Cellular & Molecular Biology - Protein Structure

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Questions and Answers

What is the primary function of enzymes in the cell?

To catalyze chemical reactions. (correct)

To transport molecules across membranes.

To provide structural integrity.

To store genetic information.

Which of the following statements about protein domains is true?

Protein domains are always linked by disulfide bonds.

Each protein domain can perform multiple functions.

Protein domains can fold into a 3D conformation independently. (correct)

Protein domains are independent units that do not have specific functions.

What role do cofactors play in enzyme functionality?

They provide structural support to the enzyme.

They help enzymes function normally by binding to them. (correct)

They are unnecessary for enzyme action.

They permanently attach to the enzyme through hydrogen bonds.

Which type of bond is primarily involved in the binding of substrates at the active site of an enzyme?

Weak non-covalent bonds. Signup and view all the answers

What is true about the regulation of enzyme activity?

Regulatory molecules can both enhance and inhibit activity. Signup and view all the answers

Which enzyme type is specifically known for adding a phosphate group to D-glucose?

Hexokinase. Signup and view all the answers

What type of cofactor is required by DNA polymerase for its activity?

An inorganic ion. Signup and view all the answers

Which statement best describes the formation of the enzyme-substrate complex?

The enzyme does not change after the reaction. Signup and view all the answers

What is the defining characteristic of quaternary structure in proteins?

It consists of two or more polypeptide chains forming a complex. Signup and view all the answers

How are α-helices stabilized within a protein structure?

Through hydrogen bonds formed every fourth amino acid. Signup and view all the answers

What is the primary basis for the formation of β-sheets in proteins?

Hydrogen bonds between segments of polypeptide chains lying side by side. Signup and view all the answers

What types of interactions play a role in stabilizing the tertiary structure of proteins?

Disulfide bonds, hydrogen bonds, and hydrophobic interactions. Signup and view all the answers

Which of the following best describes the role of hydrophobic side chains in protein folding?

They cluster in the interior of proteins in an aqueous environment. Signup and view all the answers

What type of protein structure is exemplified by immunoglobulins?

Quaternary structure featuring multiple polypeptide chains. Signup and view all the answers

How many polypeptide chains form the quaternary structure of hemoglobin?

Four polypeptide chains. Signup and view all the answers

Which statement about tertiary structure is true?

It is influenced by interactions among side chains of amino acids. Signup and view all the answers

What is the significance of the primary structure in protein function?

It is the sequence of amino acids and dictates all higher-level structures. Signup and view all the answers

In which type of environment do hydrophilic side chains tend to be located within a folded protein?

On the surface, interacting with the aqueous environment. Signup and view all the answers

What are molecules called that decrease the activity of an enzyme?

Inhibitors Signup and view all the answers

What characteristic defines competitive inhibitors?

They are structurally similar to the substrate. Signup and view all the answers

What happens to the reaction rate of an enzyme due to non-competitive inhibition?

It remains constant irrespective of substrate concentration. Signup and view all the answers

What is the consequence of protein misfolding in cells?

Formation of amyloid fibrils. Signup and view all the answers

Which of the following diseases is associated with the formation of amyloid plaques?

Alzheimer’s disease Signup and view all the answers

What is the primary consequence of abnormal protein conformation in sickle cell anemia?

Rigid and sticky red blood cells. Signup and view all the answers

What is formed from the accumulation of amyloid fibrils?

Amyloid plaques Signup and view all the answers

What typically triggers the autophagy process in the degradation of misfolded proteins?

Presence of misfolded proteins Signup and view all the answers

What role do allosteric sites play in non-competitive inhibition?

They change the enzyme's active site conformation. Signup and view all the answers

Which of the following is NOT a reason for misfolded proteins to accumulate?

Enhanced chaperone protein activity. Signup and view all the answers

What is the primary role of covalent bonds in biological molecules?

They share electrons to stabilize atoms' outer shells. Signup and view all the answers

Which type of bond is formed between two amino acids in a polypeptide chain?

Peptide bond Signup and view all the answers

What defines the unique properties of different amino acids?

The specific side chain attached to the α-carbon. Signup and view all the answers

Which term best describes the final 3D shape of a protein?

Functional conformation Signup and view all the answers

Which factor can lead to protein misfolding and associated diseases?

Changes in protein conformation Signup and view all the answers

How do hydrophilic side chains interact with water?

They form hydrogen bonds with water. Signup and view all the answers

Which of the following is NOT a type of weak non-covalent interaction?

Covalent bonds Signup and view all the answers

What is the process of protein folding primarily driven by?

Hydrophobic forces and interactions. Signup and view all the answers

Which statement about ionic bonds in proteins is true?

They form between charged side chains. Signup and view all the answers

What is the relationship between peptide bonds and water?

Peptide bonds are formed by the removal of water. Signup and view all the answers

Which property does NOT characterize hydrophobic side chains?

They dissolve easily in water. Signup and view all the answers

What is the role of enzymes in relation to chemical bonds?

They catalyze reactions that break specific bonds. Signup and view all the answers

What is the significance of the sequence of amino acids in a polypeptide chain?

It dictates the protein's shape and function. Signup and view all the answers

What type of interaction predominates when non-polar molecules aggregate in an aqueous environment?

Hydrophobic forces Signup and view all the answers

What role do chaperone proteins play in protein folding?

They speed up the folding process by providing energy. Signup and view all the answers

Which level of protein structure is primarily defined by the sequence of amino acids?

Primary structure Signup and view all the answers

What type of bonding is responsible for the formation of β-sheets in proteins?

Hydrogen bonds Signup and view all the answers

During protein folding, what is one consequence of incorrect folding due to improper chaperone function?

The protein becomes tangled with other chains. Signup and view all the answers

Which of the following is NOT a characteristic of the tertiary structure of proteins?

It is defined solely by the amino acid sequence. Signup and view all the answers

Which of the following compartments does NOT typically assist in the protein folding process?

Endosome Signup and view all the answers

What is the purpose of ATP hydrolysis in the context of chaperone proteins?

To provide energy for the folding process. Signup and view all the answers

In the context of protein structure, what does the term 'polypeptide backbone' refer to?

The central chain of amino acids connected by peptide bonds. Signup and view all the answers

Study Notes

Cellular & Molecular Biology - MD105

Course is taught by Dr. C. Michaeloudes
Offered by the European University Cyprus, School of Medicine
Topics covered include protein structure and function, lecture objectives, chemical bonds, electrons and bonding, covalent bonds, weak non-covalent interactions, hydrophobic forces, amino acid structure, polypeptide chains, protein synthesis, protein folding, chaperone proteins, levels of protein structure organization, protein folding, where protein folding occurs, protein domains, enzyme function, enzyme cofactors, enzyme activity, regulatory molecules, competitive inhibition, non-competitive inhibition, protein misfolding and disease, misfolded proteins, misfolding and neurodegenerative diseases, sickle cell anaemia

Protein Structure and Function

Lecture objectives include understanding amino acid structure, polypeptide chain formation, protein folding levels, 3D conformation importance and protein roles in cells.
The role of enzymes and enzyme activity regulation is also covered.
The role of protein misfolding in disease is also mentioned.

Chemical Bonds

Chemical bonds hold atoms together to form molecules.
Chemical bonds are attractive forces between atoms or molecules.
Chemical bonds in biological molecules include covalent and weak non-covalent bonds.

Electrons and Bonding

Atomic nucleus consists of protons (positive charge) and neutrons (neutral).
Electrons orbit the nucleus in shells.
Shells can hold a maximum number of electrons.
Atoms with complete outer shells are very stable.
Atoms with incomplete outer shells interact to fill shells.

Covalent Bonds

Covalent bonding involves sharing electrons between atoms.
Shared electrons hold the nuclei together.
Covalent bonds are the strongest bonds in cells.
Covalent bonds are broken and formed via chemical reactions catalyzed by enzymes.
Disulfide bonds are covalent bonds between thiol groups in amino acids.

Weak Non-Covalent Interactions

Electrostatic attractions result from electron transfer creating charged ions.
Positive and negative ions attract.
Hydrogen bonds form between a slightly positive hydrogen and a slightly negative oxygen or nitrogen atom.
Van der Waals attractions are transient attractions due to electron fluctuations.

Hydrophobic Forces

Hydrophobic forces are not considered bonds.
Hydrophobic molecules aggregate away from water in an aqueous environment.

Amino Acid Structure and Formation of Polypeptide Chains

Amino acids are small organic molecules with a carboxyl group (-COOH) and an amino group (-NH2) attached to a central α-carbon.
The α-carbon has a specific side chain distinguishing amino acids.
Twenty different amino acids have unique chemical properties due to their side chains.
Side chains give amino acids unique chemical properties.

Protein Domains

Proteins are divided into functional units (40-350 amino acids).
Each domain has a specific function, like DNA-binding or calcium-binding.

Enzyme Function

Enzymes catalyze nearly all reactions in cells.
They accelerate reaction rates.
Enzymes bind to and convert substrates into products.
Enzyme substrates bind to the enzyme's active site which has a specific shape.
Enzyme reactions often involve making or breaking covalent bonds in substrate molecules.
Enzymes are grouped into classes based on chemical reactions.

Enzyme Cofactors

Some enzymes require cofactors, non-protein molecules, for normal function.
Cofactors can be inorganic ions (e.g., Fe2+ or Mg2+).
Cofactors can also be organic molecules (e.g. vitamins).

Enzyme Activity

Enzyme activity rate increases with substrate concentration up to a point.
Enzyme activity can be regulated by other molecules.

Regulatory Molecules

Enzymes can be regulated by molecules that either increase or decrease activity.
Activators increase activity, inhibitors decrease it.
Competitive and non-competitive inhibitors are types of enzyme inhibitors.

Protein Misfolding and Disease

Misfolded proteins are degraded by lysosomes.
Mutations, defective lysosomes, and abnormal chaperone protein function can lead to protein aggregation and formation of amyloid fibrils and plaques.

Misfolding and Neurodegenerative Diseases

Accumulation of amyloid plaques on neurons causes neurodegenerative diseases, Alzheimer's Disease, Huntington's Disease, Bovine spongiform encephalopathy, and Creutzfeldt-Jakob disease.

Sickle Cell Anaemia

A single nucleotide mutation in haemoglobin leads to a different amino acid, valine, in place of glutamate.
This causes abnormal protein conformation, rigid protein fibers, and red blood cell abnormalities (sickle cells), ultimately leading to anaemia and blood vessel obstruction.

Protein Folding

Polypeptide chains fold into 3D shapes to form functional proteins.
Protein folding is assisted by chaperone proteins.
The final shape is the functional conformation.
Changes in protein conformation lead to changes in protein function.
Proteins fold in the endoplasmic reticulum, mitochondria, cytoplasm, and nucleus.

Levels of Protein Structure Organization

Primary structure: Amino acid sequence.
Secondary structure: Hydrogen bonds create a-helices and B-sheets.
Tertiary structure: 3D folding due to interactions between side chains.
Quaternary structure: Multiple polypeptide chains form a complex.

Protein Function

Proteins perform many different jobs in cells, including acting as enzymes, hormones, motor proteins, structural components, antibodies, or transport proteins.

Studying That Suits You

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Description

Test your knowledge on protein structure and function in this quiz designed for MD105. Covering topics such as amino acid structure, polypeptide formation, and enzyme activity, this quiz will challenge your understanding of protein roles in cellular processes. Explore the significance of protein folding and its implications in diseases like sickle cell anemia.