Cell Structure and Stem Cells

• Here are the study notes

Cell Structure

• Cell theory describes cells as the building blocks of all plants and animals.
• All cells originate from pre-existing cells through division.
• Cells are the smallest units that carry out all vital physiological functions.
• Each cell maintains homeostasis at a cellular level.
• Stem cells are undifferentiated biological cells that differentiate into specialized cells and divide to produce more stem cells through mitosis.
• The body has many different kinds of cells.
• Human cells have about 200 different types, with approximately 20 different structures or organelles within them.

Types of Stem Cells

• Embryonic stem cells are isolated from the inner cell mass of blastocysts.
• Adult stem cells are found in various tissues.
• In adults, stem and progenitor cells serve as a repair system.
• In a developing embryo, stem cells differentiate into all specialized cells, including ectoderm, endoderm, and mesoderm (germ layers), which give rise to all body tissues and organs.

Stem Cell Potency

• Potency is the differentiation potential of a stem cell.
• Totipotent stem cells can differentiate into embryonic and extraembryonic cell types and construct a complete, viable organism; these cells are produced from the fusion of an egg and sperm cell.
• Pluripotent stem cells are descendants of totipotent cells and can differentiate into nearly all cells, derived from the three germ layers.
• Multipotent stem cells can differentiate into a number of cell types within a closely related family.
• Oligopotent stem cells can differentiate into only a few cell types, such as lymphoid or myeloid stem cells.
• Unipotent cells can produce only one cell type but have the property of self-renewal, distinguishing them from non-stem cells.
• Stem cell division can be symmetric or asymmetric, resulting in stem cells, progenitor cells, or differentiated cells.
• Potential uses of stem cells include treating stroke, traumatic brain injury, learning defects, Alzheimer's and Parkinson's diseases, baldness, blindness, deafness, and spinal cord injuries.

Cell Types

• Cells consist of a surrounding membrane, protoplasm (cell contents in thick fluid), and organelles (structures for cell function), controlled by DNA.
• Prokaryotic cells lack a nucleus or membrane-bound organelles and are the simplest type of cells.
• Gram-positive bacteria have a thick cell wall made of peptidoglycan.
• Gram-negative bacteria have a thinner layer of peptidoglycan.
• Eukaryotic cells possess a membrane-bound nucleus and compartmentalize cellular functions within organelles.
• The three main parts are plasma membrane, cytoplasm (cytosol + organelles), and nucleus.

Plasma Membrane

• Is a phospholipid bilayer with cholesterol, attached carbohydrates (glycolipids and glycoproteins), and proteins (integral and peripheral).
• Consists of amphipathic phospholipids with hydrophobic fatty acid tails and hydrophilic phosphate group heads.
• Functions include acting as a barrier, controlling entry of materials, receiving chemical and mechanical signals, and transmitting signals between intra- and extra-cellular spaces.
• The polar regions of phospholipids are oriented toward the surfaces of the membrane due to their attraction to the polar water molecules in the extracellular fluid and cytosol.
• Proteins can be integral proteins (closely associated with the membrane lipids) or peripheral proteins (located at the membrane surface)
• There are a variety of membrane functions achieved via anchored proteins:
• Anchoring
• Recognition
• Enzymes
• Channels
• Receptors
• Carriers

Cell Junctions

• Include desmosomes (anchoring proteins), tight junctions (sealing membranes), and gap junctions (protein channels).
• They hold adjacent cells firmly together in areas of stretching (desmosomes), they prevent extra cellular leakage (tight) and are a method of communication between cells (gap).

Cytoplasm

• Consists of a fluid portion (cytosol) and organelles.
• Organelles include the endoplasmic reticulum (ER), Golgi complex, lysosomes, peroxisomes, proteasomes, and mitochondria.
• The non membranous organelles are:
• Cytoskeleton
• Microvilli
• Centrioles
• Cilia
• Flagella
• Ribosomes
• The membranous organelles are:
• Mitochondria
• Nucleus
• Endoplasmic Reticulum
• Golgi Apparatus
• Lysosomes
• Peroxisomes

Cytoskeleton

• Maintains shape of cell, positions organelles, and changes cell shape, includes microfilaments, intermediate filaments, and microtubules.
• The centrosome is composed of two centrioles arranged perpendicularly, composed of microtubules and Pericentriolar material Function: moves chromosomes to ends of cell during cell division

Endoplasmic Reticulum

• A network and folded membranes with rough ER (studded with ribosomes; sites of protein synthesis) and smooth ER (lacks ribosomes; functions in lipid synthesis, glucose release, drug detoxification).

Golgi Complex

• Flattened membranes modify proteins into glycoproteins and lipoproteins.
• They can become parts of plasma membranes, can be stored in lysosomes, or are exported by exocytosis.

Lysosomes

• Spherical or oval structures that contain digestive enzymes.
• Help in final processes of digestion within cells, carry out autophagy, and eliminate of worn-out cells.

Mitochondria

• Major site of ATP production and CO2 formation.
• Have some DNA and ribosomes.
• Abundant in muscle, liver, and kidney cells.

Nucleus

• Round or oval structure surrounded by nuclear envelope with nuclear pores.
• Contains nucleolus, makes ribosomes that pass into cytoplasm through nuclear pores.
• DNA, associated with proteins, threads known as chromatin.

Transport Across Membranes

Cellular Process

• Passive Transport happens when no energy is used, with kinetic Energy and both solutes, solvents diffuse.
  • Osmosis is how the solvent diffuses through a semi-permeable route from low to high gradients
• Simple Diffusion
• solute diffuses from High -> Low
• Down to its gradient
• Happens through the lipid bilayer
• Facilitated Diffusion -Ion channel gated by channel proteins -The route is Ligand, Voltage or Mechanically gated

Active transport

• Primary: when ATP directly used → activate PUMP= Pressure and a Charge Gradient
• Energy required = against concentration gradient = via pump = can be saturated

Secondary

• Use electrochemical gradient made by Primary active transport =

• Specific ion channel, carriers for specific particles and Ions channel's saturation. Vesicular transport (macromolecule)

• The route is Transporters that bind to carrier protein, pass through Big polar molecule (unionised) glucose, fructose, galactose, vitamins with saturation There are two methods

• Transcytosis

• Endocytosis

• Exocytosis