Topic 1b - Biological Molecules and Transport in Cells Flashcards
What is an enzyme?
proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction
What do enzymes do?
- reduce the need for high temperatures
- speed up the useful chemical reactions in the body
- help speed up process of breaking down substances
What do the enzymes produced by living things act as?
Biological catalysts
What is the rule for enzymes and catalysing reactions?
- The active site can only catalyse one reaction at a time.
- Once all the active sites are full, increasing the amount of substrates has no effect on the rate, as there are no available enzymes to catalyse further reactions.
- Increasing the substrate concentration has no effect, so the rate will depend on the number of enzymes around
What is a catalyst?
a substance which increases the speed of a reaction, without being changed or used up in the reaction
What is a substrate?
the substance the enzyme acts on
What is the active site lock and key theory?
When the enzyme is in the optimum temperature, it doesn’t let a chemical reaction occur, with a substrate.
When the enzyme isn’t at optimum temperature, the substrate binds with the enzyme, and then a chemical reaction takes place. After the chemical reaction occurs, products are released.
What is the rate of reaction and temperature graph trend?
Increasing the temperature, increases the rate of reaction because the reactions have more energy, so they move about more, and collide with each other more often
What does the enzyme rate of reaction and temperature graph show?
- Changing the temperature, changed the rate of an enzyme-catalysed reaction.
- A higher temperature increases the rate at first, but if it gets too hot, some of the bonds holding the enzyme together break. This changes the shape of the enzyme’s active site, so the substrate won’t fit anymore (it is denatured).
- Enzymes in the human body usually work best around 37 degrees celsius.
At what temperature to human enzymes denature?
around 45 degrees celsius
What does the substrate concentration graph show?
- The higher the substrate concentration, the faster the reaction, because it is more likely that the enzyme will meet up with a substrate molecule.
- There is a steady increase in rate as more substrate molecules are available.
- After that, there are so many substrate molecules that the enzymes have as much as they need, as all the active sites are full, and adding more makes no difference, so the rate remains constant.
What is respiration?
the process of breaking down glucose, which transfers energy
What does a high pH mean?
it’s alkaline
What does a low pH mean?
it’s acidic
What happens if the pH is too low or too high?
the pH interferes with the bonds holding the enzyme together, which changes the shape of the active site and denatures the enzyme
At what pH does pepsin work best at?
pH 2
What is the optimum pH for enzymes?
pH 7
How do you investigate the effect of pH on amylase?
1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it reaches the optimum temperature of the amylase you are using. (Use a thermometer to measure the temperature.) Try to keep the temperature of the water constant throughout the experiment.
3) Use a syringe to add 3 cm^3 of amylase solution and 1 cm^3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the boiling tube into the beaker of water and wait for five minutes.
4) Next, use a different syringe to add 3 cm3 of a starch solution to the boiling tube.
5) Immediately mix the contents of the boiling tube and start a stop clock. 6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every thirty seconds and put a drop into a well on the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
8) Remember to control any variables each time you repeat the experiment to make it a fair test. Variables that need controlling include the concentration and volume of the amylase and starch solutions and the temperature of the reaction mixture.
What is the rate of reaction used to measure?
how much something changes over time
How do you calculate the rate of reaction?
rate = 1000 ÷ time taken
What is a biological molecule?
molecules found in living organisms
What are some examples of biological molecules?
- Carbohydrates
- Lipids
- Proteins
What do enzymes catalyse?
breakdown reactions
What are some examples of enzymes catalysing break down reactions?
- Many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules. These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. They can then pass into cells to be used by the body.
- Plants store energy in the form of starch (a carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars). These can then be respired to transfer energy to be used by the cells
What does enzyme amylase break down starch to?
maltose
How do you investigate the effect of pH on amylase?
1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it reaches the optimum temperature of the amylase you are using. (Use a thermometer to measure the temperature.) Try to keep the temperature of the water constant throughout the experiment.
3) Use a syringe to add 3 cm3 of amylase solution and 1 cm3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the boiling tube into the beaker of water and wait for five minutes.
4) Next, use a different syringe to add 3 cm3 of a starch solution to the boiling tube.
5) Immediately mix the contents of the boiling tube and start a stop clock. 6. Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this, use a dropping pipette to take a fresh sample from the boiling tube every thirty seconds and put a drop into a well on the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.
8) Remember to control any variables each time you repeat the experiment to make it a fair test. Variables that need controlling include the concentration and volume of the amylase and starch solutions and the temperature of the reaction mixture. See p.10 for more on fair tests.
How do you calculate the rate of reaction?
rate = 1000 ÷ time taken
What is the unit for the rate of reaction?
s^-1
What is the rate used to measure?
how much something changes of time
What is a biological molecule?
a molecule found in living organisms
What are some examples of biological molecules?
- Carbohydrates
- Proteins
- Lipids
What do enzymes catalyse?
breakdown reactions
What are some examples of enzymes catalysing breakdown reactions?
- Many of the molecules in the food we eat are too big to pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules. These can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream. They can then pass into cells to be used by the body.
- Plants store energy in the form of starch (a carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars). These can then be respired to transfer energy to be used by the cells
What are carbohydrase enzymes?
Carbohydrases convert carbohydrates into simple sugars. Amylase is an example of a carbohydrase. It breaks down starch.
What are protease enzymes?
Protease enzymes catalyse the conversion of proteins into amino acids
What are lipase enzymes?
Lipase enzymes catalyse the conversion of lipids into glycerol and fatty acids
Why do organisms need to be able to synthesise carbohydrates, proteins and lipids?
for their smaller components
How are enzymes involved in sythesising reactions?
Enzymes are used to catalyse the reactions involved, however these enzymes are different to the ones in breakdown reactions.
How can carbohydrates be sythesised?
by joining together simple sugars (e.g., glycogen synthase is an enzyme that joins together lots of chains of glucose molecules to make glycogen (a molecule used to store energy in animals))
How are proteins synthesised?
By joining amino acids together. Enzymes catalyse the reactions needed to do this.
How are lipids synthesised?
Enzymes are involved in the synthesis of lipids, from fatty acids and glycerol
How do you prepare a food sample which is liquid, to test for biological molecules?
If you are testing a liquid like milk or egg whites, you don’t need to prepare your sample, and like this. You can just go straight ahead and test it?
How do you prepare a food sample which is solid, to test for biological molecules?
1) Get a piece of your food and break it up using a pestle and mortar.
2) Transfer the ground up food to a beaker and add some distilled water.
3) Give the mixture a good stir with a glass rod.
4) Allow the mixture to settle out and then pipette out some of the liquid. This is your sample.
What are the two sugars, sugar is classified as, due to its chemical properties?
- reducing sugars (e.g., glucose)
- non-reducing sugars (e.g., sucrose)
What solution is used to test for sugars?
Benedict’s solution
What are reducing sugars found in?
biscuits and cereal
How do you test for reducing sugars?
1) Transfer 5 cm^3 of a food sample to a test tube.
2) Prepare a water bath so that it’s set to 75 °C.
3) Add some Benedict’s reagent (which is blue) to the test tube (about 10 drops) using a pipette.
4) Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes. Make sure the tube is pointing away from you.
5) During this time, if the food sample contains a reducing sugar, a coloured precipitate (solid particles suspended in the solution) will form. The solution in the test tube will change from the normal blue colour to green, yellow or brick-red. The higher the concentration of reducing sugar, the further the colour change goes - you can use this to compare the amount of reducing sugar in different solutions.
What solution is used to test for starch?
iodine solution
What foods contain lots of starch?
pasta, rice and potatoes
How do you test for starch?
1) Transfer 5 cm^3 of a food sample to a test tube.
2) Then add a few drops of iodine solution (iodine dissolved in potassium
iodide solution) and gently shake the tube to mix the contents. If the sample contains starch, the colour of the solution will change from browny-orange to blue-black.
What solution is used to test for proteins?
Biuret solution
What foods contain lots of protein?
meat and cheese
How do you test for proteins?
- Transfer 2 cm^3 of a food sample to a test tube.
2) Add 2 cm^3 of potassium hydroxide solution to make the solution alkaline.
3) Add a few drops of copper(II) sulfate solution (which is bright blue).
4) If the food sample contains protein, the solution will change from blue to pink or purple. If no protein is present, the solution will stay blue.
What solution is used to test for lipids (fats and oils)?
Emulsion solution
What foods are lipids (oils and fats) found in?
olive oil, margarine, and milk
How do you test for lipids (oils and fats)?
1) Transfer some of the food sample into a test tube.
2) Add 2 cm^3 of ethanol to the test tube.
3) Shake the test tube well for about 1 minute until the test substance dissolves.
4) Pour the solution into a test tube containing 2 cm^3 of distilled water.
5) If there are any lipids present, they will precipitate out of the liquid and show up as a milky emulsion. The more lipid there is, the more noticeable the milky colour will be.
What are calorimetry experiments used to do?
Work out how much energy different foods contain?
How do you do the calorimetry experiment?
1) Weigh a small amount of dry food and then skewer it on a mounted needle.
2) Add a set volume of water to a boiling tube (held with a clamp)
this will be used to measure the amount of energy that’s transferred when the food is burnt.
3) Measure the temperature of the water with a thermometer, then set fire to the food using a Bunsen burner flame.
4) Immediately hold the burning food under the boiling tube until it goes out. Then relight the food and hold it under the tube - keep doing this until the food won’t catch fire again.
5) Measure the temperature of the water again and record the temperature change.
How do you calculate the total amount of energy in food?
energy in food = mass of water * temperature change of water * 4.2
What are the units for the energy in food?
J (joules)
What are the units for the mass of water?
g (grams)
What is the temperature change of water measured in?
degrees celsius
How do you calculate the energy in each gram of food?
energy per gram of food = energy in food ÷ mass of food
What are the units for the energy per gram of food?
J/g (joules per gram)
What can substances pass in and out of cells by?
- diffusion
- active transport
- osmosis
What is diffusion?
The spreading out of particles from an area of high concentration (where there is lots of them) to an area of low concentration (where there is only a few of them)
Where does diffusion happen?
In both solutions and gases
What is a passive process?
Where energy isn’t required to make something work (e.g., in diffusion)
How are cell membranes are partially permeable?
They only let some molecules into cells, but not others. Only very small molecules can diffuse through cell membranes (e.g., oxygen( which is needed for respiration), amino acids, glucose and water)
What molecules cannot fit through the cell membrane?
protein and starch
What is osmosis?
Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration (low solute concentration) to a region of lower water concentration (high solute concentration).
Which way do water molecules pass through osmosis?
They pass through both ways, as the water molecules move about freely all the time, but because there are more water molecules on one side than on the other, there is a steady net (overall) flow into the region with fewer water molecules (the solution with the high solute concentration). This means that the more concentrated solution gets more diluted (made thinner or weaker by adding water or another solvent to it).
What is the concentration surrounding the cell, and the concentration of the fluid inside the cell like?
They both have different concentrations. This means that water will either move into the cell from the surrounding solution, or out of the cell, by osmosis.
What happens if the cell is short of water?
If a cell is short of water, the solution inside it will become quite concentrated (i.e. there’ll be a low concentration of water molecules). This usually means the solution outside the cell is more dilute (there’s a higher concentration of water molecules), and so water will move into the cell by osmosis. If a cell has lots of water, the solution inside it will be more dilute, and water will be drawn out of the cell and into the fluid outside by osmosis.
What is active transport?
Active transport is the movement of particles against a concentration gradient (i.e. from an area of lower concentration to an area of higher concentration) using energy transferred during respiration.
This process requires energy, unlike diffusion. It allows cells to absorb solution from very dilute substances.
What is an example of active transport?
When there’s a higher concentration of nutrients in the gut than in the blood, the nutrients diffuse naturally into the blood, but sometimes there’s a lower concentration of nutrients in the gut than in the blood.
Active transport allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way. This is essential to stop us starving. It means that glucose can be taken into the bloodstream when its concentration in the blood is already higher than in the gut. The glucose can then be transported to cells, where it’s used for respiration.
How do you investigate the effect of sugar solutions on plant cells?
1) Prepare sucrose solutions of different concentrations ranging from pure water to a very concentrated sucrose solution.
2) Use a cork borer to cut a potato into the same sized pieces (the pieces need to be about 1 cm in diameter and preferably from the same potato).
3) Divide the cylinders into groups of three and use a mass balance to measure the mass of each group.
4) Place one group in each solution.
5) Leave the cylinders in the solution, for at least 40 minutes (making sure that they all get the same amount of time).
What are the dependent, control and independent variables of the effect of sugar solutions on plant cells experiment?
- Dependent variable: cylinder mass
- Independent variable: concentration of sucrose solution
- Control variable: volume of solution, size of potato cylinders, amount of drying or age of potatoes used
What are the error that may occur during effect of sugar solutions on plant cells experiment?
- potato cylinders weren’t fully dried, so excess water would have given a higher mass
- water evaporated from beakers, so the concentration of the sugar solutions would change
How can we stop any error from occurring in the effect of sugar solutions on plant cells experiment?
Do the xperiment 3 times and find the mean percentage change at each concentration
How do you calculate the percentage change in mass?
percentage change in mass = ((final mass - initial mass) ÷ initial mass) * 100
What do the results on a graph show for the effect of sugar solutions on plant cells experiment?
- At the points above the x-axis, the concentration of water molecules in the sucrose solutions is higher than in the cylinders. The cylinders gain mass as water is drawn in by osmosis.
- At the points below the x-axis, the concentration of water molecules in the sucrose solutions is lower than in the cylinders. This causes the cylinders to lose water, so their mass decreases
- The point at which the line of best fit crosses the x-axis (where the percentage change in mass is 0) is the point at which the concentration of the sucrose solution is the same as the concentration of the solution in the potato cells. You can estimate the concentration of the solution inside the potato cells by reading the value off the x-axis at this point.
What is the unit of concentration?
‘M’ or ‘mol dm^-3’
