8 yeast metabolism : sugars Flashcards
What is the primary aim of yeast metabolic function?
Yeast cells aim for cellular growth and proliferation, assimilating nutrients from the medium and removing waste products efficiently to out-compete potential competitors.
What is the role of ATP in yeast energy generation?
ATP acts as the ‘molecular unit of currency’ for energy; it conserves energy in high energy bonds, which are broken during chemical reactions to release energy.
What are the key coenzymes involved in yeast metabolic reactions?
Key coenzymes include NAD+, NADP+, and FAD+, which can be reversibly reduced or oxidized to hold and release electrons for metabolic reactions.
What is wort and its significance for yeast?
Wort is a brown sugary liquid that acts as a growth medium for yeast, containing essential nutrients and fermentable sugars required for reproduction and survival.
What is the sugar composition of wort?
Maltose is the most abundant sugar in wort, constituting about 55-65% of fermentables, with the remainder mainly comprising glucose, fructose, sucrose, maltotriose, and non-fermentable sugars.
How do yeast cells assimilate sugars from wort?
Yeast assimilates wort sugars in the order of glucose, fructose, sucrose, maltose, and maltotriose; carbohydrate uptake is influenced by the presence of glucose which can repress the metabolism of complex sugars.
What is the primary pathway for sugar utilization in yeast?
The main pathway for sugar utilization in yeast is glycolysis (Embden-Meyerhof-Parnas pathway), which is always active and can operate in reverse as gluconeogenesis when sugar is not present.
What does the glycolysis pathway involve in yeast metabolism?
Glycolysis involves a preparatory phase using 2 ATP and a payoff phase producing 4 ATP and 2 NADH, resulting in the production of 2 pyruvate molecules.
What is the PP pathway and its significance in yeast metabolism?
The Pentose Phosphate Pathway (PP pathway) provides a route for pentose sugar utilization and is important for generating NADPH needed in lipid synthesis and converting 6-carbon sugars into 5-carbon sugars, which are important for DNA synthesis.
What is gluconeogenesis and its relevance in industrial fermentations?
Gluconeogenesis is the reverse of glycolysis, used under aerobic conditions to metabolize non-sugar resources like ethanol and glycerol; not desirable in industrial fermentations as it can remove ethanol produced during propagation.
How is sugar metabolism affected by aerobic and anaerobic conditions in yeast?
Under aerobic conditions, sugars are metabolized to H2O and CO2 via the TCA cycle and Electron Transport Chain, while under anaerobic or glucose-repressed conditions (Crabtree effect), sugars are converted to ethanol and CO2.
What is the TCA cycle and where does it occur?
The TCA cycle occurs in the mitochondria, converting pyruvate into Acetyl-CoA and cycling to release CO2, generate NADH, FADH, and ATP which are used in the electron transport chain.
How does the electron transport chain function in yeast?
Electrons from NADH fuel the Electron Transport Chain within the mitochondrial membrane to generate ATP, using an electrochemical gradient created by proton pumps within the chain.
What is the Crabtree effect in yeast?
The Crabtree effect describes the phenomenon where high glucose levels lead to a preference for fermentation over respiration, even under aerobic conditions, allowing rapid sugar uptake and energy conversion.
How does the Pasteur effect impact yeast metabolism?
The Pasteur effect describes the inhibition of ethanol production in the presence of oxygen, decreasing the rate of glycolysis and ensuring carbon enters the Krebs cycle, leading to higher ATP yield.
What are additional routes for carbon metabolism in yeast?
Yeast can convert glucose into storage carbohydrates like glycogen and trehalose, which can be used when growth is restricted or under stress; these processes are crucial for yeast’s survival and adaptability to changing conditions.
How do yeast cells handle environmental stress in terms of carbohydrate metabolism?
Under stress, yeast accumulates trehalose, which acts as an anti-stress compound, helping to manage adverse conditions by protecting cell integrity and functions.
What is the significance of pyruvate conversion to acetyl-CoA in yeast?
In fermentative conditions, pyruvate is converted to acetyl-CoA via the ‘acetate route,’ which is crucial for the synthesis of amino acids and fatty acids, essential for cell membrane integrity, protein synthesis, and flavor development in fermented products.
