5. Alternative Pathways Flashcards
What are aerobic catabolic pathways
Pathway which energy is released through breakdown of larger molecules into smaller molecules (ie, standerd cellular respiration)
What are the 5 factors that affect aerobic catabolic pathways
- Supply and demand of glucose
- Avalability of oxygen
- Enzyme regulation
- Concentration of nutrients
- Tempeture
- Explain supply and demand
- A higher demand for energy = a higher demand for glucose
- Gluconeigenesis can provide some needed glucose if not readily avaluale
What is glucogenesis
The biosynthesis (production within living cells) of glucose from non-carbohydrate sources
What are the two major sites of gluconeogenisis
- Liver - main site; 50% of glucogenisis occurs here
- Kidneys - main site DURING FASTING or starvation; only provide 10% of newly synthesize glucose molecs
**These are the major sites as these organs contain full complement of nessessary enzymes
What is the biomedical importance of gluconeogenesis (4)
- Maintain of normal blood glucose levels durign fasting or starvation
- Energy source - esspecially the centeral nervous system and RBCs (bc glucose is brains principle energy source)
- Energy sourve of skeletal msucles under ANEAROBIC condutions
- Maitnence of Kreb cycle intermediate levels in tissues
Glucogenesis - what are the three substrates used to make glucose
- Lactate -
- Glycerol - from fat hydrolisis during periods of fasting as an alternate source of energy sparing other organs dependent entirely on glyucose as fuel
- Glucogenic AAs - whose carbon sekeltons from tissue protien breakdown during starvation are used in hepatic (liver) glucose synthesis
How can lactate be used as a substrate for glucogenosis
In anaerobic conditions, pruvate can be converted to lactate then become glucose through the cori cycle
How do lipids catabolize (break down)
Trigylceride molecs break down to glycerol or fatty acids.
- Glycerol molecs form glucose (gluconeogenisis) or DHAP turninging into G3P. - Fatty acids can enter the mitochondrial matrix and undergo beta oxidation to become acetyl-CoA
How do protiens catabolise
- Protiens break into AA.
- Deamination - first step in protein catabolism, involves removal of the amino group NH2 of an amino acid as ammonia NH3.
List the three main Glycogenic AAs
- Alanine - can be converted to pyruvate
- Aspartic acid - can be converted to oxaloacetate
- Glutamic acid - can be converted into alpha ketoglutarate
Can all AAs be converted to glucose
All AAs except leucine are glucogenic AA and hence can (ultimately) be converted to glucose
What is fermentation
A cellular respiration pathway that transfers electrons from NADH to an organic electron acceptor molecule
What is the issue with fermentation
It is not as efficient at supplying energy as aerobic respiration
What are the two most common pathways of fermentation
- alcohol fermentation
- lactate fermentation
WHERE does ethonal/alcohol fementation take place
Yeast cells
HOW does elthonal/alcohol femeentation take place
- Pyruvate is immediately decarboxylated into acetaldehyde (CH3COH)
- NADH is then oxidized back into NAD+ and the protons (H+) turn into acetaldehyde into ethanol
** Still only net of 2 ATP
WHERE does lactate fementation take place
Animal cells
WHY does lactate fermention take place
When humans arent getting enough oxygen
HOW does lactate fermentation take place
- Pyruvate is converted into lactic acid (lactate) in one step
- NADH is converted into NAD+
What happens to pyruvate if oxygen PRESENT
- Pyruvate enters the mitochondrion
- Krebs cycle and ETC occur
- Large amount of ATP produced
What happens to pyruvate if oxygen NOT PRESENT
- Converted into ethanol or lactate (depending on the organism)
- NAD+ is regenerated
- A small amount of ATP is produced
What is the purpose of fementation
- To replenish NAD+ that is needed for coupled reaction in glycolysis
** Without NAD+, glycolysis wont take place, and no ATP can be made. With fermentation, 2ATP can be created per glucose
Why the shortage of NAD+ when there is no oxygen
Without oxygen, the ETC gets backed up and cannot proceed. NADH is not converted to NAD+
What are the three most important regulatory enxymes
- Hexokinase
- PFK
- Pyruvate Kinase
What inhibits Hexokinase
Glucose-6-phosphate
- By completion of active site
- By allosteric interaction at a separate enzyme site
** Cells trap glucose by phosphorylating it, preventing exit on glucose carriers
Why is the regulation of Hexokinase needed
Product inhibition of hexokinase ensures that cells will not continue to remove glucose from the blood, ig [glucose-6-phosphate] in the cell is ample
What is the role of pyruvate kinase
Enzyme that catalyzes the reaction of PEP (phosphoenolpyruvate) to pyruvate in glycolysis (step 10)
What is pyruvate kinase activated and inhibited by
Activated:
- Direct by active site
- Fructose-1,6-bisphosphate
- PEP
Inhibited
- By allosteric site
- Citrate, ATP, alanine (allosteric inhibitor)
What is the role of PFK
- Converts F6P to F1,6,BP in step 3 of glycolysis
- PFK is an allosteric enzyme
What is PFK activated and inhibited by
Activated by:
- ADP
Inhibited by:
- ATP
- Citrate
Why do protiens Catabolize
To rebuild required protiens
Where does protien catabolision(?) take place
Occurs in liver, removed by kidney
