Cellular Respiration & Metabolism Flashcards
Define metabolism
all of an organism’s chemical reactions
What is the purpose of metabolism?
Manages material and energy resources
What is a metabolic pathway?
A series of reactions to produce products, each step is catalyzed by different enzymes
What are the two kinds of metabolic pathways?
- catabolic
2. anabolic
Define catabolic pathways and provide an example
exergonic reactions that break down of complex molecules to simpler ones
releases energy
ex. cellular respiration
T or F: catabolic pathways are endergonic/endothermic. Why/why not?
FALSE.
Catabolic pathways are EXOthermic/Exergonic because they release energy
Define anabolic pathways and provide an example
Endergonic reactions that build complex molecules from simpler ones
Requires an energy input/consumes energy
ex. fatty acid or protein synthesis
Describe photosynthesis and provide the general chemical formula
A reaction that consumes energy from sunlight and converts it into chemical energy and is stored in organic compounds
6CO2 + 6H2O + light –> C6H12O6 (glucose) + O2
Define cellular respiration and provide the general formula
The break down of organic molecules in order to produce ATP and energy
C6H12O6 + O2 –> 6CO2 + 6H2O + energy (ATP + heat)
Describe ATP
Adenosine triphosphate is an energy source that powers cellular work to keep organisms alive
Function:
- mediates most energy coupling in the cells
- an immediate source of energy for cells
- acts as a nucleoside triphosphate in the synthesis of RNA
What is ATP composed of?
a ribose (sugar), adenine (nitrogenous base), and a chain of three negatively charged phosphate groups
What are three kinds of cellular work that ATP is involved in?
- chemical work (endothermic reactions)
- Transport work (active transport)
- mechanical work (movement of cells or cell parts)
How are the bonds between phosphate groups in ATP broken? And what is formed when this occurs?
The weak bonds between phosphate groups are broken by hydrolysis in an exergonic reaction causing…
ADP (Adenosine Diphosphate) and an inorganic phosphate to form and release significant energy
What happens to the inorganic phosphate that detaches from ATP when ADP is formed?
It is transferred to a reactant or transport protein
Cellular respiration is key in recycling which two molecules back into ATP?
recycling ADP and inorganic phosphate
Describe redox reactions
chemical reactions that involve the transfer of electrons between an oxidizing agent and a reducing agent
Which kind of reactions (exo or endo) undergo redox reactions?
Exothermic reactions yield energy because of the transfer of electrons (this energy is then used to synthesize ATP)
Describe reduction reactions
Reduction is the GAINING of electrons (element becomes MORE negative)
Describe oxidation reactions
Oxidation is the LOSS of electrons (element becomes LESS negative)
Describe reducing agent
The element/molecule that oxidizes (becomes less negative) because it has donated an electron and has reduced the other element/molecule
Describe oxidizing agent
The element/molecule that is reduced (becomes more negative) because it has gained an electron by oxidizing the other molecule/element
What is a trick to remember redox
OILRIG
Oxidation is LOSS
Reduction is GAIN
In this example, which element is the reducing agent and which is the oxidizing agent:
Xe- + Y –> X + Ye-
X is oxidized (becomes less negative) so it is the reducing agent
Y is reduced (becomes more negative) so it is the oxidizing agent
T or F: Oxidation can occur without oxygen being present
TRUE
Why is oxygen such a strong oxidizing agent?
Because it is highly electronegative so it can easily strip electrons from other elements/molecules
How are redox reactions involved in cellular respiration?
Glucose and other food molecules are OXIDIZED (lose e-)
Oxygen (present in aerobic cellular respiration) REDUCES (gains the e-)
electrons are transferred from glucose to oxygen through a series of steps that involve redox reactions
Why are electrons passed from glucose to oxygen through a series of steps rather than just in one step?
So that the harvest of energy will be more efficient. If electrons were transferred directly to oxygen in one step there would be a huge explosion and waste of energy
T or F: each step between glucose and oxygen is catalyzed by an enzyme?
True
T or F: Electrons are transferred indirectly between glucose and oxygen along with a hydrogen proton?
True
Which enzymes are involved with the transfer of electrons?
- NAD+
- Dehydrogenase
Describe NAD+
A coenzyme that acts as an electron carrier to transport electrons from glucose to the electron transport chain
Describe dehydrogenase
An enzyme that oxidizes the substrate by removing 2e- and 2 H+ and reduces NAD+ to NADH by giving it 2e- and 1 H+
T or F: electrons lose a ton of energy when they are transferred from the substrate to NAD+
FALSE, they lose very little energy because NAD+ is a very efficient electron carrier
Through which mechanism do electrons travel to reach O2?
The Electron Transport Chain (ETC)
What are the 4 major steps of cellular respiration? Where does each step occur?
- Glycolysis
- occurs in the cytosol - Pyruvate oxidation
- occurs in the matrix of the mitochondria of eukaryotes
- cytosol of prokaryotes - Citric Acid Cycle (CAC)
- occurs in the mitochondria of eukaryotes
- cytosol of prokaryotes - Oxidative phosphorylation
- occurs in the mitochondria of eukaryotes
- plasma membrane of prokaryotes
What are the two ways cellular respiration makes ATP?
- Substrate level phosphorylation
2. Oxidative phosphorylation
Describe substrate-level phosphorylation
A way that cellular respiration produces ATP (although small amounts are produced)
This occurs during glycolysis and the CAC
Makes ATP by directly transferring phosphate groups from the substrate to ATP
T or F: Substrate level phosphorylation is responsible for producing the majority of ATP in cellular respiration. Why/why not?
FALSE. Oxidative phosphorylation is responsible for producing the most ATP
Describe oxidative phosphorylation
A way that cellular respiration produces most of the ATP
Uses the ETC and chemiosmosis to make ATP by making ADP and inorganic phosphate
Describe glycolysis
The first step in cellular respiration that involves molecules of glucose being digested/broken down into molecules of pyruvate
1 molecule of glucose (6C) –> 2 molecules of pyruvate (3C each)
In glycolysis, 1 molecule of glucose has how many carbons? And is broken down into how many of which molecules? How many carbons do the products each contain?
Glucose has 6 carbons
Converted into two pyruvate molecules
Each pyruvate has 3 carbons
What are the two phases in glycolysis?
- Energy investment phase:
- first 5 steps that invest energy and use 2 ATP - energy payoff phase:
- last 5 steps that produce 4 ATP (made by substrate level phosphorylation) and 2 NADH
What are the inputs, outputs, and net products of glycolysis?
INPUTS:
- glucose
- 2 ATP
- 2 NAD+, 4 e-, and 4+
OUTPUTS:
- 2 Pyruvate
- 4 ATP
- 2 NADH
NET PRODUCTS:
- 2 pyruvate, 2 H2O
- 2 ATP
- 2 NADH + 2 H+
Describe pyruvate oxidation
if the cellular respiration will continue aerobically, pyruvate is transferred into the matrix (innermost part) of the mitochondria
Both pyruvate molecules are oxidized (lose e-) and converted into Acetyl Coenzyme A
How many carbons does a molecule of acetyl coenzyme A have? What does this imply?
2 carbons per molecule of acetyl CoA
Implies that the conversion between one 3-C pyruvate molecule to a 2-C molecule of Acetyl CoA loses a molecule of CO2
T or F: Acetyl CoA can be regenerated and used again and again for pyruvate oxidation. Why/why not?
True because it is an enzyme
How many molecules of Acetyl per molecule of glucose will enter the citric acid cycle?
2 molecules of acetyl per molecule of glucose
What is the reaction equation for pyruvate oxidation?
Pyruvate + CoA + NAD+ —> acetyl CoA + CO2 + NADH + H+
Describe the Citric Acid Cycle
2 acetyl groups (contain two carbons each) per glucose molecule enter the CAC (WITHOUT CoA) to be processed through 8 steps.
Each turn of the CAC has 2 carbons enter as one acetyl group and 2 different carbons leave as oxidized CO2 (so for one glucose molecule, the cycle turns twice because 2 acetyl groups enter)
The CAC generates 1 ATP per turn by substrate level phosphorylation but most energy is transferred to NAD+ and FAD where they are reduced to NADH and FADH2 and carry electrons to the ETC
What does each turn of the CAC produce per 1 one molecule of glucose?
One turn produces 2 carbons and 1 ATP molecule
T or F: oxygen is directly required for the CAC?
FALSE. but it does need NAD+ and FAD for electron transport which require O2 (indirectly needs it)
Describe the electron transport chain (ETC)
the ETC is a series of proteins with bound non-protein components that are essential to the catalytic function of enzymes
STEPS:
- each carrier is reduced when it accepts electrons and is oxidized as it is stripped of electrons
- each carrier is slightly more electronegative than the previous so that the electrons can be passed to the next and move down the chain
- NADH donates electrons to the first electron carrier in complex I
- FADH2 adds electrons to complex II but is not as efficient so releases 2/3 as much energy as NADH (makes fewer ATP)
- Coenzyme Q takes electrons from complexes I and II to complex III
- Cytochrome c carries the electrons from complex III to IV
- a cytochrome in complex IV donates electrons to O2 to make H2O
- energy released during the ETC is coupled with ATP synthesis with the help of ATP Synthase enzymes
Where is the ETC located and how does the structure of the mitochondria increase cellular respiration rates?
ETC is embedded in the inner mitochondrial membrane which is folded to form cristae
–> increase surface area so that thousands of copies of ETC can exist in one mitochondrion
Describe oxidative phosphorylation
When the electrons have been transferred to O2 from the ETC, O2 makes H2O
Then the enzyme ATP Synthase makes ATP from ADP and inorganic phosphate
Describe ATP Synthase
An enzyme that makes ATP from ADP and inorganic phosphate during oxidative phosphorylation
What is the mechanism that pumps protons across the membrane by the complexes as electrons are transferred through the ETC?
Electrogenic pump
Describe chemiosmosis
The energy coupling mechanism that uses energy stored in H+ gradient across a membrane to drive cellular work
Uses H+ gradient to power ATP synthesis
- H+ is bound to a rotor in ATP Synthase causing it to spin and activate catalytic sites
ATP is synthesized as H+ moves down their electrochemical gradient
In summary, how many ATP molecules does NADH and FADH2 produce?
NADH produces 2.5 ATP
FADH2 produces 1.5 ATP
*taking into account the cost of moving ATP out of the mitochondria to cytosol for use
What is the total amount of ATP produced by cellular respiration per molecule of glucose?
30-32 molecules of ATP produced per molecule of glucose
How efficient is cellular respiration at producing ATP?
Only about 34% efficient, theoretically, oxidation of glucose could produce 94 ATP molecules
the rest of the energy is lost as heat
Describe anaerobic cellular respiration
A catabolic process that occurs without the presence of oxygen
Instead of oxygen, the final electron acceptor is a different electronegative molecule (one less EN than oxygen)
Describe fermentation
An anaerobic catabolic process that partially degrades sugars (like glucose) to produce some ATP from glucose without an ETC (no oxygen involved)
Fermentation produces a specific product like lactic acid or ethyl alcohol
Describe lactic acid fermentation
Pyruvate is directly reduced by NADH to form lactate as an end product without the release of CO2
Describe alcohol fermentation
Pyruvate is converted into ethanol in two steps:
- CO2 is released from the pyruvate which is then converted into acetaldehyde (2-C compound)
- Acetaldehyde is reduced by NADH to ethanol which generates the supply of NAD+ required for glycolysis to continue
What are the 3 possible fates of pyruvate?
- in aerobic respiration, pyruvate will move into the mitochondria and be oxidized into acetyl CoA
- in anaerobic respiration, pyruvate will be undergo alcohol fermentation and be converted into ethanol (ethyl alcohol)
- Or in anaerobic respiration, pyruvate will undergo lactic acid fermentation and be converted into lactate
What is the general pathway of carbohydrate catabolism in the cell?
Glycolysis can accept a wide range of carbohydrates for catabolism
- starch is hydrolyzed into glucose which can be then be further broken down by glycolysis and the citric acid cycle
- glycogen can also be hydrolyzed into glucose between meals to power respiration
What is the general pathway of fat catabolism in the cell?
Fats are digested into glycerol and fatty acids so the glycerol can be converted into glyceraldehyde 3-phosphate (an intermediate of glycolysis)
But most of the energy of fats are stored in the fatty acids, so BETA OXIDATION breaks down the fatty acids
Describe Beta Oxidation and which macromolecule does it act on?
Fats store energy mostly in their fatty acid components so for fats to be catabolized, their fatty acids are broken down by beta oxidation to be converted into 2-C fragments that can enter the CAC as Acetyl CoA
NADH and FADH2 are also produced by beta oxidation and can enter the ETC to produce more ATP
What is the general pathway of protein catabolism in the cell?
Proteins are digested into their amino acid constituents and if the amino acids are in excess, enzymes convert them to intermediates of glycolysis to then enter the CAC (the amino groups are removed)
the nitrogenous remains are excreted as a form of ammonia by the animal
What is deamination?
A process that removes Amino groups from amino acids during the catabolism of proteins
Define phosphofructokinase
An allosteric enzyme with receptor sites for specific inhibitors and activators
What role does phosphofructokinase play in regulating cellular respiration rate?
It is inhibited by ATP and activated by AMP (Adenosine Monophosphate)
When there is an excess of ATP, Phosphofructokinase is inhibited to slow down glycolysis until cellular work converts ATP back to ADP faster than ATP can be regenerated
Accumulation of citrate in the mitochondria will force citrate to move to the cytosol which will also inhibit the enzyme
How is the rate of cellular respiration regulated?
With the help of the allosteric enzyme phosphofructokinase
Which stages of cellular respiration CAN occur without oxygen?
Glycolysis can occur without oxygen but this will happen under anaerobic fermentation conditions
Which stages of cellular respiration CANNOT occur without oxygen?
Pyruvate oxidation
CAC
Oxidative phosphorylation (ETC and chemiosmosis)
Describe energy coupling
The use of an exergonic process to drive an endergonic process
Define allosteric regulation
the process of stabilizing the structure of an enzyme in its active form by binding a molecule
What purpose does allosteric regulation serve?
it allows cells to regulate metabolic pathways by controlling when and where various enzymes are active
T or F: in many cases, the molecules that naturally regulate enzyme activity (allosteric regulation) behave similar to reversible noncompetitive inhibitors. why/why not?
TRUE because these molecules can change the shape and functioning of an enzyme’s active site by binding to a site elsewhere on the enzyme
Define feedback inhibition
a metabolic pathway is stopped due to the binding of an enzyme-substrate’s end product to that enzyme
Define cooperativity in terms of enzymes
a type of allosteric regulation that increases the response of enzymes to substrates
How does hydrolysis of ATP power cellular work?
By releasing free energy that can be coupled to other reactions
Define cofactors
a nonprotein enzyme helper, usually a metal ion
Define coenzymes
A nonprotein enzyme helper, usually an organic molecule (a specific type of cofactor)
Give an example of feedback inhibition in cellular respiration
ATP acts as an allosteric inhibitor to enzymes in ATP-producing pathways
How does the active site of an enzyme lower the activation energy barrier and therefore catalyze a reaction?
By orientating substrates correctly to bind with the active site
How is energy released from an ATP molecule?
By the hydrolysis of one of the phosphate groups to form ADP and inorganic phosphate
T or F: Enzymes can lower the activation energy of reactions
TRUE
T or F: Enzymes can change the equilibrium point of reactions
FALSE
T or F: enzymes can change the net energy output of a reaction
FALSE
Describe the energy relationship between anabolic and catabolic pathways
Anabolic pathways synthesize complex organic molecules using the energy produced by catabolic pathways
