Biochemistry Week 9 Protein Metabolism Flashcards
proteins and amino acids
⢠The body of a 70 kg male contains ~12 kg of protein (of which ~7 kg is skeletal muscle) and ~200 g of free amino acids ⢠20 different amino acids ⢠9 of these are considered essential - i.e., they must be supplied in the diet: remaining amino acids can be synthesised. Different amino acids essential to different stages of life.Histidine Methionine Phenylalanine Threonine Tryptophan Lysine3 branched chain amino acids Leucine Isoleucine Valine
anabolism vs catabolism
Anabolism - build and catabolism - breakdown - visible - muscle wastage - or increase in muscle.
Were you present when you were born
No all cells have broken down by then - takes about 20 years for all the carbon to recycle itself out of your body. Rebuilt with the food you have consumed
effect of exercise on muscle synthesis and breakdown
at rest muscle breakdown is higher than muscle synthesis - no exercise - loose muscle.Breakdown during the day - more synthesis at night.Exercise response - single bout will change the rate of synthesis for several days.
nitrogen balance
Up to a certain point increase in protein = increase in nitrogen balance but at a certain point - plateau is reached. Threshold, limit to achieve a nitrogen balance
Protein intake is proportional to total energy intake
Most athletes consume enough protein through increased energy intake.Increase calories = increase protein through this food - depends upon a balanced diet
An increase in muscle mass is only achieved through positive protein balance
Positive protein balance is when synthesis exceeds breakdown Must have: ⢠â Protein synthesis and/or ⢠â Protein breakdown
Muscle conditions
⢠Dystrophy - - issues with muscle building or breakdown e.g. Duchenne muscular dystrophy (DMD) - genetic issue - mutation on the X chromosome with the gene coding for dystrophin protein - leads to muscle wasting - only effects males - females carriers not sufferers - issues with function.⢠Cachexia - Ayogi et al 2015 Cancer cachexia, mechanism and treatment. World journal of gastrointestinal oncology. Muscle wastage in cancer patients is a problem.
Negative and positive protein balance
Positive protein balance after feeding, negative protein balance during fastingEndurance athletes often get done for taking anabolic agents - trying to stimulate the protein synthesis process - to help recovery - exercise causes muscle breakdown.Exercise before breakfast - canabolising the muscle in your body your using to do that exercise for the muscle to do that exercise.When you exercise becomes important.Positive synthesis and fasting balanceMore meals - stimulate more growth - positive.Less meals - negative balance needs to maintain or scheduled for purpose.
Interaction of exercise and nutrient intake results in muscle protein accretion
effected by diet and exercise patterns strength training fasting - loss - strength training while fed much larger increase.Training and feeding status directs net protein balance levels.
Endurance exercise
Generally assumed that endurance exercise is catabolic in nature⢠Increased whole body protein degradation during 4 h treadmill exercise (Rennie et al., 1981) ⢠Increased net release of amino acids during 2 h knee extensor exercise (van Hall et al., 1999) ⢠Later stable isotope study confirmed that muscle protein breakdown is increased during endurance exercise (Hulston et al., 2011)Shows that during endurance exercise you are breaking down a lot of protein - net negative balance - turnover favours the breakdown.
Leucine oxidation at rest and during low intensity (50% VO2max) treadmill exercise
⢠Leucine oxidation effected by exercise intensity, training status, and carbohydrate availability ⢠Leucine lost to oxidation is quite considerable during prolonged exercise, and especially when training twice of more each daylow intensity - long time at start breakdown a lot - the quite standard -introduce some glucose - protein breakdown comes down. Substrate utilisation of your muscles based on the exercise intensity and the available substrates.
Measuring muscle protein
Measuring muscle protein - Collect exhaled breath - infusing amino acids directly into the blood stream - labelled so able to be detected.- Go into muscle through muscle biopsy - can see if its in the muscle, if its been used or if its still in the blood stream.
Protein flux
change and flow of amino acids through the system - amino acids going in coming out and some in the muscle - have synthesis and breakdown - can look at whats happening - by sampling the tissue.
Protein turnover during endurance exercise
Note: rates of leg protein synthesis/breakdown calculated from leg phenylalanine uptake/release assuming 233 µmol phe/g proteinCan look at the rate of protein synthesis that's occurring in a muscle during exercise.
Endurance exercise stimulates postexercise MPS
Significant changes in the mixed muscle protein synthesis that occurs when we feed protein in addition to carbohydrate.Wont just use protein - use carb as a control - continued metabolic mill to run while mediating the protein.Carbohydrate/protein blend can look at muscle protein synthesis rate in the myofibrillar (fibre) and the mitochondria.Get differences - carbs and proteins at the muscle fibre level is giving us a higher synthesis rate - it is a significant difference.
How much protein to ingest post exercise
Plateau - in albumin synthesis past 20g - the same in most muscles - even double the protein - no more synthesis.
Is the source (type) of protein important?
⢠What are some of the potential sources of dietary protein? - Meat/ animal (beef, chicken, pork, fish etc..) - Dairy (milk proteins; whey & casein) - Plant (nuts, soy, wheat, pea etc..) - variety and volume is much larger.
Milk proteins versus soy: acute MPS response
Whey vs soy increase protein synthesis further using whey than soy - more difficult to build the muscle.Due to amino acid content - different - different chemical structure. Different speed and site of digestion and absorption Leucine content - possibleLeucine is the marker - use whey as protein - area under the curve increased - more leucine - with time it goes back down. 2 hours after ingestion higher leucine level in the blood - more available to the muscle.
Leucine threshold proposal
Theory - leucine trigger - suggests that we need a certain level of amino acids in the system so the intra cellular concentration of leucine once it goes above a certain threshold will allow us to prime our metabolic pathways for protein synthesis. Leuciene at certain level start to get leucine transported - stimulate protein synthesis via the mTOR pathway.mTor pathways are common in all individuals - impacted by disease - bed rest - effect this pathway - research this some more.
Timing of protein ingestion and muscle anabolism (growth)
"It isn't what you eat, it depends when you eat it - that's how muscles grow." (Prof. Mike Rennie, 2001)."Or so we thought Change in all literature The concept of the post exercise 'anabolic window' has become so engrained in the resistance training community that it is practically dogmaticDelaying amino acid (or protein) intake by a few hours is unlikely to influence muscle growth!
Embedded in the inner membrane of the mitochondrion are:
the components of the electron transport chain.The components of the electron transport chain are found in the inner membrane of the mitochondrion. The enzymes of the tricarboxylic acid cycle (Krebs' cycle) are found in the inner matrix of the mitochondrion. Glycogen and triacylglycerol molcules are found in the cytosol and GLUT4 molecules are found in both the cytosol and the cell membrane of muscle fibres.
The synthesis of glucose from lactate, glycerol, or amino acids is called:
gluconeogenesisThe synthesis of glucose from lactate, glycerol, or amino acids is called gluconeogenesis (production of glucose from non-carbohydrate sources). Glycogenolysis is the breakdown of glycogen, glycolysis is the pathway converting glucose phosphates into pyruvate or lactate; lipolysis is the breakdown of fat (triacylglycerol) into free fatty acids and transamination is the transfer of an amino group from an amino acid to a keto acid.
Liver glycogen breakdown is stimulated by
The hormones glucagon (secreted from the alpha cells of the pancreas) and adrenaline (secreted from the adrenal glands) both stimulate liver glycogen breakdown. Insulin (secreted from the beta cells of the pancreas) inhibits liver glycogen breakdown
The process of breaking down triacylglycerol into free fatty acids and glycerol is called:
lipolysisLipolysis is the process of breaking down triacylglycerol (storage form of lipid or fat) into free fatty acids and glycerol. This can occur in both adipose tissue and muscle fibres. Beta oxidation is the subsequent oxidation of fatty acids that takes place in the mitochondriaand lipogenesis is the process of synthesizing fat.
Most of the free fatty acids are transported in the blood:
bound to albuminMore than 99% of the free fatty acids in the blood are transported by the plasma protein albumin. Lipoproteins contain fat but in the form of triacylglycerol, phospholipids and cholesterol. Antibodies (also known as immunoglobulins) are involved in immune defence. Red blood cells are important in oxygen transport because of the haemoglobin they contain.
Fatty acids are transported into the mitochondria bound to:
carnitineFatty acids are transported into the mitochondria bound to carnitine. Fatty acids are only broken down and oxidized in the mitochondria. However, neither fatty acid nor fatty acyl-CoA molecules can simply diffuse across the mitochondrial outer and inner membranes. Fatty acyl-CoA molecules in the muscle sarcoplasm are transported into the mitochondria via formation of an ester of the fatty acid with carnitine. Thiokinase is the enzyme that joins a molecule of Coenzyme A to a fatty acid to form fatty acyl-CoA. Acetyl CoA is formed in the beta oxidation of fatty acids in the mitochondria.
The β-oxidation of a molecule of palmitic acid, CH3(CH2)14CO2H
yields 8 molecules of acetyl-CoA and some ATP and waterThe β-oxidation of a molecule of the 16-carbon fatty acid palmitic acid, CH3(CH2)14CO2H yields 8 molecules of the 2-carbon molecule acetyl-CoA and some ATP and water. Acetyl CoA subsequently can enter the Krebs' cycle and is completely oxidised to carbon dioxide and water with the generation of more ATP.
Which of the following releases most energy when completely oxidised in the body?
One gram of palmitic acidThe oxidation of one gram of a fat such yields more energy than protein, amino acids (e.g. leucine), carbohydrates (e.g. glucose) or alcohol. Palmitic acid is a fatty acid that yields about 9 kcal (38 kJ) per gram when it is completed oxidised to carbon dioxide and water. The others yield less than 5 kcal per gram.
When branched chain amino acids are deaminated in muscle, the ammonia produced is mostly:
converted into alanine and glutamine and released from the muscleWhen branched chain amino acids are deaminated in muscle, the ammonia produced is mostly converted into alanine and glutamine. These amino acids are released from the muscle into the circulation and are taken up by the liver where the amino groups are removed and converted into urea (their carbon skeletons can be used to form glucose). Urea is subsequently excreted in the urine which is formed in the kidneys.
Which of the following promotes glucose and amino acid uptake by muscle?
InsulinInsulin is the hormone that promotes glucose and amino acid uptake by muscle. Adrenaline and glucagon promote liver glycogen breakdown and cortisol promotes protein breakdown
During exercise, adrenaline secretion from the adrenal glands is stimulated by:
increased sympathetic nerve activityAdrenaline secretion from the medulla (inner part) of the adrenal glands is stimulated by an increase in sympathetic nerve activity. The latter occurs during exercise and other forms of stress including falls in the plasma glucose concentration. One of the actions of adrenaline is to promote lipolysis which causes a rise in the plasma free fatty acid concentration. ACTH (adrenocorticotrophic hormone) is released from the anterior pituitary gland in response to stress and stimulates cortisol secretion from the cortex (outer part) of the adrenal glands.
How many CO2 and ATP molecules are formed during onecomplete turn of the tricarboxylic acid cycle (Krebs' cycle)?
2CO2 and 1ATPTwo molecules of CO2 and only one molecule of ATP are formed during one complete turn of the tricarboxylic acid cycle (Krebs' cycle). The main function of the tricarboxylic acid cycle is to generate the reduced coenzymes NADH and FADH2. More ATP can be resynthesized subsequently in the process of oxidative phosphorylation involving the components of the electron transport chain.
Oxygen is used:
in the conversion of fatty acids to acetyl CoA.Oxygen is used in the beta oxidation of fatty acids to form acetyl CoA. Oxygen is not used in glycogenolysis (glycogen breakdown), glycolysis (the conversion of glues phosphates to pyruvate) or the tricarboxylic acid cycle (Krebs' cycle). Type 1 fibres use oxygen in the processes of beta oxidation of fatty acids and oxidative phosphorylation in the mitochondria but so too do Type II fibres as they also contain some mitochondria (though not as many as in Type I fibres).
Pairs of electrons carried in the form, FADH2 and NADH+H, collectively contain enough free energy to rephosphorylate:
5 ATP Pairs of electrons carried in the form of FADH2 contain enough free energy to rephosphorylate 2 ATP and pairs of electrons carried in the form of NADH+H contain enough free energy to rephosphorylate 3 ATP, so collectively this amounts to 5 ATP.