Chapter 6 Flashcards
Where is energy stored?
chemical bonds of molecules
How is energy released and transformed?
by the metabolic pathways of living cells
How does a complex chemical transformation occur?
in a series of separate, intermediate reactions that form a metabolic pathway
How are reactions catalysed?
by specific enzymes
Are most metabolic pathways in all organisms similar or dissimilar?
similar
What does it mean for eukaryotes to have compartmentalised metabolic pathways?
certain reactions occur inside specific organelles
How is each metabolic pathway controlled?
by key enzymes that can be inhibited or activated, thereby determining how fast the reactions will go
free energy
chemical energy available to do work
What do the laws of thermodynamics say about energy?
a biochemical reaction may change the form of energy but not the net amount
exergonic
releases energy from the reactants
endergonic
energy must be added to the reactants
coupled reactions
an energy-releasing reaction is coupled in time and location to an energy-requiring reaction
What are two widely used coupling molecules?
coenzymes ATP and NADH
Where is the energy released in exergonic reactions captured?
in chemical reactions when ATP is formed from adenosine diphosphate and inorganic phosphate
What are some cellular activities that require free energy derived from the hydrolysis of ATP?
~active transport across a membrane
~condensation reactions that use enzymes to form polymers
~motor proteins that move vesicles along microtubules
What does an ATP molecule consist of?
nitrogen-containing base adenine bonded to ribose, which is attached to a sequence of three phosphate groups
What is the reaction for hydrolysis of ATP?
ATP + H2O –> ADP + Pi + free energy
Is ATP hydrolysis endergonic or exergonic?
endergonic
substrate-level phosphorylation
enzyme-mediated direct transfer of phosphate from another molecule to ADP
redox reaction
a reaction in which one substance transfers one or more electrons to another substance
reduction
the gain of one or more electrons by an atom, ion, or molecule
oxidation
the loss of one or more electrons
What is the relationship between how reduced a molecule is and the energy stored in its covalent bonds?
in general, the more reduced a molecule is, the more energy is stored in its covalent bonds
NAD
the coenzyme nicotinamide adenine dinucleotide, used by cells as an electron carrier in redox reactions
NAD+
oxidized form of NAD
NADH
reduced form of NAD
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+
How does ATP participate in the flow of energy within cells?
ATP supplies the energy for many energy-requiring processes, including anabolism
oxidative phosphorylation
the coupling of NADH oxidation to the production of ATP
cellular respiration
the set of metabolic reactions used by cells to harvest energy from food
What is the chemical equation that shows the complete oxidation of glucose to CO2?
Glucose + 6 O2 –> 6 CO2 + 6 H2O + energy
In the oxidation of glucose to CO2, how much energy is produced per mole of glucose?
686 kcal per mole of glucose
aerobic conditions
in the presence of O2
glycolysis
the six-carbon monosaccharide glucose is converted into two three-carbon molecules of pyruvate
pyruvate oxidation
two three-carbon molecules of pyruvate are oxidized to two two-carbon molecules of acetyl CoAand two molecules of CO2
citric acid cycle
two two-carbon molecules of acetyl CoA are oxidizes to four molecules of CO2
Where does glycolysis take place?
in the cytosol
What does glycolysis involve?
ten enzyme-catalysed reactions
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
coenzyme A
written as CoA, this is used in various biochemical reactions as a carrier of acetyl groups
What is the main role of acetyl CoA?
~donate its acetyl group to the four-carbon compound oxaloacetate, forming the six-carbon molecule citrate
acetyl CoA
starting point for the citric acid cycle
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)
What does the released energy from exergonic oxidation reactions in the citric acid cycle do?
Gets trapped by NAD+, forming NADH
How do cells fully use the energy harvested in catabolism?
transfer energy from NADH and FADH2 to the phosphoanydride bond of ATP
oxidative phosphorylation
NADH oxidation is used to actively transport protons across the inner mitochondrial membrane, creating a proton gradient
What happens when there is a proton gradient across the mitochondrial membrane?
the protons diffuse back across, driving the synthesis of ATP
respiratory chain
series of redox electron carrier proteins
electrons
when the electrons from the oxidation of NADH and FADH2 pass from one carrier protein to the next in the chain
Are the oxidation reactions endergonic or exergonic?
exergonic
How do exergonic reactions help in the electron transport chain?
they release energy that is used to actively transport H+ ions across the membrane
What is the reduction coupled with the oxidation of NADH into NAD+?
water formed from oxygen gas
What is the key role of O2 in cells?
to act as an electron acceptor and then become reduced
ATP synthase
an enzyme that uses the H+ gradient to drive the synthesis of ATP
chemiosmosis
the movement of ions across a semipermeable barrier from a region of higher concentration to a region of lower concentration
In which direction do substances diffuse in?
From regions of higher concentration to regions of lower concentration
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
How do protons cross the membrane, since they cannot readily diffuse across the non polar membrane?
through the ATP synthase
What is the structure of the ATP synthase?
F0 unit and the F1 unit
F0 unit of ATP synthase
transmembrane domain that functions as the H+ channel
F1 unit of ATP synthase
contains the active sites for ATP synthesis
Where does chemiosmosis occur in eukaryotes?
mitochondria and chloroplasts
How is the H+ gradient in mitochondria set up?
using energy released by the oxidation of NADH and FADH2
How many molecules of ATP are produced per fully oxidized glucose?
32
How is most of the ATP produced in cellular respiration formed?
by oxidative phosphorylation
anaerobic
absence of O2
Why can the respiratory chain not operate in anaerobic conditions?
because the NADH produced by glycolysis would not be oxidised, so glycolysis would stop
fermentation
a method that allows organisms to reoxidize NADH even in anaerobic conditions, thus allowing glycolysis to continue
What is the overall yield of ATP from fermentation?
2 ATP per glucose
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
lactic acid fermentation
pyruvate serves as the electron acceptor and lactate is the product
alcohol fermentation
pyruvate is converted to ethanol; takes place in certain yeasts and some plant cells under anaerobic conditions
carbon skeletons
molecules with covalently linked carbon atoms
What do polysaccharides get hydrolysed into?
glucose
How does the glucose that is hydrolysed from polysaccharides provide energy?
energy is captured in ATP
What do lipids get hydrolysed into?
glycerol and fatty acids
How does the glycerol that is hydrolysed from lipids provide energy?
converted into dihydroxyacetone phosphate
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
What do proteins get hydrolysed into?
amino acid building blocks
How do the amino acids that are hydrolysed from lipids provide energy?
feed into glycolysis or the citric acid cycle at different points
gluconeogenesis
when glycolytic and citric acid cycle intermediates are reduced and form glucose
anabolic interconversions
many catabolic pathways can operate essentially in reverse, with some modifications
Where does the energy released by catabolic pathways in almost all organisms ultimately come from?
the sun
photosynthesis
an anabolic process by which the energy of sunlight is captured and used to convert carbon dioxide and water into glucose and oxygen
light reactions
convert light energy into chemical energy in the form of ATP and the reduced electron carrier NADPH
carbon-fixation reactions
use the ATP and NADPH made by the light reactions, along with CO2, to produce carbohydrates
light
a form of electromagnetic radiation
electromagnetic radiation
propagated in waves
What is the relationship between energy in radiation and wavelength?
amount of energy in the radiation is inversely proportional to its wavelength
photons
packets of light energy which have no mass
What are the two behaviours of light?
travels in waves, also behaves as particles
How do receptive molecules harvest energy for biological processes?
by absorbing only specific wavelengths of light – photons with specific amounts of energy
What happens when a photon meets a molecule?
scattered/reflected, transmitted, or absorbed
scattered/reflected
photon bounces off molecule
transmitted
photon passes through the molecule
absorbed
photon gets absorbed by the molecule, adding energy to the molecule
What happens when a molecule acquires the energy of a photon?
raised from a ground state (lower energy) to an excited state (higher energy)
pigments
molecules that absorb wavelengths in the visible spectrum
What determines the colour of a pigment?
the scattered or transmitted wavelengths
chlorophyll
absorbs both blue and red light, so it appears green
absorption spectrum
plot light absorbed by a purified pigment against wavelength
action spectrum
plot of biological activity of an organism against the wavelengths of light to which it is exposed
light-harvesting complexes
energy-absorbed antenna systems of pigments
photosystem
a large multiprotein complex where light energy is converted into chemical energy
Where is the photosystem?
spans the thylakoid membrane
What are the components of the photosystem?
multiple antenna systems with their associated pigment molecules
reaction center
part of the photosystem; has antenna systems around it
What does the reaction centre do?
converts the absorbed light energy into chemical energy
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
Photosystem I
absorbs light energy at 700nm and passes an excited electron to NADP+, reducing it to NADPH
Photosystem II
absorbs light energy at 680nm, oxidises wter molecules, and initiates the electron transport chain that produces ATP
What is the order of the photosystems in electron transport reactions?
Photosystem II, then Photosystem I
cyclic electron transport
only uses photosystem I and produces ATP but not NADPH
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
Calvin cycle
metabolic pathway occurring in the stroma of the chloroplast
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)
fixation of CO2
CO2 added to an acceptor molecule, the immediate six-carbon molecule product breaks down into two three-carbon molecules called 3PG
What enzyme catalyses the fixation of CO2?
rubisco
reduction of 3PG to form glyceraldehyde 3-phosophate
series of reactions that involves a phosphorylation and a reduction, producing glyceraldehyde 3-phosphate
regeneration of the CO2 acceptor, RuBP
most of the G3P ends up as RuMP, and ATP converts it into RuBP
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
autotrophs
photosynthetic organisms
heterotrophs
cannot photosynthesise
