Bio 1005 Chapter 4 Photosynthesis Dr. Joseph Silver

this chapter deals with 1. what is photosynthesis 2 this chapter deals with 1. what is photosynthesis 2. pigments involved in photosynthesis 3. the light reaction 4. the dark reaction

photosynthesis depends on cells capturing the energy in some wavelengths of visible light

it is estimated that only about 1% of the suns energy is captured by plants

there are two types of photosynthesis 1 there are two types of photosynthesis 1. anoxygenic (does not produce oxygen) 2. oxygeneic (produces oxygen)

anoxygenic photosynthesis takes place in strange places purple, green sulfur, green non-sulfur, & heliobacteria which live in extreme environments anoxygenic photosynthesis is a very primitive form of photosynthesis where energy (energized electrons) is gotten from molecules without oxygen such as H2S or FeCl3

oxygenic photosynthesis takes place in cyanobacteria, 7 groups of algae, all land plants this is modern photosynthesis responsible for oxygen in our atmosphere water is used as an electron donor

chloroplasts - have an outer and inner membrane - the inner membrane has many folds - thylakoid surface contains photosynthetic pigments - a stalk of thylakoids forms a grana - the grana are surrounded by a fluid stroma - the stroma contains glucose forming enzymes - chloroplast DNA is in the stroma

there are 3 steps to photosynthesis 1. capture light energy 2 there are 3 steps to photosynthesis 1. capture light energy 2. make ATP & NADPH steps 1 & 2 require light 3. use ATP & NADPH to make glucose step 3 (carbon fixation) does not need light

photosynthesis 6C02 + 12H2O + light(energy)  C6H12O6 + 6H2O + 6O2 you should see that this equation is the reverse of cellular respiration

outer membrane inner membrane intermembrane space thylakoid stroma pigments photosystems

Greeks – growth from soil Jan Helmont(1600s) – growth from soil & water Joseph Priestly(1700s) – plants add “life” to air Jan Ingenhousz(1700s) – O2 off & carbon to carbohydrate F.F.Blackman(1900s) – only one part needs light Robin Hill(1950s) – use of radioactive labels to trace chemicals through a biological pathway found that electrons from water used to make sugar Calvin – using radioactive tracers showed the steps of the dark reaction (using CO2 + ATP to make sugar)

let’s digress for a moment and talk about a subject no one wants to talk about transmutation

visible light is only a small part of the electromagnetic spectrum

a particle of light = a photon a chemical which absorbs light energy = a pigment the shorter the wavelength of light the more energy the light contains

pigments absorb light which cause excited electrons to be released which are picked up by electron carriers which will be used to construct ATP & sugar

plant cells contain 3 types of pigments 1. chlorophyll a 2 plant cells contain 3 types of pigments 1. chlorophyll a 2. chlorophyll b 3. carotenoids

the main pigment = chlorophyll a 2nd is chlorophyll b 3rd = carotenoids (also antioxidants)

plant pigments absorb energy in the violet, blue and red areas they do not absorb in the green area they look green because green is not absorbed green energy is reflected away from the chloroplasts

SO lets do the light reaction and light dependent reaction

just as in mitochondria the energized NADs and ATP of the light cycle go to the Calvin or dark cycle where their energy is used to make sugar from 6CO2

the light and dark cycles accomplish carbon fixation as sugar production and ATP and NADPH formation these products are transported to a mitochondrion and will be used to make ATP ??????

you need to go through the Calvin cycle twice to make 1 molecule of glucose

1. photosynthesis = sugar production then 2 1. photosynthesis = sugar production then 2. sugar enters the glycolysis pathway and 3. pyruvate enters Krebs cycle (cell respiration) and many ATP are made

the amount of energy in the universe is constant energy can change place and form but cannot be created or destroyed

any work that is done is not 100% efficient some energy is always lost as heat so as work is done the universe becomes less ordered the amount of disorder or entropy is always increasing when 2 chemicals react and heat is released this free energy is available to be used for work this heat or free energy is known as G

A + B = K +  -G (exergonic) needs activation  spon A + B +  = M +G (endergonic) non spontaneous

a spontaneous rx can take place very slowly but when the cell needs to do work it may rx be too slowly so biological systems have a group of chemicals known as enzymes which greatly reduces the amount of energy needed for the rx to take place enzymes lower the energy of activation

Enzymes are mostly proteins they lower the energy of activation their effect is to increase the rate of rx by 1,000,000s affected by temp, conc, pH, pressure, salt conc

enzymes work by providing a substrate or surface upon which the reactants can interact and produce a product the enzyme is not destroyed as it does it’s work it will keep working until it is no loner needed

you cannot allow enzymes to just keep working enzymes are inhibited by 1. molecules competing for the activation sites competitive inhibition 2. the product of a reaction inhibits the first step of the rx noncompetitive inhibition or

enzyme activity is increased by two factors 1. cofactors and 2 enzyme activity is increased by two factors 1. cofactors and 2. coenzymes cofactors are many of the inorganic chemicals Mg, Ca, Al, Zn, coenzymes are organics such as vitamins, hormones, sterols,