CHAPTER 6

BIOCHEMICAL PATHWAYS

BIOCHEMICAL REACTIONSBIOCHEMICAL REACTIONS

Organisms obtain energy through enzyme-Organisms obtain energy through enzyme-controlled biochemical reactionscontrolled biochemical reactions

Release energy stored in chemical bondsRelease energy stored in chemical bonds The ultimate source of all energy is the sun The ultimate source of all energy is the sun

Converted to chemical energy through Converted to chemical energy through photosynthesisphotosynthesis

Organisms convert this chemical energy (food) Organisms convert this chemical energy (food) into usable energy through cellular respirationinto usable energy through cellular respiration

Controlled releaseControlled release Large organic molecules are broken downLarge organic molecules are broken down

Photosynthetic organisms produce food for Photosynthetic organisms produce food for their own use and for otherstheir own use and for others

BIOCHEMICAL REACTIONSBIOCHEMICAL REACTIONS

All organisms carry out cellular All organisms carry out cellular respiration which may be:respiration which may be:

Aerobic – uses oxygenAerobic – uses oxygen Anaerobic – does not use oxygenAnaerobic – does not use oxygen

Organisms can be classified based on how Organisms can be classified based on how they obtain nutrients:they obtain nutrients:

Autotrophs – make their own food (green plants, Autotrophs – make their own food (green plants, algae)algae)

Heterotrophs – obtain food from their Heterotrophs – obtain food from their surroundings (all animals, fungi)surroundings (all animals, fungi)

BIOCHEMICAL REACTIONSBIOCHEMICAL REACTIONS

Some bacterial cells can produce food Some bacterial cells can produce food through chemosynthesis (chemical through chemosynthesis (chemical reactions)reactions)

Occur within the cytoplasmOccur within the cytoplasm In eukaryotic cells, these reactions are In eukaryotic cells, these reactions are

carried out in specific organellescarried out in specific organelles Photosynthesis – chloroplastsPhotosynthesis – chloroplasts Cellular respiration – mitochondriaCellular respiration – mitochondria

BIOCHEMICAL PATHWAYSBIOCHEMICAL PATHWAYS Can be classified two ways:Can be classified two ways:

Catabolic reactionsCatabolic reactions - breakdown of organic - breakdown of organic molecules; releases energymolecules; releases energy

Anabolic reactionsAnabolic reactions - synthesis of new - synthesis of new organic molecules; requires energyorganic molecules; requires energy

Energy for these reactions is supplied Energy for these reactions is supplied by adenosine triphosphate (ATP)by adenosine triphosphate (ATP)

Energy is released when ATP is broken Energy is released when ATP is broken down into ADPdown into ADP

Reformed when a phosphate group is Reformed when a phosphate group is added to ADP (phosphorylation reaction)added to ADP (phosphorylation reaction)

““Like charging a Like charging a battery”battery”

The “actual” processThe “actual” process

AMPAMP

ADPADP

ATPATP

AEROBIC CELLULAR AEROBIC CELLULAR RESPIRATIONRESPIRATION

The breakdown of glucose molecules in The breakdown of glucose molecules in the presence of oxygenthe presence of oxygen

Carbon dioxide and water are producedCarbon dioxide and water are produced

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat) (ATP + heat)

glucose + oxygen glucose + oxygen →→ carbon dioxide + water + carbon dioxide + water + energyenergy

AEROBIC CELLULAR AEROBIC CELLULAR RESPIRATIONRESPIRATION

Begins in the cytoplasm and is Begins in the cytoplasm and is completed in the mitochondria.completed in the mitochondria.

Series of enzyme-controlled reactions Series of enzyme-controlled reactions that are divided into three pathways:that are divided into three pathways:

Glycolysis Glycolysis Krebs cycle (citric acid Krebs cycle (citric acid cycle)cycle)

Electron transport systemElectron transport system

GLYCOLYSIS GLYCOLYSIS GlycolysisGlycolysis – the breakdown of glucose; – the breakdown of glucose;

occurs in the cytoplasmoccurs in the cytoplasm Glucose (6-carbon atoms) is broken into Glucose (6-carbon atoms) is broken into

two 3-carbon molecules called two 3-carbon molecules called pyruvatepyruvate (pyruvic acid). (pyruvic acid).

2 ATP molecules are produced 2 ATP molecules are produced Electrons released from these reactions Electrons released from these reactions

are transferred to the electron transport are transferred to the electron transport chain.chain.

Will be attached to oxygen atomsWill be attached to oxygen atoms

GLYCOLYSISGLYCOLYSIS

KREBS CYCLEKREBS CYCLE The pyruvate produced in the cytoplasm The pyruvate produced in the cytoplasm

moves into the mitochondria, releasingmoves into the mitochondria, releasing Carbon dioxide (remnants of pyruvate)Carbon dioxide (remnants of pyruvate) Electrons Electrons 2 ATP molecules2 ATP molecules

The electrons are transferred to NADH The electrons are transferred to NADH and FADH2 (electron carriers), which and FADH2 (electron carriers), which take them to the electron transport take them to the electron transport system.system.

KREBS CYCLEKREBS CYCLE

ELECTRON TRANSPORT ELECTRON TRANSPORT CHAINCHAIN

When electrons receive additional energy When electrons receive additional energy they move to a higher energy level. they move to a higher energy level.

When the electrons fall back to their When the electrons fall back to their original position they give up that energy. original position they give up that energy.

Special molecules (NADH, NADPH, FADH2) Special molecules (NADH, NADPH, FADH2) capture these excited electrons and capture these excited electrons and transfer them to other chemical reactionstransfer them to other chemical reactions

Tied to the formation of ATPTied to the formation of ATP Oxidation-reduction reactionsOxidation-reduction reactions

Electrons usually come from hydrogen Electrons usually come from hydrogen creating H+ (hydrogen nucleus)creating H+ (hydrogen nucleus)

ELECTRON TRANSPORT ELECTRON TRANSPORT SYSTEMSYSTEM

Electrons are transferred through a Electrons are transferred through a series of reactions until they are series of reactions until they are accepted by oxygenaccepted by oxygen

Oxygen combines with hydrogen ions Oxygen combines with hydrogen ions to make water.to make water.

This process generates large This process generates large amounts of ATPamounts of ATP

32 ATP total 32 ATP total

Electron Transport Electron Transport SystemSystem

FERMENTATIONFERMENTATION(Anaerobic Respiration)(Anaerobic Respiration)

Two main types of fermentation:Two main types of fermentation: Alcoholic fermentationAlcoholic fermentation Lactic acid fermentationLactic acid fermentation

Alcoholic fermentation – used by Alcoholic fermentation – used by yeast cells in the absence of oxygenyeast cells in the absence of oxygen

Pyruvate from glycolysis is converted to Pyruvate from glycolysis is converted to ethanol and carbon dioxide ethanol and carbon dioxide

The yeast cells gain 2 ATPThe yeast cells gain 2 ATP

FERMENTATIONFERMENTATION

Lactic acid fermentation – pyruvate from Lactic acid fermentation – pyruvate from glycolysis is converted to lactic acidglycolysis is converted to lactic acid

2 ATP molecules are produced2 ATP molecules are produced In bacteria, the build up of lactic acid In bacteria, the build up of lactic acid

interferes with metabolic functions and they interferes with metabolic functions and they die.die.

Humans use lactic acid waste products from Humans use lactic acid waste products from these types of bacteria to make yogurt, these types of bacteria to make yogurt, cultured sour cream, cheeses, and other cultured sour cream, cheeses, and other fermented dairy products.fermented dairy products.

ANAEROBIC ANAEROBIC RESPIRATIONRESPIRATION

In humans, red blood cells produce energy In humans, red blood cells produce energy through lactic acid fermentationthrough lactic acid fermentation

They don’t have mitochondriaThey don’t have mitochondria

Muscle cells can use aerobic and anaerobic Muscle cells can use aerobic and anaerobic respiration. respiration.

For anaerobic respiration, lactic acid For anaerobic respiration, lactic acid accumulates resulting in fatigue, cramping, accumulates resulting in fatigue, cramping, and pain.and pain.

Must stop the activity or muscles will dieMust stop the activity or muscles will die When enough oxygen is available, lactic acid When enough oxygen is available, lactic acid

is converted to pyruvic acid Krebs cycle will is converted to pyruvic acid Krebs cycle will proceed.proceed.

ANAEROBIC RESPIRATIONANAEROBIC RESPIRATION

RESPIRATIONRESPIRATION

FAT RESPIRATIONFAT RESPIRATION Fats and proteins can also be used as a Fats and proteins can also be used as a

source of energy.source of energy. Fats are digested to fatty acids and glycerolFats are digested to fatty acids and glycerol Proteins are digested to amino acidsProteins are digested to amino acids

Requires several more complex steps. Requires several more complex steps. In fats, fatty acids and glycerol are broken In fats, fatty acids and glycerol are broken

down through the Krebs cycle in the down through the Krebs cycle in the mitochondria.mitochondria.

Can produce more ATP than carbohydratesCan produce more ATP than carbohydrates Serve as long term energy storageServe as long term energy storage Twice as much energy per gram of fat than gram Twice as much energy per gram of fat than gram

of carbohydrateof carbohydrate

PROTEIN RESPIRATIONPROTEIN RESPIRATION

After proteins are broken down to amino After proteins are broken down to amino acids, the amino group is removed. acids, the amino group is removed.

The carbon skeleton enters the respiratory The carbon skeleton enters the respiratory cycle as acetyl, pyruvic acid, or other cycle as acetyl, pyruvic acid, or other molecules found in the Krebs cycle.molecules found in the Krebs cycle.

The removed amino group is converted to The removed amino group is converted to ammonia.ammonia.

Excreted as ammonia, uric acid, or urea (very Excreted as ammonia, uric acid, or urea (very toxic; must be eliminated)toxic; must be eliminated)

Proteins cannot be stored, so they are Proteins cannot be stored, so they are converted to fat or carbohydrates.converted to fat or carbohydrates.

PHOTOSYNTHESISPHOTOSYNTHESIS

Process in which energy from sunlight is Process in which energy from sunlight is converted to chemical energy.converted to chemical energy.

Anabolic processAnabolic process Used by plants, algae, and some bacteriaUsed by plants, algae, and some bacteria

The green pigment chlorophyll absorbs The green pigment chlorophyll absorbs sunlight.sunlight.

Takes place in chloroplasts, which have Takes place in chloroplasts, which have 2 regions:2 regions:

Granum – stacks of membranous sacs Granum – stacks of membranous sacs (thylakoids) that contain chlorophyll(thylakoids) that contain chlorophyll

Stroma - the space between the membranes Stroma - the space between the membranes

PHOTOSYNTHESISPHOTOSYNTHESIS Can be summarized by the following Can be summarized by the following

equation:equation:

Light energy + 6 CO2 + 6 H2O → C6H12O6 Light energy + 6 CO2 + 6 H2O → C6H12O6 + 6 O2+ 6 O2

carbon dioxide + watercarbon dioxide + water→→ glucose + glucose + oxygenoxygen

Opposite of cellular respiration!Opposite of cellular respiration!

PHOTOSYNTHESIS

PHOTOSYNTHESISPHOTOSYNTHESIS Three separate events:Three separate events:

Light-capturing eventsLight-capturing events Light-dependent reactionsLight-dependent reactions Light-independent reactionsLight-independent reactions

Visible light is a combination of Visible light is a combination of different wavelengths of light seen different wavelengths of light seen as different colors.as different colors.

Chlorophyll absorbs red and blue light, Chlorophyll absorbs red and blue light, reflects greenreflects green

Pigments called carotenoids (yellow, Pigments called carotenoids (yellow, orange, red) also capture light, produce orange, red) also capture light, produce excited electrons – visible in the fallexcited electrons – visible in the fall

PHOTOSYNTHESISPHOTOSYNTHESIS Light-capturing eventsLight-capturing events

Pigments capture light energy which causes Pigments capture light energy which causes some electrons to become “excited” some electrons to become “excited”

Pigments are arranged into clusters called Pigments are arranged into clusters called photosystems – helps concentrate energyphotosystems – helps concentrate energy

Light-dependent reactionsLight-dependent reactions Take place in the thylakoid membranes of the Take place in the thylakoid membranes of the

granagrana Excited electrons are passed through an electron Excited electrons are passed through an electron

transport system, producing ATP and NADPH transport system, producing ATP and NADPH (electron carrier)(electron carrier)

Some electrons split water producing oxygen Some electrons split water producing oxygen gas, hydrogen ions, and additional electronsgas, hydrogen ions, and additional electrons

PHOTOSYNTHESISPHOTOSYNTHESIS

Light-independent reactionsLight-independent reactions Occur in the stroma Occur in the stroma Energy from excited electrons is used to Energy from excited electrons is used to

make glucose, lipids, phospholipids, make glucose, lipids, phospholipids, steroids, and other organic molecules steroids, and other organic molecules from carbon dioxidefrom carbon dioxide

Some of these molecules may also be Some of these molecules may also be used to produce DNA, RNA, or ATPused to produce DNA, RNA, or ATP

OTHER ASPECTS OF OTHER ASPECTS OF PLANT METABOLISMPLANT METABOLISM

Plants produce carbohydrates, fats, Plants produce carbohydrates, fats, proteins, and nucleic acids from the proteins, and nucleic acids from the products of photosynthesisproducts of photosynthesis

Can produce some toxins and organic Can produce some toxins and organic molecules that are used as medicinesmolecules that are used as medicines

May also produce vitamins for themselves May also produce vitamins for themselves and other organismsand other organisms

Produce oxygen in photosynthesis which is Produce oxygen in photosynthesis which is used for cellular respiration by all living used for cellular respiration by all living thingsthings

AUTOTROPHS AND AUTOTROPHS AND HETEROTROPHSHETEROTROPHS

All living things need oxygen for cellular All living things need oxygen for cellular respirationrespiration

Green plants produce oxygen in Green plants produce oxygen in photosynthesis, but they also use it in photosynthesis, but they also use it in cellular respirationcellular respiration

Produce more than enough and release the restProduce more than enough and release the rest Animals are dependent on plants not only Animals are dependent on plants not only

for oxygen, but also for essential nutrients for oxygen, but also for essential nutrients to maintain metabolism and construct to maintain metabolism and construct tissuestissues

Animals supply materials needed by plants Animals supply materials needed by plants and vice versa.and vice versa.

Essential to life on EarthEssential to life on Earth

Need to KnowNeed to Know

What is cellular respiration?What is cellular respiration? What are the 3 steps?What are the 3 steps? How much ATP is formed at each step?How much ATP is formed at each step? Where in the cell do these occur?Where in the cell do these occur? What is ATP?What is ATP? What is photosynthesis?What is photosynthesis? What are the 3 steps?What are the 3 steps? Where do these processes occur in a Where do these processes occur in a

cell?cell?

CHAPTER 6

BIOCHEMICAL PATHWAYS

AMPAMP

ADPADP

ATPATP

PHOTOSYNTHESIS

CHAPTER 6

BIOCHEMICAL PATHWAYS

AMPAMP

ADPADP

ATPATP

PHOTOSYNTHESIS