DNA Replication in Prokaryotes and Eukaryotes

Questions and Answers

Which of these statements about DNA replication in prokaryotes and eukaryotes is true?

Both types begin new DNA strands with a small primer of RNA. (correct)

Eukaryotic cells have only one point of origin for replication.

Replication is faster in eukaryotic cells.

Prokaryotes replicate DNA in the nucleus.

What is the primary reason telomeres need protection in eukaryotic cells?

They have single-stranded overhangs that look like damaged DNA.

How do DNA polymerases I, II, and III differ?

In their exonuclease activities.

What happens during the repair mechanism for thymine dimers?

Adjacent thymine bases covalently bond to one another. Signup and view all the answers

Which statement is true about the synthesis of the leading and lagging strands during DNA replication?

The leading strand is continuously synthesized in the 5'-3' direction. Signup and view all the answers

What is helicase?

An enzyme that untwists the double helix of DNA at the replication forks. Signup and view all the answers

Define semiconservative replication.

Method of replication that implies each new strand of DNA is half original and half new. Signup and view all the answers

What type of bond holds two nucleotides together?

Hydrogen bonds. Signup and view all the answers

What is a replisome?

A complex of DNA polymerase and other enzymes that catalyzes the synthesis of DNA. Signup and view all the answers

What is excision repair?

A repair mechanism where DNA gets repaired after damage and mutations. Signup and view all the answers

What role does RNA polymerase play?

It links RNA nucleotides together during transcription. Signup and view all the answers

What is transcription?

The process whereby the DNA sequence in a gene is copied into mRNA. Signup and view all the answers

What is a transcription unit?

A region of DNA that is transcribed into an RNA molecule. Signup and view all the answers

Define promoter.

A specific region of a gene where RNA polymerase can bind and begin transcription. Signup and view all the answers

What occurs during the initiation of transcription?

RNA polymerase binds to the promoter. Signup and view all the answers

Describe elongation of transcription.

RNA polymerase unzips DNA, RNA elongates in the 5'-3' direction. Signup and view all the answers

What happens during termination of transcription?

RNA polymerase falls off DNA and the RNA transcript is released. Signup and view all the answers

Define translation.

The process of synthesizing proteins from messenger RNA. Signup and view all the answers

What does tRNA stand for?

Transfer RNA. Signup and view all the answers

What is a codon?

A sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule. Signup and view all the answers

What are anticodons?

Three-base sequences in a transfer RNA molecule that pair with complementary codons in mRNA. Signup and view all the answers

What is the role of the small ribosomal subunit?

It matches tRNA molecules to mRNA. Signup and view all the answers

What is the function of the large ribosomal subunit?

It is the larger of the two subunits of a functional ribosome. Signup and view all the answers

What are peptide bonds?

Bonds between amino acids. Signup and view all the answers

What are amino acids?

The building blocks of proteins. Signup and view all the answers

What are releasing factors?

Proteins that allow for the termination of translation. Signup and view all the answers

What are point mutations?

Changes in a DNA sequence caused by substitution of one nucleotide for another. Signup and view all the answers

What are chromosomal mutations?

Changes in a DNA sequence that affect an entire chromosome or multiple chromosomes. Signup and view all the answers

What are frameshift mutations?

Mutations that cause the shifting of multiple nucleotides. Signup and view all the answers

What is a ribosome?

Cytoplasmic organelles at which proteins are synthesized. Signup and view all the answers

What does the DOGMA of molecular biology state?

DNA > RNA > Proteins. Signup and view all the answers

What are retroviruses known for?

Using reverse transcriptase to copy their RNA genome into DNA. Signup and view all the answers

What is gene expression?

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Study Notes

DNA Replication in Prokaryotes vs. Eukaryotes

DNA replication processes are fundamentally similar in both prokaryotes and eukaryotes.
DNA helicase unwinds the DNA, while polymerases synthesize new strands.
Semi-conservative replication produces leading and lagging strands.
Lagging strands consist of Okazaki fragments that connect later.
Prokaryotic cells contain 25 times less DNA than eukaryotic cells.
Replication in prokaryotes initiates at one point, proceeding bidirectionally in the cytoplasm.
Eukaryotic replication has multiple origins and occurs unidirectionally within the nucleus.
Eukaryotes utilize four or more polymerases, while prokaryotes have one or two.
Prokaryotic replication is faster, with some bacteria completing it in 40 minutes versus up to 400 hours for humans.
Eukaryotes possess specialized mechanisms to replicate telomeres, unlike prokaryotes with circular chromosomes.

Telomeres in Eukaryotic Cells

Telomeres consist of single-stranded overhangs that resemble damaged DNA, requiring protection.
Incomplete end replication at the lagging strand creates these overhangs.
Telomere ends can form protective loops by binding to complementary repeats in double-stranded DNA.
Proteins associated with telomeres shield them from DNA repair pathways.

DNA Polymerases Comparison

All three DNA polymerases exhibit 5' to 3' polymerase activity but differ in exonuclease functions.
DNA polymerase I has both 3' to 5' and 5' to 3' exonuclease activity for proofreading and removing RNA primers.
DNA polymerase II acts as a repair polymerase, able to restart replication with proofreading capability.
DNA polymerase III primarily synthesizes DNA during replication and also has proofreading ability.

Thymine Dimers Repair

Adjacent thymine bases may covalently bond, leading to mutations.

Leading vs. Lagging Strand Synthesis

The leading strand is continuously synthesized towards the replication fork in a 5'-3' direction.
The lagging strand is synthesized in fragments (Okazaki fragments) away from the fork using multiple RNA primers.
Both strands are read in a 3'-5' direction and become identical in the new DNA molecule.

Helicase

Helicase is an enzyme responsible for unwinding the DNA double helix at replication forks.

Semiconservative Replication

Each new DNA strand consists of one original and one newly synthesized strand.

Hydrogen Bonds

Hydrogen bonds connect two nucleotides, stabilizing the DNA structure.

Replisome

A replisome is a complex of DNA polymerase and other enzymes facilitating DNA synthesis.

Excision Repair

A mechanism to repair DNA post-damage, correcting mutations.

RNA Polymerase

RNA polymerase is essential for transcription, linking RNA nucleotides together.

Transcription Overview

Transcription is the process of copying a DNA sequence into mRNA.

Transcription Unit

A transcription unit is a DNA region transcribed into RNA.

Promoter

The promoter is a specific DNA region where RNA polymerase attaches to initiate transcription.

Transcription Process

Initiation: RNA polymerase binds to the promoter.
Elongation: RNA polymerase unwinds DNA and synthesizes RNA in a 5'-3' direction.
Termination: RNA polymerase detaches from the DNA, releasing the RNA transcript.

Translation Overview

Translation involves the synthesis of proteins from RNA instructions.

tRNA

Transfer RNA (tRNA) carries amino acids to ribosomes during protein synthesis.

Codons and Anticodons

Codons: Sequences of three nucleotides forming genetic code units.
Anticodons: tRNA sequences that pair with complementary mRNA codons.

Ribosomal Subunits

Small ribosomal subunit matches tRNA to mRNA.
Large ribosomal subunit is the larger functional component of the ribosome.

Peptide Bonds

Peptide bonds form between amino acids during protein synthesis.

Amino Acids

Amino acids are the fundamental building blocks of proteins.

Releasing Factors

Proteins facilitating the termination of the translation process.

Mutations

Point mutations result from nucleotide substitutions.
Chromosomal mutations affect entire chromosomes or several at once.
Frameshift mutations cause shifts in nucleotide sequences.

Ribosomes

Ribosomes are cellular structures where proteins are synthesized.

Molecular Biology Dogma

The central dogma describes the flow of genetic information: DNA → RNA → Proteins.

Retroviruses

Retroviruses utilize reverse transcriptase to convert their RNA genomes into DNA.

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Description

Explore the similarities and differences in DNA replication mechanisms between prokaryotic and eukaryotic cells. Discover the roles of helicase, polymerases, and the structure of leading and lagging strands. This quiz delves into the unique challenges faced by eukaryotes and the efficiency of prokaryotic replication.