Prophase I
Each chromosome appears in the condensed form with two chromatids. Homologous pairs of chromosomes associate with each other. The pairs cross over at chiasma. Metaphase I The spindle forms at the poles and the pairs of chromosomes line up on the equator. Anaphase I The centromeres don’t divide. One chromosome from each homologous pairs moves to opposite poles of the cell. The chromosome number is now half the original number. Telophase I The nuclear membrane re-forms and the cells begin to divide. Metaphase II New spindles are formed and the chromosomes line up on the equator. Anaphase II The centromeres divide and the chromatids move to opposite ends of the cell. Telophase II Nuclear envelopes re-form and four daughter cells are formed with only 23 unpaired chromosomes meaning they are haploid cells.
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Investigate how enzyme concentration affects the initial rate of an enzyme-controlled reaction11/10/2015 Introduction: The aim of the experiment is to investigate the effect of concentration of trypsin, using a suspension of casein as the substrate and to understand why this initial rate is important. I aim to track how the colour of milk changes as it is broken down by the protease enzyme trypsin. I aim to record how much light passes through the solution of intervals of 10 seconds. Method: First I diluted the 1% trypsin solution with distilled water to produce the solutions of 0.2%, 0.4%, 0.6% and 0.8%. I needed 10 cm3 of each concentration, so 2cm3 of trypsin was used to 8cm3 of distilled water for 0.2% and so on. I then placed 2 cm3 of 1% trypsin solution and 2 cm3 of distilled water into a cuvette. Use this as a reference cuvette to set the colorimeter absorbance to zero. Next I measured 2 cm3 of milk into a second cuvette and added 2 cm3 of trypsin. Quickly I placed the solution into the colorimeter and started the stopwatch. The colourimeter showed us the absorbency for us to record at 10 second intervals for 5 minutes, or until there is little change in absorbency. I the repeated this for each concentration with a new cuvette. This diagram below shows the principles behind the colourimeter. The graph below shows how the percentage of light transmitted increases as time increases. I can work out the general rate of reaction by dividing the final 100% by the time taken. This shows the average gradient giving the initial rates of enzyme activity. 0.2%-0.33 0.4%-0.71 0.6%-0.59 0.8%-1 As we can see from the two graphs, the general trend is that as the concentration of the enzyme increases the rate of enzyme activity on the substrate also increases. Therefore Increasing enzyme concentration will increase the rate of reaction, as more enzymes will be colliding with substrate molecules which shows that collision theory and the induced fit hypothesis work hand in hand.
First we prepared a slide with the culture using an inoculation loop that we preheated over the bunsen burner to kill any contaminant. We evenly spread the specimen on the slide to ensure that it did not clump. Next we fixed the culture to the slide by heating the slide over a bunsen burner. We made sure not to hold the slide over the flame too long or it will denature the specimen. A few drops of crystal violet stain was covered over the specimen and left to stand for 60 seconds. We then poured off the crystal violet stain and gently rinse the excess stain with distilled water. This step relates to what we learned in class because the crystal violet stain is allowed to bind to the large layer of peptidoglycan molecules of the Gram + bacteria if present. The washing away step will highlight which bacteria are Gram- because they lipopolysaccharide molecules attached to the "outer membrane" of the Gram - bacteria are unable to absorb the stain into its layers of peptidoglycan underneath. As a result the stain simply washes right off. Next we added a few drops of iodine solution and let it stand for another 60 seconds then rinsed the slide with distilled water. The objective of this step is to fix the crystal violet to the peptidoglycan molecules on the Gram + bacteria. After that we added a few drops of ethanol and let the solution trickle down off the slide until it had removed enough of the colour to drip off clear. Then immediately rinsed the slide off with distilled water after 5 seconds. We were careful not to pour too much ethanol or this will cause the Gram + bacterial cells (in addition to the Gram - bacteria), to lose all previous stains and the purpose of experiment will be defeated. Finally we added a few drops of basic counterstain safranin on the slide and let it sit for a final 60 seconds, then wash off the solution with distilled water. The objective of this step is to stain the thin under peptidoglycan layer of the Gram - bacteria a pink / red color so it is visible under the light microscope. Lactose is the main sugar found in milk. It is broken down during a hydrolysis reaction by an enzyme called lactase found in our body. All baby mammals are able to produce this enzyme however it is usually switched off during adolescence.
But, a mutation emerged around 7000 years ago which allowed adults to keep producing lactase. Now 35 per cent of people can digest milk as adults. Some people are still unable to produce lactase. In people who lack this enzyme, lactose passes into the colon where it feeds bacteria that generate gas and fluid, resulting in painful bloating, cramps and diarrhoea a condition known as lactose intolerance or malabsorption. This story relates to our work in class as it highlights how each enzyme is required for the breakdown of unique substrates. Lactase for example uses the induced fit hypothesis to breakdown lactose in its specialised active site to galactose and the more useful monosaccharide glucose. It also illustrates how people suffer when they lack the required enzyme as there is not other enzyme that can carry out this function. Reference: https://www.newscientist.com/article/dn27938-everything-you-need-to-know-about-lactose-intolerance/ In my first blog I will be discussing the properties of water and what makes it so special. This will help answer how water is essential for life on Earth and how it has enabled even the largest organism to flourish. In this blog we will also explore how the chemistry of water was discovered through time, and the secrets we are still attempting to unravel.
Water possesses many unique properties which we often don't consider to be important that are unlike many other molecules: The fact that water is a liquid at room temperature is the most important quality it holds. Because of its polar covalent bonding, (with hydrogen at delta positive and oxygen at two delta negative) strong hydrogen bonds form between molecules which makes the intermolecular force harder to break, increases its boiling point. This gives water a high specific heat capacity (heat needed to raise BP by 1 degrees centigrade) allowing stable conditions for habitats such as aquatic life to flourish in lakes and oceans. Water being in a liquid form also makes transportation within organisms far easier than a highly viscous or solid solution. It can also act as a medium for reactions to take place because it is in a liquid. The fact water is colourless is also a very important feature as it is responsible for the evolution of life beyond prokaryotes. Although we cant be certain, it is widely accepted that life on earth began approximately 3.6 billion years ago in our oceans. Life started as simple, single celled organisms known as prokaryotes A prokaryote is a single-celled organism that lacks a nucleus, mitochondria, or any other membrane-bound organelle. For life to evolve into the complex eukaryotes which are the cells that make up most modern day organisms it had to cross over through the vital stage of cyanobacteria which is a slightly more complex form of single celled organism that relies on photosynthesis. Therefore without colourless water the cyanobacteria would not be able to photosynthesise underwater thus halting life at prokaryotes. Another property that water has allowing life on Earth to flourish is its cohesion. Hydrogen atoms have single electrons which spend most of their time toward the oxygen atom, leaving their outsides positively charged. The oxygen atom has eight electrons, and often a majority of them are around on the side away from the hydrogen atoms, making this face of the atom negatively charged. Since opposite charges attract, the hydrogen atoms of one water molecule like to point toward the oxygen atoms of other molecules. This creates what's known as "hydrogen bonds" between molecules make water extraordinarily sticky. This is vital for life in plants as it allows plants to draw up water in long chains through the xylem. This allows plants to effectively siphon water against gravity and draw up water through the stalk for photosynthesis. Because of these "hydrogen bonds" water also holds a unique property when freezing. Usually when a liquid freezes, liquid particles move closer together and form strong bonds with one another. This allows more particles in the same area, the solid is denser than the liquid. However when water freezes the negative charges on the oxygen push the particles apart. This means that at 4 °C it becomes less dense as the water molecules begin forming hexagonal crystals of ice as the freezing point is reached. This is important for life as if ice did sink, it could cause entire lakes and other collections of water to freeze solidly, killing all life. Instead floating ice that's less dense forms an insulating layer over the lake preventing it from freezing. This allows life in lake to continue and not freeze. However if there was very little water none of these properties would be essential. Water is special because of is its abundance; water is the 2nd most common particle after hydrogen and makes up 70% of our planets surface area (300 million cubic miles). This allows ideal conditions for using water in photosynthesis and drinking, as well as ideal living conditions for aquatic life. The discovery of the chemistry of water started in 1766. An Englishman Henry Cavendish isolated a gas that he called "flammable air" because it burned readily. Priestley noted that when flammable air and common air were ignited with a spark in a closed vessel, a small amount of "dew" formed on the glass walls. When Cavendish repeated the experiment, he found that the dew was actually water. This is know as the oxyhydrogen effect Cavendish assumed that water was present in each of the two airs before ignition. In June 1783, Lavoisier reacted oxygen with inflammable air, obtaining "water in a very pure state." He correctly concluded that water was not an element but a compound of oxygen and flammable air, or hydrogen as it is now known. Despite the amount of research put into water scientists still do not know everything. Ice still holds many questions; the hexagonal lattice shapes in ice can be altered if pressure and the temperature of this ice is changed. Ice can rearrange itself into 15 known different ways showing how the properties can be changed without affecting the formula. However scientists are still unsure how this works and are also convinced there are still more formations of ice to be discovered. It is also not fully understood why ions act differently around water. When an ion comes into contact with water the structure of water is changed causing it to immerse itself around the ion. |