Hsc Biology Great Notes!

Topics: Blood, Carbon dioxide, Oxygen Pages: 22 (6753 words) Published: May 26, 2011
9.2 - Maintaining a Balance:
1. Most organisms are active within a limited temperature range: * Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity in substrates: * Role of enzymes in metabolism:

* Metabolism refers to all the chemical reactions occurring in organisms * Enzymes are biological catalysts which increase the rate of chemical reactions * Without enzymes, metabolism would be too slow to support life * Chemical composition of enzymes:

* All enzymes are made of protein
* Proteins consist of one or more polypeptide chain. * These are composed of long chains of amino acids joined together by peptide bonds * Structure of enzymes:
* In enzymes, the polypeptide chain is folded into a 3-dimensional globular shape * Part of the enzyme is called the active site. This part attaches to the substrate * The substrate are the molecules the enzymes acts upon * Specificity of enzymes:

* Enzymes are highly specific in their action; this means that each enzyme acts on one substrate only * This is because the shape of the active site of the enzyme matches the shape of the substrate material * The molecules the enzyme act upon are called the substrate * The substrate molecules bind to the active site and a chemical reaction occurs * The products are the substances that the substrate(s) become. One substrate can be split, or two substrates can be joined * Models to explain specificity:

* The Lock and Key Model suggests that the substrate fits exactly into the active site of the enzyme like a key fits into a lock. It assumes that the enzyme had a rigid and unchanging shape. * The Induced Fit Model states that the binding of the substrate to the enzyme ‘induces’ a temporary change in shape of the enzyme. The new shape of the enzyme better accommodates the shape of the substrate and a reaction occurs. * Identify the pH as a way of describing the acidity of a substance: * The substance that makes a solution acidic is hydrogen ions * pH is a measure of the acidity or the alkalinity of a substance * pH is a measure of the concentration of hydrogen ions per litre of solution * The pH scale is from 0 to 14: a pH of 7 is neutral (pure water); above 7 is alkaline and below 7 is acidic * Identify the effect of increased temperature, change in pH and change in substrate concentrations on the activity of enzymes: * Enzyme function is affected by many factors, including: * Temperature:

* Sensitivity to temperature relates to the protein structure of enzymes * As temperature increases, enzyme activity increases, up to the optimum temperature * This is because the enzyme and substrate molecules are moving faster (more kinetic energy) and therefore more collisions between enzyme and substrate occur * At high temperatures, the shape of the enzyme changes, and some of the enzymes can no longer accommodate the substrate. Activity decreases. However, if the temperature cools down, activity will start again * At VERY high temperatures, the enzyme is denatured; i.e. the chemical bonds holding the protein molecule together are broken and the shape is permanently changed. The enzyme is destroyed, can no longer accommodate the substrate, and will remain inactive even if the temperature returns to the optimum

* pH:
* Enzymes work best at an optimum pH
* This is usually within a very narrow range
* Extremes of acidity or alkalinity can affect the bonds holding the 3D globular shape of the enzyme, denaturing the enzyme. * Substrate concentration:
* An increase in substrate...
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