Biologi powerpoint 1

Cell Composition and Structure

Cells are the smallest living structural and functional units of all organisms. They originate from the division of pre-existing cells through processes such as mitosis and meiosis, allowing for genetic information to be passed on to daughter cells during this process. All metabolic processes necessary for life occur within cells, making them integral to the overall function of living organisms. Furthermore, all cells are composed of the same chemical compounds, which contribute to their structure and functionality.

Macromolecules

Macromolecules are essential to cell structure and function, consisting primarily of four major biological classes:

• Proteins: These macromolecules serve various roles, including structural support (e.g., enzymes, antibodies) and regulatory functions. They can act as enzymes to catalyze biochemical reactions, provide mechanical support, facilitate transport across membranes, and enable cell signaling processes.

• Nucleic acids: These include DNA and RNA, which are vital for the storage, transmission, and expression of genetic information. DNA serves as the blueprint for all genetic information, while RNA plays a crucial role in translating that information into proteins.

• Carbohydrates: These macromolecules are involved in energy storage and supply, as well as providing structural support in cells. They serve as important fuel sources and also play key roles in cellular recognition and signaling.

• Lipids: Essential for maintaining cell membrane structure and involved in energy storage, lipids are hydrophobic molecules that form bilayers around cells, creating a barrier that separates the interior of the cell from its external environment.

Metabolism

Metabolism encompasses all biochemical reactions occurring in cells, regulating energy exchange, growth, and reproduction. It includes two primary pathways:

• Anabolic pathways: These energy-requiring processes synthesize complex molecules from simpler ones, thereby contributing to the building and growth of cellular structures.

• Catabolic pathways: In contrast, these reactions involve breaking down complex molecules into simpler ones, releasing energy in the process. This energy can then be harnessed for various cellular activities.

Areas of Cell Study

Many areas contribute to our understanding of cells, including the following:

• Cytology: The study of cell structure and function, focusing on identifying and characterizing cells' various types and functions.

• Cytochemistry: This field involves the analysis of cell chemicals, aiding in the understanding of cellular processes through biochemical techniques.

• Cytopathology: This branch studies diseases at the cellular level, examining how diseases alter normal cell structure and function.

• Cytophysiology: Cytophysiology focuses on the functioning of cells within the biological context, understanding how cells respond to various stimuli and maintain homeostasis.

• Cytogenetics: The study of chromosomes and genetic material, cytogenetics explores how genetic information is organized, inherited, and expressed within cells.

Types of Cells

Prokaryotic Cells

• Characteristics: Prokaryotic cells are distinguished by their lack of a nucleus. They are smaller in size, typically ranging from 0.1 to 5 micrometers. Major representatives include bacteria and archaea.

• Anatomy: Key anatomical features include the pilus, a hair-like structure that facilitates attachment; a capsule for protection; a cell wall that maintains cell shape; a plasma membrane; cytoplasm; ribosomes; a nucleoid region containing genetic material; and plasmids, which can carry additional genes that may be beneficial to the cell.

Eukaryotic Cells

• Characteristics: Eukaryotic cells are larger and more complex than prokaryotic cells, with sizes typically ranging from 10 to 100 micrometers. They include animal, plant, fungal, and protist cells, showcasing a higher level of organization.

• Anatomy: Eukaryotic cells contain various organelles with specific functions:

  • Nucleus: The control center of the cell, housing genetic material and overseeing cellular functions via biochemical processes.

  • Mitochondria: Often referred to as the powerhouse of the cell, mitochondria are involved in energy production through cellular respiration.

  • Endoplasmic Reticulum (ER): The rough ER, studded with ribosomes, is essential for protein synthesis, while the smooth ER focuses on lipid production and detoxification of metabolic byproducts.

  • Golgi Apparatus: This organelle modifies, sorts, and packages proteins and lipids for transport to their desired destinations.

  • Lysosomes: These organelles contain enzymes necessary for the digestion of macromolecules, allowing for the recycling of cellular components.

  • Peroxisomes: These are involved in metabolic reactions, such as the degradation of fatty acids and detoxification of hydrogen peroxide.

  • Cytoskeleton: Composed of protein filaments like actin and microtubules, the cytoskeleton provides structural support and is crucial for cell shape, movement, and division.

Organelles in Eukaryotic Cells

Eukaryotic cells feature a diverse set of membrane-bound organelles, including:

• Double membrane-bound organelles: Such as the nucleus, mitochondria, and chloroplasts (in plant cells).

• Single membrane-bound organelles: These include the Golgi apparatus, lysosomes, peroxisomes, endoplasmic reticulum, and vacuoles.

• Non-membrane bound organelles: Features like the cytoskeleton, ribosomes, and centrosomes fall into this category.

Chemical Components of Cells

All cells comprise both inorganic and organic compounds:

• Water: Comprising approximately 70% of cell composition, water is essential for various chemical reactions and acts as a solvent for numerous cellular processes.

• Inorganic compounds: These include vital elements like carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, which together participate in critical biological functions.

• Organic compounds: Comprising macromolecules like proteins, carbohydrates, lipids, and nucleic acids, these compounds are integral to a cell's structure and function.

Water in Biological Systems

Water constitutes a substantial portion of cells (70-80%) and serves as a solvent for biochemical reactions. Its unique properties contribute significantly to cellular functions, including maintaining pH balance, facilitating metabolic processes, and acting as a medium for chemical reactions that occur within the cell.

The Structure of Water Molecules

A water molecule consists of one oxygen atom covalently bonded to two hydrogen atoms, connected via hydrogen bonds. This results in a dipolar structure, which is crucial for its solvent properties, allowing it to dissolve various polar substances essential for life.

Carbon's Role in Cells

Carbon serves as the backbone of all organic molecules, displaying unique properties that make it the foundation of biological macromolecules. Its ability to form four covalent bonds enables the formation of chains, branches, and cyclic structures, leading to the vast diversity of organic compounds found in living organisms.

Organic Molecules in Cells

Cells contain four major classes of organic molecules, which are vital for various cellular processes:

• Carbohydrates: Typically serve as key energy sources and structural components. They can be classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. For instance, starch serves as an energy storage form in plants, while glycogen serves the same role in animals.

• Lipids: These hydrophobic molecules play critical roles in energy storage, providing essential structural components for cell membranes, and functioning in cell signaling and hormone production. Categories include triglycerides, phospholipids, and steroids.

• Proteins: These perform a vast array of functions within cells, including catalysis of biochemical reactions, providing structural support, facilitating transport, and enabling signaling processes between cells.

• Nucleic acids: These macromolecules, including DNA and RNA, are essential for the storage and transmission of genetic information, orchestrating the synthesis of proteins and regulating cellular activities.

Eukaryotic Cell Structures

This encompasses critical components:

• Nucleus: The central control hub of the cell that houses genetic material and regulates cellular functions through orchestrating biochemical processes.

• Endoplasmic Reticulum (ER): The smooth ER is involved in lipid production, while the rough ER, with its ribosomes, plays a vital role in synthesizing proteins that will be secreted or sent to lysosomes.

• Golgi Apparatus: This organelle modifies, sorts, and packages proteins for their transport to different destinations within or outside the cell.

• Mitochondria: Known as the powerhouse of the cell, mitochondria are critical for ATP generation through cellular respiration, a multi-step process that yields energy from organic molecules.

Comparing Plant and Animal Cells

Plant cells uniquely contain chloroplasts for photosynthesis and have a rigid cell wall for structural support, while animal cells possess lysosomes for digestion and centrioles facilitating cell division. Despite these differences, both cell types share common organelles essential for fundamental cellular functions.

Endosymbiotic Theory

The Endosymbiotic Theory proposes that eukaryotic cells originated from symbiotic relationships formed between early prokaryotic cells. Compelling evidence supporting this includes the presence of similarities between bacterial DNA and that of mitochondria and chloroplasts, which hints at their earlier independent existence.

Summary of Cellular Metabolism

Cellular metabolism is a complex interplay of catabolic and anabolic pathways essential for energy production and material processing within cells. The process of cellular respiration occurs in distinct steps, including glycolysis, the Krebs cycle, and the electron transport chain, which together maximize ATP production, thus sustaining cellular functions and fostering growth.