Enzymes, intro to cellular respiration Flashcards
There are different forms of some enzymes that…
assist different reactions.
- cytosolic version of enzyme
- mitochondrial version of enzyme (ex slide 5 lecture 12)
Can enzymes work in forward and reverse directions?
Some enzymes can
activity
total amount of reactant converted to product (over time)
number of enzyme molecules
genes
activity of each enzyme molecule
pH, temperature etc.
concentrations of substrates
inhibitors and activators
inhibitors
molecules that interact in some way with the enzyme to prevent it from working in the normal manner
enzyme activator
molecules that bind to enzymes and increase their activity
factors that affect enzyme activity
cofactors
cofactors
nonprotein enzyme helpers coenzyme inorganic (such as a metal ionic form) -ex magnesium needed for hexokinase -forms complex with ATP
Coenzyme
organic cofactor
EX. vitamins
The regeneration of ATP
an organism at work us ATP continuously, but ATP is a renewable resource that can be regenerated by the addition of phosphate to ADP
what happens if the inhibitor attaches to the enzyme by covalent bonds?
inhibition is usually irreversible
Many enzyme inhibitors bind to the enzyme by weak interactions…
in which case inhibitions is reversible.
some reversible inhibitors resemble the normal substrate molecule…
and compete for admission into the active site
Competitive inhibitors
reduce the productivity of enzymes by blocking substrates from entering active sites
How can competitive inhibitors be overcome?
by increasing the concentration of substrate so that as active sites become available, more substrate molecules than inhibitor molecules are around to gain entry to the sites
noncompetitive inhibitors
do not directly compete with the substrate to bind to the enzyme at the active site. Instead they impede enzymatic reactions by binding to another part of the enzyme.
What does the noncompetitive inhibitors interaction cause?
This interaction cause the enzyme moleules to change its shape in such a way that the active site becomes less effective at catalyzing the conversion of substrate to product.
What does regulation of enzyme activity help?
helps control metabolism
Allosteric regulation
protein’s function at one site is affected by the binding of a regulatory molecule to a separate site.
allosteric activator
binds to the allosteric regulatory site
how can a substrate activate the enzyme?
by stabilizing it
feedback inhibition
When ATP allosterically inhibits an enzyme in an ATP generating pathway, the result is feed back inhibition
What happens in feedback inhibition?
a metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway.
certain cells use this five step pathway to synthesize the amino acid isoleucine from threonine…
as isoleucine accumulates, it slows down its own synthesis by allosterically inhibiting the enzyme for the first step of the pathway. feedback inhibition thereby prevents the cell from wasting chemical resources by making more isoleucine than is necessary
If the cell is not using products(isoleucine)….
…product of the pathway builds up
if the cell is using product (isoleucine)…
product of the pathways does not build up
-initial substrate can bind to active site
sites of enzyme activity
- cytoplasm/cytosol
- membranes
- plasma membrane
- endomembranes
- mitochondrial membrane,
- thylakoid membrane
how is sunlight a part of metabolism?
by converting the energy of sunlight to a usable form of chemical energy, photosynthesis is the source of virtually all metabolic energy in biological lsystems
major catabolic pathways- exergonic breakdown of organic molecules
- fermentation
- anaerobic respiration
- aerobic respiration-oxygen
- glycolysis
- Krebs cycle
- oxidative phosphorylation
Aerobic respiration
a form of cellular respiration that requires oxygen in order to generate energy
oxidized
glucose and other substrates are
“burned”
oxidation
loss of electrons
reduction
gain of electrons
fermentation
catabolic process, is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen
aerobic respiration
most efficient catabolic pathway,
oxygen is consumed as a reactant along with the organic fuel.
cells of most eukaryotic and many prokaryotic organisms can carry out aerobic respiration.
anaerobic respiration
some prokaryotes use substances other than oxygen as reactants in a similar process that harvests chemical energy without oxygen
Cellular respiration
includes both aerobic and anaerobic processes, but is often used to refer to the aerobic process.
is the set of metabolic reactions and processes that take place in the cells that take place in the cells of organisms to convert biochemical energy from nutrients into ATP.
considered an exothermic redox reaction, releases heat.
what reactions are involved in respiration?
catabolic reactions
redox reaction
transfer of one or more electrons from one reactant to another
what makes them good fuels?
organic molecules that have an abundance of hydrogen are excellent fuels because their bonds are a source of hilltop electrons, whose energy may be released as these electrons fall down an energy gradient when they are transferred to oxygen.
How is the redox reaction involved in cellular respiration?
occurs when glucose C5H12O6 (Fuel) is oxidized to carbon dioxide,
Hydrogen (H) and electrons removed from glucose
oxygen (O2) is reduced to water-hydrogen added to oxygen
biological oxidation
series of steps
Abiotic oxidation of free hydrogen gas
heat light
explosion
uncontrolled
Biological electron carrier NAD+ (nicotinaminde adenine dinucleotide)
The H atoms are not transferred directly to O, but instead are usually passed first to an electron carrier, a coenzyme called NAD+
Why is NAD+ well suited as an electron carrier?
because it can cycle easily between oxidized (NAD+) and reduced (NADH) states
How does NAD+ trap electrons from glucose and the other organic molecules in food?
enzymes called dehydrogenases remove a pair of hydrogen atoms from the substrate, thereby oxidizing it, the enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+, The other proton is released as a H ion (H+) into the surrounding solution
Why is oxygen the terminal electron acceptor need in CR?
The low energy electrons that emerge from the electron transport system are taken up by O2. The negatively changed O molecules take up protons from the medium and form water.
cellular respiration
glucose is oxidized to carbon dioxide and oxygen is reduced to water
electrons lose energy as….
they are transferred to oxygen
Electrons are passed from glucose to NAD+…
(forming NADH) in a stepwise fashion through ETC to oxygen
Energy released is used to make….
ATP
how is oxidative phosphorylation powered?
powered by redox reaction
ETC
most ATP
O is last electron acceptor
substrate level
phosphorylation:
enzyme transfers Pi
directly from substrate to ADP
What happens if energy is released from a fuel all at once?
it cannot be harnessed efficiently for constructive work.
Glycolysis
a series of reactions that ultimately splits glucose into pyruvate.
occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.
Citric acid cycle
a chemical cycle involving 8 steps that completes the metabolic breakdown of glucose molecules begun in glycolysis by oxidizing acetyl to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol or prokaryotes; together with pyruvate oxidation, the second major stage in cellular respiration.
glycolysis
- Splitting of sugar
- breaks down glucose into two molecules of pyruvate (a 3 carbon sugar)
- harvests chemical energy by oxidizing glucose to pyrucate
What phases does glycolysis go through?
2 phases, 10 steps
energy investment phase
energy payoff phase
glycolysis, which occurs in the cytosol, begins the degradation process by…
breaking glucose into two molecules of a compound called pyruvate
What happens in glycolysis?
6 carbon sugars is split into two 3 carbon sugars. these smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate
Energy investment phase
the cell actually spends ATP
Steps in investment phase
- glucose is phosphorylated-chemically reactive,becomes charged, trapped in cell
- glucose is converted to its isomer
- another phosphate added to fructose-6-phosphate
- fructose bisphosphate split into 2 trioses (isomers of each other)
payoff phase
- each G3P is oxidized to 1,3 bisphosphoglycerate, NAD+ reduced to NADH
6.enzyme(kinase) transfers phosphate groups from substrate to
ADP->ATP: substrate level phosphorylation-exergonic reaction
-product has high potential energy - relocation of phosphate group
8.dehydration reaction to form PEP
9.Phosphate groups added to ADPs->2ATP (substrate level phosphorylation), conversion of PEP to pyruvate - pyruvate
Used by glycolysis
Glucose (what your breaking down)
O2 (it accepts protons and electrons at the end to produce water)
ADP+Pi (is used to make ATP)
Produced by glycolysis
CO2 ( its how all the carbons from glucose escape)
ATP (the entire point of these processes)
what is both used and produced in glycolysis?
NADH (first made then used in the ETC)
NAD+
Glycolysis is…
- in cytosol
- oxidation of glucose to 2 pyruvate, 2 ATP net, pyruvate to TCA, HADH to ETC
O2 is present:
pyruvate to the citric acid cycle in mitochondrion
O2 absent
pyruvate oxidized via fermentation
Where does the citric acid cycle / Krebs cycle occur?
In mitochondrial matrix in eukaryotes
in cytosol of prokaryotes
pyruvate first converted to…
acetyl CoA upon entry into mitochondrion.
Acetyl CoA is…
oxidized by Krebs cycle
Conversion of pyruvate to Acetyl CoA
- pyruvate enters mitochondria by active transport
- carboxyl group removed carbon dioxide produced (will diffuse out)
- Two carbon fragment oxidized, NAD reduced to NADH
- Coenzyme Q added to acetyl group, AcetylCoA has very high potential NRG
The citric acid cycle
has 8 steps, each catalyzed by a specific enzyme
for each turn of the citric acid cycle, two carbons enter in the the relatively reduced form of an acetyl group
The citric acid cycle steps
- Acetyl group of acetyl CoA combines with oxaloacetate, forming citrate-the rest of cycle converts the citrate 6Cs back to oxaloacetate 4Cs-carbon leaves as CO2
- Citrate converted to its isomer
- Oxidation of isocitrate, reduction of NAD+ to NADH and CO2 is produced
- CO2 is removed from alpha ketoglutarate-attachement of CoA-reduction of NAD+ to NADH intermediate oxidized
- CoA displaced, GDP phosphorylated(ATP can be generated from by GTP)
- Succinate oxidized; hydrogens transferred to FAD
- Malate oxidized, NAD+reduced to NADH
- Oxaloacetate regenerated
NADH produced at…
3 steps
The citric acid cycle is..
- in mitochondrion
- acetyl CoA combined with oxaloacetate to form citrate,citrate cycle back to oxaloacetate
Where is oxidative phosphorylation found?
in the cristae of the mitochondrion of eukaryotes, plasma membrane of prokaryotes
what is oxidative phosphorylation?
folding of the membrane increase the surface area for the enzymes
electron transport chain
- collection of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells, in prokaryotes they reside in the plasma membrane.
- the folding of the inner membrane to form cristae increases its surface area, providing space for thousands of copies of the chain in each mitochondrion
