Week 3 formative quiz Flashcards
Pancreatic lipase breaks down triacylglycerols into free fatty acids and monoacylglycerol
True - these are broken down in the small intestine
Acetyl-CoA is the gateway for food molecules into the citric acid cycle
True. Amino acids, fatty acids and glucose (via pyruvate) all enter the citric acid cycle via acetyl-CoA.
Digestion of dietary polysaccharides and disaccharides involves hydrolysis reactions
True
Factors stabilising protein structure include both covalent and non-covalent bonds
True - the 3 dimensional structure of a protein is maintained by weak forces like hydrogen bonds and Van der waals forces as well as covalent links between amino aids
The rate limiting step in fatty acid synthesis is production of malonyl CoA from acetyl CoA carboxylase
True - This is the rate limiting enzyme in production of fatty acids. It is activated by citrate (signals that there is enough glucose - so make FA) and deactivated by palmitoyl CoA (enough fatty acid made so halt synthesis). It is also regulated by phosphorylation and dephosphorylation through concentrations of insulin, glucagon and epinephrine
Glucose molecules are removed from glycogen in the form of glucose 6-phosphate
False. Glucose monomers are removed from the non-reducing ends as glucose 1-phosphate
Concerning enzymes: A competitive inhibitor structurally resembles the normal substrate
True. A competitive inhibitor binds to the same substrate binding site and is therefore likely to be structurally similar to the substrate
Cholesterol biosynthesis is regulated by the concentration of acetyl CoA.
False - Cholesterol synthesis is regulated by the rate limiting enzyme HMG CoA reductase. Statins inhibit this enzyme which is exploited in medicine to reduce plasma cholesterol levels by inhibiting cholesterol synthesis
Isoenzymes (isozymes) are enzymes that catalyse more than one chemical reaction
False. Isoenzymes are enzymes that catalyse the same reaction but differ in structure
Glucokinase has a high Km for glucose, and hexokinase a low Km for glucose
True. Glucokinase, which is present in the liver, has a high Km and therefore low affinity for glucose but has a high Vmax and can therefore “grab” large amounts of glucose after a meal
Catabolism of glucose to carbon dioxide generates, per mol of glucose, 2 mol ATP, 2 mol GTP, 10 mol NADH and 2 mol FADH2
True - Remember, you get 2 mol of pyruvate per mol of glucose so you get two turns of the citric acid cycle
The R-group of an aliphatic amino-acid contains a hydrocarbon ring
False. The R-group of an aliphatic amino-acid consists of a hydrocarbon chain, eg alanine or leucine. The R-group of an aromatic amino-acid contains a hydrocarbon ring, eg phenylalanine or tyrosine.
All unsaturated fatty acids are essential
False - Only linolenic and linoleic fatty acids are essential. Animals do not have the enzymes that introduce double bonds between carbon 9 and 10 and so need to get these from the diet. Aracadonic acid is essential if these are not available but aracadonic acid can be made from linolenic acid
Fatty acids are degraded 2 carbons at a time in the cytosol
False - Fatty acids are degraded 2 carbons at a time in the mitochondrial matrix
Kidney failure can cause hyperammonaemia
True
Fatty acid synthase requires acetyl CoA, ATP and NADH to produce fatty acids
False - NADPH NOT NADP is required. This is produced from the pentose phosphate shuttle and through the citrate shuttle pathway
Glycolysis means ‘sugar splitting’
True. The six-carbon glucose molecule is split into two three-carbon pyruvate molecules
Glycolysis means ‘sugar splitting’
True. The six-carbon glucose molecule is split into two three-carbon pyruvate molecules
The citric acid cycle only operates under anaerobic conditions
False - the citric acid cycle only operates under aerobic conditions. It is the clever extra step after glycolysis that allows you to harvest electrons that can be used to completely oxidise food molecules to CO2 and H2O
Phenylketonuria is characterised by low plasma concentration of phenylalanine and high plasma concentration of tyrosine
False. Classical phenylketonuria results from the lack of the enzyme phenylalanine hydroxylase which converts phenylalanine to tyrosine. There is therefore a high concentration of phenylalanine and a low concentration of tyrosine in the blood
Bile salts are a transporter of lipids after breakdown
False - lipids are broken down to acetyl coA and this is used as fuel. There is no involvement of bile acids in transport after breakdown - it is key for emulsification of ingested fats
Amino acids are an essential source of the body’s nitrogen
True - carbohydrates and fats contain no nitrogen, we do not take any from the air, therefore amino acids are our major source of nitrogen
Structurally, proteins may be classified as globular, fluid or membranous
False - the 3 categories you have heard about are globular, fibrous and membraneous
Corticosteroids are used ti inhibit cyclooxyrgenase and reduce pain and inflammation
False - corticosteroids inhibit phospholipase A2 to prevent aracadonic acid production from membrane phospholipids and reduce pain and inflammation
The citric acid cycle is a major source of the reduced co-substrates that feed electrons into the terminal respiratory system.
True - The citric acid cycle generates NADH and FADH2 that pass their high energy electrons to the electron transport chain