Enzymes Enzymes are proteins that act as biological catalysts They lower the activation energy of a...
If you can't read please download the document
Enzymes Enzymes are proteins that act as biological catalysts They lower the activation energy of a specific chemical reaction Catalysts – speed up the
Enzymes Enzymes are proteins that act as biological catalysts
They 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
Slide 2
Enzymes: Vocabulary Check Catalyst: 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
Slide 3
Enzymes Lower Activation Energy
Slide 4
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
Slide 5
Enzymes change substrates into products
Slide 6
How do enzymes work? Substrate specificity Induced fit versus
Lock and key mechanism
Slide 7
Enzymes have active site (s) An intricate pocket or cleft a 3-
dimensional entity structurally tailored to accept a particular
substrate Only fits its particular substrate
Slide 8
What are the models used to describe enzyme action?
Slide 9
Lock and key mechanism Induced fit mechanism
Slide 10
The induced fit theory The 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....
Slide 11
Naming Enzymes (the official classification)
Slide 12
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
Slide 13
Key properties of enzymes 1. All enzymes are proteins 2.
Enzymes are denatured (inactivated) by extreme temperatures 3.
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
The best way to understand temperature, pH and substrate
concentration effects is through paying with this game.... and
here's another....
Slide 16
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
Slide 17
The effect of temperature For most human enzymes the optimum
temperature is about 37C Many are a lot lower. For example, cold
water fish can die at 30C 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 100C Most enzymes are fully denatured at 70C
Slide 18
Factors which affect enzyme activity 2: pH Optimum pH values
Enzy me activit y Tryps in Pepsi n pH 1 3 5 7 9 11
Slide 19
The effect of pH The pH of a solution affects the shape of an
enzyme At non-ideal pH values, the active site is distorted and the
substrate molecules will no longer fit Extreme pH levels will
produce denaturation Many enzymes have pH values which are NOT
neutral (pH = 7): e.g. pepson, trypsin in the stomach and gut
Slide 20
Denaturation Denaturation 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 cant be killed!
Slide 21
What does enzyme denaturation mean?
Slide 22
Factors which affect enzyme activity 3: Substrate and enzyme
concentration From: http://www.skinnersbiology.co.uk/enzyme.htm
August 26 th 2012
Slide 23
Substrate concentration: Enzymic reactions Reaction velocity
Substrate concentration V max
Pepsin All about pepsin pepsin working in the stomach pepsin
working in the stomach
Slide 27
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.
Slide 28
Catalase Better, stronger, faster
Slide 29
What does hydrogen peroxide do in the body? H 2 O 2 is a strong
oxidising agent produced as a by- product of metabolism Can damage
cells Instantaneously broken down by catalase
Slide 30
What is hydrogen peroxide Bleach stain remover Wound treatment
(?)
Slide 31
Where is Hydrogen peroxide located?
Slide 32
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
Slide 33
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
Slide 34
What is the hypothesis you are going to test? Research Question
: Does catalase concentration affect the rate at which catalase
breaks down H 2 O 2 ? What is the hypothesis you are going to test?
Quantitative experiment How can we measure the rate at which
catalase breaks down H 2 O 2 ?
Slide 35
Does enzyme concentration affect the rate at which catalase
breaks down H 2 O 2 ? Working Observation Most enzymes have maximal
efficacy at a specified temperature (somewhere between 30 37 0 C in
mammals) Temperature extremes should reduce the rate at which
catalase breaks down H 2 O 2
Slide 36
Experimental Design Working Observation: As enzyme
concentration increases, the rate of breakdown of H 2 O 2 by
catalase should increase (Null hypothesis: a change in enzyme
concentration has no effect on the rate of H 2 O 2 decomposition by
catalase does not change) (Alternative hypothesis: enzyme
concentration is directly related to the rate of H 2 O 2
decomposition by catalase )
Slide 37
Quantitative experiment How can we measure the rate at which
catalase breaks down H 2 O 2 ? Quantity of oxygen produced over a
set time (volume, %, pressure)
Slide 38
Starting questions 1. What apparatus and other materials will
you need for your experiment?
Slide 39
A few starting questions: 1. How exactly will you measure the
reaction between H 2 O 2 and catalase??
Slide 40
How exactly will we measure the reaction between H 2 O 2 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
Dependent Variable % of oxygen in closed chamber Independent
Variable Catalase concentration % Controlled variables pH
Temperature Substrate concentration Uncontrolled variables Human
error timing and measurement Catalase experiment
Slide 44
Starting questions: 3. Can you think of other factors that may
affect enzyme activity? Substrate concentration Temperature pH
Human error
Slide 45
Starting Questions How will we record our data? Results
table?
Slide 46
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?
Slide 47
Predictions/ Conclusions Make a prediction about your
conclusions. Do you expect to find support for your hypothesis? Why
or Why not?