82 Questions
Which of the following hormones is responsible for minimizing urinary excretion of calcium?
Parathyroid hormone (PTH)
What is the effect of low serum magnesium on parathyroid hormone (PTH) production?
It stimulates PTH production
What is the primary source of calcitriol synthesis?
Skin
Which of the following is a cause of hypercalcemia?
Primary hyperparathyroidism
What is the role of calcitriol in calcium absorption?
It promotes the synthesis of calcium-binding protein
What is the primary cause of hypocalcemia?
Reduced intestinal Ca absorption
Which of the following hormones stimulates the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D?
Parathyroid hormone (PTH)
What is the main component of bones where phosphates are found?
Hydroxyapatite
What is the effect of calcitriol on osteoclastic activity?
It stimulates osteoclastic activity
Which of the following hormones plays a small role in calcium-phosphorus balance under physiological circumstances?
Calcitonin
What is the primary role of 2,3-diphosphoglycerate (2,3-DPG) in erythrocytes?
Oxygen release
What percentage of phosphorus is found in the extracellular fluid?
1%
What is the most common cause of hyperphosphatemia?
Acute and chronic renal failure
What is the primary function of magnesium in the body?
ATP activation
What percentage of magnesium is found in the extracellular fluid?
1%
What is the role of magnesium in enzyme reactions?
Cofactor
What is the primary function of the ionized calcium (Ca2+) in the body?
Regulating neuromuscular excitability and muscle contraction
Which of the following statements is true about calcium in the body?
90% of calcium is found in the form of hydroxyapatite and phosphate complexes
What is the normal range of serum calcium concentration in the body?
2.10 – 2.70 mmol/L
What is the role of albumin in calcium homeostasis?
Binding to calcium ions to maintain a stable serum concentration
What is the primary function of calcium in the activation of coagulation factors?
Activating clotting factors
What is the consequence of an imbalance in calcium homeostasis?
Neuromuscular excitability and muscle contraction are impaired
What is the proportion of calcium bound to proteins in the serum?
40% of total calcium
What is the percentage of calcium found in the extracellular tissue (ECT)?
1% of total calcium
What is a major obstacle for β-lactam antibiotics in reaching their targets, the PBPs, in gram-negative bacteria?
The outer membrane
What are the protein channels in the outer membrane of gram-negative bacteria through which β-lactam antibiotics diffuse?
Porins
Why can β-lactam antibiotics easily reach their targets in gram-positive bacteria?
Because the outer membrane is absent
What type of antibiotics are penicillins, cephalosporins, carbapenems, and monobactams?
β-Lactam antibiotics
What is the function of porins in the outer membrane of gram-negative bacteria?
To diffuse through the outer membrane
Why are β-lactam antibiotics ineffective against bacteria that are not exposed to them?
Because the antibiotic cannot reach the target
What is the function of β-lactamase enzymes in bacteria?
To inactivate β-lactam antibiotics
What is the common feature among all penicillin derivatives?
The presence of a thiazolidine-β-lactam ring
What is the result of modifying the R side chain in penicillins?
Altered pharmacologic properties and antibacterial spectra of activity
What is the purpose of combining penicillins with β-lactamase inhibitors?
To expand the number of bacterial species susceptible to penicillins
What determines the antibacterial activity of penicillins?
The presence of a thiazolidine-β-lactam ring
What is the characteristic of members within a class of penicillins?
Similar pharmacokinetic properties and spectra of activity
Which type of bacteria is susceptible to natural penicillins?
Gram-positive bacteria (Staphylococcus aureus)
What is the effect of pumps, penicillinases, and porins working together?
A dramatic change in susceptibility to antibiotics
Which Streptococcus species is susceptible to natural penicillins?
Streptococcus pyogenes
What is the antimicrobial activity of natural penicillins against Neisseria meningitidis?
Highly susceptible to natural penicillins
Which of the following bacteria is susceptible to natural penicillins?
Streptococcus pyogenes
What is the antimicrobial activity of natural penicillins against Listeria monocytogenes?
Highly susceptible to natural penicillins
Which of the following is NOT susceptible to natural penicillins?
Escherichia coli
What is the antimicrobial activity of natural penicillins against Clostridia species?
Variable susceptibility to natural penicillins
What is the main function of efflux pumps in some bacteria?
To transport antibiotics back out to the environment
What is the main difference between extended-spectrum penicillins and natural penicillins?
Their activity against enteric gram-negative rods
What is the function of penicillins?
To inhibit cell wall synthesis
What is the role of β-lactamases in bacteria?
To degrade β-lactams before they reach the PBPs
What is the effect of β-lactam antibiotics on bacteria that do not produce peptidoglycan?
They are not effective in inhibiting the growth of these bacteria
What is the primary benefit of adding a β-lactamase inhibitor to an extended-spectrum penicillin?
Improved resistance to β-lactamase
Why do β-lactam antibiotics need to successfully navigate around certain pitfalls to be effective?
Because they can be blocked by efflux pumps, β-lactamases, and other mechanisms
What is the main difference between aminopenicillins and natural penicillins?
Their spectrum of activity against enteric gram-negative rods
What is a characteristic of β-lactam antibiotics?
They are a heterogeneous group of compounds
What is the effect of adding a β-lactamase inhibitor to an aminopenicillin?
Increased resistance to β-lactamase
What is the result of β-lactams binding to PBPs with low affinity?
The β-lactams are unable to inactivate the PBPs
What is the primary mechanism of action of penicillins?
Inhibition of cell wall synthesis
What is the main difference between antistaphylococcal penicillins and natural penicillins?
Their activity against staphylococcal bacteria
What is the primary benefit of using extended-spectrum penicillins?
Improved activity against enteric gram-negative rods
What is the primary energy source utilized to power processes such as active transport of nutrients and generation of ATP?
Proton motive force
Where is the energy stored in the process of generating a proton gradient?
Between the interior and exterior of the cell
What is the process by which bacteria utilize DNA information to synthesize an RNA molecule?
Transcription
What is the term used to describe the energy stored in the proton gradient?
Potential energy
What is the term used to describe the flow of protons down the gradient?
Proton flow
What is the primary function of RNA polymerase in bacterial cells?
To synthesize mRNA
Where does the process of transcription occur in bacterial cells?
In the cytoplasm
What is the purpose of harnessing energy from fuel consumption in bacterial cells?
To generate ATP
What is required to add a single amino acid to a growing protein?
The energy of three or four nucleoside triphosphates
What is the role of bacterial enzymes in protein production?
To transcribe template bacterial genes into RNA
What is the significance of the difference between bacterial and human cellular components in protein production?
It makes protein production in bacteria amenable to inhibition by antibiotics
What is the purpose of acquiring raw materials in protein production?
To synthesize new proteins
What is the role of RNA in protein production?
To translate RNA into protein
What is the significance of the human body as a 'country' for bacteria?
It is a source of resources for bacterial growth
What is the role of template bacterial genes in protein production?
To transcribe template bacterial genes into RNA
What is the result of inhibiting protein production in bacteria?
Bacteria are inhibited from replacing old worn-out parts and building new bacteria
What is the precursor of THF that humans readily absorb from their diet?
Folate
Which enzyme is responsible for replicating the bacterial chromosome?
DNA polymerase
What is the result of twisting one end of the DNA while holding the other end fixed?
Increased supercoiling
What is the role of topoisomerase in DNA replication?
Regulating supercoiling
What is the number of nucleotide pairs per helical turn in a relaxed DNA structure?
10
What is the consequence of having a chromosome composed of helical DNA?
Formation of supercoils
What is the role of dihydropteroate synthase in THF synthesis?
Synthesizing dihydropteroate
Why is the THF synthesis pathway an attractive target for antimicrobial compounds?
Because most bacteria are unable to synthesize THF
Study Notes
Hormonal Regulators of Ca-P Balance
- Parathyroid hormone (PTH) is a polypeptide hormone synthesized and secreted by chief cells of the parathyroid glands.
- Decreased Ca2+ and low serum magnesium stimulate PTH secretion.
- PTH increases blood Ca concentration in three ways:
- Minimizes urinary excretion of Ca by increasing reabsorption in renal tubules.
- Stimulates conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol) in kidneys.
- Mobilizes Ca and P from bones with calcitriol.
Calcitriol
- Calcitriol is a vitamin D-derived hormone synthesized in the skin from 7-hydroxycholesterol via UV radiation.
- Calcitriol promotes synthesis of calcium-binding protein essential for Ca and P absorption in small intestinal cells.
- Together with PTH, calcitriol stimulates osteoclastic activity, releasing Ca and P from bones.
Calcium
- 99% of body's total calcium is bound in bones and teeth, mainly in the form of hydroxyapatite and phosphate complexes.
- 1% of calcium is found in the extracellular fluid (ECF), predominantly in the form of free, ionized Ca2+ (50%) and bound Ca (50%).
- Serum concentration of total calcium is maintained between 2.10-2.70 mmol/L.
Phosphates
- Most phosphorus in the body exists in the form of phosphates, with 85% found in bones.
- Phosphates in soft tissues are bound in numerous organic compounds, including nucleic acids and phospholipids of cell membranes.
- Phosphates play a key role in energy metabolism of cells and release of O2 in tissues.
Hyperphosphatemia and Hypophosphatemia
- Hyperphosphatemia is usually due to increased intake, decreased renal excretion, and redistribution from ICF to ECF.
- Acute and chronic renal failure is the most common cause of hyperphosphatemia.
Magnesium
- 60% of magnesium is bound in bone to hydroxyapatite crystals, almost 40% is in muscle and soft tissue cells, and only about 1% is in the extracellular fluid.
- Magnesium is the second most important intracellular cation after potassium, necessary for ATP activation.
- Magnesium is a cofactor of more than 300 enzymes, catalyzing reactions using ATP.
Factors Affecting β-Lactam Antibiotics
- β-Lactam antibiotics cannot kill bacteria if they cannot reach their targets, the PBPs (penicillin-binding proteins)
- Gram-negative bacteria have a protective outer membrane that β-lactams must breach through porins, protein channels in the outer membrane
- Some bacteria produce efflux pumps that transport β-lactams out of the periplasmic space
- β-Lactamases can degrade β-lactams before they reach the PBPs
- Some bacteria produce PBPs that do not bind β-lactams with high affinity
- The absence of peptidoglycan in some bacteria makes them unaffected by β-lactams
β-Lactam Antibiotics
- The four major classes of β-lactam antibiotics are penicillins, cephalosporins, carbapenems, and monobactams
- All β-lactam antibiotics exert their action by binding to PBPs
- β-Lactamases are enzymes that cleave β-lactam antibiotics, inactivating them
Penicillins
- Consist of a thiazolidine ring attached to a β-lactam ring modified by a variable side chain
- The thiazolidine-β-lactam ring is required for antibacterial activity, while the side chain can be modified to produce different penicillin derivatives
- Classes of penicillins include natural penicillins, antistaphylococcal penicillins, aminopenicillins, and extended-spectrum penicillins
- Some penicillins are combined with β-lactamase inhibitors, expanding their antibacterial spectrum
Natural Penicillins
- Have moderate activity against aerobic gram-positive bacteria and anaerobic bacteria
- Have poor activity against aerobic gram-negative bacteria and most atypical bacteria
- Active against Streptococcus pyogenes, viridans group streptococci, some Streptococcus pneumoniae, some enterococci, Listeria monocytogenes, Neisseria meningitidis, and some Haemophilus influenzae
Extended-Spectrum Penicillins
- Active against even more enteric gram-negative rods and Pseudomonas aeruginosa
- The addition of a β-lactamase inhibitor to an extended-spectrum penicillin extends its activity to most enteric gram-negative bacilli
Protein Production in Bacteria
- Protein production in bacteria is a process that involves the synthesis of proteins using DNA, RNA, and amino acids.
- The process requires energy from nucleoside triphosphates, which is stored in the form of a proton motive force.
- The proton motive force is generated by the flow of protons down a gradient between the interior and exterior of the cell.
Transcription
- Transcription is the process by which DNA is used to synthesize messenger RNA (mRNA).
- The enzyme RNA polymerase is used by bacteria to accomplish transcription.
- Tetrahydrofolate (THF) is required for the synthesis of nucleotides during transcription.
Tetrahydrofolate Synthesis
- Bacteria synthesize THF from para-aminobenzoate (PABA) and dihydropterin pyrophosphate.
- The enzymes dihydropteroate synthase and dihydrofolate reductase are involved in the synthesis of THF.
DNA Replication
- DNA polymerase is responsible for replicating the bacterial chromosome.
- Other enzymes, such as topoisomerases, are also required for DNA replication.
- Topoisomerases regulate supercoiling, or twisting, of the DNA molecule.
Supercoiling of DNA
- Supercoiling occurs when the double helix structure of DNA is twisted, resulting in additional stress on the DNA molecule.
- This stress is accommodated by the formation of supercoils.
Protein Synthesis
- Protein synthesis in bacteria requires raw materials such as RNA, amino acids, and energy-containing nucleoside triphosphates.
- The energy of three or four nucleoside triphosphates is required to add a single amino acid to a growing protein.
- Bacterial enzymes are used to translate RNA into protein.
- Protein production in bacteria is amenable to inhibition by antibiotics due to differences in bacterial components compared to human cells.
This quiz covers the main hormonal regulators of calcium-phosphorus balance in the body, including parathyroid hormone, calcitriol, fibroblast growth factor, and calcitonin.
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