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University Degree: Cell Biology

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  1. What is the concentration of the Cell Sap in a Potato?

    When the plant cells start to take up water by osmosis, they start to swell. They become turgid when they have a large amount of water stored in vacuole. They become hard due to the pressure increasing inside the cell as the vacuole is exerting turgor pressure, so that eventually the internal pressure of the cell is so high that no more water can enter the cell. The opposite of turgid is flaccid. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and as a result, they become flaccid as the cells are said to be plasmolysed.

    • Word count: 2583
  2. Plasma Membranes in Eukaryotic Organisms

    This 'channel' in the membrane can also be seen as a pore for what solutes, minerals and ions can potentially pass through. The principle of the model also says that molecules can move freely within the membrane, but the idea of the fluid "mosaic" is that it as been sectioned off into various parts and each part fulfils a certain function. The theory of the fluid mosaic model is that protein interaction can limit the movement of single molecules within the fluid mosaic model.

    • Word count: 3331
  3. Polymerase Chain Reaction

    The gel was run for approximately 1 1/2 hours at 240 volts, and then the gel was placed in an ethidium bromide solution for 10 minutes to help stain the DNA. Then the TA photographed it under a UV light. Results: After the gel electrophoresis procedure was complete, we were able to generate the PCR result The figure on the picture found in the appendix depicts the results that were obtained from the gel electrophoresis done for the PCR. The lanes were numbered from left to right as Cs (crime scene), 4, 3, 2, and 1.

    • Word count: 1030
  4. Mitochondria and The Golgi Complex

    Audesirk, Teresa; Audesirk, Gerald; "Fifth Edition Biology Life on Earth" Prentice-Hall; 1999 The Molecular Biology of The Cell. Second Edition. New York. Garland Publishing, Inc. 1989 1d Single-membrane structure. The thickness of structure C shows to be only a single membrane cell. Also the structure when compared to other similar looking cells on the diagram, such as structure D, looks less rigid and unstable. I believe structure D to be a double-membrane structure 2a Large molecular structure increases penetration rate 2b Small Number of Hydroxyl groups decrease the penetration rate 2c Low lipid solubility decreases penetration rate 2d The Hydrophilic nature increases penetration rate 3a 3b The cytoskeleton is a network of protein elements that extends through the cytoplasm in eucaryotic cells.

    • Word count: 939
  5. Describe the Mechanism of Peptide Bond Hydrolysis by Serine Proteases and discuss the specificity of these enzymes

    This is because for every pair of amino acids linked by a peptide bond there are six atoms that lie in the same plane. Therefore it is essential to use a proteclytic enzyme or a protease to promote peptide bond cleavage. Serine proteases are used in the hydrolysis of peptide bonds and include chymotrypsin, elastase and trypsin. Proteases catalyse peptide bonds in polypeptides and proteins and according to Mathews et al (2000) serine proteases are distinct because they all have a serine residue that plays a critical role in the catalytic process.

    • Word count: 675
  6. Most cells are very small. What physical and metabolic constraints limit cell size? What problems would an enormous cell encounter? What adaptations might help a very large cell survive?

    Other cells, like neurons, have axonal extensions that can travel a few meters long in some organisms. For the most part, however, cells are very small. So, what are the constraints that limit the cell to its small physical size? What types of problems would a cell that diverges from these constraints encounter? Finally, how do those cells that are very large, compared to the majority of cells, adapt to their larger size? These are the questions that will be explored. Cells are small. The cell is the smallest unit of life; it is a functional and structural unit, enclosed by a membrane, that can metabolize and self-replicate (Tortora).

    • Word count: 925
  7. Discuss the roles of the following in protein synthesis in mammalian cells:- the large and small subunits of the ribosome, mRNA, tRNA, release factors, SRP

    the process of translation needs to be explained in more detail. The pathway of translation is divided into three main steps; initiation, elongation and termination. The mRNA has a protein coding region which is composed of a non-overlapping string of codons called an open reading frame. At the beginning of the open reading frame is a start codon and at the end there is a stop codon. In eukaryotes the start codon is always 5'-AUG-3' and specifies the first amino acid and defines the reading frame for the rest of the codons.

    • Word count: 1023
  8. Medico-legal Problems of establishing the Time of Death

    Examples include the amount and distribution of rigor mortis, the change in body temperature, and the degree of putrefaction of the body. * The concurrence method. Comparing the occurrence of events which took place at known times with the time of occurrence of the event under investigation, i.e. death. For example, a wrist watch stopped by a blow during an assault, the extent of digestion of the last known meal. Various postmortem changes which may give the forensic scientist an approximate evaluation of the possible time of death Many physico-chemical changes begin to take place in the body immediately or shortly after death and progress in a fairly orderly fashion until the body disintegrates.

    • Word count: 4675
  9. Complement Practical

    Another common pathway is the alternative pathway. This is of major importance in host defence against bacterial infection as it is activated by invading microorganisms and does not require antibody, therefore this pathway is antibody independent. It provides an amplification loop for the classical pathway of complement activation as one of the activated components of the classical pathway can also initiate the alternative pathway. The third and final pathway is the lectin-mediated pathway. This pathway is activated by the binding of a mannose-binding protein present in blood plasma to mannose-containing carbohydrates on the surface of bacteria or viruses.

    • Word count: 2329
  10. Biological Membranes

    Introduction - Cell membranes and the misconception. The complexity. 2) How the structure of the membrane was thought of to be as before and after. 3) How the membrane is examined. How the cell membrane is formed and its importance and functions. 4) How substances and water pass in and out of cell membranes. 5) Environmental variables affecting how the membrane works. 6) Organelles having suitable membranes. 7) Conclusion - How important the membrane is to the whole cell and even the smallest parts of it inside.

    • Word count: 1586
  11. What are the roles of N- and O-glycans? Use examples to illustrate your answer.

    Misfolded or unassembled subunits are reglucosylated by a glucosyltransferase. This allows them to rebind Clx and enter a cyclical pathway until they achieve their correctly folded structure and are released. Glycosylation and ER associated degradation: If a protein remains in a misfolded state, it is eventually targeted for retrograde transport and can be eliminated directly in a process known as ER associated degradation (ERAD). Once again, it is the glycosylation state of the misfolded protein that will target it for degradation.

    • Word count: 1654
  12. Effect of temperature on membrane permeability

    This shows that the plasma membrane must be denatured. In the cells of a beetroot plant, a substance called anthocyanin is contained within the plasma membrane. It is anthocyanin which gives the beetroot its characteristic blue/purple colour. If a cell is damaged in a beetroot plant and the membrane is broken, the anthocyanin 'bleeds' from the cells like a dye. In this experiment the temperature denatures the membrane causing it to bleed the dye out of the cell. Although the above values are a range of values obtained from the investigation, it does not actually show close the figures are to one another.

    • Word count: 2306
  13. Explain how the action potential is generated and is transmitted along the axon. Include information about the effect of myelin on the speed of transmission.

    The axon, connected to the soma by the axon hillock, is composed of myelin and nodes of Ranvier, through which the impulses pass. Finally, the impulses reach the axon terminal, and through the synapse, get transmitted to the next neurone. The neurone's resting membrane potential represents its stability, when not stimulated or firing. The cell's charge is -70 mV, the cell is negatively charged whereas the outside is less. The membrane controlling ions moving in and out the cell through ion channels using ion pumps (sucking in or extruding the ions)

    • Word count: 726
  14. An experiment to investigate the change in cell potential with concentration.

    of silver nitrate solutions, by diluting each solution accordingly and replacing the salt bridge each time. Calculations: (1) log([Ag+ (aq)]/ M - see table (2) Electrode potential of the silver half cell for each concentration: * 0.1 M silver nitrate solution: Taking E? of copper half cell to be actual value of: + 0.34 V: E? cell = E?positive - E?negative (or E rgt -E lft) + 0.27 = e - (+ 0.34) ? E? of silver electrode = + 0.61 V * 0.01 M silver nitrate solution: Taking E?

    • Word count: 1713
  15. Components of Biological Membranes.

    This suggested that the lipid bilayer supplies the backbone of the membrane, and proteins associated with the membrane are not fixed in regular positions. This model has yet to be disproved and will therefore be the basis of this essay. The lipid component. Lipid and protein are the two predominant components of the biological membrane. There are a variety of lipids found in membranes, the majority of which are phospholipids. The phosphate head of a lipid molecule is hydrophilic, while the long fatty acid tails are hydrophobic.

    • Word count: 2492
  16. Animal Physiology - The Nervous System - To understand Resting and Action Potential

    An unexcited neurone is at its resting state - refer to figures 21,22 booklet 1. Figure 22 shows that the invertebrates may have large neurones as in the giant squid, they are good model systems. NB: The electrical currents of membrane potentials are formed from the net flux of charged particles that move across the membrane. Resting Membrane Potentials (RMP) The RMP arises as a small build up of negative charges forming just inside the neurone, there is also an EQUAL build up of positive charges on the outside of the neurone. The RMP is measured in millivolts (mV)

    • Word count: 711
  17. Ribosomes; Structure and function.

    Found in greater concentrations in cells that retain proteins, they manufacture proteins that are either held in solution in the cytoplasm or those used in the formation of cytoplasmic structural and motile elements. Bound ribosomes are situated on the outside of the endoplasmic reticulum1 forming rough ER (RER) and a large number are seen in cells that make proteins to be secreted out of the cell, such as pancreatic cells producing digestive proteins. The bound ribosomes form proteins that may be utilised for the cell membrane, packaged into vesicles for storage, as well as those required for export from the cell.

    • Word count: 1383
  18. The biochemical nature oflight detection and emission

    For example freshwater fish have a rhodopsin containing 3,4-didehydroretinal, which has a red shifted UV absorption band. The opsins found in all organisms show strong homology for one another. All rhodopsins seem to be involved in light detection, with the notable exception of bacteriorhodopsin, which pumps protons using energy from light photons in order to generate ATP in anaerobic conditions i.e. is not a light sensing protein. Halobacteria do however have two sensory rhodopsins. Sensory rhodopsin I (archaeorhodopsin) has all trans retinal as the prosthetic group in its native state. It is photoisomerised by green-orange light (lmax = 587 nm)

    • Word count: 1750
  19. Investigation to determine the water potential of potato cells.

    The temperature will therefore be regulated to room temperature. The size of the potato chip will affect the final mass, if I use a thin chip and a fat chip the average mass change per gram will be different because if they are placed in distilled water then the thin chip will become turgid long before the fat chip does because the water has to diffuse from the outside of the chip to the centre of the chip. The volume of the solution used will affect the concentration of the solution so I must keep the concentration of the solution constant, it will be kept at 20cm3.

    • Word count: 2999
  20. The Cytoskeleton - Its Functions and Structure

    it was stated as the cytoskeleton consisting of only three types of fibre listed above but I have found on the internet that there was a fourth type of protein fibre involved. These fibres are known as microtrabeculae. I think the obvious reason for this is that 'Molecular Biology of the Cell' was published in 1993 and information on the internet is updated regularly therefore this fourth type of protein fibre must have been discovered recently. This backs up my statement that there is much ongoing research involving the cytoskeleton.

    • Word count: 2577
  21. Compare and Contrast Vertebrate and Invertebrate Vision

    Each ommatidium samples a different part of the visual field through a separate lens. In a simple eye, each receptor cell samples part of the field through a lens shared by all receptor cells. In compound eyes, each ommatidium samples an angular cone-shaped portion of the environment, taking in about 2-3� of the visual field. In contrast, each receptor of a simple eye may sample as little as 0.2� of the visual field. In addition, the simple eye, inverts the image that falls on the retina.

    • Word count: 2309
  22. The structure and function of membranes, with reference to membrane constituents and different types of membrane.

    All these molecules are amphipathic and therefore they have a polar 'head' and a hydrophobic 'tail'. They are based on the glycerol molecule, a triol, which uses one of its slightly polarised -OH groups to bind to a phosphate group. Then, two fatty acid chains are attached to the other two hydroxyl groups on the glycerol. The fatty acid chains consist of a hydrocarbon chain of 16-20 carbons although the one bound to the middle hydroxyl group often has a cis double bond which makes it bend slightly away from the other chain.

    • Word count: 2107
  23. Osmosis - diffusion - cemi permeable membrane

    * Cork borer (1) * A knife * Electric balance * 2 molar sucrose solution (1): CAMBRIDGE ADVANCED SCIENCES. BIOLOGY 1 PUBLISHED BY THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE. Page 55-56. The following diagram shows the motion of water particles from an area of high concentration of water to an area of low concentration: Water molecule Sugar molecule Partially Permeable Membrane I will draw a graph of the result (sucrose concentration against change in mass of potato cylinders). The point where the line meets the x-axis (sucrose concentration) is the water potential of the potato. The Pilot: this is the experiment that I will carry out to get a general idea of the area in the graph that I will focus on to find the exact value of the water potential of the potato.

    • Word count: 1616
  24. Discuss the stereochemistry of monosaccharides, nucleotides and amino acids

    [f]Enantiomers are categorised into D and L forms according to their similarities with the corresponding forms of glyceraldehyde, the two enantiomers of which are shown below: Structure glyceraldehyde enantiomers [g] http://themedicalbiochemistrypage.org/carbohydrates.php It is clear that the D enantiomer has the hydroxyl group on the right hand side of the chiral carbon, whereas the L form has it on the left. The D and L forms of monosaccharides are therefore mirror images of each other. In biological systems, sugars are almost always in the D form ? for example the high specificity of enzymes means that they only recognise the D form and so will only catalyse polypeptide synthesis/ hydrolysis when D enantiomers are used.

    • Word count: 1728
  25. Describe the structural compartmentation of mammalian cells and the differing functions of these compartments

    Figure 1, a cartoon picture of a typical eukaryotic cell depicting all the compartments[2] Plasma membrane contains the content of the cell. It holds the structural integrity of the cell but at the same time it is also very flexible to allow for movement. The membrane has three other important functions: it has ability to identity molecules and other cells on the surface; it has a selective barrier which allows the membrane to control the exchange of molecules in and out of the cell and it can communicate between cells with its receptor on the surface.[5] The plasma membrane is composed of a bilayer of phospholipids.

    • Word count: 1653

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