Cellular Homeostasis as complex chemicals reactions Biology 11 G.Burgess 2007

Eukaryotic cells Review Eukaryotic cells all have membrane bound organelles Phospholipid bilayer separates the cell from the fluids in its surrounding environment. This helps prevent outside chemicals from interfering with the chemical reactions happening inside the cell. Organelles are separated from fluids of the cytoplasm by lipid layers as well. This helps prevent chemicals, in the cytoplasm, from interfering with the chemical reactions happening inside the organelle. All membranes have proteins that enable water soluble materials to enter the cell and its organelles. Fat soluble materials are able to enter the cell through diffusion.

Cell processes Photosynthesis: series of chemical reactions which change solar energy to chemical energy Cellular respiration: series of chemical reactions which transfer stored chemical energy to useable molecular energy Absorption: either the moving of lipid soluble materials across a cell membrane or a series of reactions enabling water soluble materials to cross the cell membrane Reproduction: series of reactions that duplicate cellular contents and divides the contents into daughter cells

Cell Organelles and Functions Golgi body: package and transport macromolecules through the cell. macromolecules: large chemical compounds, usually lipids of proteins: ie. Sebum, hormones, hydrolytic enzymes, digestive compounds, etc… Mitochondria: performs cellular respiration for the production of ATP Vesicles: transport and store macromolecules, many are made by the Golgi body Nucleus: double membrane bound organelle, contain the DNA and is the site for formation of mRNA for protein production Chloroplast: performs photosynthesis for converting of solar energy to chemical energy Lysosome: vesicle containing hydrolytic enzymes for digestion of macromolecules and apoptosis (cell death)

Cell Organelles and Functions continued… Ribosome: translates mRNA codes to protein strands for making hormones, enzymes, transport proteins, etc. Endoplasmic reticulum: network of tubes that separate chemical reactions occurring in the cytoplasm of the cell. It also is used to transport materials throughout the cell. Two types: rough (with ribosomes) and smooth (without ribosomes) Vacuole: organelle that stores food or metabolic waste products. Materials are brought into the cell through endocytosis and expelled out of the cell through excytosis. Plastids: double membrane bound organelles that contain sets of inner membranes. ie. chloroplast (photosynthesis), leucoplast (store starch), chromoplast (colour)

Cell Membrane Keeps the cell separate from the external environment and regulates materials that are able to enter and leave the cell. Fluid mosaic model: Composed of lipids held together by cholesterols, and proteins Lipids: act as barrier to water Cholesterols: add strength to lipid membrane Proteins: enable ions and water soluble materials to enter the cell, give the cell identity and may act as attachment sites for other cells or macromolecules.

Carbohydrates Forms all sugars and starches in plants, animal form = glycogen Component of simple sugars (glucose, fructose, galactose); C 6 H 12 O 6 composed of C,H, and O. ( ratio of 2H to 1O ) Primary source of stored molecular energy. End result of Photosynthesis (glucose) 1 glucose molecule = monosaccharide Two glucose molecules form a disaccharide. More than two sugar molecules joined make a polysaccharide.

Lipids Primary component in fats, oils and waxes Composed of C, H and O in no particular ratio. Made from glycerol and fatty acids (glycerides) 1 fatty acid = monoglyceride 3 fatty acids = triglyceride Store excess energy and used in the building of membranes. Saturated fat: fats that contain the maximum number of hydrogen atoms and are all single bonds Unsaturated fat: fats that have some double bonds between carbons and do not contain the maximum number of hydrogen atoms. Trans-fat: an unsaturated fat where the hydrogen atoms on either side of a double bond are on the same side.

Proteins Found as hormones, enzymes, antibodies, transport molecules and structural components of cells, other than cell membrane. composed of C, H, O and N a single protein may be formed from 100’s of amino acids two amino acids make a dipeptide (more make up a polypeptide) DNA and hormones are examples of polypeptides. The type of polypeptide formed depends on the number and sequence of the amino acids that make it. (there are 20 different amino acid groups). DNA and hormones are examples of polypeptides. The type of polypeptide formed depends on the number and sequence of the amino acids that make it.(there are 20 different amino acid groups).

Digestion and Synthesis of organic molecules Digestion refers to the breakdown of organic molecules into smaller/ simpler pieces. Synthesis refers to the formation or joining of simple organic pieces into larger more complex ones.

Digestion and Synthesis of organic molecules (continued) These processes are completed by condensation reactions and hydrolysis reactions. Condensation reaction: dehydration reactions occur when a hydroxyl is removed from one molecule and a hydronium is removed from another as the two molecules form a larger molecule. The combining of hydroxyl and hydronium forms water Hydrolysis: water is added to a reaction separating the hydronium and hydroxyl forming two smaller molecules. **Hydroxyl and hydronium groups serve to complete the molecular charges of the smaller molecules.

Condensation Reaction C 6 H 12 O 6 + C 6 H 12 O 6  C 12 H 22 O 11 + H 2 O Hydrolysis Reaction C 12 H 22 O 11 + H 2 O  C 6 H 12 O 6 + C 6 H 12 O 6 The body uses these reactions to form needed structural and chemical components.

Transport Mechanisms Materials need to be transported through out an organism or cell. Hemoglobin is an example of a transport molecule. It transports oxygen from the lungs to tissues in the body. Cells use transport molecules to allow materials to cross through the cell membrane. Either by passive or active transport.

Passive transport Molecules enter a cell without the need for ATP. Always from area of high concentration to area of low concentration 1. Diffusion: transport of lipid soluble materials across the cell membrane (ie. Vitamin A, K, alcohols, some metal compounds) 2. Facilitated transport: transport of water soluble materials with the help of transport proteins.

Diffusion The passing of materials from the fluid environment across the cell membrane to the cytoplasm Does not require ATP Materials cross the membrane with out the need of transport proteins

Facilitated Transport Passive transport that moves water soluble materials across the cell membrane ie. water molecules, glucose, cations, and anions Channel Proteins: form a hole through which materials may pass. Carrier proteins: capture molecules and ions, change shape and release materials into cytoplasm Gate proteins: open when signal molecule attaches ‘opening the gate’ to allow materials to pass into the cytoplasm.

Channel Protein

Carrier Protein

Gate Protein

Why transport Proteins? Enable the cell to maintain and regain needed chemical components for metabolism and cell function. Help cell to maintain concentrations of chemicals and water To get rid of excess materials without interfering with continual cell processes.

Cellular Homeostasis and water concentrations Three basic types of cellular environments; 1. Isotonic solutions: these solutions have the same or similar amounts of dissolved materials as the cytoplasm of a cell 2. Hypotonic solutions: have a greater concentration of water than what is present in the cell 3. Hypertonic solutions: have greater amounts of dissolved materials than what is present inside the cell. Each of the solutions describe have an effect on the cell’s ability to survive.

Cellular Homeostasis and water concentrations Isotonic Solutions: do not have an effect on a cell, as they mimic the cell’s inner solution. Ie. saline solution for eyes. Hypotonic Solutions: will cause a cell to enlarge or break. Since the concentration of water is greater outside the cell, the water will flow into the cell until equilibrium is found. Hypertonic Solutions: will cause a cell to shrink or collapse. Since the environment has a greater concentration of dissolved materials, water from the cell will move to the environment until the environment has the same concentration of water as the cell.

Active Transport Proteins These proteins, called pumps, move molecules and ions against concentration gradients. They move materials from areas of low concentration to high concentration. To do this they require ATP. The Na-K pump (sodium potassium pump) is an example of an active transport protein.

Active Transport Pump

Links of interest Robert Horvitz's Work on Cell Death, Horvitz, B. and M.Hengartner, Gene accessed Feb.2,