respiration1 Flashcards
1
Q
What is cellular respiration?
A
The breakdown of complex organic molecules linked to the synthesis of ATP • Glycolysis • Link reaction (or fermentation for anaerobic respiration) • Krebs cycle • Electron transport chain
2
Q
What is glycolysis?
A
• Anaerobic process • Glucose (6 carbon sugar), split into two smaller pyruvate molecules (3 carbon molecules) • ATP and reduced NAD (nicotinamide adenine dinucleotide) are also produced
3
Q
What are the main steps in
glycolysis?
A
1. Phosphorylation of glucose to hexose bisphosphate using ATP 2. Lysis - splitting each hexose bisphosphate molecule into into 2 triose phosphate molecules 3. Phosphorylation - adding another phosphate group to each triose phosphate forming triose bisphosphate molecules, using free inorganic ions present in the cytoplasm 4. Oxidation (aka dehydrogenation) of each triose bisphosphate to form 2 pyruvate molecules. NAD coenzymes (from dehydrogenase enzymes) accept the removed hydrogens, and they are reduced to form reduced NAD molecules. At the same time 4 ATP molecules are produced using phosphates from the triose bisphosphate molecules
4
Q
How is glycolysis an example
of substrate level
phosphorylation?
A
ATP is formed without the involvement of the electron transport chain • ATP is formed by the transfer of a phosphate group from the phosphorylated intermediate (triose bisphosphate) to ADP
5
Q
What is the overall net ATP
yield from glycolysis?
A
• 2 ATP molecules are used to prime the process at the beginning • 4 ATP molecules are produced • Overall net ATP yield is 2 molecules of ATP
6
Q
What is the reduced NAD used
for?
A
Used in a later stage to synthesise
more ATP
7
Q
Describe the structure of
mitochondria in eukaryotic
cells
A
• Outer mitochondrial membrane - separated the contents of the mitochondrion from the rest of the cell, creating a cellular compartment with ideal conditions for aerobic respiration • Inner mitochondrial membrane - contains electron transport chains and ATP synthase • Cristae - projections of the inner membrane which increase the surface area available for oxidative phosphorylation • Intermembrane space - proteins are pumped into this space by the electron transport chain. The space is small, so concentration builds up quickly • Matrix - contains enzymes for the Krebs cycle and the link reaction, also contains mitochondrial DNA
8
Q
What takes place in the
matrix?
A
The link reactions and the Krebs
cycle
9
Q
What does the matrix contain
to help with its function?
A
• Enzymes that catalyse the stages of the reactions • Molecules of the coenzymes NAD and FAD • Oxaloacetate - 4-carbon compound that accepts the acetyl group from the link reaction • Mitochondrial DNA • Mitochondrial ribosomes
10
Q
What does the outer
membrane contain to help with
its function?
A
• Made up of phospholipids • Contains proteins, some of which form channels or carriers that allow the passage of molecules e.g. pyruvate, into the mitochondrion
11
Q
What does the inner membrane
contain to help with its
function?
A
• Lipid bilayer • Less permeable to small ions e.g. H+, than the outer membrane • Folds into cristae to give large surface area for electron carrier and ATP synthase enzymes
12
Q
What does the intermembrane
space contain to help with its
function?
A
In close contact with the mitochondrial matrix, so the molecules of reduced NAD and FAD can easily deliver hydrogens to the ETC
13
Q
Electron transport chain
A
ATP Synthase Enzymes
14
Q
What is the link reaction also
known as?
A
Oxidative decarboxylation
15
Q
What happens in the link
reaction?
A
Pyruvate is decarboxylated and dehydrogenated, catalysed by pyruvate dehydrogenase • No ATP is produced during this reaction
16
Q
What are the steps in the link
reaction?
A
1. The carboxyl group is removed and is the origin of some of the CO2 produced during respiration 2. This decarboxylation of pyruvate, together with dehydrogenation, produces an acetyl group 3. The acetyl group combines with coenzyme A (CoA) to become acetylcoenzyme A (acetyl CoA) 4. The coenzyme NAD becomes reduced by accepting hydrogen • The overall process is known as oxidative decarboxylation (decarboxylation because CO2 is removed, and oxidation because hydrogen is removed) Reactants: 2 pyruvate + 2NAD + 2CoA Products: 2CO2 + 2 reduced NAD + 2 acetyl CoA
17
Q
How does pyruvate enter the
mitochondrial matrix?
A
By active transport via specific
carrier proteins
18
Q
What happens to the products
of the link reaction?
A
Acetyl CoA delivers the acetyl group to the next stage of aerobic respiration - the Krebs cycle • Reduced NAD is used in oxidative phosphorylation to synthesise ATP • CO2 with either diffuse away and be removed as a metabolic waste, or be used as a raw material in photosynthesis
19
Q
Where does the Krebs cycle
take place?
A
In the mitochondrial matrix. Each
complete cycle results in the
breakdown of an acetyl group
20
Q
What are the stages in the
Krebs cycle?
A
1. The acetyl group released from acetyl CoA combines with oxaloacetate (4-carbon compound) to form citrate (6- carbon compound) 2. Citrate is decarboxylated and dehydrogenated, producing a 5- carbon compound, 1 CO2 and 1 reduced NAD 3. This 5-carbon compound is further decarboxylated and dehydrogenated, producing a 4- carbon compound, 1 CO2 and 1 reduced NAD 4. 4-carbon compound temporarily combines with and is them released from coenzyme A. Substrate-level phosphorylation takes place, producing one molecules of ATP 5. 4-carbon compound is dehydrogenated, producing a different 4-carbon compound and 1 reduced FAD 6. Rearrangement of atoms in the 4-carbon molecule is catalysed by an isomerase enzyme, followed by further dehydrogenation. Oxaloacetate is regenerated so the cycle can continue
28
Q
What is the total ATP
theoretical yield per molecule
of glucose in aerobic
respiration?
A
38
Q
What are the steps in alcoholic
fermentation?
A
1. Each molecule of pyruvate produced during glycolysis is decarboxylated and converted into ethanal. Catalysed by pyruvate decarboxylase 2. Ethanal accepts hydrogen atoms from reduced NAD, and is reduced to ethanol. Catalysed by ethanol dehydrogenase 3. Reduced NAD is re-oxidised and made available to accept more hydrogen atoms from triose phosphate, so glycolysis can continue
39
Q
What are the steps in the
lactate fermentation pathway?
A
1. Pyruvate produced during glycolysis, accepts hydrogen atoms from the reduced NAD, also made during glycolysis. Catalysed by lactate dehydrogenase • Pyruvate is reduced to lactate • The reduced NAD becomes reoxidised 2. Reoxidised NAD can accept more hydrogen atoms from triose phosphate during glycolysis, so glycolysis can continue to produce enough ATP to sustain muscle contraction for a short period
45
Q
How are lipids respired?
A
1. Using energy from the hydrolysis of 1 ATP to 1 AMP, each fatty acid is combined with CoA 2. The fatty acid-CoA complex is transported into the mitochondrial matrix and broken down into 2-carbon acetyl groups, each attached to CoA 3. This beta oxidation pathway generated reduced NAD and reduced FAD 4. The acetyl groups are released from CoA, and enter the Krebs cycle
47
Q
How are proteins respired?
A
• Excess amino acids are deaminated in the liver • The rest of the amino acid molecule (a kept acid) enters the respiratory pathway as pyruvate, acetyl CoA, or a Krebs cycle acid e.g. oxaloacetic acid
51
Q
A
