cell bio chapter 9 Flashcards
1st law of thermodynamics
centers around the conservation of energy, stating that the total energy of
a system & its surroundings remains constant; energy can neither be created nor
destroyed, but can be converted from one form to another.
2nd law of thermodynamics
centers around the degree of disorder in a system (entropy, S), stating
that it increases over time
T/F: Cells intuitively appear to violate the 2nd law, as their molecules are more ordered
(lower entropy) than their precursors
true
which one is correct?
- a cell is not an isolated system, with changes in entropy within a cell will be
balanced by changes in its environment - the formation of a peptide bond releases energy in the form of heat,
which increases the thermal motion & degree of disorder of surrounding molecules - In order for biochemical reactions that lower entropy to occur, the heat released by
the reaction must be sufficient to generate a greater increase in entropy in the
surrounding.
Gibbs free energy (G).
The change in free energy (∆G) of a reaction combines the effects of changes in
enthalpy (the heat released or absorbed, ∆H) & entropy (the degree of resulting
disorder, ∆S) according to the following equation (where T is the absolute temperature):
∆G = ∆H - T ∆S
T/F: All spontaneous chemical reactions proceed in the energetically favorable direction,
accompanied by a decrease in free energy (∆G < 0)
true
T/F: The ∆G of a reaction is determined not only by the intrinsic properties of the
reactants & products, but also by their concentrations & other reaction conditions,
such as temperature
true
T/F: The standard free-energy change (fixed concentrations & pressure, ∆G°) is directly
related to its equilibrium position
true
what does this equation say?
A ↔ B
∆G = ∆G° + RT ln [B]/[A]
*R = gas constant
The standard free-energy change (fixed concentrations & pressure, ∆G°) is directly
related to its equilibrium position
when ∆G = 0, what happens?
At equilibrium, ∆G = 0 & the reaction does not proceed in either direction
what is k in this equation?
∆G° = -RT ln K
The equilibrium constant for the reaction, (K = [B]/[A])
T/F:
* If the actual ratio [B]/[A] is greater than the equilibrium ratio (K), ∆G will be > 0 & the
reaction will proceed in the reverse direction (i.e. B → A)
* If the ratio [B]/[A] is less than K, ∆G will be < 0 & the reaction will proceed in the
forward direction (i.e. A → B).
true
T/F : Many biological reactions are thermodynamically unfavorable (∆G > 0) under cellular
conditions & require an additional source of energy
true
Adenosine 5’-triphosphate (ATP)
plays a central role in the process of unfavorable reactions by acting as a store of free energy within the cell, where the phosphodiester bonds in its phosphate
groups are high energy because their hydrolysis is accompanied by a relatively large
decrease in ∆G
glycolysis
- breakdown of glucose, initial stage in the breakdown of glucose & occurs in the absence of oxygen
- complete oxidative breakdown of
glucose yields a large amount of free energy - To harness the free energy in usable form, glucose is oxidised within cells in a series of steps coupled to the synthesis of ATP
- provides all metabolic
energy in anaerobic organisms,
however it is only the first stage of
glucose degradation in aerobic cells
T/F: In addition to producing ATP, glycolysis converts 2 molecules of NAD+ to NADH, in
which NAD+ acts as an oxidizing agent that accepts electrons from glyceraldehyde-3-
phosphate.
true
what does NADH do?
The NADH formed as a product must be recycled by serving as a donor of electrons
for other oxidation-reduction reactions within the cell. In anaerobic conditions, the NADH formed during glycolysis is reoxidised to NAD+ by
the conversion of pyruvate to lactate or ethanol.
what is the role of NADH in aerobic organisms?
the NADH serves as an additional source of energy by
donating its electrons to the electron transport chain, where they are ultimately used
to reduce O2 to H2O, coupled with the generation of additional ATP.
The citric acid Cycle
serves as the mitochondrial hub for the final steps in carbon skeleton oxidative catabolism for carbohydrates, amino acids, and fatty acids.
where does glycolysis take place in the cell?
cytosol
metabolism of pyruvate
- glycolysis>pyruvate
- oxidative decarboxylation in the presence of coenzyme A (CoA-SH)
coenzyme A (CoA-SH)
serves as a carrier of acyl groups in
various metabolic reactions
main storage forms of energy
polysaccharides & lipids
T/F: Polysaccharides are broken down into free sugars which are metabolized by
glycolysis & the citric acid cycle
True
T/F: lipids are more efficient than polysaccharides regarding energy storage & yielding substantially more energy per unit
weight
True
lipid metabolism
- first step: the hydrolysis of triacylglycerols into
glycerol & free fatty acids. - second step: fatty acids are then degraded in
stepwise oxidative process, 2 C
atoms at a time, yielding acetyl CoA
& a fatty acyl-CoA shorter by one 2-C unit - acetyl-CoA then enters the citric
acid cycle, with degradation of the
fatty acid remainder proceeding in
the same manner
T/F: Most of the usable energy obtained from the breakdown of carbohydrates or fats is
derived from electron transport & oxidative phosphorylation.
true
what are the products of citrc acid cycle ?
NADH & FADH2 are produced from the citric acid cycle in the mitochondrial matrix
in anaerobic conditions what happens to NADH?
reoxidized to NAD+ by
the conversion of pyruvate to lactate or ethanol.
electron transport chain
ultimately used
to reduce O2 to H2O, coupled with the generation of additional ATP.
T/f: glycolysis produces Pyruvate,
NADH, & ATP by oxidizing glucose
True
central pathway of oxidative metabolism is ….
Kreb cycle ( citric acid cycle)
first step of lipid metabolism
hydrolysis of triacylglycerols> glycerol and fatty acid
what happens to fatty acid from hydrolysis of triacylglycerols?
degraded in
stepwise oxidative process, 2 C
atoms at a time, yielding acetyl CoA
& a fatty acyl-CoA shorter by one 2-C
unit
what happens to the acetylCoA from degradation of fatty acid ?
enters Kreb
T/F: Most of the usable energy obtained from the breakdown of carbohydrates or fats is
derived from electron transport & oxidative phosphorylation.
true
where most of the usable energy obtained from the breakdown of CH or fats derived from?
electron transport & oxidative phosphorylation.
what happens to electrons from NADH & FADH2?
transferred to molecular oxygen, which is coupled
to the formation of an additional 34 ATP molecules by oxidative phosphorylation.
where does electron transport chain occurs?
inner membrane of mitochondria ( for eukaryotic cells) & plasma membrane ( for aerobic bacteria)
complex V
restricted channel that allows the energy in the electrochemical
gradient to be harnessed & converted to ATP
components of ATP synthase of complex v
2 structurally distinct
components, F0 & F1, linked by a slender stalk.
F0
The F0 portion is an electrically driven motor that
spans the membrane & provides a channel through
which protons are able to flow back into the
mitochondria
F1
catalyzes the synthesis of ATP from ADP
& Pi
what does the energetically favourable return of protons do for complex v?
- roots in the F0, and then coupled to ATP synthesis by the spinning of a subunit
of F1, which catalyzes the synthesis of ATP from ADP
& Pi
T/F: flow of 4 protons back across the membrane
through F0 is required to drive the synthesis of 1 ATP
molecule by F1
True
for 4 ‘protons to cross the mebrane , how many ATP is used fromF1?
1 ATP
how many ATP is used for oxidation of NADH?
3 ATP
How many ATp is used for oxidation of FADH2?
2
