Components of Biological Membranes.
Components of Biological Membranes Introduction. Biological membranes surround all living cells, and may also be found surrounding many of an eukaryotes organelles. The membrane is essential to the survival of a cell due to its diverse range of functions. There are general functions common to all membranes such as control of permeability, and then there are specialised functions that depend upon the cell type, such as conveyance of an action potential in neurones. However, despite the diversity of function, the structure of membranes is remarkably similar. All membranes are composed of lipid, protein and carbohydrate, but it is the ratio of these components that varies. For example the protein component may be as high as 80% in Erythrocytes, and as low as 18% in myelinated neurones. Alternately, the lipid component may be as high as 80% in myelinated neurones, and as low as 15% in skeletal muscle fibres. The initial model for membrane structure was proposed by Danielli and Davson in the late 1930s. They suggested that the plasma membrane consisted of a lipid bilayer coated on both sides by protein. In 1960, Michael Robertson proposed the Unit Membrane Hypothesis which suggests that all biological membranes -regardless of location- have a similar basic structure. This has been confirmed by research techniques. In the 1970s, Singer and Nicholson announced a modified version
Discuss how changes in control of the cell cycle contribute to cancer development Cancer is a multifarious disease, with a common feature that most tumours harbour one or more genetic mutations that allow them to advance outside their normal growth restr
Discuss how changes in control of the cell cycle contribute to cancer development Cancer is a multifarious disease, with a common feature that most tumours harbour one or more genetic mutations that allow them to advance outside their normal growth restraints. This proliferation is normally harnessed by the control of the cell division cycle, which in turn, is majorly regulated by the cyclin dependent kinases (Cdks) family of serine/threonine kinases and their regulatory partners, the cyclins (Errico, et al., 2009). In this essay, the roles of Cdks, cyclin complexes, regulatory proteins and other cell-cycle regulatory processes will be underlined, followed by an analysis of the genetic lesions in these regulators which may contribute to tumorigenesis. Fundamentally, cancer, or a neoplasm is a disease where cellular proliferation is no longer under normal growth control. The growth of this clone of cells exceeds, and is uncoordinated with that of normal surrounding tissues (NHS, 2009). Ultimately, this deregulation of growth and division of the cancer cells disrupts and interferes with the normal functioning of the body, either at its origin or through spreading to another location, eventually resulting in the potential death of the sufferer if left untreated. Other complex characteristics include the ability of the cancer cells to induce vascularisation of the tumour in
Macromolecular composition of a liver cell
Macromolecular Composition of the Liver cell Abstract A liver cell is to be homogenised and fractionated into a nuclei rich sediment and a nuclei free supernatant using centrifugation. After treatment with perchloric acid the samples are centrifuged producing supernatants containing glycogen, and these are decanted and stored. The sediments are washed, then treated with KOH and perchloric acid and centrifuged again. This supernatant contains ribonucleotides and it is also stored. The remaining precipitates are suspended in KOH and incubated to ensure it is fully dissolved. The addition of various reagents to each of the supernatants and suspended sediments will allow for an examination of the distribution of RNA, DNA, glycogen and protein, and for an explanation of why this is so. Introduction For supernatants to be produced for examination of this kind, the liver cells must be fractionated to allow specific organelles and molecules to be collected. This is done through homogenisation and differential centrifugation. During homogenisation citric acid is added and in put in a pre-cooled homogeniser; liver is easily broken up. It would be relatively much more difficult to homogenise a plant cell due to the presence of a cell wall, an outer layer that maintains cell shape and is made of cellulose, other polysaccharides and protein (Campbell and Reece, 2005). A centrifuge
The solubilisation and purification of an intrinsic membrane protein presents problems distinct from those encountered in purifying a conventional soluble protein. Discuss this statement.
The solubilisation and purification of an intrinsic membrane protein presents problems distinct from those encountered in purifying a conventional soluble protein. Discuss this statement. Word count: 1860 In order to answer the question, this essay will first describe how soluble proteins are purified. It will then describe the process of solubilising an integral membrane protein specifically, and demonstrate differences between the two processes. There are several methods for the purification of proteins in aqueous solution. Since these methods discriminate based on one characteristic that may be shared by several proteins, it is almost always necessary to use multiple methods to purify a protein from its cellular environment. First, the cell must be homogenised in order to make all the proteins within available. In theory, this presents a problem since proteins are mixed with proteases, and could be degraded. In practice vacuoles form spontaneously and quickly to mitigate this effect so it is not a problem that has to be contended with. After homogenisation, there are several chromatographic methods available to purify proteins completely. Size exclusion chromatography separates proteins based on molecular weight, as smaller proteins are retarded by the resin and so take longer to flow through. Ion exchange chromatography involves charged resin which binds charged amino
Ribosomes; Structure and function.
Ribosomes; Structure and function 9 April 2003 Carly Brooks Ribosomes are cytoplasmic organelles discovered in both prokaryotic and eukaryotic organisms. Found in great abundance up to 10,000 in bacterial cells and many times more in eukaryotic cells, they comprise of proteins and rRNA molecules known as subunits, to form a large ribosomal complex. Both eukaryotic and prokaryotic ribosomes in association with transfer RNA (tRNA), act as a site for mRNA translation, assembling a specific sequence of amino acids into polypeptide chains, once the mRNA joins the two component subunits (large and small) of the ribosome. The tRNA is covalently bonded to an individual amino acid and has a complimentary nucleotide sequence, an anticodon, to each mRNA codon which form base pairs, adding specificity to the selection of the corresponding amino acids. The mRNA is linked by hydrogen bonds to the tRNA and is held in proximity to the amino acid so that a peptide bond is formed, this process occurs again and each amino acid is polymerized into a growing peptide chain. Ribosomes exist in two distinct forms; free and bound and may be positioned in several locations throughout the cell depending on cell function. Free ribosomes can occur individually, a monosome, or in clusters called polyribosomes or polysomes and are found in the
The biochemical nature oflight detection and emission
The biochemical nature of light detection and emission In this essay I aim to describe the range of biochemical pathways and mechanisms used by living organisms both to detect and to emit light. I will discuss general principles employed, and illustrate the range of different biochemistry involved by the use of many specific examples. Light Detection I will discuss the mechanism and function of light detection by five groups of light detecting molecule. The biggest of these is the rhodopsin group of proteins, I will also look at the role of phytochromes, cryptochromes, flavoproteins and porphirins in light detection. Rhodopsins are found in a diverse array of organisms, all featuring a retinoid prosthetic group linked to a an apo-protein, opsin via a protonated schiff base linkage. Electrons from the schiff base lone pair occupy an extra orbital (the 'n orbital'), therefore electrons can undergo a n-p* transition as well as a p-p* transition. Retinal proteins were first discovered in 1876 by Bell, who observed a reddish pigment that bleaches on exposure to light, which he called visual purple. Most rhodopsins contain retinal as the prosthetic group, but some have one of the other chromophores as shown below. 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
How does Notch signalling mediate lateral inhibition? How is this mechanism thought to regulate timing in neurogenesis
Institute of Psychiatry MSc Neuroscience 2007 - 2008 FULL TIME STUDENT ESSAY Module 1: Essay Question No: 10 TITLE How does Notch signalling mediate lateral inhibition? How is this mechanism thought to regulate timing in neurogenesis? WORD COUNT: 2996 CANDIDATE NUMBER: K22563 PAGE NUMBER:15 How does Notch signalling mediate lateral inhibition? How is this mechanism thought to regulate timing in neurogenesis? In my essay I will be focusing on how Notch signals in the nervous system and how the ligand Delta mediates Notch signalling. In addition, I will also be explaining how various genes also play a role in lateral inhibition via Notch signalling. Furthermore I will explain how this mechanism regulates neurogenesis. Specification of cells at distinct times and places plays an important role for the production of cellular diversity in the vertebrate nervous system. Molecular signals that influence the generation of distinct cell types are spatially and temporally controlled. So therefore the neural pattern formation needs coordination of signals that provide temporal and spatial coordination. Lateral inhibition is one mechanism by which patterns of different cell types are produced and is a type of intercellular interaction by which a cell adopting the primary fate can inhibit its immediate neighbours from doing the same and therefore they adopt the secondary
Mitochondria and The Golgi Complex
Work Book Section II a(i) Mitochondria a(ii) The structure and shape of the shape in the diagram suggested to me that it was a mitochondria cell. The structure of the all round shape and also the inner walls to the mitochondria cell. b(i) Golgi Complex b(ii) and 1c A membrane bound compartment in the interior of a cell. This compartment is involved in modifying, sorting and packaging lipid, carbohydrate and protein molecules for secretion or for delivery to other organelles. www.lsdn.com/glance_glossary.shtml One of the organelles that is in both the animal and the plant cells is the golgi apparatus. In this organelle, the endoplasmic reticulum (ER) sends vesicles(The function of the vesicles are to mainly transport proteins and other cellular material between cells and organelles) to the Golgi complex where they fuse with the cell membrane. Their membrane, which has now added to the membrane of the sacs of the golgi, empties it's contents of it into the golgi sac. 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 d 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
SKIN CANCER Skin cancer is the most common of all the types of cancers (Skin Cancer). It is a disease where malignant, or cancerous cells can be found in some layer of the skin. The epidermis, or the top layer of the kin, has three kinds of cells: basal cells, squamous cells, and the melanocytes (Skin Cancer). The melanocytes produce melanin, which is pigment that gives the skin its colour. Sometimes clusters of melanocytes can form growths called moles. These moles can sometimes become cancerous. Skin cancer tumours are formed when these cells excessively divide. They are known as malignant tumours. The tumours are not skin cancer when they are designated as benign. The cancer cells in the malignant tumours can break away and spread throughout the body. This can occur by way of the blood stream of lymphatic system (Melanoma). Skin cancer is categorized into three types: basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. Basal cell carcinoma is, by far, the most common form of skin cancer (Skin Cancer). Luckily, it will never spread throughout the body. Basal cell skin cancer usually forms due to years and years of skin damage. Therefore, it is most often found on the sun-exposed areas of older adults. Such areas include the nose, face, back, and neck. Basal cell carcinoma is definitely curable with treatment. The second most common
Using Spectroscopy to Evaluate the Absorption of Light for Different Substances
Using Spectroscopy to Evaluate the Absorption of Light for Different Substances Erin Laura and Polina, Section 13 BIOL 130, Monday 7:00-9:50pm Rm B2 151 Performed on October 20th, 2008 Introduction The purpose of experiment one was to determine the concentration of the unknown solution by using spectroscopy and comparing that substance to substances of known concentrations. In experiment two, the purpose was to discover the regions of the visible light spectrum are absorbed by both samples of chlorophyll. The spectrophotometer was an exceptionally useful tool for this lab. Spectroscopy is valuable for identifying substances through absorption of light which is done by measuring substances and comparing them to other known substances. Specifically a spectrophotometer is a device that measures the absorption of radiation at a particular wavelength. This is done by a light bulb shining, refracting its light into one beam, which then passes through an exit slit, then through the test solution and to a detector. This detects the amount of light that passed through the substance and a readout shows the amount of light that was absorbed (Jones, A, et al, 2007). Beer's Law states that concentration of a substance is directly proportional to its amount of light absorption (Department of Biology, 2008). The number of molecules of the solute is related exponentially to the amount