C1.2 - cell respiration Flashcards
What is ATP?
ATP – THE ENERGY UNIT OF THE CELL
ATP stands for adenosine triphosphate.
When ATP is split into ADP (adenosine diphosphate) and phosphate energy is released
How much energy does ATP release and what reaction takes place when a phosphate is removed?
Removing 1 phosphate group from each molecule in one mole of ATP releases 30.5 kJ of energy
This is a hydrolysis reaction (requires water), and is catalysed by enzymes called ATPases
What is the ATP to ADP cycle?
ATP to ADP is hydrolysis
ADP to ATP is condensation
Can you name some biochemical processes which require the use of ATP?
Biochemical processes that utilise ATP include:
Biosynthesis of macromolecules (e.g. polymer assembly)
Active transport
Nerve transmission (e.g. propagation of action potentials)
Growth and repair (e.g. mitotic division)
Movement (e.g. muscle contraction)
Emission of light (e.g. bioluminescence)
Acronym to remember = BANG ME
What is NADH
The most common hydrogen carrier is NAD+ which is reduced to form NADH (NAD+ + 2H+ + 2e– → NADH + H+)
What is FAD
A less common hydrogen carrier is FAD which is reduced to form FADH2 (FAD + 2H+ + 2e– → FADH2)
What are the 4 phases of cell respiration?
GLYCOLYSIS – glucose converted to pyruvate (cytoplasm)
LINK REACTION – in mitochondria
KREBS CYCLE – acetyl CoA converted to carbon dioxide (mitochondria)
ELECTRON TRANSPORT SYSTEM – Hydrogen ions converted to water and bulk of ATP synthesised (mitochondria)
What is glycolysis and can you name what is formed?
Series of reactions in which a 6C sugar is broken down into two 3 Carbon sugars (triose phosphate) and then pyruvate
This happens in the cytoplasm
Occurs in 4 stages and oxygen is not required
Phosphorylation
Lysis
Oxidation
ATP formation
After lysis each reaction happens twice so 4 molecules of ATP are formed but since 2 were needed at the start of the reaction there is a net gain of 2 ATP
2 pyruvates are also formed
Oxidation of NAD
Dehydrogenase enzyme works with NAD (coenzyme) to remove Hydrogen from Triose Phosphate
NAD accepts H ions and electrons and therefore forms REDUCED (NADH) and H+
2NAD+ + 4H+ + 4e- 🡪 2NADH + 2H+
Can you outline the steps of the link reaction?
Occurs in mitochondria
Pyruvate diffuses into matrix of mitochondria for metabolism
Pyruvate is decarboxylated
Pyruvate is also oxidised.
Forming NADH and an acetyl group (2 Carbon)
This joins with coenzyme A.
This connects glycolysis to the Krebs cycle
(which is why we call it the Link Reaction)
Can you outline the steps of the krebs cycle?
- ACoEA from link reaction combines with 4 Carbon called Oxaloacetate to form Citrate (6 Carbon)
Coenzyme A goes back into Link Reaction
- 6C citrate converted to 5C compound
When a Carbon dioxide is removed, this is decarboxylation
Dehydrogenation/oxidation also occurs
H removed by NAD
Forming reduced NAD
- 5C molecule converted to 4C molecule (oxaloacetate)
Decarboxylation and dehydrogenation occur
Another co enzyme (FAD) works alongside NAD to remove hydrogen and get reduced
ATP produced by direct transfer of phosphate from an intermediate compound (name not needed) to ADP
This is substrate level phosphorylation (direct transfer of phosphate from one group to another)
Summary (per cycle):
TWO molecules of Carbon Dioxide lost (separate reactions)
ONE molecule of ATP formed
THREE molecules of NADH
ONE molecule of reduced FAD (another H acceptor molecule)
The whole cycle turns TWICE per glucose
What is the electron transport chain?
Electrons are passed between the carriers and energy is transferred to ADP and Pi (forming ATP)
This is controlled and the energy can be used by the cell
Can you outline what happens in the electron transport chain?
1.
NAD reduced and FAD reduced (from Krebs Cycle) have their protons (hydrogen ions) removed by dehydrogenase enzyme
They become NAD+ and FAD+ (reused in Krebs Cycle)
H atom splits into protons (H+) and Electrons (e-)
2.
e- move along the electron transport chain (three proteins, embedded in the membrane that act as electron carriers)
They lose energy at each carrier
3.
The energy that the e- lose along the ETC is used to pump protons (H+) from the matrix, into the intermembrane space
- The concentration of protons (H+) is now higher in the intermembrane space than the matrix, forming a proton (or electrochemical) gradient of H+ ions
5.
H+ move down the gradient back into matrix via ATP synthase. This movement drives the synthesis of ATP from ADP and Pi
This movement is called CHEMIOSMOSIS
6.
Back in the matrix at the end of the ETC, H+, e- and Oxygen (from the blood) combine to form water. Oxygen is called the final electron acceptor
What is oxidative phosphorylation?
Final stage of aerobic respiration (2 phases – electron transport chain and chemiosmosis)
Remember those H+ that were produced in Glycolysis, Link Reaction and Krebs Cycle
They get transported (along with their electrons) along a series of carriers
To be combined with oxygen to form water
