Post on 24-Feb-2016
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EnzymesEnzymes are proteins that act as
biological catalystsThey lower the activation
energy of a specific chemical reaction
Catalysts – speed up the chemical reaction and are not changed by the reaction
Lowering the activation energy has a profound effect on how rapidly the reaction is completed
Enzymes: Vocabulary CheckCatalyst: A substance that speeds up a chemical
reaction without itself being changed
Enzyme: A biological catalyst that is usually a protein
Substrate: The reactant(s) upon which an enzyme has its action
Product: A substance that results from a chemical reaction
Enzymes Lower Activation Energy
What are enzymes? Enzymes are typically
proteins Enzymes are specific Enzymes act as
catalysts to speed up the rate of reaction of a biological process
Enzymes are not used up by the reaction they catalyse
Enzymes change substrates into products
How do enzymes work?Substrate specificityInduced fit versus Lock and key mechanism
Enzymes have active site (s)
An intricate pocket or cleft – a 3-dimensional entity – structurally tailored to accept a particular substrateOnly fits its particular substrate
What are the models used to describe enzyme
action?
What are the models used to describe enzyme
action?
Lock and key mechanismInduced fit mechanism
The induced fit theoryThe substrate plays a role in determining the final shape of the enzyme and that the enzyme is has some flexibility. This explains why certain compounds can bind to the enzyme but do not react because the enzyme has been distorted too much. Other molecules may be too small to induce the proper alignment and therefore cannot react. Only the proper substrate is capable of inducing the proper alignment of the active site
Induced fit in a moment....
Naming Enzymes (the official classification)
Naming Enzymes (simplified classification)
Enzymes can be named according to the type of reaction that they catalyse Carbohydrases Lipases Proteases
Enzymes can be named according to the substrate the interact with:
Maltase Sucrase
Some enzymes just have individualised names: Pepsin
Trypsin
Catalase
Key properties of enzymes1. All enzymes are proteins2. Enzymes are denatured (inactivated) by extreme
temperatures3. Enzymes work best at a particular temperature
(which depends on the organism)4. Enzymes work best at a particular pH (which
depends on the organism)5. Enzymes are catalysts (not degraded, ccan be
used over and over again)6. Enzymes are specific
Factors affecting Enzymes
1.Temperature2.pH3.Substrate concentration4.Enzyme concentration
The best way to understand temperature, pH and substrate concentration effects is through paying with this game....and here's another....
Factors which affect enzyme activity 1: Temperature
From: GCSE Bitesize:26.08.12 http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev4.shtml
The effect of temperature
For most human enzymes the optimum temperature is about 37°C
Many are a lot lower. For example, cold water fish can die at 30°C since many of their enzymes denature
Many plant enzymes have optimal temperature of 28 – 30 C
A few bacteria in hot springs have enzymes that can withstand very high temperatures up to 100°C
Most enzymes are fully denatured at 70°C
Factors which affect enzyme activity 2: pH
Optimum pH values
Enzyme
activity
Trypsin
Pepsin
pH1 3 5 7 9 11
The effect of pH The pH of a solution affects the shape of an
enzymeAt non-ideal pH values, the active site is
distorted and the substrate molecules will no longer fit
Extreme pH levels will produce denaturationMany enzymes have pH values which are NOT
neutral (pH = 7): e.g. pepson, trypsin in the stomach and gut
DenaturationDenaturation is a change in the shape of an
enzyme which prevents it from fulfilling its function.
Enzymes (and other proteins) can be denatured by heat, pH changes, or certain chemicals
NB: Denaturation is not the same as ‘killing’ – proteins and enzymes are not living things, so can’t be killed!
What does ‘enzyme denaturation’ mean?
Factors which affect enzyme activity 3: Substrate and enzyme concentration
From: http://www.skinnersbiology.co.uk/enzyme.htmAugust 26th 2012
Substrate concentration: Enzymic reactions
Reaction velocity
Substrate concentration
Vmax
Celebrity enzymes
1.Amylase2.Pepsin3.Pectinase 4.Catalase
Amylase all about amylase... amylase digestion
Pepsin All about pepsin pepsin working in the sto
mach
Pectinase Pectinase is widely used to
increase the yield in fruit juice extraction, and also to make juice clear rather than cloudy
Pectinase breaks down the pectin chains in the middle lamellae connecting fruit cells
Pectinases and amylases can both break down these insoluble polysaccharide compounds within fruit cells, releasing soluble sugars which clarify the juice producing a clearer, sweeter product.
What does hydrogen peroxide do in the body?
H2O2 is a strong oxidising agent produced as a by-product of metabolism
Can damage cells
Instantaneously broken down by catalase
What is hydrogen peroxide Bleach
stain remover
Wound treatment (?)
Where is Hydrogen peroxide located?
What is catalase? A biological enzyme present
in all living cells exposed to oxygen
‘Extremely high turnover number’
Catalyses the decomposition of hydrogen peroxide to water and oxygen
Your Research Challenge
Investigate the effect of enzyme concentration on yeast (saccharomyces cerevesiae) catalase enzyme activity using quantitative methods
p. 44 of your IGCSE book
What is the hypothesis you are going to test?
Research Question:
Does catalase concentration affect the rate at which catalase breaks down H2O2?
What is the hypothesis you are going to test?
Quantitative experimentHow can we measure the rate at which catalase breaks down
H2O2?
Does enzyme concentration affect the rate at which catalase breaks down H2O2?
Working Observation
Most enzymes have maximal efficacy at a specified temperature (somewhere between 30 – 37 0C in mammals)
Temperature extremes should reduce the rate at which catalase breaks down H2O2
Experimental DesignWorking Observation: As enzyme concentration
increases, the rate of breakdown of H2O2 by catalase should increase
(Null hypothesis: a change in enzyme concentration has no effect on the rate of H2O2 decomposition by catalase does not change)
(Alternative hypothesis: enzyme concentration is directly related to the rate of H2O2 decomposition by catalase )
Quantitative experimentHow can we measure the rate at which catalase breaks
down H2O2?
Quantity of oxygen produced over a set time (volume, %, pressure)
Starting questions1. What apparatus and other materials will you
need for your experiment?
A few starting questions:1. How exactly will you ‘measure’ the reaction between
H2O2 and catalase??
How exactly will we ‘measure’ the reaction between H2O2 and catalase?
We will measure the rate of reaction between catalase and hydrogen peroxide indirectly by measuring the pressure change in a closed chamber, using a Vernier Gas pressure probe
Data Collection
Dependent Variable
Independent Variable
Controlled variables
Uncontrolled variables
Catalase experiment
Dependent Variable % of oxygen in closed chamber
Independent Variable Catalase concentration %
Controlled variables pHTemperature
Substrate concentration
Uncontrolled variables Human error – timing and measurement
Catalase experiment
Starting questions:3. Can you think of other factors that may affect enzyme
activity?
Substrate concentration
Temperature
pH
Human error
Starting Questions…How will we record our data?“Results table?
…and a few questions about study design…
1. Which concentrations should we test? – and why?
2. Do you want this to be a controlled experiment? What will be the control group?
3. How many test groups should we have?
4. How many times will you repeat each test?
5. How will we prepare our stock catalase solutions?
Predictions/ ConclusionsMake a prediction about your conclusions.
Do you expect to find support for your hypothesis?
Why or Why not?