Enzymes and the digestive system

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  • Created by: r98
  • Created on: 11-04-16 18:08
What is digestion?
The process in which large molecules are hydrolysed by enzymes into small molecules which can be absorbed and assimilated.
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What are the major parts of the digestive system?
The oesophagus, stomach, small intestine, large intestine, rectum, salivary glands, and the pancreas.
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What is the oesophagus made of? What is it adapted for?
It's made of a thick muscular wall. It's adapted for transport rather than digestion or absorption.
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What is the role of the stomach?
To store and digest food.
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What can be found in the wall of the stomach?
Glands that produce enzymes (which digest proteins) and glands that producd mucus.
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What is the role of the mucus in the stomach?
The mucus prevents the stomach being digested by its own enzymes.
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What happens to food in the small intestine?
It's further digested.
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What is the role of the small intestine?
To absorb the products of digestion into the bloodstream.
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Where do the enzymes, in the small intestine, originate from?
Some are produced by its walls and some come from glands that pour their secretions into the small intestine.
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What adaptions have led to the small intestine having a large surface area?
Its inner walls are folded into villi, and on the epithelial cells of each villus, are millions of microvilli.
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What is the role of the large intestine? What happens to the food in it?
To absorb water. Food becomes drier & thicker, forming faeces.
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What is the final section of the intestines? What is stored there?
The rectum. Faeces are stored here.
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What is egestion?
The process of periodically removing faeces via the ****.
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Where are the salivary glands? What enzyme do they secrete?
They're situated near the mouth. Their secretions contain amylase, which is passed into the mouth via a duct.
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What & where is the pancreas? What does it produce?
It's a large gland, below the stomach. It produces pancreatic juice, which contains proteases, lipase and amylase.
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What are the 2 stages of digestion?
Physical breakdown & chemical digestion.
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What is the role of the teeth?
To break down food into smaller pieces, which provides a large surface area for chemical digestion.
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Apart from the teeth in the mouth, how else is food physically brokendown?
Food is churned by the muscles in the stomach wall.
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What is the purpose of chemical digestion?
To breakdown large, insoluble molecules into smaller, soluble ones.
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What process do all digestive enzymes function by?
By hydrolysis.
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What is hydrolysis?
The splitting up of molecules by adding water to the chemical bonds thatbhod them together.
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What is the general term for enzymes that function by hydrolysis?
Hydrolases.
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What are the 3 important digestive enzymes?
Carbohydrases, lipases & proteases.
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What do carbohydrases break down?
Carbohydrates -----> monosaccharides (ultimately)
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What do lipases break down?
Lipids (fats and oils) -----> glycerol & fatty acids
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What do proteases break down?
Proteins -----> amino acids (ultimately)
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What's the difference between absorption and assimilation?
Absorption is taking soluble molecules into the body, assimilation is incorporating absorbed molecules into body tissues.
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What is a monomer?
One of many small molecules that combine to form a larger one (polymer).
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What is a polymer?
A large molecule made up of repeating smaller molecules (monomers).
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In a carbohydrate, what is the name of a single monomer unit?
monosaccharide.
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What is a pair of monosaccharides called?
Disaccharide.
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What is formed when more than two monossacharides combine?
A polysaccharide.
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What's the general formula of a monosaccharide?
(CH2O)n, where 'n' can be any number from 3 to 7.
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What is the formula of the monosaccharide glucose?
C6H12O6.
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What groups of saccharides are reducing sugars?
All monosaccharides and some disaccharides.
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What is a reducing sugar?
A sugar that can donate electrons to (or reduce) another chemical, in this case Benedict's reagent.
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What is the test for a reducing sugar known as?
The Benedict's test.
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What is Benedict's reagent?
An alkaline solution of copper(II) sulfate.
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How is the test for a reducing sugar carried out?
2cm^(3) of food sample being tested in placed in a test tube (it has to be in liquid form), then an equal volume of Benedict's reagent is added, the mixture is then heated in a water bath for 5 mins.
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What has to be done to the food sample if it's not already in liquid form?
Grind it up in water.
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What would be the observation for a positive Benedict's test for a reducing sugar?
An insoluble red precipitate of copper(I) oxide would be formed.
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What are maltose, sucrose, lactose, examples of?
Disaccharides.
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What disaccharide is formed when glucose links to glucose?
Maltose
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What disaccharide is formed when glucose links to fructose?
Sucrose.
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What disaccharide is formed when glucose links to galactose?
Lactose.
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What type of reaction is it when 2 monosaccharides join? What is lost during the reaction?
It's a condensation reaction. A molecule of water is removed.
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What is the bond called that forms between two monosaccharides?
Glycosidic bond.
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Why is sucrose known as a non-reducing sugar?
Because it doesn' t change the colour of Benedict's reagent when it's heated with it.
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What must first happen to a non-reducing sugar to detect its presence?
It must first be broken down into its monosaccharide components by hydrolysis.
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What is the first 3 steps when testing for a non-reducing sugar carried out?
First, place 2cm^(3) of food sample (in liquid form) in test tube, add 2cm^(3) of Benedict's reagent & heat in water bath for 5 mins. If there's no colour change of Benedict's reagent, then a reducing sugar is not present.
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What are the last 4 steps when testing for a non-reducing sugar?
Add another 2cm^(3) of food sample to 2cm^(3) of dilute HCl, heat in water bath for 5 mins. Then add sodium hydrogencarbonate solution (to neutralise the HCl). Re-test the solution by heating with 2cm^(3) of Benedict's reagent for 5mins in water bath
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What observations would be seen if a non-reducing sugar (that had been hydrolysed) was re-tested with Benedict's reagent?
The Benedict's reagent would turn orange-brown.
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Are polysaccharides insoluble? Why?
Yes, they're insoluble, as they are very large molecules.
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What are polysaccharides suitable for?
Storage.
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What does a polysaccharide break down into when it's hydrolysed?
Disaccharides and monosacharides.
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What polysaccharide isn't used for storage but gives structural support to plant cells?
Cellulose.
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What polysaccharide is found in plants, in the form of small granules or grains?
Starch.
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How is the test for starch carried out? What colour would the solution go if starch was present?
Put 2cm^(3) of food sample in test tube, add 2 drops of iodine solution & shake. The presence of starch is indicsted by blue-black colouration.
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What is the colour of the iodine solution before starch is added?
Yellow.
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Why are enzymes produced in different parts of the digestive system?
Because each enzyme works fastest at a different pH.
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Where is the enzyme amylase produced?
In the mouth and pancreas.
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What does amylase do to starch? What is the product of this reaction?
Amylase hydrolyses the alternate glycosidic bonds of starch molecule, producing maltose.
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What enzyme hydrolyses maltose into a-glucose?
Maltase.
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What produces maltase?
The lining of the intestine.
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What is the purpose of saliva entering the mouth during the chewing of food?
Saliva contains salivary amylase, which hydrolyses the starch in the food into maltose. It also contains mineral salts that help to maintain the pH at around neutral, which is the optimum pH for salivary amylase.
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How is further hydrolysis of starch prevented, when the food is swallowed and enters the stomach?
The acidic conditions of the stomach denature the salivary amylase, preventing further hydrolysis of the starch.
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Where does the food go when it leaves the stomach? What does the food then mix with?
It passes into the small intestine, where it mixes with pancreatic juice.
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What hydrolysis the remaining starch into maltose?
Pancreatic amylase.
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How is the pH of the small intestine maintained at around neutral? Why is it important that a neutral pH is maintained?
The pancreas and the walls of the intestine produce alkaline salts, which maintain the pH at around neutral, so the amylase can function.
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How is food pushed along the small intestine?
By muscles in the intestine wall.
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What does the epithelial lining of the small intestine produce? What is the purpose of this product?
It produces maltase, which hydrolyses maltose (from the breakdown of starch) into a-glucose.
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Why must food containing sucrose be physically broken down by the teeth?
It's usually contained within cells, so these must be broken down by teeth to release it.
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What happens to sucrose in the small intestine?
It's hydrolysed by sucrase, which breaks the single glycosidic bond in sucrose, producing glucose and fructose.
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Where is sucrase produced?
The epithelial lining of the small intestine.
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What enzyme does the epithelial lining of the small intestine produce, that can hydrolyse lactose? How does this enzyme breakdown lactose into its monosaccharides?
Lactase, this hydrolyses the glycosidic bond that links the glucose and galactose monosaccharides.
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Babies only form of food is milk, what does this suggest about their lactase production?
Babies produce relatively large amounts of lactase.
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What happens when undigested lactose reaches the small intestine?
Microorganisms break it down, this produces small soluble molecules and a large volume of gas.
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Why is diarrhoea a symptom of lactose intolerance?
The soluble molecules lower the water potential of the material in the colon, this creates a water potential gradient that causes water to move by osmosis from the epithelial cells into the lumen of intestines.
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What is lactose intolerance?
When people do not produce sufficient lactase to digest all the lactose that they consume.
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How can adults manage their lactose intolerance?
By avoiding foods containing lactose.
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How can people with lactose intolerance consume sufficient calcium in the absence of milk?
By eating foods rich in calcium or by adding the enzyme lactase to milk before drinking it.
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What is the monomer from which polypeptides are formed?
Amino acid.
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What do polypeptides form when they combine?
Proteins.
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In an amino acid, what are the four different chemical groups attached to?
A central carbon atom.
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In an amino acid, what are the four different chemical groups attached to the central carbon atom?
Amino group (-NH2), carboxyl group (-COOH), hydrogen atom (-H), R group.
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Does the R group vary in amino acids?
Yes, each amino acid has a different R group.
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In an amino acid, is the amino group an acidic or basic group?
A basic group.
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In an amino acid, is the carboxyl group an acidic or basic group?
An acidic group.
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What is the reaction called when two amino acids combine? What product is formed?
Condensation reaction. A dipeptide is formed.
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How is the water molecule, that's made when 2 amino acids combine, made?
By combining the -OH from a carboxyl group of one amino acid with an -H from the amino group of another amino acid.
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What is the name of the bond that links two amino acids together? Where is the bond formed?
Peptide bond. It's formed between the carbon atom of one amino acid and the nitrogen atom of the other.
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What is the process of many amino acids joining together to form a polypeptide called?
Polymerisation.
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What forms the primary structure of a protein?
The sequence of amino acids in a polypeptide chain.
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What determines the ultimate shape and therefore function of a protein?
Its primary structure.
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Is a protein's shape specific to its function?
Yes, it's very specific to its function.
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What can a change in just a single amino acid in the primary sequence lead to?
A change in the shape of the protein and this may stop it from carrying out its function properly.
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How is the secondary structure of a protein formed?
When weak hydrogen bonds form between the O (which has an overall negative charge) of the -C=O group and the H (which has an overall positive charge) of the -NH group. This causes the polypeptide chain to twist into an a-helix.
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How is the tertiary structure of a protein formed?
When the a-helices of the secondary protein structure are twisted and folded even more.
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What bonds help to maintain the tertiary structure of a protein?
Disulfide bonds which are strong and not easily broken, ionic bonds which are formed between carboxyl groups and amino groups (that aren't involved in peptide bonds) but they're easily broken by pH changes, hydrogen bonds; numerous but easily broken.
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What is the quaternary structure of a protein?
A number of polypeptide chains linked together. There may also be a non-protein (prosthetic) group attached.
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What is the test for proteins called?
The Biuret test.
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What does the Biuret test detect?
Peptide links.
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How is the Biuret test carried out?
Add equal volumes of solution to be tested and sodium hydroxide in a test tube, add a few drops of copper(II) sulfate solution and mix. Purple colouration indicates the presence of peptide bonds and hence a protein.
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What would be observed during the Biuret test if a protein was not present?
The solution remains blue.
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Are enzymes globular or fibrous proteins?
Globular.
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What do enzymes act as?
Catalysts.
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What do catalysts do?
They alter the rate of a chemical reaction without undergoing permanent changes themselves.
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How do enzymes acting as catalysts speed up chemical reactions?
By lowering the activation energy of a reaction.
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What is the molecule on which the enzyme acts called?
The substrate.
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What is formed when the substrate 'fits' into the active site of an enzyme?
An enzyme-substrate complex.
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How is the substrate molecule held in the active site?
By bonds that temporarily form between certain amino acids of the active site and groups on thr substrate molecule.
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What is the lock and key model of enzyme action?
Enzymes work in the same way as a key operates a lock. In a similar way a substrate will only fit the active site of one particular enzyme. The shape of the substrate (key) exactly fits the active site of the enzyme (lock).
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What evidence is there to support the lock and key model of enzyme action?
The observation that enzymes are specific in the reactions that they catalyse.
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What is a limitation of the lock and key model of ennzyme action?
The enzyme is considered to be a rigid structure. But, it's been observed that when molecules bind to an enzyme at any other place other than the active site, it caused the enzyme to change shape. Meaning that the sructure was not rigid but flexible.
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What is the alternative model to the lock and key model of enzyme action?
The induced fit model of enzyme action.
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What is the induced fit model of enzyme action?
It proposes that the enzyme changes its shape slightly to fit the profie of the substrate; the enzyme is flexible and can mould itself around the substrate. The enzyme has a certain general shape but this alters in the presence of the substrate.
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How does the induced fit model of enzyme action suggest the activation energy is lowered?
As the enzyme changes shape, it puts a strain on the substrate molecule. This strain distorts a particular bond and consequently lowers the activation energy needed to break the bond.
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What 2 things does the induced fit model explain that the lock and key model can't?
How other molecules can affect enzyme activity, & how the activation energy is lowered.
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What two 'events' are most frequently measured, when measuring the rate of an enzyme-cataysed reaction?
The formation of products of the reaction, or the disappearance of the substrate.
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How does a rise in temperature effect the rate of an enzyme-catalysed reaction?
It increases the kinetic energy of the molecules, so the molecules move around more rapidly and collide with each other more often. In this case, the enzyme and substrate molecules collide more often in a given time, rate of reaction increases.
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What happens if the temerature gets too high in an enzyme-catalysed reaction?
It causes hydrogen bonds and other bonds in the enzume molecule to break, resulting in the enzyme changing shape so substrates start to fit less easily and then not at all. This is when the enzyme stops working altogether and is said to be denatured.
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Most enzymes have an optimum temperature of about 40 degrees, however body temperature is 37 degress, why is that?
Additional energy (food) would be needed to maintain the higher temperature. Other proteins may be denatured at higher temps. At higher temp, any further rise in temp (e.g. during illness) would denature the enzymes.
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What is pH a measure of?
The hydrogen ion concentration of the solution.
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What is one of the ways, involving charges, that pH affects enzyme action?
A change in pH alters the charges on the amino acids that make up the active site. Enzyme-substrate complexes can no longer form as substrates can't bind to acitive site.
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What is one of the ways, involving shape, that pH affects enzyme action?
A change in pH can cause bonds that maintain enzyme's tertiary structure to break,lso enzyme changes shape, altering the shape of active site, so substrate can't fit. The enzyme's been denatured.
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To start with, what is the rate of reaction like when there is a fixed amount of enzyme to which substrate is slowly added?
The rate of reaction increases in proportion to the amount of substrate. At low conc of substrate, the enzymes aren't working to full capacity as not all active sites are filled.
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When is the rate of reaction at its maximum? (referring to substrate & enzyme concentration)
When all the active sites become filled by the substrate molecules.
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How does adding more substrate affect the rate of reaction which has already got to its maximum speed?
It has no effect on the rate of reaction. In an excess of substrate, the rate of reaction levels off.
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What are they two types of reversible inhibitors?
Competitive & non-competitive inhibitors.
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What do competitive inhibitors bind to?
The active site of the enzyme.
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On an enzyme, where do non-competitive inhibitors bind to?
At a position other than the active site.
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Why can a competitive inhibitor occupy the active site of an enzyme?
Because it has a similar shape to the substrate.
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What do competitive inhibitors compete with, and for what?
They compete with the substrate for the available active sites.
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How do non-competitve inhibitors stop an enzyme from functioning?
By altering the shape of the enzyme's active site in such a way that substrate molecules can no longer occupy it, so the enzyme can't function.
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How would an increase in substrate concentration change the effect of a non-competitive inhibitor?
It doesn't change the effect of the inhibitor because the substrate and the inhibitor are not competing for the same site.
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