Unit 3.1.2 - The Digestive System Flashcards
Digestion is the process where?
Large molecules care hydrolysed by enzymes to produce smaller molecules that can be absorbed and assimilated
What does absorption mean?
It is when molecules move from the digestive system into the blood
What does assimilated mean?
Where absorbed molecules are incorporated into body tissues
What are the two types of digestion?
Chemical and physical
What is meant by physical digestion?
It is when food is broken down into smaller pieces by the teeth in the mouth or by the churning movements of the stomach muscles
What is meant by chemical digestion?
Where polymers are broken down into monomers by hydrolysis
What are the monomers for carbohydrates called?
Monosaccharide
What are the monomers for protein called?
Amino acid
What is the difference between monosaccharaides and amino acids in terms of the elements they contain?
Monosaccharaides contain carbon, hydrogen and oxygen and amino acids contain the same elements as well as nitrogen
What is a polymer?
A large molecule made up of repeating smaller molecules called monomers
What reaction do you do to join polymers?
Condensation reaction
What reaction do you do to break up polymers?
Hydrolysis reaction
Out of a condensation reaction and hydrolysis reaction which ones requires water molecules and which one released water molecules?
Condensation reaction releases a water molecules and a hydrolysis reaction takes in a water molecule
Draw what happens during a hydrolysis reaction between polymers?
See flash card 2
Draw and label the parts of the digestive system?
See flash card 1
Starch is broken down into? by which enzyme?
Maltose by amylase
Maltose is broken down into? by which enzyme?
Glucose by maltase
Lipids are broken down into? by which enzyme?
Fatty acids + glycerol by lipase
Proteins are broken down into? by which enzymes?
Polypeptides by endopeptidase
Polypeptides are broken down into? by which enzymes?
Amino acids by exopeptidase
Name two examples of endopeptidase?
Pepsin and trypsin
Name an example of exopeptidase?
Peptidase
How is starch converted into glucose?
It is hydrolysed into maltose by the enzyme amylase, the maltose is then hydrolysed into glucose by the enzyme maltase
What is amylase released by?
The salivary glands and the pancreas
What is maltase released by?
The intestinal epithelium
What is lipase released by?
The pancreas and intestinal epithelium
Endopeptidase and exopeptidase are both examples of ?
Proteases
How is the salivary gland important in digestion?
It produces saliva which contains the enzyme amylase, saliva also lubricates the food making it easier to swallow
Where is bile produced, stored and released into?
Bile is made by the liver, stored in the gall bladder and then secreted into the small intestine
Give two reasons why bile is important in the digestive system?
It neutralises stomach acid so the enzymes in the small intestine aren’t denatured by the acidic pH value, it also emulsifies the lipids increasing the surface area of the lipase enzyme to work on
Name three functions for proteins within all living organisms? (not along the lines of growth and repair)
Antibodies, hormones and enzymes
What bonds join the amino acids to make proteins?
Peptide bonds
Draw the general structure of an amino acid?
See flash card 3
What is the difference between amino acids in terms of structure?
They all have a different variable group
What reaction would join two amino acids together?
A condensation reaction
What reaction can break apart polypeptide chains and what molecule is released during this reaction?
Hydrolysis - water
Draw a hydrolysis reaction that will break apart a dipeptide?
See flash card 4
Draw a condensation reaction that will join two amino acids to make a dipeptide?
See flash card 5
Two amino acids joined together are called a?
Dipeptide
What are the three levels within protein structure called?
Primary, secondary, tertiary and quaternary
What is the primary structure of a protein?
A sequence of amino acids joined together by peptide bonds
What is the secondary structure of a protein?
When the polypeptide chains begin to become folded to form beta pleated sheets and alpha helixes, hydrogen bonds hold their shapes
What is the tertiary structure of a protein?
Pleated sheets and helixes fold over each other even more and other ionic, disulphide and hydrogen bonds form holding this shape
What is a quaternary structure of a protein?
More than one polypeptide chain/tertiary structure protein together
What test can you do for proteins?
The biuret test for proteins
Describe what you do during a biuret test for proteins and the results you could get?
1.) add a few drops of sodium hydroxide to the solution
2.) then add copper sulphate to the solution
If a protein is present the solution will turn purple, if there are no proteins the solution will remain blue
After the biuret test for protein the solution is blue, are proteins present?
No
After the biuret test for protein the solution is purple, are proteins present?
Yes
What is an enzyme?
A biological catalyst that speeds up the rate of reaction without being used up or changed
How do enzymes speed up the rate of reaction?
They offer an alternative route for the reaction to take place with a lower activation energy
When an enzyme binds to the active site what is formed?
Enzyme - substrate complex
How do enzyme - substrate complexes lower the activation energy is two substrate molecules need to be joined?
It means the substrates are held close together so that the molecules can form bonds more easily
How do enzyme - substrate complexes lower the activation energy is a substrate molecules need to separated apart?
The enzyme substrate complex means there is a strain on the bonds within the substrate, so the substrate can break apart more easily
What are the two models that show how enzymes work called?
The lock and key model and the induced fit model
What does the lock and key model show about enzymes and their substrates?
The enzymes active site is complementary in shape to the substrate so they can bind to form enzyme substrate complexes
What does the induced fit model show about enzymes and their substrates?
The enzymes active site is similar in shape to the substrate, this means when the substrate binds to the active site the active site changes shape slightly so that the substrate fits perfectly
Why can enzymes only catalyse one reaction?
Because only one substrate will fit into the enzymes active site
What is the shape of an enzymes active site determined by?
The enzymes tertiary shape
What three things effect the rate of reaction of an enzyme?
Temperature, pH and substrate concentration
Why does increasing the temperature increase the rate of reaction of an enzymes up to a point?
The substrate molecules have more kinetic energy and are more likely to collide with the enzymes active site, each collision also happens with more energy so each collision is more likely to result in a reaction.
What happens to the rate of reaction of an enzyme if you increase the temperature too much - past its optimum temperature?
The rate of reaction begins to rapidly decrease this is because the enzyme molecules vibrate too much and the bonds holding the enzyme together break and so the tertiary structure of the enzyme and its active site change, this means it can no longer form enzyme substrate complexes and is denatured
What happens to the rate of reaction of an enzymes if the pH is too high or too low?
The H+ and OH- ions disrupt the bonds holding the enzymes together, so the tertiary structure and the active sites change, this means it can no longer form enzyme substrate complexes and is denatured
Why does increasing the substrate concentration increase the rate of reaction up to a point?
If there are more substrate this means that enzyme substrate complexes will be more likely and so increasing the rate of reaction
What happens to the rate of reaction of an enzymes if you continue to increase the substrate concentration and why?
The graph will level off, this is because all the active sites will be occupied and so no more enzyme substrate complexes can form and so the rate of reaction of the enzymes level off
What is the point called when all the active sites are occupied?
Saturation point
What two things can prevent enzyme activity?
Competitive inhibitors and non-competitive inhibitors
How do competitive inhibitors work?
They are a similar shape to the substrate molecules and so they can bind to the active sites and block it so no substrate molecules can fit
How do non-competitive inhibitors work?
They bind to the enzyme away from the active site, and they cause the active site to change shape
Draw the structure of alpha glucose?
See flash card 6
What bonds are formed between two monosaccharaides?
Glycosidic
What is the difference between a polysaccharide and a disaccharide?
A disaccharide is two monosaccharaides and a polysaccharide is more than two
Draw the condensation reaction between two alpha glucoses?
See flash card 7
What reaction can join two monosaccharaides together?
Condensation reaction
What reaction can break a disaccharide into two monosaccharaides?
Hydrolysis reaction
Name three disaccharides?
Maltose, sucrose and lactose
What two monosaccharaides are in maltose?
Glucose and glucose
What two monosaccharaides are in sucrose?
Glucose and fructose
What two monosaccharaides are in lactose?
Glucose and galactose
What enzyme can break maltose down into glucose and glucose?
Maltase
What enzymes can break sucrose down into glucose and fructose?
Sucrase
What enzyme can break lactose down into glucose and galactose?
Lactase
What is lactose intolerance caused by?
When you don’t have enough of the enzyme lactase to break down the lactose in diary properly
What are the symptoms of lactose intolerance?
Stomach cramps, excessive flatulence and diarrhoea
How can lactose intolerance cause stomach cramps and excessive flatulence?
The undigested lactose is fermented by bacteria and produces a gas which causes the stomach cramps and excessive flatulence
How can lactose intolerance cause diarrhoea?
Because the lactose isn’t being broken down you will have a high concentration of lactose in the intestines, this lowers the water potential this means water moves in by osmosis increasing the water content in your faeces making them runny
What can two categories can sugars be classified into?
Reducing and non reducing sugars
What test can you do for the presence of reducing or non reducing sugars?
Benedict’s test
Describe the benedict’s test for a reducing sugar and the results you would expect?
Heat with benedict’s reagent, if the sample turns brick red then a reducing sugar is present, if there are no reducing sugars the solution will remain blue
Describe how you use benedict’s test to test for a non reducing sugar?
After doing the first test and finding no reducing sugars present, you boil a new sample with dilute hydrochloric acid and then neutralise with sodium hyrogencarbonate
Then you boil it again with the benedict’s reagent, if the sample turns brick red then a non reducing sugar is present, if there are no non reducing sugars the solution will remain blue
When testing for a non reducing sugar why do you boil the sample with hydrochloric acid first?
To break any disaccharides into monosaccharaides
What is an example of a non reducing a reducing sugar?
Non reducing - sucrose
Reducing - lactose and maltose
What two polysaccharides is starch a mixture of?
Amylose and amylopectin
What test can you do for the presence of starch?
Add iodine solution to the test sample, if starch is present the solution will go a dark blue black colour, if no starch is present the solution will remain a browny-orange colour
