topic 8 - metabolism Flashcards
what is metabolism?
sum total of all chemical reactions that occur within an organism in order to maintain life
how are metabolic processes controlled and coordinated?
series of enzyme catalyzed reactions
how are metabolic pathways organized and why are they important?
allow for greater level of regulation, organized into chains or cycles
what is activation energy? (EA)
the certain amount of energy needed for a chemical reaction to proceed
what do enzymes do to the rate of a biochemical reaction?
increase the rate of the reaction by lowering the Activation Energy required for the reaction
how do enzymes lower the EA?
bind to the substrate and destabilize the bonds of the substrate –> less energy is required to convert it into a product
what is an exergonic reaction?
reactants contain more energy than the products, free energy is released into the system
USUALLY CATABOLIC (energy is released from broken bonds)
what is an endergonic reaction?
reactants contain less energy than the products, free energy is lost to the system
usually anabolic, as energy is required to synthesize bonds
what is an enzyme inhibitor?
molecule that disrupts the normal reaction pathway between an enzyme and a substrate
what are the two types of enzyme inhibition?
competitive inhibition
noncompetitive inhibition
what is competitive inhibition
molecule other than the substrate binding to the enzyme’s active site
inhibitor is structurally and chemically similar to the substrate
prevents substrate binding, can be reduced by increasing substrate concentration
what is noncompetitive inhibition?
molecule binding to an allosteric site
causes a conformational change to the enzyme’s active site
substrate can no longer bind
why is enzyme inhibition necessary?
prevents the formation of a product
what is an example of a noncompetitive inhibitor?
cyanide
prevents ATP production via aerobic respiration
what is an example of a competitive inhibitor?
relenza
treats influenza
what is feedback inhibition? and what is another name for it?
end product inhibition
form of negative feedback by which metabolic pathways can be controlled
final product in a series of reactions inhibits an enzyme from an earlier step in the sequence (noncompetitive inhibition)
what is the purpose of feedback inhibition?
to ensure product levels are tightly regulated
what is an example of feedback inhibition and how does it work?
Inhibition of the pathway that converts threonine to isoleucine (essential amino acid)
steps:
ISOLEUCINE is synthesized in a 5 step process (using 5 enzymes)
threonine is converted into an intermediate compound by an enzyme
isoleucine can bind to an allosteric site on this enzyme
excess production of isoleucine inhibits further synthesis
how can the rate of a reaction be calculated?
rate of reaction (s^-1) = 1 / time taken (s)
what are three factors that affect enzyme activity?
pH
temperature
substrate concentration
rank the rate of reaction of uninhibited reactions, reactions with a competitive inhibitor, and reactions with a noncompetitive inhibitor from greatest to lowest
1/2 = uninhibited + competitive (V max is the same)
3. noncompetitive reaction
as enzyme inhibitors lower reaction rates by reducing levels of uninhibited enzymes
how are inhibitors used in medicine?
used to treat infectious diseases by targeting the enzymes involved in pathogenesis
what is rational drug design?
computer modelling techniques to invent a compound that functions as an inhibitor
OIL RIG meaning
Oxidation is Loss (of electrons)
Reduction is Gain (of electrons)
what is Adenosine triphosphate?
ATP, high energy molecule that functions as an immediate power source for cells
why is ATP readily reactive?
phosphorylation makes molecules less stable
how is energy released from ATP?
when ATP is hydrolyzed, the energy stored in the terminal phosphte bond is released
what are the two functions of ATP within the cell
energy currency of the cell (releases energy when hydrolyzed to ATP)
transfers phosphate group to other organic molecules, rendering them less stable and more reactive
how is ATP synthesized from ADP?
using energy from: solar energy (photosynthesis converts light energy into chemical energy)
oxidative processes (cell respiration breaks down organic molecules to release chemical energy)
what is cell respiration?
controlled release of energy from organic compounds to produce ATP
what is anaerobic respiration?
incomplete breakdown of organic molecules for a small yield of ATP (no oxygen)
what is aerobic respiration?
complete breakdown of organic molecules for a larger yield of ATP (oxygen is required)
why is the breakdown of organic molecules staggered?
activation energy is divided across several steps and released energy is not lost (transferred to activated carrier molecules)
how is the chemical energy from the breaking down of organic molecules due to cell respiration transferred?
redox reactions
why are carrier molecules called hydrogen carriers or electron carriers?
they gain electrons and protons (H+ ions)
what is the most common hydrogen carrier and what is it reduced to? INCLUDE FORMULA
NAD+, reduced to form NADH
NAD+ + 2H+ +2e- –> NADH + H+
what is a type of hydrogen carrier (other than NAD+)
FAD
where is the electron transport chain?
cristae
true or false: anaerobic respiration can generate ATP from hydrogen carriers
FALSE, only aerobic respiration can generate ATP from hydrogen carriers as process requires oxygen to function
what is the first stage of aerobic respiration and what does it do?
link reaction, transports pyruvate into the mitochondria
what happens during the link reaction?
- pyruvate transported from cytosol to mitochondrial matrix
- pyruvate –> CO2 through decarboxylation
- 2C molecule oxidized to produce a reduced carrier
- acetyl compound + coenzyme A combine and form acetyl CoA
how many times does the link reaction occur per molecule of glucose and why
twice, glycolysis splits glucose into two pyruvate molecules
what is the second stage of aerobic respiration? where does it occur?
The Krebs Cycle, matrix of the mitochondria
what is another name for the Krebs Cycle?
citric acid cycle. tricarboxylic acid (TCA) cycle
what happens during the Krebs Cycle?
- acetyl CoA combines with a 4C compound
- 6C compound is broken down into original 4C (2 molecules of CO2 produced)
- multiple oxidation reactions result in the reduction of hydrogen carriers
- small yield of ATP (one molecule) via substrate level phosphorylation
how many times does the Krebs Cycle occur and why?
twice, link reaction produces two molecules of acetyl CoA (one for each pyruvate)
what does the Krebs Cycle produce per molecule of glucose?
4 x CO2
2 x ATP
6 x NADH + H+
2 x FADH2
what is the final stage of aerobic respiration? where does it occur?
electron transport chain, inner mitochondrial membrane
what is the effect of the structure of the inner membrane
arranged into cristae (folds) to increase SA available for transport chain
what are the steps of oxidative phosphorylation?
- proton pumps create an electrochemical gradient (proton motive force)
- ATP synthase uses the subsequent diffusion of protons (chemiosmosis) to synthesize ATP
- oxygen accepts electrons and protons to form water
what happens during proton motive force?
carrier moelcules donate electrons to an electron transport chain located on the mitochondrial cristae
electrons lose energy as they are passed along the chain, used to pump H+ ions along the matrix
build up of protons in the intermembrane space creates an electrochemical gradient
what is the transmembrane enzyme that returns protons to the matrix?
ATP synthase
how are de-energized electrons removed from the electron transport chain? what is the byproduct?
final electron acceptor (oxygen)
water as a byproduct
how many ATP molecules are made from reduced carriers?
32
what is oxidative phosphorylation?
energy stored within the reduced hydrogen carriers is released to synthesize ATP
give a quick summary of oxidative phosphorylation
Hydrogen carriers donate high energy electrons to the electron transport chain (located on the cristae)
As the electrons move through the chain they lose energy, which is transferred to the electron carriers within the chain
The electron carriers use this energy to pump hydrogen ions from the matrix and into the intermembrane space
The accumulation of H+ ions in the intermembrane space creates an electrochemical gradient (or a proton motive force)
H+ ions return to the matrix via the transmembrane enzyme ATP synthase (this diffusion of ions is called chemiosmosis)
As the ions pass through ATP synthase they trigger a phosphorylation reaction which produces ATP (from ADP + Pi)
The de-energised electrons are removed from the chain by oxygen, allowing new high energy electrons to enter the chain
Oxygen also binds matrix protons to form water – this maintains the hydrogen gradient by removing H+ ions from the matrix
what is aerobic respiration
breakdown of glucose in the presence of oxygen to produce water and CO2
includes: glycolysis, link reaction, krebs cycle, electron transport chain
what are the three MAIN stages of aerobic respiration? what are the products?
decarboylation: 6 CO2
oxidation: 10 NADH, 2 FADH2
phosphorylation: 36 ATP
products of each type of reaction within aerobic respiration?
glycolysis: 2NADH, 2ATP (net, substrate level)
link reaction: 2CO2, 2NADH
krebs cycle: 4CO2, 6NADH, 2FADH2, 2 ATP (substrate level
electron transport chain: 32 ATP (oxidative)
how many ATP are consumed in glycolysis?
2
what is the first step in the controlled breakdown of carbohydrates and where does it occur?
glycolysis, cytosol
what are the four key events of glycolysis?
- phosphorylation (hexose is phosphorylated by 2 molecules of ATP)
- lysis (6C is split into two 3C sugars)
- oxidation (hydrogen is removed from each of the 3C sugars to reduce NAD+ to NADH, two molecules of NADH are produced)
- ATP formation (substrate level phosphorylation)
is glycolysis aerobic or anaerobic
anaerobic
what is fermentation?
after glycolysis, if oxygen is not present, the pyruvate is not broken down further and no more ATP is produced (incomplete oxidation)
converted into lactic acid (animals) or ethanol and CO2 (plants and yeast)
is fermentation reversible?
yes
what are mitochondria
powerhouse of the cell, synthesize lareg amounts of ATP via aerobic respiration
how is the structure of a mitochondrion adapted to the function it performs?
The inner membrane is folded into cristae to increase the surface area available for the electron transport chain
The intermembrane space is very small (maximises the electrochemical gradient that results from proton accumulation)
The mitochondrial matrix contains suitable enzymes and an appropriate pH for the Krebs cycle to occur
The outer membrane contains the necessary transport proteins for shuttling pyruvate into the mitochondria (link reaction)
what is electron tomography?
Electron tomography is a technique by which a 3-dimensional image of an internal cellular structure can be generated
Samples are repeatedly imaged at different angles (using a transmission electron microscope) and the images are compiled
what is photosynthesis?
process by which cells synthesize organic molecules from inorganic molecules in the presence of sunlight
what is an example of a photosynthetic pigment?
chlorophyll
what does the conversion of light energy into chemical energy require
energy transfer molecules (electron carriers) + ATP
how is the structure of a chloroplast adapted to the function it performs?
Granum are made up of stacks of thylakoids to increase the surface area available for the electron transport chain
The thylakoid lumen is very small (maximises the electrochemical gradient that results from proton accumulation)
The stroma contains suitable enzymes and an appropriate pH for the Calvin cycle to occur (light independent reactions)
what are the two stages of photosynthesis?
light dependent reaction
light independent reaction
steps of light dependent reactions (IN THREE SIMPLE STEPS)
- light is absorbed by chlorophyll (releases energized electrons used to produce ATP)
- electrons are donated to carriers
- electrons lost from chlorophyll are replaced by water, themn split to produce O and H
where do light independent reactions occur?
fluid filled interior of the chloroplast called the stroma
where do light dependent reactions occur
intermembrane space of membranous discs called thylakoids
steps of light independent reactions (general, 2 steps)
- ATP + hydrogen/electrons are transferred to stroma
2. hydrogen/electrons combine with CO2 to form complex organic compounds (energy comes from ATP)
what happens in non-cyclic photophosphorylation?
- chlorophyll in PSI and PSII absorb light, triggering the release of energized electrons
- electrons from PSI reduce NADP
- electrons from PSII move through an ETC before replacing the electrons from PS I
- ETC produces ATP (photophosphorylation)
- electrons lost from PS II are replaced by water
what is photoactivation
chlorophyll in PS I and PSII absorb light which triggers the release of energized electrons
what happens in cyclic photophosphorylation?
- only chlorophyll in PS I are activated by light
- electrons move through ETC before returning to their original location
- ETC produces ATP
- does not produce NADPH
can cyclic photophosphorylation produce organic molecules
no
maximal absorption wavelength of PS I? what about PS II?
PS I = 700 nm
PS II = 680 nm
what is photophosphorylation
the production of ATP by light dependent reactions
how are cyclic and noncyclic photophosphorylation different?
cyclic: only PS I water is not required oxygen is not evolved NADPH is not synthesized produces ADDITIONAL ATP
noncyclic PS I and PS II photolysis of water is required oxygen is evolved NADPH is synthesized products can be used for light independent rxns
what are the steps of light independent reactions?
- carbon fixation
- reduction of GP
- regeneration of RuBP
what are light independent reactions known as?
calvin cycle
what happens in carbon fixation?
- Rubisco catalyzes the carboxylation of RuBP (attaches CO2 molecule)
- 6C compound breaks into two 3C copmounds (glycerate-3-phosphate, GP)
- one cycle = 3 molecules of RuBP + 3 molecules of CO2 –> 6 molecules of GP
what happens during the reduction of GP?
- GP is phosphorylated by ATP and reduced by NADPH
- GP molecule is converted into TP (triose phosphate)
- one cycle requires six of each molecule
what happens during the regeneration of RuBP?
- one molecule of TP forms half a sugar
- remaining TP molecules reform RuBP
- regeneration of RuBP requires energy derived from the hydrolysis of ATP
what was the lollipop experiment
radioactive C-14 was added to a lollipop apparatus with green algae
different carbon compounds were identified using chromatography and autoradiography
Calvin Cycle was shown
what are chloroplasts
solar energy plants of a cell (convert light energy into chemical energy)
what type of issue possesses chloroplasts
photosynthetic tissue (leaves, not roots of plants)
