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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

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enzymes
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
enzymes vocabulary check
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
what are enzymes
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
how do enzymes work
How do enzymes work?
  • Substrate specificity
  • Induced fit versus Lock and key mechanism
enzymes have active site s
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

what are the models used to describe enzyme action1
What are the models used to describe enzyme action?
  • Lock and key mechanism
  • Induced fit mechanism
the induced fit theory
The induced fit theory

The substrateplays 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 simplified 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 enzymes
Key properties of enzymes
  • All enzymes are proteins
  • Enzymes are denatured (inactivated) by extreme temperatures
  • Enzymes work best at a particular temperature (which depends on the organism)
  • Enzymes work best at a particular pH (which depends on the organism)
  • Enzymes are catalysts (not degraded, ccan be used over and over again)
  • Enzymes are specific
factors affecting enzymes
Factors affecting Enzymes
  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
slide15

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
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
The effect of temperature
  • For most humanenzymes 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 denaturedat 70°C
factors which affect enzyme activity 2 ph

Enzyme activity

Trypsin

Pepsin

5

11

9

3

1

7

pH

Factors which affect enzyme activity 2: pH

Optimum pH values

the effect of ph
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
denaturation
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 can’t be killed!

factors which affect enzyme activity 3 substrate and enzyme concentration
Factors which affect enzyme activity 3: Substrate and enzyme concentration

From: http://www.skinnersbiology.co.uk/enzyme.htm

August 26th 2012

substrate concentration enzymic reactions

Vmax

Reaction velocity

Substrate concentration

Substrate concentration: Enzymic reactions
celebrity enzymes
Celebrity enzymes
  • Amylase
  • Pepsin
  • Pectinase
  • Catalase
amylase
Amylase
  • all about amylase...
  • amylase digestion
pepsin
Pepsin
  • All about pepsin
  • pepsin working in the stomach
pectinase
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.
catalase
Catalase
  • Better, stronger, faster
what does hydrogen peroxide do in the body
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
What is hydrogen peroxide
  • Bleach
  • stain remover
  • Wound treatment (?)
what is catalase
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
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
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 experiment

How can we measure the rate at which catalase breaks down H2O2?

does enzyme concentration affect the rate at which catalase breaks down h 2 o 2
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 design
Experimental Design
  • Working 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 experiment
Quantitative experiment
  • How can we measure the rate at which catalase breaks down H2O2?
  • Quantity of oxygen produced over a set time (volume, %, pressure)
starting questions
Starting questions
  • What apparatus and other materials will you need for your experiment?
a few starting questions
A few starting questions:
  • How exactly will you ‘measure’ the reaction between H2O2 and catalase??
how exactly will we measure the reaction between h 2 o 2 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

starting questions1
Starting questions:

3. Can you think of other factors that may affect enzyme activity?

  • Substrate concentration
  • Temperature
  • pH
  • Human error
starting questions2
Starting Questions…
  • How will we record our data?
  • “Results table?
and a few questions about study design
…and a few questions about study design…
  • Which concentrations should we test? – and why?
  • Do you want this to be a controlled experiment? What will be the control group?
  • How many test groups should we have?
  • How many times will you repeat each test?
  • How will we prepare our stock catalase solutions?
predictions conclusions
Predictions/ Conclusions
  • Make a prediction about your conclusions.
  • Do you expect to find support for your hypothesis?
  • Why or Why not?
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