Respiration Flashcards
Aerobic respiration
Requires oxygen and produces carbon dioxide, water and much atp
Anaerobic respiration
Takes place in the absence of oxygen and produces lactate(animals) or ethanol and carbon dioxide (plants and fungi) but only a little atp in both cases
What are the 4 stages of aerobic respiration
- Glycolysis
- Link reaction
- Krebs cycle
- oxidative phosphorylation
1)Glycolysis
Where it occurs and what processes occurs
-Occurs in cytoplasm
-a hexose (6-carbon) sugar, usually glucose, is split into two molecules of the 3-carbon molecule, pyruvate
-the number of smaller enzyme controlled reactions can be grouped into 4:
•phosphorylation of glucose to glucose phosphate (glucose is made more reactive by adding two phosphate molecules)
•splitting of the phosphorylated glucose(each glucose molecule is split into two 3-carbon molecules known as triose phosphate)
•oxidation of triose phosphate (hydrogen is removed from each TP molecules and transferred to a hydrogen carrier molecule known as NAD to form reduced NAD
•the production of atp (enzyme controlled reactions convert each triose phosphate into another 3-carbon molecule called pyruvate. Two molecules of atp are regenerated from adp.
-the overall yield from glycolysis is two molecules of atp, two molecules of reduced NAD and two molecules of pyruvate.
2)The link reaction
-the pyruvate made during glycolysis are actively transported into the matrix of the mitochondria. Here reactions take place:
•pyruvate is oxidised to acetate (3-carbon pyruvate loses a CO2 and two hydrogen molecules.
•the 2-carbon acetate combines with W molecule called coenzyme A to produce a compound called acetylcoenzyme A
-equation: pyruvate + NAD +coA = acetyl CoA + reduced NAD + CO2
3)Krebs cycle
-occurs in matrix of mitochondria
•the 2-carbon acetylcoA from kink combines with a 4-carbon molecule to produce a 6-carbon molecule
•this 6-carbon molecule loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP produced as a result of substrate level phosphorylation
•the 4-carbon molecule can now combine with a new molecule of acetylcoA to begin the cycle again.
-is important as it breaks down macromolecules into smaller ones, produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation, regenerated the 4-carbon molecule that combines with acetylcoenzymeA (which would otherwise accumulate) and it is a source of intermediate compounds used by cells in the manufacture of important substances.
Coenzymes
Not enzymes, but molecules
Eg NAD
FAD
NADP
For each molecule of pyruvate, the link reaction and Krebs cycle produce
- reduced coenzymes such as NAD and FAD
- one molecule of ATP
- three molecules of carbon dioxide
Oxidative phosphorylation
-occurs in mitochondria within the Cristae
Involves the transfer of electrons down the electron transfer chain: chemiosmotic theory:
-hydrogen atoms (from glycolysis and krebs) combine with coenzymes NAD and FAD
-reduced NAD and FAD donate electrons of hydrogen atoms to the first molecule in the electron transfer chain
-electrons pass along the chain in a series of oxidation reduction reactions, releasing energy causing active transport of protons across the inner mitochondrial membrane and into the inner mitochondrial space.
-protons accumulate in inter membranal space before diffusing back to mitochondrial matrix through ATP synthase channels embedded in inner mitochondrial membrane
-end of chain. electrons combine with these protons and oxygen to form water. oxygen is therefore the final acceptor of electrons in the chain
the greater the energy released in a step, the more of it is released as heat and the less there is available for more useful purposes. when energy is released a bit at a time, more can be harvested for benefit of organism. thus passed along chain, each with slightly lower energy level–down an energy gradient (energy released gradually and usefully.)
what are the alternative respiratory substrates?
lipids and proteins (don’t need to be converted to carbohydrate first)
respiration of lipids
before they are first hydrolysed to glycerol and fatty acid:
- glycerol is phosphorylated and converted to TP which enters glycolysis and krebs
- fatty acid is broken down to 2-carbon which is converted to acetyl coenzyme A whcich enters krebs
produces 2-carbon and many hydrogen atoms, thus release more than double the energy of the same mass carbohydrate
respiration of prteins
is firdst hydrolysed to amino acids->amino group is rmeoved (deamination) before entering the respiratory pathway at different points (depemding on number of carbon)
3-carbon compounds >pyruvate
4-and5-carbon compounds>intermediates in krebs
what will occur if aerobic respiration ran out of oxygen?
the krebs and electron transfer chain cannot continue cus soon all the FAD and NAD will be reduced.
- for glycolysis to continue, products of pyruvate and hydrogen must be constantly removed or glycolysis will stop.
- replenishment of NAD is achieved by pyruvate molecule from glycolysis accepting the hydrogen from reduced NAD
where can anaerobic respiration occur?
plants
microorganisms (yeast)