Cellular Respiration Flashcards
What is cellular energetics?
The study of energy metabolism in a cell or the transformation/transfer of energy
What is nicotinamide adenine dinucleotide? What does it do?
Coenzyme that accepts excited electron (H atom) from one molecule and transfers it to another via enzyme catalyzed redox reaction
What are the forms of nicotinamide adenine dinucleotide? Which is more energized?
a) NAD+
- Oxidized form (lost an H)
- Oxidizing agent in reaction
b) NADH
- Reduced form (gained an electron)
- Reducing agent in reaction
- More energized form as it’s gained 2 excited electrons
What is adenosine triphosphate? What does it do? What is its reaction?
Molecule that transforms energy by coupling
ATP = ATP + Pi
What is the structure of ATP? How is it used?
- Adenine
- Ribose
- 3 phosphate groups
2 terminal phosphates are joined with high energy/reactive bonds that have low activation energy so transferred easily
How are coupled reactions indicated?
With a swoop
What are coupled reactions used for?
- Mechanical work (eg. muscle contraction)
- Transport work (eg. active transport pumps)
- Chemical work (eg. protein synthesis)
How is ATP regenerated?
ATP is regenerated by phosphorylating ADP which is endergonic and requires the input of more than 30.5 kJ/mol
What is a redox reaction? What happens?
- Transfer of excited electrons
- Electron in elevated energy level maintains its energy when transferred to other molecules
- Increases free energy of receiving molecule
- Electron is often accompanied by proton (so a hydrogen ATOM is transferred)
- Reactions involve the loss and gain of hydrogen
What is a phosphorylation reaction? What is a molecule called involved? What are the types of phosphates?
- Transfer of phosphate group from ATP to a molecule (ATP = ADP + Pi)
- Phosphates can be inorganic (Pi) or high energy (ATP)
- Increases free energy of receiving molecule
What is the hydrolysis of ATP for? What happens? What does it produce?
- Releases large sum of energy
- Exergonic, with free energy of -30.5 kJ/mol under standard conditions
- Coupled with endergonic reactions
- Transfers terminal phosphate of ATP to another molecule during enzyme catalyzed reaction
- Produces phosphorylated intermediate (higher free energy and more unstable)
What is the reaction pathway for cellular respiration?
- Glycolysis: anaerobic breakdown of glucose into 2 molecules of pyruvate (cytosol)
- Krebs Cycle: cyclical pathway that captures high energy electrons
- Electron Transport Chain: series of redox reactions that supply energy for oxidative phosphorylation
Does glycolysis lose carbons?
No. 6C from glucose to 2 molecules of pyruvate (3C each).
When does fermentation occur? What does it do? Is it efficient?
- Occurs under anaerobic conditions (no O2)
- Prevents the glycolytic pathway from stopping by regenerating NAD+
- Very inefficient (2 ATP x 30.5kJ/mol over 2870 kJ/mol = 2%) even with glycogen (3 ADP = 3%)
What is fermentation for multicellular organisms called? What happens? What are the consequences?
Lactate Fermentation
Pyruvate → Lactic acid
NADH → NAD+ coupled
Lactic acid reduces pH of cell which affects enzyme conformation.
What is fermentation for single celled organisms called? What happens? What are the consequences?
Alcohol Fermentation
Pyruvate → Acetaldehyde (2C) → Ethanol
NADH → NAD+ coupled
The 1 C is lost to CO2 (decarboxylation, lost oxygen too)
Ethanol is toxic after 11% so organism must be small and live in aqueous environment so it can diffuse out.
Where do glycolysis/krebs/ETC take place?
Glycolysis: cytosol
Krebs: matrix
ETC: inner mitochondrial membrane
What is the reaction for pyruvate oxidation?
Pyruvate (3C) = Acetyl COA (2C)
1C leaves as CO2
COA comes in
NAD+ = NADH coupled
Catalyzed by multi-enzyme complex called pyruvate dehydrogenase
What are the coenzymes involved with Krebs cycle?
- NAD+: electron shuttle (2e makes NADH; one H to neutralize)
- FAD: electron shuttle (2e = FADH2)
- CoA: makes molecules reactive, signal something important will happen
What is the electron transport chain?
Series of protein bound to inner mitochondrial membrane transfer electrons between them via redox reactions
What is the process for the ETC?
- Electrons are transferred by NADH and FADH2 using redox reactions
- 3 proteins are coupled to proton pumps
- Free energy change in redox reaction provides energy to transfer H ions from matrix to intermembrane space
- Proton gradient (proton motive force) is created with H ion concentration higher in intermembrane space than matrix
- Final electron acceptor is O2
Why do you need a final electron acceptor for ETC?
Must be there or else no way to oxidize last cytochrome (protein with a heme group) so it can’t accept electrons from previous protein
Where does NADH and FADH2 enter for ETC?
- NADH enters at 1st protein: activates 3 pumps
- FADH2 enters at 2nd protein: activates 2 pumps
What is chemiosmosis?
process that uses chemical potential to do cellular work (eg. ETC)
How much ATP is created and which method during cellular respiration?
Total of 36; 2 from glycolysis (SLP), 2 from Krebs (SLP), 32 from ETC (OP)
Where does the equation for cellular respiration come from?
C6H12O6 + 6 O2 = 6 H2) + 6 CO2 + ATP
Glucose + Electron Acceptor (12 Hs need 1/2 O2) = 6 H2O (6O2 forms water) + 6 CO2 (6 C of glucose end up as CO2) + ATP
What is ATP synthase?
Transmembrane protein in inner mitochondrial membrane
Summarize what goes into and out of each of the 3 processes.
Glycolysis: Glucose = 2 Pyruvate + 2 ATP + 2 NADH
Krebs: 2 Pyruvate = 6 CO2 + 2 ATP + 8 NADH + 2 FADH2
ETC: 10 NADH + 2 FADH2 + O2 = 6 H2O + 32 ATP
What are some aspects of cellular respiration that show the structure-function relationship?
- Space between intermembrane space and matrix allows for concentration gradient as ions can’t get through the member
- ATP channel allows ATP to exit mitochondria for cell to use
- Binding of proteins in ETC ensures electrons are transferred in order in inner membrane
- Folding of cristae increases surface area which means many copies of ETC
- Outer membrane establishes inner memrane space
What is the purpose of cellular respiration?
To slowly release the chemical potential energy in food through a series of enzyme catalyzed reactions and capture some of the energy in a usable form (ATP) for endergonic reactions.
Where does the food for cellular respiration come from?
Heterotrophs: must eat to obtain substrate for cellular respiration
Autotrophs: make food for cellular respiration through process of photosynthesis; still make energy for metabolic processes by cellular respiration
What is the purpose of photosynthesis?
To produce molecules that can be used as substrate for cellular respiration and for synthetic pathways (eg. proteins, cell walls).
What are the requirements of photosynthesis?
- Energy (ATP in chemical reactions): needs to be generated from light
- Carbon source: atmospheric CO2 through stroma
- Reducing Power: must supply H to break double bonds; uses electron carrier NADP+ (oxidized) to NADPH (reduced)
What are pigments? Why are they able to do their job? What happens to the light absorbed by a pigment? Are the absorption spectrums identical?
- Molecules that absorb light
- Occurs due to arrangement of bonds in molecules (chains of Cs so hydrophobic)
- Has unique absorption spectrum because energy required to excite electron is exact
- Any light that is not absorbed is reflected; therefore pigment appears that colour
More specifically, what is a photosynthetic pigment?
Any pigment that absorbs solar energy for photosynthesis
What is chlorophyll a? What does it absorb? What is its structure?
- Major photosynthetic pigment that is present in all organisms that can photosynthesize
- Has porphyrin ring head that has Mg2+ in center and hydrocarbon tail
- Absorbs in blue-violet and red portion of spectrum
What do accessory pigments do? What are the types?
Absorb wavelengths that chlorophyll a cannot, increasing efficiency of light absorption and creates action spectrum broader than chlorophyll a spectrum
Chlorophyll b: similar absorption to chlorophyll a except has 1 function group different; results in slightly different absorption spectrum
Carotenoids
Xanthophylls
What are the types of graphs for pigment?
Absorption Spectrum: series of wavelengths that can be absorbed by pigment
Action Spectrum: graph showing rate of photosynthesis at different wavelengths
What is the structure of chloroplasts?
- 2 membranes and thylakoid (disc) and stroma (fluid)
- Contains pigment molecules
- Hydrophobic
What are some aspects of photosynthesis that show the structure-function relationship?
- Thylakoid surface area is increased by stacked as flattened discs called grana
- Pigments are hydrophobic so located in thylakoid membrane
- Capture of light is made efficient by organization of pigments into photosystems
- Protein Z
- There is a system for cyclic for more ATP
- CO2 enters through stroma
- Products of light and dark reactions can be used for each other
- Separation for H+ concentration gradient to build up
What is a general summary of the photosynthetic pathway?
- Light Reactions
- Require light which is absorbed by photosynthetic pigment molecules
- Produce NADPH and ATP - Calvin Cycle
- Incorporates CO2 into organic molecules such as G3P (carbon fixation)
- Require energy of ATP and reducing powder of NADPH (endergonic)
What makes up the light reactions?
- Photoexcitation
- ETC
- Chemiosmosis
What happens during photoexcitation?
- Light strikes pigment molecules, exciting electrons
- Pigments of antenna complex absorbs photons and transfers the energy to reaction centre
- When 2 photons are transferred to reaction centre, the P680 or P700 molecule loses 2 electrons (oxidized = missing electrons that must be replaced)
What is a photosystem? What are the 2 types? What should you consider about the 2 chlorophyll a pigments?
complex of chlorophyll, proteins, and other organic molecules within thylakoid membrane
PS I: P700 which absorbs maximally at 700 nm
PS II: P680 which absorbs maximally at 680nm
Each photosystem has unique primary electron acceptors
What is the antenna centre?
part of photosystem that absorbs light and transfers it to reaction centre
What is the reaction centre?
just the chlorophyll a and the primary electron acceptor
How does energy transform throughout photosynthesis?
- Light energy is transformed into energy in excited electrons
- Energy in excited electrons is transformed into a H+ concentration gradient
- Energy in H+ concentration gradient is transformed into chemical potential energy as ATP
What is the process of non-cyclic electron flow?
- Electrons of PS II go through ETC, pumping protons
- Electrons go to PS I, replacing its electrons lost
- PS I ejects elecrtons to go through ETC
- Final electron acceptor is NADP+, resting electron acceptor is NADPH
What is the process of cyclic electron flow?
- Final electron acceptor is P700
- Electrons to replace ejected electrons come from P700
- Electron ejected from P700 is passed to ferredoxin (PS I ETC protein) and continues down PS II ETC chain to protein pump then P700
What happens during chemiosmosis?
- Both cyclic and non-cyclic electron flow supply energy to pump protons
- Energy in electron is used to pump H+, which results in [H+] gradient used by ATP synthase (ADP + Pi = ATP)
Where does the electrons to replace the ones lost by P680 come from?
- Electrons to replace ejected electrons for - PS II come from H2O
- Protein Z (PS II) splits H2O into ½ O2 (leaves cell), 2 H+ (remain in thylakoid space), and 2 e (P680)
- Requires light energy
What does each type of electron flow produce and which photosystems are used?
Non-Cyclic:
- Uses both photosystems
- Produces both ATP (PS II) and NADPH (PS I)
Cyclic:
- Uses PS I
- Produces only ATP
Where does the Calvin cycle take place?
Stroma
What are the 3 phases of the Calvin cycle and what happens (products, reactants, etc.)?
- Carbon Fixation
- CO2 is added to RuBP (5C sugar) which is catalyzed by rubisco (enzyme)
- 3 CO2 and 3 RuBP must be used - Reduction Reactions
- ATP energizes (phosphorylation)
- NADPH reduces intermediate (reducing power)
- 1 G3P exits
- Undergoes reverse glycolysis in cytosol (G3P + G3P = Glucose) - RuBP Regeneration
- 5 G3P remain and are rearranged to regenerate 3 RuBP
- Requires 3 ATP
What is the equation for photosynthesis and why is it like so?
6 CO2 + 12 H2O = C6H12O6 + 6 O2 + 6 H2O
CO2: used in Calvin cycle to produce G3P, which requires ATP and NADPH
Water: supplies electrons in PS II
O2: generated when H2O is broken down
In the end, where does glucose come from and how many ATP and NADPH are required?
G3P + G3P in reverse glycolysis in cytosol
Needs 18 ATP and 12 NADPH
What molecule contains the greatest amount of chemical potential energy?
Pyruvate
How do you get the energy for ATP synthesis?
- Substrate Level Phosphorylation: the usage of an exergonic reaction to supply energy needed to phosphorylate ADP (eg. PEP to Pyruvate)
- Oxidative Phosphorylation: uses energy in a proton concentration gradient to supply energy to phosphorylate ADP
Which of the two reactions studied is catabolic and which is anabolic?
Cellular Respiration: catabolic
Photosynthesis: anabolic
Photosynthesis is a redox reaction; what is oxidized and reduced?
Glucose: oxidized
Oxygen: reduced
Can cells store large amounts of ATP?
No as ATP is very unstable and will break down at any given moment.
How is cellular respiration controlled?
With allosteric enzymes working with indicators noting in a decrease of ATP and increase of ADP/Pi (needs energy) as well as a decrease of NAD+ and increase in NADH (need O2).
What are examples of the control of cellular respiration?
Glucose = Glucose-6-Phosphate is inhibited if builds up
Glucose-6-Phosphate = Fructose-1,6-Bisphosphate is activated if energy is needed and inhibited if not
Isocitrate = Alpha-Ketoglutarate is “ and also activated if O2 is high and inhibited if not
Why can’t humans undergo photosynthesis since it’s so efficient?
Humans are far too large
Where do the reactions occur for photosynthesis?
Light Reactions: thylakoid membrane
Calvin Cycle: stroma
Does FADH2 have more or less energy than NADH?
Less
How is pyruvate transported into the mitochondria?
Facilitated diffusion
