Protein Structure and Function Quiz

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Questions and Answers

Diagnosis of acute viral hepatitis may be estimated by determination of activity of which enzyme?

Kreatine kinase (MB isoform)

Gamma-glutamyltranspeptidase (correct)

Lactate dehydrogenase (isoforms 4, 5)

Lactate dehydrogenase (isoforms 1, 2)

Diagnosis of acute pancreatitis may be estimated by determination of activity of which enzyme?

Amylase (correct)

Lactate dehydrogenase (isoforms 1, 2)

Alanine aminotransferase

Lipase

Aerobic dehydrogenation is a variant of oxidation reaction, which enzyme catalyzes this reaction?

Cytochrome oxidase (correct)

Monoaminooxidase

Cytochrome P450

Phenylalanine monooxygenase

Which type of oxidation reactions involve removal of electrons?

Monoaminooxidase Signup and view all the answers

What significant role do monooxygenases play?

Xenobiotics detoxication Signup and view all the answers

Main function of glycosphingolipids is:

Components of cellular membranes Signup and view all the answers

Main function of glycerophospholipids is:

Components of cellular membranes Signup and view all the answers

What is true as a description of chylomicrons?

They have the largest diameter among all lipoproteins Signup and view all the answers

Transport of exogenous lipids from intestine to tissues is provided by…

Chylomicrons Signup and view all the answers

Ketone bodies can be synthesized in…

Hepatocytes Signup and view all the answers

Normal serum concentration range of ketone bodies is…

0-30 mg/l Signup and view all the answers

Normal serum concentration range of cholesterol is…

3.5-5.2 mmol/l Signup and view all the answers

Normal serum concentration range of free fatty acids is…

0.48-0.68 mmol/l Signup and view all the answers

Normal serum concentration range of total lipids is…

4-8 g/l Signup and view all the answers

The source of carbon atoms for fatty acids synthesis is…

Acetyl-CoA Signup and view all the answers

Choose the metabolic pathway in which amino acids cannot be used:

Protein synthesis Signup and view all the answers

Choose the urea cycle reaction which is catalyzed by a mitochondrial enzyme:

Synthesis of Krebs cycle intermediate Signup and view all the answers

Choose the substance that is regenerated in each round of transdeamination reactions:

Glutamate Signup and view all the answers

Methylation (transmethylation) reactions are used for:

Urea synthesis Signup and view all the answers

Deficiency of folic acid and cobalamin may cause:

Anemia Signup and view all the answers

Ammonia is toxic due to?

Decrease of glutamate concentration in mitochondria Signup and view all the answers

Accumulation of arginine in blood is a result of a genetic defect in synthesis of:

Argininosuccinase Signup and view all the answers

Alkaptonuria is a result of genetic defect in:

Homogentisate oxidase Signup and view all the answers

Accumulation of argininosuccinate in blood is a result of a genetic defect in synthesis of:

Argininosuccinase Signup and view all the answers

Classic variant of phenylketonuria is a result of genetic defect in:

Phenylalanine hydroxylase Signup and view all the answers

Genetic disorder (metabolic disease) hyperammonemia type I is a result of a defect in the:

Carbamoylphosphate synthase I Signup and view all the answers

Functions of serotonin include:

Neurotransmitter in sympathetic nervous system Signup and view all the answers

Biogenic amines are inactivated by:

Methylation Signup and view all the answers

Functions of adrenaline include:

Neurotransmitter in CNS Signup and view all the answers

Regeneration of methionine from homocysteine requires:

N5,N10-methylene-H4-folate Signup and view all the answers

Functions of histamine include:

Inducer of gastric juice secretion Signup and view all the answers

The bases which can be found in purine nucleotides are:

Adenine and guanine Signup and view all the answers

The bases which can be found in pyrimidine nucleotides are:

Thymine and cytosine Signup and view all the answers

Monomers in the structure of RNA are:

AMP Signup and view all the answers

Monomers in the structure of DNA are:

dATP Signup and view all the answers

Nucleotides which can be used in DNA biosynthesis are:

dCTP Signup and view all the answers

Nucleotides which can be used in RNA biosynthesis are:

AMP Signup and view all the answers

The bond between nucleotides in the primary structure of nucleic acid is...

5',3'-phosphodiester bond Signup and view all the answers

The complementary pair of bases in the secondary structure of DNA is...

Guanine-Thymine Signup and view all the answers

The secondary structure of DNA is stabilized by...

Hydrogen bonds Signup and view all the answers

Choose the tetrapeptide which has TWO amino acid residues with hydrophobic side chains:

Trp-Ile-Cys-Val Signup and view all the answers

Choose the tetrapeptide which has THREE amino acid residues with hydrophilic side chains:

Val-Cys-Met-Ser Signup and view all the answers

Choose the tetrapeptide which has N-terminal amino acid residue with hydrophobic side chain:

Phe-Tyr-Lys-Val Signup and view all the answers

Choose the tetrapeptide which has TWO amino acid residues with hydrophilic side chains:

Asn-Val-Val-Met Signup and view all the answers

Choose the tetrapeptide which has C-terminal amino acid residue with hydrophilic side chain:

Val-Ser-Tre-Met Signup and view all the answers

Choose the tetrapeptide which has THREE amino acid residues with hydrophilic side chains:

Ser-Gly-Trp-Pro Signup and view all the answers

The primary structure in ALL proteins is stabilized with…

Peptide bonds Signup and view all the answers

The secondary structure of proteins is stabilized ONLY with…

Hydrogen bonds Signup and view all the answers

The tertiary structure of proteins is stabilized with…

Covalent or/and noncovalent bonds Signup and view all the answers

The quaternary structure of proteins is stabilized mainly with…

Noncovalent bonds and hydrophobic interactions Signup and view all the answers

Indicate a function which is NOT performed by proteins in humans:

Storing of genetic information Signup and view all the answers

How is glucagon inactivated?

Proteolysis Signup and view all the answers

Choose a pair of hormones regulating exchange of water and minerals.

Aldosterone and vasopressin Signup and view all the answers

Choose a pair of hormones regulating reproductive functions.

Testosterone and estradiol Signup and view all the answers

Choose a pair of hormones regulating exchange of calcium and phosphates.

Calcitriol and calcitonin Signup and view all the answers

All effects listed below are shared by glucagon and cortisol except...

Stimulation of lipogenesis in the adipose tissue Signup and view all the answers

Choose appropriate effects of cortisol.

Stimulate lipogenesis in the adipose tissue Signup and view all the answers

Choose appropriate effects of insulin action on cells.

Stimulate lipogenesis in the adipose tissue Signup and view all the answers

Choose appropriate effects of adrenalin.

Stimulate glycogenolysis in muscles Signup and view all the answers

Choose appropriate effects of glucagon.

Increase glycogen breakdown in the liver Signup and view all the answers

Choose appropriate effects of insulin action on cells.

Increase glycogen synthesis in the liver Signup and view all the answers

All metabolic pathways listed below do not work in erythrocytes except:

Oxidative phosphorylation Signup and view all the answers

Choose substance which decreases Hb affinity to oxygen.

2,3-bisphosphoglycerate Signup and view all the answers

Choose a variant of Hb which cannot transport oxygen in blood.

CarboxyHb Signup and view all the answers

ATP in red blood cells is used mainly for...

Active transport Signup and view all the answers

Increase of affinity and rate of O2 binding to Hb is a result of...

Positive cooperative effect Signup and view all the answers

Study Notes

Protein Structure, Properties, and Functions

A protein's primary structure is stabilized by peptide bonds.
The secondary structure of proteins is stabilized by hydrogen bonds.
The tertiary structure of proteins is stabilized by covalent and noncovalent bonds.
The quaternary structure of proteins is stabilized by noncovalent bonds and hydrophobic interactions.
Functions of proteins in humans:
- Transport of hormones in blood
- Muscle contraction
- Storage of genetic information
- Catalysis of reactions
Globulins are poorly dissolved in pure water, but their solubility can be increased by adding small amounts of NaCl.
Protein-ligand interactions:
- Examples: antigen-antibody, hormone-receptor, and protein-heavy metal ion interactions
- Binding of ligand is highly specific and necessary for performing specific biological functions

Enzymes and Cofactors

Cofactors:
- Vitamin B5 (nicotinic acid): part of coenzyme NAD
- Vitamin B2 (riboflavin): part of coenzyme FAD
- Vitamin B1 (thiamin): part of coenzyme TPP
- Vitamin B6: part of coenzyme pyridoxal phosphate
- Vitamin B9 (folic acid): part of coenzyme THF
Enzyme cofactor functions:
- FAD: intermediate carrier of hydrogen atoms
- HS-CoA: intermediate carrier of acyl groups
- NAD: intermediate carrier of hydrogen atoms
- THF: intermediate carrier of one-carbon groups
- Pyridoxal phosphate: intermediate carrier of amino groups
Enzyme classification:
- Transferases: catalyze the transfer of functional groups
- Ligases: catalyze the formation of covalent bonds
- Lyases: catalyze the cleavage of various chemical bonds
- Oxidoreductases: catalyze oxidation and reduction reactions

Energy Exchange

Aerobic dehydrogenation: catalyzed by cytochrome oxidase
Anaerobic dehydrogenation: catalyzed by succinate dehydrogenase
Oxidation by removal of electrons: catalyzed by cytochrome a
Dehydrogenation: a type of oxidation reaction in which electrons are removed from the substrate
Monooxygenases: play a significant role in xenobiotics detoxication and the generation of reductive potentials
Caloric coefficients:
- Carbohydrates: 4.1 kcal/g
- Proteins: 4.1 kcal/g
- Lipids: 9.3 kcal/g
Daily requirements for food components (according to the WHO recommendations):
- Lipids: 1-2 g/kg body weight
- Proteins: 1-2 g/kg body weight
- Carbohydrates: 2-3 g/kg body weight
Krebs cycle enzymes:
- Citrate synthase
- Aconitase
- Isocitrate dehydrogenase
- α-ketoglutarate dehydrogenase complex
- Succinyl-CoA-synthase
- Succinate dehydrogenase
- Fumarase
- Malate dehydrogenase
Inhibitors of the respiratory chain:
- Complex I: rotenon
- Complex II: carboxin
- Complex III: antimycin
- Complex IV: carbon monoxide
Uncoupling effect on oxidative phosphorylation:
- Caused by Dinitrophenol, Acetylsalicylic acid, and other substances

Carbohydrates

Classification of carbohydrates:
- Monosaccharids: e.g., galactose
- Disaccharids: e.g., sucrose
- Homopolysaccharids: e.g., glycogen
- Heteropolysaccharids: e.g., hialuronic acid
Metabolic pathways:
- Glycolysis: anaerobic oxidation of glucose
- Gluconeogenesis: synthesis of glucose from non-carbohydrate substances
- Pentose phosphate pathway: generation of NADPH+H+
- Glycogenesis: synthesis of glycogen from glucose
- Glucogenolysis: breakdown of glycogen to glucose### Carbohydrate Metabolism
Digestion of glycogen and starch in the oral cavity is catalyzed by amylase.
Digestion of disaccharides in the small intestine is catalyzed by sucrase, lactase, and maltase.
All sugars can be absorbed in the intestinal wall, except lactose, ribose, and galactose.
Products of food carbohydrates digestion in the GIT can be absorbed by active transport, facilitated diffusion, and simple diffusion.
Hormones that have a hyperglycemic effect are glucagon, adrenalin, and cortisol, whereas insulin decreases blood glucose concentration.
A patient has hyperglycemia if the concentration of glucose in blood is above 6.2 mmol/l, and hypoglycemia if it's below 3.6 mmol/l.
Normal range of glucose concentration in blood in adults is 2.2-4.4 mmol/l.
Physiologic hypoglycemia can be found in healthy persons in cases of starvation, and physiologic hyperglycemia in cases of overconsumption of food carbohydrates, long-term hard physical activity, or emotional stress.

Lipids

Saturated fatty acids include palmitic acid, and polyunsaturated fatty acids include linoleic acid.
Monounsaturated fatty acids include oleic acid.
Eicosanoids are products of metabolism of the fatty acid arachidonic acid.
The main function of triacylglycerols is energy storage.
Cholesterol plays several physiological functions, including being a precursor for steroid hormones, and a component of cell membranes.
The main function of eicosanoids is to act as regulative molecules of the paracrine system.
Fatty acids may perform functions such as being structural components of cell membranes, and sources of energy.
The main function of glycosphingolipids is to act as components of cellular membranes.
The main function of glycerophospholipids is to act as components of cellular membranes.
Ketone bodies can be synthesized in hepatocytes.
Normal serum concentration range of ketone bodies is 0-30 mg/l.

Proteins and Amino Acids Exchange

Essential amino acids include phenylalanine, methionine, tryptophan, and cysteine.
Nitrogen equilibrium may be observed in healthy adults, and negative nitrogen balance may be observed in starvation state.
Positive nitrogen balance may be observed in healthy children, and in cases of protein synthesis.
Chymotrypsinogen is activated by trypsin.
Amino acids can be used in protein synthesis, gluconeogenesis, and oxidative breakdown.
Transamination is a process of transfer of an amino group from an amino acid to a keto acid.
Transdeamination includes two reactions: transamination with oxaloacetate, and oxidative deamination of Asp.
Enzymes that catalyze transdeamination reactions have cofactors such as pyridoxalphosphate and NAD+.
Decarboxylation of amino acids and their metabolites needs a cofactor such as pyridoxalphosphate.
The amino acid pool includes approximately 30 grams of free amino acids.
Amino acids cannot be used in glycolysis.
Choose the substance which is regenerated in each round of transdeamination reactions: α-ketoglutarate.

Nucleic Acids and Nucleotides

The bases that can be found in purine nucleotides are adenine and guanine.
The bases that can be found in pyrimidine nucleotides are thymin and cytosin.
Monomers in the structure of RNA are AMP, GMP, CMP, and UMP.
Monomers in the structure of DNA are dAMP, dGMP, dCMP, and dTMP.### DNA Biosynthesis
Nucleotides used in DNA biosynthesis: dATP, dGTP, dCTP, dTTP
Bond between nucleotides in primary structure of nucleic acid: 3',5'-phosphodiester bond
Complementary pair of bases in secondary structure of DNA: Adenine-Thymine, Guanine-Cytosine
Secondary structure of DNA is stabilized by: hydrogen bonds

DNA Folding

Sequence of DNA folding events: Nucleosomes → 30-nm fibrils → Loops → Chromosomes
Length of separate DNA molecule: several centimeters
Enzyme that unwinds double helix during DNA replication: Helicase
Enzyme that prevents supercoil formation during DNA replication: Topoisomerase
Enzyme that synthesizes oligoribonucleotide during DNA replication: Primase

Regulation of Metabolism

Hormone synthesis locations:
- Glucagon: Pancreatic gland
- Thyroxine: Thyroid gland
- Adrenalin: Medulla of suprarenal glands
- Somatotropin: Pituitary gland
Hormone types:
- Peptide hormones: Glucagon, growth hormone, insulin
- Derivatives of amino acids: Adrenalin, thyroxine, T3, T4
- Steroid hormones: Aldosteron, cortisol, calcitriol, testosteron
Hormone receptors:
- Insulin, growth hormone, glucagon: outer cell membrane
- Thyroxine, aldosteron: nucleus
- Adrenalin: outer cell membrane
Hormone inactivation:
- Insulin: Oxidative deamination and conjugation
- Adrenalin: Oxidative deamination and methylation
- Glucagon: Proteolysis

Biochemistry of Blood, Liver, Kidney, and Connective Tissue

Metabolic pathways in erythrocytes:
- Pentose phosphate pathway
- Anaerobic glycolysis
- Glutathione regeneration
Substances that decrease Hb affinity to oxygen: 2,3-bisphosphoglycerate
Variants of Hb: OxyHb, MetHb, HbF, CarboxyHb
ATP usage in red blood cells: For active transport
Pathologic variant of Hb: HbS
Hyperazotemia: Urea nitrogen percentage more than 30%
Glucokinase kinetic properties: High value of Km, not inhibited by glucose-6-phosphate
Lipoproteins produced by hepatocytes: VLDL and HDL
Bilirubin detoxication in the liver: Glucuronidation

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Prepare for your examination test with these questions on protein structure, properties, and functions. Identify tetrapeptides with hydrophobic and hydrophilic side chains.