Protein Structure and Function

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Questions and Answers

What are the most structurally complex and sophisticated molecules?

Proteins

What type of bond links amino acids together?

Covalent peptide bond

Which of the following determines the folding of protein chains?

Ionic bonds

Hydrogen bonds

Peptide bonds

Noncovalent bonds (correct)

What does the 3-D structure of a protein depend on?

Amino acid sequence Signup and view all the answers

The final folded shape of a protein is that which maximizes its free energy.

False Signup and view all the answers

What assists proteins to fold in their correct shapes?

Molecular chaperones Signup and view all the answers

Which structural feature is a result of hydrogen bonding between N-H and C=O?

Secondary structure Signup and view all the answers

Alpha helices are abundant in cell membranes.

True Signup and view all the answers

What is an example of a protein that consists of amino acid sequence?

Enzyme Signup and view all the answers

What characterizes the primary structure of proteins?

Amino acid sequence Signup and view all the answers

What is domain shuffling?

Accidental joining of DNA sequences leading to multidomain proteins Signup and view all the answers

Match the following protein structures to their descriptions:

Primary structure = Amino acid sequence Secondary structure = Alpha helices and beta sheets Tertiary structure = 3-D shape Quaternary structure = More than one polypeptide Signup and view all the answers

What are paralogs?

Genes that evolve independently within the same organism Signup and view all the answers

Orthologs are proteins that have different functions in different organisms.

False Signup and view all the answers

What type of proteins are serine proteases?

Protein cleaving enzymes Signup and view all the answers

What is the role of the SH2 domain?

Responds to cell signals to cause selected protein molecules to bind Signup and view all the answers

What type of binding occurs at the binding site of a protein?

Noncovalent bonds Signup and view all the answers

Study Notes

Protein Structure

Proteins are the most complex molecules.
Amino acids are linked together by covalent peptide bonds.
The polypeptide backbone consists of repeating sequences of atoms.
Amino acid side chains are attached to the backbone and are not involved in peptide bonds.
The folding of a protein chain is determined by noncovalent bonds.
The 3-D structure of a protein is determined by its amino acid sequence.
The final folded shape of a protein minimizes its free energy.
The conformation of a protein can fluctuate due to thermal energy and interactions with other molecules.
Molecular chaperones assist proteins in folding into their correct shapes.

Secondary Structure

α-helix and β-sheet structures form due to hydrogen bonding between the N-H and C=O groups of the polypeptide backbone.
α-helixes are abundant in cell membranes, with their nonpolar regions exposed and polar regions inside.
β-sheets are parallel or antiparallel chains held by hydrogen bonds.
α-helixes form when a single polypeptide chain twists into a cylinder with H-bonds between every fourth peptide bond.
α-helixes can wrap around each other to form coiled coils, where the nonpolar parts of the two helices are on the inside.

Protein Domains

Larger proteins consist of smaller protein domains.
SH2 domains are involved in cell signaling and cause protein binding.
Src protein kinase contains SH2, SH3, and a C-terminal domain for catalytic activity.
Intrinsically disordered regions (IDRs) act as flexible hinges between domains.
Proteins are constantly in motion, and this flexibility can expose binding sites for other molecules.
Thousands of possible protein polypeptides exist, but only a small fraction are stable and found in cells.

Protein Families and Evolution

Gene duplication allows gene copies to evolve independently, leading to new functions.
Protein families are groups of proteins with similar structures and functions.
Paralogs are proteins within the same species that evolved from gene duplication.
Orthologs are proteins with the same function but found in different species.
Serine proteases are a family of enzymes with similar structures but different functions.

Domain Shuffling

Domain shuffling involves the accidental joining of DNA sequences, creating multidomain proteins.
New binding surfaces arise where two domains meet.
Protein modules are mobile domains that can move between different proteins, leading to diverse functions.
Some domains with N and C terminals on opposite poles lead to extended structures.
Other domains with N and C terminals close together are plug-in type, inserting into loops of other proteins.

Protein Binding

Binding site: a region on a protein's surface that binds to another molecule through noncovalent bonds.
Subunits: individual polypeptide chains that make up a protein complex.
Dimer: a protein composed of two subunits.
Haemoglobin, for example, contains two alpha globin subunits and two beta globin subunits.

Protein Classification

Globular proteins: polypeptide chains that fold into a compact, spherical shape.
Fibrous proteins: extended polypeptide chains, forming structures with high tensile strength.

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Description

This quiz explores the intricate details of protein structure, focusing on the formation of peptide bonds, the importance of amino acid sequences, and the roles of noncovalent bonds in determining protein folding. Additionally, the secondary structures such as α-helices and β-sheets are examined, showcasing their formation and characteristics. Test your knowledge on these essential concepts of biochemistry.