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
During flow through the citric acid cycle, oxidation of cycle intermediates occurs in four separate reactions
True - Three generating NADH and one generating FADH2
Dietary disaccharides are digested in the stomach
False. Dietary disaccharides such as lactose, sucrose and maltose are digested in the small intestine to glucose, galactose and fructose
Concerning enzymes: When working at Vmax, an enzyme is saturated with substrate
True. When the enzyme is saturated with substrate and all the active sites are occupied, the enzyme will be working at its maximum rate (velocity)
The ‘primary structure’ of a protein is the predominant three-dimensional configuration that it adopts
False. The primary structure refers to the sequence of amino acids in a protein. The 3-dimensional structure is referred to as the tertiary structure
Glycogen is a polymer with many reducing ends
False. Glycogen is a polymer with many non-reducing ends
Because of the toxicity of ammonia, nitrogen is transported through plasma as the non-toxic molecule glutamate
False. Glutamate is initially formed by transamination reactions, but it is It is then converted to alanine which is transported in the blood
All lipids increase the risk of cardiovascular disease
False - VLDL and LDL if in high concentrations in the blood or trans fatty acids can accelerate cardiovascular disease. However, omega 3 fatty acids can lower cholesterol levels and help prevent the severity of cardiovascular disease
Concerning enzymes: At Vmax, substrate occupies all available active sites of the enzyme
True. Hence the rate (velocity) of the reaction as at its maximum
Phenylketonuria results from a genetic inability to synthesise the coded amino-acid phenylalanine
False. Classical phenylketonuria results from the lack of the enzyme phenylalanine hydroxylase which converts phenylalanine to tyrosine. There is therefore an excess of phenylalanine
Uncoupling agents inhibit the passage of electrons along the terminal respiratory system.
False. Uncoupling agents still allow the passage of electrons along the terminal respiratory system, but they render the inner mitochondrial membrane permeable to protons so the proton gradient cannot be generated. O2 is still reduced to H2O, but no ATP is made and the excess energy is released as heat. You should have heard of brown fat and of malignant hyperthermia in this context
Both glucose and galactose occur as six carbon rings
True - Both glucose and galactose can exist in a linear or cyclic form so can both adopt a ring structure
Bile salts are best described as fat emulsifiers
True - A key step in fat digestion is the emulsification of lipids with bile salts and with the help of lipases and peristalsis creates micelles that can be absorbed by cells in the small intestine
Enzymes increase the rate of a reaction by lowering the activation energy
True
Glycogen is osmotically inactive
True - This is an important benefit of storing glucose molecules as glycogen rather than as free glucose
Beta oxidation requires 2 main steps
False - It requires 3 main steps i) fatty acid activation ii) transport into the mitochondrial matrix by carnitine shuttle and iii) degradation which has 4 main enzyme reactions
Some of the potential energy of fuel molecules is saved during flow through the citric acid cycle
True - The energy from breaking carbon bonds is harvested as high energy electrons which are eventually passed via NADH and FADH2 to the electron transport chain to generate ATP
Concerning enzymes: At ½ Vmax, the substrate concentration is equal to Km.
True. This is the definition of Km. A low Km indicates a good fit between the enzyme and its substrate
Concerning enzymes: A low Km indicates a poor fit between the enzyme active site and the substrate
False. A low Km indicates a good fit between the enzyme active site and the substrate
Ketone bodies can be used by the brain and red blood cells as a source of energy when glucose is depleted.
False - Ketones can be used readily by the brain but NOT by red blood cells. Red blood cells do not have mitochondria or the enzymes associated with conversion of ketone bodies to acetyl coA
Fructokinase catalyses the conversion of dietary fructose to fructose 6-phosphate
False - Fructokinase catalyzes the phospehorylation of fructose to fructose-1-phosphate
Conjugated proteins are those which are composed of two or more separate amino-acid chains
False. A conjugated protein is one that functions by being attached to another non-protein group, eg glycoproteins, lipoproteins and metalloproteins
Most enzymes are globular proteins
True. As opposed to fibrous proteins which tend to be contractile of structural, or membranous proteins which include transporters and cell adhesion molecules
Digestion of dietary protein begins in the duodenum
False. It begins with the secretion of pepsinogen (and hence pesin) in the stomach. It follows with the secretion of trypsin, chymotrypsin, and peptidases in the small intestine
A peptide bond involves a link between a carbon atom and an oxygen atom.
False. A peptide bond, the link between individual amino acids in a protein, is between a carbon atom and a nitrogen atom
In the citric acid cycle, high energy electrons are stored in the form of NADH and FADH2
True
An isomerase is an enzyme that transfers groups between 2 molecules
False. An isomerase transfers groups within molecules – ie it forms an isomer
‘Denaturation’ of a protein refers to its degradation to component amino-acids.
False. In denaturation the weak bonds (eg hydrogen bonds) that maintain the secondary, tertiary and quaternary structures are lost but the covalent links between amino acids is retained
All proteins are enzymes
False. Proteins have a massively diverse range of functions, eg structural, contractile, hormonal, defensive, transport, storage or receptors
The citrate shuttle moves acetyl CoA from the mitochondria to the cytosol to make fatty acids
True - This step is necessary to transfer the acetyl CoA from the mitochondrial matrix where it is made to the cytosol for FA synthesis. This only happens where the citrate levels in the mitochondria are high and fatty acyl molecules are low in conc.
Concerning enzymes: Increasing the concentration of substrate may relieve competitive but not non-competitive inhibition
Concerning enzymes: Increasing the concentration of substrate may relieve competitive but not non-competitive inhibition
Acetoacetate is the only ketone body detected by a urine dipstick test
True - The test used to detect ketonuria only picks up acetoacetate not Beta-hydroxybutarate. (remember this by a-pee-to-acetate!!) Acetone is usually exhaled. Beta-hydroxybutyrate can be detected in blood using a separate test
Concerning enzymes: A coenzyme is an enzyme involved in an earlier or later stage of the same metabolic pathway
False. A coenzyme is a non-protein substance that is required for the function of the enzyme
All of the genetically coded amino acids can be synthesised in the body
False. 11 out of the 20 coded amino acids can be synthesized in the body and are classed as “non-essential”. The other 9 are “essential” and are needed in the diet. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine
Movement of glucose out of cells requires it to be dephosphorylated
True. Phosphorylation of glucose is a handy trick for trapping glucose within cells. Glucokinase does the job in the liver, and hexokinase does it in other tissues
As electrons pass along the terminal respiratory system, they are pumped across the inner membrane of the mitochondria
False. Electrons pass along the inner membrane of the mitochondria and their energy is used to pump protons across the membrane
The main place fat digestion takes place is the mouth and stomach
False - The main site of digestion of fats is the small intestine. Acid lipases in the mouth and stomach can digest some fats but this is limited
The rate limiting step in fatty acid synthesis is production of malonyl CoA from acetyl CoA carboxylase
False - 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.
One turn of the citric acid cycle generates one molecule of carbon dioxide.
False. One turn of the citric acid cycle generates two molecules of carbon dioxide
Isoenzymes (isozymes) are enzymes that catalyse more than one chemical reaction
False. Isoenzymes are enzymes that catalyse the same reaction but differ in structure
