cell respiration

ATP

adenosine triphosphate, a nucleotide because it consists of the base adenine, 5 carbon sugar ribose and three negatively charged phosphate groups

properties that make ATP suitable for energy transfer

• soluble in water

• neutral pH

• cannot pass freely through the phospholipid bilayer

• third phosphate group can be easily removed and reattached through hydrolysis and condensation

• hydrolysis releases a small amount of energy

three types of activity that cells need energy for:

• synthesizing macromolecules through anabolic reactions

• active transport

• movement

interconversions between ATP and ADP

• nergy is released when ATP→ ADP

• energy is required to convert ADP and a phosphate back to ATP

• happens via chemosynthesis

cell respiration

• energy is released by oxidising carbohydrates, fats and proteins

• glucose and fatty acids are used as respiratory substrates

• cell respiration and gas exchange must occur together

aerobic respiration in animals and plants

glucose + oxygen →ADP converts to ATP→ co2 + h2o

anaerobic respiration in animals and plants:

glucose →ADP converts to ATP→ lactase

aerobic respiration in yeast and fungi

glucose →ADP converts to ATP→ ethanol + co2

lactate

waste product of anaerobic respiration in muscles, toxic in high concentrations, so limits the amount of anaerobic respiration and intense physical activity that can be done

is aerobic or anaerobic cell respiration more effective

aerobic

oxygen debt

demand for oxygen that builds up during anaerobic respiration

respirometers

• respirometers measure oxygen consumption

NAD

nicotinamide adenine dinucleotide, main electron carrier in respiration

oxidation and reduction

• occur together to transfer electrons, linked by electron carriers

• NAD+ 2 H+ + 2 e- → NADH+ H+ (or reduced NAD)

• reduction: gain of hydrogen, loss of oxygen

• oxidation: loss of hydrogen, gain of oxygen

glycolysis

first part of aerobic respiration: glucose or another monosaccharide is the substrate. this process happens in the cytoplasm of cells, where glucose is converted to pyruvate. a small amount of ATP is formed without using any oxygen

4 steps of glycolysis

1. phosphorylation of glucose

2. lysis

3. oxidation

4. ATP formation

phosphorylation of glucose

glucose is phosphorylated ( a phosphate is added, this step uses ATP because phosphorylation needs 2 ATP molecules) → glucose-6-phosphate is formed→ molecule is split in half→ fructose 6 phosphate→ second phosphorylation→ fructose-1,6-biphosphate

lysis

• fructose biphosphate→ split into two→ 2 triose phosphate

  • a triose phosphate is a simple sugar with 3 carbon atoms

oxidation

triose phosphates are oxidised (an H atom is removed)→ the H is accepted by NAD, turning it into reduced NAD→ triose phosphate with → second phosphate group is attached → biophosphoglycerate as product

ATP formation

bisphosphoglycerate (made of 2 molecules)→ each molecule yields 2 ATP so total 4 molecules→ ADP becomes ATP with a phosphate gruop beign added→ produces pyruvate (1 glucose→ 2 pyruvate)→ net yield of 2 ATPS because 2 were used in stage 1

NAD is regenerated when

2 hydrogen atoms are transferred to another molecule, oxidising reduced NAD.

lactic fermentation

NAD is also regenerated during the process when pyruvate is converted into lactate via oxidation. form of anaerobic cell respiration

anaerobic cell respiration in yeast

• ethanol fermentation: pyruvate can be converted to ethanol and co2 instead of lactate:

  1. decarboxylation reaction: co2 is removed from pyruvate → ethanal

  2. 2 hydrogens are transferred from reduced NAD to ethanal→ ethanol

  • this process is used in baking adn brewing

  • yeast: unicellular fungus that occurs naturally where sugar is available, respires aerobically or anaerobically.

  • yeast gives bread a lighter texture and helps it rise (co2 bubbles). ethanol evaporates during baking

  • beer making: starch→ converted to sugar using amylase→ fermentation

bioethanol

renewable energy source that can be used to fuel vehicles

krebs cycle:

cycle of oxidation of acetyl groups in the matrix of the mitochondrion. essential for aerobic respiration

oxaloacetate

4 carbon dicarboxylic acid

how many carbons in a citrate

6

link reaction

forms reduced NAD and acetylcoA, which is necessary to start the reaction

pyruvate moves into mitochondria→ decarboxylation occurs (one caroxyl group occurs, being removed as co2)→ coA is added→ pyruvate is oxidised and NAD is reduced,→ reduced NAD is formed→ acetylcoA (2 carbons)→ whole process happens twice → total of two molecules of reduced NAD and 2 molecules of acetylcoA are formed

krebs cycle steps

the acetylcoA is attached to oxaloacetate→ coA is removed→ left with citrate(6C)→ decarboxylation occurs leaving a 5C molecules (leaving behind a co2)→ 5C carbon gets oxididsed→ NAD is reduced to form reduced NAD→ 4C molecule, oxaloacetate→ one more molecule of NAD and another electron carrier, FAD is reduced to become reduced FAD and a molecule of ADP is reduced, which then forms 1 molecule of ATP

total results of the krebs cycle

• 2 co2, 3 NAD, 1 reduced FAD, 1 ATP, but the entire cycle will then repeat twice for each molecule of glucose, so the final results are 4 co2, 6 NAD, 2 reduced GAD and 2 ATP

  • 1 acetly group is consumed

electron transport chain

sequence of electron carrriers that pass electrons, occurs on the folds of the cristae

what happens on the electron transport chain

reduced NAD and FAD donate electrons to other electron carriers to continue the chain→ become just NAD and FAD→ some energy is freed every time an electron is donated, which is then used used for proton pumps to generate a high concentration gradient of protons in the intermembrane space of a mitochondrion.

reduced NAD

more energy, pumps 10 protons

reduced FAD

pumps 6 protons

chemiosmosis

movement of protons from a high concentration to a low concentration through ATP synthase to convert ADP to ATP

ATP synthase

a transmembrane protein that acts as channel protein for the facilitated diffusion of the protons and acts as an enzyme to catalyze the conversion of ADP to ATP

this process provides the most ATP

role of oxygen in the krebs cycle

at the end of the electron transport chain, there are electrons left over, which is where oxygen comes in as the terminal electron acceptor. oxygen combines with electrons and protons to create h2o. if oxygen runs out, → electrons are not removed→ reduced NAD accumulates→ link reaction and Krebs cycle stop

2 main regions of the ATP synthase:

• globular region that projects into the matrix

• section made of transmembrane units embedded in the inner mitochondrial membrane

the drum

consists of subunits, each of which has a binding site for a proton

two half channels

one allows protons to enter and bind to the drum, the other allows bound protons to exit to the matrix. the drum has to rotate for the protons to pass through, generating kinetic energy

stalk

connected to the drum, projects into the matrix. it rotates with the drum

rotor

drum and stalk

globular part

surrounds the stalk, consists of the α and β subunits

β subunits:

has an active site for catalysing the phosphorylation of ADP to ATP. during rotating, the subunit is changed→ ADP and phosphate groups bind to an active site→ atp released

rotor arm

prevents rotation of the α and β subunits. This consists of two parts (b2 and δ) linked to the proton channel (a).

predicting rates of ATP production:

• per turn of rotor: 3 β subunits→ 1 ATP

• one rotaton: requires 1 proton to pass through 10 subunits

• 2.5 ATP: 1 reduced NAD

• 1.5 ATp: 1 reduced FAD

lipids and carbohydrates as respiratory substrates:

• carbohydrates: anaerobic respiration is possible, and energy yield is 17 kj/g

• lipids: anaerobic respiration is not possible, and energy yield is 37 kj/g