Biochemistry Chapter 1: Cell

Historical Notes

• Robert Hooke discovered the term "cell" in 1665, referring to the small empty chambers in cork structure.
• He was the first to identify cells from plant tissue.

Cell Theory

• A cell is the basic structural and functional unit of living organisms.
• The activity of an organism depends on the collective activities of its cells.
• According to the principle of complementarity, the activities of cells are dictated by their structure, which determines function.

Eukaryotic vs. Prokaryotic Cell

• Eukaryotes have a membrane-bound nucleus and membrane-bound organelles, whereas prokaryotes lack these features.
• Eukaryotes contain mitochondria, endoplasmic reticulum, and Golgi complex, whereas prokaryotes do not.
• Eukaryotes divide by mitosis, whereas prokaryotes divide by binary fission.

Molecular Composition of Cell

• Water accounts for about 70-75% of the cell weight.
• Organic compounds (nucleic acids, proteins, carbohydrates, and lipids) account for 25-30% of the cell weight.
• Inorganic compounds make up the remaining cell weight.

Cell Membrane Transport

• Plasma membrane, also known as cell membrane or cytoplasmic membrane, is a selectively permeable boundary of the cell.
• It is composed of a phospholipid bilayer with cholesterol, proteins, and carbohydrates.

Cell Life Cycle

• Cell division involves mitosis.
• Genetic material is replicated and separated into two daughter cells.

Organelles

1. Plasma Membrane

• Acts as a physical barrier to movement into and out of the cell.
• Regulates material movement and cell communication.

2. Nucleus

• Control center of the cell, containing DNA that serves as a blueprint for protein synthesis.
• The nucleus is enclosed within a double membrane called the nuclear envelope.

3. Cytoplasm

• Provides support for organelles and serves as a viscous fluid medium.
• Contains inclusions, such as glycogen granules, pigments, and mucous membranes.

4. Mitochondria

• Responsible for providing ATP through oxidative phosphorylation.
• Structured as double-membrane-bound organelles containing a circular strand of DNA.

5. Lysosomes

• Responsible for the production of energy in the form of ATP.
• Contain digestive enzymes that break down and recycle cellular waste.

6. Endoplasmic Reticulum

• Divided into rough endoplasmic reticulum (with ribosomes) and smooth endoplasmic reticulum.
• Involved in protein synthesis, modification, and transport.

7. Golgi Apparatus

• Series of elongated, flattened sac-like membranous structures.
• Modifies, packages, and sorts materials, that arrive from the endoplasmic reticulum in transport vesicles.

8. Peroxisomes

• Small, spherical membrane-bound organelles formed from the endoplasmic reticulum.

• Involved in the modification, transport, and storage of cellular materials.### Peroxisome

• Hydrogen peroxide is toxic to the cell and is the basis of the name of the peroxisome

• Peroxisome helps to disarm pre-radicals and has no protein synthesis

• Catalase helps to convert hydrogen peroxide into water and oxygen, neutralizing the toxicity of the cell

Smooth Endoplasmic Reticulum

• Involved in lipid metabolism, fat synthesis, breakdown, and detoxification of drugs and pesticides
• Structure: extensive interconnected membrane network lacking ribosomes
• Functions: detoxifying specific harmful substances either produced by the cell or taken into the cell

Prokaryotic Cell

• Eubacteria and Archaebacteria are the most abundant organisms on earth
• Eubacteria consists of single cell nuclei; lacks nucleus and contains DNA and single cellular chromosome
• Can be gram positive and gram negative
• Examples: Lactobacilli, Escherichia Coli, Aspergillus, Azospirillum
• Archaebacteria are considered as the ancient form of microorganisms
• Functions: maintains integral structural support and organization of cells
• Does not contain a membrane-bound nucleus
• Each cell is surrounded by a plasma membrane
• Has no subcellular organelles, only mesosomes
• Deoxyribonucleic acid (DNA) is condensed within the cytosol to form the nucleoid

Cytoskeleton

• Structure: organized network of protein filaments
• Functions: maintains integral structural support and organization of cells
• Microfilaments maintain cell shape and provide mechanical support to structures
• Intermediate filaments give mechanical support to structures and help in cell wall formation
• Microtubules provide structural support and help in DNA replication
• Helps in the distribution of the daughter cell

Cell Membrane Transport

• Passive transport process: does not require energy (ATP)
• Types of passive transport: diffusion, osmosis, and facilitated diffusion
• Diffusion: movement of a substance from an area of its higher concentration to an area of its lower concentration
• Simple diffusion: type of diffusion of dissolved solutes through the plasma membrane
• Facilitated diffusion: type of diffusion that requires a protein carrier
• Osmosis: diffusion of water point across a selectively permeable membrane

Active Transport Process

• Uses energy (ATP) provided by the cell
• Example: sodium-potassium pump
• The sodium-potassium pump binds three sodium ions and a molecule of ATP
• The splitting of ATP provides energy to change the shape of the channel
• The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind

Endocytosis and Exocytosis

• Endocytosis: bulk movement of substance into the cell by vesicles forming at the plasma membrane
• Exocytosis: bulk movement of substance out of the cell by fusion of secretory vesicles with the plasma membrane
• Phagocytosis: process of cell eating, engulfing particulate matter
• Pinocytosis: process of cell drinking, engulfing fluid

Cell Division

• Cell division: the process by which one cell divides into two cells
• Mitosis: consists of four stages - prophase, metaphase, anaphase, and telophase
• The result is two daughter nuclei, each identical to the mother nucleus
• Prophase: chromatin condenses into chromosomes, and the nuclear envelope disappears
• Metaphase: chromosomes align at the center of the cell
• Anaphase: chromatids separate at the centromere and migrate to opposite poles
• Telophase: two new nuclei assume their normal structure, and cell division is completed

Cell Life Cycle

• Growth requires cell division
• Four stages in cell cycle: synthesis, gap 1 phase, gap 2 phase, and mitosis phase
• Interphase: the longer phase of the cell cycle where the cell is active and preparing for cell division