Lecture 4 Review

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Questions and Answers

What is the primary function of RNA polymerase during transcription?

To replicate DNA for cell division

To synthesize RNA from a DNA template (correct)

To translate RNA into proteins

To splice RNA molecules

Which strand of DNA is used as the template for synthesizing RNA during transcription?

Lagging strand

Anti-sense strand

Template strand (correct)

Coding strand

Why does the RNA sequence produced during transcription differ from the DNA coding strand?

The RNA sequence is synthesized from proteins

The RNA sequence is double-stranded

The RNA sequence incorporates uracil instead of thymine (correct)

The RNA sequence is synthesized in the 3’ to 5’ direction

What percentage of the human genome consists of protein-coding genes?

1% Signup and view all the answers

Which process describes the conversion of DNA instructions into RNA?

Transcription Signup and view all the answers

What is the primary function of acyl-tRNA synthetases?

To attach amino acids to the appropriate tRNA Signup and view all the answers

How many amino acyl-tRNA synthetases are there at a minimum?

At least one for each amino acid Signup and view all the answers

What is the role of ribosomal RNA (rRNA) in translation?

To catalyze peptide bond formation Signup and view all the answers

What characterizes the 'RNA world' hypothesis in the origin of life?

RNA can encode genetic information and perform catalytic activities Signup and view all the answers

What components make up a complete ribosome?

4 rRNA molecules and 82 proteins Signup and view all the answers

What are the building blocks of RNA?

Nucleotides Signup and view all the answers

Which sugar is used in RNA instead of deoxyribose used in DNA?

Ribose Signup and view all the answers

What is the role of phosphodiester linkage in RNA?

To form polymers of nucleotides Signup and view all the answers

How are RNA molecules structurally different from DNA?

RNA has a single-stranded structure Signup and view all the answers

What type of structures can RNA fold into due to base-pairing?

Complex 3D structures Signup and view all the answers

Which nucleotide is found in RNA instead of thymine?

Uracil Signup and view all the answers

What process links monomers to form RNA polymers?

Condensation Signup and view all the answers

In which cellular location is RNA synthesized?

Nucleus Signup and view all the answers

What is the start codon in eukaryotic cells?

AUG Signup and view all the answers

How many stop codons exist in the genetic code?

Three Signup and view all the answers

In which direction is mRNA translated?

5’ to 3’ Signup and view all the answers

What role do amino acyl-tRNA synthetases play in translation?

They couple the correct amino acid to its tRNA. Signup and view all the answers

What is the role of the start codon AUG in translation?

It initiates translation and defines the reading frame. Signup and view all the answers

What does the anticodon of tRNA do?

It binds to the corresponding codon on mRNA. Signup and view all the answers

Which direction do polypeptides get synthesized?

NH2 to COOH Signup and view all the answers

What happens when translation reaches a stop codon?

Release factors bind and terminate translation. Signup and view all the answers

What is the primary role of the promoter in prokaryotic transcription?

It determines the template strand and start site for RNA synthesis. Signup and view all the answers

In which direction does RNA polymerase synthesize RNA?

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

How many errors does RNA polymerase typically make in RNA synthesis?

1 error per 1,000 nucleotides Signup and view all the answers

Which type of RNA is directly involved in carrying amino acids during protein synthesis?

tRNA Signup and view all the answers

What distinguishes messenger RNA (mRNA) from other types of RNA?

It serves as a template for protein synthesis. Signup and view all the answers

Which enzyme is primarily responsible for synthesizing RNA during transcription?

RNA polymerase Signup and view all the answers

What type of RNA is predominantly involved in forming the ribosome?

rRNA Signup and view all the answers

What happens when RNA polymerase encounters a terminator sequence during transcription?

RNA polymerase stops and detaches from DNA. Signup and view all the answers

What role do transcription factors play in the transcription process?

They assist in RNA polymerase binding to the promoter. Signup and view all the answers

What is the size range of messenger RNA (mRNA)?

100 - 10,000 nucleotides Signup and view all the answers

What is the primary function of mRNA in the process of gene expression?

To carry genetic information from DNA to ribosomes for protein synthesis Signup and view all the answers

Which of the following best describes alternative splicing?

The generation of different mRNAs and proteins from the same gene Signup and view all the answers

What are exons?

Sequences that are preserved in the mRNA after splicing Signup and view all the answers

How does capping and polyadenylation affect mRNA stability?

They help in the recognition and export of mRNA from the nucleus. Signup and view all the answers

What is the role of RNA polymerase during transcription?

It synthesizes strands of mRNA from the DNA template. Signup and view all the answers

In which direction is mRNA read during translation?

5’ to 3’ Signup and view all the answers

What is a codon?

A three-nucleotide sequence that corresponds to a specific amino acid Signup and view all the answers

What can result from the process of splicing?

The production of multiple proteins from a single gene Signup and view all the answers

How many possible codons can be formed using a three-nucleotide sequence?

64 Signup and view all the answers

What is the consequence of having introns in eukaryotic genes?

They can be removed through splicing to create functional mRNA. Signup and view all the answers

Study Notes

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Transcription - Synthesis of RNA

Transcription is the process of synthesizing RNA from a DNA template.

The Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information: DNA → RNA → protein.
DNA (deoxyribonucleic acid) contains the genetic code.
RNA (ribonucleic acid) acts as an intermediary, carrying the genetic code.
Proteins are synthesized according to the instructions encoded in mRNA.
DNA in the nucleus directs RNA synthesis.
RNA is transported to the cytosol to direct protein synthesis.

Building Blocks of RNA

RNA monomers are called nucleotides.

RNA vs. DNA: Monomers

RNA uses ribose as its sugar, while DNA uses deoxyribose.
RNA has uracil (U) where DNA has thymine (T).

Nucleotides in RNA

Nucleotides in RNA are linked by phosphodiester linkages.
These linkages connect the 3' carbon of one nucleotide to the 5' carbon of the next.

RNA Structure

RNA is typically single-stranded.
RNA can fold into complex three-dimensional structures.

Advantages of RNA for Cells

RNA is synthesized from DNA, enabling cells to separate transcription and translation, improving regulation and control of gene expression.
This avoids exposing sensitive DNA to environments such as the cytosol before the information has a chance to be used.
RNA is more easily altered and destroyed then DNA and more susceptible to environmental conditions.

Transcription

It is the process by which RNA is synthesized from a DNA template .
It results in a single-stranded RNA molecule (transcript).
It is carried out by RNA polymerases, which read the DNA template and synthesize a complementary RNA molecule.
RNA synthesis is only in the 5' → 3' direction.

Eukaryotic Genes

Many contain introns.

Function of Exons and Introns

Exons are the sequences that remain in mRNA.
Introns are removed after transcription.

Alternative Splicing

Generating different mRNA from a single gene, which can then be translated into many different proteins.
The genome produces many more proteins than the number of genes present.

mRNA Capping and Polyadenylation

mRNA modifications affect mRNA stability (how quickly it's degraded ) and translation efficiency (how efficiently it's translated).

Export of mRNA

After transcription and modification, mRNA is exported from the nucleus to the cytosol for translation.

Genetic Information Transmission (mRNA)

mRNA directs the synthesis of proteins.
The sequence is read in 5' to 3' direction for translation.

Genetic Code

mRNA is translated into the amino-acid sequence of a protein.
A set of three nucleotides (codon) defines an amino acid.
There are 64 possible codons, but 20 amino-acids.

Reading Frames

An RNA molecule has three potential reading frames.
Cells need a mechanism to determine the correct reading frame to synthesize the correct proteins.

Start/Stop Codons

The start codon AUG defines the reading frame.
There are three stop codons (UAA, UAG, and UGA).

Translation (mRNA Decoding)

mRNA is decoded on ribosomes.
This is known as 'translation'.
Ribosomes are complex molecular machines containing rRNA molecules and proteins.

tRNA and Amino Acids

Transfer RNA (tRNA) molecules couple codons and amino acids.
tRNA has an anticodon sequence that matches mRNA codons.
Aminoacyl-tRNA synthetases attach the correct amino acid to its specific tRNA.
At least one aminoacyl-tRNA synthetase exists for each amino acid.

Ribosomal RNA (rRNA)

rRNA molecules are essential components of ribosomes.

RNA World Hypothesis

The idea that RNA may have been the primary genetic material in early life, holding both informational and catalytic activities (ribozymes).

Regulation of Prokaryotic Transcription

RNA polymerase binds to the promoter (specific DNA regions) to initiate transcription.
A transcription factor (sigma factor in prokaryotes) helps to locate the promoter.
RNA is synthesized in the 5’→3’ direction using the template strand of DNA.
RNA polymerase stops at the termination sequences on the DNA, and is released from the DNA.

Genes and DNA Strands

Genes can be encoded in both DNA strands.
The promoter's location and orientation help determine where RNA synthesis begins and which strand serves as the template.

Multiple RNA Polymerases

Multiple RNA polymerases can simultaneously transcribe a gene.

Different Types of RNA

Various RNA types (mRNA, tRNA, rRNA, and others) work together in protein synthesis.

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Description

Test your knowledge on the process of RNA transcription and the central dogma of molecular biology. This quiz covers key concepts about the synthesis of RNA from DNA, the building blocks of RNA, and comparisons between RNA and DNA. Perfect for students studying molecular biology.