DNA Replication Elongation Process

Questions and Answers

Which of the following statements about telomeres and aging is correct?

Telomeres are unaffected by telomerase activity throughout life

Insufficient telomerase leads to telomere shortening during aging (correct)

Telomeres actually replicate without the need for telomerase

Telomeres lengthen as we age due to improved telomerase activity

What is the main role of TERT in telomeric replication?

To synthesize RNA from DNA

To initiate the process of cell division

To guide proper attachment of the enzyme (correct)

To extend telomeres during DNA replication

What is the primary function of messenger RNA (mRNA)?

To form part of the ribosome structure

To replicate DNA strands during synthesis

To carry genetic information from DNA for protein synthesis (correct)

To transport amino acids to the ribosome

Which nitrogenous base pair is correctly matched in RNA base pairing?

C - G Signup and view all the answers

Which type of RNA is primarily responsible for forming part of the ribosome?

rRNA Signup and view all the answers

What role does transfer RNA (tRNA) play in translation?

It carries amino acids to the ribosome to build an amino acid chain. Signup and view all the answers

Which statement accurately describes the genetic code?

It is nearly universal among different species, with some exceptions. Signup and view all the answers

What characteristic of the genetic code describes its redundancy?

Multiple codons can specify the same amino acid. Signup and view all the answers

Which of the following statements is true about the genetic code's structure?

The genetic code is comma-less, meaning there are no breaks or markers between codons. Signup and view all the answers

What does the term 'colinear' refer to in the context of the genetic code?

The order of codons in mRNA determines the order of amino acids in the protein. Signup and view all the answers

Which DNA polymerase is responsible for the continuous synthesis on the leading strand?

DNA Pol δ Signup and view all the answers

What role does the FEN1 enzyme play during DNA replication?

It removes RNA primers. Signup and view all the answers

What is the primary function of telomerase in eukaryotes?

It maintains telomere length. Signup and view all the answers

What occurs during the polymerase switching mechanism in DNA replication?

DNA Pol α/primase complex dissociates to allow DNA Pol δ or ε to bind. Signup and view all the answers

Why can DNA Polymerase α not fill the gaps left at the 5’ ends of newly synthesized DNA?

It requires a free 3’-OH end to initiate synthesis. Signup and view all the answers

What happens during the termination phase of DNA replication?

Replication forks converge on the same stretch of DNA. Signup and view all the answers

What is the consequence of having no free 3’-OH groups during DNA replication?

Gaps cannot be filled by DNA polymerases. Signup and view all the answers

Okazaki fragments are primarily associated with which strand during DNA replication?

Lagging strand Signup and view all the answers

What direction is the genetic code always read?

5’ to 3’ Signup and view all the answers

Which of the following is a start codon in the genetic code?

AUG Signup and view all the answers

What do exons represent in a gene?

Coding sequences Signup and view all the answers

Which sequence is NOT involved in the initiation of transcription?

Poly-A tail Signup and view all the answers

What is the role of introns in gene expression?

They are involved in RNA splicing. Signup and view all the answers

Which of the following correctly defines the role of enhancers in transcription?

They stimulate the transcription rate. Signup and view all the answers

What is the first step in the transcription process?

Initiation Signup and view all the answers

What defines the end of a transcriptional unit?

Terminator sequence Signup and view all the answers

What is the primary role of aminoacyl tRNA synthetase in translation?

To chemically link tRNA to amino acids Signup and view all the answers

Which site on the ribosome does the tRNA carrying the growing polypeptide chain occupy during translation?

P site Signup and view all the answers

What is the function of eukaryotic initiation factors (eIFs) during mRNA translation initiation?

To block the A site from being bound to a tRNA Signup and view all the answers

During elongation, what occurs to the tRNA that is situated at the P site after its amino acid is added to the peptide chain?

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

What happens during the translocation phase of translation?

The ribosome moves along the mRNA by 3 nucleotides Signup and view all the answers

Which component is involved in recognizing the start codon during translation initiation?

Initiator tRNA with bound Methionine Signup and view all the answers

What is a significant characteristic of ribosomes during the process of translation?

Many ribosomes can be attached simultaneously to a single mRNA molecule Signup and view all the answers

What is the initial step in mRNA translation?

Initiation Signup and view all the answers

Study Notes

Elongation in DNA Replication

Clamp loader (RF-C) and sliding clamp (PCNA) assemble at primer-template junctions.
Polymerase switching occurs: DNA Pol α/primase complex dissociates, replaced by DNA Pol δ or ε for extension.
DNA polymerases synthesize DNA in a 5’ → 3’ direction, requiring a free –OH end.
Leading strand synthesized continuously by DNA Pol δ from the 3’ → 5’ parental strand toward the replication fork.
Lagging strand synthesized discontinuously by DNA Pol ε, forming Okazaki fragments away from the replication fork.
FEN1 and RNaseH remove RNA primers, allowing DNA Polymerase α to fill gaps with DNA.
DNA ligase seals the sugar-phosphate backbones between DNA fragments.

Termination of DNA Replication

Termination occurs when replication forks converge on the same DNA stretch, signaling completion.
Helicase and topoisomerase leave when they exhaust space to operate.

Telomeric Replication/Synthesis

Telomeres maintain chromosomal stability, preventing degradation.
Eukaryotic telomeres consist of short, repeated nucleotide sequences, extending through the action of telomerase.
Telomerase includes TERC (telomerase RNA component, catalytic subunit) and TERT (telomerase reverse transcriptase, guides enzyme attachment).
Telomeres shorten with age, leading to senescence/apoptosis due to insufficient telomerase.

Central Dogma of Molecular Biology

Developed by Francis Crick in 1958, illustrating the flow of genetic information from DNA to RNA, resulting in protein synthesis.

RNA Overview

RNA (Ribonucleic acid) acts as a messenger, is single-stranded, and is located in the nucleus and cytoplasm.

Types of RNA

Messenger RNA (mRNA) carries genetic information from DNA to ribosomes.
Ribosomal RNA (rRNA) is a component of ribosomes and aids in protein synthesis.
Transfer RNA (tRNA) delivers amino acids to ribosomes, matching anticodons with mRNA codons during translation.

Codons and the Genetic Code

A codon is a three-nucleotide sequence in mRNA that corresponds to a specific amino acid.
The genetic code is composed of nucleotide triplets, is degenerate, non-overlapping, comma-less, nearly universal, collinear, and directional.
Contains start codon (AUG, Methionine) and stop codons (UGA, UAG, UAA).

Genes and Gene Expression

Genes are hereditary units located on chromosomes, encoding RNA or protein products.
Transcription transfers information from DNA to RNA, utilizing RNA polymerase to synthesize mRNA.
Key elements of a eukaryotic gene include promoter sequences, exons, introns, terminator sequences, enhancers, and silencers.

Transcription Process

Initiation involves binding of RNA polymerase to promotor regions.
Elongation is the synthesis of RNA based on the DNA template.
Termination signifies the end of transcription, releasing the newly formed RNA strand.

Translation Overview

Occurs in the cytoplasm, where mRNA is converted into a protein sequence.
mRNA combines with ribosomes; polypeptides are synthesized as ribosomes simultaneously translate one mRNA molecule.

tRNA Charging

Requires aminoacyl-tRNA synthetase to link tRNA with its corresponding amino acid.

Ribosome Composition

The ribosome consists of three sites: Aminoacyl (A) site, Peptidyl (P) site, and Exit (E) site.

Steps in mRNA Translation

Initiation includes assembly of ribosome components and binding of the initiator tRNA.
Elongation adds amino acids to the growing polypeptide chain via peptide bonds.
Termination concludes protein synthesis at stop codons.

Initiation Mechanism

In eukaryotes, a cap-dependent mechanism assembles ribosomal subunits at the 5’ cap of mRNA.
Translational initiation involves eukaryotic initiation factors stabilizing the start codon and tRNA.

Elongation Process

Eukaryotic elongation factors transport tRNA to the ribosome; peptide bonds form between amino acids, progressing the polypeptide chain.

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Description

This quiz covers the elongation phase of DNA replication, focusing on key components such as the clamp loader (RF-C), sliding clamp (PCNA), and polymerase switching. Learn how DNA polymerases synthesize DNA in the 5' to 3' direction and the roles of different polymerases during this critical process.