38. Catabolism, Glycolysis

Question 1

what is microbial metabolism?

Answer 1

• sum of chemical reactions in the cell

Question 2

what are the components of metabolism?

Answer 2

• catabolism
  – harvest energy released from breakdown of compounds
  – energy used to synthesis energy carriers (ATP)
• anabolism
  – uses energy stored as ATP to synthesis and assemble subunits (building blocks) of macromolecules that make up cell

Question 3

why must energy be conserved?

Answer 3

• organisms require source of energy for growth
  – living organisms preserve their internal order by taking free energy from surroundings and returning to their surrounding an equal amount of energy as heat and entropy
• metabolism regulated to conserve raw materials and energy
  – and maintain balance between catabolism and anabolism
• control must be exerted to ensure resources are not expended on products that do not contribute to growth / survival

Question 4

what are the forms of energy from the environment?

Answer 4

• radiant energy
  – phototrophs
• oxidation of organic / inorganic molecules
  – chemotrophs

Question 5

how do most living cells use energy?

Answer 5

• use energy stored in chemical bonds of organic molecules
• obtain this energy in usable form
  – organisms utilise process of gradual oxidation (controlled burning)
  – enzymes catalyse a series of oxidation steps (pathway)

Question 6

what is oxidation and reduction?

Answer 6

• oxidation
  – removal / loss of electrons
• reduction
  – gain of electrons
• most oxidation reactions involve loss of H+ atoms
  – dehydrogenation reaction

Question 7

how are energy carries generated?

Answer 7

• cells use redox reactions to extract energy from nutrients such as glucose
• energy released through oxidation of molecules needed temporarily stored before channelled into biosynthetic pathways
  – ensure large portion of energy released is captured in chemically useful form (rather than lost as heat)
• typically stored as chemical bond energy in activated carrier molecules
  – ATP
  – and closely related: NADH & NADPH

Question 8

what is ATP?

Answer 8

• adenin triphosphate
  – practical form of energy in a cell
• can act as energy receiver / donor
  – because central role in metabolism (referred to as common chemical intermediate)
  – cells perform certain process to earn ATP for other processes requiring energy input
• ATp formed by joining
  – inorganic phosphate (Pi)
  – to adenosine disphosphate (ADP)
  during catabolism of glucose

Question 9

what are electron carriers?

Answer 9

• NAD+
  – nicotinamide adenine dinucleotide
  – degreadation reactions (reduced to NADH)
• NADP+
  – nicotinamide adenine dinucleotide phosphate
  – anabolic reactions (reduced to NADPH)
• FAD
  – flavin adenine dinucleotide
  – reduced to FADH2

Question 10

what is the generation of energy carriers?

Answer 10

• catabolism
  – drives synthesis of energy carriers
  – high-energy molecules (like ATP) release energy when bond is split to form product (ADP + Pi)
• formation of ATP from ADP and phosphate is energetically unfavourable
  – must be coupled to energetically favourable reactions

Question 11

what is carbohydrate catabolism?

Answer 11

• most microorgaisms oxidise carbohydrates as primarysource of cellular energy
  – ancient metabolic reaction
  – in cytoplam of all living cells
  – cells perform reaction in presence / absence of oxygen

Question 12

what processes is carbohydrate catabolism used in?

Answer 12

• cellular respiration
  – aerobic
  – anaerobic
• fermentation

Question 13

what is glycolysis?

Answer 13

• embden-meyerhof pathway
  – stepwise degradation of glucose (and other simple sugars) to pyruvate
• carried in cytosol of cells
  – cytosol is aqueous environment of cell cytoplasm
• unique
  – anaerobic
  – aerobic
• pyruvate end product
  – stands at junction of subsequent aerobic and anaerobic pathways
  – depended on availability of oxygen and electron transport chain

Question 14

what are some alternative glucose degradation pathways?

Answer 14

• pentose phosphate pathways
  – an/aerobic functionality
  – provides C5, C4 and NADPH from glucose
  – synthesis of pentose sugars (used in nucleotide synthesis)
• Entner-Doudoroff pathway
  – alternative to glycolysis, used by soil microbes and few other gram-negative bacteria
  – glucose degraded to pyruvate
  – yield of 1 ATP, NADH, NADPH

Question 15

what are the phases of glycolysis?

Answer 15

• 10 step pathways
  – 1 glucose = 2 pyruvate + 2 ATP
• energy investment
• energy generation

Question 16

what is the energy investment phase?

Answer 16

• 5 reactions
• glucose into 2 molecules of G3P (glyceradlehyde 3-phosphate)
• consumes 2 molecules ATP

Question 17

what is the energy generation phase?

Answer 17

• 5 reactions
• 2 molecules G3P to 2 molecules pyruvate
• generates 4 ATP
  – net gain of 2
• substrate-level phosphorylation
  – transfer of phosphate from high-energy molecule to ADP
• 2 molecules NAD+ to 2 NADH
  – NADH must be reoxidised

Question 18

how is glycolysis regulated?

Answer 18

• direct stimulation / inhibition of critical enzymes
• catalysed by enzyme PFK
  – phosphofructokinase
• step 1
  – making PFK
  – regulated by AMP (adenosine monophosphate), ATP, citrate
• ATP is negative regulator fo PFK
  – if sufficient ATP, glycolysis not required to make more
• citrate can inhibit PFK
  – first product of citric acid cycle (pathway during aerobic respiration)
  – build up = glycolysis slow down
  – citric acid cycle backed up
• AMP positive regulator of PFK
  – cell low ATP = more ATP generated from ADP converting to ATP and AMP
  – high levels AMP = energy starved, and glycolysis run quickly to replenish ATP

Question 19

what are the metabolic fates of NADH and pyruvate?

Answer 19

• NADH recycled to NAD+
  – NAD+ need for glycolysis (if not can become limiting)
  – can be recycled by an/aerobic paths (result in further metabolism of pyruvate)
• availability of oxygen decides fate of pyruvate