Lecture 10a Flashcards
True or false
chemical elements essential to life are recycled
true
what does photosynthesis do?
it generates oxygen and organic molecules that are used by the mitochondria of eukaryotes as fuel for cellular respiration.
respiration breaks this fuel down which generates ATP
how are complex organic molecules broken down?
broken down by digestion into simpler components that are absorbed by the blood and transported to all cells
what are three processess where we get ATP?
1) glycolysis with fermentation
2) aerobic cellular respiration
3) anaerobic cellular respiration
what is glycolysis with fermentation?
a process in which organic compounds are incompletely broken down to produce a few ATP under anaerobic conditions
anaerobic = no oxygen
what are the two types of fermentation?
1) alcohol fermentation:
- produces ethanol and organic acids
- perfomes by many bacteria under anaerobic conditions
2) lactic acid fermentation
- produces lactate
- performed by certain fungi, bacteria and animals under anaerobic conditions
what is aerobic cellular respiration?
- uses oxygen to breakdown glucose to produce large quantities of ATP
- **most efficient catabolic pathway **
used by eukaryotes and certain prokaryotes
what is anaerobic cellular respiration?
- uses molecules such as nitrate or sulfate instead of oxygen to breakdown glucose to produce large quantities of ATP
used by certain prokaryotes
what is the equation for cellular respiration with glucose?
the transfer of electrons releases the energy from glucose and this energy is used to synthesize ATP
why can’t we perform aerobic cellular respiration in one step?
because the body temperature is not high enough to initiate the instantaneous combination of hydrogen with oxygen
- if energy is released all at once, it cannot be used efficiently for constructive work.
why does every oxidation reaction need to be accompanied by a reduction reaction?
because the electrons released during the oxidation process cannot exist in a free state in living cells
a lot of work is powered by simple electron transfers
what is redox reactions?
reduction + oxidation = redox
what is oxidation?
the loss of electrons by a less electronegative molecule, releases energy
- loss of electrons
- removes a hydrogen
- adds oxygen
- caused by an oxidizing agent
what is reduction?
gaining electrons by a more electronegative molecule, receives energy
- positive charge reduced ( by adding e-)
- gain of electrons = gaining energy
- adds hydrogens
- removes oxygen
- caused by a reducing agent
which molecule is the reducing agent and which is the oxidizing agent?
C6H8O6 = reducing agent
NO2 = oxidizing agent
what are electron carrier molecules and give two main ones?
electron carriers are molecules that are used to transfer electrons and protons to oxygen
NAD+ ( nicotinamide adenine dinucleotide ) - oxidized forn NAD+ and reduced form NADH
FAD (flavi adenine dinucleotide) - oxidized form FAD and reduced form FADH2
NADH and FADH2 temporarily store large amounts of free energy
what is the most versatile electron acceptor in cellular respiration and functions in several redox steps in the breakdown of sugar?
NAD+
NAD+ functions as an oxidizing agent and temporarily stores free energy
what is the coenzyme to enzymes called dehydogenases ?
NAD+
what does the enzyme dehydrogenases do?
they remove a pair of hydrogen atoms ( 2 electrons and 2 protons ) from the substrate thus oxidizing it.
the enzyme is delivering the two electrons and 1 proton to its coenzyme (NAD+). the other proton is released as a hydrogen ion (H+) into the surroundings.
how is NADH an electron shuttle?
when NADH tranfers the electrons to other molecules it also tranfers some energy thus leading to the synthesis of ATP.
why do H2 and O2 when mixed, combine explosively?
they combine explosively due to a release of energy as the electrons of hydrogen are pulled to the electronegative oxygen.
why does respiration use an electron transport chain (ETC)?
to break the fall of electrons to oxygen into several energy-releasing steps
electron transport chain
where is ETC and what is it made of?
consists of proteins built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of respiring prokaryotes.
electron energy level decreases with each transfer
electrons removed from glucose are shuttled by NADH to the top ( high energy level ) end of the chain. At the bottom ( lower energy end ) )2 captures these electrons along with hydrogen nuclei forming water.
explain the process of ETC
- each downhill carrier protein is more electronegative than the other and thus capable of oxiding its uphhill neighbor ( oxidizing = loosing electrons when you have a low electronegative molecule, thus releases energy)
- oxygen is at the bottom of the chain
- the electrons tranferred from glucose -> NAD+ -> NADH = falls down a energy gradient to a far more stable location in the electronegative O2 atom.
what is the structure of the mitochondria?
double membrane
what are the two different environments that the mitochondria can maintain?
- inner-membrane space ( between the inner and outer membranes )
- matrix ( enclosed by the inner membrane, contains many different enzymes as well as the mitochondrial DNA and ribosomes)
name the structures of the mitochondria?
where does ETC and chemiosmosis occur in the mitochondria?
occur in the inner membrane
both these processes combined together constitute oxidative phosphorylation
does the oxidation of NADH and FADH2 by ETC decrease or increase the activation energy needed for the synthesis of ATP?
it decreases it
what is substrate-level phosphorylation?
the mechanism when a smaller amount of ATP is formed directly in a few reactions of glycolysis and the citric acid cycle.
- this ATP synthesis happens when the enzyme transfers a phosphate group from a substrate molecule to ADP rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation
this type of synthesis of ATP accounts for almost 90% of the ATP generated by respiration
what are the 4 stages of aerobic cellular respiration?
1) glycolysis
2) pyruvate oxidation
3) citric acid cycle (krebs cycle)
4) oxidative phosphorylation (ETC)
stage 1
what occurs in glycolysis?
- is the splitting of sugar
- the first of two catabolic pathways that breakdown glucose and other organic fuels for energy
- occurs in the cytoplasm
- end products = pyruvate and NADH
- with O2 present, the chemical energy stored in the end products can be extracted from the mitochondria through aerobic cellular respiration (a lot of ATP )
- if O2 is absent then pyruvate and NADH will be used in the cytoplasm for fermentation ( less ATP )
what are the two phases of glycolysis?
1) energy investment phase:
- 1 molecule of glucose used
- 2 molecules of ATP used
2) energy payoff phase:
- 4 molecules of ATP formed( by substrate level phosphorylation)
- 2 molecules of NADH formed
- 2 molecules of pyruvate formed
two ATPs invested per glucose = energy investment phase
glucose is converted into what in an energy investment phase?
converted from a 6 carbon sugar into a 3 carbon sugar called glyceraldehyde-3-phosphate (G3P)
using 2 ATP molecules
what are the two important regulatory enzymes for glycolysis?
Hexokinase & Phosphofructokinase(PFK)
increase in AMP = activates PFK
increase in citrate and ATP = inhibits PFK
what helps drive glycolysis in one direction?
- phosphorylation of glucose occuring right as it enters the cell converting it into a different molecule
- maintains glucose concentration gradient
remember that glucose uptake occurs via facilitated diffusion through glucose carriers such as GLUT4
what are the two steps in glycolysis in which ATP is consumed?
1) in step 1 where glucose is converted to glucose-6-phosphate (G6P) by hexokinase
2) in step 3 where fructose-6-phosphate (F6P) is converted into fructose-1,6-biphosphate (F1-6BP) by PFK
Glyceraldehyde-3-phosphate (G3P) is the last molecule prior to the energy-payoff phase
what phase of glycolysis is this?
energy payoff phase
4 ATP formes
2 NADH formed
2 pyruvate formed
what are the two steps in glycolysis in which ATP is generated?
energy gained
1) in step 7 where 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerokinase
2) in step 10 where phosphoenolpyruvate (PEP) is converted into pyruvate by pyruvate kinase (PK)
the conversion of G3P into 1,3-bisphosphoglycerate yields energy in the form of NADH
glycolysis
what phase is this?
payoff phase
what is the last step of glycolysis?
pyruvate kinase
when does substrate-level phosphorylation of ATP synthesis occur?
occurs when an enzyme transfers a phosphate group from a subtrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation.
review
what is PFK inhibited/activated by?
inhibited by dropping levels of ATP and citrate and AMP levels rise PFK is allosterically activated
when the activity of PFK is inhibited it stops the process of cellular respiration
what can make do with glycolysis alone?
yeast and bacteria - by fermentation
how many NADH per glucose molecule?
in glycolysis
2 NADH per glucose molecule
