Cellular processes, control (2) + (5) Flashcards
where does glycolysis occur
the cytoplasm
briefly describe the difference between the presence of oxygen for cellular respiration in plants/fungi and animals
The presence of oxygen will allow the glucose (now as two molecules of pyruvate after glycolysis) to be fully oxidised.
Oxygen acts as the final electron acceptor in the ETC, allowing NAD and FAD to be oxidised. Therefore the Krebs cycle and Link reaction and ox. phos. can continue to convert pyruvate.
In the absence of oxygen, pyruvic acid is broken down into ethanal and carbon dioxide, and not fully oxidised. Pyruvic acid is converted to lactic acid and carbon dioxide is released. Glucose is not fully oxidised.
where does the Krebs cycle occur
in the mitochondrial matrix
- outline what pyruvate is converted to in Links*
- and what happens to it in the Krebs cycle*
Pyruvate (2C) is converted to Acetyl CoA (2C).
Acetyl CoA binds to 4C intermediate, producing citric acid (6C).
It is oxidised and decarboxylated to produce a 5C intermediate.
That is oxidised and decarboxylated to produce a 4C intermediate (which binds to 2C pyruvate derivative, continuing the cycle).
how much ATP is produced in aerobic respiration
there is a net gain of 38 ATP molecules from one molecule of glucose
how do animals and plants make glucose
Plants are photoautotrophs/chemoautotrophs- absorb light energy and use CO2 and water to produce glucose.
Animals consume carbohydrates which are hydrolysed into glucose or other molecules to be used in respiration.
where does photolysis occur
in the granum of the chloroplast
why must DNA produce genetically identical DNA when replicating
old cells/organelles/molecules die and must be replaced, it must be genetically identical so that they have the exact same structure and function as the previous molecules, which is decided by the sequence of nucleotide bases. DNA must also be able to be passed onto offspring.
what is necessary for DNA replication to occur (4)
- the actual DNA to act as an exact template
- a pool of relevant and freely available nucleotides
- a supply of the relevant enzymes to catalyse/speed up the rate of reaction
- ATP to provide energy for these reactions
what happens to the DNA structure during replication
the double helix unzips, uncoils and unwinds so that each strand is exposed for the free nucleotides to bond to
why is the new strand of DNA semi-conservative
50% of the genetic material comes from the original strand, and 50% from free nucleotides and the new strand not previously a part of the original strand
why does nucleic acid sequence determine which protein is produced in protein synthesis
the sequence determines which amino acids are translated, which give a specific sequence which determines how the protein folds and coils, in particular because it determines the R groups, which have different interactions, determining the tertiary structure of the protein
how can the four DNA nucleotides be classified
PYRIMIDINES- cytosine and thymine, single carbon ring structure PURINES- adenine and guanine, double carbon ring structure COMPLEMENTARY BASE PAIRING C and G triple hydrogen bond T and A double hydrogen bond Purines bond with Pyrimidines, which allows a constant distance to always be maintained between the two strands. There is always an equal quantity of A and T, and an equal quantity of C and G.
explain 5’ and 3’ in DNA
the two polynucleotide strands of the double helix are ANTIPARALLEL, running in opposite directions. For one strand the phosphate group end (5’) is at the top, and for the other the hydroxyl group (3’) is at the top. They are bonded together by hydrogen bonds.
what is the function of mRNA and why is it necessary
To transport the genetic material needed to code for proteins at the ribosomes in the cytoplasm from the double-membrane bound nuclear envelope where DNA is protected from the cytoplasm, stored and transcribed. DNA is too large a molecule to leave the nucleus. Therefore its genetic code is transcribed onto mRNA. mRNA corresponds to a single gene, compared to DNA, which is an entire chromosome long.
differences and similaritiesbetween DNA and RNA
D1. SUGAR- deoxyribose/ribose, 4 O atoms, 5 O atoms D2. thymine is replaced by URACIL (still pyrimidine, double bonds with A) D3. RNA polymers are small enough to leave the nucleus and travel to ribosomes D4. RNA is involved in protein synthesis S1. complementary base pairing rules- number of H bonds and between what S2. nucleotides form polynucleotides in the same manner- phosphodiester bonds between Pi on C5 and OH on C3
why does DNA need to be replicated
for new cells needed for growth or repairof tissues
what is DNA replication
the process of copying and duplicating a DNA molecule in a semiconservative way, i.e. the copy contains one of the original strands paired with a newly synthesized strand that is complementary in terms of AT and GC base pairing
outline the 3 stages of DNA replication
- the DNA double helix structure must unwind and 2. the H bonds holding the two strands together must be hydrolysed by DNA HELICASE, which travels along the sugar-phosphate backbone, leaving the nucleotides exposed 2. free nucleotides H bond to the exposed nucleotides using the complementary base pairing rules, forming H bonds between them 3. the new adjacent nucleotides then form phosphodiester bonds between them, catalysed by DNA POLYMERASE, creating a new polynucleotide
what risk is there during DNA replication for the organism
random and spontaneous mutations may occur, where complementary base pairing is not followed and leads to an incorrect sequence of bases
in what way is the genetic code carried before translation
in a TRIPLET CODE; each sequence of three bases forms a codon, which codes for a specific amino acid A section of DNA that contains the complete sequence of codons is a gene.
why is the genetic code described as ‘degenerate’
there are 64 possible base triplets/codons (4x4x4) including one start and three stop codons which means that DNA does not overlap There are 20 amino acids, which can be coded for by more than one codon. Therefore the 64 codons are degenerate.
what are the 6 stages in DNA transcription to mRNA
- In the nucleus, RNA polymerase attaches to the DNA molecule. It uncoils and unzips the double helix structure, hydrolysing the hydrogen bonds between the base pairs, starting at the START codon.
- Free RNA nucleotides bond to the exposed bases on the template/antisense strand by their complementary pairs. Adenine bonds with uracil instead of thymine. (C+G)
- Free RNA nucleotides do not bond with the coding/sense strand because it is the strand that needs to be copied in order to translate the correct amino acids to produce specific proteins.
- RNA polymerase catalyses the bonding of nucleotides together by phosphodiester (covalent) bonds in a condensation reaction, which forms an mRNA polynucleotide.
- H bonds form between the two strands and they coil into the double helix structure. The entire process continues until RNA polymerase reaches the STOP codon.
- mRNA detaches from the DNA molecule and leaves the nucleus via a nuclear pore.
name the two strands of DNA that are involved in transcription
- SENSE/ coding strand (5’ to 3’)
- It is transcribed to mRNA but does not bond to free RNA nucleotides because it is the one that needs to be copied.
- ANTISENSE/ template strand (3’ to 5’)
- It is not transcribed to mRNA but bonds to free RNA nucleotides in the nucleus.
what are the 7 stages of translation
- After leaving the nucleus, the START codon of the mRNA binds to a specific site on a ribosome, which holds the mRNA in position.
- transfer (t)RNA is a strand of RNA folded so that the anticodon is at one end of the molecule. It carries amino acids corresponding to the anticodon.
- a complementary anticodon of tRNA from the cytosol binds to the START codon, and brings the first amino acid in the sequence.
- tRNA molecules continue to bring complementary anticodons and amino acids to the mRNA molecule until the STOP codon.
- At the same time, peptidyl transferase catalyses the bonding of the amino acids by peptide bond to form a polypeptide chain.
- As amino acids bond, they fold into secondary and tertiary structure, which is determined by the sequence of amino acids.
- The protein may then be released to the Golgi Apparatus for modification/packaging.
name 4 biological processes that require energy and the 3 main types of activity
Muscle contaction, memory formation, cell division, transmission of nerve impulses 1. synthesis 2. transport eg. pumping ions across cell ms by active transport 3. movement eg. protein fibres in muscle cells for muscle contraction
what is the structure of an ATP molecule
a nitrogenous base, adenine, a pentose sugar, ribose, and three phosphate groups
Adenine is on the 1st carbon and phosphates on the 5th carbon
(it is a nucleotide)
how does ATP release energy
approx. 30.6kJmol-1 energy is released when ATP is hydrolysed to ADP and Pi (inorganic phosphate) a little energy is required to form the bond between Pi and ADP again, releasing water. Net release of energy.
why is ATP not a good long-term energy store
(+ why it is a good immediate store)
The instability of bonds between phosphates in ATP.
Fats and carbohydrates are better suited- the energy released in breakdown of these molecules (in cellular respiration) is used to create ATP by phosphorylating ADP. This constant interconversion means ATP is a good immediate energy store. It is a single-step process to hydrolyse ATP. Small quantites of energy are released, preventing large losses of heat energy. Suitable for the metabolic reactions within the cell.
what are the 5 properties of ATP
- Small- therefore it can move easily in and out of cells
- Water soluble- energy-requiring processes occur in aqueous environments eg. cytosol
- Contains bonds between phosphates with intermediate energy, large enough to be useful for cellular reactions but not so large that energy is wasted as lost heat energy
- Small quantities of energy are released- suitable to cellular needs, energy not lost as heat energy
- Easily regenerated, can be ‘recharged’ with energy- phosphorylated and dephosphorylated
what is a somatic cell
a body cell i.e. any cell in a multicellular organism that is not a gamete/sex cell
what is the life cycle of a cell (1 mark)
from the formation of the cell to eventual division into two daughter cells
which stages are within the cell life cycle
I interphase: growth and synthesis: G1, S, G2
II mitosis: nuclear division: P, M, A, T
III cytokinesis: cell division
what are the 4 stages of INTERPHASE I
G1 = growth phase
S = synthesis phase (DNA is replicated)
G2 = second growth phase
G1 can enter G0, which is programmed cell death (apoptosis)
there are check points during the cell cycle: G1 checkpoint checks for cell size, nutrients, DNA damage
G2 checkpoint checks for cell size and DNA and organelle replication
why might a cell enter the G0 phase
- a resting phase- a period of inactivity or dormancy before entering G1 again
- apoptosis - programmed cell death
- specialised cells
- senescence - cell ageing
what occurs during MITOSIS II
The four stages: Prophase, Anaphase, Metaphase, Telophase
Within these phases: Appearance of chromosomes
Distribution of chromosomes to daughter cells
Nuclear division
what occurs during CYTOKINESIS III
in animals, cytoplasm divides
in plants, cytokinesis does not occur; the cell wall is laid between two daughter cells
what occurs to DNA during prophase
the DNA of the cell condenses to change from chromatin to form chromosomes
what is chromatin made of
DNA supercoiled around histone proteins
a nucleosome is 8 histone molecules with DNA wrapped around them
what is a chromosome
a continuous stretch of DNA containing segments; genes; that code for proteins
how many chromosomes do humans have in a somatic cell
46, made of 23 pairs, of which half have been inherited from one parent and half from the other (mother and father)
what do homologous chromosomes share
how do they change after DNA replication
the same length
centromeres in the same position
the same genes at the same locus
genes may have alternative alleles, DNA inbetween the genes will be different
after DNA replication, each chromosome is made of two identical ‘sister’ chromatids
what are nonsister chromatids
any two chromatids in a pair of homologous chromosomes that are not sister chromatids i.e. two molecules of condensed DNA joined by a centromere, with alleles of the same gene at the same locus, and of the same length
what are the two names for genes on the chromosomes
autosomal genes on the first 22 pairs
sex-linked genes on the 23rd pair (the sex chromosomes)
what are the 3 identifying factors of interphase
- intact nuclear envelope
- chromatin (replicating towards the end of S phase) nucleolus present
- pair of centrioles present
what are the 5 identifying factors of prophase
- centrioles move to opposite poles
- spindle fibres starts to form at opposite poles from centrioles, made of microtubules
- nuclear envelope degrades
- pair of identical chromatids on each chromosome
- centromere present, joining sister chromatids
what are the 3 identifying factors of metaphase
- homologous chromosomes line up at the metaphase plate/equator
- spindle fibres, formed from microtubules, at both poles
- they attach to the centromeres of the sister chromatids
what is the identifying factors of anaphase
- sister chromatids separate and are pulled to opposite poles by contracting spindle fibres attached to the centromeres
what are the 5 identifying factors of telophase
- centrioles replicate
- chromatin reforms/ nucleolus reappears
- nuclear envelope reforms
- cytoplasm divides
describe what occurs during cytokinesis in plant and animal cells
ANIMALS
equator region invaginates, cytoplasm is split, two daughter cells formed
PLANTS
cell wall laid between separated nuclei at the equator, cannot invaginate due to rigid cellulose cell wall
however, division does occur in meristematic tissue in the cambium of roots, shoots, buds
what is the significance of mitosis??
>mitotic division chromosomes ensures that 1. equal quantity of DNA to both daughter cells 2. the DNA is genetically identical for both daughter cells (i.e. genetic variation is only caused by mutation)
>growth of multicellular organisms
>tissue repair
>asexual reproduction 1. binary fission in unicellular organisms 2. vegetative propagation: cloned/new plants grow from parts of parent plants (when there is meristematic tissue) eg. runners, tubers, strawberries
what is meiosis
the formation of gametes
what is the significance of MEIOSIS
< sexual reproduction a diploid organism (two sets of homologous chromosomes, one from each parent) produces haploid gametes (a single set of unpaired chromosomes) which contain half the DNA in a somatic cell
< genetic variation in the daughter cells, important for survival of a species, such as against disease
< number of chromosomes is halved there are two divisions resulting in four daughter cells with half the number of chromosomes
outline INTERPHASE for meiosis
DNA replicates in S phase
centrosomes replicate
organelles replicate
outline PROPHASE 1
chromatin condenses to form bivalents i.e. pairs of homologous chromosomes
nuclear envelope degrades
centrosomes move to opposite poles, spindle fibres start to form, made of microtubules
genetic recombination occurs; at chiasmata, sections of chromatids crossover with the same length of non-sister chromatid i.e. the chiasmata is at the same locus of the chromatids
outline METAPHASE 1
spindle fibres attach to centrosomes on the bivalents, which are lined up on the equator
independent assortment; there are 2 possible orientations for each bivalent, leading to 2(22) possible assortments, as each bivalent lines up independent of the other 22.
outline ANAPHASE 1
reduction division
pair of homologous chromosomes is split up by contracting spindle fibres and sister chromatids remain attached to their centromere
the resulting cells are haploid
outline TELOPHASE 1 and CYTOKINESIS
two haploid cells form, centrosomes replicate, nucelar envelope reforms, there are 23 homologous chromosomes (46 chromatids), cell membrane invaginates to form cleavage furrow, cytoplasm divides etc.
outline PROPHASE II
(short INTERPHASE II, no DNA replication occurs)
homologous chromosomes appear due to condensed chromatin, joined by centromeres, nuclear envelope degrades, centrioles move to opposite poles, spindle starts to form
outline METAPHASE II
homologous chromosomes line up along equator, spindle attaches to centromere, sister chromatids are no longer identical
independent assortment; 2(22) possible assortments as chromosomes line up independent of each other
outline ANAPHASE II
what is photosynthesis/ what is it carried out by
autotrophic nutrition carried out by plants, algae and cyanobacteria. The basis for through energy flow food chains.
what is recycled and what is not recycled in photosynthesis-respiration
R: organic molecules, O2, CO2, H2O, ATP
N R: light, heat
energy flows into and out of an ecosystem, while the chemical elements essential to life are recycled
why are leaves green
the chlorophyll molecules in chloroplasts absorb violet-blue and red light, the colours most effective in driving photosynthesis, and reflect or transmit green light
where in the chloroplast does the light-dependent reaction occur
on the thylakoid membranes, involving two membrane-bound photosystems: photosystem II and photosystem I
where in the chloroplast does the light-independent reaction occur
describe the structure and contents of a photosystem on the thylakoid membrane
photosystems are the protein complexes where light energy is absorbed
Each photosystem is comprised of a primary pigment reaction centre containing the primary pigment chlorophyll a
and an antenna containing accessory pigments, which pass the light energy they absorb onto chlorophyll a
these are photosynthetic pigments, of which there are many types
photosystems are found between the lipid and protein layers of the membranes
describe the different types of chlorophyll
chlorophyll has a porphyrin ring containing magnesium and a hydrocarbon tail known as phytol
chlorophyll a has a blue-green colour and absorbs red and violet light
TWO TYPES: P680 in photosystem II
P700 in photosystem I
chlorophyll b is an accessory pigment that has a yellow-green colour the same structure as chlorophyll a apart from one functional group
at which wavelengths is light absorbed in photosystems
680nm in P680 in chlorophyll a in photosystem II
700nm in P700 in chlorophyll a in photosystem I
chlorophyll a also absorbs wavelengths of light around 440nm (violet-blue light)
chlorophyll b absorbs light of wavelengths 400-500nm and 640 nm
the other accessory pigments have 3 peaks- they absorb in the blue-green range
what are accessory pigments
yellow, orange, red or brown photosynthetic pigments that pass the light energy absorbed onto chlorophyll a
also known as CAROTENOIDS
two groups: carotenes eg. B carotene and xanthophylls
why is there a variety of photosynthetic pigments
to maximise the absorption of light that can be utilised for photosynthesis
what is PHOTOLYSIS and what happens to its products
PHOTOLYSIS is the splitting of a water molecule using light
H2O → 2e- + 2H+ + ½O2
ELECTRONS- replace the electrons excited by light energy and removed by ETC (electron carriers)
PROTONS- used for generating energy for photophosphorylation and source of H to reduce NADP
OXYGEN- byproduct and can be used in respiration
what is the definition for chemiosmosis
the movement of protons (hydrogen ions) down their electrochemical/proton concentration gradient across a selectively permeable membrane, through a transmembrane protein enzyme complex; ATP synthase; where the energy is used to generate ATP from ADP and Pi (inorganic phosphate group)
what occurs during chemiosmosis on the thylakoid membrane
the electron passed down the ETC releases energy, which is used to pump H+ protons against their concentration gradient from the stroma into the thylakoid space. This creates a proton concentration gradient across the thylakoid membrane.
Protons move down their electrochemical/proton concentration gradient through a transmembrane protein enzyme complex, ATP synthase. The energy gained from the movement of the protns down the conc. grad. is used to add a phosphate to ADP to form ATP.
This drives photophosphorylation. (in resp. used to drive ox. phos.)
when does water stress occur and what are the effects of it
it occurs when there is a lack of water available to the plant; not enough water is taken up by the roots to replace water lost in transpiration at the leaves
- leaf tissue becomes flaccid
- -the cells become plasmolysed*
- -guard cells close the stomata*
- -rate of photosynthesis is reduced*
what are 4 main reasons that water is important for plants
water is a substrate for photosynthesis
water keeps plant cells turgid, and in particular the guard cells, which keep stomata open, allowing CO2 to enter
it has a cooling effect on the plant as it leaves the leaves during transpiration, due to the high latent heat of vaporisation
where are H+ protons pumped from/to during chemiosmosis in mitochondria
from the MITOCHONDRIAL MATRIX into the intermembrane space via the INNER MITOCHONDRIAL MEMBRANE (phospholipid bilayer imbedded with proteins eg. the electron acceptor protein complexes in the ETC)
what is the role of oxygen in aerobic respiration (+ give formula)
THE FINAL ELECTRON ACCEPTOR IN THE ETC ON THE INNER MITOCHONDRIAL MEMBRANE
it forms water when it accepts the electrons from the e.t.c. and protons
O2 + 4e¯ + 4H+ → 2H2O
what is ox. phos. (simple)
Electron transport chain; electron transport and pumping of protons (H+) which create an H+ gradient across the membrane + chemiosmosis; ATP synthesis powered by the flow of H+ back across the membrane
what is the effect of rate of photosynthesis on biomass
If rate of photosynthesis is greater than the rate of respiration, biomass will increase, i.e. CO2 is being converted to organic compounds such as starch and cellulose (something farmers would want to maximise).
what is the structure of chlorophylls (a and b) and the implication.
An Mg ion in the middle of a porphyrin ring with a long hydrocarbon (hydrophobic) chain- therefore organic solvents are used to extract the pigments for chromatography.
what is the importance of oxygen as the final acceptor of electrons
by accepting the electrons at the end of the chain, it oxidises the last protein complex so that it can receive more electrons from the chain of carriers
what occurs as oxygen removes the electrons from the e.t.c.
- more reduced hydrogen carriers can be used as substrates at the beginning of the chain
- more H+ can be pumped
- more ADP can be phosphorylated to make ATP
what occurs if oxygen is absent (5 steps)
- electrons are not removed/accepted from the end of the e.t.c.
- NADH + FADH2 are not oxidised to NAD + FAD and are not regenerated to be used as substrates in the Krebs cycle
- no more NADH + FADH2 can be used at the start of the chain
- Krebs cycle, Link reaction and e.t.c. cannot proceed due to a lack of oxidised NAD and FAD
- only the glycolysis pathway continues to form pyruvate
what is the structure of ATP
- ADENINE; a nucleotide
- RIBOSE; a pentose (5C) monosaccharide
- 3x PHOSPHATE GROUP joined by high energy bonds
wHaT iS rEsPiRaTiOn
- the conversation of energy from consumed/stored products into ATP*
- sugars, amino acids, fatty acids + glycerol undergo the respiration pathway to produce ATP from ADP + Pi*
which stored/consumed substances are used in aerobic respiration
CARBOHYDRATES; PROTEINS; LIPIDS
undergo digestion by hydrolysis
SACCHARIDES; AMINO ACIDS; FATTY ACIDS + GLYCEROL
what is the significance of the bonds between the phosphates in ATP
what is the energy used for?
- the reaction creating the bond (phosphorylation) requires energy (obtained through respiration)
- the reaction breaking the bond (dephosphorylation) releases energy (which is used to carry out work in the cell)
ATP is used in Active transport
Muscle contraction
Exo/endocytosis
Nervous transmission
Anabolism
what are the two types of phosphoryation that occur in aerobic respiration
- substrate-level phosphorylation
where an intermediate of the respiration pathway donates a phosphate group to ADP to make ATP
Pi + ADP → i + ATP
-
oxidative phosphorylation
* requires oxygen* as the final electron acceptor and hydrogen carriers/acceptors, which are the co-enzymes of the dehydrogenase enzymes of respiration- NAD and FAD
what are the products/reactants in the ATP cycle
ATP + H2O (dephosphorylation, hydrolysis) ———> ADP + Pi + H (phosphorylation, condensation reaction) ———-> ATP
what is the function of co-enzymes in aerobic respiration
the process of respiration takes hydrogens away from the intermediates of the pathway, using the dehydrogenase enzymes and donates them to the co-enzymes or hydrogen carriers
The REDUCED NAD or FAD CARRY THE HYDROGENS to the ETC in the INNER MITOCHONDRIAL MEMBRANE, where ther ENERGY is RELEASED to PHOSPHORYLATE ADP to ATP, through a series of REDOX (ox/red) reactions and the process of CHEMIOSMOSIS.
what are co-enzymes
examples: NAD in respiration, NADP in photosynthesis
what are oxidation and reduction reactions
give the chemical equation and an overview/definition of photosynthesis
- light energy + CO2 + H2O → organic compounds + O2*
1. the process by which light energy is converted to chemical energy (ATP and NADPH2) on the thylakoid membranes in order to fix inorganic carbon (CO2) into organic compounds in the stroma of chloroplasts
what are the two double membranes/envelopes surrounding the mitochondria and chloroplasts and how does the way that H+ protons move differ between them
In the chloroplast:THYLAKOID MEMBRANE, INNER MEMBRANE,INTERMEMBRANE SPACE, OUTER MEMBRANE,
H+ are pumped from the stroma into the thylakoid space, across the thylakoid membrane, and flow down their proton/electromagnetic/concentration gradient into the stroma through ATP synthase
in light-dependent reaction
In the mitochondria: INNER MITOCHONDRIAL MEMBRANE, INTERMEMBRANE SPACE, OUTER MEMBRANE
H+ are pumped from
what is the structure of ATP
ADENINE:
RIBOSE:
3x PHOSPHATE GROUP:
which form of light on the electromagnetic spectrum drives photosynthesis
VISIBLE LIGHT-
400nm = shorter wavelength, higher energy
750nm = longer wavelength, lower energy
what is an absorption spectrum
a graph showing the curves representing the wavelengths of light best absorbed by types of photosynthetic pigment
what are the axes for an absorption spectrum
x axis = wavelength of light (nm)
y axis = absorption of light by chloroplast pigments
what is an action spectrum
a graph that plots the rate of photosynthesis against wavelength
- the action spectrum resembles the absorption spectrum of chlorophyll a, but not exactly due to the absorption of light by accessory pigments eg. chlorophyll b, xanthophylls etc.*
- wherever maximum rate of light absorption = max. rate of photosynthesis*
what are the axes for an action spectrum
x axis = wavelength (nm)
y axis = rate of photosynthesis (measured by O2 released)
explain what occurs during chromatography of photosynthetic pigments (_ steps)
- a pencil line is drawn near the bottom of the paper because pen ink contains pigments
- a solvent front is at the top of the paper to measure the Rf value from. It is placed in silica gel
- the paper is placed in an organic solvent because the pigments are lipid based and therefore would not dissolve in water (hydrophobic) the solvent is lower than the pencil line
- Rf value is calculated
what is the equation for Rf value
<span>distance travelled by pigment</span>
Rf = ————————–
distance
how does chlorophyll harvest light energy
each photosystem contains a light-harvesting complex/antenna complex of 200-300 photosynthetic pigments
when a photon of light strikes a pigment molecule, the energy is transferred from accessory pigment molecules until it reaches chlorophyll a at the primary pigment reaction centre
what happens when a photon of light strikes a chlorophyll a molecule
a photon of light strikes magnesium in the porphyrin ring oh chlorophyll a in photosystem II, exciting two electrons in the outer orbital to a higher energy state, where it is accepted by a primary electron acceptor.
what occurs if there is no electron acceptor to accept the pair of excited electrons from photosystem II
without an electron acceptor or the ETC, the e- would fall back down the energy level, emitting light; fluorescence
what is non-cyclic photophosphorylation
- the products of non-cyclic photophosphorylation are ATP and reduced NAPH; it utilises PSII and PSI, connected by an electron transport chain*
1. a photon of light strikes Mg in chlorophyll a in PSII
2. a pair of electrons are excited to a higher energy level and removed by an electron acceptor to the electron transport chain, where they move down successive energy levels
3. the electron lost is replaced by an electron obtained from the photolysis of water
4. (CHEMIOSMOSIS) the energy released when the excited electron moves down the ETC is used to pump H+ protons against their gradient from the stroma to thylakoid space, creating a proton gradient across T.M., causing the protons to then move down their proton gradient into the stroma through ATP synthase.
5. energy gained from the movement of protons down their gradient is used to phosphorylate ADP and Pi to form ATP.
6. low energy electrons continue down the ETC to PSI, where they are further excited to a higher energy level when a photon of light strikes
7. they are added to protons and NADP to form NADPH by the action of the enzyme NADP reductase
give the definition of PHOTOPHOSPHORYLATION
the conversion of light energy to phosphorylate (add a phosphate group to) a molecule of ADP to form ATP (energy currency of living organisms)
what is the reaction for reduced NADP
NADP+ + H+ + 2e- → NADPH (reduced NADP)
give an overview of non-cyclic photophosphorylation
>produces ATP, NADPH, O2
>involves hydrolysis of water into electrons, protons and oxygen
>uses both PSII and PSI
what is cyclic photophosphorylation
>only PSI is involved, electrons are excited in its primary pigment reaction centre, they pass down the ETC
>energy from the electrons is used to pump H+ across the thylakoid membrane
>only ATP is produced, by ATP synthase phosphorylating ADP to form ATP, by the protons flowing down their concentration gradient
>no photolysis of water
give the four differences between cyclic and non-cyclic photophosphorylation
- N-C: PSII & PSI C: PSI
- N-C: photolysis occurs C: photolysis does not occur
- N-C: electrons leaving PPRC add to NADP and H+ to form NADPH C: electrons leaving PPRC are excited by further light energy to be cycled back through the ETC and PSI
- N-C: products are NADPH2, ATP and ½O2C: only ATP is produced
what happens to the products of the light-dependent stage of photosynthesis
ATP and NADPH2 are used to drive the reactions of the light independent stage; they convert G3P to triose phosphate
what are the 6 steps in the Calvin Cycle (starting with an overview sentence)
- a cyclical series of enzyme-catalysed reactions used to fix carbon dioxide into organic compounds
- carbon dioxide is fixed to ribulose 1,5 bisphosphate (5C) by RuBisCO (ribulose bisphosphate carboxylase oxygenase), known as carbon fixation
- an unstable 6C compound is formed and immediately breaks down to two molecules of glycerate-3-phosphate
- G3P is reduced to two molecules of triose phosphate (GALP or glyceraldehyde-3-phosphate) using hydrogens from the NADPH2 and energy from ATP
- 5/6 TP is recycled back to ribulose 5 phosphate and 1/6 are converted to organic compounds
- Ribulose 5 phosphate is phosphorylated using ATP molecules to ribulose 1,5 bisphosphate
what are the numbers of carbons in each compound in the Calvin Cycle and how many of each compound are made for each molecule of glucose
3x CO2 (1C)
3x six-carbon intermediate (6C)
6x glycerate-3-phosphate (3C)
6x ATP, 6x ADP+Pi, 6x NADPH2, 6x NADP
6x triose phosphate (3C)
5x triose phosphate (3C)
3x ribulose 5 phosphate (5C)
3x ribulose 1,5 bisphosphate (5C)
where is the compensation point on a graph of O2/CO2 uptake/evolution against light intensity
The line will start below 0, i.e. where the rate of respiration is greater than the rate of photosynthesis, i.e. where O2 uptake/CO2 evolution is greater than O2 evolution/CO2 uptake.
The line will increase towards 0 as light intensity increases; when it reaches the line it is the compensation point, i.e. the quantity of O2 being taken in is compensated for by O2 evolution. Equally, energy required for one reaction/the reactants are compensated for by the other reaction. Rates of respiration/photosynthesis are equal.
Above the compensation point, the rate of photosynthesis is greater than the rate of respiration and more CO2 uptake/O2 evolution is occuring.
give an overview of photosynthesis in _ steps
- in the light dependent stage, light energy is converted to the chemical energy of ATP and NADPH2 on the thylakoid membranes
- H2O is split and ½O2 is released into the atmosphere
- The Calvin cycle then occurs in the stroma, where ATP and NADPH2 are used to fix carbon and convert Ribulose 1,5 bisphosphate to triose phosphate
- ADP, inorganic phosphate and NADP are returned to the thylakoid membranes, while 1/6 TP is used to synthesise organic molecules- AAs, saccharides, proteins, lipids
what is the key difference between substrate-level phosphorylation and oxidative phosphorylation
substrate-level phosphorylation: ATP is made by direct enzymatic transfer of a phosphate group from an organic substrate to ADP
oxidative phosphorylation: requires a final electron acceptor; oxygen, and hydrogen carriers/acceptors that carry H+ to the ETC, where redox reactions and chemiosmosis release energy to phosphorylate ADP to ATP (requires a membrane)
what is an oxidation reaction
addition of O2
loss of electrons
loss of H
LOSS OF ENERGY
what is a reduction reaction
- loss of O2*
- gaining electrons*
- gaining H*
- GAIN OF ENERGY*
how do molecules gain energy
by the addition of electrons, hydrogen or phosphate
what is the PROCESS, SUBSTRATES, PRODUCTS, LOCATION for
glycolysis
- process; glucose (6C) to 2x pyruvate (3C)*
- substrates; glucose, ATP, ADP and Pi, NAD*
- products; pyruvate, ATP, NADH (ADP and Pi)*
- location; cytoplasm (pyruvate enters mitochondrial matrix)*
what is the PROCESS, SUBSTRATES, PRODUCTS, LOCATION for
the link reaction
process; pyruvate → acetyl CoA (CO2 evolution)
substrates; pyruvate, NAD, CoA
products; CO2, NADH, acetyl CoA
location; mitochondrial matrix
what is the PROCESS, SUBSTRATES, PRODUCTS, LOCATION for
krebs cycle/citric acid cycle
process; acetyl CoA ⇒ oxaloacetate → NADH + FADH2 (CO2 evolution)
substrates; acetyl CoA, NAD, FAD, ADP + Pi
products; ATP, NADH, FADH2, CO2, CoA
location; matrix
what is the PROCESS, SUBSTRATES, PRODUCTS, LOCATION for
oxidative phosphorylation/the electron transport chain
process; ADP + Pi → ATP
substrates; NADH, FADH2, oxygen, ADP and Pi
products; NAD, FAD, ATP, water
location; inner mitochondrial matrix
what is the structure of a mitochondria
matrix, inner mitochondrial membrane has folds ‘cristae’ and is the site of electron transport chain, where there are stalked particles (ATP synthase) which is the site of respiratory ATP synthesis, intermembrane space, outer membrane
explain GLYCOLYSIS
occurs in cytoplasm
first three steps require an input of energy, to allow the breaking of the hexose sugar (6C) into 2x triose sugars (3C)
there is a net yield of 2 ATP
glycolysis can occur in the absence of oxygen, it is the pathway of anaerobic respiration
pyruvate (final product) does not enter the Krebs cycle is there is no oxygen present
glucose → (input of 2 ATP) hexose bisphosphate → triose phosphate → (ADP is phosphorylated- substrate-level, NAD is reduced) glycerate 3 phosphate → (ADP is phosphorylated- substrate-level) pyruvate X2
hexose bisphosphate = fructose 1,6 bisphosphate
explain the LINK REACTION
pyruvate (product of glycolysis) enters the mitochondrial matrix from the cytoplasm (via a transmembrane carrier protein called a symport protein, using energy from flow of H+ protons from the chemiosmotic gradient, reducing the actual energy yield from the aerobic respiration of glucose)
pyruvate undergoes decarboxylation - removal of CO2
it undergoes dehydrogenation - removal of H, reducing NAD to NADH
Co-enzymeA (CoA) is added to the resulting acetate to form acetylCoA
acetylCoA will enter the Krebs cycle for the complete oxidation of glucose
explain the KREBS/CITRIC cycle + purpose
-purpose = complete oxidation of 2 carbon acetyl to CO2 and removal of hydrogens by the dehydrogenase enzymes to donate to the hydrogen carriers (co-enzymes) NAD and FAD to reduce them to NADH and FADH2
the reduced hydrogen carriers/acceptors are the substrates for the electron transport chain. Substrate-level phosphorylation occurs, producing ATP. For each molecule of glucose, 2x LR and 2x Krebs C. KC is also the entry point for other respiratory substrates eg. amino acids
ACETYLCOA (2C) - CoA + OXALOACETATE (4C) = CITRATE (6C) - CO2 - H (to NAD) = 5C - CO2 - H (to NAD) - Pi (to ADP) = SUCCINATE (4C) - H (to FAD) = 4C + H2O = 4C - H (to NAD) = oxaloacetate (4C)
what is the electron transport chain
a series of proteins embedded in the inner mitochondrial membrane, which folds to form cristae in order to increase the surface area. This allows there to be many ETCs in each mitchondria.
what is the role of the co-enzymes in ox. phos. and what happens to what they carry
NADH releases its hydrogens to the first complex in the ETC; the hydrogens dissociate into electrons (1) and protons (2)
- The electrons are carried along the chain, sequentially reducing the complexes as they reach them and oxidising them as they leave.
- The protons are pumped from the matrix into the intermembrane space, creating a proton conc. gradient. The energy required is supplied by the energy of the electrons.
FADH2 donates its electrons at the second complex on the chain so fewer protons are pumped relative to NADH.
NAD and FAD are oxidised and return to the Krebs cycle.
what is the function of the proton concentration gradient being set up
For CHEMIOSMOSIS: The P C/electrochemical gradient across the inner mitochondrial membrane drives phosphorylation of ADP to ATP by the transmembrane complex ATP synthase.
what is the definition for chemiosmosis and in which cellular processes does it occur
The process by which the energy stored in the form of a proton concentration gradient across a membrane is used to from ATP from ADP and Pi
i.e. chemiosmosis couples the ETC to ATP synthesis
Aerobic respiration (oxidative phosphorylation), photosynthesis (oxidative phosphorylation), entry of sucrose into the phloem for translocation, symport of pyruvate into mitochondrial matrix
what is anaerobic respiration (definition, 2marks)
outline process
a form of cellular respiration, occuring when oxygen is absent or under stress, that generates energy in the form of ATP by the oxidation of nutrients and using an electron acceptor other than oxygen
- also known as fermentation*
- >reactions of glycolysis to form pyruvate*
- >reduction of pyruvate to another compound (depending on type of cell, ethanol, lactate) in order to recycle NAD so that glycolysis can continue in the absence of oxygen*
where do co-enzymes NAD and FAD remove H protons from (oxidise) and what do the protons do at the ETC
glycolysis and Krebs cycle/citric acid cycle
a series of redox reactions
what is the definition for oxidative phosphorylation
electron transport + chemiosmosis
what is the equation for ANAEROBIC RESPIRATION in yeast
pyruvate → pyruvate decarboxylase ⇒ CO2
⇒ ethanal → ethanol dehydrogenase → NADH –> NAD ⇒ ethanol
NAD is recycled for use in glycolysis in absence of O2
what is the equation for ANAEROBIC RESPIRATION in mammalian cells
pyruvate → lactate dehydrogenase → NADH –> NAD ⇒ lactate
- NAD is recycled for use glycolysis in the absence of O2*
- In “oxygen debt” lactate is converted back to pyruvate*
why do some cells use FERMENTATION (4 marks)
In the absence of O2, cells use fermentation to produce ATP by substrate-level phoshorylation in order to continue metabolic/cellular activity.
Pyruvate acts as an electron acceptor in order to oxidise NADH to NAD, which can be reused in glycolysis to produce small quantities of ATP.
Two common end products are lactate and ethanol.
what is the yield of ATP from one molecule of glucose (aerobic) and give equation
theoretical yield = 38 ATP
- +4 -2 in glycolysis*
- +2 in Krebs*
- +30 from 10NADH2 in ox phos*
- +4 from 2FADH2 in ox phos*
what is the actual yield for aerobic respiration (2 marks)
approx. 32 molecules of ATP
for example due to loss of energy as heat and transfer of pyruvate into the mitochondria etc.
what is the yield of ATP from one molecule of glucose in anaerobic respiration
(give the equation)
2 molecules of ATP total
- 2 ATP lost in glycolysis*
- 4 ATP gained in glycolysis from substrate-level P*
- 2NADH2 used up, 2NADH2 made to regenerate NAD, no ox. phos.*
is aerobic or anaerobic resp. more efficient
AEROBIC RESPIRATION IS APPROX. 15x MORE EFFICIENT than anaerobic respiration in converting energy of glucose
how much free energy is released in oxidising glucose by oxygen
and how much free energy is released per mole of ATP hydrolysed to ADP
approx. -3000 kJ per mole of glucose
30. 5 kJ per mole of ATP
what is the difference between using different respiratory substances in aerobic respiration
The energy value (KJg-1) for lipids is twice that for carbohydrates because lipids have more hydrogens in their molecules
(Proteins is similar to carbs)
where do the monomers for LIPIDS, CARBOHYDRATES and PROTEINS enter the cellular respiration pathway?
Carboydrates are hydrolysed to monosaccharides eg. glucose, which enter glycolysis.
Lipids are hydrolysed to glycerol, which enters glycolysis, and fatty acids, which enter the Link reaction (acetyl CoA)
Proteins are hydrolysed to amino acids, which can enter at glycolysis, Link reaction or Krebs cycle. Ammonia (NH3) is released.
what is protein synthesis
the creation of protein molecules by amino acid synthesis (producing amino acids from molecules such as glucose or from the molecules in our diet, transcription and translation occurs within cells that produce proteins from the genetic code)
what is transcription
Transcription is the process by which an mRNA template is synthesised using DNA to provide a template
, encoding the sequence of the protein in the form of a trinucleotide code, is transcribed from DNA to provide a template for translation.
what is translation
Translation is the process in which amino acids are coded for by mRNA in a specific order according to the codons specified by the genetic code.
They are bonded together by peptide bonds to produce a polypeptide chain. It occurs in the cytoplasm on free ribosomes or those on the RER.
