Proteins Flashcards

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Questions and Answers

What is elastin?

An insoluble protein polymer synthesized from a precursor, tropoelastin.

What is the amino acid structure of elastin primarily composed of?

Phenylalanine, Serine, Threonine

Glycine, Alanine, Valine (correct)

Methionine, Cysteine, Glutamic Acid

Lysine, Proline, Asparagine

What is desmosine?

A unique cross-link in elastin made of four Lysine residues connected through their side chains.

What are some disorders associated with elastin?

α1-antitrypsin deficiency, Marfan Syndrome, Cutis Laxa. Signup and view all the answers

What is the primary cause of emphysema?

Cigarette smoking. Signup and view all the answers

What is Marfan Syndrome?

An inherited degenerative disorder of the connective tissue. Signup and view all the answers

What is Cutis Laxa?

A rare connective tissue disorder where the skin becomes inelastic and hangs loosely. Signup and view all the answers

What kind of proteins are integral membrane proteins?

Proteins that penetrate the hydrophobic regions of the phospholipid bilayer. Signup and view all the answers

What are glycoproteins?

Proteins that are covalently attached to oligosaccharides. Signup and view all the answers

What distinguishes ligases from other enzyme types?

They synthesize bonds using the hydrolysis of ATP. Signup and view all the answers

What is the role of protein chaperones?

They assist in the proper folding of proteins. Signup and view all the answers

What can cause protein denaturation?

Changes in pH, heat, organic solvents, and mechanical mixing. Signup and view all the answers

What are prion diseases?

Diseases caused by infectious prion proteins forming insoluble aggregates. Signup and view all the answers

What are amino acids?

Make up proteins; there are about 20 of them. Signup and view all the answers

What are proteins?

The primary structural and functional polymers in living systems. Signup and view all the answers

What are proteins linked by?

Peptide bonds. Signup and view all the answers

What is a peptide?

A short protein consisting of 2 to ~50 amino acids. Signup and view all the answers

What is a peptide bond?

A covalent amide bond formed between the α-carboxyl group of one amino acid and the α-amino group of another. Signup and view all the answers

What are electrostatic interactions?

Ionic bonds formed between oppositely-charged amino acid side chains. Signup and view all the answers

What are dipole-dipole interactions?

Hydrogen bonds formed between hydrogen ions shared between two amino acid side chains. Signup and view all the answers

What are hydrophobic interactions?

Interactions where hydrophobic amino acids tend to collect in the interior of proteins. Signup and view all the answers

What are covalent interactions?

Disulfide bonds that stabilize the 3D protein structure. Signup and view all the answers

What are the small amino acids?

Glycine and Alanine. Signup and view all the answers

What are the branched-chain amino acids?

Valine, Leucine, and Isoleucine. Signup and view all the answers

What are the hydroxyl amino acids?

Serine and Threonine. Signup and view all the answers

What are the sulfur amino acids?

Cysteine and Methionine. Signup and view all the answers

What are the aromatic amino acids?

Phenylalanine, Tyrosine, and Tryptophan. Signup and view all the answers

What are the acidic amino acids?

Glutamate and Aspartate. Signup and view all the answers

What are the basic amino acids?

Lysine, Arginine, and Histidine. Signup and view all the answers

Explain Proline.

Proline has its nitrogen in a ring structure, making it unique among amino acids. Signup and view all the answers

What is sickle-cell anemia?

A condition in hemoglobin caused by a substitution of nonpolar valine for polar glutamate in β subunits. Signup and view all the answers

Explain normal Hemoglobin.

Hemoglobin is composed of 4 protein subunits (2 α- and 2 β-chains). Signup and view all the answers

Explain Sickle Cell Hemoglobin.

Sickle Cell Hemoglobin substitutes valine for glutamic acid in the 6th position of both β-chains. Signup and view all the answers

Explain the Clinical Diagnosis.

Measurement of free amino acids in urea is useful in clinical diagnosis. Signup and view all the answers

What are protein functions?

Proteins perform specific functions such as binding, structural support, enzymatic catalysis, and regulation. Signup and view all the answers

What is the primary structure of a protein?

The amino acid sequence determined by the gene's DNA. Signup and view all the answers

What is the secondary structure of a protein?

This can be an α helix, β sheet, or both. Signup and view all the answers

What are supersecondary structures?

Involve the association of secondary structures in a specific arrangement. Signup and view all the answers

What is the tertiary structure?

The folding of the secondary structure into a functional 3D shape. Signup and view all the answers

How many interactions are needed for tertiary structure?

Four interactions. Signup and view all the answers

What is the quaternary structure of a protein?

Formation involving more than one polypeptide chain. Signup and view all the answers

How many interactions are needed for quaternary structure?

Three interactions (all but covalent). Signup and view all the answers

When is a protein soluble?

When polar amino acids are clustered on its surface. Signup and view all the answers

When is a protein classified as a membrane protein?

When nonpolar amino acids cluster on the surface. Signup and view all the answers

What is a homoprotein?

Simple proteins that contain exclusively amino acids. Signup and view all the answers

What are heteroproteins?

Conjugated proteins that contain a non-protein part. Signup and view all the answers

What are fibrous proteins?

Proteins such as Keratin, Collagen, and Elastin. Signup and view all the answers

What are globular proteins?

Proteins like myoglobin that perform metabolic work. Signup and view all the answers

Name the fibrous proteins.

Keratin, Collagen, Elastin. Signup and view all the answers

What is Keratin?

A fibrous protein that is a main constituent of structures growing from the skin. Signup and view all the answers

What are the two types of Keratin deficiencies?

Epidermolysis Bullosa Simplex and Monilethix. Signup and view all the answers

What is Collagen?

A fibrous protein found in the extracellular matrix. Signup and view all the answers

Explain Collagen.

A protein consisting of three different subunits formed into a triple helix. Signup and view all the answers

What is the nascent peptide?

The repeating collagen in alpha-helix with high glycine and proline content. Signup and view all the answers

How does Hydroxyproline stabilize collagen?

Hydroxylation requires vitamin C and is a post-translational modification. Signup and view all the answers

What is Tropocollagen?

The basic unit of collagen formed by cleavage of staggered ends. Signup and view all the answers

What are collagen fibrils?

Structures formed by covalent cross-linking via Lysyl Oxidase. Signup and view all the answers

What is extensive hydrogen bonding?

Strengthening through using carbonyl and amine of glycine. Signup and view all the answers

What is needed for proper collagen formation?

Vitamin C. Signup and view all the answers

What is Scurvy?

A condition due to lack of Vitamin C that affects collagen cross-linking. Signup and view all the answers

What is Ehlers-Danlos syndrome?

A group of inherited connective tissue disorders caused by collagen synthesis defects. Signup and view all the answers

What is Osteogenesis imperfecta?

Known as brittle bone syndrome, affecting bone strength. Signup and view all the answers

What are the four different types of Osteogenesis imperfecta?

Type I, Type II, Type III, and Type IV. Signup and view all the answers

What are the symptoms of Osteogenesis imperfecta?

Blue sclera, early hearing loss, and weak bones. Signup and view all the answers

What is Elastin?

A stretchable, elastic fibrous protein located in connective tissues. Signup and view all the answers

Study Notes

Amino Acids

Over 300 amino acids exist in nature; only 20 are used in mammalian proteins.
Amino acids classified by side chains into categories: Small, Branched-chain, Hydroxy, Sulfur, Aromatic, Acidic, and Basic.

Proteins

Serve as structural and functional polymers in living organisms.
Involved in energy usage, nerve transmission, muscle contraction, blood clotting, immune defense, and transport of vital substances.
All proteins feature an N-terminal with a free amine group and a C-terminal with a free carboxyl group.

Peptides and Bonds

Peptides are short chains of amino acids (2 to 50).
Peptide bonds form covalent amide bonds between the carboxyl group of one amino acid and the amino group of another, making proteins water-soluble.

Interactions in Proteins

Electrostatic interactions attract oppositely charged side chains while repelling like charges.
Dipole-Dipole interactions or hydrogen bonds involve sharing of hydrogen ions between side chains.
Hydrophobic interactions occur as hydrophobic amino acids cluster in the interior of globular proteins, excluding water.

Types of Amino Acids

Small amino acids: Glycine and Alanine, found where polypeptide chains are close.
Branched-chain amino acids: Valine, Leucine, Isoleucine with hydrophobic properties.
Hydroxyl amino acids: Serine and Threonine, capable of forming hydrogen or covalent bonds with sugars and phosphates.
Sulfur amino acids: Cysteine and Methionine; cysteine can form disulfide bonds to stabilize protein structure.
Aromatic amino acids: Phenylalanine, Tyrosine, and Tryptophan; they can form hydrogen bonds and are generally hydrophobic.
Acidic amino acids: Glutamate and Aspartate, negatively charged at physiological pH, important for forming strong hydrogen bonds.
Basic amino acids: Lysine, Arginine, and Histidine, which carry a positive charge.

Unique Amino Acids

Proline has a ring structure, affects flexibility, and is typically found at bends in polypeptides.
Sickle-cell anemia occurs when valine replaces glutamate in hemoglobin, producing distorted red blood cells.

Hemoglobin Structures

Normal hemoglobin consists of four subunits (2α and 2β chains).
Sickle Cell hemoglobin can polymerize under low oxygen conditions, leading to sickle-shaped cells, which cause severe anemia.

Protein Functions

Protein functions include binding, cellular structure, enzymatic catalysis, mechanical support, regulation, storage, and transport.
Structure determines protein functionality.

Protein Structures

Primary structure refers to the amino acid sequence.
Secondary structure includes α-helices and β-sheets, stabilized by hydrogen bonds.
Tertiary structure is the overall 3D conformation influenced by several types of interactions (electrostatic, hydrogen bonds, hydrophobic, and disulfide bonds).
Quaternary structure involves multiple polypeptide chains organized through non-covalent interactions.

Protein Solubility

Proteins are soluble when polar amino acids are on the surface and membrane proteins when nonpolar amino acids are exposed.

Protein Classification

Homoproteins contain only amino acids; heteroproteins include non-protein prosthetic groups.
Fibrous proteins (e.g., Keratin, Collagen, Elastin) provide structural support and are water-insoluble.
Globular proteins (e.g., myoglobin) are generally water-soluble and perform metabolic functions.

Keratin

A fibrous protein, primarily makes up skin appendages like hair and nails.
Exists in two forms: α-keratin (in mammals) and β-keratin (in birds).

Collagen

Most abundant protein in the extracellular matrix, vital for connective tissue strength.
Composed of triple helices that form fibrils through covalent cross-linking.

Collagen Disorders and Deficiencies

Scurvy, resulting from vitamin C deficiency, impairs collagen cross-linking leading to weakened connective tissues.
Ehlers-Danlos syndrome results from collagen synthesis defects, leading to stretchy skin and fragile joints.
Osteogenesis imperfecta is known for fragile bones due to mutations in collagen.

Elastin

A highly stretchable protein found in connective tissues, allowing tissues to regain shape after stretching.
Deficiencies or mutations can lead to disorders like Marfan Syndrome and α1-antitrypsin deficiency, leading to emphysema.

Testing and Diagnosis

Clinical diagnosis can involve measuring free amino acids in urine and plasma to detect metabolic abnormalities.### Marfan's Syndrome
Marfan's syndrome is characterized by tall stature, elongated limbs, and long thin fingers.
Affects multiple organ systems including the eyes, heart, blood vessels, and skeleton.
Major complication includes heart valve and aortic defects which can lead to life-threatening ruptures.
Strenuous activities can exacerbate aortic aneurysms and lead to joint or lens injuries.

Cutis Laxa (CL)

Cutis laxa is a rare connective tissue disorder resulting in loose and inelastic skin.
Can be inherited or acquired and may develop due to inflammatory rashes or spontaneously.
Various inheritance patterns exist: autosomal dominant, autosomal recessive, and X-linked recessive.
Associated with a mutation in the FBLN5 gene impairing elastogenesis, particularly in recessive forms.

Cell Membrane Proteins

Integral membrane proteins penetrate the hydrophobic phospholipid bilayer, playing critical biological roles.
Peripheral membrane proteins are loosely associated with membranes, often linked to integral proteins.
Glycoproteins, sugar-coated proteins, are important for cell-cell recognition and interaction.
Enzymes in the membrane facilitate chemical reactions essential for metabolism.

Functions of Cell Membrane Proteins

Membrane proteins account for approximately 25% of all cellular proteins.
Essential for cellular communication including transport of molecules, cell recognition, and communication.
Active transport mechanisms (e.g., ATPase) use energy to move ions against concentration gradients.

Integral Membrane Proteins (Integrins)

Integral membrane proteins are essential for membrane structure and function, interacting with the phospholipid bilayer.
Typically removed from membranes only through strong detergents that disrupt hydrophobic interactions.
They include hormone receptors, ion channels, and transporters pivotal for cellular functions.

Examples of Integrins

Include hormone receptors, transporters like Na+ - K+ ATPase, and various enzymes.
Notable example: β-adrenergic receptor spans the membrane seven times, indicating its integral role in signaling.

Membrane Transporters

Comprise proteins with transmembrane domains that facilitate both active and passive transport of substances across membranes.
Active transport involves energy use (e.g., Na-K ATPase), while passive transport relies on diffusion.

ABC Transporters

Largest family of transporters, crucial for nutrient uptake, drug excretion, and cellular functions.
Utilize ATP hydrolysis for the transport of substrates across cellular membranes.
Key features include ATP Binding domains and transmembrane domains formed by alpha helices.

Peripheral Membrane Proteins

Loosely associated with cell membranes and typically attached to integral proteins.
Example: Cytochrome C in the electron transport chain.

Glycoproteins

Proteins covalently bonded to oligosaccharides, significant for cell surface recognition and interaction.
Key roles in antigenicity, membrane receptor function, and extracellular matrix components.

Key Enzymes Classification

Oxidoreductases: Transfer electrons between molecules.
Transferases: Move functional groups between molecules.
Isomerases: Rearrange molecular structures.
Lyases: Add or remove atoms from double bonds.
Ligases: Form bonds using ATP hydrolysis.
Hydrolases: Cleave bonds through water addition.

Glutathione

A critical tri-peptide composed of Glu, Cys, and Gly, playing roles in protein synthesis and antioxidant defenses.
Protects cells from oxidative stress and facilitates amino acid transport across membranes.

Protein Misfolding

Errors in protein folding can lead to diseases, caused either by spontaneous folding mistakes or genetic mutations.
Misfolded proteins are often tagged for degradation, impacting bodily functions.

Diseases Linked to Protein Misfolding

Examples include cystic fibrosis (misfolded CFTR), Marfan syndrome (misfolded fibrillin), and various cancers linked to tumor suppressor protein misfolding.
Protein aggregation disorders include Alzheimer's, Parkinson's, and spongiform encephalopathies.

Amyloidoses

Defined by abnormal fibrillar protein formation, primarily β-pleated sheets.
Result in insoluble amyloid deposits affecting tissue function.

Prion Diseases

Caused by infectious prion proteins leading to transmissible spongiform encephalopathies (TSEs) such as Creutzfeldt-Jakob disease.
These diseases are characterized by insoluble fibril aggregation, causing severe neurodegeneration.

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Test your knowledge of proteins and amino acids with these flashcards. Learn about the types and functions of amino acids and their role in protein structure and function. This quiz is perfect for biology students and anyone interested in understanding proteins better.