Cell Theory and Types of Cells

• The cell is the basic structural and functional unit of life
• Cell biology is the study of cells and their functions
• All living organisms are composed of one or more cells
• New cells arise from pre-existing cells by cell division

Cell Theory

• All living organisms are composed of cells
• The cell is the basic unit of life
• All cells arise from pre-existing cells.

Types of Cells

• There are two main types of cells: prokaryotic and eukaryotic
• Prokaryotic cells lack a nucleus and other membrane-bound organelles
• Eukaryotic cells have a nucleus and other membrane-bound organelles

Prokaryotic Cells

• Bacteria and Archaea are prokaryotic cells
• They are typically smaller and simpler in structure compared to eukaryotic cells
• The genetic material (DNA) is located in the cytoplasm in a region called the nucleoid
• Prokaryotic cells have a cell wall that provides support and protection
• Many prokaryotic cells have flagella for movement
• Ribosomes are present for protein synthesis
• Some prokaryotes have plasmids, which are small, circular DNA molecules that carry extra genes

Eukaryotic Cells

• Eukaryotic cells are found in plants, animals, fungi, and protists
• Have a true nucleus, which contains the cell's DNA
• The nucleus is surrounded by a nuclear envelope
• Contain various membrane-bound organelles, such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes
• Plant cells also contain chloroplasts for photosynthesis
• Eukaryotic cells are generally larger and more complex compared to prokaryotic cells

Cell Structures and Functions

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

Cell Membrane

• The cell membrane is a selectively permeable barrier that surrounds the cell, separating its internal environment from the external environment
• Composed of a phospholipid bilayer with embedded proteins
• Regulates the movement of substances into and out of the cell
• Involved in cell communication and cell adhesion

Cytoplasm

• The cytoplasm is the gel-like substance within the cell, excluding the nucleus
• Contains various organelles and cellular components
• Site of many metabolic reactions

Nucleus

• The nucleus contains the cell's genetic material, DNA, which is organized into chromosomes
• Controls cell growth, metabolism, and reproduction
• Surrounded by a double membrane called the nuclear envelope
• Contains a nucleolus, which is involved in ribosome synthesis

Ribosomes

• Ribosomes are responsible for protein synthesis
• Found in the cytoplasm or attached to the endoplasmic reticulum
• Translate genetic information from mRNA into proteins

Mitochondria

• Mitochondria are the powerhouses of the cell
• Generate energy through cellular respiration
• Have a double membrane structure with an inner membrane folded into cristae
• Contain their own DNA and ribosomes

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum is a network of membranes involved in protein and lipid synthesis
• Rough ER is covered in ribosomes and involved in protein synthesis and modification
• Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage

Golgi Apparatus

• The Golgi apparatus processes and packages proteins and lipids
• Modifies, sorts, and packages proteins and lipids into vesicles for transport to other parts of the cell or for secretion

Lysosomes

• Lysosomes contain enzymes that break down cellular waste and debris.
• Involved in intracellular digestion and recycling of cellular components

Vacuoles

• Vacuoles are storage organelles found in plant and animal cells
• Store water, nutrients, and waste products
• In plant cells, the central vacuole helps maintain cell turgor pressure

Chloroplasts

• Chloroplasts are found in plant cells and algae
• Carry out photosynthesis, converting light energy into chemical energy
• Contain chlorophyll, which captures light energy
• Have a double membrane structure and contain thylakoids, which are arranged in stacks called grana

Cytoskeleton

• The cytoskeleton is a network of protein fibers that provides structural support to the cell
• Involved in cell movement, cell division, and intracellular transport
• Composed of microtubules, intermediate filaments, and microfilaments (actin filaments)

Cell Functions

• Cell functions include metabolism, growth, reproduction, communication, and differentiation

Metabolism

• Metabolism is the sum of all chemical reactions that occur in a cell
• Includes catabolism (breaking down molecules) and anabolism (building molecules)
• Enzymes catalyze metabolic reactions

Growth

• Cell growth involves increasing in size and mass
• Requires the synthesis of new cellular components

Reproduction

• Cell reproduction involves cell division, which produces new cells
• Prokaryotic cells reproduce by binary fission
• Eukaryotic cells reproduce by mitosis or meiosis

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 cell activities and maintaining homeostasis

Cell Differentiation

• Cell differentiation is the process by which cells become specialized in structure and function
• During development, cells differentiate into various cell types, such as nerve cells, muscle cells, and blood cells
• Differentiation is regulated by gene expression and environmental factors

Cell Transport

• Cell transport involves the movement of substances across the cell membrane
• Passive transport does not require energy and includes diffusion, osmosis, and facilitated diffusion
• Active transport requires energy and includes pumps and vesicular transport

Passive Transport

• Diffusion is the movement of molecules from an area of high concentration to an area of low concentration
• Osmosis is the movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration
• Facilitated diffusion involves the movement of molecules across the cell membrane with the help of transport proteins

Active Transport

• Active transport requires energy, usually in the form of ATP
• Pumps transport molecules against their concentration gradient
• Vesicular transport involves the movement of large molecules or particles into or out of the cell via vesicles
• Endocytosis is the process by which cells take in substances from the external environment by engulfing them in vesicles
• Exocytosis is the process by which cells release substances to the external environment by fusing vesicles with the cell membrane

Cell Energy

• Cells require energy to perform various functions
• Energy is stored in the form of ATP (adenosine triphosphate)
• ATP is produced during cellular respiration and photosynthesis

Cellular Respiration

• Cellular respiration is the process by which cells break down glucose to produce ATP
• Occurs in the mitochondria
• Includes glycolysis, the Krebs cycle, and oxidative phosphorylation

Photosynthesis

• Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose
• Occurs in the chloroplasts
• Includes the light-dependent reactions and the Calvin cycle

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication
• Consists of interphase (G1, S, and G2 phases) and mitotic phase (mitosis and cytokinesis)
• Interphase is the period of cell growth and DNA replication
• Mitosis is the process of nuclear division
• Cytokinesis is the division of the cytoplasm
• The cell cycle is regulated by various checkpoints to ensure proper cell division