How is energy stored and released in cells?
Stored in chemical bonds
Released and transformed by metabolic pathways
What is free energy
energy available to do work
What 5 principles govern metabolic pathways
1) chemical transformation occurs in a series of intermediate reactions that form metabolic pathways
2) Each reaction is catalyzed by a specific enzyme
3) Most metabolic pathways are similar in all organisms
4) In eukaryotes, many metabolic pathways occur inside specific organelles
5) Each metabolic pathway is controlled by enzymes that can be inhibited or activated
What does it meant that energy-transforming reactions are often coupled?
Energy releasing reaction is coupled with an energy requiring reaction
Give the equation for hydrolysis of ATP and how much free energy is released
ATP + H2O -> ADP + Pi + free energy (about -7.3 kcal/mol)
What is a method of releasing energy other than ATP hydrolysis?
REDOX reactions (transfer of H atoms)
- the more reduced a molecule is, the more energy is stored in bonds (H bonds)
- Energy is transfered from reducing agent to reduced product
What enzyme is a key electron carrier in redox reactions?
NAD+ and NADH (oxidised and reduced forms)
Reduction is endergonic, Oxidation is exergonic
What is a catabolic reaction
releases energy by oxidation - to drive chemical reactions
What is an anabolic reaction
simpler substances are combined to form more complex molecules (usually requiring energy/ATP)
How is energy transfered from NADH to ATP and why is this important?
Energy transfered by oxidativ phosphorylation
Important because exergonic reactions produce NADH and endergonic reactions require ATP
What is cellular respiration
Set of metabilic reactions used by cells to harvest energy from food
- Involves energy released when molecules with many C-C and C-H bonds are oxidised to CO2
About how much of energy released in cellular respiration is harvested
34%
What are the 3 pathways of catabolism of glucose under aerobic conditions (Presence of O2)
3 linked biochemical pathways
- Glycolysis - glucose converted to pyruvate
- Pyruvate oxidation - Pyruvate oxidised into acetyl CoA and CO2
- Citric acid cycle - acetyl CoA oxidised to CO2
Where does glycolysis occur
Cytosol
What are the products of glycolysis
2 Pyruvate (Pyruvic acid)
2 ATP
2 NADH
Step 6 an 7 of glycolyis occur repeatedly in metabolic pathways - what are they and their products
6) Redox - exergonic - glyceraldehyde 3-phosphate is oxidised and NAD+ is reduced - produces NADH
7) Substate level phosphorylation - exergonic - energy released transfers phosphate from 1,3 biphosphogycerate to ADP - produced ATP
Where does pyruvate oxidatio occur
mitochondria in eukaryotes
What does pyruvate oxidation produce?
Acetyl CoA
NADH
Where does the cytric acid cycle occur?
Mitochondria in eukaryotes
How many times does the cytric acid cycle occur for every glucose molecule that enters glycolysis
twice
What are the products of the cytric acid cycle
A CoA is oxidised to 2 CO2
What is electron transport in the Cellular respiration process and its purpose
Electrons form the oxidation of NADH and HADH2 pass from one carrier to the next in the chain - create a proton gradient
Electron transport carriers are in inner mitrochonrrial membane and contain enzyme ATP synthase - use proton gradient to drive ATP production by chemiosmosis
Define chemiosmosis
the movement of ions across aa semipermeable barrier from a region of higher concentration to lower concentration
What does ATP synthase do?
converts potential energy of concentration gradient into chemical energy in ATP
What is the structure of ATP synthase - How does this let it convert energy into ATP
molecular motor with 2 subunits
- F0 - transmembrane domain(H+ channel)
- F1 - 6 subunits. F0 rotates when H passess through, causing F1 to rotate
ADP and Pi bind to active sites that become exposed on the F1 unit as it rotates -> ATP formed
Where does chemiosmosis occur in prokaryotes and eukaryotes
prokaryotes - proton gradient across cell membrane
Eukaryotes - mitochondria and chloroplasts
What is the role of O2 in cellular respiration
most ATP is formed by oxidative phosphorylation - reoxidation of NADH
O2 is reduced
How is NADH reoxidised in anaerobic conditions
Fermentation (many different types)
What is the difference in yield of ATP in aerobic vs anaerobic conditions
Aerobic - 32 ATP
Anaerobic - 2 (produced in glycolysis)
What are 2 main types of fermentation
Lactic acid - produce lactate
- Pyruvate reduced to lactic acid, NADH oxidised to NAD+
Alchoholic - produces ethanol
- Pyruvate converted to acedaldehyde and CO2 released, NADH reduces acedaldehyde to ethanol and regenerates NAD+
Where does alcohol fermentation occur
Only in certain yeasts and some plants
How are anabolic and catabolic pathways integrated
Both required for maintaining energy balance
Anabolic pathways use energy to produce molecules and Catabolic pathways breakdown molecules to produce energy
Anabolic pathways can simply be catabolic pathways in reverse
What are common processes in catabolism
- Polysaccharides hydrolyzed to glucose (enters glycolysis)
- Lipids -> fatty acids and glycerol. Can be convered into Acetyl CoA
- Proteins hydrolyzed into amino acids - can feed into glycolysis of citric acid cycle
How are amounts of molecules maintained at fairly constant levels in the metabolic pool
regulation of enzymes via allosteric regulation and feedback inhibition (Fast) and also altering transcription of genes that encode enzymes (SLOWO
How are catabolism, anabolism and photosynthesis linked
Cellular respiration linked by their reactants and products and b ATP and reduced coenzymes
What is the equation for cellular respiration
Glucose + 6O2 -> 6CO2 + 6H2O + cellular energy
What is the equation for photosynthesis
CO2 + H2O + Light energy -> Carbohydrates + O2
What are the 2 pathways of photosynthesis
Light reaction - converts light into chemical energy (ATP and reduced electon carrier NADPH)
Carbon-fixation reaction - uses ATP and NADPH to produce carbohydrates
How is the amount of light energy related to its wavelength
Inversely proportional energy to wavelength
What are pigments
molecules that absorb wavelengths in the visible spectrum
What is the absorption spectrum vs action spectrum
Absorption - Plot of light energy absorbed against wavelength
Action - Plot of biological activity of an organism against wavelength
What pigments absorb light energy in plants
2 Chlorophylls - Chlorophyll a and chlorophyll b
- Also accessory pigment sthat absorb wavelength between red and blue and transfer some energy to chlorphylls
How are pigment arranged?
in light-harvesting complexes or antenna systems
Photosystem spans the thylakoid membrane in the chloroplast consists of multiple antenna systems surrounding a reaction centre
How is light energy converted into chemical energy?
Chlorophyll absorbs light - enters excited state - rapidly returns to ground state releasing an excited electron
- electron is given to acceptor molecule which is reduced (becoming chemical energy in H bond)
How is ATP produced from photosynthesis
Excited electron is accepted by the fist carrier in the electron transport system
Final acceptor is NADP+ which is reduced
ATP is produced Chemiosmotically (proton gradient) during electron transport
Plants have 2 photosystems - wha are the differences
Photosystem I - absorbs ligth energy at 700nm and passes and excited electron to NADP+ - reduces to NADPH
Photosystem II - absorbs light at 680 nm, oxidises water and initiates ATP production
How is water oxidises by photosystem II
when electron is given up, Chl* is unstable and grabs an electron from H2O - splitting H-O-H bonds
How is Chl* in photosystem I restabilized after giving up an electron
Grabs electron from the last carrie i the transport system of photosystem II
Reuces NADP+ to NADPH
What is he cyclic electron transport
Uses only photosystem I and produces only ATP
Electron passed from Chl* through electron transport chain and recycled back to the same Chl
What is the purpose of carbon fixation pathways
Require ATP
For energy storage as carbohydrates
What is the Calvin cycle
Energy in ATP and NADPH is used to ‘fix’ CO2 in reduced form in carbohydrates
occurs in stroma of chloroplast
Each reaction is catalyzed by a specific enzyme
What are the 3 processes of the calvin cycle
1) fixation of CO2
Co2 added to Ribuluse 1,5 biphosphate (RuBP) -> 6-carbon molecules result -> split into two 3-carbon molecules 3-phosphoglycerate (3PG)
2) 3PG is reduced to form glyceraldehyde 3 phosphate
3) CO2 Acceptor RuBP is regenerated form G3P
What is the difference between autotrophs and herterotrophs
Autotrophs (photosynthetic organisms) use most of energy provided by photosynthesis to support their growth and reproduction
Heterotrophs cannot photosynthesize and depend on autotrophs for chemical energy.
Where does almost all the energy on earth come from
the C-H bonds generated by the calvin cycle