DNA Expression and Protein Synthesis

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Questions and Answers

What is the complementary strand for the DNA sequence 5’-CCTAGAA-3’?

3’ AAGATCC 5’

5’ GGTATTC 3’

3’ GGATCTT 5’ (correct)

5’ GGATCTT 3’

If the leading strand of DNA is 5’-CGCATGTAGCGA-3’, what is the correct complementary (parent) strand?

3’-CGTACGTACGCT-5’

3’-TGCTACATCGTA-5’

3’-GCGTACATCGCT-5’ (correct)

5’-GCGTACATCGCT-3’

Which of the following describes why protein cannot be synthesized directly from DNA?

Proteins are synthesized in the nucleus.

RNA must carry the genetic code to ribosomes. (correct)

Ribosomes can only read RNA sequences.

DNA is more stable than RNA.

Which enzyme is primarily involved in the transcription of RNA from a DNA template?

RNA polymerase Signup and view all the answers

During transcription, which base pairs with adenine in RNA?

Uracil Signup and view all the answers

What is the main function of hemoglobin in the human body?

Transport oxygen Signup and view all the answers

Which of the following represents an example of a structural protein?

Myosin Signup and view all the answers

What type of RNA is responsible for bringing amino acids to the ribosome during protein synthesis?

tRNA Signup and view all the answers

What is the main reason multiple copies of mRNA are produced during transcription?

To ensure more ribosomes can synthesize the protein simultaneously Signup and view all the answers

What does the termination sequence signal in the transcription process?

The stop of transcription by RNA polymerase Signup and view all the answers

Which type of RNA serves as the delivery system of amino acids to ribosomes?

Transfer RNA (tRNA) Signup and view all the answers

What is likely true about the length of messenger RNA (mRNA)?

It varies in length depending on the gene copied Signup and view all the answers

What happens to newly synthesized pre-mRNA before it can leave the nucleus?

It undergoes post-transcriptional modifications Signup and view all the answers

What protein is primarily involved in binding with rRNA to form ribosomes?

Ribosomal proteins Signup and view all the answers

How many base pairs long is transfer RNA (tRNA)?

70 to 90 Signup and view all the answers

Which statement correctly describes the role of RNA polymerase during transcription?

It synthesizes mRNA from DNA templates Signup and view all the answers

What establishes the correct reading frame during translation?

The initiator tRNA–AUG pairing Signup and view all the answers

During the elongation stage of translation, which enzyme catalyzes the formation of peptide bonds?

Peptidyl transferase Signup and view all the answers

What happens to the empty tRNA after it has released its amino acid?

It moves to the E site and is released Signup and view all the answers

Which of the following best describes a mutation?

A permanent change in the nucleotide sequence of DNA Signup and view all the answers

What do we call large-scale mutations that may affect multiple genes?

Chromosomal mutations Signup and view all the answers

What is the role of mutagens in DNA changes?

They increase the rate of DNA sequence changes Signup and view all the answers

What type of mutations often result in a loss-of-function or gain-of-function of a gene?

Point mutations Signup and view all the answers

When does termination of protein synthesis occur?

When a stop codon appears in the A site Signup and view all the answers

What role does the 3’ poly(A) tail play in a pre-mRNA molecule?

It protects the molecule from degradation by cytosolic enzymes. Signup and view all the answers

What is the function of the spliceosome?

It removes introns from the mRNA. Signup and view all the answers

What is the primary role of RNA polymerase in transcription?

To bind to the promoter and initiate transcription Signup and view all the answers

Which nucleotide base pairs with adenine in RNA?

Uracil Signup and view all the answers

Which statement about alternative splicing is true?

It allows for different combinations of exons to produce multiple mRNAs. Signup and view all the answers

What is a key difference between prokaryotic and eukaryotic transcription regarding the promoter sequence?

Eukaryotic promoters typically have a TATA box Signup and view all the answers

What is the purpose of a G-cap in mRNA?

To act as a site of attachment for ribosomes. Signup and view all the answers

Why does the A-T base pairing in the promoter facilitate RNA polymerase function?

It uses less energy to break the bonds Signup and view all the answers

What does the anticodon on tRNA correspond to?

A three-nucleotide sequence on mRNA. Signup and view all the answers

How many genes do humans have in relation to the number of proteins they can produce?

Around 20,000 genes can produce approximately 100,000 proteins. Signup and view all the answers

In which direction does RNA polymerase synthesize the RNA strand?

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

Which strand of DNA is not copied during transcription but has the same sequence as the RNA molecule?

Coding strand Signup and view all the answers

What characterizes introns in RNA sequences?

They are removed during the splicing process. Signup and view all the answers

What occurs after RNA polymerase synthesizes the RNA molecule?

The DNA double helix reforms Signup and view all the answers

Which component is crucial for the translation of mRNA into proteins?

tRNA. Signup and view all the answers

How does RNA polymerase create the RNA strand during transcription?

It adds nucleotides in the 5’ to 3’ direction Signup and view all the answers

What is the role of the anticodon on the tRNA?

It pairs with the corresponding codon in mRNA. Signup and view all the answers

According to the wobble hypothesis, what is the significance of the third nucleotide in the mRNA codon?

It can vary while still allowing the same tRNA to attach. Signup and view all the answers

Where does the tRNA molecule enter the ribosome during translation?

A site Signup and view all the answers

What is the specialized initiator tRNA responsible for during the initiation phase of translation?

Pairing with the AUG start codon. Signup and view all the answers

What does the process of aminoacylation involve?

Binding a tRNA molecule to its corresponding amino acid. Signup and view all the answers

What happens after the initiator tRNA pairs with the AUG start codon during translation?

The large ribosomal subunit binds to complete the ribosome. Signup and view all the answers

What contributes to the polarity of amino acid monomers?

N-H and O-H bonds in the structure. Signup and view all the answers

How many amino acids are typically needed to correspond with 61 codons in the genetic code?

20 Signup and view all the answers

Study Notes

DNA Expression: Protein Synthesis

DNA expression is the process of using DNA information to create proteins.
It involves two main steps: transcription and translation.

DNA Replication

Complementary strand: Given a DNA sequence 5'-CCTAGAA-3', the complementary strand would read 3'-GGATCTT-5'.
Leading strand: The leading strand of a DNA molecule is 5'-CGCATGTAGCGA-3'.
Complementary (parent) strand to the leading strand: The complementary (parent) strand to the leading strand is 3'-GCGTACATCGCT-5'.
Lagging strand: If the leading strand is 5'-CGCATGTAGCGA-3', the lagging strand would be 5'-TCGATACATCGC-3'.

Transcription

DNA must be converted to RNA before protein synthesis.
Transcription is the process of copying DNA information into RNA.
Transcription occurs in the nucleus.
RNA polymerase is the enzyme responsible for transcription.
The promoters are sequences of nucleotides before the gene.

Transcription - Initiation

RNA polymerase binds to the DNA and unwinds it near the beginning of the target gene.
RNA polymerase binds to a promoter. Promoters have DNA sequences like TATA box in eukaryotes.
The promoter sequence exists just before the gene and allows for RNA polymerase binding.
A-T base pairs are used to make the promoters because they only have 2 hydrogen bonds to break. This uses less energy than the 3 hydrogen bonds of G-C bonds.

Transcription - Elongation

RNA polymerase does not need a primer for RNA synthesis.
It follows a 5' to 3' direction.
The mRNA elongates as nucleotides are added, one by one.
The DNA strand unwinds as the RNA polymerase moves along it in the forward direction.
The growing RNA strand becomes a single nucleotide chain.

Transcription - Termination

Transcription ends when RNA polymerase recognizes a termination sequence.
In prokaryotes, a protein binding to the mRNA can stop transcription.
A termination sequence is the sequence of bases at the end of a gene that signals RNA polymerase to stop transcribing.

Different Types of RNA

Messenger RNA (mRNA) carries genetic code from DNA to the ribosomes.
Transfer RNA (tRNA) translates mRNA into proteins by carrying amino acids to the ribosomes.
Ribosomal RNA (rRNA) is part of the ribosomes.

Post-transcriptional Modifications

Newly synthesized pre-mRNA is not ready to leave the nucleus.
Modifications include adding a 5' cap and a 3' poly(A) tail.
The 5' cap is (5' G-cap) a sequence of 7 Gs that signals ribosomes to start translation.
The 3' poly(A) tail protects pre-mRNA from enzymes in the cytosol.

Alternative Splicing

Exons may be joined in different combinations to produce different mRNAs from the same gene
Alternative splicing is a process that produces different mRNAs from the same pre-mRNA
This allows for one gene to produce more than one type of protein.

Transcription: Prokaryotes vs Eukaryotes

Location: Transcription is in the cytoplasm of prokaryotes, in the nucleus of eukaryotes.
Enzymes: Prokaryotes use one type of RNA polymerase; Eukaryotes use multiple types for protein-coding genes.
Promoters: Prokaryotic promoters are simpler; eukaryotic promoters are complex.
Termination: Prokaryotic termination is done by proteins binding to mRNA, in eukaryotes, the polyuracil site helps terminate.
Introns and exons: Prokaryotes do not have introns; eukaryotes have both introns and exons.
Product: Prokaryotes produce mRNA; eukaryotes produce pre-mRNA that requires modifications before becoming mature mRNA.

Translation:

Translation is the process of reading mRNA and synthesizing a protein.
tRNA molecules bring amino acids to the ribosome according to the mRNA sequence.

Ribosome Structure

Ribosomes are the sites of protein synthesis.
They contain rRNA and ribosomal proteins.

tRNA Definitions

Anticodon: The sequence on tRNA that matches the mRNA codon.
Codon: A sequence of three nucleotides on mRNA that codes for a particular amino acid.

The Wobble Hypothesis

The wobble hypothesis describes how the same tRNA can recognize multiple codons.
The third base in a codon can wobble.

Further Definitions

Aminoacylation: The process of attaching an amino acid to a tRNA molecule. This process is necessary before translating a protein.
Aminoacyl-tRNA: tRNA molecule with its associated amino acid.

Initiating Translation

Translation begins when the large and small ribosomal subunits bind to mRNA, along with the initiator tRNA (met-tRNA).
An initiator tRNA-mRNA binding site exists.
Met-tRNA starts in the P site.

Elongating the Polypeptide Chain (Steps)

Methionine-tRNA is in the P site. The A site is empty.
A second tRNA with an amino acid binds to the next codon. (A Site).
A peptide bond forms between these two amino acids.
Ribosome moves along mRNA
The initial tRNA leaves.
Repeat Steps 2-4.

Termination of Protein Synthesis

When a stop codon arrives, the protein release factor binds to the A-site.
The polypeptide chain is released.
The ribosomal subunits separate from the mRNA.

DNA Mutations

Mutations: Permanent changes in the nucleotide sequence of a cell's DNA.
Chromosomal mutations: Large-scale mutations that affect multiple genes (e.g., deletions, duplications, inversions, translocations).
Single-gene mutations: Point mutations that affect a single gene, often through substitution, insertion, or deletion of a base pair.
Mutagens: Substances or events that increase the rate of mutations (e.g., transposons, chemicals, radiations).

Frameshift Mutation, Silent Mutation, Missense Mutation, Nonsense Mutation

Frameshift Mutation: Changes the reading frame (codon sequence) of the mRNA, which often changes the protein sequence drastically.
Silent Mutation: Doesn't change the amino acid sequence of the protein due to multiple codons for the same amino acid.
Missense Mutation: Changes the amino acid sequence.
Nonsense Mutation: Introduces a premature stop codon in the mRNA sequence, leading to a truncated or non-functional protein.

Prokaryotes vs Eukaryotes (Translation)

Location: Translation occurs in the cytosol in prokaryotes; partially in mitochondria and chloroplasts of eukaryotes.
Initiation: Prokaryotes pair directly to ribosomes, eukaryotes have to bind to mRNA 5' cap.
Elongation: Prokaryotes do 15-20 cycles per second, eukaryotes do 1-3 cycles per second.
Termination: Both use release factors.
Polysomes: Prokaryotes have multiple ribosomes translating at the same time (polyribosomes), so do eukaryotes.

Translation Protein Challenge

Determine the associated mRNA sequence and original DNA sequence that create the given protein sequence.

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Description

This quiz covers the fundamental processes of DNA expression, including transcription and translation. It also explores concepts related to DNA replication, such as complementary and leading strands. Test your understanding of these essential biological processes!