Genetic Code and Protein Synthesis

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Questions and Answers

What is the flow of information in the central dogma of molecular biology?

DNA → mRNA → Protein (correct)

Protein → RNA → DNA

RNA → DNA → Protein

DNA → Protein → RNA

In eukaryotic cells, what happens to pre-mRNA after transcription?

It remains unchanged for protein synthesis.

It is modified and processed into mRNA. (correct)

It is transported to the cytoplasm without modifications.

It is directly translated into protein.

What is the role of RNA polymerase during transcription?

It synthesizes RNA from a DNA template. (correct)

It copies the RNA sequence into a DNA template.

It assembles amino acids into polypeptides.

It modifies the RNA after transcription.

Which of the following statements about codons is true?

Codons consist of three nucleotides. Signup and view all the answers

What base in RNA replaces thymine found in DNA?

Uracil Signup and view all the answers

During translation, what do ribosomes synthesize using mRNA?

Polypeptides Signup and view all the answers

Which process occurs in the cytoplasm of prokaryotic cells?

Both B and C Signup and view all the answers

What is the primary function of mRNA?

To carry the genetic code from DNA to ribosomes. Signup and view all the answers

What is the purpose of mRNA splicing in eukaryotic cells?

To remove non-coding regions and join coding sequences together Signup and view all the answers

What are the sequences that are retained in finished mRNAs called?

Exons Signup and view all the answers

What creates variations in the mRNA produced from a pre-mRNA transcript?

Alternative splicing Signup and view all the answers

Which components are involved in the process of mRNA splicing?

snRNPs and spliceosomes Signup and view all the answers

What is the significance of introns in eukaryotic pre-mRNA?

They are removed during mRNA processing. Signup and view all the answers

Why is transcription necessary for protein synthesis?

It prevents the direct use of DNA. Signup and view all the answers

Which of the following statements about exons is true?

Exons can vary between different mRNA molecules due to alternative splicing. Signup and view all the answers

How many introns can be present in a pre-mRNA transcript?

More than 70 Signup and view all the answers

What is the role of AUG in mRNA translation?

It is always the first codon read in translation. Signup and view all the answers

Which of the following statements correctly describes the genetic code?

It is universal across all living organisms. Signup and view all the answers

What is a transcription unit?

The part of the gene that is copied into RNA. Signup and view all the answers

How does RNA polymerase synthesize RNA?

It assembles RNA nucleotides in a 5'→3' direction. Signup and view all the answers

Which of these components is essential for the initiation of transcription?

Transcription factors Signup and view all the answers

What happens during transcription termination?

The RNA transcript and RNA polymerase II are released at a stop codon. Signup and view all the answers

Which characteristic of the genetic code contributes to its degeneracy?

It allows multiple codons to specify the same amino acid. Signup and view all the answers

Why is the genetic code described as commaless?

Codons are joined without any punctuation. Signup and view all the answers

Which statement is true about the transcription process?

Only one of the two DNA strands acts as a template for RNA synthesis. Signup and view all the answers

Which of the following statements accurately describes the parts of a gene?

The transcription unit is involved in RNA synthesis. Signup and view all the answers

Study Notes

The Genetic Code

Francis Crick coined the term "central dogma" to describe the flow of information from DNA to RNA to protein.
Transcription is the process of copying information encoded in a DNA template strand into a complementary RNA strand.
Translation uses the information in the RNA copy to assemble amino acids into a polypeptide.

Overview: Transcription and Translation

Transcription: RNA polymerase copies the DNA sequence of a gene into an RNA sequence.
Translation: mRNA associates with a ribosome, where amino acids specified by the mRNA are joined together to form a polypeptide.

Prokaryotes and Eukaryotes

Eukaryotic transcription takes place in the nucleus and produces a precursor-mRNA (pre-mRNA).
Pre-mRNA undergoes modifications and has extra segments removed by RNA processing.
Prokaryotic transcription occurs in the cytoplasm and produces a functional mRNA directly.

DNA and RNA

RNA uses uracil (U) instead of thymine (T) in its nucleotide sequence.
The sequence of RNA nucleotides in mRNA is translated into a polypeptide containing 20 different types of amino acids.

Genetic Code

Each three-letter "word" (triplet) of the code is called a codon.
Three-letter codons in DNA are transcribed into complementary three-letter RNA codons.

Start and Stop Codons

There are 64 different three-letter combinations possible from four mRNA nucleotides (43).
61 sense codons specify amino acids, while three are stop codons.
AUG (methionine) is the start codon.
UAA, UAG, and UGA are stop codons that do not code for amino acids and stop polypeptide synthesis.

Features of the Genetic Code

Two amino acids, methionine and tryptophan, are specified by a single codon. The rest have multiple codons (degeneracy).
The genetic code is commaless, meaning there are no markers to indicate the end of one codon and the beginning of the next.
The genetic code is universal, meaning it is essentially the same in all living organisms and viruses.

Eukaryotic Transcription

A gene consists of a promoter (control sequence for transcription) and a transcription unit (the section of the gene copied into an RNA molecule).
Transcription occurs in three stages: initiation, elongation, and termination.

Transcription Initiation

Initiation involves the assembly of molecular machinery at the promoter, including:
- Transcription factors (TFs) that bind to the promoter in the TATA box.
- RNA polymerase, which catalyzes the assembly of RNA nucleotides into an RNA strand.
DNA unwinds to expose the template strand, and RNA polymerase II begins RNA synthesis.

Transcription Elongation and Termination

Elongation: RNA polymerase II moves along the gene, extending the RNA chain as DNA unwinds ahead of it.
Termination: the RNA transcript and RNA polymerase II are released from the DNA template when a stop codon is reached.

Differences in Replication and Transcription

Only one DNA strand acts as a template for RNA synthesis.
Only the coding sequence of a single gene is copied.
RNA polymerase catalyzes the assembly of RNA nucleotides without needing a primer.

RNA Processing in Eukaryotes

mRNAs contain both coding and noncoding regions, which are important in protein synthesis.
Eukaryotic protein-coding genes are transcribed into pre-mRNA, which undergoes processing in the nucleus to produce translatable mRNA.

Introns and Exons

Introns are non-protein-coding sequences removed during processing.
Exons are amino acid-coding sequences retained in the finished mRNA.

mRNA Splicing

mRNA splicing occurs in the spliceosome, formed between pre-mRNA and small ribonucleoprotein particles (snRNPs), where introns are removed from pre-mRNAs and exons are joined together.

Alternative Splicing

Pre-mRNAs can be spliced in different combinations to produce different mRNAs from a single gene, increasing the number and variety of proteins.

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Description

This quiz explores the fundamental processes of transcription and translation, as well as the differences between prokaryotic and eukaryotic mechanisms. Test your understanding of how genetic information flows from DNA to RNA and ultimately to proteins. Delve into the roles of RNA polymerase, ribosomes, and pre-mRNA processing.