Introduction to Biology

• Biology is the scientific study of life.
• It explores the structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms.
• Biology encompasses a wide range of fields, including botany, zoology, microbiology, genetics, and ecology.

Central Concepts in Biology

• Cell theory states that all living organisms are composed of cells, and that cells are the basic units of structure and function in living organisms.
• Evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection.
• Genetics is the study of heredity and variation of inherited characteristics.
• Homeostasis is the ability of an organism to maintain a stable internal environment.
• Energy is required by all living organisms to carry out life processes.

Cell Biology

• Cell biology studies the structure, function, and behavior of cells.
• It examines cells at the molecular and microscopic level.
• Cell biology includes understanding cell signaling, cell cycle, and cell death.

Cell Structure

• Cells are broadly classified into two types: prokaryotic and eukaryotic.
• Prokaryotic cells lack a nucleus and other membrane-bound organelles.
• Eukaryotic cells possess a nucleus and other membrane-bound organelles, such as mitochondria and endoplasmic reticulum.

Key Cellular Components

• Plasma membrane: a selectively permeable barrier that separates the internal cell environment from the external environment.
  • Composed of a lipid bilayer with embedded proteins.
• Nucleus contains the cell's genetic material (DNA) and controls the cell's growth, metabolism, and reproduction.
  • Surrounded by a nuclear envelope with nuclear pores.
• Cytoplasm: the gel-like substance within the cell that contains organelles and other cellular components.
• Ribosomes are responsible for protein synthesis.
  • Found in both prokaryotic and eukaryotic cells.
• Endoplasmic reticulum (ER) is involved in protein and lipid synthesis.
  • Rough ER contains ribosomes, while smooth ER does not.
• Golgi apparatus modifies, sorts, and packages proteins and lipids for transport.
• Mitochondria generate energy for the cell through cellular respiration.
  • Have a double membrane structure.
• Lysosomes contain enzymes for breaking down cellular waste and debris.
• Cytoskeleton: a network of protein filaments that provides structural support and facilitates cell movement.
  • Includes microtubules, intermediate filaments, and actin filaments.

Cell Membrane

• The cell membrane is a phospholipid bilayer containing embedded proteins and cholesterol.
• It regulates the movement of substances into and out of the cell.
• Membrane proteins can function as transporters, receptors, enzymes, or anchors.
• The fluid mosaic model describes the cell membrane as a dynamic structure with lipids and proteins moving laterally.

Cell Communication

• Cells communicate with each other through chemical signals.
• Signaling pathways involve the reception, transduction, and response to signals.
• Types of cell signaling include:
  • Endocrine signaling: hormones are released into the bloodstream.
  • Paracrine signaling: signals affect nearby cells.
  • Autocrine signaling: signals affect the cell that produces them.
  • Direct contact: signals pass through cell junctions.
• Receptors bind to signaling molecules and initiate a cellular response.

Cell Cycle

• The cell cycle is the series of events that take place in a cell leading to its division and duplication.
• It consists of two main phases: interphase and mitotic phase (M phase).
• Interphase includes G1, S, and G2 phases.
  • G1 phase: cell growth and preparation for DNA replication.
  • S phase: DNA replication.
  • G2 phase: further growth and preparation for mitosis.
• M phase includes mitosis and cytokinesis.
  • Mitosis: nuclear division, resulting in two identical nuclei.
  • Cytokinesis: division of the cytoplasm, resulting in two separate daughter cells.
• Cell cycle checkpoints ensure proper progression through the cell cycle.

Cell Division: Mitosis and Meiosis

• Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
  • Prophase: chromosomes condense and become visible.
  • Metaphase: chromosomes align at the metaphase plate.
  • Anaphase: sister chromatids separate and move to opposite poles.
  • Telophase: chromosomes arrive at the poles, and nuclear envelopes reform.
• Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.
  • Meiosis I separates homologous chromosomes.
  • Meiosis II separates sister chromatids.

Cellular Respiration

• Cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water.
• It occurs in three main stages:
  • Glycolysis: glucose is broken down into pyruvate in the cytoplasm.
  • Citric acid cycle (Krebs cycle): pyruvate is oxidized to produce ATP, NADH, and FADH2 in the mitochondrial matrix.
  • Oxidative phosphorylation: electrons from NADH and FADH2 are passed along an electron transport chain to produce a proton gradient, which drives ATP synthesis.

Photosynthesis

• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy in the form of glucose.
• It occurs in two main stages:
  • Light-dependent reactions: light energy is used to split water molecules, producing ATP and NADPH.
  • Light-independent reactions (Calvin cycle): ATP and NADPH are used to convert carbon dioxide into glucose.

Genetics and Heredity

• Genetics is the study of heredity and variation in living organisms.
• Genes are the units of heredity and are composed of DNA.
• DNA (deoxyribonucleic acid) is the molecule that carries genetic information.
• Chromosomes are structures within the cell that contain DNA.
• Genotype is the genetic makeup of an organism.
• Phenotype is the observable characteristics of an organism.
• Mendelian genetics describes the basic principles of inheritance.

Molecular Biology

• Molecular biology studies the molecular basis of biological activity.
• It focuses on the structure, function, and interactions of biological molecules, such as DNA, RNA, and proteins.
• Key processes in molecular biology include:
  • DNA replication: the process of copying DNA.
  • Transcription: the process of synthesizing RNA from a DNA template.
  • Translation: the process of synthesizing proteins from an RNA template.

Cell Specialization and Differentiation

• Cell differentiation is the process by which cells become specialized in structure and function.
• During development, cells receive signals that determine their fate.
• Stem cells are undifferentiated cells that can differentiate into various cell types.

Cell Death

• Apoptosis is programmed cell death, a normal part of development and tissue maintenance.
• Necrosis is uncontrolled cell death, often caused by injury or infection.

Application of Cell Biology

• Understanding cell biology is crucial for developing treatments for diseases, such as cancer and genetic disorders.
• Cell biology techniques are used in biotechnology, drug discovery, and regenerative medicine.