BIOL 111 Exam 3
Chapter 15
Genes and Proteins:
Genes, which are carried on chromosomes, are linearly organized instructions for making the RNA and protein molecules that are necessary for all of the processes of life
Examples: interleukin-2 protein and alpha-2u-globulin protein
Flow of Genetic Information:
The central dogma: a theory that describes genetic flow
1. DNA is transcribed into mRNA
2. mRNA strands are translated into proteins
Instructions on DNA are transcribed onto messenger RNA
Ribosomes read the genetic information inscribed on a strand of mRNA
Ribomsomes then string amino acids into a polypeptide (protein)
Degeneracy of the genetic code:
Nucleotides in an mRNA sequence code for amino acids in 3 nucleotide sets known as codons
The reading frame (ORF) refers to which nucleotide starts the 1st codon
There are 64 possible codons that code for 20 amino acids and 3 stop codons (nonsense codons)
Multiple codons can specify one amino acid
Genes (& Proteins):
A specific sequence of nucleotides on a strand of DNA
Genes typically lead to the production of a specific protein product
This can/does lead to the development of a specific trait
Beadle and Tatum experiments (1941) with neurospora crassa (bread mold) showd “1 gene = 1 protein”
The Genetic Code:
The Messenger RNA:
mRNA is a copy of protein-coding information in the coding strand of DNA
Substitution of U in the RNA for T in the coding sequence
RNA is synthesized in its 5’-3’ direction, using the enzyme RNA polymerase
As the template is read, the DNA unwinds ahead of the polymerase and then rewinds behind it
Frameshift Mutations:
Deletion of 2 nucleotides shifts the reading frame of an mRNA and changes the entire protein message
Creates a nonfunction protein or terminates protein synthesis altogether
Gene Expression - Basic Principles:
The process by which DNA directs protein synthesis includes 2 major processes
1. Transcription
Synthesis of RNA under the direction of DNA
Produces messenger RNA (mRNA)
Produces template for translation
2. Translation
The synthesis of a polypeptide under the direction of an mRNA
Occurs on ribosomes
Gene Expression:
Prokaryotes - NO NUCLEUS
Transcription and translation take place in the cytoplasm, occurring at the same time
Eukaryotes
Transcription takes place in the nucleus
Translation takes place in the cytoplasm
Unique Features of Prokaryotic Gene Expression:
Gene expression occurs solely in the cytoplasm
Transcription and translation happen in the same location
Prokaryotes do not require RNA transcript modification
RNA transcripts can be translated immediately after being transcribed
Genes can be transcribed and translated at the same time
Multiple polymerases can transcribe a single gene
Numerous ribosomes can concurrently translate the mRNA transcripts into polypeptides
Specific transcripts and/or specific proteins can rapidly reach high concentrations in a cell
Using the Genetic Code:
The gene sequence determines the sequence of nt along the length of a mRNA
RNA is comprised of G, C, A, and U
Thymine substituted for uracil in RNA
RNA polymerase is the enzyme that carries out transcription
Types of Eukaryotic Polymerases
RNA Polymerase I
Transcribes rRNA (ribosomal RNA) genes
RNA Polymerase II
Transcribes protein-coding genes
RNA Polymerase III
Transcribes rRNA, tRNA, and small nuclear RNA genes
Steps of Transcription Initiation:
Transcription factors bind to the promoter region of the gene to be transcribed
The factors recruit RNA polymerase and bind with it to form the initiation complex
RNA polymerase recognizes the transcriptional start sequence and begins synthesizing the RNA transcript in a 5’ to 3’ direction
The Steps of Transcription Elongation:
The production of the RNA transcript
RNA Polymerase unwinds DNA to access the template strand
Only exposes ~10-20 DNA nucleotides as at a time
Links RNA nucleotides using DNA as a template
Produces the RNA transcript in a 5’ to 3’ direction
Typically produces the RNA transcript at ~40 nucleotides/second
Steps of Transcription Termination:
RNA polymerase reaches and transcribes the termination sequence
The RNA transcript is released by RNA polymerase
RNA polymerase detaches from the DNA, officially ending transcription
Sequence: DNA at the end of a gene that is transcribed and signals the R transcript is complete
A common example of a method helped to signal termination is the formation of a “hairpin” structure in the RNA transcript
Initiation in Prokaryotes:
Very similar to eukaryotes - promoter and -10 region
Has a -35 region. Together with -10, it is called the sigma factor. Similar to the transcription factor. Binds and signals where transcription should take place.
Elongation in Prokaryotes:
Same as eukaryotes
Prokaryotic RNA pol tracks along the DNA template
Synthesizes mRNA in the 5’ to 3’ direction
Unwindes and rewinds the DNA as it is read
Occurs at a rate of ~40 nt/second
Termination in Prokaryotes:
2 types of termination signals
Rho-dependent (controlled by Rho protein)
Rho-independent (controlled by sequences in the DNA Strand.) E.g.: hairpin formation in mRNA
Post-Transcriptional Processing in Eukaryotes:
Eukaryotic cells must modify RNA after transcription & and before translation
Enzymes in the eukaryotic nucleus modify pre-mRNA in specific ways before the genetic messages move to the cytoplasm
5’ guanine cap cap added
3’ poly A tail added
Introns removed (exons spliced) - makes it ready to by translated by making one continuous coding sequence that still has protection on 5’ and 3’ end
Post-Transcriptional Processing: RNA Splicing: The process of removing introns and joining together to form a mature mRNA
Ensures that only coding sequences are translated (exons)
Cuts out introns (noncoding sequences) and links together exons
Accomplished using specialized protein complexes known as spliceosomes
Made of protein and catalytic RNA (ribozymes - ribo + enzymes)
Polypeptides within proteins often have discrete structural and functional regions called domains
Each exon can encode for a different domain (still part of the same protein)
Alternative Splicing: process of selecting different combos of splice sites within a pre-mRNA to produce variably spliced mRNA
Introns provide alt. cut sites for this.
** creates different proteins with each splice. If cell is not in need of a specific protein, it won’t use energy by splicing an exon that it does not need
rRNA and tRNA Processing - when they get transcribed, they never get translated. Their processing allows them to carry out various functions through shaping. (rRNA binds to ribosome*check defs for both r and t RNA):
Intramolecular cleavage
Splicing
Methylation: adding a functional group (CH3) to a transcript. Makes them less processable. If the cell doesn’t need proteins made from rRNA and tRNA at a given time, adding lots of methyl turns of their processing.
Protein Synthesis:
Decodes mRNA to produce a polypeptide
Polypeptides are formed when the amino grup of one amino acid forms an amide (i.e., peptide) bond with the carboxyl group of another amino add
The reaction is catalyzed by ribosomes, using ribozymes and catalytic rRNA
mRNA : 5’ ----- 3’
Protein : N’ (amino) -------- C’ (carboxyl)
Peptide bonds: links the carboxl (COOH) end of one amino acid with the amino end of another, expelling one water molecule.
Translation Process:
Initiation
mRNA attaches to the smaller subunit of the ribosome
AUG (= mehionine) is the start codon - a tRNA (the one that matches with the first codon) with the appropriate anticodon attaches
The larger subunit of the ribosome then comes in
Elongation
tRNAs move in with the appropriate amino acid, the amino acid chain grows using peptidyl transferase (involves transferring the polypeptide from one tRNA to the next)
Termination
STOP codon is reached
The amino acid chain then in processed
In eukaryotes, the amino acid chain moves into the endoplasmic reticulum to be further processed
Molecular Components of Translation:
Transfer RNAs (amino acid binding)
Ribosome
mRNA (messenger RNA)
Polypeptide
ATP
The Structure and Function of tRNA (transfer RNA)
Molecules of tRNA are not all identical
Each carries an amino acid on one end
Each has an antiocodon on the other end
A tRNA molecule consists of a single RNA that is only about 80 nuclotides long. It is also roughly L-shaped
Aminoacyl-tRNA: joins each amino acid to the correct tRNA
Uses ATP
Catalyzes covalent bonding
The Ribosome:
Responsible for translating mRNA into protein
Consists of a large and small ribosomal subunit
Assembly of the subunits on the tRNA binding sits
During translation, charged tRNAs enter the Acceptor site and the anticodon on the tRNA base pairs with the codon in the mRNA
The Polypeptide:
Produces through assembly of amino acids bonded together in the specific sequence
Interaction of one of the tRNA in P site with another tRNA in A site
Directed by bonding an mRNA codon to the anticodon of a tRNA
Occurs in ribosomes found in the cytoplasm of the cell
Translation Initiation:
Brings together mRNA, initiator tRNA, and 2 subunits of ribosomes
General Steps:
1. mRNA binfs the small ribosomal subunit
2. The START codon is located (first AUG)
3. The initiator tRNA binds to the START codon
4. Energy is used to recruit and bing the large ribosomal subunit
Translation Elongation: Amino acids are bonded together to build the polypeptide chain out of the P site
* peptide bond @ step 2
Translation Termination:
Reached when the STOP codon is recognized in the mRNA
No tRNA matches the STOP codon
Termination Steps:
1. The STOP codon in the mRNA is reached and recognized
2. A release factor is recruited and binds to the STOP codon causing the hydrolysis of the polypeptide from the tRNA
3. This bonding and a bit of energy is utilized to cause the dissociation of translation components
Protein Folding, Modification, and Targeting
During and after translation, amino acids may be chemically modified
Signal sequences at amino end direct protein to destination
Signal-recognition particles (SRP) act as conductors
Signal sequence removed
Chaperones help proteins fold properly
Mutations:
Spontaneous Mutations
Occur randomly during DNA replication, recombination, or repair
Induced Mutations
Mutagens are agents of mutation
Chapter 6
Energy and Metabolism:
The energy that sustains most of the earth’s life comes from the sun
Bioenergetics - the study of energy flow through a living system
Metabolism: all chemical reactions of a cell or organism
Metabolic pathway- series of biochemical reactions that converts one or more substrates into a final product
Example: sunlight energy captured during photosynthesis is used to synthesize glucose
Example: the energy stored in glucose is released during cellular respiration
2 types of reactions/pathways to maintain cell’s energy balance:
Those that require energy and synthesize larger molecules are called anabolic
Those that release energy and break down large molecules into smaller molecules are called catabolic
Types of Energy:
Energy - the ability to do work
Objects in motion have kinetic energy
Example: chemical/electrochemical gradients across the plasma membrane
Objects that have potential to move have potential energy
Example: gasoline stores PE in its bonds. When it is burned it releases energy to move the car.
Chemical energy - energy stored in chemical bonds (potential) then released (kinetic)
Free Energy:
Bioenergetics of a system = amount of energy exchanged in metabolic reactions
Gibb’s Free Energy (G) = amount of energy available to do work (useable energy)
All chemical reactions affect G
ΔG = ΔH - TΔS
ΔH is change in total energy of the system (enthalpy)
T is temperature in Kelvins (celcius+273)
ΔS is change in entropy (energy lost in disorder)
Free Energy - Exergonic Reactions:
If energy is released in a chemical reaction:
ΔG < 0
Products will have less free energy than substrates
Classified as exergonic
Exergonic reactions are spontaneous because they can occur without addition of energy
Spontaneous reactions do not necessarily occur quickly
Free Energy - Endergonic Reactions:
If a chemical reaction requires input of energy:
ΔG > 0
Products will have more free energy than substrates
Classified as endergonic
To Sum It Up:
Activation Energy: the energy required for a reaction to proceed
Causes reactant(s) to become contorted and unstable, allowing bond(s to be broken or made
Unstable state is called the transition state
In transition state the reaction occurs very quickly
Heat energy is the main source for activation energy in a cell
Heat helps reactants reach transition state (ex.: rusting of iron over time)
The Laws of Thermodynamics:
Thermodynamics - study of energy and energy transfer involving physical matter
First law of thermodynamics - the total amount of energy in the universe is constant
Energy cannot be created or destroyed
Second law of thermodynamics - the transfer of energy is not completely efficient
In chemical reactions some energy is lost and unusable
Increases entropy
Entropy:
Entropy changes as phases change ; solid → liquid = increased entropy
Adenosine Triphosphate (ATP):
Provides the energy for a cell’s endergonic reactions (products > reactants)
These are the reactions that are not spontaneous (positive deltaG)
ATP Structure:
Composed of adenosine backbone with 3 phosphate groups attached
Adenosine = nitrogenous base adenine + 5-carbon ribose
3 phosphate groups = alpha, beta, and gamma
Bonds between phosphate groups are high-energy
When broken the products have lower free energy than the reactants
ATP Hydrolysis:
ATP + H_2O → ADP + P_i + free energy
Delta G = -7.3 kcal/mol (nearly double in cells)
ATP is unstable and hydrolyzes quickly
Energy lost as heat if not coupled to endergonic reaction
When coupled with an endergonic reaction, much of the energy can be transferred to drive that reaction
ATP hydrolysis is reversible
The sodium-potassium pump:
deltaG = + 2.1 kcal/mol
3 Na OUT 2 K IN
Exergonic w/ endergonic
Enzymes:
Primarily protein catalysts the speed up reactions by lowering the required activation energy
Binds with reactants and promote bond-breaking and bond-forming processes
Very specific, catalyzing a single reaction
Does NOT change reaction’s deltaG
Enzyme-substrate specificity:
3D shapes (enzyme and substrate) determine specificity
Substrates interact at enzyme’s active sites
Enzymes can catalyze a variety of reactions
E+S ES EP E+P
Induced Fit
At active site, a mild shift in shape optimizes reaction(s)
Slight change maximizes catalysis
Enzyme remains unchanged following reaction (resets)
Protein Structure
3D shape of protein determined by amino acid sequence
Amino acids of active site is important for enzymes function because it allows binding with unique substrate(s)
Cellular environment is important for enzyme function
Suboptimal temperatures can denature the enzyme (loss of shape)
Suboptimal pHs can redunce substrate-enzyme binding. pH deviation disrupts protein, which in turn disrupts enzyme
Lowering Activation Energy
An enzyme can help the substrate reach its transition state in one of the following ways:
Position two substrates so they align perfectly for the reaction
Provide an optimal environment (acidic or polar, for ex.) within in the active site for the reaction
Contort/stress the substrate so it is less stable and more likely to react
Temporarily react with the substrate (chemically change it) making the substrate less stable and more likely to react
Enzyme Regulation:
Helps control environment to meet their specific needs (don’t wanna waste enzymes)
Ex. digestive cells in stomach work harder after a meal than during sleep
Enzymes can be regulated by:
Modification to temperature and/or pH
Production of molecules that inhibit or promote enzyme function
availability of coenzymes or cofactors
Enzyme Inhibition:
Competitive inhibitors
Have similar function to substrate and compete w/ substrate for active site
Noncompetitive inhibitors
Bind to enzyme any different location and reaction rate
Competitive inhibition slows reaction rates but does not affect the maximal rate
Noncompetitive inhibition slows rates and reduces the maximal rate
Maximal Rate - speed of a reaction when substrate concentration is not limited ‘
Enzyme Regulation - Allostery:
Allosteric inhibitors modify active site = substrate binding is reduced or prevented
Allosteric activators modify active site = affinity for substrate increasises
Enzyme Cofactors:
Some enzymes require one or more cofactors or enzymes
Cofactors - inorganic ions (i.e. - Fe++, Mg++, Zn++)
DNA polymerase requires Zn++
Coenzymes - organic molecules (i.e. - ATP, NADH+) and vitamins
Obtained primarily from diet
Feedback Inhibtion in Metabolic Pathways:
Feedback inhibition = end-product of pathway inhibits an upstream step
Important regulatory mechanism in cells
Ex.: ATP allosterically inhibits some enzymes involved in cellular respiration
Chapter 7
Redox Reactions: chemical reactions where electrons are transferred from one molecule to another
Molecules that donate electron(s) are reducing agents and those that accept electron(s) are oxidizing agents
Molecules that gain electron(s) after the reaction are reduced and those that lose electrons are oxidized
Electron Carriers: compounds that shuttle high-energy electrons to electron transport chains to aid in ATP production
NAD occurs in an oxidized state (NAD+) or reduced state (NADH)
NADH carries 2e- and 1H+ more than NAD
NAD+ accepts electrons from redox reactions; NADH donates them
ATP in Living Systems:
Hydrolysis of ATP → ADP + P_i
Provides energy for a coupled endergonic reaction
Phosphorylation - addition of a phosphate group to a molecule
Dephosphorylation - loss of a phosphate group
Phosphorylated molecules tend to be less stable (more likely to react)
ATP is generated when ADP is phosphorylated
ADP + P_i → ATP (hydrolysis)
Energy required can come from
Substrate-level phosphorylation (a coupled exergonic reaction)
Oxidative phosphorylation requiring enzyme ATP synthase
90% of ATP produced by oxidative phosphorylation
Occurs in mitochondria and/or chloroplasts in eukaryotesm while it occurs in plasma membrane of aerobic prokaryotes
Overview of Cellular Respiration:
C6H12O6 + 6O2 → 6CO2 + 6H2O + ~36 ATP
(oxidized) (reduced)
The metabolic pathways involved are:
Glycolysis
Oxidation of pyruvate and citric acid cycle
Oxidative phosphorylation
Glycolysis:
The first metabolic pathway of glucose metabolism
Includes 10 enzymatic reactions
Nearly all organisms perform glycolysis
Occurs in the cytoplasm
O2 is not required (anaerobic) - just don’t need it yet
Glycolysis - Energy Investment Phase:
The first half of glycolysis involves 5 enzymes and uses 2 ATP
Glucose is phosphorylated 2x and then split into two 3-carbon molecules
Glyceraldehyde-3-phosphate (G3P
Glycolysis - Energy Payoff Phase:
The 2nd half of glycolysis involved phosphorylation without ATP
Produces 2 NADH and 4 ATP molecules (2 net ATP)
Generates 2 pyruvate molecules
Oxidation of Pyruvate:
In eukaryotic cells, if oxygen is present, the 2 pyruvates enter mitochondria where each is converted to Acetyl CoA before entering the CAC
1 CO2 is released (per pyruvate)
It is oxidized transferring e- to NADH
Coenzyme A is attached
Inputs: 2 pyruvate, 2 NAD+, 2 conenzyme A
Outputs: 2 CO2, 2 NADH, 2 acetyl CoA
Citric Acid Cycle:
Location: mitochondrial matrix
Step 1 - the acetyl gorup from acetyl CoA is transferred to oxaloacetate to form citrate
CoA transfers to -SH to replenish
Uses ATP as negative feedback mechanism
Through a series of reactions:
Citrate is oxidized (3 NADH & 1 FADH2 produced)
2 CO2 released
1 GTP or ATP produced
Final product of citric acid cycle is oxaloacetate
Cycle runs continuously in presence of sufficient reactants
Outputs per Glucose to this Point:
4 ATP (2 from glycolysis, 2 from CAC)
6 CO2 (2 from oxidation of pyruvate, 4 from CAC)
10 NADH (2 from glycolosis, 2 from oxidation of pyruvate, 6 from CAC)
2 FADH2 (from CAC)
Glucose is completely oxidized at the end of CAC
All possible elxetions have been removed
Oxidative Phosphorylation:
The only pathway where O2 is a reactant
Consists of en electron transport chain and chemiosmosis to generate ATP
H+ concentration gradient provides energy to power ATP synthase
The Electron Transport Chain:
Series of 4 electron transporters embedded in inner mitochondrial membrane
Shuttle electrons from NADH and FADH2 to O2
Protons (H+) are pumped from mitochondrial matrix to inner mitochondrial membrane space
O2 is reduced to form H2O
ETC - Protein Complexes:
Complex 1
NAD dehydrogenase protei enzyme w/ Fe-S cofactor
FMN prosthetic group (from B-vitamin)
Receives electrons from NADH
Pumps 4 H+ from matrix into inner mitochondrial membrane space
Complex II and Q
Complex II receives electrons from FADH2
Q (ubiquinone) passes pairs of electrons from complex one and complex two and complex three
Complex III
Cytochromes B and C (cytochrome oxidoreductase)
Cytochrome C passes single electrons from complex three to complex 4
Pumps H+ into IM space
Complex IV
Fe and Cu cofactors hold oxygen until it is reduced by 2 electrons
Reduced oxygen picks up 2 Hs to make H2O
Pumps H+ into IM space
Chemiosmosis:
H+ needs a channel to move down gradient into matrix (potential energy)
ATP synthase is H+ channel and enzyme for ADP + P_i → ATP
Kinetic energy from H+ electrochemical gradient used to form ATP
ATP Yield:
~30 - 36 ATP per glucose generated varies by species:
How many H+ pumped in ETC
How efficiently NADH from glycolysis enters into mitochondria
NAD+ vs. FAD+ in different tissues
Cellular respiration in total stores ~ 34% of the energy from glucose in ATP
Some intermediates (metabolites) used for other purposes
Metabolism Without Oxygen:
Glycolysis occurs in aerobic and anaerobic environment
NAD+ must be constantly regenerated
When O2 is present:
NAD+ created when NADH is oxidized by ETC
When O2 is lacking:
Organic molecule accepts electron (fermentation)
Fermentation regenrates NAD+
There are 2 common types of fermentation:
Lactic acid fermentation
Pyruvate + NADH ←→ lactate + NAD+
Alcohol fermentation
Anaerobic yeast species
2 reactions
1. Pyruvate + H+ → CO2 + acetaldehyde
Pyruvate decarboxylase
2. Acetaldehyde + NADH + H+ → ethanol + NAD+
Alcohol dehydrogenase
Regulation of Cellular Respiration:
Regulated by many mechanisms;
Hormonal control of glucose entry into cell
Enzyme reversibility or irreversibility (able to exceed equilibrium)
Enzyme sensitivity to pH changes due to lactic acid build-up
Feedback controls
Chapter 8
There are 2 types of autotrophs:
Photoautotrophs - use sunlight to make food (plants, algae, cyanobacteria)
Chemoautotrophs - capture energy from inorganic compounds to make food (thermophilic bacteria)
Autotrophs and Heterotrophs:
Heterotrophs - animals, fungi, most bacteria
Rely on sugars produced by autotrophs for energy
Overview of Photosynthesis:
Photosynthesis uses solar energy to produce sugar from carbon dioxide and water
Oxygen is a waste product
Photosynthesis Reactants:
Sources of components:
H2O - absorbed by roots from the soil
CO2 - acquired from air during gas exchange through stomata (small pores on leaf underside)
O2 waste product exits through stomata during exchange
Photosynthesis Equation:
6 H2O + 6 CO2 → (sunglight) → C6H12O6 + 6 O2
The metabolic pathways of photosynthesis:
The light-dependent reactions
The light-independent reactions (calvin cycle)
Energy for Photosynthesis:
Photo:
ATP and NADPH are produced by the light-dependent reactions using light energy
Synthesis:
Light independent reactions use energy from ATP, and hydrogen and electrons from NADPH, to synthesize sugars from CO2
Photosynthesis Equation:
Water splits into H and O
Electrons from H go into sugar
Oxygen released as a byproduct
Reaction Outcomes and Locations:
Light-dependent reactions convert light energy into chemical energy
Makes ATP and NADPH (electron carrier)
Occur in thylakoid membranes of chloroplasts
Calvin cycle uses the ATP and NADPH to make sugar (food)
Occurs in stroma of chloroplasts
Chloroplast Structure:
Double membrane (outer and inner)
Stroma
Grana (stacks of thykaloids)
Lumen is inside thykaloid
What is Light Energy?
Light energy is electromagnetic energy
Composed of photon particles that travels as waves
Longer wavelengths carry less energy than shorter wavelengths
Wavelengths and energy are INVERSELY proportional
We can only see a fraction of this energy (visible range)
Plants use wavelengths in this range too
Wavelengths are measured in nm
In visible range (700-400 nm), violets have shortest wavelengths and most energy
Reds have longest wavelengths, least energy
Absorption of Light:
Pigments absorb specific wavelengths of light
Each has a unique absorbance spectrum
The main pigments of thykaloid membranes are:
Chlorophyll a
Chlorophyll b
B-carotene (carotenoid)
Chlorophyll a and b capture light for photosynthesis
Leaves are green (green wavelengths are reflected)
B-carotene helps protect photosystems by dissipating excess energy
Also found in cells of carrots and oranges
Other carotenoids include lycopene (red color of tomato) and zeaxanthin (yellow of corn seeds)
Prokaryotes use bacteriochlorophyll
The Photosystems:
Photosystems II and I consists of a light-harvesting complex and a reaction center
Pigments in the light-harvesting complex pass light energy to 2 special chlorophyll a molecules in the reaction center
In the reaction center, the light excites an electron from the chlorophyll a pair, passing it to the 1st electron acceptor of the electron transport chain
A light-driven redox reaction
The lost electron is then replaced
In photosystem II the electron comes from the splitting of water, which releases oxygen as a waste product
In photosystem I the electron comes from the electron transport chain
Components of Thykaloid Membranes
Photosystems II and I
Sites of light absorption
An electron transport chain
2 enzyme complexes, NADP reductase and ATP synthase
The Electron Transport Chains:
2 parts of the ETC in light reactions:
First transports electron from PSII to PSI
Plastoquinone (Pq)
Cytochrome complex
Plastocyanin (Pc)
Second transports electron from PSI to NADP reductase
Ferredoxin
Final electron acceptor of the light reaction is NADP + → yielding NADPH
Like the ETC of cellular respiration:
H+ gradient is created as electrons fall down chain
Pumped into lumen space
ATP synthase uses gradient to generate ATP (chemiosmosis)
The Light-Independent Reactions:
RuBisCO: ribulose biphosphate carboxylase oxygenase
3 stages to Calvin Cycle:
1. Fixation: CO2 added to RuBP by enzyme RuBisCO to generate 2 x 3-PGA
2. Reduction: ATP and NADPH used to add electrons and make sugar (G3P)
2x G3P → glucose
3. Regeneration of RuBP from G3P
3 cycles of steps 1 & 2 are required to release 1 glyceraldehyde-3-phosphate
6 cycles of steps 1 & 2 are required to build glucose
Efficiency of the Calvin Cycle:
RuBisCO can function as carboxylase (calvin cyle) or oxygenase (photorespiration - does not result in sugar production)