WJEC A-level Biology 3.4 Microbiology

• What is respiration?

  The process of energy being released in cells by oxidation of organic molecules.
• What is a catabolic reaction?

  Releases energy and is used to break down large molecules into smaller ones.
• What happens in respiration?

  Reactions catalysed by enzymes break down carbohydrates, fat or proteins to release energy to produce ATP.
• What is ATP?

  Adenosine triphosphate
• What is a metabolic pathway?

  A series of chemical reactions that start with a substrate and finish with an end product. This end product forms the substrate for the next stage of the pathway.
• What is the respiration equation?

  C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy
• What needs to happen to create ATP?

  Substrate level phosphorylation and oxidative phosphorylation.
• What is substrate level phosphorylation (in terms of respiration)?

  Energy is taking in a metabolic reaction from a substrate to add a phosphate to ADP (ADP+Pi=ATP). happens in glycolysis, link reaction and Krebs cycle.
• What is oxidative phosphorylation (in terms of respiration)?

  This makes ATP for ADP and Pi with energy produces by the movement of electrons along electron carriers.
• How many stages are there in respiration, what are they?

  4. Glycolysis, link reaction, Krebs cycle and electron transport chain.
• Where does glycolysis happen?

  In the cytosol of the cytoplasm.
• Where does the link reaction occur?

  Matrix of mitochondria
• Where does the Krebs cycle occur?

  Matrix of mitochondria
• Where does the electron transport chain occur?

  Inner mitochondrial membrane.
• Which part of respiration doesn't involve oxygen

  Glycolysis
• What happens in glycolysis? Basic

  A glucose molecule gets broken into two pyruvic acid.
• What happens in glycolysis step by step?

  Glucose gets phosphorylated removed from ATP forming hexose phosphate. This splits into two lots of triose phosphate. Each triose phosphate in turned into pyruvic acid by dehydrogenation using a dehydrogenase enzyme (removing a hydrogen to add to NAD.) This creates 4 ATP by substate level phosphorylation. The reduction reaction creates two molecules of reduced coenzyme NAD.
• What is phosphorylation?


  The attachment of a phosphate group to a molecule or ion.
• What is the link reaction basic?

  Pyruvic acid diffusing into the mitochondrial matrix and gets turned into acetyl co-enzyme A.
• How does pyruvic acid get into the mitochondrial matrix?

  Facilitated diffusion by carrier proteins
• What is decarboxylation?

  The removal of carbon dioxide from a molecule
• What happens in the link reaction step by step?

  Pyruvic acid loses a carbon by decarboxylation (using decarboxylase enzyme) which forms CO2 forming acetate. Then hydrogens are removed by dehydrogenation (using dehydrogenase) reducing NAD into NADH2. Acetyl then combines with co-enzyme to form acetyl co-enzyme A. This happens twice per pyruvic acid.
• What is the function of the krebs cycle?

  To get energy from the carbon bonds to provide ATP and reduce NAD and FAD, releasing CO2.
• What happens in the krebs cycle step by step?

  Acetyl co-enzyme combines with oxaloacetate acid to form citric acid. Co-enzyme gets regenerated and goes back to the link reaction. Citric acids go under dehydrogenation reaction four times which removes hydrogen and two decarboxylation to remove carbon dioxide. Oxaloacetate gets regenerated to re-enter the kerbs cycle. The hydrogens are used to reduce 3 NAD to NADH2 and one to reduce FAD to FADH2. Enough energy is released to create one ATP by substrate level phosphorylation. This happens twice per Acetyl co A.
• What are the cristae?

  Infoldings in the inner membrane of the mitochondria.
• At the end of the Krebs cycle where is most of the energy?


  In the hydrogen atoms which are attached to the hydrogen acceptor molecules NAD and FAD.
• At what stage in respiration is the glucose completely oxidised?

  At the end of Krebs cycle.
• What happen in the electron transport chain step by step?

  The reduced coenzymes (FAD AND NAD) release hydrogens which are split into protons (H+) and electrons (e-). Electrons are passed along the electron carrier proteins in the inner mitochondrial membrane, as they go down the electron transport chain, they lose energy. Electrons release small amounts of energy by moving along the chain pumps protons through proton pumps from the mitochondrial matrix into the intermembrane space using a proton pump mechanism. This creates an electrochemical gradient across the membrane by storing protons in the intermembrane space. Protons then move from an area of high energy back down the electrochemical gradient back to the mitochondrial matrix through the ATP synthetase releasing energy to create ATP (ADP + Pi=ATP). This movement of protons (H+) is known as chemiosmosis. The whole process is oxidative phosphorylation. Oxygen combines with the protons and electrons (the parts that make up Hydrogen) to form water. 4H+ + 4e- + 2O2 --> 4H2O.
• How many proton pumps are there?

  3
• What can also be used as respiratory substrates?

  Proteins and Lipids
• If lipids are used what is split in glycolysis?

  Glycerol
• What uses lipids as its primary substrate and why?

  Liver, it has a rich blood flow to deal with the extra CO2 produced and more energy gets produced.
• What happens when proteins are used in respiration?

  Proteins are digested into amino acids then deaminated. The keto acid gets converted into acetyl co-enzyme A, pyruvic acid or some other Krebs cycle intermediate and the oxidised to produce ATP.
• What is deamination?


  The removal of an amino group from an amino acid or other compound.
• What is an anaerobe? Plus example.

  An organism that can respire with oxygen. Yeast, fungi, bacteria.
• What is the difference between aerobic and anaerobic respiration?

  Anaerobic doesn't fully break down the sugar. Aerobic fully breaks down the sugar.
• What does glucose break down into in anaerobic respiration?

  It is broken down to alcohol or lactic acid (lactate).
• What happens in anaerobic respiration?

  Only glycolysis takes place. NAD thats reduced can't get oxidised and create NADH2 meaning hydrogen doesn't pass into the electron transport chain. Pyruvic acid doesn't enter the mitochondria. It gets reduced to lactic acid or ethanol. Pyruvic acid becomes the hydrogen accepter.
• What happens in fermentation?

  Pyruvic acid gets turned into alcohol and carbon dioxide. The pyruvic acid gets decarboxylated to produce ethanal. Then reduced to ethanol by NAD passing hydrogen on.
• What are bacteria?

  Prokaryotes, smallest cellular organisms.