Cell Structure and Function - Harvesting Chemical Energy Flashcards
What is ATP?
ATP is the energy that powers cellular work
What releases energy?
The hydrolysis of ATP to ADP and inorganic phosphate releases energy
What is an anabolic pathway?
are the metabolic pathways that construct molecules, requiring energy. Complex molecules are formed from simple molecules
What is a catabolic pathway?
is the metabolic pathways that break down molecules, releasing energy. Complex molecules are broken down into simple molecules
What is an example of a catabolic pathway?
glycogen being broken down into glucose
Are catabolic and anabolic reaction spontaneous?
No
What are the main fuels needed to generate ATP?
Carbohydrates (which are broken down into simple sugars)
Proteins (which are broken down into amino acids)
Fats (which are broken down into simple fats)
What is cellular respiration?
Is the controlled release of energy from organic compounds to produce ATP
What are the four stages of cellular respiration?
Glycolysis, pyruvate oxidation, citric acid cycle, electron transport chain (chemiosmosis)
Where does glycolysis occur?
In the cytosol of the cell
Where does pyruvate oxidation occur?
The mitochondrial matrix
Where does the citric acid cycle occur?
The mitochondrial matrix
Where does the electron transport chain occur?
The inner mitochondrial membrane
Is oxygen required for glycolysis?
No
What is an aerobic reaction?
A reaction requiring oxygen
What is an anaerobic reaction?
A reaction that doesn’t require oxygen
What is invested in glycolysis?
2 ATP molecules
What occurs in the energy investment phase of glycolysis?
Two ATP molecules are invested
6 carbon glucose is split into two 3 carbon molecules (Glyceraldehyde 3-phosphate)
2 ADP is formed
What occurs in the energy payoff phase of glycolysis?
Four ATP molecules are produced
The two 3 carbon molecules are converted into two molecules of Pyruvic acid (pyruvate)
2 NADH are formed
Net products of glycolysis
2 Pyruvic acid molecules and 2 H2O molecules
2 ATP (4 ATP formed - 2 ATP invested)
2 NADH + 2H+ (from 2 NAD+, 4e- and 4H+)
What is produced in the anaerobic reaction that occurs when there isn’t enough oxygen present?
Lactic acid
2 Pyruvic acid (is oxidised) + 2NADH → 2 Lactic acid + 2NAD+
Does pyruvate oxidation require oxygen?
Yes
What steps does pyruvate oxidation link?
Glycolysis and the citric acid cycle
What is pyruvate dehydrogenase?
An enzyme that converts pyruvic acid into an acetyl group (2 carbons)
What is lost when pyruvic acid is broken down into an acetyl group?
A CO2 molecule and a H+ and H-
What picks up the H- lost by pyruvic acid in pyruvate oxidation?
the NAD+ which is reduced to NADH
Where does the H+ go in pyruvate oxidation
It is released into the mitochondrial matrix
What is coenzyme A?
The enzyme that attaches itself to the acetyl group in pyruvate oxidation, producing acetyl coenzyme A (or Acetyl CoA)
Net products of pyruvate oxidation
2 NADH (1 NADH per pyruvate)
2 CO2 molecules (1 per pyruvate)
2 Acetyl CoA (1 per pyruvate)
Does pyruvate oxidation produce ATP?
No
Does the citric acid cycle require oxygen?
Yes
Describe the reaction occurring within the citric acid cycle
Is a series of reactions where the products of each reaction act as a substrate for the next reaction
What is citrate converted into?
Isocitrate
How is a-keto glutarate formed?
Oxidative decarboxylation of isocitrate
Name of the enzyme that oxidises isocitrate
isocitrate dehydrogenase.
Net products of citric acid cycle
1 ATP 3 NADH 1 FADH2 2 CO2 ^ All per 1 PYRUVATE MOLECULE It is DOUBLE for glucose
What is substrate phosphorylation?
A metabolic reaction which results in the formation of ATP by the direct transfer of a phosphate group to ADP.
Gylcolysis and citric acid cycle make ATP via substrate phosphorylation
What is Oxidative Phosphorylation?
The process by which ATP is formed as a result of the transfer of electrons from NADH and FADH2 to oxygen by a series of electron carriers.
The electron transport chain and chemiosmosis make ATP via oxidative phosphorylation
Does the electron transport chain require oxygen?
Yes
What are the electron donors in the electron transport chain?
The NADH and FADH2 from glycolysis and citric acid cycle.
They are oxidised to donate 1 or 2 electrons
What do electrons move between in the ETC?
Each electron gives up a small amount of energy which enables H+ ions to be pumped into the inter membrane space (ie the space between the inner and outer mitochondrial membranes)
What is the function of oxygen in the electron transport chain?
Acts as the final electron acceptor at the end of the chain
Pull the electrons down the chain
Is reduced to form water
What happens if cyanide is present in the ETC? (What can block electrons from reaching oxygen and cause the death of the cell)
Cyanide blocks complex 4 (one of the ETC proteins)
It prevents the electrons reaching oxygen, they cannot form H2O and thus ATP
Causes them to die rapidly and the ETC process would be unable to occur
What protein is involved in chemiosmosis?
ATP synthase
What is chemiosmosis?
The electron transport chain results in many H+ ions being pumped into the inter-membrane space
This generates a concentration gradient where hydrogen ions in the inter-membrane space rush down the gradient through ATP synthase
The rush of H+ ions causes the turbine within ATP synthase to turn. This rotation enables the phosphorylation of ADP to generate ATP.
How much ATP is produced by chemiosmosis?
26 or 28 ATP
What can be used to derive energy from apart from glucose?
Fats, proteins, complex carbohydrates
However, they enter cellular respiration at different points: Monomers enter glycolysis and the citric acid cycle at different points
What is Phosphofructokinase?
Rate limiting for glycolysis.
What inhibits phosphofructokinase?
Inhibited by citrate and ATP
Ie the products of cellular respiration
What stimulates phosphofructokinase?
Stimulated by AMP
This accumulates when ATP is being used rapidly
What is homeostasis? (in respect to blood glucose)
Keeping things within physiological tolerable limits
Too much glucose = hyperglycaemia
Too low glucose = hypoglycaemia
What happens when there is an increase in blood glucose levels (hyperglycaemia)?
Must have levels > 6mmol/L
This is detected by beta cells in the islets of langerhans in the pancreas (RESPONSE)
Insulin binds to body cells causing them to take up glucose in to the cells. This decreases blood glucose levels and homeostasis is restored.
What happens when there is a decrease in blood glucose levels (hypoglycaemia)?
Homeostasis is disturbed by a decrease in blood glucose levels (ie <4mmol/L)
This is detected by alpha cells in the islets of lagerhands in the pancreas
Alpha cells release glucagon into the blood
Glucagon binds to liver, skeletal muscle cells and causes them to break down glycogen (stored glucose) into glucose. This increases blood glucose levels and homeostasis is restored.
What type of glands are in the Islets of Langerhan?
Pancreatic islets
What is insulin?
Produced by beta cells in the islets of langerhans in the pancreas
What happens if you lose the function of insulin?
Diabete mellitus occurs
What is diabetes mellitus?
When the ability to produce or respond to the hormone insulin is impaired.
This results in abnormal metabolism of carbohydrates and elevated levels of glucose in the blood ( > 7mmol/L)
What is type 1 diabetes?
Body does not produce insulin, as beta cells of the pancreas are destroyed (often autoimmune, genetic or through environmental factors)
Affects 5-10% of diabetics
Typically has an early onset - children or adolescents
Requires insulin replacement (injections)
What is type 2 diabetes
Body produces insulin and is present within blood, but, the insulin receptors are impaired (insulin resistance)
Most (> 90%) of diabetics are type 2
Adult onset and linked to obesity
Management involves careful energy intake
Also no glycogen is formed (ie stored glucose)
Symptoms of diabetes
- Polyphagia - significant increased hunger
2. Significant weight loss
