Metabolism Flashcards
What makes step 1 of glycolysis irreversible?
The phosphorylation of the glucose makes it so it can’t escape the cell.
What is Mg++’s role in glycolysis?
When ATP is utilized like during glycolysis Mg++ often plays a role by shielding the 3- charge of the phosphate with it’s 2+ charge. This allows the kinase enzyme to better phosphorylate glucose’s 6’ OH
What is a kinase?
A Kinase is an enzyme that helps catalyze the transfer of a phosphate group from a high energy molecule, like ATP.
What is step one of glycolysis?
The transfer of a phosphate to glucose.
What happens during step 2 of glycolysis?
An isomerase enzyme converts glucose 6 phosphate into fructose 6 phosphate.
An isomerase is used because glucose and fructose are isomers of each other.
The only thing that happens during this reaction, is the change in molecular structure. The molecular formula stays the same.
What happens during step 3 of glycolysis?
Fructose - 6 -phosphate has another phosphate added with a kinase enzyme to become fructose - 1, 6 - bisphosphate.
What happens during step 4 of glycolysis?
This is where the lysis of glycolysis occurs. A reverse aldol reaction occurs that creates glyceraldehyde - 3 phosphate and an isomer. The isomer is also converted to glyceraldehyde - 3 phosphate by an isomerase.
The net result is 2 glyceraldehyde - 3 - phosphates.
What happens during step 5 of glycolysis?
Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate, an NADH, and an H+ ion
The enzyme is a dehydrogenase.
What is a dehydrogenase?
A dehydrogenase is an enzyme that is involved with the transfer of H+.
It’s a subclass of oxidoreductases.
Any time you see an FAD+, FADH2, NAD+, or NADH you’re probably dealing with a dehydrogenase
What happens during step 6 of glycolysis?
A kinase is involved in substrate-level phosphorylation of an ADP to ATP resulting in 3 - phosphoglycerate.
Since we had two 3-phosphoglycerates formed from one pyruvate, we end up creating 2 ATPs from the two molecules.
substrate-level phosphorylation
When a kinase transfers a phosphate group from a phosphorylated compound to ADP or GDP to form ATP or GTP
What happens during step 7 of glycolysis?
A mutase (sublcass of isomerases) turns 3-phosphoglycerate into 2-phosphoglycerate
What is a mutase
A mutase is a subclass of isomerases that shifts groups within a molecule.
What happens during step 8 of glycolysis?
A dehydration reaction occurs to 2-phosphoglycerate that forms PEP (phosphoenolpyruvate)
What happens during step 9 of glycolysis?
A kinase undergoes substrate-level phosphorylation to create 2 ATPs and 2 pyruvates from 2 PEPs
What happens to pyruvate if there is no Oxygen in the cell
In animals and plants, it is converted into lactate and this regenerates NAD+ from NADH for the CAC. Lactate goes to the liver to be recycled back into Glucose, once there is excess ATP. NADH is oxidized and pyruvate is reduced.
In anaerobic microorganisms. Pyruvate is converted to acetylaldehyde and then that is converted to ethanol. NADH is oxidized to NAD+ and acetylaldehyde is reduced.
How does pyruvate become ready for the Kreb’s cycle?
A dehydrogenase enzyme attaches pyruvate to CoEnzyme A during a oxidative decarboxylation reaction to form acetyl-Coa and a NADH and CO2
What functional group does acetyl-CoA contain?
A thioester COS
Where are all the enzymes and compound of the Kreb’s cycle located?
In the mitochondrial matrix.
The only exception is the enzyme succinate dehydrogenase which is located in the inner membrane of the mitochondria
What is the overall formula of the Kreb’s cycle?
1 pyruvate + (3NAD+) + FAD + GDP + 2H20 ->
2CO2 + 3NADH + 1FADH2 + GTP + 3H+
What is the overal formula for glycolysis?
glucose + 2Pi + 2ADP + 2NAD+ ->
2 pyruvate + 2ATP + 2 NADH + 2H20 + 2H+
Does the Kreb’s cycle only produce what’s in the overall formula?
No. It also produces intermediates that can be used for the synthesis of pyrimidine nucleotides and porphoryins.
Where does the energy come from to form GTP in the Kreb’s cycle?
The thioester bond is broken, releasing a ton of energy that is used for substrate-level phosphorylation of ADP to ATP
Note: The phosphate doesn’t come from the molecule being broken. It uses Pi and ADP in the matrix.
NADH and FADH2 form how many ATP from their oxidation?
- 5 ATP for NADH (3 rounded up)
1. 5 ATP for FADH2 (2 rounded up)
What is the path of electrons on the ETC
NADH -> Complex I -> Q -> Complex III -> Cytochrome C -> Complex IV -> O2
FADH2 -> Complex II -> Q -> Complex III -> Cytochrome C -> Complex IV -> O2
How many H+ ions are brought into the inner matrix of the mitochondria during the ETC?
Complex 1 = 4 H+
Complex 2 = 0
Complex 3 = 2 H+
Complex 4 = 4 H+
What is another name for CoQ
ubiqunione
What do cytochromes have that help them in redox reactions
They usually contain some sort of metal that helps them in their redox reactions.
Gluconeogenesis
Occurs mostly in the liver and a small amount in the cortex of the kidney
It begins in the mitochondria and proceeds into the cytosol. It’s pretty much the reverse of glycolysis. There are a few other enzymes needed to help the reaction proceed in the opposite direction.
What is Biotin
Biotin is a CO2 carrier.
It adds a CO2 group to pyruvate to form oxaloacetate in the Kreb’s cycle.
What is the Cori Cycle?
The lactate created during anaerobic respiration is converted to Glucose in the liver during times of rest. (plentiful ATP)
When is glycolysis active and when is gluconeogenesis active.
When ATP is low glycolysis is active, when ATP is high gluconeogenesis is active.
Explain Starvation
When starvation occurs:
Insulin levels decrease and glucagon levels increase
triglyceride formation in adipose tissue and gluconeogenesis are now the dominant pathways
Muscle now shifts from glucose to fatty acids for fuel
What ketone bodies are formed from the TCA cycle?
acetone
acetoacetate
D-3-hydroxybutyrate
The brain utilizes acetoacetate instead of glucose
The heart can use ketone bodies as well for fuel
Diabetes mellitus
Glucose can’t be metabolized. Results in ketosis and eventually acidosis of the blood
Pentose Phosphate Pathway
The anabolic pathway that generates ribose 5 phosphate to create nucleotides and NADPH which is used for reductive biosynthesis of lipids.
It branches off of glycolysis. Once the glucose has its 6’OH phosphorylated it can branch to either pathway.
Glyoxylate Cycle
seedlings, bacteria, and algae can use acetate as their carbon source for all the carbon compounds they need to produce.
This cycle allows certain seeds to grow in the dark or underground where photosynthesis is impossible.
Takes place in glyoxysomes
glyoxysomes
Type of peroxisome
Special organelles in plants, bacteria, and algae that all the glyocylate cycle to occur. Using acetate for all carbon producing processes.
Takes acetyl CoA to Succinate bypassing steps on the kreb’s cycle.
Glycogenolysis
The breakdown of glycogen.
The liver breaks off glucose-6-phosphate from glycogen and then converts it to glucose for transport out of the cell.
Glycogen synthesis
Synthesized in reverse of glycogenolysis. A glucose-6-phosphate is oined to a glycogen strand.
What happens to excess Amino acids
There is no storage of excess amino acids. They are metabolized instead.
They undergo deamination first creating Urea. Then the carbon backbones are changed to become intermediates in the Kreb’s cycle
What is phenylketouria (PKU)?
A buildup of phenylalanine causing mental retardation.
Caused by a deficiency in the enzyme that breaks down phenylalanine.
Fatty Acid Oxidation
Occurs in the mitochondrial matrix
Fatty acids are activated on the outer membrane and carnitine carries the activated fatty acids into the matrix for fatty acid oxidation.
Fatty Acids turn into acetyl Co-A and 18 carbon fatty acid would turn into 9 acetyl CoAs and 8 FADH2 and 8 NADH. (One for each cut of the backbone)
Fatty Acid Synthesis
Occurs in the cytosol.
Made from Acetyl CoA
Cholesterol Synthesis
Synthesized from Acetyl CoA
Primarily synthesized in the Liver
Cholesterol
Precursor of steroid hormones
Has 8 chiral carbons
Involved in the synthesis of bile acids
Modulates the fluidity of eukaryotic cell membranes
Involved in the synthesis of bile acids which are in the bile and assist in absorbing dietary lipids in the small intestine. Bile acids are often depronated, becoming bile salts. They also emulsify fats.
If cholesterol in bile gets to high, precipitation occurs to form gall stones. If a blockage occurs, bile can’t enter the duodenum and the ability to digest fats is lost. Bile pigments enter the blood stream causing aundice.
Bilirubin can be conugated with a molecule of glucuronic acid
Urea cycle
This is the central pathway in nitrogen metabolism. Involved in both the anabolism and catabolism of amino acids linked to the Kreb’s cycle.
In most terrestrial vertebrates, NH4+ is turned into Urea and excreted. Most of the Urea cycle occurs in the liver with some in the Kidneys. The Urea is transported in the blood to the kidney for excretion from the body.
Before the Urea cycle begins, NH3 is turned into carbamoylphosphate and requires 2 ATP molecules.
Several enzymatic reactions occur. One is mitochondrial and the others are cytosolic
Fumurate (A Kreb’s cycle intermediate) is produced and returned to that cycle.
Hyperammonemia
An inherited disorder resulting in elevated NH4+
Coma and death occur shortly after birth if the Urea cycle doesn’t run properly. Brain damage can occur as well.
What are the nitrogenous wastes of terrestrial and aquatic animals?
Terrestrial animals and mature amphibians: Urea
Fish and marine organisms: Ammonia
Reptiles, Birds, and Insects: Uric acid
