Energy Reactions in Cells Flashcards
(36 cards)
Define Cell Metabolism.
The highly integrated network of chemical reactions that occur within cells. The network consists of many distinct chemical pathways (metabolic pathways) which link together. Some pathways occur in all cells whilst others are confined to cells with specific functions.
What are the 4 main functions of cell metabolism?
Energy for cell function and the synthesis of cell components (ATP).
Building block molecules that are used in the synthesis of cell components needed for the growth, maintenance, repair and division of the cell.
Organic precursor molecules that are used to allow the inter-conversion of building block molecules (eg acetyl CoA).
Biosynthetic reducing power used in the synthesis of cell components (NADPH).
Where do cell nutrients in the blood come from?
Diet
Synthesis in body tissues from precursors
Released from storage in body tissues
What happens to cel nutrients in the blood? And where do the processes take place?
Degradation to release energy – all tissues
Synthesis of cell components – all tissues except RBCs
Storage – Liver, adipose tissue, skeletal muscle
What is catabolism and state its characteristics
Breakdown of larger molecules into smaller ones.
Large molecules -> smaller molecules
Oxidative - release H+ ions
Releases large amounts of energy (some conserved as ATP)
Produces intermediate metabolites
What is anabolism and state its characteristics
Small molecules -> larger molecules
Reductive - uses H+ ions.
Use the intermediary metabolites and energy (ATP) produced by catabolism to drive the synthesis of important cell components
Products of catabolism and their uses
Building block materials (sugars, amino acids, fatty acids) for cell growth, repair, division
Organic precursors (acetyl coA) for inter-conversion of building block materials
Biosynthetic reducing power (NADH, NADPH)
Energy (ATP) for cell function
What is energy from catabolism used for
Anabolism - synthesis of cellular components Transport work (across membranes etc) for nutrient uptake and maintaining ion gradients (Ca, K, Na, H) Specialised functions (Mechanical work - muscle contraction, Electrical work - nervous impulse contraction, Osmotic work - kidneys)
SI unit of energy? SI unit for energy in nutrition?
1Kcal = …kJ?
Joule, Calorie, 4.2kJ
Energy values of fat, carbs, protein and alcohol (in kJ/g and Kcal/g)
fat = 37, 9 carbs = 17, 4 protein = 16, 4 alcohol = 29, 7
What is Basal Metabolic Rate (BMR) and approx value (kcal)
Energy required by an awake individual during physical, digestive and emotional rest at 18deg.C, approx 1400-1700 kcal
Types of chemical bond reactions and do they require energy or not?
Exergonic (releases energy - bonds broken) and endergonic (requires energy - bonds formed)
Characteristics on exergonic and endergonic reactions
Exergonic
ΔG > 0, reaction is spontaneous
Endergonic
ΔG
Explain the biological roles of ATP, creatine phosphate and other molecules containing high energy of hydrolysis phosphate groups
Metabolism is all about coupling the energy released from exergonic reactions to the energy required by endergonic reactions. An intermediate process is required – the ADP/ATP cycle.
Exergonic – Energy releasing (Gibbs Free Energy Δ–‘ve)
Phosphorylated Compounds
Many of these compounds have a high energy of hydrolysis
Phosphoenolpyruvate ΔG = -62 kJ.mol=1
Creatine phosphate ΔG = -43 kJ.mol=1
ATP ΔG = -31 kJ.mol=1
The phosphate-phosphate bond is a high-energy bond.
ATP4- + H2O ADP3-+HPO42- + H+
• ATP + H2O ⇨ADP + Pi
ΔG = -31 kJ.mol-1
• ADP +H2O ⇨ AMP + Pi
ΔG = -31 kJ.mol-1
Some cell types, such as muscle, need to increase metabolic activity very quickly. Therefore they need a reserve of high energy stores that can be used immediately.
Creatine + ATP ⇔ Creatine Phosphate + ADP
This reaction is catalysed by creatine kinase
When ATP concentration is high, the forward reaction is favoured (vice versa)
What are redox reactions?
Oxidative reactions when electrons are removed. In biological terms it’s the removal of Hydrogen atoms (H+ and e-). Removed Hydrogen atoms immediately react with something else, making the reactions REDOX. OIL RIG (oxidation = loss of e-, reduction = gain)
What happens when fuel molecules are oxidised (what type of reaction)
Hydrogen atoms are transferred to carrier molecules (catabolism). These carry reducing power to other (anabolic) reactions.
Where do H-carriers come from and give e.g. (in oxidised and reduced forms too)
Carriers are complex molecules that contain components from vitamins (B vitamins).
Carriers are reduced by the addition of two H atoms (H+ + e-). The H+ dissociates in solution.
Nicotinamide adenine dinucleotide
oxidised = NAD+, reduced = NADH + H+
Nicotinamide adenine dinucleotide phosphate
oxidised = NADP+, reduced = NADPH + H+
Flavin adenine dinucleotide
oxidised = FAD, reduced = FAD2H
How can energy released as reducing equivalents be used to drive energy requiring activities?
Directly - use of NADPH in biosynthesis
Indirectly - mitochondrial system to couple NADH to production of an intermediate “energy currency” molecule ATP
What is energy released in exergonic reactions used to drive?
ADP + Pi -> ATP
Part of free energy conserved as chemical bond energy of terminal phosphate group (PO4) of ATP
Why is phosphate group suitable for this role?
Phosphate-phosphate bond has high energy of bond hydrolysis
How is flow of energy controlled? (ATP)
ATP is stable in the absence of a specific catalyst so won’t react unless the catalyst is present
When are anabolic pathways activated?
When the concentration of ATP rises
When are catabolic pathways activated?
When the concentration of ATP falls and the concentrations of ADP/AMP increase
Whys is ATP known as a high energy signal?
It signals that the cell has adequate energy levels for its immediate needs
