Learning objectives:

Learning objectives: To know the importance of chemical energy in biological processes To understand the role of ATP To draw the structure of ATP To understand the stages in aerobic respiration: glycolysis, link reaction, Kreb’s cycle and the electron transport chain

What processes do cells need energy for? Movement e.g. movement of cilia and flagella, muscle contraction 2. Maintaining a constant body temperature to provide optimum internal environment for enzymes to function 3. Active transport – to move molecules and ions across the cell surface membrane against a concentration gradient

4. Anabolic processes e.g. synthesis of polysaccharides from sugars and proteins from amino acids 5. Bioluminescence – converting chemical energy into light e.g. ‘glow worms’ 6. Secretion – the packaging and transport of secretory products into vesicles in cells e.g. in the pancreas

In pairs: Draw this grid on one Miniw’board. Put or on different sides of a second mwb (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

(1) Active transport uses carrier proteins (2) Active transport needs ATP (3) Osmosis occurs from lower to higher water potential (4) Passive transport methods use ATP (5) Phagocytosis is a type of endocytosis (6) Facilitated diffusion needs ATP (7) Active transport occurs from lower to higher conc. (8) Facilitated diffusion uses carrier proteins (14) Facilitated diffusion uses channel proteins (9) Simple diffusion uses ATP (10) Endocytosis involves bulk transport into a cell (11) Pinocytosis is a type of exocytosis (12) Diffusion stops when equilibrium is reached (13) Endocytosis involves bulk transport out of a cell (15) Diffusion occurs up a concentration gradient (16) Exocytosis uses ATP (14) Facilitated diffusion uses channel proteins

Why is energy needed within cells? • Allows chemical reactions to take place • BUILD UP (synthesis) or BREAKDOWN of molecules • In order to do this, energy is required to make and break bonds

Where does the energy come from? • The SUN is the ultimate source of energy for nearly all living organisms (the exceptions being a few deep sea chemosynthetic bacteria) • Autotrophs make their own food (organic compounds) using carbon dioxide • Heterotrophs assimilate energy by consuming plants or other animals

Autotroph Organisms that can synthesise complex organic molecules from simple ones. There are two types of autotroph, depending on how they obtain their energy: i. Phototrophs:Autotrophs that use light energy e.g. Plants. ii. Chemotrophs:Autotrophs that use inorganic chemical energy e.g. sulphur bacteria

ATP

What provides the energy within cells? • ATP…Adenosine Tri Phosphate • Common to ALL living things • Any chemical that interferes with the production or breakdown of ATP is fatal to the cell and therefore the organism • Chemical energy is stored in the phosphate bonds

The role of ATP (adenosine triphosphate) • The short term energy store of the cell • Often called the ‘energy currency’ of the cell because it picks up energy from food in respiration and passes it on to power cell processes. ATP made up of: Adenine (a base) Ribose (a pentose sugar) 3 phosphate groups

1. The nitrogenous base Adenine 2. A pentose sugar Ribose 3. Phosphate groups ATP Structure ATP is a nucleotide made from:

ATP: Function 1. It is a coenzyme involved in many enzyme reactions in cells. 2. It is the major energy currency of cells entrapping or releasing energy in most metabolic pathways. 3. The energy is released from ATP in a single step and in a small manageable amount. 4. It is a small molecule so will diffuse rapidly around the cell to where it is needed. 5. It is one of the monomers used in the synthesis of RNA and, after conversion to deoxyATP (dATP), DNA.

ATP: and energy When the third phosphate group of ATP is removed by hydrolysis, a substantial amount of free energy is released, the exact amount depends on the conditions. For this reason, this bond is known as a "high-energy" bond. The bond between the first and second phosphates is also "high-energy". But note that the term is not being used in the same sense as the term "bond energy". In fact, these bonds are actually weak bonds with low bond energies. ATP + H2O -> ADP + Pi ADP is adenosine diphosphate. Pi is inorganic phosphate. * Hydrolysis: Decomposition of a substance by the insertion of water molecules between certain of its bonds. Food is digested by hydrolysis) *Free energy: The energy that can be harnessed to do work.

How does ATP provide the energy? • Chemical energy is stored in the phosphate bonds, particularly the last one • To release the energy, a HYDROLYSIS reaction takes place to break the bond between the last two phosphate molecules • Catalysed by ATP-ase • ATP is broken down into ADP and Pi • For each mole of ATP hydrolysed, about 34kJ of energy is released • Some is lost, but the rest is useful and is used in cell reactions

How ATP releases energy • The 3 phosphate groups are joined together by 2 high energy bonds • ATP can be hydrolysed to break a bond which releases a large amount of energy • Hydrolysis of ATP to ADP (adenosine diphosphate) is catalysed by the enzyme ATPase (ATPase) ATP ADP + Pi + 30 KJ mol-1 (H2O)

The 2nd phosphate group can also be removed by breaking another high energy bond. • The hydrolysis of ADP to AMP (adenosine monophosphate) releases a similar amount of energy (ATPase) ADP AMP + Pi + 30 KJ mol-1 (H2O) AMP and ADP can be converted back to ATP by the addition of phosphate molecules

The production of ATP – by phosphorylation • Adding phosphate molecules to ADP and AMP to produce ATP Phosphorylation is an endergonic reaction – energy is used Hydrolysis of ATP is exergonic - energy is released

Advantages of ATP • Instant source of energy in the cell • Releases energy in small amounts as needed • It is mobile and transports chemical energy to where it is needed IN the cell • Universal energy carrier and can be used in many different chemical reactions

What does this have to do with photosynthesis? • ATP is both synthesised and broken down during photosynthesis! 6CO2 + 6H2O = C6H12O6 + 6O2 • Light energy is required • Chlorophyll • Stored within chloroplasts • 10-50 chloroplasts per plant cell

Biochemistry of Photosynthesis An introduction…

The Leaf Plant leaves are flattened to maximise the surface area for the absorption of light. The upper and lower surfaces are covered by a waxy cuticle which slows the loss of water from the leaf. Beneath the cuticle lies the epidermis which provides some support for the leaf. The lower epidermis has small pores called stoma that allow for gaseous exchange. During the day CO2 diffuses in and O2 out, during the night CO2 diffuses out and O2 in. Water vapour also escapes from the stomata and it is this loss that creates the transpiration stream drawing mineral nutrients from the soil and up into the plant. The exchange of gases through the stomata is regulated by the guard cells which lie on either side of it. The palisade mesophyll cells are elongated and contain many chloroplasts, this is the main photosynthetic area of the plant. The spongy mesophyll has large air spaces to allow for the rapid diffusion of gases in and out of the leaf. The veins in the leaf contain vascular tissue, the xylem and phloem. The xylem provides support as well as carrying water and mineral nutrients. The phloem carries away the products of photosynthesis, primarily sucrose, to the rest of the plant.

Upper epidermis Palsade mesophyll Vein Vascular bundle Spongy mesophyll Lower Epidermis The Leaf

Cuticle Upper epidermis Chloroplasts Palisade mesophyll Air space In spongy mesophyll The Leaf

Stoma Guard Cells Lower epidermis Guard Cells and Stomata

“Life is bottled sunshine” Wynwood Reade, Martyrdom of Man, 1924

Photosynthesis – what we know (or should know!!...) • “Building from light” • Converts carbon dioxide into organic compounds • Carried out by autotrophs • All life either depends on it directly as a source of energy, or indirectly as the ultimate source of the energy in their food • 6CO2 + 6H2O = C6H12O6 + 6O2

So how do we know all this?...

The story starts a long time ago… • Aristotle (384-322BC) • Greek philosopher • He proposed that plants, like animals, require food • He concluded that green plants obtained their nourishment from the soil • Aristotle’s theory was widely accepted until the 1600’s…

Nicholas of Cusa (1401-1464) • Cardinal of the Catholic Church • Philosopher, mathematician, jurist and astronomer • He planned but never carried out an experiment to determine whether or not plants consume the soil • He proposed they did not • Revolutionary!!

Jean Baptiste van Helmont (1579-1644) • Flemish physician and chemist • Identified carbon dioxide, carbon monoxide, nitrous oxide and methane • He was a doctor. He married a wealthy noblewoman and her inheritance enabled him to retire early from medical practice and concentrate on his chemical experiments • Over 5 years, he carried out experiment originally planned by Nicholas of Cusa and concludes the increase in mass of the plant came from water. He does, however, ignore a slight decrease in soil mass

Robert Hooke • Invented the light microscope • Observed both plant and animal cells • ‘Stoma’- from the Greek word for mouth • First observed by Malphighi • Stoma were so named by Heinrich Link because of their appearance • Their function was unknown to him though

EdmeMariotte (1620-1684) • French physicist and priest • In 1660 he discovered the eye’s blind spot! • In 1676 he hypothesised that plants synthesise their food from air and water

Stephen Hales (1677-1791) • Physiologist, chemist and inventor • He studied the roles of air and water and their importance to plant and animal life • He wrote that plant leaves “very probably“ take in nourishment from the air and that light may also be involved

Charles Bonnet • Observed the emission of gas bubbles by a submerged illuminated leaf (clearly his pondweed was healthier than the pondweed we have in school!)

Joseph Priestley and his experiments… • 1733-1804 • Theologian, philosopher, clergyman, scholar and teacher • One of the scientists credited with discovering "dephlogisticated air“ –oxygen • Finds out that air which has been made ‘noxious’ by the breathing of animals or burning of a candle can be restored by the presence of a green plant • Carried out a very famous experiment using bell jars, candles, plants and mice…

Antoine Lavoisier • 1743-1794 • Investigated and later named oxygen • Recognises it is used up in both combustion and respiration • His work discredits “phlogiston”, a hypothetical substance previously believed to be emitted during respiration or combustion • One of the fathers of modern day chemistry

Jan Ingenhousz • 1730-1799 • Physicist, chemist and plant physiologist • Discovered photosynthesis (and Brownian motion!) • Showed that light is essential for photosynthesis and that only the green parts of the plants release oxygen

1782 – Jean Senebier demonstrates that green plants take in carbon dioxide from the air and emit oxygen under the influence of sunlight • 1791 – Comparetti observes green granules in plant tissues, later identified as chlorophyll

Nicolas de Saussure • 1767-1845 • Chemist and plant physiologist • Proved that the carbon assimilated from atmospheric carbon dioxide cannot fully account for the increase of dry weight in a plant • The basic equation for photosynthesis was therefore established

The Biochemistry begins… • So scientists had now worked out that Carbon Dioxide was taken in and Oxygen was given out, and that the green pigment (named chlorophyll in 1818) played a part in this process, but what actually went on inside the leaf?...

1842 – Schleiden states that he believes the water molecule is split during photosynthesis • 1844 – Hugo von Mohl makes detailed observations about the structure of chloroplasts • 1845 – Julius Robert von Mayer proposes that the Sun is the source of energy used by living organisms and introduces the concept that photosynthesis converts light energy into chemical energy • 1862 – Julius von Sachs demonstrates that starch formation in chloroplasts is light dependent

The discoveries continue… • 1864 – We have the balanced equation for photosynthesis after accurate quantitative measurements of carbon dioxide uptake and oxygen production are made… 6CO2 + 6H2O C6H12O6 + 6O2 • 1873 – Emil Godlewski proves that atmospheric CO2 is the source of carbon in photosynthesis by showing that starch formation in illuminated leaves depends on the presence of CO2

Not just any old light.. • In 1883, Engelmann illuminated a filamentous alga with light that had been dispersed using a prism • He discovered that aerobic bacteria in the water all congregated around the portions iluminated with red and blue wavelengths • This was the first action spectrum!

Solvent line Carotene Pheophytin Chlorophyll A Chlorophyll B Carotenoids Plant Pigments and Chromatography Thin layer chromatogram (TLC) of an extract of thylakoid membranes from the leaf of annual meadow grass Poa annua. TLC plastic sheets are coated with a 60 F254 silica gel which measures 0. 2 millimetres thick. A drop of extract, corresponding to the column here, was laid at the bottom of the sheet. The sheet was then placed in a beaker of solvent (75% acetone & 25% petroleum ether). The picture shows the solubility of the extract in solvent. Six bands are seen; top (orange) is carotene; 2 (green) pheophytin; 3 (green) chlorophyll A; 4 (green) chlorophyll B; 5 (yellow) & 6 (mere trace) are carotenoids. The line across the top of image is the solvent line

Chlorophyll Chlorophyll + Light = Chlorophyll+ + Electron-

Chlorophyll • Found within chloroplasts • Absorb and capture light • Made up of a group of five pigments • Chlorophyll a • Chlorophyll b • Carotenoids; xanthophyll and carotene • Phaetophytin • Chlorophyll a is the most abundant • Proportions of other pigments accounts for varying shades of green found between species of plants

Learning objectives: