Chapter 5 part 1Photosynthesis

Energy in living systems- photosynthesis: the process of converting light energy into

chemical energy- Autotrophs: make their own food- Heterotrophs: eat autotrophs (can’t make their own food)- Formula for the process is on the next slide

- ATP: adenosine triphosphate- The energy currency of the body- Three parts: base (adenine), sugar (ribose), and three phosphate

groups- The “energy” is stored in the bonds between the phosphates

(kind of like a compressed spring)- Energy is required to “break” the bond, but much more is

released when it breaks.

When energy from ATP is release (a phosphate bond is broken) the new molecule becomes ADP (adenine diphosphate)

Using energy in sunlightThe 3 stages of photosynthesis.Stage 1 Light absorption:- Part of the “light” reaction of photosynthesis- Light is a form of radiation (energy in the form or waves)

Photons- Visible light (wavelengths perceptible by human eye…think

the rainbow)- Visible spectrum: ranges from 400nm to 700nm (purple

to red)- Pigments: light absorbing substances (found in everything)- Chlorophyll: primary pigment involved in photosynthesis.

Continued….- There are 3 photosynthetic pigments- Chlorophyll B (mostly blues)- Chlorophyll A (purples and reds)- Carotenoids (blues)- Green is really the only part of the spectrum that is NOT absorbed.

Production of oxygen- Light absorbing pigments are found in Chloroplasts.

- Made up of stacks called grana- Each layer of the grana is called a thylakoid- Surface of the thylakoid is where all the magic happens.

How the magic happens:- Light strikes a thylakoid- Energy is transferred to electrons- Causes them to jump energy levels (called “excited”)- In this state, they have the ability to power reactions- However, they can’t leave space (void) behind, so other electrons fill

their space- These come from H2O

- Water is split by an enzyme in the thylakoid- Electrons are donated by the hydrogen- Leaving H+ ions and oxygen- The oxygen is released (think of the equation for Photosynthesis,

what is one of the byproducts?)

Stage 2: conversion of light energy- We now have an e- available.- It will enter PS II, photosystem 2, and move up to an

electron acceptor.- It will then move along the membrane, in a series of “steps”,

called the ETC- ETC: electron transport chain- Each “step” releases a small amount of energy- This energy is used to drive H+ ions against their

concentration gradient.

THE ETC!!!!!- Starts with e- at “top of the stairs” of PSII.- Electron moves down a system of proteins, losing some

energy- Energy is used to move H+ ions against their CG.- Until it reaches PSI- Energy from the sun, re-energizes the e-- Moves up PSI- At the top NADP+ uses the e- and an H+ to form NADPH.- NADPH is an energy carrier, similar to ATP.

Summary of the light reactionsPigment molecules in the thylakoids of chloroplasts absorb light energy. Electrons in the pigments are excited by light and move through electron transport chains in thylakoid membranes. These electrons are replaced by electrons from water molecules, which are split by an enzyme. Oxygen atoms from water combine to form oxygen gas. Hydrogen ions accumulate inside the thylakoids, setting up a concentration gradient that provides the energy to make ATP.

Stage 3: The “Dark” reactions -Not really in the dark, but light is not

required-Takes place in the stroma of a chloroplast-Called the Calvin Cycle

-Purpose: to use the CO2 and make simple sugars

-There are many complex stages

Carbon dioxide fixation: is the transfer of carbon dioxide to organic compounds (sugar). Short called “fix” carbon. The Calvin Cycle- Series of enzyme assisted chemical reactions that produce a three carbon sugar.

Steps:1. CO2 is fixed (3 molecules enter at a time)2. Re-arranges into 3 6-carbon compounds, which change shapes again3. 6 ATP are used and 6 NADPH are used to change these shapes (over several

steps)4. 6 3-carbon compounds are created, one leaves, the other 5 stay in cycle5. 3 more ATP are added, to regenerated the starting compounds (RuBP

enzyme is rubisco that get it going)

The numbers:- 3 CO2’s (go in)- 9 ATP’s (go in)- 6 NADPH’s (go in)- Single turn makes 1 simple sugar (come out)