Topic 5 summary notes (A Level Biology Edexcel B)

TOPIC 5

TYPES OF RESPIRATION
Respiration can occur in the presence of oxygen or without oxygen
~ AEROBIC RESPIRATION – occurs in the presence of oxygen
~ ANAEROBIC RESPIRATION – occurs without oxygen

Aerobic respiration produces more ATP molecules than anaerobic respiration so it’s more
desirable because the cell can produce more energy from it.

~ Aerobic respiration occurs in the cytoplasm and mitochondria
~ Anaerobic respiration only occurs in the cytoplasm

STAGES OF AEROBIC RESPIRATION
1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation in mitochondria

ANAEROBIC RESPIRATION – the partial break down of hexoses to produce a limited yield of
ATP in the absence of Oxygen.

ROUTES FOR PRODUCTS FORMED…
IN AEROBIC RESPIRATION ANAEROBIC RESPIRATION
~ In mitochondria ~ In cytoplasm
~ Complete oxidation ~ Incomplete oxidation
~ Waste products: H2O, CO2 ~ Waster products: lactic acid/ethanol and CO2
~ Net energy: 31 ATP ~ Net energy: 2ATP

STAGES OF RESPIRATION

FIRST STAGE = GLYCOLYSIS
~ Occurs in aerobic and anaerobic respiration
~ A glucose molecule is converted to 2 molecules of pyruvate
PYRUVATE – 3 carbon molecule which is used differently in aerobic and anaerobic
respiration (2 pathways)
~ It requires coenzyme NAD
~ Occurs in the cytoplasm and produces pyruvate
~ NAD helps enzymes carry out the removal of H atoms from molecules
~ OXIDATION REACTION – the removal of H atoms
~ NAD helps enzymes that catalyse oxidation reactions by accepting and carrying the
hydrogen atoms that have been removed (NAD is a carrier)

SUMMARY PROCESS OF GLYCOLYSIS
1. Glucose is phosphorylated to make phosphorylated glucose
2. Phosphorylated glucose gets split into 2 molecules

, 3. Oxidation of the split glucose to form 2 pyruvates
PROCESS IN DETAIL
1. Add 2 phosphate molecules to a glucose molecule to produce hexose bisphosphate
~ PROCESS = GLUCOSE PHOSPHORYLATION
~ Glucose becomes more reactive so it can be split more easily
~ The 2 phosphate molecules are taken form 2 ATP molecules which are
hydrolysed to obtain the phosphates

2. The hexose bisphosphate is split to produce 2 molecules of triose phosphate
~ Enzymes called dehydrogenase enzymes remove a hydrogen atom from each
of the triose phosphate molecules
~ OXIDATION takes place and each H atom is accepted by a molecule of NAD
(2NAD needed)
~ NAD molecules with H atoms are REDUCED

3. The phosphates from each trisphosphate molecule make 2 ATP molecules each
(4ATP)
~ 2 molecules of pyruvate form from 2 phosphate molecules

SUMMARY - WHATS PRODUCED AT THE END
~ 2 pyruvate molecules
~ 2 reduced NAD molecules
~ A net of 2ATP molecules (4 ATP form)

PYRUVATE TRANSPORT FOR AEROBIC RESPIRATION
The pyruvate has the potential to be broken down further to release more energy
~ If oxygen is absent – ANAEROBIC RESPIRATION
~ If oxygen is present – AEROBIC RESPIRATION
So pyruvate needs to be transported into the mitochondrial matrix for the next stages of
respiration.

1. Pyruvate is actively transported across the mitochondrial envelope and into the
matrix by a transport protein called the pyruvate-H+ symport which requires active
transport which uses ATP
SYMPORTER = takes 2 things and transports them together
~ There’s a hydrogen ion that goes with the pyruvate into the matrix

SECOND STAGE = LINK REACTION
~ It involves the conversion of pyruvate to a 2-carbon acetyl group and takes place int
the mitochondrial matrix.

PROCESS
1. From glycolysis which forms a 3C pyruvate, the link reaction converts it to acetyl 2C
2. A carboxyl group and hydrogen atoms are removed from the pyruvate
~ When a carboxyl group is removed the process is called DECARBOXYLATION