Podcast Beta
Questions and Answers
Proline has a secondary amino group and forms a rigid ______ membered ring.
5
The hydroxyl group of serine and threonine serves as a site of attachment for ______ groups in proteins.
phosphate
Disulfide bonds are formed when the -SH groups of two ______ become oxidized.
cysteines
Amino acids with acidic side chains act as proton ______ and are negatively charged at physiological pH.
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Amino acids with basic side chains act as proton ______ and are positively charged at physiological pH.
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Amino acids with basic side chains are considered to be a ______ base.
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The α-carbon of amino acids is ______ or optically active.
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Amino acids in mammals predominantly exist in the ______ form.
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Amino acids contain weakly acidic α-______ groups.
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Buffers are weak acids or bases that can resist small changes in ______.
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The Henderson-Hasselbalch equation relates pH to the concentration of ______ and its conjugate base.
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Maximum buffering capacity occurs at pH equal to Ka plus or minus ______ unit.
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Amino acids have a pK value for every dissociable ______.
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The dissociation constant for the carboxyl group is referred to as ______.
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At the pK1 value, half of the carboxyl groups in solution are ______.
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Proteins are the most abundant molecules in living ______
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Enzymes act as biological ______, increasing reaction rates.
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In muscles, ______ proteins allow for movement.
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The carbon atom in amino acids is referred to as the ______-carbon.
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At physiological pH, the carboxyl group forms a negatively charged ______ ion.
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Amino acids can be classified based on the properties of their ______ chain.
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Amino acids with non-polar side chains do not participate in ______ or ionic bonds.
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The amino group of amino acids is usually protonated as ______+ at cellular pH.
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Buffer pairs -COOH/COO- is a buffer pair in the acid pH range and -NH3+/-NH2 pair buffers in the ______ pH range.
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If pH = pK1, then equal amounts of forms I and II are ______.
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The isoelectric point (pI) is the pH at which form II is predominant, with equal amounts of forms I and ______.
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Most amino acids have a net charge of zero at ______ pH.
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Amino acids are known as ______ ions as they carry both a positive and negative charge.
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The bicarbonate buffer system can be represented by the equation CO2 + H2O H2CO3 H+ + ______.
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Drugs pass through membranes readily in their ______ form.
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Effective concentration of a drug at the absorption site depends on the concentration of the ______ and undissociated forms.
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Study Notes
Protein Function
- Most abundant molecule in living systems.
- Responsible for various vital functions such as:
- Catalysis of biochemical reactions as enzymes.
- Regulation of metabolism through polypeptide hormones.
- Facilitating movement through contractile proteins in muscles.
- Providing structural support with collagen in bone.
- Transport and storage of molecules, like hemoglobin and myoglobin for oxygen, and plasma albumin for fatty acids.
- Immune defense with immunoglobulins.
Structure of Amino Acids
- All amino acids contain:
- A primary amino group (-NH2).
- A carboxyl group (-COOH).
- A hydrogen atom.
- A distinctive side chain (R group) bonded to a central carbon atom, also known as the α-carbon.
- The structure of the R group differentiates each amino acid.
Properties of Amino Acids
- At physiological pH (~ 7.4):
- The carboxyl group is dissociated forming the negatively charged carboxylate ion (COO-).
- The amino group is protonated (NH3+).
- Under normal cellular conditions (~ pH 7.4), amino acids are zwitter ions (dipolar ions) due to:
- Carboxyl group: COO-.
- Amino group: NH3+.
- In proteins, the carboxyl group of one amino acid is bound to the amino group of the adjacent amino acid in the peptide linkage.
- The carboxyl and amino groups of amino acids are usually not involved in chemical reactions except for hydrogen bond formation.
Classification of Amino Acids
- Chemical properties and function derive from the side chain (R group).
- Amino acids are classified based on the properties of their R groups:
- Non-polar side chains (9): These side chains do not bind or release protons and do not participate in hydrogen or ionic bonds. They are further categorized as aliphatic or aromatic.
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Uncharged polar side chains (6): These side chains have a zero net charge at neutral pH. They participate in hydrogen bond formation. They also serve as attachment sites for phosphate groups (serine, threonine) and oligosaccharides (serine, threonine, asparagine) in proteins.
- Cysteine's sulfhydryl (-SH) group can lose a proton at alkaline pH and form disulfide bonds (-S-S-) in the oxidized form.
- Acidic side chains (2): These side chains are fully ionized and negatively charged at physiological pH, acting as proton donors.
- Basic side chains (3): Side chains are fully protonated and positively charged at physiological pH, functioning as proton acceptors.
Non-Polar Amino Acids
- Side chains tend to cluster together within the interior of the protein due to their hydrophobicity.
- In membrane proteins, nonpolar groups are on the outside surface of the protein to interact with the non-polar lipid membrane.
- Proline has a unique cyclic structure with a secondary amino group due to its side chain forming a 5-membered ring, playing a crucial role in collagen structure.
Optical Properties of Amino Acids
- The α-carbon of an amino acid is chiral or optically active, with the exception of glycine.
- This chirality results in D-forms and L-forms (stereoisomers, optical isomers, enantiomers).
- Mammals primarily utilize the L-form of amino acids.
Acid-Base Properties of Amino Acids
- Amino acids contain weakly acidic α-carboxyl groups and weakly basic α-amino groups.
- Acidic and basic amino acids contain ionizable groups within the side chain.
- Amino acids serve as buffers by resisting small changes in pH.
Henderson-Hasselbalch Equation
- Relates pH, pKa, and the ratio of a weak acid (HA) and its conjugate base (A-) in a buffer solution.
- Equation: pH = pKa + log([A-]/[HA]).
Titration of Amino Acids
- Amino acids have a pK value for every dissociable group.
- Alanine: titrated with NaOH, shows two pK values:
- pK1 (2.3) representing the dissociation of the carboxyl group.
- pK2 (9.7) representing the dissociation of the amino group.
- Isoelectric point (pI) is the pH at which the molecule has a net charge of zero.
- For alanine, pI is the average of pK1 and pK2.
Buffers in Amino Acid Titration
- Buffer pairs:
- -COOH/COO- pair buffers in the acid pH range.
- NH3+/-NH2 pair buffers in the basic pH range.
- pH = pK: if pH = pK1, equal amounts of forms I and II are present.
- Isoelectric point (pI):
- The pH where form II predominates with equal amounts of forms I and III.
- The average of pK1 and pK2.
Amino Acid Zwitterions
- Most amino acids have a net charge of zero at physiological pH due to the negatively charged α- carboxyl (–COO-) and positively charged α – amino (-NH3+).
- Isoelectric point (pI): pH at which the molecule has a net charge of zero.
- Amino acids are called zwitter ions (carry both a positive and negative charge) and are amphoteric.
Bicarbonate Buffer System
- CO2 + H2O H2CO3 H+ + HCO3-.
- Equation: pH = pK + log([HCO3-]/[H2CO3]).
- Regulates blood pH.
- Respiratory acidosis: increase in CO2 leads to increase in H2CO3 and decrease in pH.
- Increase in bicarbonate concentration increases pH.
Effect of pH on Drug Absorption
- Drugs readily pass through membranes in their uncharged form.
- Weak acids and weak bases:
- Weak acid (HA) ↔ H+ + A-.
- Weak base (BH+) ↔ B + H+.
- Effective concentration depends on the concentration of the dissociated and undissociated forms.
- Factors influencing the concentration of the dissociated and undissociated forms:
- pH at the absorption site.
- pKa of the ionizable group.
- Aspirin: weak acid, permeates in the HA (undissociated) form.
- Morphine: weak base, permeates membrane in its B (dissociated) form.
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Description
Explore the essential roles of proteins in living systems, including their functions as enzymes, hormones, and structural components. Additionally, delve into the structure and properties of amino acids, which are the building blocks of proteins. Understand how the unique characteristics of amino acids influence their role in biology.
