Cell Structures and Functions

The cell theory states that all living organisms are composed of one or more cells, the cell is the basic unit of structure and organization in organisms, and cells arise from spontaneous generation.

Prokaryotic cells, such as bacteria and archaea, lack a nucleus and other membrane-bound organelles, distinguishing them from eukaryotic cells.

The plasma membrane, composed of a phospholipid bilayer with embedded proteins, is impermeable, allowing all molecules to freely pass in and out of the cell.

The nucleus contains the cell's genetic material (DNA) in the form of chromosomes, and the nucleolus is the site of lipid synthesis.

The rough endoplasmic reticulum (ER) is studded with ribosomes and is primarily involved in protein synthesis and modification, while the smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.

The Golgi apparatus receives proteins and lipids from the ER, modifies, sorts, and packages them into vesicles for transport to other destinations within the cell, acting as the cell's primary 'shipping' center.

Mitochondria, with their single membrane structure, carry out photosynthesis, converting light energy into chemical energy in the form of glucose.

Lysosomes contain hydrolytic enzymes that break down macromolecules, cellular debris, and pathogens, and are involved in autophagy (self-eating) and necrosis (programmed cell death).

The cytoskeleton, composed of microfilaments, intermediate filaments, and microtubules, provides structural support, helps maintain cell shape, and facilitates cell movement and intracellular transport.

Cells communicate through various signaling molecules that bind to receptors on the cell surface or inside the cell, initiating signal transduction pathways, ultimately leading to changes in gene expression or cellular activity only.

Mitosis produces two identical daughter cells and is used for growth and repair, while meiosis produces four genetically identical daughter cells (gametes) and is used for asexual reproduction.

The cell cycle consists of four main phases: G1, S, G2, and M, with the S (Synthesis) phase being when protein synthesis occurs.

During mitosis, chromosomes condense and the nuclear envelope breaks down in prophase, chromosomes align at the metaphase plate in metaphase, sister chromatids separate and move to opposite poles of the cell in anaphase, and chromosomes decondense and the nuclear envelope reforms in interphase.

Meiosis I involves the separation of homologous chromosomes, reducing the chromosome number by half, and includes crossing over in prophase I, which increases genetic diversity.

Cell growth is only regulated by growth factors, leading to the determination of cell size by anabolic processes alone.

Apoptosis is programmed cell death essential for development and tissue homeostasis.

Cell differentiation, determined by protein expression patterns, is the process by which stem cells become less specialized in structure and function over time .

Cellular respiration involves glycolysis, the Krebs cycle, and oxidative phosphorylation, with glycolysis occurring in the mitochondrial matrix and breaking down glucose into pyruvate only.

Protein synthesis involves two main steps: transcription, where DNA is transcribed into mRNA in the cytoplasm, and translation, where mRNA is translated into a protein on ribosomes in the nucleus.

Mutations, which are changes in the DNA sequence, can be spontaneous or caused by mutagens, and can only have a harmful effect on the cell.