell wall is a rigid outer layer found in plant cells, bacteria, fungi, and algae
• It provides support, protection, and shape to the cell
• In plant cells, the cell wall is primarily composed of cellulose
• Bacterial cell walls are composed of peptidoglycan
• The composition of the cell wall varies depending on the organism

Vacuoles

• Vacuoles are large, fluid-filled sacs found in plant and fungal cells
• They store water, nutrients, and waste products
• In plant cells, the central vacuole helps maintain cell turgor pressure

Ribosomes

• Ribosomes are responsible for protein synthesis
• They are found in both prokaryotic and eukaryotic cells
• Ribosomes consist of two subunits: a large subunit and a small subunit
• They can be free in the cytoplasm or attached to the endoplasmic reticulum (RER)
• Ribosomes read mRNA and use the genetic code to assemble amino acids into proteins

Centrioles

• Centrioles are cylindrical structures involved in cell division in animal cells
• They are composed of microtubules
• Centrioles organize the mitotic spindle during cell division
• They are typically found in pairs and located near the nucleus

Cilia and Flagella

• Cilia and flagella are hair-like appendages that extend from the cell surface
• They are involved in cell movement or moving substances across the cell surface
• Cilia are shorter and more numerous than flagella
• Flagella are longer and fewer in number
• Both cilia and flagella are composed of microtubules arranged in a 9+2 pattern