Biochem Flashcards
This is the final common pathway to completely metabolize major energy fuels into CO2, water and energy:
C. Citric acid cycle
A. Embden Meyerhoff Pathway
- Glycolysis; converts glucose → pyruvate
B. Electron Transport Chain
- redox reactions that transfer electrons from an electron donor to an electron acceptor
C. Citric Acid Cycle
- key metabolic pathway that connects carbohydrate, fat, and protein metabolism
D. Hexose Monophosphate Shunt
- Products: NADPH (used in fatty acid synthesis), ribose 5-phosphate (used in nucleotides and nucleic acids synthesis), erythrose 4-phosphate (used in aromatic amino acid synthesis)
Transamination of this amino acid will produce ketoacids that can lead to glucose synthesis:
A. Aspartate
B. Lysine
C. Threonine
D. Leucine
A. Aspartate
KETOGENIC: Lysine, Leucine
Glucogenic PITTT
- Phenylalanine, Isoleucine
- Tryptophan, Tyrosine, Threonine
The reason for metastasis or the detachment of cancer cells from the main tumor to spread to other tissues:
A. Activation of the E2F family of transcription factors
B. Binding of APC protein to catenin
causing cell proliferation
C. Mutation of the Patched and Smoothened co-receptor genes
D. Non-expression of cadherin-E, a necessary
protein for cell-to-cell adhesion
D. Non-expression of cadherin-E, a necessary
protein for cell-to-cell adhesion
This antioxidant vitamin may be considered to have anti-aging effect due to it’s radical scavenging property
A. A
B. D
C. E
D. K
Vit. E
Vitamins A, D, E, and K are all fat-soluble vitamins but only vitamin E is an antioxidant. Vitamin C (water-soluble) is also an antioxidant
Prolonged hyperglycemia can lead to cell aging. Advanced glycation end products (AGEs) are formed through
A. Covalent modification of histone proteins
B. D to L racemization of component amino acids in proteins
C. Non-enzymatic glycosylation of proteins
D. Reduction of sugar components of glycoproteins into sugar alcohols
C. Non-enzymatic glycosylation of proteins
Mutations at the G-C sequences of DNA occur quite often due to conversion of 5- methycytosine to thymine through what reaction? A. Reduction B. Oxidation C. Deamination D. Hydrolysis
C - Deamination
Deamination refers to the removal of amino acid group from bases. Usual bases cytosine and 5-methylcytosine undergoes deamination. 5-methyl cytosine -> Thymine
Major coenzyme involved in amino acid metabolism is:R A. Nicotinamide adenine dinucleotide B. Lipoic acid C. Pyridoxal phosphate D. Thiamine pyrophosphate
C - Pyridoxal Phosphate
Pyridoxal phosphate transfers amino group in transamination of amino acids; decarboxylation of amino acids, and racemization of amino acids.
At the subcellular level of organization of metabolism, which of the following events will be found exclusively in the mitochondria? A. Glycolysis B. Synthesis of palmitate C. Ketone bodies synthesis D. Gluconeogenesis
C - Ketone bodies synthesis
Increased rate of fatty acid oxidation during prolonged fasting results in the formation of ketone bodies through the liver and kidney mitochondrial matrix. Ketogenesis takes place in the mitochondria of the liver.
Intracellularly, glucose becomes the initial substrate of metabolic processes in this form: A. Glucose 1-PO4 B. Glucuronic acid C. Glucose 6-PO4 D. UDP-Glucose
C - Glucose 6-PO4
Glucose is irreversibly phosphorylated to glucose 6-phosphate by the enzyme hexokinase. This reaction traps G6P in the cytosol, committing it to further metabolism in the cell.
The metabolic pathway considered as the final common pathway to completely metabolize major energy fuels into CO2, water and energy. A. Embden Meyerhoff Pathway B. Electron Transport Chain C. Citric Acid Cycle D. Hexose Monophosphate Shunt
C. Citric Acid Cycle – Kreb’s Cycle, Tricarboxylic Acid Cycle (TCA Cycle)
is the final common oxidative pathway for carbohydrates, fats and amino acids; oxidation of acetyl CoA à CO2 + H2O
Site: mitochondrial matrix
The major end product of beta oxidation of fatty acid is A. acetoacetate B. acetylCoA C. propionylCoA D. beta hydroxybutyric acid
The end products of fatty acid oxidation are FADH2, NADH, H+ and Acetyl CoA. FADH2 and NADH + H+ are oxidized by the mitochondrial electron transport system to yield ATP while Acetyl CoA is undergoes oxidation again in the Krebs cycle to yield CO2 and H2O.
During prolonged fasting and starvation, glucose homeostasis is maintained by
A. glycogenolysis
B. gluconeogenesis
C. ketogenesis
D. anaplerosis
B - gluconeogenesis
The brain is only capable of using glucose or ketone bodies as respiratory fuel. During prolonged starvation, the primary source of glucose is gluconeogenesis from amino acids arising from muscle proteolysis.
The Krebs-Henseleit Cycle in man functions principally to
A. generate carbons for amino acid synthesis and transport
B. Convert ammonia into the nontoxic and excretable form
C. provide an alternate pathway for catabolism of essential amino acid
D. maintain acid base balance
B
Convert ammonia into the nontoxic and excretable form
Ammonia is a toxic product of nitrogen metabolism which should be removed from our body. The urea cycle or ornithine cycle converts excess ammonia into urea in the mitochondria of liver cells. The urea forms, then enters the blood stream, is filtered by the kidneys and is ultimately excreted in the urine.
The overall reaction for urea formation from ammonia is as follows: 2 Ammonia + CO2 + 3ATP —> urea + water + 3 ADP
Chronic alcoholism leads to impaired metabolic consequences due to which of the following initial
effect of increased alcohol ingestion?
A. accumulation of acetylCoA and fatty acid B. increased NADH/NAD ratio C. decreased ATP synthesis D. impaired gluconeogenesis and low blood glucose levels
B. increased NADH/NAD ratio
These include the metabolism of alcohol leading to a shift in the cytosolic [NAD+]/[NADH] ratio to reduction, which in turn causes a direct inhibition of β- oxidation and enhanced triacylglycerol formation via the [glycerol-3- phosphate]/[dihydroxyacetone phosphate] ratio.
• There are also chronic effects of ethanol on hepatic enzyme activities.
• Thus, increased activity of phosphatidate phosphohydrolase, an increased
amount of fatty acid binding protein, decreased secretion of very low-density lipoprotein and impairment of the respiratory chain as a result of decreased protein synthesis or decreased amounts of ubiquinone could all lead to fat accumulation and steatosis.
Between HDL and LDL, the HDL is considered the “good” lipoprotein because it:
A. contains less free cholesterol and more cholesterol esters
B. transports cholesterol to the liver thru reverse cholesterol transport
C. is smaller in size & lower molecular weight
D. derived from VLDL and IDL
B. transports cholesterol to the liver thru reverse cholesterol transport
Reverse cholesterol transport (RCT) is a process by which cholesterol in non-hepatic tissues is transported back to the liver via plasma components, such as HDL, along with ATP binding cassette transporters, such as ABCA1 and ABCG1.
Which statement is true based on the normal oxygen-dissociation curve of hemoglobin and myoglobin?
A. Hemoglobin is a better oxygen transporter than myoglobin because it has a higher oxygen affinity
B. The oxyhemoglobin dissociation curve shifts to right as a consequence of Bohr effect & increased 2,3 bisphosphoglyceric acid
C. The p50 value increases when affinity of oxygen to both hemoglobin and myoglobin increases
D. The hyperbolic shape of the oxygen- myoglobin
dissociation curve reflects the positive cooperativity of oxygen binding of myoglobin
The causes of shift to right can be remembered using the mnemonic, “CADET, face Right!” for CO2, Acid, 2,3-DPG, Exercise and Temperature. Factors that move the oxygen dissociation curve to the right are those physiological states where tissues need more oxygen. For example, during exercise, muscles have a higher metabolic rate, and consequently need more oxygen, produce more carbon dioxide and lactic acid, and their temperature rises.
Which of these increase HDL levels?
A. saturated fatty acids
B. w-3 PUFA in diet
C. high TAG levels
D. w-6 PUFA in diet
Saturated fatty acids - Inc. HDL & HDL
w-3 PUFA in diet - Dec. TAG
High TAG levels - Dec. HDL
w-6 PUFA in diet - Dec. LDL and HDL
Which statement is true of enzymes?
A. Enzymes accelerate biochemical
reactions by increasing the energy
of activation of a reaction
B. Being a conjugated protein, the
protein portion is called a
prosthetic group
C. The active site of an enzyme is the
substrate binding site
D. An enzyme, when non
competitively inhibited, affects the Km value
B
**rationale on WR 2018 #16
In which point does fatty acid synthesis differ from fatty acid oxidation?
A. takes place in the mitochondria B. requires NADH and FADH2
C. is favored by a high
insulin/glucagon ratio
D. is an energy generating process
Fatty Acid Synthesis ● occurs in the cytoplasm ● NADPH ● high insulin/glucagon ratio ● energy-requiring
Fatty Acid Oxidation ● occurs in the mitochondria ● NADH and FADH2 ● low insulin/glucagon ratio ● energy-yielding
For which reasons are statins given in hypercholesterolemia?
A. cholesterol synthesis de novo is inhibited
B. excretion of cholesterol is promoted
C. absorption of dietary fats is inhibited
D. bile salt excretion and the enterohepatic circulation are promoted
A - cholesterol synthesis de novo is inhibited
Statins act by inhibiting HMG-CoA reductase (the first and key rate-limiting enzyme of the cholesterol biosynthetic pathway), and up-regulating LDL receptor activity.
Which is correct about oxidative phosphorylation?
A. The process involves a direct transfer of a high phosphate to an activated substrate
B. The formation of ATP is coupled to oxidation of a substrate in the Electron Transport Chain
C. ATP is produced in the cytosol and partly in the mitochondria
D. The amount of ATP produced is indirectly proportional to the concentration of ADP
B
Oxidative phosphorylation is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers. This process takes place in the mitochondria.
In Glycolysis, in order to trap glucose and commit the substrate to utilization, which reaction of glucose and other sugars is initially catalyzed? A. isomerization B. phosphorylation C. hydrolysis D. oxidation
B. phosphorylation
Glucose enters cells through specific transport proteins and has one principal fate: it is phosphorylated by ATP to form glucose 6-phosphate. This step is notable for two reasons: (1) glucose 6-phosphate cannot diffuse through the membrane, because of its negative charges, and (2) the addition of the phosphoryl group begins to destabilize glucose, thus facilitating its further metabolism. The transfer of the phosphoryl group from ATP to the hydroxyl group on carbon 6 of glucose is catalyzed by hexokinase.
True about gluconeogenesis
A. The process is inhibited by a high
energy charge
B. The process is stimulated by a high
concentration of fructose 2,6-bisphospate
C. Glucose is synthesized from non carbohydrate sources
D. All of the reactions are identical with those of glycolysis
C. Glucose is synthesized from non carbohydrate sources
Gluconeogenesis is the process of synthesizing glucose or glycogen from noncarbohydrate precursors. The major substrates are the glucogenic amino acids, lactate, glycerol, and propionate. (Harper’s Illustrated Biochemistry 30E p. 185)
Adequate calories are allotted to carbohydrates and fats in order to produce which effect?
A. Promote absorption of fat soluble vitamins and minerals
B. Prevent protein breakdown through a protein sparing effect
C. Provide enough substrates for gluconeogenesis and glycogenesis
D. Interconvert carbohydrates into fats and vice versa
B - Prevent protein breakdown through a protein sparing effect
Protein sparing (amino acid sparing) is the process by which the body derives energy from sources other than protein. Such sources can include fatty tissues, dietary fats and carbohydrates.
