Chapter 12: Cells and food Flashcards
• The basics of an oxidation/reduction reaction
- energy released from glucose, as broken down, is in form of high energy e- that make up bonds
- These high energy e- can be used to -> ATP
- Chem rxn involving transfer of e- from 1 reactant to another= called oxidation-reduction reactions
- reactant that loses e- is oxidized (gains +1 charge) and reactant that gains e- is reduced (gains -1 charge)
• The purpose of stepwise harvesting of electrons
- e- must be removed stepwise
- During each transfer, energy captured
- Once all energy been harnessed from high energy e-, they are transferred to final e- acceptor
- Enzymes remove e- one at time from glucose
- e- do not immediately enter etc
• The purpose of electron carriers and how they work (ox vs red)/why they’re needed
- Two H atoms (ie, 2 protons & 2 electrons) pulled off each C atom of glucose chain
- The 2 e- and 1 proton are transferred to NAD+ creating NADH (the other hydrogen is released as H+ )
- FAD (Flavin adenine dinucleotide) is another e- carrier sometimes used instead of NAD+
- FAD accepts two e- & two H ions (H+ ) to become FADH2
- The major phases of cell respiration and what components go into each phase and the net amount of materials that come out
I. GLYCOLYSIS
Partial glucose breakdown: require 2 initial atp
- final products: 2 pyruvate, 2 nadh and 2 atp
II. CITRIC ACID CYCLE
Full glucose breakdown → 2 accetyl coa go in
- final products: 4 nadh per pyruvate, 1 fadh2 per pyruvate, 3 co2 per pyruvate, 1 atp per pyruvate
III. OXIDATIVE PHOSPHORYLATION
Extraction of energy from e-: 10 nadh and 2 fadh2 to make 32 or 34 atp
• Differentiate between substrate level and oxidative phosphorylation
- Most ATP is made by the etc, but some can be made directly via substrate-level phosphorylation
- This occurs when an enzyme transfers a PO4 group from a substrate molecule directly to ADP, forming ATP
• Know the major intermediates of glycolysis and the TCA as pointed out in the powerpoints (aka the steps mentioned in text)
• G itself involves 10 steps, 9 intermediates, and 10 enzymes
Mechanism:
1.) Transfer of po4 group makes g charged & VERY unstable (terminal carbon of glucose, atp used)
2 & 3.) Rearrangement ->4 carbon ring, followed by + of 2nd PO4 group (ATP used)
4.) 6-carbon g is split into 2, 3-carbon molecules (GAP and DAP)
5.) DAP GAP, DAP->GAP
• DAP -> GAP readily because decreasing [GAP] drives isomerization reaction (never reaches = because GAP is constantly converted in step 6)
- rxn coefficients from this point are 2, 2 gap molecules from split
6.) enzyme adds an inorganic PO4 (not from ATP) to GAP
During this reaction, an h atom is removed from each GAP and e- are moved to 2 NAD+ via redox -> 2 NADH.
• xs H created during rxn released to cytosol as (H+) ions
7.) 1 PO4 is removed from EACH molecule of BPG to generate 2 ATP (substrate level phosphorylation)
8. h2o removed
9.) Removal of H2O = 2 PEP molecules each w/ high energy po4 group
10.) Removal of the PO4 from each PEP produces 2 more ATP from ADP which forms pyruvate
• Know the different classifications of enzymes
- Kinase – adds a phosphate group
• Isomerase – rearranges bonds within a single molecule
• Dehydrogenase – oxidizes molecules by removing a hydrogen atom and electron
• Mutase – shifts a chemical group from one position to another within a molecule
• Know how acetyl-CoA is formed from pyruvate & what is generated
- Pyruvate is produced via glycolysis in cytosol, pyruvate must be moved into mito for + breakdown
- Once in mito, decarboxylation rxn is carried out by pyruvate dehydrogenase complex (large complex of proteins)
- CO2 is released
- The remaining acetyl group of pyruvate is attached to coenzyme A -> acetyl-CoA; NADH is produced
- Acetyl-CoA enters the first step of the CAC
• Know the process of the TCA and important intermediates pointed out during lecture
• Begins when acetyl-CoA transfers the acetyl group from pyruvate to oxaloacetate which forms citrate (where the cycle gets its name)
RED = Carbon groups
originally from pyruvate
BLUE = carboxyl groups to
be given off as CO2
- Every release of CO2 is coupled to transfer of e- to NAD+
- Carries energy to etc
• Isocitrate (an isomer of citrate) releases a CO2 and forms NADH
• The resulting alpha-ketoglutarate molecule loses the second COO- group as CO2
,also forming NADH
• The resulting molecule binds back to Coenzyme A to form succinyl CoA
• CoA is removed when a PO M4 group is added in its place
• The PO4 group is quickly transferred to GDP, then to ADP to form ATP (Substrate level phosphorylation)
• Two protons & two high-energy electrons are transferred from succinate to the electron carrier flavin adenine dinucleotide (FAD) which reduces it to FADH2
• Remaining steps regenerate oxaloacetate & produce 1 NADH
• Be able to track Carbons in the cycle and tell me net gains at the end
NET GAINS (per 1 glucose molecule) 4 NADH per pyruvate (x2 pyruvates) = 8 NADH 1 FADH2 per pyruvate (x2 pyruvates) = 2 FADH2 3 CO2 per pyruvate (x2 pyruvates) = 6 CO2 1 ATP per pyruvate (x2 pyruvates) = 2 ATP
• The process of gluconeogenesis and how it’s regulated, specifically (aka enzymes)
Gluconeogenesis is the reversal of glycolysis, so it takes pyruvate and converts it back to glucose
• To reverse some of the steps, energy (ATP or GTP) is required
• Feedback regulation helps the cell decide whether to synthesize glucose or degrade it
• For example, the enzyme phosphofructokinase is allosterically regulated by a variety of metabolites
• Phosphofructokinase is activated by byproducts of ATP hydrolysis like ADP, AMP and Pi
• It is inhibited by ATP (if you have plenty of ATP, shut down glycolysis)
• Fructose 1,6 bisphosphatase is regulated by the same molecules but with an opposite outcome (high ADP? – let’s turn on gluconeogenesis to make glucose which can be broken down to make ATP)
• The importance of glycogen; how GP and GS function and how each is regulated
Glucose can be stored as glycogen and stored and later used. glucose is removed from chain of glycogen on cytosolic side by enzyme glycogen phosphorylase.
• Feedback regulation also controls the making/breaking of glycogen
• GS: is activated by high levels of glucose 6-phosphate
• GP: is inhibited by high levels of\ glucose 6-phosphate & ATP
• Humans store enough glycogen to last about a day while energy in the form of fat can be used over weeks
• Therefore, animal cells actually prefer to store their energy in the form of fat
