Gene Expression Quiz

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Questions and Answers

What is the primary purpose of transcription in gene expression?

To synthesize proteins directly from DNA

To produce RNA using information in DNA (correct)

To modify primary RNA transcripts

To separate mRNA from ribosomes

Which of the following accurately describes the relationship between genes and proteins?

Proteins can be synthesized from multiple genes simultaneously

Genes are meaningless without the presence of proteins

Genes dictate protein synthesis, linking genotype to phenotype (correct)

Genes code for RNA, which directly forms proteins

In eukaryotic cells, what occurs to primary RNA transcripts before they become functional mRNA?

They are segregated by the nuclear envelope

They are synthesized with ribosomes

They undergo RNA processing modifications (correct)

They are directly translated into proteins

What distinguishes prokaryotic translation from that of eukaryotic cells?

Translation in prokaryotes begins before transcription has finished Signup and view all the answers

What role does RNA play in the flow of genetic information?

It functions as a bridge between genes and the proteins they code for Signup and view all the answers

How many codons code for amino acids?

61 Signup and view all the answers

What is the role of the small ribosomal subunit in translation initiation?

It binds with mRNA and tRNA. Signup and view all the answers

Which of the following triplets is known as a 'stop' signal during translation?

UAA Signup and view all the answers

What is the start codon that initiates translation?

AUG Signup and view all the answers

Which two components make up ribosomal subunits?

Proteins and rRNA Signup and view all the answers

How does the small ribosomal subunit find the start codon during translation initiation?

It moves along the mRNA until it encounters the AUG codon. Signup and view all the answers

What is the function of tRNA in protein synthesis?

To transport amino acids to the ribosome Signup and view all the answers

Which of the following amino acids is coded by the UUA codon?

Leucine Signup and view all the answers

What stage follows the initiation of translation in the process of protein synthesis?

Peptide elongation Signup and view all the answers

What is the correct sequence of the steps involved in the elongation stage of translation?

Codon recognition, peptide bond formation, translocation Signup and view all the answers

What initiates the termination of translation when a stop codon reaches the ribosome?

A release factor enters the A site of the ribosome Signup and view all the answers

What does a polyribosome allow a cell to achieve during protein synthesis?

Rapid production of multiple copies of a polypeptide Signup and view all the answers

Which post-translational modification involves the addition of carbohydrate groups to a polypeptide?

Glycosylation Signup and view all the answers

Which of the following correctly describes the folding process of polypeptides?

Folding of polypeptides is a spontaneous process during or after synthesis Signup and view all the answers

What does the Central Dogma of Molecular Biology illustrate?

DNA is converted into RNA, which is then translated into proteins. Signup and view all the answers

What is the function of RNA polymerase during transcription?

It synthesizes RNA by linking RNA nucleotides together. Signup and view all the answers

What sequence does the newly synthesized mRNA follow?

It is complementary to the DNA template strand and runs 5’ to 3’. Signup and view all the answers

Which stage of transcription comes first?

Initiation Signup and view all the answers

What is meant by the term 'transcription unit'?

The short segment of DNA that is transcribed into RNA. Signup and view all the answers

What does the '1 Gene 1 Polypeptide Hypothesis' state?

One gene corresponds to one polypeptide in a protein. Signup and view all the answers

Where does RNA polymerase attach to begin transcription?

At the promoter region of the DNA. Signup and view all the answers

Which statement best describes the mRNA after RNA processing?

It is a mature molecule ready for translation in the cytoplasm. Signup and view all the answers

What is the transcription rate of RNA in eukaryotes?

40 nucleotides per second Signup and view all the answers

Which statement is true regarding the modifications made to pre-mRNA?

Both ends are usually altered. Signup and view all the answers

What role does the poly-A tail play in mRNA processing?

It protects mRNA from hydrolytic enzymes. Signup and view all the answers

What are introns?

Noncoding stretches of nucleotides Signup and view all the answers

What is the primary function of spliceosomes in RNA processing?

To splice RNA by removing introns Signup and view all the answers

Which statement accurately describes ribozymes?

They are catalytic RNA molecules. Signup and view all the answers

How do RNA synthesis and DNA synthesis differ in terms of base-pairing?

RNA follows the same base-pairing rules as DNA. Signup and view all the answers

Which function is NOT performed by the modifications made to the mRNA molecule?

Enhancing the transcription rate Signup and view all the answers

Which type of mutation involves replacing one nucleotide and its partner with another pair?

Nucleotide-pair substitution Signup and view all the answers

What is the effect of a silent mutation on the amino acid produced?

It has no effect due to redundancy in the genetic code. Signup and view all the answers

How many stop codons are present in the genetic code?

3 Signup and view all the answers

What is the function of codons in mRNA?

To specify amino acids during protein synthesis. Signup and view all the answers

What can be the consequence of insertions and deletions in a gene?

They can have a disastrous effect on the resulting protein. Signup and view all the answers

Which of the following is a start codon?

AUG Signup and view all the answers

What do codons consist of?

Triplets of nucleotides Signup and view all the answers

Which of the following amino acids is coded by the codon UGC?

Cysteine Signup and view all the answers

Which amino acid is coded by the codon UUU?

Phenylalanine Signup and view all the answers

What is the significance of redundancy in the genetic code?

It leads to more than one codon coding for the same amino acid. Signup and view all the answers

Study Notes

Gene Expression and Protein Synthesis

DNA contains specific nucleotide sequences
Inherited DNA dictates protein synthesis, leading to specific traits
Proteins link genotype (DNA) and phenotype (observable traits)

What is a Gene?

A region of DNA that codes for a functional product (protein or RNA)

Gene Expression

The process by which DNA directs protein synthesis

Central Dogma

DNA → RNA → Protein

Types of RNA

mRNA (messenger RNA): Produced in the nucleus from a DNA template, carries genetic information outside the nucleus to ribosomes.
tRNA (transfer RNA): Found in cytoplasm, carries amino acids to ribosomes during translation; each carries only one type of amino acid
rRNA (ribosomal RNA): Produced in nucleolus; joins with proteins to form ribosomes. Ribosomes can be free in the cytoplasm or bound to the endoplasmic reticulum.

The Genetic Code & Codons

20 amino acids, 4 nucleotide bases
Three nucleotides (codon) code for each amino acid
"Words" of genes are transcribed into 3-nucleotide "words" of mRNA
The "words" are translated into an amino acid chain forming a polypeptide

Transcription

One strand of DNA serves as a template to produce complementary RNA
RNA polymerase untwists DNA and adds bases to the growing mRNA molecule.
Three stages of transcription: initiation, elongation, termination

Details of Transcription

RNA polymerase binds to a promoter region on DNA
RNA polymerase untwists the DNA double helix
RNA polymerase adds complementary RNA nucleotides to the growing RNA molecule
RNA polymerase reaches a termination sequence, ending transcription

Elongation

RNA polymerase synthesizes mRNA at a rate of 40 nucleotides per second in eukaryotic cells.
RNA follows base-pairing rules: U instead of T is used.

Eukaryotic RNA Modification

Pre-mRNA is modified before it leaves the nucleus
Addition of a 5' cap and a poly-A tail
Introns (noncoding segments) are removed by splicing, connecting exons (coding segments).

Splicing

A spliceosome removes introns and joins exons of pre-mRNA in eukaryotes creating an mRNA molecule with a continuous protein coding region

RNA Splicing

Spliceosomes, catalytic RNA molecules, perform RNA splicing

Alternative RNA Splicing

Some genes can encode more than one kind of polypeptide depending on which segments are treated as exons during splicing; this produces more proteins than genes

Translation

mRNA codons are read in the 5' to 3' direction
Ribosomes catalyze the synthesis of proteins.
tRNA brings amino acids to the ribosome, matching anticodons to mRNA codons.
Three stages: initiation, elongation, termination

Ribosomes

Two subunits made of rRNA and proteins
Small subunit binds mRNA & initiator tRNA
Large subunit catalyzes bonding

tRNA

tRNA molecule contains an anticodon that matches a specific codon on mRNA

Polypeptide Chain Elongation

During elongation, amino acids are added to the polypeptide chain. Three steps:
codon recognition
peptide bond formation
translocation

Termination Stage

A stop codon signals the end of translation; the release factor binds releasing the polypeptide

Polyribosomes

Multiple ribosomes can translate a single mRNA molecule at the same time, enabling faster polypeptide synthesis.

Protein Folding & Post-Translational Modification

Polypeptide chains fold spontaneously into 3D structures.
Enzymes modify polypeptides (cleavage, adding carbohydrate).
Proteins require post-translational modifications (phosphorylation) to function.

Mutations

Mutations are changes in the genetic material of a cell or virus.
Point mutations affect one base pair. Missense mutations result in a different amino acid being incorporated into the polypeptide chain during translation.
Insertions or deletions can be disastrous for the protein that is coded by the mutated gene.

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Description

Test your understanding of the key processes involved in gene expression, including transcription, RNA processing, and translation. This quiz covers fundamental concepts such as the relationship between genes and proteins, as well as the differences between prokaryotic and eukaryotic translation.