1. Energy Reactions In Cells Flashcards
What is metabolism?
Set of processes which:
- derive energy and raw materials from food stuffs
- and use them to support repair, growth and activity of the body tissues
- to support life.
What is the difference between catabolic and anabolic pathways?
Catabolism:
- break down larger molecules into smaller ones - intermediary metabolites
- OXIDATIVE: release large amounts of free energy as H atoms - reducing power
Anabolism:
- synthesis of large cellular components from intermediary metabolites
- REDUCTIVE: use energy (H atoms) released from catabolism - ATP
What do fuel molecules provide when they are catabolised? What are these products used for?
- Building block materials: sugars, amino acids, fatty acids
- turnover of cell components (dynamic state)
- cell growth and division
- repair - Organic precursors: acetyl CoA
- interconversion of building block materials - Biosynthetic reducing power: NADH, NADPH
- Energy for cell function: ATP (adenosine triphosphate)
What is energy?
Capacity to do work
What sort of cellular work is energy required for?
- Biosynthetic work (anabolism)
- synthesis of cellular components - Transport work (across membranes)
- maintenance of ion gradients (Na+, K+, Ca2+)
- nutrient uptake - Specialised functions, e.g.
- mechanical work: muscle contraction
- electrical work: nervous impulse conduction
- osmotic work: kidney
What are the different forms of energy and which form is utilised in cells?
Heat, light, mechanical, electrical, osmotic, chemical bond (used in cells)
Why can Man not use heat energy for work?
Is isothermal
What is the difference between exergonic and endergonic chemical reactions?
Exergonic
- release energy (mostly catabolic reactions)
- reaction is spontaneous
Endergonic
- require energy input (mostly anabolic reactions)
- reaction isn’t spontaneous
What does G stand for? What is deltaG?
G = Gibbs free energy - is energy that can be used DeltaG = change in G
What is the result of a positive or negative deltaG value for a reaction?
If deltaG is negative, reaction is spontaneous. If it is positive, reaction is not spontaneous as requires energy input.
What is the difference between oxidation and reduction reactions?
Oxidation = removal of electrons (e-) OR removal of H atoms (H+ + e-).
Reduction = gain of e- or H+.
(OIL RIG : oxidation is loss, reduction is gain)
What happens to the electrons and protons released when fuel molecules are oxidised?
Transferred to carrier molecules
Name the major H carrier molecules.
Oxidised form Reduced form
NAD+ NADH + H+
NADP+ NADPH + H+
FAD FADH2
How does the concentration of oxidised and reduced forms of H carrier molecules change within a cell and what is the consequence of this?
Total concentration is constant so there must be a cycle between oxidative and reductive processes.
What do NADH + H+ and NADPH act as carrier of ‘reducing power’ for?
ATP production and biosynthesis (respectively)
How are H carrier molecules converted to reduced form?
Adding 2 H atoms ( 1 H+ dissociates into solution for NAD(P)H but not FADH2)
What do H carrier molecules contain?
B Vitamin components , e.g. FAD+ contains vitamin riboflavin B2
How can energy released as reducing equivalents be used to drive energy-requiring activities?
Directly: e.g. Use of NADPH in biosynthesis
Indirectly: e.g. Mitochondrial system to couple NADH to the production of an intermediate ‘energy currency’ molecule - ATP
What is ATP composed of?
Adenine, ribose and triphosphate
How are ATP, ADP and AMP created and what are the deltaG changes associated with this?
ATP + H2O = ADP + Pi (deltaG o’ = -31 kJ.mole-1)
ADP + H2O = AMP + Pi (deltaG o’ = -31 kJ.mole-1)
ADP + Pi = ATP + H2O (deltaG o’ = +31 kJ.mole-1)
Which signals indicate high and low energy levels in cells, and what pathways do these signals activate?
High energy signals: activate anabolic pathways
- ATP
- NADH
- NADPH
- FADH2
Low energy signals: activate catabolic pathways
- ADP, AMP
- NAD+
- NADP+
- FAD
Which enzyme converts 2 ADP to ATP + AMP?
Adenylate kinase
Which molecule acts as a reserve of high energy stores that can be used immediately when ATP levels are high? Which enzyme mediates this storage?
Phosphate bond energy can be stored as phosphocreatine. Involves addition of phosphate (ATP to ADP) to creatine by creatine kinase.
What is creatine kinase a marker for and why?
Myocardial infarction (1 CK isoform combination specific to heart muscle)
CK is released from cardiac myocytes when damaged, appears in blood a few hours later.
What is the product of normal spontaneous breakdown of creatine and phosphocreatine? When is this produced?
Creatinine
Produced by spontaneous reaction at a constant rate, unless muscle is wasting.
How is creatinine used as a clinical marker?
Creatinine excreted via kidneys.
- Excretion per 24hrs is proportional to muscle mass of individual - measure of muscle mass.
- Concentration in urine is a marker of urine dilution - can be used to estimate true urinary loss of many substances (e.g. Hormones in pregnancy) as excreted at constant rate.
What are the 4 different types of pathways of metabolism?
- Oxidative pathways
- convert food into energy.
- Biosynthetic pathways
- produce basic building blocks for cells.
- Fuel storage and mobilisation pathways
- allow fuel to be mobilised when we are not eating or need increased energy
- Detoxification pathways
- remove toxins
What is the official SI unit of food energy?
Kilojoule (kJ)
What is a Kcal?
1 kcal = amount of energy needed to raise temperature of 1 kg of water by 1 degree Celsius.
1 kcal = 4.2 kJ
How much food does one eat per year?
~ 500 kg
What are the essential components of the diet?
- Carbohydrates - mostly supply energy
- Proteins - energy and amino acids
- Fat - energy and essential fatty acids
- Minerals - essential
- Vitamins - essential
- Fibre - necessary for normal GI function
- Water - maintains hydration
What is the general formula of carbohydrates? Which groups do these molecules contain?
- (CH2O)n
- Contain:
- aldehyde (-C=OH) or keto (-C=O) group
- multiple -OH groups
How are carbohydrates classified according to unit number? Give examples of each type.
- Monosaccharide - single sugar unit, e.g. Glucose
- Disaccharide - 2 units, e.g. Sucrose
- Oligosaccharide - 3-12 units, e.g. Dextrin
- Polysaccharides - 10-1000s units, e.g. Glycogen, starch, cellulose
How many carbon atoms can monosaccharides have? What are these called?
3-9 carbon atoms
- Triose sugar = 3 carbons
- Pentose sugar = 5 carbons
- Hexose sugar = 6 carbons
How many C atoms does glucose have?
6
Name the major dietary carbohydrates.
- Glucose (predominant sugar in human blood)
- Glycogen (glucose polymer, carbohydrate storage molecule in animals)
- Sucrose (table sugar, glucose-fructose disaccharide)
- Lactose (milk sugar, galactose-glucose disaccharide)
- Fructose (fruit sugar, monosaccharide)
- Maltose (glucose-glucose disaccharide)
- Starch (glucose polymer, carbohydrate storage molecule in plants)
How are larger carbohydrates converted to monosaccharides in the body?
Digestion (enables absorption into the blood)
What are proteins composed of?
Amino acids joined by peptide bonds to form linear chains
What is the effect of digestion on protein?
Breaks protein into constituent amino acids which enter blood.
How many amino acids are used for protein synthesis in the body? How many cannot be synthesised and must therefore be obtained from diet?
- 20
- 9 essential amino acids
Name the 9 essential amino acids.
If Learned This Huge List May Prove Truly Valuable
Isoleucine, Lysine, Threonine, Histidine, Leucine, Methionine, Phenylalanine, Tryptophan, Valine.
What are conditionally essential amino acids?
Children and pregnant women have high rates of protein synthesis. Require dietary source of arginine, tyrosine and cysteine (as can’t synthesise enough to match growth).
Why are proteins of plant origin generally considered “lower quality”?
Most are deficient in 1 or more essential amino acids.
What is fat?
Lipids composed of triacylglycerols = 3 fatty acids esterified to 1 glycerol.
3 forms: saturated (no double bond), unsaturated (-C=C-) and trans.
Do fats yield more or less energy than carbs/proteins? Why?
Contain much less oxygen than carbs or proteins - more reduced so yield more energy when oxidised.
Why are fats important dietary components?
- Required for absorption of fat-soluble vitamins (A, D, E & K) from the gut.
- Provide essential fatty acids, e.g. Linoleic and linolenic acids, which cannot be synthesised in body.
Why are electrolytes important in the body? Name some examples.
- Establish ion gradients across membranes and maintain water balance.
- E.g. Sodium, potassium, chloride.
How much water and electrolytes is given to someone on IV fluids (routine maintenance).
- Water = 30 ml/kg/day
- Na+, K+, Cl- = 1 mol/kg/day each
Why are minerals important in the body? Name some examples.
- Essential for structure (bones and teeth)
- calcium and phosphorus
- Important signalling molecule
- calcium
- Enzyme co-factors
- iron, magnesium, manganese, cobalt, copper, zinc and molybdenum
- Haemoglobin component
- iron
What are the 2 main types of vitamin and how much do we require?
- Fat or water soluble
- Micro- or milligram quantities
Which diseases occur as a result of fat-soluble vitamin deficiencies?
- VitA: xerophthalmia
- VitD: rickets
- VitE: neurological abnormalities
- VitK: defective blood clotting
Give examples of diseases occurring as a result of water-soluble vitamin deficiencies.
- VitB12: anaemia
- VitC: scurvy
- Folate: neural tube defects, anaemia
- Niacin: pellagra
Where is dietary fibre found? Name examples.
Found in cereal foods (e.g. Bread, beans, fruit and veg).
E.g. Cellulose, lignin, pectins, gums.
What is cellulose? Why can we not digest it?
- Glucose polymer (like starch and glycogen).
- Don’t produce the required enzyme to break down the beta-1,6 cellulose linkages.
Why is dietary fibre important? What is the recommended average intake?
- Cannot be broken down by human digestive enzymes but essential for normal functioning of GI tract.
- Low fibre intake associated with constipation and bowel cancer.
- High fibre diet shown to reduce cholesterol and diabetes risk.
- Recommended average intake for adults = 18g/day (but average intake is below this).
