Chapter 6 Flashcards
1
Q
Where is energy stored?
A
chemical bonds of molecules
2
Q
How is energy released and transformed?
A
by the metabolic pathways of living cells
3
Q
How does a complex chemical transformation occur?
A
in a series of separate, intermediate reactions that form a metabolic pathway
4
Q
How are reactions catalysed?
A
by specific enzymes
5
Q
Are most metabolic pathways in all organisms similar or dissimilar?
A
similar
6
Q
What does it mean for eukaryotes to have compartmentalised metabolic pathways?
A
certain reactions occur inside specific organelles
7
Q
How is each metabolic pathway controlled?
A
by key enzymes that can be inhibited or activated, thereby determining how fast the reactions will go
8
Q
free energy
A
chemical energy available to do work
9
Q
What do the laws of thermodynamics say about energy?
A
a biochemical reaction may change the form of energy but not the net amount
10
Q
exergonic
A
releases energy from the reactants
11
Q
endergonic
A
energy must be added to the reactants
12
Q
coupled reactions
A
an energy-releasing reaction is coupled in time and location to an energy-requiring reaction
13
Q
What are two widely used coupling molecules?
A
coenzymes ATP and NADH
14
Q
Where is the energy released in exergonic reactions captured?
A
in chemical reactions when ATP is formed from adenosine diphosphate and inorganic phosphate
15
Q
What are some cellular activities that require free energy derived from the hydrolysis of ATP?
A
~active transport across a membrane
~condensation reactions that use enzymes to form polymers
~motor proteins that move vesicles along microtubules
16
Q
What does an ATP molecule consist of?
A
nitrogen-containing base adenine bonded to ribose, which is attached to a sequence of three phosphate groups
17
Q
What is the reaction for hydrolysis of ATP?
A
ATP + H2O –> ADP + Pi + free energy
18
Q
Is ATP hydrolysis endergonic or exergonic?
A
endergonic
19
Q
substrate-level phosphorylation
A
enzyme-mediated direct transfer of phosphate from another molecule to ADP
20
Q
redox reaction
A
a reaction in which one substance transfers one or more electrons to another substance
21
Q
reduction
A
the gain of one or more electrons by an atom, ion, or molecule
22
Q
oxidation
A
the loss of one or more electrons
23
Q
What is the relationship between how reduced a molecule is and the energy stored in its covalent bonds?
A
in general, the more reduced a molecule is, the more energy is stored in its covalent bonds
24
Q
NAD
A
the coenzyme nicotinamide adenine dinucleotide, used by cells as an electron carrier in redox reactions
25
NAD+
oxidized form of NAD
26
NADH
reduced form of NAD
27
How does catabolism play a role in the flow of energy within cells?
catabolism releases energy by oxidation; this energy can be trapped by the reduction of coenzymes such as NAD+
28
How does ATP participate in the flow of energy within cells?
ATP supplies the energy for many energy-requiring processes, including anabolism
29
oxidative phosphorylation
the coupling of NADH oxidation to the production of ATP
30
cellular respiration
the set of metabolic reactions used by cells to harvest energy from food
31
What is the chemical equation that shows the complete oxidation of glucose to CO2?
Glucose + 6 O2 --> 6 CO2 + 6 H2O + energy
32
In the oxidation of glucose to CO2, how much energy is produced per mole of glucose?
686 kcal per mole of glucose
33
aerobic conditions
in the presence of O2
34
glycolysis
the six-carbon monosaccharide glucose is converted into two three-carbon molecules of pyruvate
35
pyruvate oxidation
two three-carbon molecules of pyruvate are oxidized to two two-carbon molecules of acetyl CoAand two molecules of CO2
36
citric acid cycle
two two-carbon molecules of acetyl CoA are oxidizes to four molecules of CO2
37
Where does glycolysis take place?
in the cytosol
38
What does glycolysis involve?
ten enzyme-catalysed reactions
39
What are the two stages of glycolysis?
~the initial energy-investing reactions that consume chemical energy stored in ATP
~the energy-harvesting reactions that produce ATP and NADH
40
coenzyme A
written as CoA, this is used in various biochemical reactions as a carrier of acetyl groups
41
What is the main role of acetyl CoA?
~donate its acetyl group to the four-carbon compound oxaloacetate, forming the six-carbon molecule citrate
42
acetyl CoA
starting point for the citric acid cycle
43
How many times does the citric acid cycle operate?
twice for each glucose molecule that enters glycolysis (once for each pyruvate that enters the mitochondrion)
44
What does the released energy from exergonic oxidation reactions in the citric acid cycle do?
Gets trapped by NAD+, forming NADH
45
How do cells fully use the energy harvested in catabolism?
transfer energy from NADH and FADH2 to the phosphoanydride bond of ATP
46
oxidative phosphorylation
NADH oxidation is used to actively transport protons across the inner mitochondrial membrane, creating a proton gradient
47
What happens when there is a proton gradient across the mitochondrial membrane?
the protons diffuse back across, driving the synthesis of ATP
48
respiratory chain
series of redox electron carrier proteins
49
electrons
when the electrons from the oxidation of NADH and FADH2 pass from one carrier protein to the next in the chain
50
Are the oxidation reactions endergonic or exergonic?
exergonic
51
How do exergonic reactions help in the electron transport chain?
they release energy that is used to actively transport H+ ions across the membrane
52
What is the reduction coupled with the oxidation of NADH into NAD+?
water formed from oxygen gas
53
What is the key role of O2 in cells?
to act as an electron acceptor and then become reduced
54
ATP synthase
an enzyme that uses the H+ gradient to drive the synthesis of ATP
55
chemiosmosis
the movement of ions across a semipermeable barrier from a region of higher concentration to a region of lower concentration
56
In which direction do substances diffuse in?
From regions of higher concentration to regions of lower concentration
57
What happens if a membrane blocks diffusion?
the substance at the higher concentration has potential energy, which can be converted into other forms of energy
58
How do protons cross the membrane, since they cannot readily diffuse across the non polar membrane?
through the ATP synthase
59
What is the structure of the ATP synthase?
F0 unit and the F1 unit
60
F0 unit of ATP synthase
transmembrane domain that functions as the H+ channel
61
F1 unit of ATP synthase
contains the active sites for ATP synthesis
62
Where does chemiosmosis occur in eukaryotes?
mitochondria and chloroplasts
63
How is the H+ gradient in mitochondria set up?
using energy released by the oxidation of NADH and FADH2
64
How many molecules of ATP are produced per fully oxidized glucose?
32
65
How is most of the ATP produced in cellular respiration formed?
by oxidative phosphorylation
66
anaerobic
absence of O2
67
Why can the respiratory chain not operate in anaerobic conditions?
because the NADH produced by glycolysis would not be oxidised, so glycolysis would stop
68
fermentation
a method that allows organisms to reoxidize NADH even in anaerobic conditions, thus allowing glycolysis to continue
69
What is the overall yield of ATP from fermentation?
2 ATP per glucose
70
Why is the overall yield of ATP from fermentation restricted to the ATP made in glycolysis?
the NADH made during glycolysis is not available for re0xidation from by the respiratory chain to form ATP
71
lactic acid fermentation
pyruvate serves as the electron acceptor and lactate is the product
72
alcohol fermentation
pyruvate is converted to ethanol; takes place in certain yeasts and some plant cells under anaerobic conditions
73
carbon skeletons
molecules with covalently linked carbon atoms
74
What do polysaccharides get hydrolysed into?
glucose
75
How does the glucose that is hydrolysed from polysaccharides provide energy?
energy is captured in ATP
76
What do lipids get hydrolysed into?
glycerol and fatty acids
77
How does the glycerol that is hydrolysed from lipids provide energy?
converted into dihydroxyacetone phosphate
78
How do the fatty acids that are hydrolysed from lipids provide energy?
become acetyl CoA, which can then be catabolised to CO2 in the citric acid cycle
79
What do proteins get hydrolysed into?
amino acid building blocks
80
How do the amino acids that are hydrolysed from lipids provide energy?
feed into glycolysis or the citric acid cycle at different points
81
gluconeogenesis
when glycolytic and citric acid cycle intermediates are reduced and form glucose
82
anabolic interconversions
many catabolic pathways can operate essentially in reverse, with some modifications
83
Where does the energy released by catabolic pathways in almost all organisms ultimately come from?
the sun
84
photosynthesis
an anabolic process by which the energy of sunlight is captured and used to convert carbon dioxide and water into glucose and oxygen
85
light reactions
convert light energy into chemical energy in the form of ATP and the reduced electron carrier NADPH
86
carbon-fixation reactions
use the ATP and NADPH made by the light reactions, along with CO2, to produce carbohydrates
87
light
a form of electromagnetic radiation
88
electromagnetic radiation
propagated in waves
89
What is the relationship between energy in radiation and wavelength?
amount of energy in the radiation is inversely proportional to its wavelength
90
photons
packets of light energy which have no mass
91
What are the two behaviours of light?
travels in waves, also behaves as particles
92
How do receptive molecules harvest energy for biological processes?
by absorbing only specific wavelengths of light -- photons with specific amounts of energy
93
What happens when a photon meets a molecule?
scattered/reflected, transmitted, or absorbed
94
scattered/reflected
photon bounces off molecule
95
transmitted
photon passes through the molecule
96
absorbed
photon gets absorbed by the molecule, adding energy to the molecule
97
What happens when a molecule acquires the energy of a photon?
raised from a ground state (lower energy) to an excited state (higher energy)
98
pigments
molecules that absorb wavelengths in the visible spectrum
99
What determines the colour of a pigment?
the scattered or transmitted wavelengths
100
chlorophyll
absorbs both blue and red light, so it appears green
101
absorption spectrum
plot light absorbed by a purified pigment against wavelength
102
action spectrum
plot of biological activity of an organism against the wavelengths of light to which it is exposed
103
light-harvesting complexes
energy-absorbed antenna systems of pigments
104
photosystem
a large multiprotein complex where light energy is converted into chemical energy
105
Where is the photosystem?
spans the thylakoid membrane
106
What are the components of the photosystem?
multiple antenna systems with their associated pigment molecules
107
reaction center
part of the photosystem; has antenna systems around it
108
What does the reaction centre do?
converts the absorbed light energy into chemical energy
109
What happens when the chlorophyll molecule in the reaction centre absorbs sufficient energy?
it gives up its excited electron to a chemical acceptor; in other words: chlorophyll gets oxidised while the acceptor molecule is reduced
110
Photosystem I
absorbs light energy at 700nm and passes an excited electron to NADP+, reducing it to NADPH
111
Photosystem II
absorbs light energy at 680nm, oxidises wter molecules, and initiates the electron transport chain that produces ATP
112
What is the order of the photosystems in electron transport reactions?
Photosystem II, then Photosystem I
113
cyclic electron transport
only uses photosystem I and produces ATP but not NADPH
114
in what way is cyclic electron transport chain cyclic?
the electrons flow from the reaction centre of photosytem I, through the electron transport chain, and then back to photosystem I
115
Calvin cycle
metabolic pathway occurring in the stroma of the chloroplast
116
What are the 3 processes of the Calvin cycle?
Fixation of CO2, reduction of 3PG to form glyceraldehyde 3-phosphate, regeneration of the CO2 acceptor (RuBP)
117
fixation of CO2
CO2 added to an acceptor molecule, the immediate six-carbon molecule product breaks down into two three-carbon molecules called 3PG
118
What enzyme catalyses the fixation of CO2?
rubisco
119
reduction of 3PG to form glyceraldehyde 3-phosophate
series of reactions that involves a phosphorylation and a reduction, producing glyceraldehyde 3-phosphate
120
regeneration of the CO2 acceptor, RuBP
most of the G3P ends up as RuMP, and ATP converts it into RuBP
121
What happens to the extra G3P?
~exported out of the cloroplast to the cytosol, where it is converted to hexoses
~glucose accumulates inside the chloroplast, and then link together to form starch, which allows sucrose to get exported to the rest of the plant even when photosynthesis is not taking place
122
autotrophs
photosynthetic organisms
123
heterotrophs
cannot photosynthesise
