Lecture 5 Review

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Questions and Answers

What triggers the initiation of translation?

Binding of the large ribosomal subunit to the mRNA

Release Factors binding to stop codons

The formation of the first peptide bond

Binding of the methionine-initiator tRNA to the start codon (correct)

What is the role of the large ribosomal subunit during translation?

To catalyze peptide bond formation (correct)

To bind the release factors during termination

To scan the mRNA for the start codon

To dissociate the initiation factors

What happens when a stop codon is encountered during translation?

The ribosome continues to synthesize the peptide

A charged tRNA binds to the stop codon

The large ribosomal subunit initiates another round of translation

Release Factors bind to the stop codon (correct)

How fast does the process of protein translation typically occur?

15 amino acids/sec Signup and view all the answers

What distinguishes prokaryotic ribosomes from eukaryotic ribosomes in the context of antibiotic action?

Prokaryotic ribosomes are targeted by specific antibiotics, while eukaryotic ribosomes are not Signup and view all the answers

What does the first AUG codon signify in the process of translation?

It indicates the start of translation. Signup and view all the answers

In which direction is mRNA read during translation?

5’ to 3’ direction. Signup and view all the answers

What role do tRNAs play in translation?

They link codons of mRNA to corresponding amino acids. Signup and view all the answers

What is unique about the Methionine-initiator tRNA?

It starts the translation process. Signup and view all the answers

What is the term used for the continuous sequence of codons that specify a protein on an mRNA?

Open Reading Frame (ORF). Signup and view all the answers

What is the primary function of ribosomes during translation?

To catalyze peptide bond formation. Signup and view all the answers

What is the significance of the 5’ untranslated region (5’ UTR) in an mRNA molecule?

It regulates the initiation of translation. Signup and view all the answers

What does rRNA do in the context of translation?

It binds mRNA and matches tRNAs to codons. Signup and view all the answers

What is the primary role of ribosomes in protein synthesis?

To translate mRNA into a protein sequence. Signup and view all the answers

Which statement about amino acids is true?

Amino acids have both amino and carboxyl functional groups. Signup and view all the answers

What does the term 'N-terminus' refer to in a protein sequence?

The starting end of the polypeptide chain. Signup and view all the answers

What characterizes the secondary structure a-helix?

It forms hydrogen bonds between every 4th amino acid. Signup and view all the answers

How many different amino acids are primarily found in proteins?

20 Signup and view all the answers

What defines a codon in the genetic code?

A set of three nucleotides. Signup and view all the answers

Which level of protein structure describes the overall 3D shape of a single polypeptide chain?

Tertiary structure Signup and view all the answers

Which of the following best describes the peptide bond?

A covalent bond linking amino acids through a condensation reaction. Signup and view all the answers

How many amino acids complete one turn of an a-helix?

3.6 Signup and view all the answers

What is the significance of the start codon in mRNA?

It defines the reading frame of the mRNA for translation. Signup and view all the answers

What type of structure involves interactions between adjacent strands?

Secondary structure Signup and view all the answers

What type of side chains do hydrophobic amino acids possess?

Nonpolar side chains. Signup and view all the answers

What is NOT true about the quaternary structure of proteins?

It's the first level of protein structure. Signup and view all the answers

What is the primary function of ubiquitin in the ubiquitin-proteasome system?

To mark proteins for degradation Signup and view all the answers

Which of the following correctly describes the structure of hemoglobin?

Two copies of alpha-globin and two copies of beta-globin Signup and view all the answers

Which statement about the 3D structure of proteins is accurate?

Proteins can adopt multiple conformations. Signup and view all the answers

What role does the proteasome play in the degradation of proteins?

Unfolding and degradation of ubiquitinated proteins Signup and view all the answers

What are the components that make up the quaternary structure of proteins like neuraminidase?

Multiple identical polypeptide chains Signup and view all the answers

What primarily determines the 3D structure of a protein?

The amino acid sequence of the protein Signup and view all the answers

Which type of side chains are classified as hydrophobic?

Nonpolar side chains Signup and view all the answers

What role do chaperone proteins play in protein folding?

They help other proteins fold correctly Signup and view all the answers

Which of the following interactions is NOT involved in the stabilization of a protein's 3D structure?

Covalent bonds Signup and view all the answers

Which type of interaction drives proteins to fold into compact conformations?

Hydrophobic interactions Signup and view all the answers

In the context of protein folding, which property best describes hydrophilic molecules?

Easily dissolve in water Signup and view all the answers

What is the result of a protein reaching its minimum energy state during folding?

The protein adopts its final 3D structure Signup and view all the answers

Which amino acid characteristic significantly influences protein folding?

Chemical properties of the side chains Signup and view all the answers

Study Notes

Protein Synthesis and Structure

Learning objectives include understanding amino acid structure and diversity, how amino acids assemble into polypeptide chains, protein synthesis at the ribosome, and protein structure levels.
An animation demonstrates mRNA translation by the ribosome.

The "Central Dogma" of Molecular Biology

DNA's sequence dictates mRNA sequence through transcription.
mRNA then directs protein synthesis through translation in the cytosol.
The process is compartmentalized, with different steps happening in different cellular locations (nucleus and cytosol).

Today's Topics

Protein composition
Protein synthesis
Protein structure

Amino Acids

Amino acids are the protein monomers.
At a pH of ~7 in cells, amino and carboxyl groups are charged.
Each amino acid has a central carbon atom, an amino group, a carboxyl group, and a variable side chain (R group).

20 Different Amino Acids

Amino acids categorized as hydrophobic (water-fearing), hydrophilic (water-loving), charged polar, and acidic/basic are crucial for protein characteristics.

Peptide Bonds

Amino acids link together via peptide bonds (condensation reactions).
Losing a water molecule forms a peptide bond.

Protein Structure

Protein sequence (amino acid sequence read from N-terminus to C-terminus) is crucial for determining its 3D structure.
Methionine (Met) is the often first amino acid in a protein
MDLY is a possible example of 3- or 1-letter polypeptide sequence

Genetic Code

mRNA's nucleotide sequence translates into amino acids based on the genetic code (codons: sets of 3 nucleotides).
AUG is the start codon
There are three stop codons.

Translation

Translation happens on ribosomes, a process essential for protein synthesis dictated by an mRNA template.
Ribosomes bind mRNA and match tRNA to mRNA codons.
Ribosomes have three binding sites (E, P, and A sites) for tRNA.

Translation Initiation

Translation begins when initiator tRNA binds to the start codon (AUG).
A complex of initiator tRNA, translation initiation factors, and the small ribosomal subunit links to the 5' cap of mRNA.
The complex scans the mRNA until it binds to the first AUG, where translation begins.

Protein Translation

Translation ends when a release factor binds to a stop codon
A release factor terminates translation.

Prokaryotic and Eukaryotic Ribosomes

Prokaryotic and eukaryotic ribosomes differ.
Some antibiotics target prokaryotic ribosomes to kill bacteria.

Protein Folding

The amino acid sequence determines a protein's specific 3D structure.
Anfinsen Experiment (Nobel prize 1972) highlights this relationship.
4 types of noncovalent interactions determine protein folding.

Noncovalent Interactions

Electrostatic interactions
Van der Waals interactions
Hydrogen bonds
Hydrophobic interactions

Chaperone Proteins

Help newly synthesized proteins fold correctly.
Use ATP hydrolysis as an energy source.

Protein Structure Levels

Four levels of protein structure: primary, secondary, tertiary, and quaternary structures determine the 3D shape of the protein which in turn dictates the function of the protein.

Secondary Structure: Alpha Helix

A right-handed helix made up of amino acids.
Hydrogen bonds between backbone C=O and N-H groups at every ~4 amino acids stabilized the structure.

Secondary Structure: Beta Sheet

Interactions between adjacent strands.
Hydrogen bonds form between N-H and C=O groups.
Side chains extend alternately above and below the plane of the sheet.
Beta sheets can be parallel or antiparallel.

Tertiary Structure

A three-dimensional structure of a polypeptide chain.
Includes a protein domain.
Protein domain is a segment of a polypeptide chain that folds independently into a stable structure.

Quaternary Structure

A 3D structure of multiple polypeptide chains.

Protein Dynamics

Protein structure is not static
Proteins can adopt different conformations.

Protein Degradation

Ubiquitin-proteasome system targets and degrades proteins.
Ubiquitination marks proteins for degradation.
Proteasome a complex that degrades ubiquitinated proteins.

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Description

Test your knowledge on the intricacies of the translation process in biology. This quiz covers important aspects such as the roles of ribosomes, tRNA, and codons in protein synthesis. Understand the differences in translation between prokaryotes and eukaryotes, and assess your grasp of key concepts in molecular biology.