Proteins are polypeptides or chains of peptides (amino acids) joined together by peptide bonds. These large organic molecules have four levels of structure –
- Primary – order of amino acids in the chain
- Secondary – alpha-helices, beta-pleats and random coils
- Tertiary – the folding of the chains due to the presence of disulphide bonds
- Quarternary – when two or more polypeptide chains are folded together in a complex molecule
Enzymes are a specific type of protein that play a critically important role in living organisms. The molecules in cells are constantly interacting – being broken down, built up or exchanged. These chemical reactions constitute an organism’s metabolism. An organism is regulated and the rate of it’s chemical activity is maintained by these special proteins, known as biological catalysts. Like all proteins, enzymes are made in the ribosomes by linking together specific amino acids in the cytoplasm, according to the DNA code. Each cell contains and needs a very large number of different enzymes, but not all cells produce all enzymes – it depends on the structure and function of the cell as to which genes are ‘switched on’.
- Enzymes are proteins and are therefore made up of amino acids (containing carbon, hydrogen, oxygen and nitrogen)
- Enzymes are ‘biological catalysts’ because they speed up the rate of a chemical reaction
- Enzymes remain unchanged at the end of the reaction (not used up)
- Enzymes are only required in small amounts
- Enzymes are highly specific (one enzyme catalyses one type of reaction)
- Enzymes work best under optimum conditions of temperature and acidity
- Enzymes are ‘denatured’ (destroyed) by heat and sensitive to pH
- Enzymes work like a key fits into a lock – their shape complements the shape of the substrate materials.
- The ‘active site’ of a particular enzyme has a specific shape into which only one kind of substrate will fit
- Enzymes may need ‘co-enzymes’ (specific vitamins) or ‘co-factors’ (minerals) to help functioning
During our “step-up” program we studied the four different types of biological macromolecules, known as:
- Carbohydrates (or saccharides) made up of glucose monomers
- Lipids made up of fatty acids and glycerol
- Proteins (or polypeptides) made up of amino acids
- Nucleic acids (DNA and RNA) made up of nucleic acids
We investigated how these molecules are built up through condensation reactions, in which water is released. Hydrolysis reactions occur when these molecules are broken down with the addition of water.
Welcome back and thanks for your patience while I have been on study leave. There are only two weeks left before the Unit 3/4 Biology exam on Friday 30th October, so you should have already done the following:
- Written out a clear and concise set of study notes, outlining the main concepts in each Area of Study.
- Completed practice exams (available at the VCAA website) and identified areas where you need to do further revision.
- Joined the Elevate Education #elevatebio Video Series at http://bio.elevateeducation.com/
- You may also like to join the Study.com site for a five-day free trial and access their Immunology resources.
Some students have mentioned that they are having most difficulty remembering the cells involved and sequence of events of the cell cycle and immunology. These quick videos and other resources may assist with your revision:
Image from WorldMapper: The world as you’ve never seen it before
This map shows the size of the country in proportion to the absolute number of people that died from infectious and parasitic diseases in one year. Australia, Europe and America are barely visible due to good sanitation practices, education and high quality health care, including vaccination programs. Africa and India are disproportionately large due to HIV/AIDS (27% of total deaths); diarrhoeal diseases (17%); tuberculosis (14%); malaria (8%); measles (6%) and whooping cough (3%).
Infectious diseases have had significant impacts on population numbers, politics and society throughout history, from the Athens epidemic (430-427BC) that killed up to half the population of ancient Athens, waves of plague (‘Black death’) that killed up to 90% of Europeans in the 12th century and smallpox that ravaged populations as the Spanish and Portuguese conquistadors invaded the Americas. (“Early History of Infectious Disease” by Nelson and Williams)
More recently, vaccination programs have been very successful in eradicating smallpox and dramatically reducing the numbers of cases of polio, measles/rubella and tetanus. However, diseases such as HIV/AIDS, various influenza strains and Ebola are still causing many deaths throughout the world. The pathogens that cause these diseases are very good at evading the immune system, making it difficult for the immune system to recognise or remember them.
ELISA technique with materials supplied by Zoetis Australia.
This week we had another opportunity to connect with the Gene Technology Access Centre via Polycom. The topic of this session was the Hendra virus and a method to detect antibodies with a colour change (called ELISA – Enzyme-Linked Immuno-Sorbent Assay). We are very grateful to Zoetis for supplying the materials for this practical work and Fran at GTAC for stepping us through the process.
In a suburb of Brisbane in 1994, a horse-trainer and fourteen horses died of a mysterious illness within days of falling ill. CSIRO’s Australian Animal Health Laboratory, in Geelong, swung into action and worked intensively on blood and tissue samples for two weeks before identifying the virus responsible as Equine morbillivirus. However, further genetic analysis showed that the most appropriate classification of the virus was to place it in a new genus within the family Paramyxoviridae. It was later renamed Hendra virus, after the name of the Brisbane suburb in which the original outbreak occurred.
Zoetis Australia is a global animal health company who research and create animal medicines and vaccines, complemented by diagnostics products and genetics tests. As well as a Hendra virus vaccine, they have developed a technique for determining if an animal has virus antibodies present, which indicates that the individual has been exposed to the disease or has been vaccinated previously. We will use this technique to determine if three horses have had prior exposure to the disease or if they need to be vaccinated or receive booster shots.
In this chapter you need to become familiar with the following concepts:
- homeostasis (maintaining a stable internal environment in terms of temperature, hydration, pH, blood pressure and volume, oxygen and carbon dioxide concentration in the blood and the concentration of various ions, including sodium and glucose).
- stimulus-response and sensors-effectors
- positive and negative feedback mechanisms
- glands and hormones, including phermones
- signal transduction and signaling molecules
it is important to understand that lipid soluble hormones (lipophilic or hydrophobic) can pass through the cell membrane directly, but water-soluble hormones (hydrophilic or lipophobic) bind to a receptor molecule embedded in the cell membrane, which results in the activation of a secondary protein or messenger. This secondary messenger causes the cell to initiate a response. Signal transduction is a series of events (sometimes called a ‘cascade’) that changes the signal received by the cell.
GTAC – Introduction to Photosynthesis on YouTube
GTAC – Photosynthesis – Light Dependent Cycle and an Animation showing six cycles of the Light Independent Cycle on YouTube
Tony, from GTAC, demonstrated a photosynthesis experiment in which equal quantities of spinach leaves were placed in four clear, closed containers. Each container was subjected to light of the same intensity, but one had no filter (control) and the other three were wrapped in coloured cellophane (red, blue and green, as shown above). The coloured cellophane filters out different wavelengths of light, so the red cellophane reflects red wavelengths and allows other wavelengths to pass through. Each container had two probes, measuring oxygen and carbon dioxide concentrations in parts per million (ppm). What would you expect to happen in the cellophane-covered containers compared to the control?
Tony was also able to answer two questions that students have about DNA transcription.
(1) Where does the mRNA molecule go after transcription? “A single mRNA can be translated many times by ribosomes into polypeptides (it’s one way a cellular response dependent on gene expression can be amplified). After that mRNA is degraded, releasing individual nucleotides which can then be recycled into new mRNA. In eukaryotic cells, the mRNA is protected by the 5’ methylguanosine cap and the 3’ poly-A tail. When these are removed from the ends, presumably in response to an intracellular signal that says the mRNA is no longer required, the mRNA becomes susceptible to degradation.”
(2) When and where does transcription occur? “I would say transcription (the process by which the mRNA is first made from DNA template) occurs in the nucleus of eukaryotic cells almost continuously but the genes being expressed change throughout the cell cycle and in response to stimuli. For example, genes relevant to growth may be transcribed during G phases. A special set of genes relevant to DNA synthesis are transcribed during S phase. If a (stem) cell received a differentiation signal, a relevant set of genes would be switched on for differentiation into a particular cell type. I would say the only time transcription ceases is when the chromosomes condense for mitosis and cytokinesis. Essential proteins are still around to ensure cell division proceeds as intended. After cell division and the chromosomes de-condense, it’s back to business as usual.”
Thanks Tony for these valuable extensions to our Year 12 Biology program at Hawkesdale P12 College.
Both these roses come from the same bush in my garden at home. The one on the left is how the rose normally looks, year after year. This year, on a single branch sprouting to the side, there are about six flowers that look striped, like the one on the right. This article, from the American Rose Society, describes how a genetic mutation can cause this change in pigments.
Stripes may also result from spontaneous or induced mutations. Mutations are sudden changes that occur at a very low frequency in a gene. Spontaneous mutations (popularly known as ‘sports’) alter the existing genes and their expression, resulting in stripes. Induced mutations by irradiation or chemical mutagens also lead to genetically-altered pigmentation, and the result is stripes. Stripes may develop as a result of the transmission of genes responsible for stripes through hybridization. Viral infection that causes variegation in tulips may also cause stripes in roses. These infections could interfere with physiological functions of pigmentation, giving them a striped appearance.
It is possible that a mutation has occurred during mitosis somewhere at the base of the new branch and all the cells in the new branch carry the mutated gene, which is expressed as a striped phenotype. If this is the case, a cutting from this branch will also produce striped flowers. So, I will take a cutting and propagate this rose, to see if we can produce more of these beautiful mutants!