2.2 Yeast Metabolism Flashcards
Principle sugars of grape must
glucose and fructose, with smaller amts of sucrose and raffinose; fru + glu in equal amt makeup almost all sugar content
Sugars in molasses
sucrose mainly, smaller amts of glucose, fructose; beet = raffinose as well; glucose+fructose in almost equal amts once in cytoplasm
sugars within starchy cereals
maltose, smaller amounts of glucose, maltotriose, vs sm maltotetreose, and higher dextrins; also small amt of sucrose; sugars are transported in order of molecular size, smallest first, and not according to concentration in the wort…gluc, maltose, maltotriose, then maltotetreose
Modern cereal distilling strains ferments?
glucose, maltose, sucrose, maltotriose, and some ferment 3-gluc destrins and maltotetreose
first step in yeast metabolism of sugars
Transport into cell…need to gain access to E activity of cytoplasm: sugars up to triose diffuse freely through cell wall and transported across the cytoplasmic membrane by specific transport Es; exceptions include: sucrose and raffinose, and lactose for Kluyveromyces.
Sucrose, raffinose, and lactose cell membrane transport?
each are hydrolyzed by enzymes located within cell wall which are formed rapidly in response to the presence of these sugars; sucrose-> glucose and fructose, raffinose -> fructose, glucose, and galactose, lactose-> galactose and glucose; no spec permeases required as their breakdown products have them
Sugar transport systems into cell
- facilitated diffusion –> using conc gradient across the cytoplasmic membrane 2. Active transport –> usually requiring high energy ATP of the cell, in which case it is sugar phosphate which enters the cell, anticipating the first step of metabolism; however, 3. active systems may also involve entry of the nutrient being balanced by efflux of H+, K+, Na+, or other ions from the cytoplasm, but not sugars….whichever method, a specific permease E is obligatory, and all permease activities would not occur altogether, nor would fac diffusion and active transport of same sugar occur at same time.
cytoplasmic membrane structure
a semi-permeable bi-layer of phospholipid (phosphoglyceride) interspersed with protein molecules, the transport protein, and sterol; combo of hydrophilic (out) and phobic (inner tails) layers prevents osmosis of all but a few ions and simple organic compounds; permease Es span the thickness of membrane bi layer and by reacting w/their specific substrate provides a specific “pore” through the membrane.
Sterol and UFA synthesis in yeast cell?
involves reduction of CoE NADP which requires molecular O2 for re-oxidation; therefore anaerobic growth is limited to 1-2 generations, unless sufficient UFAs and sterols are provided ready made (only possible in culture medium), in which case anaerobic growth can continue as long as the supplement is available.
M2-M4 transport into cell
specific permeases to transport across cell wall/ membrane; maltose permease is an inducible enzyme, produced only in the presence of maltose, but also inhibited by glucose and only activated when glucose levels fall sufficiently low (varies across strains); similar situation happens with M3 and M4
the 2 biological purposes of metabolism of sugars
- to harness as much energy as possible for biosynthesis activities of the cell 2. to create the low molecular weight “building blocks” of organic compounds for the creation of new cell material; cell must be able to synthesize its own weight of biomass over 1 generation at a time; to fulfill both of these aims the metabolism of sugars is in a gradual series of E-mediated transformations.
Overall chemical equation for the EMP (Embden Meyerhof Parnas) Pathway
- Hexose + 2ATP + 2NAD +2PO3-3 –> 2pyruvate + 4ATP + 2NADH2 (a profit of 2ATP/ hexose, phosphate ions = requirement…can be added to grape or molasses if necessary)
- Hexose + 2ATP + 2NADH2 + 2PO3-3 –> 2glycerol + 2ATP + 2NAD (triggered in stressful conditions…no new ATP is generated, however, when re-ox NAD is a valuable commodity, glycerol pathway is a possible source)
Growth factors or other nutrients required for growth outside of C+N, needed only in trace amts
Ca, Cu, Fe, K, Mn, and Zn –> trace as co-factors of enzymes (water sources, or raw material…ie molasses); Nicotinamide adenine dinucleotide (NAD)= essential for many metabolic pathways–> most can synthesize from simpler C+N compounds, but some require supplement through niacin; Biotin–> requirement as E-co factor; Riboflavin, thiamine, and other E co factors –> varies b/e strains
Growth factors or other nutrients required for growth outside C+N needed in larger quantities
Na, Mg, PO3, and SO4; Na and Mg–> involved in transport across cell membranes (active systems?); PO3–> for structural phospholipids as well as the smaller amts required for ATP and similar compounds; SO4–> mainly for synthesis of 2-containing amino acids for protein synthesis.; some batches of grape must and molasses could be deficient and supplementation may be required (i.e DAP)
Mjr limit on yeast growth during a fermentation results from?
inability to synthesize the UFAs and sterols of membrane structure under anaerobic conditions…atm O2 could be provided as growth factor (lipid production, cell membrane health), although in practice the reserve of membrane material from the orig aerobic cultivation in yeast factory allows sufficient growth for successful ferms
