Chapter 5 BioD

light-dependent reactions

set of reactions in photosynthesis that use energy from light to produce ATP and NADPH

anabolic reactions

synthesis of larger molecules from smaller ones (storage, growth) (exergonic)

cellular respiration

(both autotrophs and heterotrophs) a process that uses oxygen to help break down food molecules such as sugars. The energy stored in the bonds of the food molecules is transferred to ATP. As the energy is transferred to the cells, the matter from the food molecules is released as carbon dioxide and water.

Reactions of breaking down food

(i) Release energy that can be transferred to ATP: Cells quickly use this ATP for cellular work, such as building new molecules. (ii) Oxidize food molecules and transfer electrons and energy to coenzymes: Oxidation is the process that removes electrons from molecules; reduction is the process that gives electrons to molecules. During cellular respiration, enzymes remove electrons from food molecules and then transfer the electrons to the coenzymes - nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). NAD+ and FAD receive the electrons as part of hydrogen (H) atoms, which change them to their reduced forms, NADH and FADH2. Next, NADH and FADH2 donate the electrons to the process of oxidative phosphorylation, which transfers energy to ATP. NAD+ and FAD act like electron shuttle buses for the cell. The empty buses, NAD+ and FAD, drive up to oxidation reactions and collect electron passengers. When the electrons get on the bus, the driver puts up the H sign to show that the bus is full. Then the full buses, NADH and FADH2, drive over to reactions that need electrons and let the passengers off. The buses are now empty again, so they drive back to another oxidation reaction to collect new passengers. During cellular respiration, the electron shuttle buses drive a loop between the reactions of glycolysis and the Krebs cycle (where they pick up passengers) to the electron transport chain (where they drop off passengers). (iii) Release carbon dioxide (CO2): Cells return CO2 to the environment as waste, which is great for the autotrophs that require CO2 to produce the food that heterotrophs eat. (See how it's all connected?)

Photosynthesis

(only autotrophs) the process by which plants and some other organisms use light energy from the Sun to convert water and carbon dioxide into high-energy carbohydrates such as sugars and starches and when plants remove hydrogen atoms from water to use in the sugars, they release oxygen as waste.

Photosynthesis equation

6CO2 + 6H2O ------> C6H12O6 + 6O2

Thylakoid

A flattened membrane sac inside the chloroplast used to convert light energy into chemical energy.

Granum

A stack of thylakoids in a chloroplast

ATP (adenosine triphosphate)

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. (when ATP supplies energy to a process, one of the phosphates gets transferred to another molecule, turning ATP into adenosine diphosphate. Cell recreate ATP from ADP by using energy from catabolic reactions to reattach phosphate group back into ADP.) This energy is used to drive endergonic reactions in cells. (energy from catabolic reactions is transferred to ATP, which then provides energy for anabolic reactions)

NADPH

An electron carrier involved in photosynthesis. Light drives electrons from chlorophyll to NADP+, forming NADPH, which provides the high-energy electrons for the reduction of carbon dioxide to sugar in the Calvin cycle.

Autotroph/Producer

An organism that makes its own food through photosynthesis. (plant, algae, green bacteria are examples of autotrophs)

cellular respiration equation

C6H12O6+6O2---> 6CO2+6H2O+ATP

catabolic reactions

Complex molecules are broken down to simpler ones and energy is released. (endergonic)

Glycolosys

During glycolysis, glucose breaks down into two molecules of pyruvate. The backbone of glucose has six carbon atoms, whereas the backbone of pyruvate has three carbon atoms. During glycolysis, energy transfers result in a net gain of two ATP and two molecules of the reduced form of the coenzyme NADH.

Why do we need food?

Energy Growth and repair Protection against diseases

Photosynthesis in depth

Photosynthesis occurs in two main steps: (i): The light reaction of photosynthesis transform light energy into chemical energy. The chemical energy is stored in the energy carrier ATP (during the light reactions of photosynthesis, chloroplasts absorb light energy from the Sun and then transform it into the chemical energy stored in ATP. When the light energy is absorbed, it splits water molecules. The electrons from the water molecules help with the energy transformation from light energy to chemical energy in ATP. Plants release the oxygen from the water molecules as waste, producing CO2 that you breathe) (ii): The light-independent reactions of photosynthesis produce food: ATP from the light reactions supplies the energy needed to combine carbon dioxide and water to make glucose. (To make glucose, plants first take carbon dioxide out of the air through a process called carbon fixation (taking carbon dioxide and attaching it to a molecule inside the cell). They then use the energy from the ATP and the electrons that came from water to convert the carbon dioxide to sugar.)

ATP/ADP cycle

Process by which cells regenerate ATP. ADP forms when a phosphate group is removed from ATP, then ATP forms again as ADP gains a phosphate group.

Krebs Cycle

Pyruvate is converted to acetyl-coA, which has two carbon atoms in its backbone. One carbon atom from pyruvate is released from the cell as CO2. For every glucose molecule broken down by glycolysis and the Krebs cycle, six CO2 molecules leave the cell as waste. (The conversion of pyruvate to acetyl-coA produces two molecules of carbon dioxide, and the Krebs cycle produces four.) During the Krebs cycle, acetyl-coA breaks down into carbon dioxide (CO2 ). The conversion of pyruvate to acetyl-coA produces two molecules of NADH. Energy transfers during the Krebs cycle produce an additional six molecules of NADH, two molecules of FADH2 , and two molecules of ATP.

oxidative phosphorylation

The coenzymes NADH and FADH2 carry energy and electrons from glycolysis and the Krebs cycle to the electron transport chain. The coenzymes transfer the electrons to the proteins of the electron transport chain, which pass the electrons down the chain. Oxygen collects the electrons at the end of the chain. (If you didn't have oxygen around at the end of the chain to collect the electrons, no energy transfer could occur.) When oxygen accepts the electrons, it also picks up protons (H+) and becomes water (H2O). While electrons are transferred along the electron transport chain, the proteins use energy to move protons (H+) across the inner membranes of the mitochondria. They pile the protons up like water behind the "dam" of the inner membranes. These protons then flow back across the mitochondria's membranes through a protein called ATP synthase that transforms the kinetic energy from the moving protons into chemical energy in ATP by capturing the energy in chemical bonds as it adds phosphate molecules to ADP. The entire process of how ATP is made at the electron transport chain is called the chemiosmotic theory of oxidative phosphorylation and is illustrated

stroma

The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

cellular respiration in depth

Three separate pathways combine to form the process of cellular respiration. The first two, glycolysis and the Krebs cycle, break down food molecules. The third pathway, oxidative phosphorylation, transfers the energy from the food molecules to ATP. (i) During glycolysis, which occurs in the cytoplasm of the cell, cells break glucose down into pyruvate, a three-carbon compound. (ii) After glycolysis, pyruvate is broken down into a two-carbon molecule called acetyl-coA. After pyruvate is converted to acetyl-coA, cells use the Krebs cycle (which occurs in the matrix of the mitochondrion) to break down acetylcoA into carbon dioxide. (iii) During oxidative phosphorylation, which occurs in the inner membrane or cristae of the mitochondrion), cells transfer energy from the breakdown of food to ATP.

Excess carbon dioxide

When plants have made more glucose than they need, they store their excess matter and energy by combining glucose molecules into larger carbohydrate molecules, such as starch. When necessary, plants can break down the starch molecules to retrieve glucose for energy or to create other compounds, such as proteins and nucleic acids (with added nitrogen taken from the soil) or fats (many plants, such as olives, corn, peanuts, and avocados, store matter and energy in oils).

Heterotroph/Consumer

organism that obtains food by consuming other living things

Calvin Cycle

reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugars