Cell Biology: Exploring the Inner Workings of Cells

Posted on Nov 9, 2024 in Biology

Endoplasmic Reticulum (ER)

A network of interconnected tubules and membranous vesicles extending throughout the cell. The ER is continuous with the cell membrane. There are two types:

Rough ER: Studded with ribosomes and involved in protein synthesis.
Smooth ER: Associated with lipid synthesis.

Functions: Intracellular circulation, passive and active transport of substances, distribution of cellular products, and detoxification.

Golgi Apparatus

A set of flattened, membranous sacs that release small vesicles. Discovered in 1898. It does not have ribosomes.

Functions: Stores and secretes proteins, enzymes, hormones, and some carbohydrates. Packages proteins and gives rise to lysosomes.

Vacuoles

Membrane-bound cytoplasmic spaces. Most abundant in plant cells.

Functions (in plants): Storage of reserve products or waste.

Digestive Vacuoles: Associate with lysosomes.

Vesicles

Small, round, membrane-bound sacs.

Functions: Transport and temporary storage of materials, especially in animal cells.

Genetic Material

The control center of the cell, responsible for reproduction and regulation of biomolecule formation.

Nucleus

Discovered by Robert Brown. Exclusive to eukaryotes. Spherical or ovoid in shape. Formed by the nuclear membrane (karyoplast), nucleoplasm, and nucleolus.

Nucleoid

In prokaryotes, the genetic material is dispersed in a region called the nucleoid.

Cell Cycle

Four stages:

G1: Growth phase.
S: Synthesis phase (DNA replication).
G2: Second growth phase.
M: Mitosis (cell division).

Cell Division

Somatic Cells: Diploid (two sets of chromosomes). Germ Cells: Haploid (one set of chromosomes).

Miosis: Occurs in germ cells.
Mitosis: Occurs in somatic cells. Stages:
- Prophase: Centrosome divides, chromosomes condense.
- Metaphase: Chromosomes align at the cell’s center.
- Anaphase: Chromosomes separate and move to opposite poles.
- Telophase: Nuclear membrane reforms, cytokinesis (division of the cytoplasm).

Asexual Reproduction

Offspring are genetically identical to the parent.

Budding: A bud forms on the parent and separates.
Binary Fission: Organism divides into two equal parts.
Sporulation: Nucleus divides into many parts, each becoming a spore.
Regeneration: Replacement of lost or damaged tissues.

Meiosis

Two successive cell divisions, but chromosomes divide only once.

Prophase 1: Chromosome duplication (not complete), crossing over (exchange of genetic material).
Metaphase 1: Homologous chromosomes align at the equator.
Anaphase 1: Chromosomes separate and move to opposite poles.
Telophase 1: Spindle disappears, nuclear membrane reforms.

Conjugation: Formation of cytoplasmic bridges in bacteria and protozoa.

Chloroplasts

Characteristic of photosynthetic organisms. Bound by two membranes.

Leucoplasts: White.
Amyloplasts: Store starch.
Chloroplasts: Green, site of photosynthesis.

Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Light-dependent reactions: Occur in the presence of light.
Calvin cycle (dark reactions): Do not require light.

Ribosomes

Composed of RNA and proteins. Bound to the rough ER or free in the cytoplasm. Site of protein synthesis.

Mitochondria

Powerhouse of the cell. Site of aerobic respiration.

Cellular Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Stages of Aerobic Respiration: Glycolysis, Krebs cycle, electron transport chain.

Lysosomes

Membrane-bound vesicles containing hydrolytic enzymes for digestion.

Cytoskeleton (Animal Cells)

Provides cell shape, elasticity, and facilitates movement of organelles. Composed of microtubules, microfilaments, and intermediate filaments.

Centrosome (Animal Cells)

Originates from a pre-existing centrosome. Appears before cell division. Consists of two centrioles.

Cilia and Flagella

Specialized organelles for movement. Cilia are numerous and short, while flagella are few and long.

Cell Wall

Rigid layer outside the cell membrane. Composed of cellulose (plants), chitin (fungi), or other substances (bacteria).