Lecture 2: Energy reactions in cells Flashcards
(70 cards)
What is Metabolism?
Metabolism is the set of processes which derive energy and raw materials
from food stuffs and use them
to support repair, growth and activity of the tissues of the body
to sustain life
How does biological chemistry occur? (unlike chemistry in the lab)
By making small chemical changes, one after the other
Why can we understand biochemistry relatively easily?
(Because there are many reactions) but only a relatively few reaction types
What are the chemical reactions for a particular substrate arranged into?
Reactions are organised into metabolic pathways,
which are distinct but integrated:
– Some metabolic pathways occur in all cells (e.g. glycolysis)
– Others are restricted to some cell types
– Some may be further restricted to compartments within cells (e.g. fatty acid synthesis occurs in cytoplasm, fatty acid break down occurs in mitochondria)
What are the important steps to note about metabolic pathways?
- Start Points
- End Points
- Intermediates (metabolites)
- Interconnections between pathways
What are the 2 main types of Metabolic Pathways?
- Catabolic
- Anabolic
Describe what catabolic pathways do
– Break down larger molecules into smaller ones
(e.g break down building blocks into intermediary metabolites that can then feed out into other pathways)
– Release large amounts of free energy (from the bonds they are breaking)
– Oxidative meaning during the reaction, electrons are lost from the substrate. Most of the time, a Hydrogen atom (proton) will be removed from the molecule with the electron. If we can capture that hydrogen atom, it gives us some reducing power that we can put back into the system to derive other forms of energy or to drive biosynthesis
Describe what anabolic pathways do
– Synthesise larger important cellular components
from intermediary metabolites
– Use energy released from catabolism to drive that biosynthesis ( That energy might be in the form of hydrogen atoms that have been removed from substrates or through the use of ATP, which is an energy currency within a cell
– Reductive - we are putting back on Hydrogen atoms onto the substrate
Describe the products of catabolic metabolism
Fuel molecules are metabolised to supply:
- Building block materials (sugars, amino acids, fatty acids)
– dynamic state of these cellular components (turnover)
– (building block materials used for) cell growth and division
– (building block materials used for) repair of tissues - If we break building blocks down further, we yield Organic precursors like AcetylCoA
– allow for inter-conversion of building block material (between fats and carbs for example) - Biosynthetic reducing power in the form of NADH, NADPH, FAD2H
- Energy for cell function in the form of Adenosinetriphosphate ATP
What sort of work do we require energy for?
- Biosynthetic work (anabolism) - synthesis of cellular components
- Transport work - membranes
(a) maintenance of ion gradients (Na+, K+, Ca2+)
(b) nutrient uptake - Specialised functions
(a) Mechanical work - muscle contraction
(b) Electrical work - nervous impulse conduction
(c) Osmotic work - kidney
In a normal, healthy adult, what will be equal?
Average daily energy intake (in food) = Average daily expenditure (in work and heat)
Give the order of dietary components in order of energy value
Fats
Alcohol
Carbohydrate
Protein
What is the actual definition of basal metabolic rate?
Energy required by an awake individual during physical, digestive and emotional rest at 18oC
What is diet - induced thermogenesis?
The energy required to process food: energy cost of ingestion, digestion and absorption of food
How do you convert from kcal required in 24 hours to kilojoules
1kcal = 4.2kj
so X4.2
What are the energy requirements of the body and how many kcal and kJ are required for each thing? State the values for males (70kg) and females (58kg)
- Basal Metabolic rate approx 1,700kcal (M) 1,400kcal (F) / ( 7000/5800kJ)
- Physical activity (depends on type, intensity and duration of activity) approx 1000 - 3000 kcal (4000 - 12000kJ)
- Diet Induced thermogenesis approx 150kcal / 650kJ
- Energy lost as heat
What happens when energy intake from food is greater than the energy expenditure (on DIT, BMR, PAL and energy lost as heat)?
Excess energy is stored:
a) by the growth/synthesis of new tissue (repair, children, pregnancy)
b) If those things are satisfied, the surplus energy is put into store as adipose tissue/fat
What happens when energy intake is less than the energy requirements?
- Energy stores deplete and tissue is lost:
- First fat stores deplete
- If we are really in starvation, protein stores deplete
How long can humans survive without food? (providing water is given)
20-70 days
What is the main energy type that is predominantly used to drive energy requiring activities?
Chemical bond energy
What is important about the utilisation of chemical bond energy?
It is important that it is used directly without prior conversion to heat
Man is what? What does this mean?
Isothermal and thus can’t use heat energy for work
Define the terms endergonic and exergonic
Exergonic : a reaction where the energy released is greater than the energy input
Endergonic: a reaction where the energy input is greater than the energy released
What is special about exergonic reactions?
They are the only reactions that occur spontaneously
