Central Dogma and RNA Functions

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Questions and Answers

What is the primary role of RNA in the central dogma of biology?

To provide structural support to the nucleosomes

To directly synthesize proteins within the nucleus

To store genetic information long-term

To act as an intermediary molecule carrying genetic information from DNA to ribosomes (correct)

Which of the following best describes the structural difference between euchromatin and heterochromatin?

Euchromatin is double-stranded, while heterochromatin is single-stranded.

Heterochromatin contains histones, while euchromatin does not.

Heterochromatin is composed of RNA, whereas euchromatin contains only DNA.

Euchromatin is loosely packed, allowing for DNA accessibility, while heterochromatin is tightly packed, making DNA less accessible. (correct)

If a gene is located within a region of heterochromatin, what is the likely effect on its expression?

The gene's transcription will be inhibited as the DNA is less accessible to RNA polymerase. (correct)

The gene will be replicated but not transcribed.

The gene will be transcribed more rapidly due to the tightly packed form.

The gene will have an increased rate of translation at the ribosome.

What is the primary function of tRNA during protein synthesis?

To transport amino acids to the ribosome and match them with the appropriate mRNA codon. Signup and view all the answers

Which enzyme plays the most crucial role during the transcription process?

RNA polymerase Signup and view all the answers

Which of the following is NOT found within RNA?

Thymine Signup and view all the answers

Where does the process of transcription occur?

Nucleus Signup and view all the answers

What best describes the relationship between DNA, RNA and proteins in the central dogma?

DNA is transcribed into RNA, which is then translated into protein. Signup and view all the answers

Which of the following correctly describes the directionality of the template strand and the synthesized mRNA strand during transcription?

Template strand: 3' to 5'; mRNA: 5' to 3' Signup and view all the answers

What is the role of transcription factors in the initiation of transcription?

To bind to the promoter region of the template DNA and trigger RNA polymerase binding. Signup and view all the answers

What is the sequence of the mRNA transcript synthesized from the following template DNA sequence: 3'-TTCAGG-5'?

5'-AAGUCC-3' Signup and view all the answers

What is the function of the ribosome during translation?

To construct a polypeptide chain by reading the mRNA sequence. Signup and view all the answers

What is the anticodon sequence on a tRNA that binds to the mRNA codon 5'-GUA-3'?

3'-CAU-5' Signup and view all the answers

According to the provided codon table, what amino acid is specified by the mRNA codon 5'-CCU-3'?

Proline (Pro) Signup and view all the answers

What is the role of the A site of the ribosome during translation?

Holds the tRNA carrying the next amino acid to be added to the chain Signup and view all the answers

If a tRNA has the anticodon 3'-UAG-5', what mRNA codon would it bind to?

5'-AUC-3' Signup and view all the answers

What is the sequence of a coding strand of DNA that corresponds to the following mRNA 5'-AUGCCUUGACAU-3'?

5'-ATG CCT TGA CAT-3' Signup and view all the answers

What would happen if a mutation occurred in the tRNA such that the anticodon is no longer able to bind to its corresponding mRNA codon?

Translation would stop as the next tRNA would not be able to bind Signup and view all the answers

What is the consequence of a frameshift mutation?

It changes the reading frame of mRNA and alters most amino acids downstream. Signup and view all the answers

Which of these is NOT a type of point mutation?

Insertion mutation Signup and view all the answers

Which of these is most likely result of a mutation in a somatic cell?

It will only affect one cell and its daughter cells. Signup and view all the answers

Which of the following correctly represents the mRNA sequence transcribed from the coding DNA sequence 5'-ATG ACA AAG TGT GAA TAG-3'?

5'-AUG ACA AAG UGU GAA UAG-3' Signup and view all the answers

What type of mutation occurs in sickle cell anemia?

Point mutation Signup and view all the answers

Which of these is a function of DNA polymerase I?

Edits mismatched bases in the DNA sequence during replication. Signup and view all the answers

What is the primary issue caused by the frameshift mutation in cystic fibrosis?

A channel protein that transports chloride ions is absent or non-functional. Signup and view all the answers

How can exposure to external mutagens be best limited?

By avoiding radiation and other substances that can damage DNA. Signup and view all the answers

A mutation leads to the change of a codon from UCA to UAA. What is the likely resulting effect?

A nonsense mutation resulting in premature stop codon Signup and view all the answers

Study Notes

Central Dogma

Central dogma: DNA → RNA → Protein → You!
Protein synthesis occurs in two main steps: transcription and translation.

DNA vs. RNA

DNA:
- Double-stranded
- Deoxyribose sugar
- Bases: A, C, T, G
RNA:
- Single-stranded
- Ribose sugar
- Bases: A, C, U, G

DNA Packaging in the Nucleus

DNA is highly folded.
Nucleosomes are formed by wrapping DNA around histone proteins.
Heterochromatin: tightly wound DNA; "off" state; inaccessible.
Euchromatin: loosely wound DNA; "on" state; accessible.
This state is not permanent and can change.

Importance of RNA

DNA stays in the nucleus.
RNA carries instructions from DNA to ribosomes for protein construction.
Analogy: blueprints (DNA) → site manager (RNA) → workers (ribosomes) → materials (proteins).

Types of RNA

mRNA (messenger RNA): Copies DNA segments; carries info to ribosomes; codons (3-base sequences) are read.
tRNA (transfer RNA): Transports amino acids to ribosomes; anticodons match mRNA codons.
rRNA (ribosomal RNA): Forms the ribosome structure; assembles amino acids into proteins.

Transcription

Location: Nucleus
Process: DNA → mRNA copy
Template strand: 3' to 5'; used for mRNA synthesis.
Coding strand: 5' to 3'; sequence is the same as mRNA (except U replaces T).
RNA polymerase: Enzyme building the mRNA.

Transcription Steps

Initiation: Transcription factors bind promoter region; RNA polymerase binds DNA.
Elongation: RNA bases (U replaces T) pair with DNA; RNA strand grows 5' to 3'.
Termination: RNA polymerase reaches terminator sequence and releases from DNA, releasing mRNA.

Translation

Location: Ribosomes (in cytoplasm)
Process: mRNA → protein (amino acid sequence)

Genetic Code

Universal protein code for all organisms.
Codons: 3-nucleotide sequences on mRNA that specify an amino acid.
64 codons exist, but only 20 amino acids.
Start codon: AUG (methionine)
Stop codons: UAA, UAG, UGA

Translation Steps

Initiation: mRNA, ribosome subunits, and initiator tRNA come together.
Elongation: tRNA brings amino acids; polypeptide chain grows.
Termination: Stop codon reached; polypeptide released.

Ribosome Structure

Two subunits.
A site: Holds tRNA with next amino acid.
P site: Holds growing polypeptide chain.
E site: Empty tRNA exits.

tRNA Structure

tRNA has an anticodon complementary to the mRNA codon.
Anticodon specifies which amino acid the tRNA carries.

Mutations

Any change in DNA sequence (may or may not affect protein function).
Somatic mutations: Affect the organism but are not passed to offspring.
Germline mutations: Can be passed to offspring.

Types of Mutations

Point mutations: Change in a single base.
- Silent: No amino acid change.
- Missense: Different amino acid.
- Nonsense: Premature stop codon.
Frameshift mutations: Addition or deletion of a base; changes reading frame downstream.

Causes of Mutations

Errors in DNA replication, transcription, or translation.
Mutagens (e.g., UV radiation, chemicals).

Repair of Mutations

Enzymes proofread and repair DNA errors.
DNA polymerase and excision nucleases play a role.

Mutations and Evolution

Mutations are essential for evolution, providing variations for natural selection.

Examples of Mutations

Sickle-cell anemia: Point mutation affecting red blood cell shape.
Cystic fibrosis: Frameshift mutation affecting chloride transport protein.

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Description

Explore the central dogma of molecular biology, which outlines the flow of genetic information from DNA to RNA and then to proteins. This quiz covers key concepts including the differences between DNA and RNA, DNA packaging, and the types of RNA involved in protein synthesis.