Following my attendance at the 2010 Medlink conference I have recently been working on a research paper based on the applications of nanotechnology in medicine. Once my paper is complete I shall share some of my work on here and list some of my ideas.
Nomenclature
I’m not feeling too great today so I’ll keep this post short but sweet. Today we started the topic of nomenclature, that is the naming of substances, based on their functional group. We also did a bit about drawing the molecules, their isomers, side chains and their functional groups.
This is the basic table we drew up and you should learn:
Filed under Chemistry
Alkanes
Okay so this is a bit of a jump from the last topic I did in my Chemistry section, but a lot of the stuff in chemistry is quite hard to take notes on. The alkanes are covered in the introduction to organic chemistry and are a homologous series of the hydrocarbons. A homologous series is a group of hydrocarbons which each has the same functional group, and they can be divided further depending on the number of carbon atoms they contain.
Fractional Distilation
This is the separating of hydrocarbons in crude oil by heating it and gradually cooling it down in factions.
The crude oil is first vaporised by heating and passed into the fractionating column, which is hotter at the bottom than the top. The vapour moves up through the column through a series of bubble caps. When the temperature reaches a point lower than a hydrocarbon’s boiling point, then it cools and condensed into a liquid. The liquid fractions are than siphoned off into storage containers. Shorter chained hydrocarbons have lower boiling points and as such condense near the top of the column, where as long chained hydrocarbons with high boiling points condense closer to the bottom. The residue which collects as the bottom of the column is known as bitumen and is used for making tar for surfacing roads.
Boiling points of alkanes
As the chain length of hydrocarbons increases, the boiling point increases because they are more van der Waals’ forces between the molecules as there are more points of contact. It takes more energy, and therefore a higher temperature, to overcome these forces and separate the molecules.
When molecules are branched, they will have a lower boiling point than their unbranched isomer. This is because there are less points of contact between branched molecules and they cannot be packed as tightly together, therefore there are less van der Waals’ forces and a lesser intermolecular attraction to be overcome. Therefore less energy is needed to separate the molecules.
Filed under Chemistry
Endocytosis & Exocytosis
Bulky substances are transported into and out of the cell by endocytosis and exocytosis.
Endocytosis:
This is the infolding of the cell membrane to form vesicles. A portion of the membrane invaginates to envelope the contents and draw them into the cell. Once inside, the vesicles are known as intracellular vesicles.
There are 3 types of endo-:
1. Phagocytosis (cell eating)
When a bacterium or other solid item is engulfed by a cell membrane, the intracellular vesicle that was hence formed comes into contact with a lysosome. The lysosome fuses its membrane with the vesicle to release its catabolic enzymes which break down the solid.
2. Pinocytosis (cell drinking)
This occurs when a liquid is engulfed by a cell. In cells with multiple microvilli, such as the intestinal epithelial cells, there are pinocytosis channels between the microvilli which are constantly budding off vesicles of liquid. The cell membrane wraps around a fluid and pinches off, drawing in the liquid in a vesicle, the contents of which are then either broken down or absorbed into the cytosol.
3. Receptor Mediated Endocytosis.
This is a very specific type of pinocytosis because it involves receptors….
Falling asleep now, so I’ll finish this off tomorrow. 🙂
Filed under Biology
The Plasma Membrane
An intact membrane is essential to a cell. If the plasma membrane is disrupted, the cell loses its content and dies. The membrane is very important; two vital functions are:
The regulation of the entrance and exit of molecules: The interior and exterior of the cell is mainly fluid. The membrane functions to keep the intracellular fluid constant despite molecules such as nutrients and waste constantly moving in and out.
Communication: The components of a membrane signal other cells as to what type of cell it is. It may also serve as receptors for various signal molecules that affect the cell’s metabolism.
Membrane Models:
At the beginning of the last century, scientist noted that lipid-soluble molecules entered the cells more rapidly than water-soluble molecules. This caused them to think that lipids were a component of the plasma membrane.
Later it was discovered that it consists of phospholipids and proteins. Phospholipids are lipids in which one of the fatty acid groups is replaced by H3PO4. The phosphoric acid is hydrophillic, the rest of the molecule is hydrophobic.
The ‘Fluid’ Membrane
A membrane is held together by weak hydrophobic interactions. Most membrane lipids are able to drift laterally within the membrane and occasionally flip vertically, known as ‘flip-flopping’. Phospholipids move quickly along the membrane plane, where as the proteins move relatively slowly.
Unsaturated hydrocarbon tails enhance membrane fluidity because the kinks at the carbon-carbon double bonds hinder close packing of the phospholipids. Membranes solidify at the critical temperature. This is lower in a membrane with a higher concentration of C=C bonds.
Cholesterol found in the plasma membranes of eukaryotes modulates membrane fluidity by keeping the membrane fluid in cold environments and solid in hot temperatures. Cells may also the concentration of unsaturated fats to better suit their environment.
Integral proteins, which are inserted into the membrane have hydrophobic regions, surrounded by the hydrophobic areas of the phhospholipids. Their hydrophillic ends are exposed at both sides of the membrane.
The proteins in the plasma membrane may provide a variety of major cell functions:
- Transport
- Intercellular joining
- Enzymatic activity
- Cell-cell recognition
- Signal transduction
- Attachment to the cytoskeleton and extracellular fliud.
Substances can be moved through the membrane via: Active Transport; Diffusion; and Osmosis.
Active Transport is the movement of molecules from an area of low solute concentration to an area of high solute concentration, against the concentration gradient, in a process that requires energy.
Diffusion is the passive movement of molecules from an area of high concentration to an area of low concentration.
Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a semi-permeable membrane.
Diffusion is influenced by:
- The permeability of the membrane
- The shape and size of the molecule to be transported
- Number of proteins on the cell surface
- Concentration of molecules on either side of the membrane
- Surface area of the membrane
Facilitated diffusion is a method of diffusion that uses proteins to transport substances that find it difficult to pass through a membrane. e.g. polar molecules. The proteins are known as carrier proteins.
Fick’s Law
Rate of diffusion is proportional to the surface area multiplied by the difference in concentration, all divided by the thickness of the membrane.
Rate of diffusion (fish) Surface area x Concentration gradient
thickness of membrane
Osmosis – Thermodynamics
1 molecule of water will move quickly if heat is applied, or if the water concentration in a solution is high.
If water molecules are moving from left to right, then the potential energy is greater on the left than on the right. The potential energy is known, in Biology, as water potential.
Water diffuses from an area of high water potential to a region of low water potential through a semi permeable membrane. Water potential can be regarded as the tendency of water to leave a solution.
If solute molecules are present, they always slow down the movement of the water molecules in a solution. The tendency of the water to leave the solution is reduced because water is always attracted to the solute.
Water Potential Gradient
High Pure water = 0 kPa
Dilute solution = -500 kPa
Low Concentrated solution = -1000 kPa
Water potential is never positive. When the potential is more negative, water will flow into the cell.
Isotonic – two solutions are of the same water concentration, and as such there is no net movement of water.
Hypotonic – The water potential outside of the cell is greater than the intracellular potential. As such, there is a net inflow of water. The inside of the cell is more negative.
Hypertonic – The water potential inside of the cell is greater then the extracellular potential. As such, there is a net outflow of water. There inside of the cell is less negative.
Active Transport
Active transport requires energy in the form of ATP. it trasports molecules and ions in a direction that is not natural to the normal flow. This means that there will be many mitochondria present.
The following use ATP to transport molecules and ions:
1. Membrane pumps
- An active transport mechanism that moves ions in order to obtain polarisation
- For active transport two factors need to be considered: concentration and electrical charge.
- Ions generally diffuse to form an area of high concentration to an area of low concentration and are attracted to regions with an opposite charge. Therefore we take into consideration both the concentration and elecrtochemical gradient.
- Cells maintain a potential difference across the membrane. Many studies have shown that the inside of a cell is -ve and therefore cations are attracted and anions repulsed.
- however, their relative concentrations inside and outside the of the cells helps to decide which way they move.
- Three common ions to be transported are K+, Na+ and Cl-
1. Sodium Potassium pump
- Cell surface membranes have pumps that are intrinsic proteins that span the membrane. The sodium pump removes Na+ from the cell. K+ is taken into the cell and so is coupled with the Na+ pump. It is therefore known as the Na+/P+ pump.
- The pump requires more than one third of the ATP produced by a resting animal. It is very important.
- The pump is essential for:
- controlling cell volume (osmoregulation)
- Maintaining electrical activity in nerve and muscle cells
- Driving active transport of other substances (e.g. sugars and amino acids.)
Active transport in the intestine:
Soon after feeding there is a high concentration of food in the gut. Absorption is mainly due to diffusion but it is very slow and so it is coupled with the active transport and the movement of Na+. As the sodium is actively transported out by the Na+/K+ pump, it will start to diffuse back in. A membrane rquires both Na+ and glucose and so another pump is used that transports glucose at the same time as Na+.
Filed under Biology
The Cell Membrane
So as it stands, I’m still trying to deal with the backlog of work from September, but I’m almost there, not much left to catch up on now. Anyway, this post is about the cell membrane and the history of its discovery.
1925 – Gorter and Grendel measured the amount of phospholipid extracted from red blood cells and determined that there was just enough to form a bilayer around the cell.
1935 – Danielli and Davson suggest that globular proteins are part of the membrane and proposed to sandwich model.
Late 1950s – Electron microscopy had advanced and J.D. Robertson suggested that all membranes in various cells have basically the same composition, leading to the unit membrane model.
1972 – J. S. Singer and G. L. Nicolson suggested a new structure for the cell membrane, the “Fluid Mosaic Model”. They proposed in part that the membrane is a phospholipid bilayer in which protein molecules are either partially or wholly embedded. This structure is still widely accepted at this time.
Filed under Biology
Cells
So this was the topic that kicked off my AS course, you do a lot about cells in GCSE but this just goes into a bit more detail, so it’s not that much harder. Make sure to learn all the key definitions though!
Light Microscopy
- Light microscopy is the oldest and most widely used form of microscopy
- Specimens are illuminated with light, which is focused using glass lenses and viewed using the eye or photographic cells.
- Specimens can be dead or alive, and often need to be stained to me made visible. Iodine, which stains starch blue/black, is used for plant cells, and methylene blue used for animal cells.
A couple of important definitions:
Magnification – refers to the microscope’s power to increase an object’s apparent size.
Resolution – refers to the microscope’s power to show detail clearly, so that the use is able to distinguish two points close together.
The resolving power of a microscope is limited by the wavelength of light (400-600 nm). If objects in the specimen are smaller than the wavelength of radiation being used, they do not interrupt the waves and so are not detected.
Preparation of Slides
Slides need to be made so that the specimen can be viewed time after time for a number of years.
- Fixation – Chemicals are used to preserve the specimen so that they are not distorted over time.
- Dehydration – Water is removed from the specimen using a solvent, generally ethanol. This is because water molecules with deflect the beam of electrons away from the specimen.
- Embedding – Specimens are put into wax/resin to hold the structures in place so that thin slices can be made.
- Staining – Most biological material is transparent. Therefore different stains are used to highlight different organelles.
- Mounting – Mounting on a slide will protect the specimen so that it is suitable for viewing over a long period of time. A coverslip is generally placed over the specimen.
Eukaryotes:
These are cells that contain a double-membrane bound nucleus and other membrane bound organelles, such as mitochondria, endoplasmic reticulum and the golgi apparatus.
Nucleus – This is the most visible structure in a non-dividing cell, and contains most of the cell’s genetic material. The membrane bound area that surrounds the nucleus is known as the nuclear envelope. The nuclear envelope is a double-membrane, part of the endomembrane system, consisting of an inner and outer membrane, seperated by a gap of 20-40 nm. The two membranes fuse at the tips of the nuclear pores, which allow ribosomes and RNA out of the nucleus. Within each nucleus is one (or more) nucleolus, which is an area of concentrated DNA, organised by histones.
The nucleolus is roughly spherical and functions in the synthesis of ribosomes. It consists of nucleolar organisers (specialised chromosomes) with multiple copies of the genes for ribosome synthesis. They will have considerable amounts of rRNA and protein, representing ribosomes in various stages of construction. Generally, only one nucleolus is present, however there may more more than one, dependent on the cell species and the stage of cell cycle.
Ribosomes – These are essential for the process of protein synthesis. They are built up of two subunits; a large one with two tRNA binding sites, and a smaller one which associates with mRNA in a binding groove. They are the smallest eukaryotic organelles, and they do not have a membrane. Free ribosomes are located within the cytosol and produce the proteins needed in the cell. Bound ribosomes are attached to the ER; these produce the proteins needed for secretion.
Endoplasmic Reticulum – This a network of flattened sacs, called cisternae, and membranes throughout the cell. The membrane is continuous with that of the nucleus. There are two parts the the ER: the smooth endoplasmic reticulum and the rough endoplasmic reticulum. The SER is involved in synthesising lipids and steroids, and also carbohydrate metabolism. It also plays a part in the detoxification of drugs and poisons (e.g. alcohol). It is called “smooth” as there are no ribosomes bound to it. The RER has a rough surface, due to the ribosomes bound to the cytosolic side. As the ribosomes feed polypeptide chains into the RER’s lumen, it folds them into a functional proteins. Often carbohydrates are attached to form glycoproteins. Once the ribosome has finished feeding in the polypeptide, it detaches from the ER and moves back through the cytosol.
Golgi Apparatus – Anything made the ER is transported here in vesicles, where it is modified and then sent on to another destination. The golgi, similar to the ER, is made up of a series of folded cisternae, which have a cis face, and a trans face. The cis face is the receiving side of the golgi, and this is where transport vesicles from the ER attach to the apparatus. The trans face is the shipping face; here, vesicles bud off to carry molecules to other destinations, often to be secreted out of the cell. Secretory cells, such as those in the pancreas, have larger, more prevalent golgi.
Lysosomes – These are hydrolytic enzyme complexes surrounded by a single wall membrane. They bud off from the golgi, which produces the enzymes used to break down macromolecules. The lysosomes are capable of maintaining a high concentration of H+ ions by actively pumping them into the lysosymal lumen. Due to the anabolic nature of the enzymes, excessive leakage of the lysosome can result in autodigestion. It is protected from self digestion by the inner surface of its membrane. Lysosomes play a major part in cytosis.
Prokaryotes
Prokaryotes are the most primitive cell, appearing on Earth ~3.5 billion years ago as the first sign of life. They have no membrane mound organelles, most particularly, they have no double-membrane bound nucleus. They still contain DNA, however their genetic material is shaped in a circular plasmid, rather the the eukaryotic double helix, these strands are left lying free in the cytosol. The ribosomes in prokaryotes are a lot smaller than those in eukaryotes, but the cells do have a similar metabolism. Generally they are much smaller in size, typically between 0.5-10 microns in diameter. In bacteria is the only place that nitrogen fixation occurs. Nitrogen is absorbed from the atmosphere and converted into nitrates by the organisms.
Filed under Biology
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