أسئلة المحاضرة الـ 12 بيو (قبل التعديل)

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Questions and Answers

What defines the primary protein structure?

The presence of hydrogen bonds between polypeptide chains

The three-dimensional shape of the protein

The number, type, and sequence of amino acids in a polypeptide chain (correct)

The sequence of nucleotides in DNA

Which bond is primarily responsible for maintaining the primary structure of proteins?

Hydrogen bond

Disulfide bridge

Ionic bond

Peptide bond (correct)

How many amino acids are present in one complete turn of an alpha-helix?

3.6 (correct)

What characterizes the formation of beta-pleated sheets?

Connected by hydrogen bonds between adjacent polypeptide chains Signup and view all the answers

Which statement is true about the super secondary structures in proteins?

They provide a unique structural feature for specific functions Signup and view all the answers

What is the typical characteristic of the helix-turn-helix (HTH) motif?

Consist of two alpha-helices connected by a short strand of amino acids Signup and view all the answers

What primarily stabilizes an alpha-helix structure in proteins?

Intrachain hydrogen bonds Signup and view all the answers

Which element is not involved in hydrogen bonding within protein structures?

Carbon Signup and view all the answers

What is the primary factor that leads to the formation of tertiary structure in proteins?

Interactions between side chains of amino acids Signup and view all the answers

Which type of bond is formed between the sulfur atoms of cysteine residues in proteins?

Disulfide bond Signup and view all the answers

Which forces are NOT involved in stabilizing tertiary protein structures?

Covalent bonds Signup and view all the answers

What characterizes the quaternary structure of proteins?

Multiple polypeptide chains arranged together Signup and view all the answers

Which of the following is an example of an oligomeric protein?

Hemoglobin (Hb) Signup and view all the answers

What type of bonds predominantly stabilize the quaternary structures of proteins?

Hydrogen bonds and ionic bonds Signup and view all the answers

Which of the following statements is true regarding secondary and tertiary structures of proteins?

Tertiary structure arises from the folding of secondary structures Signup and view all the answers

Which of the following proteins consists of a dimeric structure?

Creatine kinase (CK) Signup and view all the answers

Which structural feature is essential for the formation of secondary protein structures like α-helix and β-pleated sheets?

Hydrogen bonds Signup and view all the answers

What is the consequence of a change in the amino acid sequence within the primary protein structure?

Physiological defect Signup and view all the answers

Which of the following describes a characteristic of the helix-turn-helix (HTH) motif?

It consists of two α helices connected by a short amino acid strand. Signup and view all the answers

In a typical α-helix, how many amino acids are involved in one complete turn?

3.6 amino acids Signup and view all the answers

Which type of protein structure refers to the combination of α-helices and β-sheets forming specific patterns?

Super secondary structure Signup and view all the answers

What stabilizes the β-pleated sheet structure in proteins?

Hydrogen bonds between adjacent chains Signup and view all the answers

Which end of the polypeptide chain is referred to as the N-terminal end?

The end with the first amino acid's free -NH2 group Signup and view all the answers

What defines the primary structure of a protein?

The specific sequence of amino acids in the polypeptide chain Signup and view all the answers

What is the primary factor that leads to the formation of quaternary protein structure?

Special arrangement of more than one polypeptide chain Signup and view all the answers

Which forces control the tertiary structure of proteins?

Hydrogen bonds and hydrophobic forces Signup and view all the answers

Which type of bond is primarily responsible for stabilizing the tertiary structure of proteins?

Hydrogen bonds between polar side chains Signup and view all the answers

In the context of protein structure, what is a domain?

The final 3D arrangement of the protein Signup and view all the answers

Which of the following statements is true about protein oligomeric structure?

Tetramers are examples of oligomeric proteins Signup and view all the answers

What type of protein structure is characterized by interactions between oppositely charged side chains of amino acids?

Tertiary structure Signup and view all the answers

Which of these is true about hemoglobin regarding protein structure?

It is organized as a tetrameric protein Signup and view all the answers

Which bonds primarily stabilize the quaternary structure of proteins?

Non-covalent interactions, such as hydrogen or ionic bonds Signup and view all the answers

Study Notes

Protein Structure

Proteins are comprised of numerous amino acids connected by peptide bonds, creating a polypeptide chain.
The order, type, and sequence of amino acids in a polypeptide chain define the primary structure.
Any modification in an amino acid sequence can cause a physiological defect.
The primary structure is characterized by the peptide bond connecting the amino and carboxyl groups of amino acids.
N-terminal end represents the free amino group of the first amino acid.
C-terminal end signifies the free carboxyl group of the last amino acid.
The primary structure determines the subsequent structures.

Secondary Protein Structure

Secondary structure involves the folding of the polypeptide chain.
- Alpha-helix: A right-handed coiled helix stabilized by hydrogen bonds between the carbonyl oxygen of one peptide bond and the amino hydrogen of the fourth. Each turn in an alpha helix contains 3.6 amino acid residues. Hydrogen bonds are parallel to the helix axis.
- Beta-pleated sheets: Hydrogen bonds form between adjacent polypeptide chain segments, creating a pleated structure.
Secondary structures are common in globular proteins.
The folding process is spontaneous.

Super Secondary Structures (Motifs)

Super-secondary structures emerge from the combination of alpha-helices and beta-sheets.
Helix-turn-helix (HTH): Two alpha-helices connected by a short turn motif. It's a structural motif essential for DNA-binding proteins.

Tertiary Protein Structure

Tertiary structure encapsulates the three-dimensional arrangement of a polypeptide chain.
The interactions between R-groups (side chains) of amino acids dictate this folding pattern. Forces controlling tertiary structure include:
- Hydrogen bonds: between polar side chains
- Hydrophobic forces : between non-polar side chains
- Electrostatic forces (ionic bonds, salt bridges): between oppositely charged side chains
- Disulfide bonds: between cysteine residues.
Proteins fold into a stable 3D conformation called a domain.

Quaternary Protein Structure

Quaternary structure describes the arrangement of multiple polypeptide chains (subunits) in a protein.
The arrangement is stabilized by non-covalent bonds (hydrogen or ionic bonds).
Examples of oligomeric proteins with quaternary structure include hemoglobin (Hb), creatine kinase (CK), and lactate dehydrogenase (LDH), which consist of multiple protein subunits interacting together.

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