Cell Metabolism I Flashcards
look over shuttles
3 Main Stages of Cellular Metabolism:
1) glycolysis
2) TCA cycle
3) oxidative phosphorylation
Which stage produces most ATP?
oxidative phosphorilation
What are the waste products from Cellular Metabolism?
CO2
urea
What are the 6 types of reactions?
1) Group transfer (A + BX → AX + B)
2) Ligation requiring atp cleavage (A + B → A-B)
3) Isomerization (A → B)
4) Oxidative reduction (A + :B → :A + B)
5) Hydrolytic (B-C + H2O → B + C)
6) Addition/ removal of functional groups (double bonds)
Kinase is responsible for…?
Catalysing the transfer of phosphate groups from one molecule to another (group transfer)
2 main stages of glycolysis?
- Form a high energy compound (invest ATP)
2. Split a high energy compound (generate ATP)
Glycolysis Stage 1:
Equation
Type of Reaction
Glucose —hexokinase—> glucose-6-phosphate + H+
-Requires 1 ATP, which adds a phosphate to the glucose forming ADP
Group transfer
Glycolysis Stage 2:
Equation
Type of Reaction
Glucose-6-phosphate —-phosphoglucose isomerase—> fructose-6-phosphate
Isomerisation
Stage 3:
Equation
Type of Reaction
fructose-6-phosphate —-phosphofructokinase—-> fructose-1,6-biphosphate
Requires 1 ATP to form ADP
phosphofructokinase is key in the control of sugars entering glycolysis
Group Transfer
Why are stages 2 and 3 important?
To try and make the molecule symmetrical
Stage 4:
Equation
Type of Reaction
fructose-1,6-biphosphate —-aldolase—-> glyceraldehyde-3-phosphate + dihydroxyacetone phosphate
2 high energy compounds produced
Hydrolytic
Stage 5:
Equation
Type of Reaction
dihydroxyacetone phosphate —-triose phosphate isomerase(TPI)—> glyceraldehyde 3-phosphate
End up with 2x glyceraldehyde 3-phosphate (one from stage 4)
Isomerisation
Stage 5:
Equation
Type of Reaction
dihydroxyacetone phosphate —-triose phosphate isomerase(TPI)—> glyceraldehyde 3-phosphate
End up with 2x glyceraldehyde 3-phosphate (one from stage 4)
TPI deficiency is the only enzyme which is fatal if deficiency → death
Isomerisation
Stage 6:
Equation
Type of Reaction
This reaction occurs 2x:
glyceraldehyde 3-phosphate —-glyceraldehyde 3-phosphate dehydrogenase—-> 1,3-biphosphoglycerate
Requires 1 NAD+ and Pi to form NADH (per reaction)
Redox and group transfer
Stage 7:
Equation
Type of Reaction
This reaction occurs 2x:
1,3-biphosphoglycerate —-phosphoglycerate kinase—-> 3-phosphoglycerate
Requires an ADP which accepts a Pi to form ATP (per reaction)
Group transfer
Stage 9:
Equation
Type of Reaction
This reaction occurs 2x:
2-phosphoglycerate —-enolase dehydration—-> phosphoenolpyruvate + H2O
Group removal
Stage 9:
Equation
Type of Reaction
This reaction occurs 2x:
2-phosphoglycerate —-enolase dehydration—-> phosphoenolpyruvate + H2O
Group removal (also known as dehydration)
Stage 10:
Equation
Type of Reaction
phosphoenolpyruvate –pyruvate kinase—-> pyruvate
Requires an ADP which accepts a Pi to form ATP (per reaction)
group transfer
Net result of glycolysis per glucose molecule:
- 2 ATP molecules (use up 2 in part 1 and produce 4 in part 2)
- 2 NADH
What are the 3 fates of pyruvate?
1) alcoholic fermentation
2) lactate production
3) acetyl CoA production
Lactate Production:
Equation
Type of Reaction
pyruvate –LDH—> lactate (reversible)
NADH + H+ → NAD+
anaerobic when O2 is limiting factor
why is it important to regenerate NAD+ in lactate generation and alcoholic fermentation?
-with NAD+ glycolysis is able to continue, in conditions of oxygen deprivation
Why is creatine phosphate useful in muscles?
-the amount of ATP needed during exercise is only enough to sustain contraction for around one second so provides ATP for the second muscle contract
Why can Acetyl CoA readily donate acetate to other molecules?
-the thioester bond is a high-energy linkage, so it is readily hydrolysed, enabling acetyl CoA to donate the acetate (2C) to other molecules
PDH complex stands for?
Pyruvate dehydrogenase
PDH is made up of?
Thiamine pyrophosphate is a cofactor
Why is thiamine pyrophosphate useful in the PDH complex?
It readily loses the highlighted proton and the resulting carbanion attacks pyruvate
Where is thiamine derived from?
vitamin b1
What does deficiency of Vitamin B1/ thiamine cause?
Symptoms and which organ is more vulnerable?
- damage to the peripheral nervous system, weakness of the musculature and decreased cardiac output
- The brain is particularly vulnerable as it relies heavily on glucose metabolism
Creatine Phosphate as a buffer:
Equation
creatine phosphate + ADP + H+ –CK→ creatine + ATP
creatine + ATP –CK→ creatine phosphate + ADP + H+
Why is creatine phosphate useful in muscles?
-the amount of ATP needed during exercise is only enough to sustain contraction for around one second so provides ATP for the transfer of aerobic to anaerobic respiration
Where does the Krebs/TCA cycle take place?
mitochondria
Net products of TCA per glucose
- 2 molecules of CO2 (waste) -3 molecules of NADH
- 1 molecule of GTP
- 1 molecule of FADH2
why does the NADH produced in glycolysis need t to enter + NAD+ leave the mitochondria?
NADH → oxidative phosphorylation in the mitochondria
NAD+ → glycolysis
Glycerol Phosphate Shuttle:
1) free glycerol 3-phosphate dehydrogenase in the cytoplasms transfers electrons from NADH to DHAP to generate glycerol 3-phosphate.
2) A membrane bound form of the same enzyme transfers the electrons to FAD. These then get passed to co-enzyme Q, part of the electron transport chain
Transamination
An amine group is transferred from one amino acid to a keto acid forming a new pair of amino and keto acids
-formation of urea
Malate-Aspartate Shuttle:
1) transanimation
2) then the malate and aspartate are moved across the membrane through proteins
Generic mechanism for amino acids to enter glycolysis / TCA:
transanimation → ketogenic amino-acids → TCA
glycogenic a-a- → glucose production
How many molecules does the degradation of all 20 amino acids result in?
7 molecules
Protein metabolism involves which main type of reaction?
transamination
How is Alanine metabolised?
Alanine (C3) undergoes transamination by the action of the enzyme alanine aminotransferase
Why does decreased TCA activity increase chances of cancer?
it enhances aerobic glycolysis → lactate is generate even under high o2 levels
