Biochemistry of Amino Acids and Diseases

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Questions and Answers

What does the Henderson-Hasselbalch equation help predict?

The solubility of proteins in water.

Changes in pH with alterations in concentrations of HCO3– or CO2. (correct)

The temperature change of a buffer solution.

The overall charge of amino acids in a solution.

Which amino acid is NOT mentioned as having potentially charged groups in its side chains?

Serine (correct)

Arginine

Glutamate

Lysine

What constitutes the definition of ampholytes?

Substances that act only in acidic environments.

Substances that can only act as acids.

Substances that have a neutral charge at all pH levels.

Substances that can either act as an acid or a base. (correct)

Which of the following forms of a weak acid, like aspirin, can permeate through cell membranes?

Uncharged form (HA) Signup and view all the answers

When a drug is in its protonated form (BH+), how does it behave?

It typically carries a positive charge. Signup and view all the answers

How does the pKa of an ionizable group affect a drug's absorption?

It influences the ratio of charged and uncharged forms. Signup and view all the answers

What happens to the pH of a solution when the concentration of a weak acid increases?

The pH typically decreases. Signup and view all the answers

Which factor greatly affects the effective concentration of the permeable form of a drug at its absorption site?

The ratio of charged and uncharged forms. Signup and view all the answers

Which of the following statements about weak bases is true?

They release protons to form an uncharged base. Signup and view all the answers

What effect does the binding of CO2 have on hemoglobin's affinity for oxygen?

It decreases the affinity for oxygen. Signup and view all the answers

What is formed when carbon monoxide (CO) binds to hemoglobin?

Carboxyhemoglobin Signup and view all the answers

How does carboxyhemoglobin affect the oxygen-dissociation curve?

It shifts the curve to the left. Signup and view all the answers

What therapy is used to treat CO poisoning?

Hyperbaric oxygen therapy Signup and view all the answers

What happens to the remaining heme sites of hemoglobin when CO binds to one of the four heme sites?

They bind oxygen with high affinity. Signup and view all the answers

Which gas carried by hemoglobin is a potent vasodilator?

Nitric oxide (NO) Signup and view all the answers

What is the significance of cross-links in concept maps?

They help identify concepts central to more than one topic. Signup and view all the answers

What occurs at physiologic pH regarding amino acids?

The α-carboxyl group forms a negatively charged carboxylate ion. Signup and view all the answers

Which property characterizes the α-carbon of amino acids?

It is attached to four different chemical groups except in glycine. Signup and view all the answers

Which classification of amino acids is determined by the nature of the R group?

Nonpolar, uncharged polar, acidic, or basic. Signup and view all the answers

What is the primary function of buffering in amino acids?

To stabilize pH near pKa. Signup and view all the answers

Which form of amino acids is predominantly found in proteins synthesized by the human body?

L-form. Signup and view all the answers

What does the Henderson-Hasselbalch equation describe?

The quantitative relationship between pH and concentrations of weak acid and conjugate base. Signup and view all the answers

What is the role of charged amino acids in peptide chains?

They assist in maintaining pH balance. Signup and view all the answers

Which statement about proline is correct?

It contains a secondary amino group. Signup and view all the answers

At which point on a titration curve would the net charge on an amino acid be zero for a nonpolar amino acid?

Point C. Signup and view all the answers

What is the role of the steep slope in the oxygen-dissociation curve of hemoglobin?

It aids in transporting and delivering oxygen from high to low pO2. Signup and view all the answers

What effect does a lower pH have on hemoglobin's oxygen release?

It enhances the release of oxygen from hemoglobin. Signup and view all the answers

How does an increase in pCO2 influence the oxygen-dissociation curve?

It decreases deoxygenated hemoglobin's affinity for oxygen. Signup and view all the answers

What is the Bohr effect primarily associated with?

Enhanced oxygen release in response to lower pH or increased CO2. Signup and view all the answers

What happens to CO2 in metabolically active tissues?

It is converted to carbonic acid and then bicarbonate. Signup and view all the answers

What physiological change occurs when the pH is raised in the lungs?

Greater affinity for oxygen and a leftward shift in the curve. Signup and view all the answers

Why would myoglobin not be able to deliver oxygen efficiently in the same range of pO2 as hemoglobin?

Myoglobin has a hyperbolic curve with high oxygen affinity. Signup and view all the answers

What is the primary function of bicarbonate in the blood?

Serving as the major blood buffer. Signup and view all the answers

What type of curve does hemoglobin exhibit compared to myoglobin?

Sigmoidal curve. Signup and view all the answers

What effect does the presence of protons (H+) have on hemoglobin?

It acts as an allosteric effector, reducing affinity. Signup and view all the answers

What characterizes the arrangement of antiparallel β-sheets?

The N-terminal and C-terminal ends alternate. Signup and view all the answers

What types of hydrogen bonds are formed in a β-sheet created from separate polypeptide chains?

Interchain bonds. Signup and view all the answers

Which amino acid is known to cause a kink in the polypeptide chain commonly found in β-bends?

Proline. Signup and view all the answers

What is the typical composition of β-bends in terms of amino acids?

Four amino acids, often including proline and glycine. Signup and view all the answers

In globular proteins, what orientation do β-sheets commonly exhibit?

Right-handed twist. Signup and view all the answers

Approximately what fraction of an average globular protein is organized into repetitive structures?

One half. Signup and view all the answers

Which term describes the less regular structure of nonrepetitive secondary structures in proteins?

Random coil. Signup and view all the answers

What stabilizes β-bends in proteins?

Hydrogen and ionic bonds. Signup and view all the answers

Which of the following is true regarding β-sheets formed by a single polypeptide chain?

They involve intrachain hydrogen bonds. Signup and view all the answers

What role do β-bends play in the structure of proteins?

They reverse the direction of the polypeptide chain. Signup and view all the answers

Study Notes

Mobility Patterns and Diseases

Variations in amino acid mobility patterns can indicate certain diseases.

Amino Acid Charge at Neutral pH

At physiological pH, amino acids possess a negatively charged carboxyl group (–COO–) and a positively charged amino group (–NH3+).
Amino acids such as glutamate, aspartate, histidine, arginine, and lysine contain additional charged groups in their side chains.
Amino acids function as ampholytes, acting as both acids and bases.

Henderson-Hasselbalch Equation

Used to predict pH changes based on concentrations of bicarbonate (HCO3–) and carbon dioxide (CO2).
Calculates how pH responds to changes in concentrations of weak acids and their salt forms.
In the bicarbonate buffer system, it illustrates the influence of HCO3– and CO2 on pH.

Drugs and Ionizable Forms

Many drugs are weak acids or bases; their absorption depends on their charged or uncharged forms.
Acidic drugs release protons and become negatively charged, while basic drugs lose protons and become uncharged.
Uncharged forms of drugs permeate membranes more readily, influencing their effective concentration at absorption sites.

Cross-Links in Concept Maps

Concept maps can include cross-links to represent complex ideas across different topics.
Facilitates understanding of relationships in biochemistry and enhances preparation for exams like the USMLE.

Amino Acid Structure

Each amino acid has an α-carboxyl group and a primary amino group, except proline, which has a secondary amino group.
Physiological pH leads to dissociation of the α-carboxyl group and protonation of the α-amino group.
Amino acids possess distinct side chains (R groups) that classify them as nonpolar, uncharged polar, acidic (polar negative), or basic (polar positive).

Buffer Systems

Free amino acids and charged amino acids in peptide chains function as buffers.
Buffering effectiveness is highest within ±1 pH unit of the pKa, where [A–] = [HA].

Chiral Carbon

The α-carbon of amino acids (excluding glycine) is a chiral carbon connected to four different groups, exhibiting optical activity.
L-forms of amino acids are incorporated into proteins in humans.

Secondary Structure of Proteins

β-sheets can form from multiple polypeptide chains arranged parallel or antiparallel, with interchain or intrachain bonds.
α-helices and β-sheets maximize hydrogen bonding among peptide bond components.

β-Bends and Nonrepetitive Structures

β-Bends consist of four amino acids and help reverse polypeptide chain direction for compact shapes.
Nonrepetitive secondary structures occupy roughly half of globular proteins, possessing less regular organization than repetitive structures.

Oxygen-Dissociation Curve

The sigmoidal shape of the oxygen-dissociation curve in hemoglobin enables efficient oxygen transport between high and low pO2 areas.
Myoglobin has a hyperbolic curve, which limits oxygen release efficiency.

Bohr Effect

Oxygen release from hemoglobin increases with lower pH or higher pCO2, stabilizing the deoxygenated T state and shifting the curve to the right.
Higher pH and lower CO2 concentration shift the curve left and stabilize the oxygenated R state.

Carbonic Acid and Bicarbonate

Increased CO2 in active tissues leads to a lower pH as it forms carbonic acid, contributing to the unloading of oxygen from hemoglobin.
This pH gradient favors oxygen release in tissues and uptake in lungs.

CO2 Transport and Carbaminohemoglobin

CO2 is mainly transported as bicarbonate but also binds to hemoglobin to form carbaminohemoglobin, stabilizing the deoxygenated form and decreasing oxygen affinity.

Carbon Monoxide Binding

CO binds tightly to hemoglobin, shifting the oxygen-dissociation curve left and impairing oxygen release due to high affinity for heme.
CO poisoning requires treatment with high-pressure oxygen to displace CO from hemoglobin, preventing cellular damage and hypoxia.

Additional Gas Transport

Hemoglobin also transports nitric oxide (NO), which acts as a vasodilator, contributing to its functions in the body.

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Description

Explore the variations in the mobility patterns of amino acids and their implications in different diseases. Understand the net charge of amino acids at neutral pH, including the importance of charged groups and the roles of specific amino acids like glutamate and lysine.