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Questions and Answers
What is the main role of histidine in proteins like hemoglobin?
What is the main role of histidine in proteins like hemoglobin?
- Contributing to buffering capacity (correct)
- Acting as a structural component
- Facilitating oxygen transport
- Serving as a source of energy
Which property uniquely distinguishes histidine among amino acids?
Which property uniquely distinguishes histidine among amino acids?
- It is non-polar
- It is the only amino acid that is acidic
- It is the most abundant amino acid in proteins
- It has the ability to ionize at physiological pH (correct)
Which amino acid has the one-letter symbol 'G'?
Which amino acid has the one-letter symbol 'G'?
- Glycine (correct)
- Glutamate
- Glycolic acid
- Glutamine
What do the D and L designations refer to in amino acids?
What do the D and L designations refer to in amino acids?
Why is glycine considered an exception among amino acids regarding chirality?
Why is glycine considered an exception among amino acids regarding chirality?
Which letter is assigned to the amino acids aspartic acid and asparagine?
Which letter is assigned to the amino acids aspartic acid and asparagine?
What characteristic do stereoisomers of amino acids share?
What characteristic do stereoisomers of amino acids share?
Which of the following amino acids can exist as both a positively charged and neutral form?
Which of the following amino acids can exist as both a positively charged and neutral form?
What is the primary structure of a protein?
What is the primary structure of a protein?
Which type of bond connects amino acids in a protein?
Which type of bond connects amino acids in a protein?
What is the dominant component of the amyloid plaque found in Alzheimer disease?
What is the dominant component of the amyloid plaque found in Alzheimer disease?
Which characteristic structure is formed by the aggregation of Aβ peptides?
Which characteristic structure is formed by the aggregation of Aβ peptides?
How are peptide bonds characterized structurally?
How are peptide bonds characterized structurally?
What happens when amino acids are linked together through peptide bonds?
What happens when amino acids are linked together through peptide bonds?
What are neurofibrillary tangles primarily composed of in Alzheimer disease?
What are neurofibrillary tangles primarily composed of in Alzheimer disease?
What role does the amyloid precursor protein play in the formation of Aβ?
What role does the amyloid precursor protein play in the formation of Aβ?
What is the significance of knowing the primary structure of proteins?
What is the significance of knowing the primary structure of proteins?
Which of the following correctly describes how peptide chains are named?
Which of the following correctly describes how peptide chains are named?
Which disease is associated with the presence of prion proteins?
Which disease is associated with the presence of prion proteins?
What is the mechanism of the infectious agent causing scrapie in sheep?
What is the mechanism of the infectious agent causing scrapie in sheep?
What condition is required to nonenzymically break peptide bonds?
What condition is required to nonenzymically break peptide bonds?
What percentage of Alzheimer disease cases is considered familial or genetically based?
What percentage of Alzheimer disease cases is considered familial or genetically based?
What role do peptide bonds play in protein functionality?
What role do peptide bonds play in protein functionality?
How do neurotoxic amyloid plaques contribute to Alzheimer disease?
How do neurotoxic amyloid plaques contribute to Alzheimer disease?
What distinguishes antiparallel β-sheets from parallel β-sheets?
What distinguishes antiparallel β-sheets from parallel β-sheets?
Which type of bond stabilizes β-bends in polypeptide chains?
Which type of bond stabilizes β-bends in polypeptide chains?
How do β-sheets contribute to the structure of globular proteins?
How do β-sheets contribute to the structure of globular proteins?
What is the role of β-bends in protein structure?
What is the role of β-bends in protein structure?
What percentage of an average globular protein is typically organized into repetitive structures?
What percentage of an average globular protein is typically organized into repetitive structures?
What characterizes nonrepetitive secondary structures in proteins?
What characterizes nonrepetitive secondary structures in proteins?
Which amino acid is commonly associated with forming kinks in the polypeptide chain within β-bends?
Which amino acid is commonly associated with forming kinks in the polypeptide chain within β-bends?
Which statements about intrachain bonds and interchain bonds is true?
Which statements about intrachain bonds and interchain bonds is true?
What is the primary advantage of the sigmoidal oxygen-dissociation curve of hemoglobin compared to a hyperbolic curve?
What is the primary advantage of the sigmoidal oxygen-dissociation curve of hemoglobin compared to a hyperbolic curve?
Which condition enhances the release of oxygen from hemoglobin according to the Bohr effect?
Which condition enhances the release of oxygen from hemoglobin according to the Bohr effect?
What role does carbonic anhydrase play in the oxygen transport mechanism?
What role does carbonic anhydrase play in the oxygen transport mechanism?
What effect does a higher concentration of protons (H+) have on hemoglobin’s affinity for oxygen?
What effect does a higher concentration of protons (H+) have on hemoglobin’s affinity for oxygen?
What happens to the oxygen-dissociation curve of hemoglobin when pH decreases?
What happens to the oxygen-dissociation curve of hemoglobin when pH decreases?
How does the pH differ between the lungs and metabolically active tissues?
How does the pH differ between the lungs and metabolically active tissues?
What is the primary function of bicarbonate in the blood buffer system?
What is the primary function of bicarbonate in the blood buffer system?
What is the main reason why myoglobin cannot effectively deliver oxygen to tissues like hemoglobin?
What is the main reason why myoglobin cannot effectively deliver oxygen to tissues like hemoglobin?
Study Notes
Histidine and Its Role in Proteins
- Histidine is weakly basic and largely uncharged at physiological pH.
- When incorporated into proteins, its R group can be positively charged or neutral, depending on the surrounding ionic environment.
- Unique property of histidine allows it to play a crucial buffering role in proteins like hemoglobin.
- Only amino acid with a side chain that can ionize within the physiological pH range.
Amino Acid Abbreviations and Symbols
- Each amino acid has a unique three-letter abbreviation and a one-letter symbol.
- One-letter codes prioritize unique letters for single amino acids (e.g., V = valine).
- More common amino acids receive priority when multiple have similar initials (e.g., G = glycine).
- Amino acids with similar-sounding names may take easily recognizable symbols (F = phenylalanine).
- Remaining amino acids receive symbols close to their initial letter (K = lysine; B = Aspartic/Asparagine; Z = Glutamic/Glutamine; X = unidentified).
Optical Properties and Chirality of Amino Acids
- Amino acids have an α-carbon attached to four different groups, making them chiral, except glycine (which has two hydrogens).
- Exist as D and L forms, being stereoisomers that are mirror images.
Primary Structure of Proteins
- The primary structure is the sequence of amino acids in a protein, crucial for understanding genetic diseases.
- Peptide bonds link amino acids covalently, forming dipeptides (e.g., valylalanine).
- Peptide bonds resist denaturing conditions; require strong acids/bases at high temperatures to break.
Characteristics of Peptide Bonds
- Peptide bonds possess partial double-bond character, resulting in a rigid and planar structure.
- β-sheets can be formed by either parallel or antiparallel arrangements of polypeptide chains, stabilized by hydrogen bonding.
β-Bends and Nonrepetitive Secondary Structures
- β-Bends, typically containing four amino acids, reverse chain direction and create compact, surface regions on proteins.
- Nonrepetitive structures constitute roughly half of globular proteins and are less regular but not random.
Amyloid Aggregation in Diseases
- Accumulation of amyloids associated with diseases like Alzheimer's, Parkinson's, and Huntington's.
- Alzheimer’s features amyloid β (Aβ) peptide, which is neurotoxic and causes cognitive impairment.
- Aβ aggregates through enzymic cleavage of amyloid precursor protein and deposit in the brain.
- Non-genetic factors predominate in most Alzheimer cases, while tau protein abnormalities contribute to neurofibrillary tangles.
Prion Diseases
- Prion protein (PrP) is linked to transmissible spongiform encephalopathies (e.g., Creutzfeldt-Jakob disease).
- Infectivity of prion diseases is associated with PrPSc, a misfolded form devoid of detectable nucleic acid.
Oxygen Transport and the Bohr Effect
- Hemoglobin operates with a sigmoidal oxygen-dissociation curve, facilitating efficient oxygen delivery.
- The Bohr effect describes how lowered pH or elevated pCO2 enhances oxygen release by decreasing hemoglobin's affinity for oxygen.
- In metabolically active tissues, CO2 is converted to carbonic acid, lowering pH and promoting oxygen unloading, while higher pH in lungs favors oxygen loading.
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Description
This quiz explores the properties of histidine, an amino acid that exhibits unique buffering capabilities in proteins like hemoglobin. You'll learn about its ionic environment and how it can exist in either a charged or neutral form at physiological pH. Test your understanding of this essential biochemical component.
