master Flashcards
(25 cards)
What is the primary structure of a protein?
Sequence of amino acids in a polypeptide chain, joined by peptide bonds.
What is the secondary structure of a protein?
The folding of the polypeptide chain into alpha helices or beta pleated sheets due to hydrogen bonding between amino acids (between NH group of one amino acid and C=O group of the other)
What is the tertiary structure of a protein?
The 3D folding of the polypeptide chain due to interactions between the R groups of the amino acids. Therefore, hydrogen bonds, ionic bonds and disulphide bridges are formed.
What is the quaternary structure of a protein?
Made up of more than one polypeptide chain, formed by interactions between polypeptides.
Describe the lock and key model of enzyme action.
Substrate binds to the active site, which is completely complimentary to it. They bind to form an enzyme-substrate complex.
Describe the induced fit model of enzyme action.
The substrate binds to the active site, which is not completely complimentary. This causes the active site to change shape so that it becomes complimentary to the substrate and an enzyme-substrate complex forms. This causes bonds in the substrate to change, lowering activation energy.
How have models of enzyme action changed over time?
Initially, the accepted model of enzyme action was the lock and key model, which stated that the active site is fixed and it is exactly complimentary to the substrate. New molecular evidence has suggested the induced fit model, which states that the active site changes shape slightly in order for the substrate to be able to fit.
Explain the specificity of enzymes.
The specific tertiary structure determines the shape of the active site. This is dependent on the sequence of amino acids (primary structure). The active site is complimentary to a specific substrate, and only this substrate can bind to the active site, forming an enzyme-substrate complex.
Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions.
As enzyme concentration increases, the rate of reaction also increases. At this point, enzyme concentration is the limiting factor and there is an excess of substrate. The rate increases because the concentration of enzymes is increasing, and there are more active sites available for substrate to bind to, and therefore more enzyme-substrate complexes are formed. At a certain point, the substrate concentration becomes the limiting factor, so the rate will stop increasing because all of the substrate will be used up.
Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions.
As substrate concentration increases, the rate of reaction also increases. At this point, substrate concentration is the limiting factor and there is an excess of active sites. The rate increases because the concentration of substrates is increasing, and there are more substrate molecules that can bind to active sites, and therefore more enzyme-substrate complexes are formed. At a certain point, the enzyme concentration becomes the limiting factor, so the rate will stop increasing because all of the enzymes will be saturated.
Describe and explain the effect of temperature on the rate of enzyme-controlled reactions.
As temperature increases up to the optimum, the rate of reaction increases because the molecules have more kinetic energy, meaning that more collisions between enzymes and substrate molecules will occur, leading to more enzyme-substrate complexes being formed. After the optimum, the rate of reaction decreases as the enzymes denature. Due to the high temperatures, the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme break, changing the shape of the active site. Therefore, the active site is no longer complimentary, meaning that fewer enzyme-substrate complexes can form.
Describe and explain the effect of pH on the rate of enzyme-controlled reactions.
If the pH decreases or increases too much beyond the optimum, the rate of reaction decreases. This is because the H+ and OH- ions interfere with the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme. Therefore, the shape of the active site changes and is no longer complimentary to the substrate, meaning that fewer enzyme-substrate complexes can form.
Describe and explain the effect of competitive inhibitors on the rate of enzyme-controlled reactions.
As the concentration of competitive inhibitors increases, the rate of reaction decreases. Competitive inhibitors have a similar shape to the substrate, and they therefore compete for the active site. This means that the active site is occupied, so the substrate can’t bind to the active site and fewer enzyme-substrate complexes can form. Increasing the concentration of substrate will reduce the effect of the competitive inhibitor as the substrate will begin to outcompete the inhibitor.
Describe and explain the effect of non-competitive inhibitors on the rate of enzyme-controlled reactions.
As the concentration of non-competitive inhibitor increases, the rate of reaction increases. Non-competitive inhibitors bind to the allosteric site, away from the active site. This leads to the tertiary structure of the enzyme changing, and the shape of the active site changing. Therefore, the active site is no longer complimentary to the substrate, so the substrate can not bind and fewer enzyme-substrate complexes form. Increasing substrate concentration will have no effect on the rate of reaction as the change to the tertiary structure is permanent.
Why is respiration important?
Respiration produces ATP which is hydrolysed to release energy. This energy is used for important processes like protein synthesis and active transport
What are the stages of aerobic and anaerobic respiration and where do they occur?
- Aerobic Respiration
1. Glycolysis - cytoplasm (anaerobic)
2. Link reaction - mitochondrial matrix
3. Krebs cycle - mitochondrial matrix
4. Oxidative phosphorylation - inner
mitochondrial membrane - Anaerobic Respiration
1. Glycolysis - cytoplasm
2. NAD regeneration - cytoplasm
Give 2 similarities and 2 differences between Chloroplasts and Mitochondria.
Similarities
* Both organelles are double membrane bound
* Both organelles contains their own DNA and ribosomes
Differences
* The fluid inside the organelles is called the matrix in mitochondria and is called the stroma in chloroplasts
* Chloroplasts contain thylakoid membrane and grana, whereas mitochondria contain cristae
Describe the process of glycolysis
Glucose is phosphorylated to glucose phosphate using inorganic phosphates from 2 ATP molecules. This glucose phosphate is hydrolysed to 2 x 3C Triose Phosphate molecules, which are then oxidised to 2 x 3C Pyruvate, and the hydrogen removed is transferred to the co-enzyme NAD to form 2 x reduced NAD. 4 molecules of ADP are phosphorylated, forming ATP. Therefore, overall net gain is 2 x ATP, 2 x reduced NAD and 2 x 3C Pyruvate
Explain what happens after glycolysis if respiration is anaerobic
Fermentation:
1. Pyruvate is converted to lactate (animals & some bacteria) or ethanol (plants & yeast)
2. This oxidises reduced NAD, so NAD is regenerated
3. So glycolysis can continue (which requires
NAD) allowing continued production of ATP
Suggest why anaerobic respiration produces less ATP per molecule of
glucose than aerobic respiration
Only glycolysis is involved which produces a small amount of ATP. There is no oxidative phosphorylation which forms majority of ATP.
What happens after glycolysis if respiration is aerobic?
Pyruvate is actively transported into the mitochondrial matrix
Describe the link reaction
Pyruvate is oxidised and decarboxylated to 2C Acetate. CO2 is produced and NAD is reduced. Acetate combines with coenzyme A, forming Acetyl Coenzyme A. This reaction happens twice per glucose molecule and the products per glucose molecule are 2 x Acetyl Coenzyme A, 2 X CO2 and 2 X reduced NAD
Describe the Krebs cycle
Acetyl Coenzyme A combines with a 4C molecule, releasing Coenzyme A and producing a 6C molecule. The 6C molecule is decarboxylated and dehydrogenated to a 5C molecule, so Carbon Dioxide and reduced NAD is released. The 5C molecule is decarboxylated and dehydrogenated into the 4C molecule from the start. This process creates ATP, 3 molecules of reduced NAD, a molecule of reduced FAD and 2 molecules of carbon dioxide. This process occurs twice per glucose molecule.
Describe the process of oxidative phosphorylation
- Reduced NAD/FAD is oxidised to release H atoms, which then split into protons (H+) and electrons (e-)
- Electrons are transferred down electron transfer chain by redox reactions, as they move down, energy is released.
- Energy released by electrons is used to actively pump protons from matrix to the inner membrane, so proton accumulate in the intermembrane space, creating a proton gradient.
- Protons diffuse into matrix down the electrochemical gradient, via ATP synthase
- In the matrix at the end of the ETC, oxygen is the final electron acceptor. The oxygen combines with the hydrogen ions to form water
