MCBG Session 5 - Energy Reactions in Cells Flashcards
Define metabolism and explain its function.
Metabolism is the set of processes which derive energy and raw materials from food, using them for repair, growth and activity of tissues to sustain life.
Give a brief overview of how metabolism works?
Food enters the GI tract and is broken down into nutrients. These nutrients are taken up into the blood and utilised by tissues to produce energy via oxidation reactions (waste products reabsorbed into blood and lost) or converted and stored if they are in excess.
What are catabolic and anabolic pathways?
What are the key differences between the two?
Catabolic = breaking down larger molecules into smaller ones (intermediary metabolites)
- Releases large amounts of free energy
- Oxidative reaction - releases H+ ions with reducing power.
Anabolic = synthesise larger important molecules from intermediary metabolites
- Uses energy released from catabolism
- Reductive - uses H+ from catabolism
How are catabolic and anabolic pathways linked to each other?
The energy and H+ ions (reducing power) released from catabolic pathways are used for anabolic reactions.
What are the 4 main products of catabolic metabolism?§
1) Building block materials (sugars, AA’s, fatty acids)
2) Organic precursors (mainly Acetyl CoA)
3) Biosynthetic reducing agents (NADH, NADPH, FADH2)
4) Energy for cell functions (ATP)
What should the average daily energy intake (food) be equal to in healthy adults?
Daily energy expenditure (work + heat).
What is the standard unit of energy?
How many Kj’s in a Kcal?
Which food molecules have high energy values?
- Joule or Kilo Joule (Kj)
- 1 kcal (1000 cals) = 4.2Kj (4,200 J)
- Fats + Alcohol.
What are the energy requirements in Kcal and Kj for a 70kg male and 58kg female for the following:
- BMR
- Activity
- Specific dynamic action of food
BMR = 1,700/1,400 Kcal - 7,000/5800Kj Activity = 1,000-3,000 Kcal - 4,000-12,000 Kj SPAF = 150Kcal/650Kj
What happens if:
1) Energy intake>expenditure
2) Energy expenditure>intake
1) Growth - synthesis of new tissue and production of adipose tissue
2) Tissue is lost (weight lost)
What kind of energy is used to drive functions in the body?
Why is man ‘isothermal’?
- Chemical bond energy
- Man cannot use heat energy for work
Which is the difference between exergonic and endergonic reactions?
Exergonic:
- Can occur spontaneously
- Release energy - products are lower in energy than reactants
- Have -deltaG values (Gibbs free energy)
Endergonic:
- Can’t occur spontaneously
- Require energy input - products higher energy than reactance
- Have + deltaG values
What kind of reactions release chemical bond energy?
Why are these actually known as redox reactions?
- Oxidation reactions (removal of electrons or hydrogen ions)
- As all oxidation reaction are accompanied by reduction reactions - therefore they are known as Redox.
When protons and electrons are released by oxidation reactions, where are they transferred to?
Carrier molecules, that act as carriers of ‘reducing power’ for ATP production and biosynthesis. E.g.: NADH/NADPH and FAD2H. - converted to reduced form by adding 2 x H+ (which dissociate in solution - NADH + H+).
What is the energy and reducing power release from oxidative (exergonic) reactions used for?
To drive the synthesis of new molecules (anabolism) or to produce work (e.g.: exercise).
Describe the structure of ATP
What is the energy released from the breakdown of ATP –> ADP or ADP –> AMP
- Adenosine (adenine base + ribose) and 3 phosphate groups.
- -31kJ.mol (+31 for production of ATP from ADP)
Can ATP ‘store’ energy?
Why is the flow of energy from ATP controlled?
- No, there are limited amounts of ATP - it is only a carrier that cycles, not a store. Only 250g of ATP at any one point in time in the body, but your body weight amount of ATP is cycled each day - THEREFORE NEED A CONTINUOUS SUPPLY.
- ATP is stable in the absence of specific catalysts.
What pathways are activated when energy signals are high or low?
What are the high energy signals?
What are the low energy signals?
What is the role of adenylate kinase? (myokinase)
High energy = Anabolic pathways activated
Low energy = Catabolic pathways activated
High energy = ATP, NADH, NADPH, FAD2H
Low energy = ADP, AMP, NAD+, NADP+, FAD+
Adenylate kinase scavenges ADP when energy signal is low to reproduce ATP and AMP. AMP produced also acts as a low energy signal to further activate catabolic pathways.
What is used as a reserve of high energy stores that can be used immediately when cell types such as skeletal muscle require it?
Phosphocreatine (creatine phosphate) - When energy levels are high, phosphate bond energy may be stored in phosphocreatine.
How is phosphocreatine synthesised?
When is it synthesised?
- From creatine & ATP via creatine kinase enzyme
- When ATP concentrations are high, when they are low this reaction reverses to provide a short term boost of ATP to tissues.
What is creatine kinase used as a marker for and why?
- Myocardial infarction
- CK is made from 2 subunits - one isoform (CK-MM = 70% & CK-MB = 30%) is specific to heart muscle. Elevated levels of this in blood indicated MI - as CK is released from damaged myocytes.
What is creatinine a clinical marker for and why?
- Marker for urine dilution
- Breakdown product of creatine and phosphocreatine, excrete via kidneys. Can be used as a marker of urine dilution or to estimate true urinary loss of different substances, e.g.: hormones in pregnancy.
