Cell Organelles and Plasma Membrane

• Organelles are cell structures with specific functions that maintain homeostasis.

Plasma Membrane

• The plasma membrane surrounds the cell, isolating its internal environment and processes from the external environment.
• The fluid mosaic model describes the plasma membrane as dynamic, with many components able to move within the bilayer.
• The main component of the plasma membrane are membrane proteins, integral proteins (span entire membrane) and peripheral proteins (on one side only).
• Other components of the plasma membrane include cholesterol, glycolipids, glycoproteins, and carbohydrates.
• The plasma membrane transports substances via protein channels and carrier proteins.
• Receptors on the plasma membrane bind to chemical messengers, triggering a sequence of events.
• Enzymes in the plasma membrane speed up chemical reactions, vital to homeostasis.
• The plasma membrane provides structural support, shape, and structural integrity to the cell.
• It also facilitates communication between cells.
• Plasma membrane phospholipids are amphiphilic, containing a hydrophilic phosphate group head and two hydrophobic fatty acid tails, creating a water-resistant barrier.

Membrane Proteins

• Channel proteins form pores allowing small molecules and ions to pass through.
• Receptor molecules are proteins that bind to a specific molecule (ligand) and initiate a biochemical response.
• Gated channels are channel proteins that stay closed until an electrical or chemical stimulus opens them.
• Non-gated channels stay open, allowing ions and water to pass through.
• Water-soluble molecules diffuse through membrane channels.
• Lipid-soluble molecules diffuse through the phospholipid bilayer.
• Cells that respond to ligands posses receptors.
• Membrane-bound receptors are proteins at the plasma membrane that bind to ligands to send signals.
• G-proteins are found on the inner surface of the cell membrane and send signals to other cells.
• Ligands are essential for communication between cells.

Membrane Permeability

• Selectively permeable membranes allow certain molecules to cross while prohibiting others, critical for cell survival.
• Vitamin A, a fat-soluble vitamin moves across the plasma membrane via simple diffusion.
• Smelling cookies from the kitchen is an example of diffusion.
• Increase in concentration, higher temperature, smaller molecular size, increased surface area, and thinner membrane can all increase the rate of diffusion.
• During diffusion, substances move from an area of high concentration to low concentration.
• Movement of oxygen in the alveoli exemplifies diffusion.
• Osmosis is a passive process where a solvent (usually water) moves across a membrane.
• Red blood cells shrink in a hypertonic solution and burst in a hypotonic solution.
• Burned cells die.
• A solution isotonic to plasma with an osmolarity of 300 mili-osms will also have an osmolarity of 300 mili-osms.
• Drinking large volumes of water can overhydrate body cells, causing them to swell and possibly burst.
• Active transport requires energy in the form of ATP for solutes to move against their concentration gradient from low to high concentration.
• Pinocytosis occurs when a cell engulfs fluid droplets form the extracellular fluid (ECF).
• Phagocytosis occurs when a cell ingests large particles, like bacteria, dead, or damaged cells.
• During endocytosis, cells absorb material from the outside.
• During exocytosis, cells release materials from the inside.

Other Cell Components

• Messenger RNA (mRNA) carries genetic information from DNA to ribosomes to build proteins.
• Cytoplasm is found between the cell membrane and the nuclear membrane
• The cytoskeleton consists of actin filaments, intermediate filaments, and microtubules.
• Mitochondria produce energy and provide majority of ATP in cell.
• Actin filaments are the thinnest, two intertwining strands, provide structural support, tension, cell shape, cellular motion.
• The Golgi apparatus sorts, modifies, and packages proteins and lipids from ER.
• Lysosomes break down garbage and non-functional organelles.
• Cells lacking ribosomes won't be able to produce ribosomes which can cause functional impairment and cell death.
• Glycolysis is the breakdown of the use of glucose to produce energy.
• Aerobic respiration requires oxygen to break down glucose and produce energy.
• The sequence of creating proteins involves, transcription, processing, translation, polypeptide chain and processing

Transcription

• DNA is copied into a strand of messenger RNA (mRNA) in the nucleus

Processing

• The mRNA is edited and exported to the cytoplasm

Translation

• The mRNA is read at a ribosome in the cytoplasm, and the correct amino acids are brought to the ribosome by tRNA

Polypeptide chain

• The ribosome helps form bonds between the amino acids to create a polypeptide chain

Final processing

• The polypeptide chain may undergo additional processing to become a finished protein

• In the translation of DNA to mRNA: A becomes U, C becomes G, T becomes A, and G becomes C.

• If an anticodon sequence is GA, the codon sequence would be CU.

• There are 4 nucleotides in DNA: A, T, C, and G.

• In RNA, Uracil (U) replaces Thymine (T).

• DNA synthesis occurs during the S phase of interphase in cell division.

Cell Division

• The phases of mitosis are prophase, metaphase, anaphase, and telophase.
• Meiosis produces sex cells, 4 unique daughter cells with half the number of chromosomes as the parent cell.
• Mitosis produces body cells and 2 identical daughter cells with the same number of chromosomes as the parent cell.

This section covers cell organelles and the structure and function of the plasma membrane. It discusses the fluid mosaic model, membrane proteins (integral and peripheral), cholesterol, glycolipids, glycoproteins, and carbohydrates. Also covered are transport mechanisms, receptors, enzymes, and structural support provided by the plasma membrane.