Roles of Nitrogen Plants and bacteria use nitrogen in the form of NH 4 + or NO 3 - It serves as an electron acceptor in anaerobic environment Nitrogen is often the most limiting nutrient in soil and water
Nitrogen is a key element for amino acids nucleic acids (purine, pyrimidine) cell wall components of bacteria (NAM)
Ammonification or Mineralization R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N2ON2O N2N2
Mineralization or Ammonification Decomposers: earthworms, termites, slugs, snails, bacteria, and fungi Uses extracellular enzymes initiate degradation of plant polymers Microorganisms uses: Proteases,lysozymes, nucleases to degrade nitrogen containing molecules
Plants die or bacterial cells lyse release of organic nitrogen Organic nitrogen is converted to inorganic nitrogen (NH 3 ) When pH<7.5, converted rapidly to NH 4 Example: Urea NH CO 2
Immobilization The opposite of mineralization Happens when nitrogen is limiting in the environment Nitrogen limitation is governed by C/N ratio C/N typical for soil microbial biomass is 20 C/N < 20 Mineralization C/N > 20 Immobilization
Nitrogen Fixation Energy intensive process : N 2 + 8H+ + 8e ATP = 2NH 3 + H ADP + 16 Pi Performed only by selected bacteria and actinomycetes Performed in nitrogen fixing crops (ex: soybeans)
Microorganisms fixing Azobacter Beijerinckia Azospirillum Clostridium Cyanobacteria Require the enzyme nitrogenase Inhibited by oxygen Inhibited by ammonia (end product)
Rates of Nitrogen Fixation N 2 fixing systemNitrogen Fixation (kg N/hect/year) Rhizobium-legume Cyanobacteria- moss30-40 Rhizosphere associations 2-25 Free- living1-2
Bacterial Fixation Occurs mostly in salt marshes Is absent from low pH peat of northern bogs Cyanobacteria found in waterlogged soils
Nitrification Two step reactions that occur together : 1 rst step catalyzed by Nitrosomonas 2 NH O 2 2 NO H 2 O+ 4 H + 2 nd step catalyzed by Nitrobacter 2 NO O 2 2 NO 3 -
Optimal pH is between If pH < 6.0 rate is slowed If pH < 4.5 reaction is inhibited
Denitrification Removes a limiting nutrient from the environment 4NO C 6 H 12 O 6 2N H 2 0 Inhibited by O 2 Not inhibited by ammonia Microbial reaction Nitrate is the terminal electron acceptor
Metal ions Many metal ions have role in biological processes of the body The ions have different physical and chemical properties – Complex formation – Oxidation states Minerals in food
The most important ions Ion Ca 2+ Mg 2+ Fe 2+ Cu 2+ Zn 2+ Co 3+ Na + K + Role: 1.5-2% of body mass, bones, teeth Bones and teeth, intracellular activity Hemoglobin, O 2 transfer Cofactor in enzymes Cofactor in enzymes,growth, healing In vitamin B12 Water balance, nerve impulses, fluids inside and outside cells
Oxygen transport proteins hemoglobin Hemoglobin is a tetramer composed of two α and two β subunits Each subunit contains an iron-porphyrin ring that binds oxygen Oxygen binding is highly cooperative between each subunit
Hemoglobin as oxygen carrier In each hemoglobin molecule there are four heme groups Heme = Fe 2+ surrounded by phorphyrin group, As O 2 carrier: O 2 binds to Fe 2+ as a ligand Reversible process
The transport of oxygen in blood - Haemoglobin
Oxygen Transport The resting body requires 250ml of O2 per minute. We have four to six billion haemoglobin containing red blood cells. The haemoglobin allows nearly 70 times more O 2 than dissolved in plasma.
Hemoglobin Binding of O 2 alters the structure
Haemoglobin 4 x Haem group + 4 x Polypeptide chain
Hemoglobin Oxygen carrier protein 4 subunits = 2 alpha + 2 beta Normal adult = HbA = 2 2 Four heme groups - iron- porphyrin compound at O 2 binding site Iron containing porphyrin rings, only Fe2 + can bind O 2 Each heme combines with one globin protein chain Molecular weight of hemoglobin is 64,000 Each gm of Hb can carry up to 1.31ml of O 2, theoretically up to 1.39 ml/gm
Chemical Binding of Hemoglobin & Oxygen Hemoglobin combines reversibly with O 2 – Hemoglobin is the unoxygenated form – Oxyhemoglobin is when O 2 combined Association and dissociation of Hb & O 2 occurs within milliseconds – Critically fast reaction important for O 2 exchange – Very loose coordination bonds between Fe 2+ and O 2, easily reversible – Oxygen carried in molecular state (O 2 ) not ionic O 2-
Haemoglobin Saturation Haemoglobin saturation is the amount of oxygen bound by each molecule of haemoglobin Each molecule of haemoglobin can carry four molecules of O2. When oxygen binds to haemoglobin, it forms OXYHAEMOGLOBIN; Haemoglobin that is not bound to oxygen is referred to as DEOXYHAEMOGLOBIN.
Pathological Ligands of Hemoglobin Ligands form covalent bonds to the ferrous iron in Hb These bonds have more affinity to iron than oxygen which binds weakly to Hb Carbon Monoxide – 250 times the affinity than oxygen – Does not dissociate readily – Requires hours to rid body of CO Nitric Oxide – Binds to Hb 200,000 times more strongly – Hemoglobin binds irreversibly to NO – Used to treat pulmonary hypertension
Hemoglobin & Myoglobin Myoglobin is single chained heme pigment found in skeletal muscle Myoglobin has an increased affinity for O 2 (binds O 2 at lower P o 2 ) Mb stores O 2 temporarily in muscle
Myoglobin and Hemoglobin Myoglobin – Increases O 2 solubility in tissues (muscle) – Facilitates O 2 diffusion – Stores O 2 in tissues Hemoglobin – Transports O 2 from lungs to peripheral tissues (erythrocytes)
Porphyrin Porphyrin rings are biological molecules used in a variety of essential chemical processes The two most well-known porphyrins are heme and chlorophyll
Because of their large conjugated double bond system, porphyrins typically absorb visible light Chlorophylls green color, hemes red, and the blue blood of some sea creatures are all a result of this absorbance Additionally, the 4 nitrogen atoms at the center of the ring are excellent at conjugating metals because of their lone pairs As a result, porphyrins are a common way to attach metals to proteins Heme
Chlorophyll –porphyrins are important in plants, too! Chlorophyll as a Photoreceptor Chlorophyll is the molecule that traps this 'most elusive of all powers' - and is called a photoreceptor. It is found in the chloroplasts of green plants, and is what makes green plants, green. The basic structure of a chlorophyll molecule is a porphyrin ring, coordinated to a central atom. This is very similar in structure to the heme group found in hemoglobin, except that in heme the central atom is iron, whereas in chlorophyll it is magnesium.porphyrin ring eier-fig1.gif
Chrophyll Porphyrin is also part of the chlorophyll, the key substance for the photosynthesis of green plants, some algae and some bacteria. Chlorophyll absorbs mainly violet-blue and orange-red light and reflect green colour which give plants their green colour Several kinds of chlorophyll exist (chl a,chl b etc.). They differ from each other in details of their molecular structure and absorb slightly different wavelengths of light.
Chlorophyll is composed of two parts; the first is a porphyrin ring with magnesium at its center, the second is a hyrophobic phytol tail. The ring has many delocalized electrons that are shared between several of the C, N, and H atoms; these delocalized electrons are very important for the function of chlorophyll. The tail is a 20 carbon chain stabilizes the molecule in the hydrophobic core of the thylakoid membrane.
Photosynthesis Overview Two processes - each with multiple steps – Light reactions convert solar energy to chemical energy light energy drives transfer of electrons to NADP + forming NADPH ATP generated by photophosphorylation occur at the thylakoids
Photosynthesis Overview Two processes - each with multiple stages – Calvin cycle Named for Melvin Calvin who worked out many of the steps in the 1940s incorporates CO 2 from the atmosphere into an organic molecule (carbon fixation) uses energy from the light reaction to reduce the new carbon to a sugar occurs in the stroma of the chloroplast
Light is composed of particles called photons that act like waves. Visible light is also called photosynthetically available radiation (PAR). Changes in the wavelength of visible light (PAR) result in a change of color. Light with a wavelength of 450 nm is blue while light with a wavelength of 650 nm is red.
COVERTING LIGHT ENERGY TO CHEMICAL ENERGY 1. The Chlorophylls and Carotenoids are grouped in Cluster of a Few Hundred Pigment Molecules in the Thylakoid Membranes. 2. Each Cluster of Pigment Molecules is referred to as a PHOTOSYSTEM. There are Two Types of Photosystems known as PHOTOSYSTEM I AND PHOTOSYSTEM II. 3. Photosystem I and Photosystem II are similar in terms of pigments, but they have Different Roles in the Light reactions. 4. The Light Reactions BEGIN when Accessory Pigment molecules of BOTH Photosystems Absorb Light. 5. By Absorbing Light, those Molecules Acquire some of the Energy that was carried by the Light Waves. 6. In each Photosystem, the Acquired Energy is Passed to other Pigment Molecules until it reaches a Specific Pair of CHLOROPHYLL a Molecules..
Photosystem Photosystem is composed of the Light Harvesting Complex (LHC) and the reaction center. The LHC is composed of hundreds of molecules of chlorophylls and accessory pigments.
Light (dependent)Reactions Happen ONLY in sunlight – Hence they depend on light! 1.Light is absorbed by chlorophyll molecules 2.The energy generates molecules of ATP Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto
Summary Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto