Understanding Cells: Theory, Types and Structures

• Cells are the basic structural and functional units of life
• They are responsible for carrying out all the processes necessary for life

Cell Theory

• All living organisms are composed of one or more cells
• The cell is the basic unit of structure and organization in organisms
• All cells arise from pre-existing cells

Types of Cells

• There are two main types of cells: prokaryotic and eukaryotic

Prokaryotic Cells

• Prokaryotic cells do not have a nucleus or other membrane-bound organelles
• Their DNA is located in the cytoplasm in a region called the nucleoid
• They are generally smaller and simpler than eukaryotic cells
• Bacteria and Archaea are prokaryotic cells
• Prokaryotic cells possess a cell wall, a plasma membrane, cytoplasm, ribosomes, and genetic material (DNA and RNA)

Eukaryotic Cells

• Eukaryotic cells have a nucleus and other membrane-bound organelles
• Their DNA is housed within the nucleus
• Eukaryotic cells are generally larger and more complex than prokaryotic cells
• Eukaryotic cells are found in plants, animals, fungi, and protists
• Eukaryotic cells contain organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and in plant cells, chloroplasts
• The plasma membrane separates the interior of the cell from the outside environment

Cell Structures and Functions

• Cell structures include: plasma membrane, cytoplasm, nucleus, ribosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles

Plasma Membrane

• The plasma membrane is the outer boundary of the cell
• It is a selectively permeable barrier that controls the movement of substances into and out of the cell
• It is composed of a phospholipid bilayer with embedded proteins

Cytoplasm

• The cytoplasm is the region between the plasma membrane and the nucleus
• It consists of the cytosol (a gel-like substance) and organelles
• Many metabolic reactions occur in the cytoplasm

Nucleus

• The nucleus is the control center of the cell
• It contains the cell's DNA, which is organized into chromosomes
• The nucleus is surrounded by a nuclear envelope, a double membrane that separates the nucleus from the cytoplasm

Ribosomes

• Ribosomes are responsible for protein synthesis
• They are found in the cytoplasm and on the rough endoplasmic reticulum
• Ribosomes read RNA and assemble amino acids into proteins

Mitochondria

• Mitochondria are the powerhouses of the cell
• They generate ATP (adenosine triphosphate), the cell's primary energy source, through cellular respiration
• Mitochondria have a double membrane structure, with an inner membrane folded into cristae

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum is a network of membranes involved in protein and lipid synthesis
• There are two types of ER: rough ER (RER) and smooth ER (SER)
• RER is covered in ribosomes 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
• It receives vesicles from the ER, modifies their contents, and sorts them for delivery to other parts of the cell
• The Golgi apparatus consists of flattened membranous sacs called cisternae

Lysosomes

• Lysosomes contain enzymes that break down cellular waste and debris
• They are involved in digestion and recycling of cellular components
• Lysosomes fuse with vesicles containing materials to be digested

Vacuoles

• Vacuoles are storage sacs within the cell
• They can store water, nutrients, and waste products
• Plant cells often have a large central vacuole that helps maintain cell turgor (rigidity)

Cell Wall

• Plant cells, bacteria, fungi, and algae have a cell wall
• The cell wall provides support and protection to the cell
• Plant cell walls are primarily composed of cellulose

Chloroplasts

• Chloroplasts are organelles found in plant cells and algae
• They are the sites of photosynthesis, where light energy is converted into chemical energy in the form of glucose
• Chloroplasts contain chlorophyll, a pigment that absorbs light

Cell Size

• Cell size is limited by the surface area to volume ratio
• As a cell increases in size, its volume increases faster than its surface area
• A higher surface area to volume ratio is more efficient for transport of materials into and out of the cell

Cell Specialization

• Cells can differentiate to perform specific functions in multicellular organisms
• Different cell types have different structures and organelles that are suited to their particular roles
• Examples of specialized cells include nerve cells, muscle cells, and red blood cells

Cell Communication

• Cells communicate with each other through chemical signals
• Signals can be transmitted through direct contact, local signaling, or long-distance signaling
• Cell communication is essential for coordinating activities in multicellular organisms

Cell Division

• Cell division is the process by which cells reproduce
• There are two main types of cell division: mitosis and meiosis
• Mitosis is nuclear division that results in two identical daughter cells, used for growth and repair
• Meiosis is nuclear division that results in four daughter cells with half the number of chromosomes as the parent cell, used for sexual reproduction

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication
• The cell cycle consists of interphase (G1, S, G2 phases) and the mitotic phase (mitosis and cytokinesis)

Cell Transport

• Cells transport materials across the plasma membrane through various mechanisms
• Passive transport does not require energy and includes diffusion, osmosis, and facilitated diffusion
• Active transport requires energy and includes the use of transport proteins and vesicles for endocytosis and exocytosis

Cell Metabolism

• Cell metabolism refers to the chemical reactions that occur within a cell
• These reactions include catabolism (breakdown of complex molecules) and anabolism (synthesis of complex molecules)
• Enzymes play a critical role in catalyzing metabolic reactions

Cell Respiration

• Cell respiration is the process by which cells break down glucose to generate ATP
• It occurs in three main stages: glycolysis, the Krebs cycle, and the electron transport chain
• Most ATP is produced during the electron transport chain, which takes place in the mitochondria

Photosynthesis

• Photosynthesis is the process by which plants and algae convert light energy into chemical energy
• It occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle)
• The light-dependent reactions capture light energy and convert it into chemical energy in the form of ATP and NADPH
• The light-independent reactions use ATP and NADPH to fix carbon dioxide and produce glucose

Explore cells, the fundamental units of life, and their functions. Learn about cell theory, and the differences between prokaryotic and eukaryotic cells. Discover cell structures and their roles.