Chapter 17 - Energy for Biological Processes Flashcards
Need for energy (think metabolic activities)?
- Active Transport ; uptake of nitrates by root hair cells, loading sucrose into sieve tube cells, selective reabsorption of glucose and amino acids in the kidney and the conduction of nerve impulses
- Anabolic reactions - building of polymers like proteins/polysaccharides and nucleic acids essential for growth and repair
- Movement brought about by cilia/flagella/contractile filaments in muscle cells
Energy….
CANNOT BE CREATED OR DESTROYED
Why is there an interconversion of glucose and ATP?
A glucose molecule contains more energy than the single metabolic reactions needed to break it down and thus the energy contained within a molecule of glucose is used to synthesise many molecules of ATP and it is these molecules that drive cellular reactions (enough energy provided on a cellular level)
How do organisms release energy?
As heat (low energy radiation) through respiration - exothermic process
What is the ultimate source used to fuel metabolic reactions?
Radiation from the sun - transferred back to the atmosphere as heat
Photosynthesis?
Make use of energy in the bonds of organic molecules like glucose ; light is trapped by chlorophyll molecules and this energy is used to drive the synthesis of glucose from carbon dioxide and water
Respiration
Respiration is the process by which organic molecules such as glucose are broken down into smaller inorganic molecules like CO2 and H2O - energy stored in the bonds of glucose is used to make ATP
Photosynthesis and respiration relationship
Photosynthesis is the reaction behind the production of most of the biomass on the earth and respiration is the process by which organisms break down biomass to provide the ATP needed to drive the metabolic reactions that take place in cells
Photosynthesis
6CO2 + 6H20 -> C6H12O6 + 602
Respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O
Breaking bonds
Requires energy
Forming bonds
Releases energy
Bond energy
Energy required to break/form 1 mol of a bond
How to decide whether a reaction is exo/endothermic?
Depends on the total number and strength of bonds that are formed/broken during the reaction
Inorganic molecules vs organic molecules bond strength?
Water and CO2 release a lot of energy when they break and also require a lot of energy to break
Organic molecules like glucose and amino acids contain many more bonds but these are far weaker and thus release less energy and require less energy to be broken
Respiration
Large organic molecules are broken down forming small inorganic ones - total energy required to break the bonds in a complex organic molecule is less than the energy released in the formation of all the bonds in the smaller inorganic products and thus the excess energy released is used to synthesise ATP
Respiration
EXOTHERMIC
PHOTOSYNTHESIS
ENDOTHERMIC
What happens in respiration?
Organic molecules have a lot of C-H bonds which are non-polar and do not require a lot of energy to break. The carbon and hydrogen released is then used to form strong bonds with oxygen atoms, forming CO2 and water - resulting in the release of large quantities of energy
Photosynthesis
More energy is put in when breaking bonds than is released when bonds form
Photosynthesis chain of reaction?
Light provides energy to form chemical bonds in ATP - ATP bonds broken to release the energy needed to make glucose
Respiration chain of reaction?
Organic molecules like glucose are broken down and energy released is used to synthesise ATP - ATP is then used to supply the energy needed to break bonds in the metabolic reactions of the cell
Chemiosmosis
ATP produced in both photosynthesis and respiration is synthesised by chemiosmosis - involves diffusion of protons from a region of high concentration to a region of low concentration through a partially permeable membrane
What does movement of protons do?
Releases energy that is used to attach inorganic phosphate to ADP - to make ATP
Chemiosmosis depends on the creation of a proton concentration gradient - energy to do thus comes from high-energy electrons
What are two ways in how electrons are excited?
Electrons in chlorophyll are excited by absorbing light from the sun
High energy electrons are released when chemical bonds are broken in respiratory substrate molecules like glucose
How do excited electrons generate a proton gradient?
By passing into an electron transport chain
Electron transport chain
Made up of a series of electron carriers - each with a lower energy level - as high energy electrons move from one carrier to another, energy is released and used to pump protons across a membrane creating the gradient
Why is the proton gradient maintained?
Because the membrane is impermeable to hydrogen ions
So how can protons move back through the membrane?
Through hydrophilic membrane channels linked to the enzyme ATP synthase which catalyses their formation of ATP - flow of protons provides the energy used to synthesise ATP from ADP and pi
Purpose of Chemiosmosis?
Transfer energy into a usable form - ATP - whether it’s for synthesising glucose (photosynthesis) or in respiration (metabolic processes)
Process of protons moving through ATP synthase
Facilitated diffusion (hydrophilic channel)
Organisms that can photosynthesise - plants and algae
Autotrophic
Both autotrophic and heterotrophic organisms break down complex organic molecules like glucose…
During respiration - to release energy needed to drive metabolic processes
Photosynthesis equation
6CO2 + 6H2O - > C6H12O6 + 6O2
Chloroplast adaptation?
Network of membranes in chloroplast provides a large SA to maximise absorption of light - flattened sacs called thylakoids which are stacked to form grana
What are grana joined by?
Membranous channels called lamellae
What is embedded within thylakoid membranes?
Chlorophyll
Fluid enclosed in chloroplast?
Stroma - site of many chemical reactions
Chlorophyll
Pigment only absorbs specific wavelengths - mainly absorbs red and blue light while reflecting green light
Primary pigment
Chlorophyll a
Other pigments
Chlorophyll b, xanthophylls, carotenoids
What is an antennae complex?
Secondary pigments and proteins, embedded in thylakoid membrane of chloroplast - form a light harvesting system which absorbs/harvests light energy of different wavelengths and transfers energy quickly to the reaction centre, chlorophyll a is LOCATED IN REACTION CENTRE
What is a secondary pigment otherwise known as?
Accessory pigment
Purpose of antennae complex?
Maximises absorption of light to feed into reaction centre
If sunlight is too intense?
Chlorophyll is destroyed - that is why chlorophyll is continuously synthesised during the summer to maintain the level needed to photosynthesis at the required rate
Stationary phase
Layer of silica gel applied to the glass
Mobile phase
Solution containing a mixture of pigments
Retention factor indicates
Different solubilities of pigments in mobile phase and their different interactions with the stationary phase - move at different rates
Pigment that is most soluble
Travel the longest distance
Two stages in photosynthesis?
Light-dependent stage - energy from sunlight absorbed and used to form ATP + hydrogen from water used to reduced coenzyme NADP to reduced NADP
Light-independent stage - hydrogen from NADPH and CO2 used to build organic molecules such as glucose (ATP supplies energy needed)
What organic molecules produced from light independent reactions?
Lipids, glucose and amino acids
Non-cyclic photophosphorylation
PSII followed by PSI
Reaction centre of PSI absorbs light at a higher wavelength (700nm) than PSII (680nm)
Light absorbed excites electrons at the reaction centres of the photosystems
Where do excited electrons go?
Released from PSII and passed onto electron transport chain ; ATP produced by process of Chemiosmosis
Electrons lost from reaction centre at PSII are replaced from water molecules broken down using energy from the sun
Excited electrons at PSI?
Passed to another electron transport chain - ATP produced again - electrons lost here are replaced by those that have just travelled along first electron transport chain from PSII
Electrons leaving electron transport chain at PSI are accepted + H+ by NADP to form NADPH
Purpose of photolysis?
Water molecules are split into hydrogen ions, electrons and oxygen molecules using energy from the sun - electrons released replace the electrons lost from PSII
Formula for photolysis
H2O -> (using energy from sun) 2H+ + 2e- + 1/2O2
What about other products of photolysis?
Oxygen released as by-product
Protons are released into the lumen of thylakoids - increasing proton concentration across the membrane ; drive the formation of more ATP moving back through membrane
Once hydrogen ions return to the stroma?
Combine with NADP to form NADPH (with electron from PSI) ; used in light independent reactions ; removes H+ ions from stroma to maintain proton gradient across thylakoid membranes
Cyclic photophosphorylation
Electrons leave electron transport chain after PSI can be returned to PSI and instead of being used to form NADPH, they are used to produce more ATO without any electrons supplied from PSII
NO REDUCED NADP PRODUCED
Where does light indecent stage take place?
Stroma
What is required from light dependent stage for light independent stage?
ATP and NADPH and CO2
Calvin cycle
1) CO2 enters spongy mesophyll by diffusion ; combined with ribulose bisphosphate RuBP ; carbon in carbon dioxide is thus Fixed - RUBisCO catalyses the reaction and an unstable 6 carbon intermediate is produced
2) Unstable compound immediately breaks down forming 2 3-carbon glycerate 3-phosphate GP molecules
3) Each GP molecule is converted to another 3 carbon molecule, TP, Triose phosphate, using a hydrogen atom from reduced NADP and energy supplied by ATP (BOTH SUPPLIED FROM LIGHT-DEPENDENT REACTIONS OF PHOTOSYNTHESIS)
4) Triose phosphate is recycled to regenerate RuBP so that Calvin cycle can continue BUT also starting point for synthesis of many complex molecules like carbohydrates, proteins, lipids and nucleus acids
3 steps of Calvin cycle?
Fixation - CO2 is fixed
Reduction + GP is reduced to TP by addition of Hydrogen from NADPH using energy supplied by ATP
Regeneration - RuBP is regenerated from recycled TP
RuBisCO
Very inefficient as it is competitively inhibited by oxygen - a lot of it is needed - most abundant enzyme in the world
Limiting factor
Light intensity
Carbon dioxide concentration
Temperature
Light intensity
Needed as an energy source ; as light intensity increases, ATP and reduced NADP are produced at a higher rate from the light-dependent reactions
Carbon dioxide concentration
Carbon dioxide is needed as a source of carbon so increasing carbon dioxide concentration increase the rate of carbon fixation in the Calvin cycle and therefore the rate of TP production
Temperature
As temperature increases, rate of enzyme activity increases until the point where proteins denature - increases the rate of enzyme controlled reactions like carbon fixation. Rate of photorespiration also increases meaning higher photosynthetic rates may not be seen at higher temperatures even if enzymes are not actually denatured
Stomata
Closes to avoid water loss via transpiration during dry spells - closure of stomata stops the diffusion of carbon dioxide into the plant, reducing the rate of light-independent reaction and eventually stopping photosynthesis
Law of limiting factors state that…
Rate of a physiological process will be limited by the factor which is in shortest supply
What should be used to provide carbon dioxide?
Sodium hydrogen carbonate
What should be done before readings are taken?
Apparatus should be left to equilibrate for 10 minutes before readings are taken
Oxygen sensor also needs to be calibrated using oxygen concentration
Reducing light intensity?
Reduces the rate of the light-dependent stage of photosynthesis ; reduces quantity of ATP and reduced NADP
ATP and reduced NADP are needed to convert GP to TP… concentration of GP will thus increase and concentration if TP will decrease ; less TP thus means regeneration of RuBP will also decrease
Temperature effect
RuBisCO in carbon fixation ; enzyme that is used in catalysis ; at lower temperatures enzyme and substrate molecules have less kinetic energy resulting in fewer successful collisions and a reduced rate of reaction. Decreasing temperature results in lower concentrations of GP, TO and RuBP
Is denaturation reversible?
No
Low concentrations of CO2
Lead to reduced concentrations of GP (as there is less carbon dioxide to be fixed) and TP ; concentration of RuBP will increase as it is still being formed from TP but not being used to fix carbon dioxide
Data loggers
Electronic devices used to record data - light intensity, temperature and pressure etc
Equipped with microprocessor which inputs digital data and internal memory for data storage
Readings are taken with high degrees of accuracy and can be taken over long periods of time ; many readings in a short time
Oxygen sensor may also need to be calibrated using the oxygen concentration of air - desired intervals
