Chapter Nine Flashcards
What are the principles of metabolic pathways?
- Complex transformations occur in a series of separate reactions
- Each reaction is catalyzed by a specific enzyme
- Many metabolic pathways are similar in all organisms
- In Eukaryotes are compartmentalized in specific organelles
- Key enzymes can be inhibited or activated to alter the rate of the pathway
What is the general reaction, the reactants, and products in the burning/metabolism of glucose?
C6H12O6 + 6O2 –> 6CO2 + 6H20 + free energy
Is the burning/metabolism of glucose endergonic or exergonic, and what is the net delta G + or -?
it is highly exergonic and the net delta G is -686 kcal/mol
What does the burning/metabolism of glucose drive?
it drives the endergonic formation of many ATP molecules.
What is an oxidation/reduction (redox) reaction?
when electrons are transferred between two molecules in a reaction
What happens when something is reduced or oxidized?
when something is reduced it gains an electron
when something is oxidized, it loses its electron
What is the agent that reduces and what is the agent that oxidizes?
the agent that reduces is the molecule that loses it electron, SINCE it is the reason the other molecule is reduced
the agent that oxidizes is the molecule that gains electron SINCE it is the reason the other molecule lost its electron.
The transfer of electrons is often associated with?
the transfer of hydrogen ions
a hydrogen atom is H+ ion plus a negatively charged electron
When a molecule loses H atoms what does it mean?
it becomes more oxidized
less hydrogens = more oxidized = less free energy
What is NADH, FADH2, and NADPH?
they are key coenzyme electron carriers in redox reactions
NADH = nicotinamide adenine dinucleotide
What is the oxidized form of NADH, and how many electrons / protons does the molecule transfer?
the oxidized form is NAD+ and it transfers 2 electrons and one proton (H+)
When NADH loses an electron to O2, which is oxidized and which is reduced? Is this exergonic or endergonic?
{NADH + (H+) + O2 –> (NAD+) + H2O}
The oxygen is reduced and the NADH is oxidized.
This reaction is exergonic because the NADH loses an electron and therefore releases energy.
What are the five energy-yielding metabolic pathways?
- Glycolysis
- Fermentation
- Pyruvate Oxidation
- Citric acid cycle or Krebs cycle
- Respiratory chain / ATP synthesis
Where does glycolysis occur and does it occur when oxygen is present or in the absence?
glycolysis occurs in the cytoplasm (cytosol) of the cell outside the mitochondria
glycolysis is anaerobic (it does not require oxygen), but functions the same even if oxygen is available
Where does fermentation occur and does it function with or without the presence of oxygen?
fermentation occurs in the cytoplasm
it occurs in the absence of oxygen
Where does pyruvate oxidation occur and does it function with or without the presence of oxygen?
it occurs in the mitochondrial matrix
it ONLY functions in the presence of oxygen.
Where does the citric acid cycle occur and does it function with or without the presence of oxygen?
it occurs in the mitochondrial matrix
it ONLY functions in the presence of oxygen
Where does the electron transport cycle / respiratory chain occur and does it function with or without the presence of oxygen?
it occurs in / through the inner membrane of the mitochondrial matrix - why the cristae has folds
it ONLY functions with the presence of oxygen
What does aerobic respiration mean?
it requires oxygen (ADD AFTER DISCUSSION)
What does anaerobic respiration mean?
it doesn’t require oxygen (ADD AFTER DISCUSSION)
Define glycolysis and explain.
it is separate from cellular respiration, but is required to perform cell respiration
catabolic process that converts glucose into 2 pyruvate molecules
involves energy investment phase (1-5)
involves energy payoff phase (6-10)
What are the input / output of glycolysis?
Input: 2 ATP, 2 NAD+, 1 Glucose (6 carbon), 2 Pi
Output 4 ATP, 2 NADH, 2 Pyruvate (3 carbon)
Net yield: 2 ATP, 2 NADH, 2 Pyruvate
Where are glycolysis’ products used, i.e how is it connected to the other pathways?
The 2 NADH produced are used down the line in the ETC
The 2 Pyruvate are the input for the next pathway, pyruvate oxidation
Without glycolysis, no other pathway has a chance.
Every pathway requires many specific (…….)
all of the reactions inside each pathways have their own specific enzyme that catalyses
What are the inputs and outputs of pyruvate oxidation?
Inputs: 2 pyruvate, 2 NAD+ 2 Coenzyme A
Outputs: 2 Acetyl CoA (2 carbon), 2 NADH, 2 CO2
Where are the products of pyruvate oxidation used, i.e how is it connected to other pathways?
The CO2 is released outside of the cell
The acetyl CoA is used in the citric acid cycle
The 2 NADH are used later in the ETC
What are the inputs and outputs of the krebs cycle?
Inputs: 2 Acetyl CoA, 6 NAD+, 2 FAD, 2 ADP, and 2P(i) water
Outputs 4 CO2, 2 ATP, 6 NADH, 2 FADH2
Where are the products of the krebs cycle used, i.e how it is connected to other pathways?
The CO2 is released
The NADH, and FADH2 are used in the ETC
The krebs cycle relies on pyruvate oxidation to provide the acetyl CoA
What are the inputs and outputs of oxidative phosphorylation (ETC + ATP synthesis)?
Inputs: 10 NADH, 2 FADH2, H+, 28 ADP, Pi
Outputs: 10 NAD+, 2 FAD, H2O, 28 ATP
Where are the products of oxidative phosphorylation used, i.e how is it connected to other pathways and the cell at large?
Of the 10 NAD+ 2 are used back in glycolysis, 2 back in pyruvate oxidation, and 6 in the krebs cycle
The 2 FAD are used in the krebs cycle
The water is used for its presence of H+ to be pumped back into the inter-membrane space
How else is oxidation phosphorylation connected to the rest of the pathways, specifically the last step of the ETC?
For the first three pathways in aerobic respiration to continue, NADH must be oxidized again, and FADH2 must as well.
Since they donate their electrons to O2, if oxygen is low, they can’t donate them and the “aerobic” pathway gets backed up
What is oxidative phosphorylation?
When NADH and FADH2, in the presence of O2 are oxidized and their electrons are used during a series of steps to synthesize ATP
What is the electron transport cycle?
when the electrons from NADH and FADH2 pass through a series of protein complexes inside the inner membrane
the electrons flow results in a (high potential energy) proton concentration gradient across the membrane
(inner-membrane space high and mitochondrial matrix low)
What is chemiosmosis?
when protons naturally flow back across the membrane through a channel protein ATP synthase (uniporter) (facilitated diffusion) which couples this diffusion with ATP synthase
What happens to the free energy of the (system?) electron carriers as the ETC progresses?
The free energy goes down because the electron carriers are oxidized and the energy of the electrons is being used to pump the H+ into the inter-membrane space.
Explain the role of potential energy in the ETC and chemiosmosis.
the carrier protein complexes use the potential energy of the electrons to move the H+ ions
once the ions have been translocated, the hydrogen ions then move through ATP synthase for two reasons
- The difference in chemical potential
- The electrical potential due to the charge difference
Where do the electrons that are responsible for pumping H+ ions into the inter-membrane space come from?
In complex 1 they come from NADH
In complex 2 they come from FADH2
What is the importance of the proton/ H+ gradient?
If a concentration gradient doesn’t exist between the matrix and inter-membrane space that allows for facilitated, passive transport of ions (energy is in the gradient) - that power the synthesis of ATP, the cell will quickly become starved of energy
What is the proton motor force?
the force generated across a membrane that has two components:
a chemical potential (difference in proton concentration)
a electric potential due to the + charge on the proton
What is the final electron acceptor?
Oxygen is the final electron acceptor, when the electrons are donated to an oxygen atom
What is fermentation and is it aerobic or anaerobic?
similar to cellular respiration, fermentation also breaks down glucose in order to harvest chemical energy
However it is different than cell respiration in that it does not use oxygen
What the two types of fermentation?
Lactic Acid
Alcoholic
Explain glycolysis and lactic acid fermentation.
It occurs in microorganisms and some vertebrate muscle cells - PYRUVATE IS FINAL ELECTRON ACCEPTOR
key enzyme is lactate dehydrogenase
Input is Glucose, 2 ADP, 2 Pi, 2 NAD+
Output is 2 lactate, 2 NAD+, 2 ATP
Explain glycolysis and alcoholic fermentation.
It occurs in yeasts and some plant cells - PYRUVATE IS THE FINAL ELECTRON ACCEPTOR
two enzymes are required
Input is Glucose, 2 ADP, 2 Pi, 2 NAD+
Output is 2 ethanol, 2 ATP, 2 CO2, 2 NAD+
Give examples of Catabolic interconversions.
- Polysaccharides are hydrolyzed to glucose which enters glycolysis
- Lipids broken down - glycerol broken down and enters glycolysis
- Fatty acids are broken down and enter the citric acid cycle
- Proteins hydrolyzed to amino acids which feed into glycolysis or citric acid cycle
What is glycogenesis?
it is glucose formed from citric acid cycle and glycolysis intermediates
How are metabolic pathways regulated?
- change amount of active enzyme by regulating gene expression
- Change enzyme activity by covalent modifications (phosphorylation)
- Feedback inhibition by allosteric enzymes
If an abundance of oxygen is available what happens to the enzyme that regulates glycolysis?
the enzyme is inhibited
