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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
The Gene Technology Access Centre have some excellent resources for VCE Biology, including this slideshow and activity sheets “exploring protein structure“. The image above is one view of a representation of the enzyme amylase, which breaks starch down into sugars. You can see the green alpha-helices, yellow beta-sheets and blue random coils in the secondary structure of this protein. You may also be able to see the ‘co-factors’ or molecules which assist at the active site of this enzyme. Amylase relies on the co-factors calcium and chloride to function efficiently. What are the dietary sources of calcium and chloride?
At the Gene Technology Access Centre on Monday we spent the day learning about the structure and function of enzymes. As well as a lecture and practical experiment, we had the opportunity to use a computer program for protein modelling. GTAC has some great online resources for teaching and learning, including this slideshow about Enzyme Action.
Enzymes have specific characteristics:
– enzymes are proteins, made up of amino acids
– enzymes have specific primary, secondary and tertiary structures
– enzymes are specific to substrates
– enzymes are biological catalysts (they speed up a reaction)
– enzymes have optimum temperature and pH ranges
– enzymes are not changed or used up in a reaction
– enzymes have an active site, which is where the substrate is broken down or the products are made
– enzymes can contain co-factors (ions, such as chlorine or calcium) that assist to attract the reactants to the active site
We worked with amylase, an enzyme that breaks starch down into disaccharides. We used iodine to indicate the presence of starch and a photo spectrometer to measure the degree of staining of the medium. The higher the photo spectrometer reading, the more starch, which meant the less enzyme action. We stopped the reaction using an acid, which denatures the enzyme and prevents the break down of starch. Our results showed that the optimum temperature of amylase activity was about 40 degrees and the optimum pH was 6. This is what you might expect from human amylase, which would be working at normal body temperature (37 degrees) and neutral (or slightly acidic) pH in the mouth.
Students enjoyed this class, consolidating their knowledge of carbohydrates, lipids and nucleic acids using soft lollies and toothpicks today. They were able to show that disaccharides are made up of two monosaccharides and polysaccharides are made up of many sugar units (using fruit pastilles) and that lipids consist of a glycerol unit (jersey caramel) and 3 fatty acid chains (jelly snakes). Phospholipids consist of a phosphate group (marshmallow), a glycerol (jersey caramel) and two fatty acid chains. DNA consists of a sugar (fruit pastille) and phosphate (marshmallow) backbone and pairs of nitrogenous bases (jelly joiners), arranged in a double helix. Some showed the two hydrogen bonds between Adenine and Thymine and the three hydrogen bonds between Cytosine and Guanine.
As our next lesson will not be until after the VCE Study Camp, please continue to read through Chapter 2 (Membranes and Cell Organelles), as the practical experiment we are doing at Federation University is all about cell membranes. You will need to understand the following terms and definitions:
prokaryotic and eukaryotic
diffusion and osmosis (passive transport)
hydrophilic and hydrophobic (or lipophilic)
channel-mediated and carrier-mediated
phagocytosis, pinocytosis, exocytosis and endocytosis
ribosomes, endoplasmic reticulum and golgi complex
lysosomes, peroxisomes and endosomes
chloroplasts – including lamella, grana and thylakoids
I suggest you create a set of Quizlet flashcards using these terms and definitions.
Nucleic acids (DNA and RNA) are the next group of macromolecules that we are looking at. Nucleic acids are made up of monomer units that consist of a phosphate group, a sugar unit and a nitrogenous base. The nitrogenous bases in DNA are Thymine (T), Adenine (A), Guanine(G) and Cytosine (C). In RNA, the Thymine (T) is replaced by Uracil (U). Thymine (or Uracil in RNA) always pairs with Adenine (2 hydrogen bonds) and Guanine always pairs with Cytosine (3 hydrogen bonds).
Lipids are fats (solid at room temperature – from animals) and oils (liquid at room temperature – from plants). Next time you are in the supermarket, notice how many different types of fats and oils you can buy, from butter and lard to olive oil and sunflower oil. Triglycerides, cholesterol and phospholipids are all examples of this class of macromolecules, which are characterised by long carbon chains and being organic molecules, insoluble in water.
Last week we started looking at the large molecules that make up all living organisms – carbohydrates, lipids, proteins and nucleic acids. Due to their size, number of monomers and different combinations of monomers and how they are joined, there are huge number of these macromolecules, so they are grouped according to common characteristics. All carbohydrates are made up of Carbon, Hydrogen and Oxygen atoms and have the general formula (CH2O)n. How many carbon atoms do you think triose, pentose and hexose have?
Monosaccharides: glucose, fructose, galactose
Disaccharides: sucrose, lactose
Polysaccharides: chitin (insect exoskeletons and fungi cell walls), cellulose and glycogen