Photosynthesisand cellularrespiration
Transcript of Photosynthesisand cellularrespiration
Cellular RespirationCellular Respiration
Cellular Respiration Overview
Transformation of chemical energy in food into chemical energy cells can use: ATP
These reactions proceed the same way in plants and animals. Process is called cellular respiration
Overall Reaction:– C6H12O6 + 6O2 → 6CO2 + 6H2O
Cellular Respiration Terms
Photoautotrophs – change light energy into chemical energy stored in bonds of glucose and polysaccharides (green plants, cyanobacteria)
Heterotrophs – feed on other organisms for chemical energy
Chemoautotrophs – microorganisms that can obtain energy from inorganic sources (Fe or S compounds in volcanoes, deep sea vents…)
Glucose – primary source of energy for most organisms
Cellular respiration – process by which glucose is broken down and energy stored in bonds is released, can be aerobic or anaerobic
Aerobic – oxygen used as an oxidizing agent (electron acceptor)
Anaerobic – uses a molecule other than oxygen as an oxidizing agent
Cellular Respiration Overview
Purpose of Cellular Respiration:Trap free energy in form of ATPMove H+ electrons from glucose to oxygen
creating 6 H2OBreak bonds between 6C atoms in glucose
creating 6 CO2
Formation of ATP
2 Ways ATP is formed:1. Substrate-level
Phosphorylation ATP formed directly in
enzyme catalyzed reaction
P containing compound transfers P gp to ADP making ATP
4 ATP created this way from 1 molecule glucose
2.Oxidative Phosphorylation ATP formed indirectly in more complex process co-enzyme NAD+ (nicotinamide adenine
dinucleotide) removes 2 H+ atoms and is reduced to NADH+ + H+
another co-enzyme, FAD (flavin adenine dinucleotide) also reduced by 2 H+ to become FADH2
these co-enzymes act as mobile energy carriers in cell, moving energy from one stage of cellular respiration to another where its used to create ATP
4 Stages of Cellular Respiration
Name Details
Stage 1 Glycolysis 10 step process in cytoplasm
Stage 2Pyruvate Oxidation
1 step process in mitochondria
Stage 3 Kreb’s Cycle 8 step cycle in mitochondria
Stage 4Electron Transport Chain
multi-step process in mitochondrial membrane
1. Glycolysis
Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate– Process is an ancient one-all organisms from simple
bacteria to humans perform it the same way– Yields 2 ATP molecules for every one glucose
molecule broken down (creates 4 ATP but uses 2)– Yields 2 NADH per glucose molecule (used later to
create more ATP)– cellResp_main
4 Parts to Glycolysis
1. Glucose activation 2 molecules ATP
transfer P to glucose results in 2 ADP and
F1,6 BP (fructose 1,6 biphosphate)
2. Sugar Splitting F1,6 BP splits into 1
G3P (glyceraldehyde 3-phosphate) and 1 DHAP (dihydroxyacetone)
DHAP is then immediately converted into G3P by enzyme isomearase (result is 2 G3P)
3. Oxidation
• both G3P are oxidized by NAD resulting in 2 NADH.
• this releases energy and 2 ATP produced by substrate level phosphorylation.
• result is 2 molecules of 1,3 BPG (biphosphoglycerate)
4. ATP Formation
• phosphate gps of BPG are transferred to 2 ADP creating 2 ATP by substrate level phosphorylation
• end result is 2 molecules pyruvate
Glucose + 2 ADP + 2 Pi + 2 NAD+
2 pyruvate + 2 ATP + 2 NADH
Aerobic or Anaerobic Respiration?
After glycolysis, life diverges into two forms and two pathways
if O2 is present, pyruvate from glycolysis moves from cytoplasm into mitochondria to start aerobic cellular respiration
if no O2 is present, pyruvate enters anaerobic cellular respiration (aka fermentation)
Aerobic Cellular Respiration
Oxygen required=aerobic 3 more sets of reactions which occur in the
mitochondria– Pyruvate Oxidation– Kreb’s Cycle– Electron Transport Chain
2. Pyruvate Oxidation
3 step reaction:
1. carboxyl gp removed as CO2
2. remaining 2 carbon group is oxidized by NAD+, forming NADH and becomes acetate
3. co-enzyme A attaches to acetate, forming acetyl-coenzyme A
cellResp_main acetyl-co A formed by catabolism of carbs,
proteins, and lipids in eukaryotes if ATP levels are high, acetyl-co A will be directed
into synthesis of fatty acids for long term energy storage
if ATP needed, acetyl-co A is directed to next part of cellular respiration: Kreb’s Cycle
Kreb’s Cycle (Citric Acid Cycle)
Completes the breakdown of glucose– Occurs in matrix of mitochandria– 8 step process, each step catalyzed by a specific
enzyme– Product of 8th reaction (oxaloacetate) is a reactant in
the 1st reaction (cycle)– Takes the pyruvate (3-carbons) and breaks it down, all
6 carbon and oxygen atoms end up in CO2 and H2O
– Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce 6 NADH and 2 FADH2 which are transported to the final step
Production of only 2 more ATP (substrate level phosphorylation)
cellResp_main
Electron Transport Chain
NADH & FADH2 loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase).
made of 4 lg protein molecules and 2 smaller mobile protein carriers proteins are arranged in order of electronegativity, so each one will
be reduced (gain 2e-) then immediately oxidized (lose 2e-) as electrons drop down stairs, energy released to form a total of 32
ATP oxygen waits at bottom of staircase, picks up electrons and protons
and in doing so becomes water
cellResp_main
Steps of ETC
1. NADH gives 2e- to NADH dehydrogenase, first protein in ETC.
2. Electrons (e-) pass through the ETC, releasing energy.
3. Energy is used to pump H+ ions across membrane into intermembrane space.
4. Build up of H+ ions in the space creates an electrochemical gradient.
5. H+ ions want to diffuse back across membrane but are unable to and must use special protein channels called ATPase complex (facilitated diffusion).
6. Pores in the protein channels contain an ATP-synthesizing enzyme called ATP synthase. So as the H+ ions move through the channels, Pi (inorganic phosphate) is joined to ADP to create ATP.
7. Every e- NADH drops off will pump 3 H+ ions across the membrane, therefore producing 3 ATP.
8. FADH2 skips the first protein and drops its e- off further down chain so only 2 H+ ions are pumped across, therefore producing only 2 ATP.
9. When e- from NADH and FADH2 reach last protein in chain called cytochrome oxidase, they have lost energy.
10. Once cytochrome oxidase has 4e-, it gets oxidized by O2 (high electronegativity). O2 takes the e- and combines them with four H+ ions from the matrix to produce 2 H2O molecules.
VCAC: Cellular Processes: Electron Transport Chain: The Movie
Energy Tally
36 ATP for aerobic vs. 2 ATP for anaerobic
– Glycolysis 2 ATP
– Kreb’s 2 ATP
– Electron Transport 32 ATP 36 ATP
Anaerobic organisms can’t be too energetic but are important for global recycling of carbon
Other Catabolic Pathways
Carbohydrates broken into monosaccharide, then broken down for
energy avg. yield of 16 kJ/g of energy
Proteins broken down into amino acids to be used to produce
cell’s proteins amino groups removed in deamination and converted into
ammonia (wastes) rest of a.a. continue through glycolysis or Kreb’s cycle
Lipids
triglycerides broken into glycerol and fatty acids glycerol broken down into glucose or G3P and
goes through glycolysis fatty acids go into matrix of mitochandria and
undergo oxidation – get converted in acetyl groups which combine with co-enzyme A to produce acteyl-coA (used in Kreb’s cycle)
much more ATP formed than from carbs. ex lauric acid (12 C fatty acid) – produces 92 ATP
avg yield is 38kJ/g of energy
Anaerobic Cellular Respiration
Some organisms thrive in environments with little or no oxygen– Marshes, bogs, gut of animals, sewage treatment
ponds No oxygen used= ‘an’aerobic Results in no more ATP if no O2 available to ETC it stops and NADH can’t
drop off H+ ions free NAD+ can’t return to pick up more electrons
and hydrogens in glycolysis, causing it to stop
organisms have alternative methods to get energy
ex. NADH can drop off H+ ions to certain organic molecules instead of ETC (fermentation)
End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)
PhotosynthesisPhotosynthesis
Photosynthesis
Method of converting sun energy into chemical energy usable by cells
done by autotrophs takes place in specialized
structures inside plant cells called chloroplasts
1. Capturing light energy2. Using captured energy to make ATP and NADP+
(energy carrying co-enzyme like NAD. It is reduced by 2 H atoms to NADPH+ + H+)
3. Using ATP and energy from NADPH to synthesize molecules like glucose.
first 2 steps require sunlight (light dependant) and occur in chlorophyll
last step does not necessarily need sunlight (light independent) and takes place in stroma
3 Steps of Photosynthesis
Light-Dependent Phases
occurs in thylakoid membrane light energy converted to chemical energy of
ATP & NADPH (reduced NADP = NADPH) photosystems (highly organized light capturing
complexes) are found in thylakoid membranes and made of 2 parts:
antenna complex – system of chlorophyll molecules and pigments that transfers energy to reaction centre
reaction centre – protein complex containing chlorophyll a that absorbs energy from antenna complex and raises it to high energy level to start photosynthesis
there are 2 kinds of photosytems (I and II) depending on which wavelength of light chlorophyll a absorbs
Steps in Light Dependent Reactions
1. Photoexcitation: Sunlight hits leaf and some energy passes into stroma
then absorbed by antenna complex of photosystem II and passed along to chlorophyll a.
2. Electron Transport: An electon gets boosted to a higher level and passed
along a ETC (like in cellular respiration) in thylakloid membrane.
This energy boost also causes H2O to split which releases H+ ions and O2 which is vital to other living things.
e- passes through several carriers via redox reactions releasing energy as they pass through the proteins. H+ ions are pumped from stroma into intermembrane space which creates electrochemical gradient.
3. Chemiosmosis: H+ ions move through ATPase complex back into stroma
converting ADP to ATP a process called photophosphorylation. It takes 4 H+ to make 1 ATP.
At same time light of a different wavelength is also striking photosystem 1. e- from P1 pass through another ETC, then move to enzyme NADP reductase that reduces NADP to NADPH which moves to Light Independent Phase.
Reactants: H2O, sunlight
Products: ½ O2, NADPH, ATP
YouTube - Light (Dependant) Reactions of Photosynthesis Animation
2. Light Independent Reactions (the Calvin Cycle)
ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.
called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)
occur in stroma don’t require light also known as C3 Cycle
Steps in Light Independent Phase:
1. Carbon Fixation CO2 molecule combines with 5C molecule called
RuBisCO (ribulose biphosphate) to produce 2, 3C molecules called 3-PGA (3-phosphoglycerate).
2. Reduction Reactions 3-PGA phorphorylated by ATP then reduced by NADPH
to produce G3P (glycerate 3-phosphate).3. RuBisCO Regeneration G3P phosphorylated by ATP to re-create RuBisCO to
restart the cycle. For every 2 G3P, 1 molecule glucose is removed from cycle, so need 6 CO2 to create 1 glucose.
Other Methods of Carbon Fixation
Type of carbon fixation
Stomata open
Advantages Examples
C3 dayUses fewer
ATPMost plants
C4day Faster
photosynthesisCorn, sugar
cane, grasses…
CAMnight Water
efficiency
Succulents, cacti, orchids, pineapple…