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Questions and Answers
What is the minimum molecular weight for a polypeptide to be classified as a protein?
What is the minimum molecular weight for a polypeptide to be classified as a protein?
Which of the following amino acids is an exception to the general rule of chirality in naturally occurring amino acids?
Which of the following amino acids is an exception to the general rule of chirality in naturally occurring amino acids?
What structural feature is found in all amino acids?
What structural feature is found in all amino acids?
Which statement about amino acids is accurate based on their acidic and basic properties?
Which statement about amino acids is accurate based on their acidic and basic properties?
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At low pH conditions, which of the following will occur to the carboxyl group (-COOH) of an amino acid?
At low pH conditions, which of the following will occur to the carboxyl group (-COOH) of an amino acid?
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What occurs at higher pH levels regarding the amino group on amino acids?
What occurs at higher pH levels regarding the amino group on amino acids?
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What is the isoelectric pH dependent on?
What is the isoelectric pH dependent on?
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Which of the following proteins is classified as fibrous?
Which of the following proteins is classified as fibrous?
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Which essential amino acid is required for infants but not universally considered essential for adults?
Which essential amino acid is required for infants but not universally considered essential for adults?
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Which of the following amino acids is essential and must be consumed in the diet?
Which of the following amino acids is essential and must be consumed in the diet?
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If glycine (G) and alanine (A) are mixed, which of the following represents all possible dipeptides?
If glycine (G) and alanine (A) are mixed, which of the following represents all possible dipeptides?
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What is a major characteristic of globular proteins compared to fibrous proteins?
What is a major characteristic of globular proteins compared to fibrous proteins?
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How many total tripeptides can be formed from glycine (G), alanine (A), and phenylalanine (P) if each must be present?
How many total tripeptides can be formed from glycine (G), alanine (A), and phenylalanine (P) if each must be present?
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Which food has the highest protein content according to the data provided?
Which food has the highest protein content according to the data provided?
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Which level of protein structure describes the sequence of amino acids in the peptide chain?
Which level of protein structure describes the sequence of amino acids in the peptide chain?
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Which protein function is primarily associated with muscle movement?
Which protein function is primarily associated with muscle movement?
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What type of amino acid cannot be synthesized by the body and must be obtained through diet?
What type of amino acid cannot be synthesized by the body and must be obtained through diet?
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What is true about conditionally essential amino acids?
What is true about conditionally essential amino acids?
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Which protein structure level describes the 3D conformation of the entire polypeptide?
Which protein structure level describes the 3D conformation of the entire polypeptide?
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Which of the following is a protective protein?
Which of the following is a protective protein?
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What is a primary challenge of vegetarian diets regarding protein intake?
What is a primary challenge of vegetarian diets regarding protein intake?
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What type of structure arises from weak attractive forces between hydrophobic parts of a protein chain?
What type of structure arises from weak attractive forces between hydrophobic parts of a protein chain?
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What is the primary difference between hemoglobin and myoglobin?
What is the primary difference between hemoglobin and myoglobin?
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What does the 'lock and key' mechanism describe regarding enzymes?
What does the 'lock and key' mechanism describe regarding enzymes?
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Which statement correctly describes denaturation of a protein?
Which statement correctly describes denaturation of a protein?
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What is a characteristic feature of collagen?
What is a characteristic feature of collagen?
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Where in the protein structure is the active site located?
Where in the protein structure is the active site located?
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What technique is used to describe the arrangement of secondary structures in proteins like fingernails and silk?
What technique is used to describe the arrangement of secondary structures in proteins like fingernails and silk?
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Which term describes proteins that contain more than one polypeptide chain?
Which term describes proteins that contain more than one polypeptide chain?
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Study Notes
Amino Acids/Proteins
- Proteins/polypeptides are chains formed by the condensation/combination of 20 different α-amino acids.
- Polypeptides can be di-, tri-, etc., up to 10 amino acids.
- Proteins are longer than 10 amino acid units, with molecular weights greater than 10,000.
- Amino acids have both a carboxyl group (-COOH) and an amino group (-NH₂).
- All amino acids in proteins have the -NH₂ group attached to the α-carbon of the -COOH group.
- All naturally occurring α-amino acids, except glycine, are chiral and the L-stereoisomer.
- There are 20 α-amino acids in naturally occurring proteins.
- Each amino acid has a common name often ending in "-ine".
- Approximately 150 other physiologically important amino acids exist, including GABA (a neurotransmitter).
Amino Acid Structure
- Amino acids are categorized based on the properties of their R groups.
- Nonpolar R groups (hydrophobic) include glycine, alanine, proline, valine, tryptophan, isoleucine, methionine, leucine, and phenylalanine.
- Polar R groups (hydrophilic) include serine, asparagine, glutamine, threonine, tyrosine, histidine, cysteine, aspartic acid, glutamic acid, lysine, and arginine.
Peptide Bonds
- Peptide bonds form when the carboxyl group of one amino acid reacts with the amino group of another amino acid, releasing a water molecule.
- This process is known as condensation.
- When peptide bonds are broken by hydrolysis, the hydroxyl and hydrogen from water are added to the amino acid.
- Dipeptides are formed by linking two amino acids.
- Tripeptides involve three amino acids.
pH Dependent Properties
- Zwitterionic structures in amino acids contain both N-H⁺ and COO⁻ groups.
- At low pH, the COO⁻ group is protonated.
- At higher pH, the N-H⁺ group loses a hydrogen ion.
- The isoelectric pH differs for each amino acid.
Protein Structure Levels
- Primary structure: the sequence of amino acids and the position of disulfide bridges in the polypeptide chain.
- Secondary structure: the conformation/shape of the backbone of the protein, which includes α-helices and β-sheets.
- Tertiary structure: the three-dimensional structure of the entire polypeptide chain.
- Quaternary structure: exists for proteins with more than one polypeptide chain, describing the arrangement of those chains.
Insulin
- Insulin is a protein with a specific amino acid sequence.
Hemoglobin and Myoglobin
- Hemoglobin has four polypeptide chains and possesses quaternary structure, carrying O₂, CO₂, and H⁺ in the blood.
- Myoglobin has a single amino acid chain (153) that carries O₂ from blood vessels to muscles.
Enzyme Structure
- Many enzymes are proteins.
- Their specific binding properties to a substrate depend on their overall molecular shape/conformation.
Protein Denaturation
- Denaturation is a process that changes protein structure, making it incapable of performing its normal function.
- Heating egg whites and permanent hair waving are examples of denaturation which can be irreversible or reversible.
Protein Classification
- Proteins are classified by structure into simple (fibrous and globular) and conjugated proteins (lipo-, glyco-, and hemo- proteins).
- Fibrous proteins (e.g., collagen, elastin, keratins, myosins) are insoluble and structural.
- Globular proteins (e.g., albumins, globulins, enzymes) are soluble and reactive.
Protein Functions
- Proteins perform diverse functions: enzymatic catalysis, muscle contraction, hormone transport (eg., insulin), neurotransmitter signaling , storing nutrients (eg., casein in milk), transporting other molecules (e.g., hemoglobin, transferring, ceruloplasmin), immunologic roles (eg., antibodies), hormones, enzymes, and as structural components.
(Non)Essential Amino Acids
- Essential amino acids (10) cannot be synthesized in the body and must be obtained from the diet (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and arginine in infants).
- Non-essential amino acids (10) can be synthesized in the body from metabolic breakdown products.
Vegetarian Diets
- A key challenge in vegetarian diets is obtaining sufficient high-quality protein with a correct balance of essential amino acids.
Protein Content of Foods
- Different foods have varying protein contents (e.g., cheese has high, cassava has low).
Malnutrition
- Malnutrition is the inability to obtain sufficient complete proteins, specifically essential amino acids, hindering proper body function.
- Symptoms include emaciation, bloated abdomen, lack of pigmentation, and mental apathy, sometimes leading to eventual death.
Glycolipids
- Glycolipids are derived from ceramides with directly attached carbohydrates.
- Unlike sphingomyelin, they lack a phosphocholine group.
Glycoproteins
- Glycoproteins contain oligosaccharide (glycans) chains attached to polypeptide chains through glycosylation.
- Glycosylation occurs during co- and post-translational protein modification.
Functions of glycoproteins
- Glycoproteins have diverse functions including structural components (e.g., collagen), lubricants (e.g., mucins), transport molecules (e.g., transferrin), immunologic molecules (e.g., antibodies), hormones (e.g., thyroid stimulating hormone), enzymes, and cell-recognition sites.
Glycolipid structure
- Glycolipids such as cerebrosides contain a carbohydrate component linked to ceramide via an O-glycosidic bond.
- They are abundant in brain and myelin sheaths, containing a single or short chain of sugars.
Roles of Glycolipids
- Glycolipids play important roles in cell signaling, growth, development, and antigenic activity, acting as surface receptors and influencing cell transformation.
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Description
Test your knowledge on the fundamental aspects of amino acids and proteins in this biochemistry quiz. Explore questions about molecular weight, chirality exceptions, and the structural features common to all amino acids. Evaluate your understanding of their properties under various pH conditions.
