What is the oesophagus adapted for and how?
The oesophagus is adapted for transporting food from the mouth to the stomach by having a thick muscular wall.
What is the structure of the stomach and its role?
The stomach is a muscular sac with an inner layer that produces enzymes, which digest proteins. Other glands produce mucus, which stops the stomach from being digested by its own enzymes. Its role is to store and digest protein.
What is the structure of the small intestine and its role?
The small intestine is a long muscular tube that further digests food via enzymes secreted from the walls and glands. The inner walls are folded into villi, which itself has millions of microvilli on the epithelial cells of each villus, providing a very large surface area for absorbing the products of digestion into the blood.
What is the role of the large intestine?
To absorb water.
What is the rectum?
Where faeces are stored before being egested.
Where are the salivary glands located and what do they do?
Salivary glands near the mouth release the enzyme amylase, which breaks starch down into maltose. Secretions are passed via a duct into the mouth.
What does the enzyme amylase do?
Breaks starch down into maltose.
What is the pancreas and what does it produce?
The pancreas is a large gland underneath the stomach. It produces pancreatic juice, which contains proteases (digests proteins), lipase (digests lipids), and amylase (digests starch).
What does pancreatic juice contain?
Proteases, lipase, and amylase.
What do proteases do?
What do lipases do?
What two stages does digestion take place in?
1) Physical breakdown
2) Chemical digestion
What happens in physical breakdown of food?
Large food is broken down into small pieces via the teeth, making it possible to ingest food and providing a large surface area for chemical digestion. Food is also churned by the muscles in the stomach wall.
What happens in chemical digestion of food?
Large molecules are hydrolysed (split up via adding water to the chemical bonds that hold them together) by enzymes into small molecules, which can be absorbed and assimilated.
How do enzymes break down a large molecule?
Enzymes are specific and so more than one enzyme is needed to break down a large molecule. One enzyme splits a large molecule into sections, and these sections are hydrolysed further into smaller molecules by one or more extra enzymes.
What are three examples of digestive enzymes?
What do carbohydrases do?
Break down carbohydrates to monosaccharides.
What do lipases do?
Break down lipids to glycerol and fatty acids.
What do proteases do?
Break down proteins to amino acids.
What is assimilation?
This is where molecules are incorporated into body tissues and/or used in processes within the body.
Why does a large variety of life exist on earth?
Carbon atoms readily form bonds with other carbon atoms, allowing a sequence of combinations of various lengths to be built up to form a backbone along which other atoms can be attached, which permits an immense number of molecules.
What is a monomer?
An individual molecule that makes up a chain of several molecules
What is a polymer?
A long chain formed of repeating monomer units.
What is the basic monomer unit in carbohydrates?
A sugar - AKA sachharide.
What chemical formula do monosaccharides have?
(CH₂O)<i>n</i>, where n = any number between 3 and 7.
What is the chemical formula for the monosaccharide hexose sugar glucose?
What is the structure of alpha glucose?
- Top left = H
- Top right = H
- Bottom left = HO
- Bottom right = HO
What types of sugar are reducing sugars?
All monosaccharides and some disaccharides.
What does it mean to be a reducing sugar?
A sugar that donates electrons to another chemical.
If you're investigating to see if a reducing sugar is present within a solution, after doing the Benedict's reagent + heat test, what colour should the solution turn if the sugar is present?
Orange/brown or red.
What is the test for a reducing sugar?
1) Add 2cm^3 of food sample to a tube. If not already in liquid form, grind up in water.
2) <b>Add </b>2cm^3 of <b>Benedict's reagent.</b>
3) <b>Heat the mixture</b> gently in boiling water for five minutes.
4) <b>The concentration of reducing sugar is as follows (from none to high):</b>
Blue -> green -> yellow -> orange -> red.
Which disaccharide does glucose-glucose form?
Which disaccharide does glucose-fructose form?
Which disaccharide does glucose-galactose form?
What kind of reaction happens when two monosaccharides join together?
A condensation reaction - a molecule of water is removed.
Which bond is formed when two saccharides join together?
A glycosidic bond.
What is a condensation reaction?
Forming a bond via the removal of water.
What is a hydrolysis reaction?
Splitting a bond via the addition of water.
Why can non-reducing disaccharides (e.g. sucrose) not be detected using the Benedict's reagent + heat test?
They do not give up electrons to it.
What is the test for a non-reducing sugar?
1) Do the Benedict's reagent + heat test for a reducing sugar first.
2) Add dilute hydrochloric acid to the sample and heat it. This will hydrolyse any disaccharide present into its constituent monosaccharides.
3) Add some sodium hydrogencarbonate solution to the sample in order to neutralise the hydrochloric acid.
4) Retest using Benedict's reagent + heat. It should turn orange-brown if a non-reducing sugar was present in the original sample.
What are polysaccharides?
Monosaccharides that are joined by glycosidic bonds that were formed by condensation reactions.
Why are polysaccharides insoluble and what does this feature make them good for?
They are very large molecules. Being insoluble, they are good for storage and structural support.
What is starch?
Starch is a polysaccharide found in many plants in the form of grains. It is formed by linking between 200 and 100,000 alpha-glucose molecules by glycosidic bonds in a series of condensation reactions.
How do you test for starch?
1) Place 2cm3 of the sample in a test tube.
2) Add two drops of iodine solution and stir.
3) If starch is present, the solution will turn blue-black.
Why are enzymes produced in different parts of the digestive system?
Each enzyme works fastest in a different pH.
What is the process of starch digestion?
1) Food is taken into the mouth. Chewing by the teeth breaks it up into small pieces, giving it a large SA:V.
2) Saliva enters the mouth via salivary glands. It contains salivary amylase, which hydrolyses any starch in the food to maltose. It also contains mineral salts, helping maintain a neutral pH - what amylase works best at.
3) The food is swallowed and enters the stomach. Conditions are acidic, so amylase is denatured - no more starch can be hydrolysed.
4) Food is passed into the small intestine, where it mixes with pancreatic juice from the pancreas. This juice contains pancreatic amylase, continuing to hydrolyse remaining starch into maltose.
5) Muscles in the intestine wall push food along the small intestine, whose epithelial lining produces the enzyme maltase, which hydrolyses the maltose into alpha-glucose.
What is the process of sucrose digestion?
1) Sucrose must be released from within cells by chewing, firstly.
2) The sucrose passes through the stomach and small intestine, whose epithelial lining produces sucrase.
3) Sucrase hydrolyses the single glycosidic bond in sucrose to produce the two monosaccharides that make up sucrose - glucose and fructose.
What is the process of lactose digestion?
1) Lactose is digested in the small intestine, whose epithelial lining produces the enzyme lactase.
2) Lactase hydrolyses the glycosidic bond that links glucose and galactose.
Why do you stop producing much lactase as you get older?
Milk is no longer as large a part of your diet as it was when you were a baby.
Why are some people lactose intolerant?
They do not produce sufficient lactase to digest all the lactose they consume.
What happens to the lactose that lactose intolerant people consume?
Microorganisms break down the lactose when it reaches the large intestine, producing a large volume of gas, resulting in bloating, nausea, diarrhoea, and cramps.
Which three enzymes out of the following does the small intestine produce?
Sucrase, maltase, amylase, lactose.
Sucrase, maltase, and lactose.
What are amino acids?
The basic monomer units that combine to make a polymer called a polypeptide.
What can polypeptides be combined to form?
What is the structure of an amino acid?
- Amino group on top (-NH2)
- R group on left (different in each amino acid)
- Hydrogen atom on right
- Carboxyl group on bottom (-COOH)
- Carbon atom in centre, bonded to all above molecules.
What do amino acids combine to form and what reaction does this use?
A dipeptide - condensation reaction.
How is a dipeptide formeed from two amino acid monomers?
Water is made from combining the OH from the carboxyl group with the H from another amino acid. The two amino acids are linked by a peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.
What process involves many amino acids joining together and what does it form?
Polymerisation, forming a chain of amino acids called a polypeptide.
What is the primary structure of a protein and what does it determine?
The sequence of the amino acid chain. This determines its ultimate shape and function.
What could happen if you make a single change to the amino acid structure of a protein and why?
This can lead to a change in the shape of the protein and may stop it from carrying out its functions. A protein's shape is very specific to its function.
What is the secondary structure of a protein?
The shape formed by the amino acid chain when the amino acids bend and twist to form the most stable arrangement. It bends because the -C=O group and -NH group on either side of every peptide bond readily form weak hydrogen bonds.
What are the shapes of alpha helixes and beta-pleated sheets?
Alpha-helix: spiral shaped.
Beta-pleated sheet: flat.
What is the tertiary structure of a protein?
This is where the alpha-helices of the secondary structure of the protein gets twisted and folded even more to give the complex 3D structure of each protein. The 3D shape makes each protein distinctive, allowing it to recognise and be recognised by other molecules.
What three types of bond maintain the tertiary structure of a protein?
1) Disulphide bonds.
2) Ionic bonds.
3) Hydrogen bonds.
Give the properties of a disulphide bond.
Very strong; not easily broken down.
Give the properties of ionic bonds.
Between any carboxyl and amino groups not involved in forming peptide bonds. Weaker than disulphide bonds; easily broken down by changes in pH.
Give the properties of hydrogen bonds.
Numerous, but easily broken.
What is the quaternary structure of a protein?
This is where the protein consists of more than one polypeptide - they bind together to form one molecule. There may also be non-protein (prosthetic) groups associated with the protein.
What is the test for a protein?
Add a few drops of Biuret reagent to the sample and mix gently. A purple colour shows the presence of peptide bonds and, hence, protein. A blue colour shows no protein presence.
What are enzymes?
Globular proteins that act as catalysts.
What do catalysts do?
They alter the rate of a chemical reaction without undergoing permanent changes themselves, so they can be reused repeatedly.
How do enzymes work?
They work by lowering the activation energy level needed to activate the reaction between chemicals. Enzymes allow reactions to take place at a lower temperature than normal.
Are enzymes specific?
How does the active site in an enzyme work?
The active site is complementary to the substrate (molecule on which the enzyme acts). They fit neatly together to form an enzyme-substrate complex. The substrate is held within the active site by bonds that temporarily form between amino acids of the active site and groups on the substrate molecule.
What is the lock and key model?
This model proposes that enzymes work in the same way as a key operates only a single lock. A substrate will only fit the active site of one particular enzyme.
What observation supports the lock and key model?
Enzymes are specific in the reactions they catalyse.
What limitation does the lock and key model hold?
It has been observed that other molecules can bind to enzymes at sites other than the active site, changing the shape of the enzyme - showing that enzymes are not rigid, but flexible.
What is the induced fit model?
This model is more refined than the lock and key model. It proposes that the enzyme changes its shape slightly to fit the substrate. It is flexible - it has a general certain shape, but this alters in the presence of a substrate. As the enzyme changes shape, this strain distorts a particular bond, and, consequently, lowers the activation energy needed to break the bond.
What two things can the induced fit model better explain?
1) How other molecules can affect enzyme activity.
2) How activation energy is lowered.
What is the effect of temperature on enzyme action?
- An increase in temperature increases the kinetic energy of the molecules.
- The molecules move around more rapidly and collide with each other more often.
- More enzyme and substrate molecules bind together more often in a given time, so the rate of reaction increases.
- As the temperature increases, hydrogen bonds and other bonds in the enzyme start to break. The enzyme and its active site change shape, slowing the rate of reaction.
- If the temperature gets too high, the enzyme becomes denatured permanently - it stops working altogether.
What is the effect of pH on enzyme action?
- A change in pH alters the charges on the amino acids that make up the active site of the enzyme. The substrate can no longer bind to the active site, and the enzyme-substrate complex cannot be formed.
- A change in pH can cause the bonds that maintain the enzyme's tertiary structure to break. The enzyme changes shape, so the substrate can no longer fit.
What is pH?
A measure of hydrogen ion concentration.
What is the effect of substrate concentration on enzyme action?
- The more substrate there is, the faster the rate of reaction, as more active sites are being occupied.
- However, once all of the active sites are occupied at any one time, the reaction of reaction has reached its maximum - anymore extra substrate will have no effect on the rate of reaction, as all active sites are occupied.
What are enzyme inhibitors?
Enzyme inhibitors are substances that directly or indirectly interfere with the functioning of the active site of an enzyme, and so reduce its activity.
What two types of reversible inhibitors are there?
1) Competitive inhibitors.
2) Non-competitive inhibitors.
What do competitive inhibitors do?
- They have a molecular shape similar to that of the substrate, allowing them to occupy the active site of the enzyme.
- They compete with the substrate for active sites.
- If the substrate concentration is increased, the inhibitor effect is reduced.
- The greater the concentration of the inhibitor, the longer it will take for all substrate molecules to occupy the active sites.
What do non-competitive inhibitors do?
- These attach themselves the enzyme as a site other than the active site.
- This attachment alters the shape of the enzyme's active site, so substrate molecules can no longer occupy it.
- An increase in substrate concentration does not decrease the effect of the inhibitor.