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AS and A Level: Molecules & Cells

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  1. The importance of cell membranes.

    Membranes are made of phospholipids and proteins, as well as some carbohydrates. More specifically the make up of a membrane is a phospholipid bilayer; consisting of hydrophobic and hydrophilic regions. The structure is determined by the properties of the polar lipids. The hydrophilic heads of the phospholipid are in contact with the extracellular and intracellular fluid (intracellular fluid being the solution between cells), whilst the water hating hydrophobic tails lie in the centre of the bilayer. Inside of the membrane are peripheral and integral proteins, glycoproteins, cholesterol and glycolipids. Glycoproteins are formed when carbohydrates are attached to the proteins in the membrane, and glycolipids form when the carbohydrates are attached to the phospholipids.

    • Word count: 625
  2. How does temperature affect the rate at which amylase breaks down starch?

    Amylase is an enzyme found in saliva that helps to break down starch. Starch is a reserve form of glucose that is produced when there is excess photosynthesis taken place in plants, and when it is broken down it tastes like glucose. This is why when you chew a piece of bread it tastes sweet after a few seconds: the amylase has broken down the starch into maltose. From the preliminary tests I found it to be most informative to use 20ml of starch with 10ml of amylase.

    • Word count: 542
  3. Investigate the effect of temperature on the action of rennin and milk.

    I think below this temperature the rennin will work slower this is because the enzyme is a protein and proteins need a high temperature to work. I think that above 50 the rennin will denature this is because the rennin is a protein and proteins can not work at a temperature that is too high. (50 being too high) This is backed up by a simulation I did on the computer to show an experiment investigating the effect of temperature on amylase.

    • Word count: 829
  4. Explain how Monoclonal Antibodies can be produced and how they can be used to target specific cells and chemicals.

    For certain laboratory research it is useful to have a pure preparation of antibodies with single specificity. These types of antibody are called 'monoclonal antibodies'. Monoclonal antibodies do not differ structurally from other natural antibodies. The property that makes monoclonal antibodies unique is that all the molecules in any single preparation are identical. Their reaction with any antigen is also exactly the same each time. It is this constancy in preparation and in their effect that makes them so useful.

    • Word count: 849
  5. Comparison of a plant and animal cell.

    To help the nucleus function properly, both the animal and plant cell have a cell membrane which covers the whole of the outside of the cell, and the nucleus tells it what to do. The membrane also allows cell identification, and helps it to join itself to other things. To keep the shape of the cell membrane, animal and plant cells both have cytoplasm, which is made up of 90% water. This is what all the other organelles are held in, but which are free to move around in.

    • Word count: 788
  6. I'm aiming to work out the temperature which stops catalysts in the enzymes breaking down substances.

    Protease which converts proteins into amino acids. There are two tests which you can perform to test for enzymes. These are the Benedicts' test which tests for sugars and the Iodine test which tests for starch. Enzymes are biological catalysts which control chemical reactions. Enzymes are shaped like proteins. The shape is held together by weak hydrogen bonds which can be disrupted by heat and pH specifics (breakdowns in different pHs). They also have a specific 'Active Site.' Heat, the surface area and the concentration can affect the rate of the reaction. The reaction will increase if the temperature is increased because the heat energy gives the particles more energy, which means that there will be more movement in the particles.

    • Word count: 702
  7. In And Out Of Cells - Membrane Structure & Passive Trasport.

    These particles are also randomly distributed to produce a patchwork, mosaic-like effect. In this model, the membrane is comprised of a phospholipid layer and protein molecules, some of which have carbohydrate chains attached to them. The phospholipid layer has a hydrophilic phosphorus head and a hydrophobic lipid tail. The phosphorus head is on the outside with the lipid tails facing in towards each other. Water - soluble molecules are unable to pass through the membrane due to the hydrophobic nature of the lipids and their polar charges. As this means many essential molecules are unable to pass directly through the phospholipid layer, protein molecules present in the structure of the cell membrane enable such molecule to pass through.

    • Word count: 569
  8. What Factors Affect How Fast Enzymes Work?

    Other factors like the pH and the concentration of the enzyme will affect the rate of reaction too. Amylase molecules have a very precise shape. The active site is exactly the right size and shape for the starch molecules to fit into. When a starch molecule 'slots' into the active site, the enzyme pulls the amylase molecule out of shape and making it split into smaller molecules. High temperatures make enzymes inactive: this is because they are proteins, which are damaged by temperatures above about 40�c. Most enzymes work best at a pH of about seven. This is because they are damaged by very acidic or very alkaline conditions.

    • Word count: 908
  9. The effect of enzyme concentration on the activity of amylase.

    The variables that have to be kept constant throughout all of the experiments are Temperature, surface area and pH. Variables: These factors could affect the rate of reaction on an enzyme: * pH * Concentration * Temperature * Surface Area pH - Enzymes function at different pH values. In neutral conditions the amount of oxygen gas given of in an enzyme-catalysed reaction will increase. Concentration - In concentrated solution there are more collisions between each particle, so the reaction occurs more quickly.

    • Word count: 730
  10. The Effect of Substrate Concentration on the Rate of Decomposition of Immobilised Liver Catalase.

    Altering the concentration of H2O2 will affect the rate at which the decomposition takes place and therefore the amount of O2 produced. The concentrations that I will be using are: 1. 10% 2. 20% 3. 30% 4. 40% I am going to be using a 10ml sample of H2O2 soln in each experiment ? 1ml of hydrogen peroxide soln = 10% concn 9ml = 90% concn APPARATUS: * 2 Boiling tubes, 10ml Measuring cylinder, 2x100cm3 Beaker, Delivery tube, test tube rack, syringe, bottle of distilled water, sieve, 50cm3 beaker, stopwatch.

    • Word count: 969
  11. The Application Of Enzymes In Industry And Medicine.

    Also in biological detergents lipase and amylase are included. Lipases work on stains resulting from fatty products, such as oils and fats. Amylases work on starchy food deposits. In the more recently developed washing powders, which enhance colours and reduce bobbling, cellulases are one of the types of enzyme included as well as proteases, lipases and amylases. Cellulases are thought to remove detached cellulose fibrils, which cause a dulling of the colour as dirt is trapped on the rough surface of the fabric. (2) Enzymes are very important in products developed for the pre-soaking or spot application on to laundry.

    • Word count: 995
  12. Haemoglobin is the oxygen carrying pigment found in red blood cells; it is a globular protein, made up of 4 polypeptide chains.

    The outward pointing hydrophilic R groups on the surface of the molecule are important in maintaining its solubility. Each polypeptide chain contains a haem group. A group like this, which is an important, permanent, part of a protein molecule but is not made of amino acids, is called a prosthetic group. Each haem group contains an iron ion, Fe2+. One oxygen molecule 02 can bond with each iron ion.

    • Word count: 483
  13. The experiment we are testing is to see how the surroundings of the amylase and starch affect the rate of reaction and how starch changes amylase into simple sugars.

    In this experiment we will look for starch and see if sugars are present at different temperatures. Prediction: I predict that the enzyme will only work at a specific temperature. The results therefore will not show strongly until we get the right temperature. If the temperature is not right then the enzyme wont form and will be denatured. This happens when the heat starts too destroy the enzymes structure and form. The structure and form are crucial to the enzyme working that if these are not right then the enzymes will become less effective. So I predict that when the temperature increases the starch to be digested will decrease and will be faster to digest.

    • Word count: 815
  14. Mitosis is the process whereby cells divide to form 2 daughter cells that have the same number and quantity of chromosomes as the original, parent, cell and therefore producing genetically identical offspring.

    and growing in size and overall preparing for the next division Interphase can be categorized into several stages, gap 0, gap 1, s phase (synthesis), gap 2 once these stages are complete mitosis follows. The cell cycle: highlighting the stages of interphase and mitosis In gap 0 the cell may be in a temporary resting stage or perhaps has reached the end of its development and may stop dividing. For example this can occur in neuron cells. Gap 1 is where the cells begin preparation for the mitotic stage.

    • Word count: 744
  15. To see if temperature makes a difference to the time taken for starch to be broken up and turned into glucose by amylase.

    * They are sensitive to pH * They can be used over and over again Working best at a neutral pH value and at the bodies temperature, a rise above 50 degrees celsius changes the shape of an enzyme and they can no longer work. In my experiment Amylase is the enzyme, which is made in the salivary gland and released in the mouth. The starch is the food which the amylase will act on, this is called the substrate.

    • Word count: 830
  16. The Applications of Enzymes in Industry and Medicine.

    These enzymes only need a low temperature of around 50�C, and this means a saving of energy, as less electricity is used by the appliance but the difficult stains are still removed. In the dairy industry, enzymes are used to remove lactose from milk as some people are allergic to lactose. The enzyme lactase is added to the milk and hydrolises the lactose to glucose and galactose. Enzymes are also used to assist the extraction of fruit juices from fruits such as oranges and apples.

    • Word count: 977
  17. The Structure and Funtion of the Cell Membrane

    The cell or plasma memebrane are found in all living cells and carry out many of the cells functions. Membranes are extremely small and thin, so to examine them you need to use an electron microscope. Under the electron microscope they look like solid structures, but they actually move constantly, joining with other membranes. By using the electron microscope we can deduce that the membrane has three layers, two dark layers which are protein with a light layer in the middle which is the bilayer.

    • Word count: 867
  18. To find out how temperature affects the breakdown of starch by the enzyme amylase.

    At each time interval of 2 minutes take the dropper take a sample of solution and place the sample in the droplet tray. If the solution is blue/black there is still starch present. When it turns brown there is no longer any starch. When the solution is brown stop the timer and record the result. Repeat the experiment at 30, 40 and 50 degrees. I will have to be careful to keep my experiment fair.

    • Word count: 504
  19. A metabolic pathway in yeast using immobilisation

    binds to the active site of the enzyme (free yeast). The active site is an area of an enzyme, which the substrate fits in order to catalyse a reaction to which carbon dioxide and alcohol is produced. Immobilised enzymes are enzymes bounded immovably to a surface and not allowed to dissolve in a solution. Also looking at my graph there is a pattern, this is that as the carbon dioxide increases with time the rate of reaction increases for the beads. The beads are immobilised enzymes. The rate of reaction increases because the enzyme (immobilised enzymes)

    • Word count: 639
  20. Properties of Hydrocarbons - To find out how the flammability and thickness of oil products changes with boiling point.

    The slide itself will be a literal slide. With this in place we then get the oil in question [5 used in this experiment] we then very carefully release one drop of oil and begin timing it. It will then slide down the slide and once it hits the heat proof mat we then stop the stop watch, and record the time, after doing this for the first oil, we need to thorooughly wash and dry the slide and repeat it for the other 4 oils.

    • Word count: 697
  21. The role of proteins

    The structure of a protein is very important in enzymes as the tertiary structure of an enzyme gives it its active site. The active site is where the substrate binds to in a reaction. If the active site were a different shape, the substrate would not fit in it so the enzyme would not catalyse the reaction. The enzyme reduces the amount of activation energy that is needed for a reaction to take place so that rate of reaction increases.

    • Word count: 919
  22. The Functions of Cell Membrane

    The phospholipids are fluid and move about rapidly by diffusion in their own layer, thus affecting the fluidity and permeability of the membrane. The protein molecules form an irregular arrangement and float about in the fluid phospholipid bilayer forming a fluid mosaic pattern. Proteins which occur on the surface of the phospholipid layer are called extrinsic/peripheral proteins; those which extend into it are called intrinsic/integral proteins and some extend completely across the layer are known as transmembrane proteins. The proteins provide structural support for the membrane and assist the active transport of materials across the membrane.

    • Word count: 873
  23. Investigation of the effect of temperature on the enzyme controlled reaction

    These two reasons indicate that in principle, increasing the temperature will increase the rate of the catalyzing reaction. Safety a.) Goggles essential to protect eyes & avoid contact with skin - Iodine solution id harmful and corrosive on skin and eyes. All enzymes are potential allergens. b.) Take care with Bunsen burner flame (use blue flame when heating and yellow /orange at other times) Apparatus 2 x Goggles/ test tube rack/ 10 x test tubes/ 2 x 2ml syringes/ Marker pen/ Iodine solution in dropper bottle (full)/ stopclock/ 5 x spotting tiles/ 5 x thermometer/ 4 x glass rod/ tissue/5 x250 ml beakers Access to Starch suspension (1.0%)/ Amylase (0.5)

    • Word count: 664
  24. To plan an investigation into the effect of substrate concentration on the activity of the enzyme catalase.

    Holds water and upside down measuring cylinder for viewing oxygen bubbles Conical flask - Where the yeast solution and substrate shall be mixed A cork with one capillary tube coming out of it - To attach the flask to the water tank so the oxygen can pass through Stopwatch - To measure length of time it takes for oxygen to stop Diagram Plan We shall be changing the concentration of our substrate, the hydrogen peroxide to get the results for our experiment.

    • Word count: 973
  25. Control of internal environment of living organisms.

    This regulation is called homeostasis (staying the same). Most of the body's homeostatic systems rely on negative feedback systems to resist change. In these systems there needs to be a detector which can measure the value that needs to be controlled.

    • Word count: 406

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