1.15 to 1.17 enzymes Flashcards
state how a catalyst affects the rate of a reaction (1)
a catalyst increases the rate of a reaction (1)
name the part of an enzyme where substrate molecules bind (1)
active site (1)
enzymes have a ‘high specificity’ for their substrates. describe what this means. (1)
it means usually only one type of substrate will fit into the active site of a specific enzyme (1)
explain why increasing the substrate concentration fails to affect the rate of an enzyme-controlled reaction after a certain point. (2)
after a certain point, all of the active sites on the enzymes are full (1) and increasing the substrate concentration does not result in more substrate molecules entering the active sites of enzymes, so the rate of the reaction is not affected (1).
enzyme A’s activity will be different at 38°C and 60°C. explain why (3)
At 38°C enzyme A will most active as this is its optimum temperature (1). at 60°C, enzyme A is denatured and will not be active (1) because the shape of the active site has changed (1)
describe and explain the effect on enzyme activity of increasing the pH above the optimum level. (3)
the enzyme activity decreases (1) because the pH affects the bonds in the enzyme, causing the active site to change shape (1) and denaturing he enzyme (1)
explain why the breakdown of large molecules into smaller components is necessary for organisms (2)
organisms need to be able to break down large molecules into smaller components so that they can be absorbed into the bloodstream and into cells (1) to be used for growth and other life processes (1)
[orlistat is a drug that is used to help lower obesity rates. it works by preventing lipase from working in the digestive system.]
explain why patients taking orlistat may have oily faces. (3)
orlistat prevents lipase from working so lipids are not broken down (1) into fatty acids and glycerol (1). this means lipids are not absorbed into the blood and instead pass through the digestive system and into the faeces. (1)
What are enzymes?
Biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves
What is an advantage of enzymes in the body?
They enable cellular reactions to take place at lower temperatures
What is the active site of an enzyme?
The region of an enzyme to which a substrate molecule binds and the reaction takes place
Describe the ‘lock and key’ model
- Substrate collides with the active site of an enzyme
- Substrate binds, enzyme-substrate complex forms
- Substrate converted to products
- Products released from the active site which is now free to bind to another substrate
What factors affect the rate of an enzyme-controlled reaction?
● Temperature
● pH
● Substrate concentration
Explain how increasing temperature initially affects the rate of an enzyme-controlled reaction
● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
Explain how pH affects the rate of an enzyme-controlled reaction
● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases
Explain how the substrate concentration affects the rate of an enzyme-controlled reaction
● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus
How can the rate of an enzyme-controlled reaction be calculated when given a value for time?
rate = 1/time
What are the units for rate?
s^-1
Why must large organic molecules be broken down into smaller, simpler molecules in the body?
● Large molecules are too big to be absorbed across the surface of the gut wall
●∴ large molecules are broken down into smaller molecules for absorption into the bloodstream
Give an example of the breakdown of large molecules into smaller molecules in plants
Starch is broken down by enzymes into simpler sugars which are respired to release energy.
What type of molecules are proteins and carbohydrates?
Polymers
What are the monomers of carbohydrates?
Simple sugars
Which group of enzymes catalyses the breakdown of carbohydrates?
Carbohydrases
Which type of carbohydrase catalyses the breakdown of starch?
Amylase
What are the monomers of proteins?
Amino acids
Which type of enzyme catalyses the breakdown of proteins?
Proteases
What is the function of lipases?
Enzymes which catalyse the breakdown of lipids into fatty acids and glycerol
Why are small molecules synthesised into larger organic molecules in the body?
Large molecules are used for storage (e.g. glycogen) or are used to build structures(e.g. organelles).
Which enzyme catalyses the formation of glycogen from glucose?
Glycogen synthase
How can the amount of energy contained in food be measured?
Measured using calorimetry
What is calorimetry?
A method of measuring the heat transfer during a chemical reaction
Describe the method used to measure the amount of energy in a sample of food
- Add a set volume of water to a boiling tube, record initial temperature
- Record the mass of a small sample of food (e.g. bean)
- Stick the sample onto a mounted needle
- Using a Bunsen burner light the food sample
- Hold the sample under the boiling tube until it burns up
- Record the maximum temperature reached by the water
- Record the final mass of the food sample
How can the amount of energy in the food sample be calculated?
energy in food (J) = mass of water (g) x temperature change of water (°C) x 4.2
energy (J/g) = energy in food (J) / mass of food burnt (g)
Digestion?
A process that breaks down large insoluble molecules into smaller useful soluble molecules via enzymes, chemicals and mechanical action
Large insoluble molecules?
Such as carbohydrates, proteins and lipids, need to be broken down during digestion into dissolvable products that can be absorbed by the body
Small soluble molecules?
Products of digestion such as glucose, amino acids, glycerol and fatty acids, these molecules are small enough to be absorbed by the body for specific uses
Absorption?
Small soluble molecules can be absorbed in the small intestine following digestion, they diffuse into the blood and are then transported around the body for specific purposes
Carbohydrates
Provide energy for chemical reactions and can break down into sugars
Proteins
The building blocks of cells and tissues that can break down into amino acids
Lipids
An energy store of fats and oils that can break down into glycerol and fatty acids
Conversion of glucose to complex carbohydrates
Glucose, a product of digestion, can be converted into new complex carbohydrates such as glycogen
Glucose
A soluble product of digestion, essential for respiration to release energy and is also needed to synthesise new molecules
Formation of lipid molecules
Glycerol and fatty acids, products of digestion, join together to form new lipids
Protein synthesis
Amino acids, products of digestion, join together in specific arrangements to form new proteins for growth and repair
Enzymes
Biological catalysts which speed up reactions without being used up, essential for the digestion of large insoluble molecules
Amylase
A carbohydrase enzyme found in saliva and the small intestine that breaks the chemical bonds in starches
Carbohydrases
Enzymes that speed up the breakdown of carbohydrates into simple sugars
Lipase
Enzyme found in the small intestine that breaks down lipids into glycerol and fatty acids
Protease
Enzyme found in the stomach and small intestine that breaks down proteins into amino acids
Metabolic reactions
Enzymes are involved in many important reactions in the body, building large molecules from small ones as well as breaking down large molecules into small ones
Metabolism
the sum of all the reactions in a cell or the body including reactions such as respiration or the synthesis of new molecules
Enzymes as proteins
Enzymes are made up of specific sequences of amino acids, which are linked to form chains that fold up into the specific shape of the overall enzyme protein
Importance of amino acid sequence
The sequence of amino acids determines the overall structure and function of a protein such as an enzyme, different amino acids could lead to proteins with altered structures or functions
