subject guide notes

C1.2.1—ATP as the molecule that distributes energy within cells

Adenosine triphosphate is an RNA nucleotide

is composed of:

nitrogenous base adenine

5-carbon sugar ribose

tail of 3 phosphate molecules

it can be exchanged for different biochemical processes

C1.2.2—Life processes within cells that ATP supplies with energy

active transport across membranes

transport of molecules is often passive

but when the molecules are moved against their concentration gradient, then active transport is used

• ATP binds to the transport molecule

• it releases its 3rd phosphate & the energy is transferred to the transport molecule

anabolism

ATP is used to form the peptide bonds holding together amino acids

movement

ATP provides energy for muscle contraction

C1.2.3—Energy transfers during interconversions between ATP and ADP

hydrolysis reaction needed to convert ATP to ADP

• the third phosphate in the phosphate tail is broken off

  • water is added

• is an exergonic reaction = energy is released

generation of ATP involves addition of third phosphate

• water is removed & temporarily stores the energy

• is an endergonic reaction = energy required to synthesize ATP

• process of adding a phosphate is known as phosphorylation

C1.2.4—Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds

cell respiration is the main process that provides cells with energy

glucose is the main respiratory substrate

• if its used up or absent - lipids or fatty acids are used as respiratory substrate

• if no carbs or lipids available - proteins & amino acids are used (last reserve)

is different from gas exchange, which occurs in the alveoli of lungs & is used to transport oxygen to cells in body, and carry carbon dioxide away from them

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans

*for the equations, its just “respiratory substrate + smthg = waste products + ATP”

mitochondria is required only for aerobic respiration (cuz this respiration occurs in the mitochondria)

anaerobic respiration can be effective in generating a large amount of ATP for short, intense exercises, such as sprinting

C1.2.6—Variables affecting the rate of cell respiration

temp, pH, substrate concentration & oxygen concentration - factors that affect rate of cell respiration

respirometer is an apparatus that measures rate of respiration

C1.2.7—Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration

NAD (Nicotinamide adenine dinucleotide) is a coenzyme

• it can be reduced & oxidised, allowing it to function as a hydrogen carrier

NAD will oxidise other molecules & accept those released electrons (becomes reduced)

in cell respiration - this involves the transfer of hydrogen

• hydrogen contains electrons

• molecule oxidised is also dehydrogenated

NAD becomes reduced - NADH

is important cuz NADH now carries electrons & hydrogen ions (protons), which drive oxidative phosphorylation at the end of aerobic respiration

redox reactions involve both oxidation & reduction

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD

in both aerobic & anaerobic cell respiration, the first step is glycolysis

occurs in cytoplasm

involves splitting of 1 glucose molecule (6-carbon compound) into 2 molecules of pyruvate (3-carbon compound)

each step of glycolysis is catalysed by its own enzyme

4 main phases

phosphorylation

2 molecules of ATP phosphorylate glucose molecule

• one phosphate is transferred from the ATP to the glucose

• so ATP becomes ADP

makes glucose unstable

lysis

glucose is split into 2, forming 2 G3P molecules

oxidation

each G3P molecule is dehydrogenated & oxidised

2 molecules of NAD are reduced to 2 molecules of NADH

ATP formation

each G3P undergoes substrate-level phosphorylation

this produces 2 molecules of ATP & produces 2 pyruvate

1 glucose = use 2 ATP = produce 2 ATP = uses 2 NAD & NADH = 2 pyruvate

C1.2.9—Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration

allows NAD to be regenerated so that glycolysis can continue & ATP can be produced

NAD is regenerated by reducing the pyruvate & converting it into lactate

• NADH is oxidised to NAD

the NAD can now be used again during the oxidation phase of glycolysis

• is known as lactic acid fermentation

i think ATP is also produced

C1.2.10—Anaerobic cell respiration in yeast and its use in brewing and baking

besides the regeneration of NAD, the pathways of anaerobic cell respiration are the same in humans & yeast

anaerobic respiration in yeast produces 2 products: CO2 & ethanol

when yeast respire anaerobically, this is how they regenerate their NAD through one of these different methods:

decarboxylation

decarboxylate the pyruvate, releasing CO2 molecule

this converts pyruvate into ethanal

reduced

the ethanal is then reduced by NADH into ethanol

this regenerated NAD & ATP

again, each step in the process uses its own enzyme

yeast is used in baking

• it feeds on the sugars in the dough & respires anaerobically

• carbon dioxide thats produced, causes the bubbles to rise

• any ethanol produced, evaporates away during the baking process

in brewing, yeast feeds on the sugars

• the ethanol produced is the desired product of this fermentation process

• carbon dioxide

C1.2.11—Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration

in link reaction, each pyruvate is converted into acetyl CoA

the 2 pyruvates move to matrix of the mitochondria via active transport

they undergo oxidative decarboxylation

• so enzymes remove one hydrogen (which contains electrons) & one carboxyl group

NAD reduced to NADH

each pyruvate is now a 2-carbon acetate

they each combine with molecule coenzyme A & form 2 molecules of acetyl CoA

NOTE - CoA can oxidise fatty acids in order to produce Acetyl CoA with 2 carbons

this reaction is slower, but is possible

C1.2.12—Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

Krebs Cycle is a series of chemical reactions that completes the breakdown of glucose & produces ATP, NADH & FADH

occurs in mitochondrial matrix

acetate from the acetyl CoA, binds with oxaloacetate (4 carbon molecule) = citrate/citric acid (6-carbon compound)

• releases coenzyme A back to continue the link reaction

oxidative decarboxylation occurs

• CO2 molecule remove

• NAD reduces to NADH

• citrate is oxidised & dehydrogenated into a 5-carbon compound

oxidative decarboxylation occurs again

• CO2 molecule released

• NAD reduced to NADH

• one ATP molecule generated through substrate-level phosphorylation

• remaining carbon compound now has 4 carbons left

  • all 6 of the carbons from the original glucose molecule hv been released as 6 molecules of carbon dioxide

but oxaloacetate has to be regenerated in order to continue the cycle

• the 4-carbon compound is oxidised

  • reduces NAD to NADH

  • reduces FAD to FADH₂

oxaloacetate can now bind with another acetate

*this cycle occurs once for each pyruvate

since 2 pyruvates were formed from the link reaction, the Krebs Cycle works twice

C1.2.13—Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion

occurs in the inner mitochondrial membrane

involves using the reduced FAD & NAD to produce many ATP molecules

ETC is composed of 4 membrane-bound protein complexes & 2 electron carriers

NADH delivers 2 electrons its carried from either glycolysis, link reaction or Krebs Cycle, to the first protein complex

• the electrons power the pumping of hydrogen ions/protons across the membrane to the intermembrane space

  • hydrogen ions hv to be pumped cuz the membrane is impermeable to them & they’re moving against their concentration gradient

also when the electrons are passed, there’s a transfer of energy

• NADH oxidises to NAD

as electrons are transported along the ETC, they pump more H+

• but they lose their energy as they travel through the ETC

FADH₂ delivers its 2 electrons to the second protein complex = fewer protons pumped

C1.2.14—Generation of a proton gradient by flow of electrons along the electron transport chain

narrow space between inner & outer membrane & protons dont diffuse across membrane by themselves = high proton concentration established in intermembrane space

• forms proton gradient across inner membrane

  • high concentration on intermembrane side

  • low concentration on matrix side

the membranes prevent H+ from moving down their concentration gradient

C1.2.15—Chemiosmosis and the synthesis of ATP in the mitochondrion

chemiosmosis is the process where energy stored in the proton gradient is used to produce ATP

H+ hv to move through ATP synthase in order to move down their concentration gradient & move back across the inner membrane

the proton motive force (flow of protons) releases the required energy to phosphorylate ADP using inorganic phosphate, & form ATP

• is called oxidative phosphorylation

as H+ flow through ATP synthase, it rotates & generates ATP

C1.2.16—Role of oxygen as terminal electron acceptor in aerobic cell respiration

once electrons hv passed through ETC, they need somewhere to go

oxygen is the terminal electron acceptor in the ETC

• each oxygen molecule splits & accepts 4 electrons & 4 protons (H+)

• becomes 2 water molecules

when oxygen isn’t present to accept these electrons, more electrons cant join the ETC

• NAD & FAD cant be regenerated by oxidation, meaning there’s no supply of these hydrogen carriers to continue the link reaction & krebs cycle

C.1.2.17—Differences between lipids and carbohydrates as respiratory substrates

amount of hydrogen available when molecule breaks down = determines the energy content of a respiratory substrate

• more hydrogen = more NAD can be reduced = more protons transported across inner membrane = greater proton motive force = more ATP production

disadvantage - oxygen needed

lipids can reduce more NAD than carbs (like glucose)

• is cuz they hv long chains of carbons with hydrogens

anaerobic respiration occurs only if glucose is substrate ( i think cuz lipids cant be broken down through glycolysis)

lipids cannot be broken down through glycolysis

when lipid molecule is respired, its broken down into glycerol & fatty acids

• glycerol used in glycolysis

• fatty acids broken down into acetyl groups

  • become acetyl CoA through link reaction

lipids also produce a higher yield of ATP compared to carbs & proteins