Cell Biology: Structure, Processes, and Functions
Cell Biology: An Overview
Cell Division
Mitosis
Mitosis, the process of nuclear division that results in two identical daughter cells, involves several stages:
- Prophase: Dispersed chromatin condenses into visible chromosomes.
- Metaphase: Chromosomes reach maximum condensation and align at the metaphase plate.
- Anaphase: Sister chromatids separate and move towards opposite poles of the cell.
- Telophase: Chromatids decondense, nuclear membranes reform, and cytokinesis (division of the cytoplasm) begins.
Meiosis
Meiosis, the cell division process that produces gametes (sex cells), consists of two consecutive divisions:
- Meiosis I:
- Prophase I: Homologous chromosomes pair up and exchange genetic material (crossing over).
- Metaphase I: Homologous chromosome pairs align at the metaphase plate.
- Anaphase I: Homologous chromosomes separate and move to opposite poles.
- Telophase I: Two daughter cells are formed, each with half the number of chromosomes as the parent cell.
- Meiosis II:
- Prophase II: Chromosomes condense.
- Metaphase II: Chromosomes align at the metaphase plate.
- Anaphase II: Sister chromatids separate and move to opposite poles.
- Telophase II: Four haploid daughter cells (gametes) are formed.
Cell Types
Eukaryotic Cells
Eukaryotic cells, such as animal and plant cells, have a nucleus enclosed by a double membrane and contain membrane-bound organelles.
Prokaryotic Cells
Prokaryotic cells, such as bacteria, lack a nucleus and membrane-bound organelles. Their DNA is dispersed in the cytoplasm.
Metabolic Processes
Anabolism
Anabolism refers to the synthesis of complex molecules from simpler ones, requiring energy (ATP).
Catabolism
Catabolism involves the breakdown of complex molecules into simpler ones, releasing energy.
Cellular Respiration
Cellular respiration is a catabolic process that breaks down glucose to produce ATP. It occurs in three stages: glycolysis, the Krebs cycle, and oxidative phosphorylation.
Fermentation
Fermentation is an anaerobic (oxygen-independent) catabolic process that produces ATP and organic byproducts, such as ethanol or lactic acid.
Biological Molecules
Carbohydrates
Carbohydrates are composed of carbon, hydrogen, and oxygen. They serve as energy sources (e.g., glucose), energy storage (e.g., starch in plants, glycogen in animals), and structural components (e.g., cellulose in plant cell walls).
Lipids
Lipids are hydrophobic molecules composed of carbon, hydrogen, and oxygen. They function as energy storage (e.g., fats), structural components (e.g., phospholipids in cell membranes), and hormones (e.g., steroids).
Proteins
Proteins are complex molecules composed of amino acids. They have diverse functions, including structural support (e.g., collagen, keratin), transport (e.g., hemoglobin), regulation (e.g., insulin), movement (e.g., muscle proteins), and catalysis (e.g., enzymes).
Nucleic Acids
Nucleic acids, DNA and RNA, are composed of nucleotides. DNA stores genetic information, while RNA plays various roles in gene expression, including protein synthesis.
Autotrophic and Heterotrophic Nutrition
Autotrophs
Autotrophs, such as plants, can produce organic matter from inorganic substances through processes like photosynthesis.
Heterotrophs
Heterotrophs, such as animals, obtain organic matter by consuming other organisms.
Animal and Plant Cells
Animal Cells
Animal cells have a plasma membrane, cytoskeleton, cytoplasm containing various organelles (e.g., ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria), and a nucleus.
Plant Cells
Plant cells differ from animal cells by having a cell wall, chloroplasts for photosynthesis, a large central vacuole, and a displaced nucleus.