ENZYMES AND THE DIGESTIVE SYSTEM

ashiana121
Flashcards by ashiana121, updated more than 1 year ago
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Questions and answers on enzymes and digestion, carbohydrates (monosachharides, disaccharides), digestion of carbohydrates, proteins, enzymes, factors affecting enzyme action (temp, pH etc) and inhibition

Resource summary

Question Answer
What are the seven main parts of the digestive system? (inc. 2 glands) Oesophagus, stomach, small intestine, large intestine, rectum - glands: salivary glands, pancreas
Is the oesophagus adapted for digestion or for transport? Transport
What is the role of the stomach? To store and digest food
What does the inner layer of the stomach produce? Enzymes
What other substance does the stomach produce? Mucus
What do each of these substances do? Enzymes - break down proteins Mucus - prevents the enzymes from breaking down the stomach
What are the inner walls of the small intestine folded into? Villi
What does this give them? A large surface area
How is the surface area of the small intestine further increased? Microvilli on the surface of the villi
What does the large intestine absorb? Water
What is the name of the process through which digested food is removed via the anus? Egestation
Where are the salivary glands? The mouth
Which enzyme is in the secretions of the salivary glands and what does it do? Salivary amylase - hydrolyses starch into maltose
Where is the pancreas situated? Below the stomach
The pancreas secretes pancreatic juice. What type of enzymes are in the pancreatic juice and what do they do? (3) Proteases to digest proteins; lipases to digest lipids; amylase to digest starch
What are the two stages of digestion? Chemical digestion and physical breakdown
Which two features physically break down food so that the surface area is increased? The teeth, the muscles in the stomach
What is the definition of chemical digestion? Breaking down large, insoluble molecules into smaller, soluble ones
What carries out chemical digestion? Enzymes
All digestive enzymes function by _________ Hydrolysis
Which are the three main types of digestive enzymes? Carbohydrases, lipases and proteases
What do carbohydrases break down and into what? Carbohydrates, ultimately into monosaccharides
What do lipases break down and into what? Lipids into glycerol and fatty acids
What do proteases break down and into what? Proteins, ultimately into amino acids
What is absorption? Taking soluble molecules into the body
What is assimilation? Incorporating the absorbed molecules of digestion into the body tissues
Carbohydrates are carbon molecules combined with what? Water
What do carbon atoms readily make bonds with? Other carbon atoms
What name is given to a single unit (that makes up a chain)? Monomer
What name is given to many monomers joined together in a chain? Polymers
What is the monomer unit of a carbohydrate? A saccharide
What is a single monomer therefore called? A monosaccharide
What name is given to a pair of monosaccharides? Disaccharides
What name is given to large number of monosaccharides joined together? Polysacchardides
What is the general formula for monosaccharides and what are two features of them? (CH2O)n - sweet tasting and soluble
What is the name of the test used to test for reducing sugars? Benedicts test
What is reduction? A chemical reaction involving the gain of electrons
Therefore, what is a reducing sugar? A sugar that can donate electrons (reduce) another chemical
What are the steps for the Benedicts test? 1. Food sample dissolved in water 2. Equal volume of Benedicts reagent added 3. Heat mixture gently on a water bath for 5 minutes
If a reducing sugar is present in the sample, what is the result of the test? An insoluble red/orange/brown precipitate (copper oxide)
What are the three disaccharides? Maltose, sucrose and lactose
What two monosaccharides form maltose? Glucose and glucose
What two monosaccharides form sucrose? Glucose and fructose
What two monosaccharides form lactose? Glucose and galactose
By what reaction do monosaccharides join together? A condensation reaction
What does this involve? The removal of a water molecule
What is the name given to the bond that is formed? A glycosidic bond
By what process are disaccharides broken down into their constituent monosaccharides? Hydrolysis
What does this involve? The addition of water
Give an example of a disaccharide that is a reducing sugar Maltose
Other disaccharides, such as sucrose, are non-reducing sugars. From the results of a Benedicts test, how do we know this? The colour of the sample and the Benedicts reagent do not change colour when heated
What is the first part of the test that can be done to test for non-reducing sugars? (after the initial Bdicts test in which the solution remained blue) Add another 2cm3 of the sample to 2cm3 of dilute HCl - heat in water bath for 5 mins
What does the HCl do? Hydrolyses any disaccharide present into their constituent monosaccharides
What substance is then added to the solution to neutralise the HCl? Sodium hydrogen carbonate (NaHCO3)
Why is this necessary? Benedict's reagent doesn't work in acidic conditions
What can we use to check that the solution is alkaline? pH paper (universal indicator paper)
What is added to this solution and how long is it heated in a water bath for? Benedict's reagent - heated for 5 mins
If a non-reducing sugar was present in the original sample, what colour will the solution now go? Orange-brown
Why is this? Due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar
Many monosaccharides join to form polysacchairdes under what reaction? Condensation reaction
Being very large, polysaccharides are ___________ Insoluble
What does this feature make them suitable for? Storage
When hydrolysed, what do polysaccharides break down into? Monosaccharides and disaccharides
Give an example of a polysaccharide that is not used for storage but for structural support (and in what) Cellulose - structural support in cell walls
Starch is also a polysaccharide. What monosaccharides link together to form starch? Alpha glucose
What substance do we use to test for starch? Iodine solution
When iodine solution is dropped on to/in to the sample being tested for starch content, what colour will it go? Blue-black
Why does it often take more than one enzyme to completely break down a large molecule? Enzymes are specific; one enzyme breaks down a molecule into smaller sections and other enzymes break down these smaller sections
What is the name given to the individual units that the enzymes are broken down into? Monomers
In starch digestion, what is the first enzyme called and where it is produced? Amylase - by the salivary glands and by the pancrease
What does amylase hydrolyse? The alternate glycosidic bonds of the starch molecules
What does this produce? The disaccharide maltose
Which enzyme hydrolysed maltose into alpha glucose? Maltase
Where is maltase produced? The lining of the intestine
Food is taken into the mouth and chewed by the teeth. This breaks the food into small pieces, giving it a what? Large surface area
Where is saliva secreted from? The salivary glands
Which of the enzymes is in saliva? Salivary amylase
What else is in saliva that helps amylase to work? Mineral salts to maintain pH at around neutral - optimum for amylase for work
What does the HCl in the stomach do? Denatures salivary amylase and so prevents further hydrolysis of starch
What secretion is the food mixed with as it passes from the stomach to the small intestine? Pancreatic juices
What enzyme is in the pancreatic juice? Pancreatic amylase
What does pancreatic amylase do? Hydrolyses the remaining starch into maltose
What else is in pancreatic juice? Mineral salts - again to maintain pH at neutral so amylase can function
What do muscles in the intestine wall do? Move food along down the small intestine
Which enzyme does the epithelial lining of the small intestine produce? Maltase
Maltase hydrolyses maltose into _______ Alpha glucose
Where is the enzyme that breaks down sucrose secreted? The small intestine epithelial lining
What is this enzyme called? Sucrase
Why is it essential for foods containing sucrose to be broken down by the teeth? Because sucrose is usually contained within the cells
What does sucrase hydrolyse? The single glycosidic bond between glucose and fructose
In what products is lactose found? Dairy
Where is lactose digested and by what enzyme? Small intestine - lactase
What two monomers are joined by a single gylcosidic bond that make up lactose? Glucose and galactose
Why do babies have large amounts of the lactase enzyme? Milk is the only food they eat
As milk becomes a smaller part of our diet in adults, what happens to the production of lactase during childhood? It naturally diminishes
However what can happen? The reduction is so great some people produce little or no lactase at all
Because there is no lactase to break down the lactose when it reaches the small intestine, what breaks it down instead? Microorganisms
What do the microorganisms release in large volumes? Gas
What does this result in? Bloating, nausea, diarrhoea and cramps
How can this be avoided? By avoiding products containing lactose
What is the main problem this causes? Calcium deficiency
How can this be solved? Eating calcium rich foods or adding lactase to products containing lactose before eating it
What are enzymes made from? Proteins
What are the monomer units that make up polypeptides? Amino acids
What can polypeptides be combined to form? Proteins
How many amino acids naturally occur in proteins? 20
Name the parts of an amino acid Amino group, carboxyl group, hydrogen atom, R group, central carbon atom
What is the formula of the carboxyl and amino groups? Carboxyl -COOH Amino -NH2
Two amino acids joined together is known as a __________ Dipeptide
What reaction occurs when two amino acids join together? Condensation reaction
This involves the removal of a water molecule. Where does this water molecule come from? An -OH from the carboxyl group of one amino acid and a -H from the amino group of another amino acids
A proteins shape is ______ to its function Specific
In the secondary structure of proteins, the polypeptides can be twisted into a 3D shape. What is a name given to this 3D shape, and what bonds make the long polypeptide chain twist? Alpha helix - hydrogen bonds
What happens to the alpha helices of the secondary structure for it to form the tertiary structure of a protein? Twisted and folded more
A number of different bonds hold together this tertiary structure. What are the names of these bonds? (3) Ionic bonds, hydrogen bonds and disulphide bonds
Which are the strongest bonds and which are the weakest? Strongest - disulphide Medium - ionic Weakest - hydrogen
What is the quaternary structure of a protein? Numerous polypeptide chains combined. May be prosthetic groups associated e.g haemoglobin
What test do we use to test for proteins? Biuret test
What does Biurets reagents detect? Peptide bonds
What colour will the solution go if peptide bonds (therefore a protein) are present? Purple
What happens if there is no peptide bonds, and therefore no protein? The solution remains blue
Which part of an enzyme does the reaction take place in? The active site
What is the molecule called that binds to the active site? The substrate
What does the 'lock and key' model state? The active site of an enzyme is complementary to the substrate - they fit exactly like a lock and key
What does the 'induced fit' model state? The active site is flexible and can change shape - substrate and active site are not completely complementary - the active site changes shape when the substrate binds to fit it in
Enzymes are biological catalysts that lower the what? Activation energy of a reaction
What 5 factors can affect enzyme action? Temperature - pH - substrate concentration - enzyme concentration - inhibitors
What is the approx. optimum temperature for human enzymes? 40 degrees celcius
What happens if the temperature is increased beyond this? Shape of active site changes (heat breaks h-bonds) and enzyme does not function/becomes denatured
What does a change in pH change about the enzyme? The shape of the active site
What does this mean? The substrate can no longer fit & reaction can no longer be catalysed
What happens to the rate of reaction as the enzyme concentration increases? It increases
What happens to the rate of reaction when the concentration of the substrate is increased and why? It increases - more substrate molecules can collide with enzymes
However what happens at higher substrate concentrations? The enzyme active sites become saturated with substrate so there are few enzymes - the rate levels off
What are the two types of inhibitor? Competitive and non-competitive
Which inhibitor molecules have a shape similar to that of the substrate molecules? Competitive
What do competitive inhibitors compete with and what for? Compete with substrate molecules for the active site
Why don't non-competitive inhibitors bind to the active site of an enzyme? The shape of non-competitive inhibitors is not similar to that of the substrate
Where do non-competitive inhibitors bind to? A site that is NOT the active site
What does this do? Changes the shape of the active site - so that the substrate no longer fits
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