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/ |