Cell Respiration (SL) Flashcards
What is Cell respiration and what is the main source for this?
Cell respiration is the controlled release of energy from organic molecules to produce ATP
The main organic compound used for this process is carbohydrates (glucose), although lipids and proteins can also be digested
Outline the main role and structure of ATP and briefly mention how it is produced (as per definition of cell respiration)
ATP (adenosine triphosphate) is a high energy molecule that functions as an immediate source of power for cell processes
One molecule of ATP contains three covalently linked phosphate groups – which store potential energy in their bonds
When ATP is hydrolysed (to form ADP + Pi) the energy stored in the phophate bond is released to be used by the cell
Cell respiration uses energy stored in organic molecules to regenerate ATP from ADP + Pi (via oxidation)
What are the uses of ATP? Mnemonic: BANG ME
Biochemical processes that utilise ATP include:
Biosynthesis of macromolecules (e.g. polymer assembly)
Active transport (e.g. endocytosis / exocytosis)
Nerve transmission (e.g. propagation of action potentials)
Growth and repair (e.g. mitotic division)
Movement (e.g. muscle contraction)
Emission of light (e.g. bioluminescence)
What is the reason for cells requiring a continual source of ATP for cell activities?
When ATP as the energy source is used in cells, almost all of it is ultimately converted to heat. It may seem that this heat is useful in keeping the organism warm, but it cannot be reused for cell activities and is eventually lost to the environment. Therefore, ATP needs to be produced constantly in order for there to be sufficient energy for cellular activities to be carried out at the optimum rate and efficiency.
What is Anaerobic respiration?
Anaerobic respiration is the partial breakdown of carbohydrates (glucose) in the cytosol in the absence of oxygen, which gives a small yield of ATP.
Anaerobic cell respiration is useful in three situations:
- When a short but rapid burst of ATP production is needed
- When oxygen supplies run out in respiring cells
- In environments that are oxygen deficient
Both anaerobic and aerobic respiration pathways begin with the anaerobic breakdown of glucose in the cytosol by glycolysis. What is the outcome of glucose in glycolysis and what else does glycolysis produce?
Glycolysis breaks down glucose (6-C) into two molecules of pyruvate (3C), and also produces:
Hydrogen carriers (NADH) from an oxidised precursor (NAD+) A small yield of ATP (net gain of 2 molecules)
What are the products of anaerobic cell respiration in humans and plants? And what is the nature of this conversion?
In animals, the pyruvate is converted into lactic acid (or lactate)
In plants and yeasts, the pyruvate is converted into ethanol and carbon dioxide
The conversion of pyruvate into lactic acid (animals) or ethanol and CO2 (plants / yeasts) is reversible
What is the purpose of anaerobic respiration in glycolysis?
The purpose of anaerobic respiration is to restore stocks of NAD+ – as this molecule is needed for glycolysis
By restoring stocks of NAD+ via anaerobic pathways, the organism can continue to produce ATP via glycolysis
Explain lactate production in humans via anaerobic respiration during exercise.
Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP
When exercising at high intensity, the cells’ energy demands will exceed what the available levels of O2 can supply aerobically
Hence the body will begin breaking down glucose anaerobically to maximise ATP production
This will result in an increase in the production of lactic acid, which leads to muscle fatigue
When the individual stops exercising, oxygen levels will increase and lactate will be converted back to pyruvate
What is Aerobic respiration and briefly state what happens in it?
Aerobic cell respiration requires the presence of oxygen and takes place within the mitochondrion
Pyruvate is broken down into carbon dioxide and water, and a large amount of ATP is produced (~34 – 36 molecules)
What does aerobic respiration consists of?
Although aerobic respiration typically begins with glycolysis in carbohydrates, glycolysis itself is an anaerobic process
Aerobic respiration consists of the link reaction, citric acid cycle (or Krebs cycle) and the electron transport chain
What is yeast fermentation used for?
In yeasts, fermentation results in the production of ethanol and carbon dioxide – which can be used in food processing:
Bread – Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking
Alcohol – Ethanol is the intoxicating agent in alcoholic beverages (concentrations above ~14% damage the yeast)
What is bacterial fermentation used for?
Bacterial cultures can also undergo fermentation to produce a variety of food products
Yogurt / Cheese – Bacteria produce lactic acid anaerobically, which modifies milk proteins to generate yogurts and cheeses
