week 2 Flashcards
define cellular respiration
metabolic process with which an organism obtains energy by oxidising nutrients and releasing waste products of H20 and CO2
what are catabolic and anabolic reactions
catabolic: energy released through breakdown of larger molecules
anabolic: energy required to build up larger molecules eg proteins
what are the 3 overall stages of respiration
glycolysis, TCA/Krebs, ETC
explain what occurs in the glycolysis stage of respiration
breakdown of glucose to capture energy, done via phosphorylation to yield ATP, and REDOX reactions yield electrons carried by electron carrier NADH
all occurs in the cytosol and can proceed in the absence of oxygen
what is the resulting products of the glycolysis stage
1 glucose molecule yields 2 pyruvate, 2 H20 2 ATP and 2 NADH
what occurs during TCA/Krebs cycle
occurs within the mitochondria and yields energy in the form of ATP and electrons carried by NADH and FADH2 to be used in the ETC
Acetyl-CoA combines with oxaloacetate, and is regenerated at the end of the cycle so a new molecule of Acetly-CoA can be converted
what occurs during the ETC
occurs in mitochondria, electrons carried by NADH and FADH2 are released, and travel through a series in molecules in the inner mitochondrial membrane
during movement energy is used to pump H+ molecules across the inner membrane, forming an electrochemical gradient.
causes ions to flow back across the membrane through ATPsynthase, known as chemiosmosis
oxygen is reduced to water as it is the final electron acceptor, combining with H+
what is the result of the TCA cycle
2 ATP, 8 NADH, 2 FADH and 6CO
TCA cycle must be completed twice for one original glucose molecule
overall what is the input and output of glycolysis
2 ATP used, 4 ATP made, net 2 ATP made from each glucose molecule
when is resiration affected by lack of oxygen
glycolysis can still occur but it cannot proceed to stage 2
lactate is made in animals and ethanol in plants
what enzyme adds phosphate
kinase
what enzyme splits things
lyase
what enzyme cleaves water
enolase
what does isomerase do
converts molecule from one isomer to another, no splitting
what do dehydrogenase enzymes do
oxidises a substrate by reducing an electron acceptor
what is the basic equation for respiration
glucose + oxygen -> CO2, H2O and ATP
define photosynthesis
converting CO2 and H2O into carbohydrates using cellular energy
where does photosynthesis occur (larger organism)
in phototrophs which are organisms that capture photons, produce compounds and acquire energy
what is a dark reaction
a reaction that doesn’t require light and occurs in the stroma in solution
it reduces gaseous CO2 to carbohydrates
requires energy from NADPH and ATP
what is a light reaction
a reaction that requires light and occurs in the thylakoids
electrons are excited when light hits chlorophyll, electrons move through the ETC, generating ATP and NADPH
H2O is split to release oxygen
the energy is used in the dark reactions, and O2 is released into the air
how are chloroplasts structured
double membranes, stacks of thylakoids within the membrane with stroma inbetween (this is the solution where dark reactions take place)
how do chlorophylls capture light most effectively
they contain a tetrapyrrole ring (chlorin), and contain Mg2+ at the centre with pyrroles surrounding
their shape also means they have a higher chance of capturing light
what are the different types of chlorophyll in plants and bacteria
chlorophyll a and b in plants
bacteriochlorophylls a and b similar and major pigments in anaerobic photosynthetic bacteria
what are antenna pigments and name some types of them
light absorbing molecules in thylakoid membranes of chloroplasts
include carotenoids, phycocyanin and phycoerythrin
what are the purpose of antenna pigments
to extend the range of light capture, especially in green
how is light energy captured using antenna pigments and chlorophylls
they exchange light energy (excited electrons) until captured
what are PS1 and PS2
photosystems that operate in series connected by cytochrome bf complex
they contain many proteins and pigments embedded in the thylakoid membrane
how do PS 1 and 2 work
electrons are excited in both and go through cascade between them
enters in PS1 in oxidised state, then becomes reduced
what is the structure of DNA
sugar phosphate backbone, strands running antiparallel
10 base pairs per turn of the double helix
bases are on the inside, phosphate on the outside
space filling model show major and minor groove in the double helix
why is it called the semi-conservative model of dna replication
explains how DNA copies itself before cell division, and each new DNA molecule consists of one original strand and one newly synthesised strand
why is the semi conservative model so important
it ensures accurate DNA copying with fewer mutations
allows genetic information to be passed on during cell division
keeps DNA structures stable across generations
what are the three steps of replication
Initiation (Unwinding the DNA)
Elongation (Building the new strands)
Termination (Finalising the process)
what occurs during initiation
happens in nucleus of eukaryotic cells and cytoplasm of prokaryotes
helicase unzips DNA by breaking hydrogen bonds between bases
Topoisomerase prevents DNA from supercoiling or tangling during unwinding
Single Strand binding proteins (SSBs) keep the DNA strands separated and stable
results in a replication form - one in prokaryotes and many in eukaryotes
what ocurs during elongation
DNA polymerase adds new nucleotides
primase adds a short RNA primer which tells DNA polymerase where to start copying
Leading strand shows continuous copying in the 5’ to 3’ direction
Lagging strand shows fragmented copying, where DNA polyermase works in short segments (Okazaki fragments)
each fragment needs a new primer before DNA polymerase can add nucleotides
DNA ligase joins the fragments together into a continuous strand
what occurs during termination
RNA primers are removed, DNA polymerase fills the gaps with DNA
DNA ligase connects any remaining fragments, leaving 2 identical DNA molecules, each with one original strand and one new strand
what wavelengths do PSI and PSII absorb
PSI paired for P700 - absorbs light up to 700nm
PSII paired for P680 - absorbs light up until 680nm
how does the Z scheme work - details
it is the path of electron flow and reduction potentials of the components in photosynthesis
the absorption of light energy converts P680 and P700 (poor reducing agents) to excited molecules (good reducing agents)
light energy drives electron flow uphill
light is captured by antenna complexes
for 2 H2O oxidised to O2, 2 NADP+ are reduced to 2 NADPH
how was the Calvin cycle discovered
identified in 1948, led to the Nobel prize in chemistry
key enzyme is RuBisCo
discovered using radioactive carbon-14 (¹⁴C) labelling to track the sequence of carbon transitions. By introducing ¹⁴CO₂ into algae and stopping photosynthesis at different time intervals, Calvin identified the order in which intermediate compounds formed.
the cycle regenerates RuBP allowing constant fixation of CO2
how were dark reactions identified
a fast CO2 injection and a rapid ‘quench’ of perchloric acid to stop reactions
2D chromatography improves separation of intermediates
what is photorespiration
it recycles the toxic products of the oxygenation reaction; it consumes NADH, ATP to give glyoxylate, serine, glycine and CO2
catalysed by RuBisCo like photosynthesis
what is RuBisCo’s main substrate
CO2 in photosynthesis, to incorporate CO2 into an organic molecule
how have angiosperms evolved to ‘feed’ RuBisCo during photosynthesis
C4 and CAM photosynthesis
how have cyanobacteria and algae evolved to ‘feed’ RuBisCo during photosynthesis
cyanobacteria: form carboxysomes
algae: form pyrenoids
how does C4 photosynthesis work
it fixes HCO3- with pyruvate into malate, then transports malate to a second cell for decarboxylation and refixation by RuBisCo
more efficient because it fixes HCO3- first, and avoids O2
it depends on spatial separation of C4 and C3 fixation reactions
the only major C4 crop is maize
summary = C4 respiration gets around the CO2 limitation by introducing a pre-fixation step to capture C as a 4-carbon acid
what is CAM photosynthesis
CAM = crassulacean Acid Metabolism
it depends on separation of timing of the C4 and C3 fixation reactions
CAM plants store C4 acids (malate) in the vacuole for decarboxylation and refixation by RuBisCo in the day
CAM requires fine control of gene expression over the day/night cycle
CAM uses ‘introverted’ cycle of stomatal opening/closing to save water and concentrate CO2 in the leaf
only major CAM crop is pineapple
what is C3 photosynthesis
most common - default pathway
carbon gets fixed by RuBisCo
sometimes photorespiration mistakenly happens when RuBisCo binds with CO2 instead of O2, reducing efficiency
it depends on rubisco selectivity between CO2 and O2
what conditions suit C4 and CAM photosynthesis
well suited to growth under high light - extra energy - and reduced water availability
