Replication

Question 1

What are the components of a nucleotide?

Answer 1

A nucleotide is composed of three components: a sugar molecule (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base.

Question 2

What is the significance of the sequence of bases in a nucleic acid chain?

Answer 2

The sequence of bases along a nucleic acid chain carries genetic information. The specific order of the bases encodes the instructions for the synthesis of proteins and other cellular functions.

Question 3

How does DNA replication occur?

Answer 3

DNA replication occurs through a process called semi-conservative replication. Each DNA strand serves as a template for the creation of a new complementary strand. The result is two identical DNA molecules, each containing one original strand and one newly synthesized strand.

Question 4

How is protein synthesis related to DNA and RNA?

Answer 4

DNA itself is not directly involved in protein synthesis. Instead, DNA is transcribed into mRNA through a process called transcription. The mRNA molecules then serve as templates for protein synthesis

Question 5

What is the role of messenger RNA (mRNA) in protein synthesis?

Answer 5

Messenger RNA (mRNA) is a type of RNA molecule that carries the genetic information from DNA to the cellular machinery responsible for protein synthesis. mRNA acts as an intermediary, conveying the instructions encoded in DNA to guide the synthesis of proteins.

Question 6

What is the relationship between transcription and translation?

Answer 6

Transcription is the process where DNA is copied into mRNA, while translation is the process where mRNA is used as a template to synthesize proteins according to the genetic instructions encoded in the mRNA.

Question 7

What is the genetic code, and what does it define?

Answer 7

The genetic code defines the relationship between the sequence of bases in DNA (or its mRNA transcript) and the sequence of amino acids in a protein. It is nearly the same in all organisms and consists of codons, which are sequences of three bases that specify a particular amino acid.

Question 8

Why are naturally occurring DNA molecules long?

Answer 8

Naturally occurring DNA molecules are long because they need to carry the genetic information necessary for the functioning of organisms, even in the simplest ones

Question 9

Can you provide examples of DNA lengths in different organisms?

Answer 9

Polyoma virus: Two intertwined strands, each 5100 nucleotides long.
E. coli: A single DNA molecule consisting of two chains, each with 4.6 million nucleotides.
Human genome: Approximately 3 billion nucleotides in each chain of DNA, divided among 23 distinct chromosomes of different sizes.
Indian muntjac: The genome is nearly as large as the human genome but distributed on only 3 chromosomes. The largest chromosome has two chains of over 1 billion nucleotides each.

Question 10

How many nucleotides are present in each chain of the human genome?

Answer 10

Each chain of the human genome contains approximately 3 billion nucleotides.

Question 11

What is the significance of codons in the genetic code?

Answer 11

Codons are sequences of three bases (nucleotides) in DNA or mRNA that code for specific amino acids or serve as start or stop signals in protein synthesis. The genetic code is degenerate, meaning that multiple codons can code for the same amino acid.

Question 12

Can you explain the concept of gene expression and its relationship to DNA, RNA, and proteins?

Answer 12

Gene expression refers to the process by which information encoded in genes is used to create functional proteins or other cellular products. It involves the transcription of DNA into mRNA and the subsequent translation of mRNA into proteins. Gene expression is a fundamental process for the functioning and development of organisms.

Question 13

What proteins are involved in DNA replication?

Answer 13

DNA polymerases, primase, DNA helicase, DNA ligase, single-stranded binding proteins, and various other proteins that assist in the initiation, elongation, and termination stages of replication

Question 14

What is the role of DNA polymerases in DNA replication?

Answer 14

DNA polymerases play a crucial role in DNA replication. They promote the formation of bonds between individual units of the DNA molecule, called nucleotides, and add them step by step to build a new DNA chain.

Question 15

What are the activated precursors required for DNA synthesis?

Answer 15

deoxynucleoside 5’-triphosphates (dATP, dGTP, dCTP, and TTP) along with the presence of magnesium ions (Mg2+).

Question 16

How is the new DNA chain assembled during replication?

Answer 16

The new DNA chain is assembled directly on a preexisting DNA template. The DNA polymerases read the template DNA strand and add complementary nucleotides to the growing DNA chain, ensuring that the bases on the incoming nucleotides match the bases on the template strand.

Question 17

What is the function of primase in DNA replication?

Answer 17

Primase is an enzyme involved in DNA replication that initiates the synthesis of RNA primers. These primers provide a starting point for DNA polymerases to begin synthesizing a new DNA strand.

Question 18

How is the accuracy of DNA replication maintained?

Answer 18

The accuracy of DNA replication is maintained through a multilayered system. Accurate DNA synthesis itself has a certain error rate, but it is reduced by proofreading processes during DNA synthesis. Additionally, postreplication mismatch repair further reduces errors by detecting and correcting mistakes after replication.

Question 19

What is the error rate required to replicate the human genome without mistakes?

Answer 19

To replicate the human genome without mistakes, an error rate of less than 1 error per 3x10^9 base pairs must be achieved.

Question 20

What are the different layers of the system that ensure accurate DNA synthesis?

Answer 20

The system that ensures accurate DNA synthesis involves multiple layers. It includes accurate DNA synthesis itself, which has an error rate of approximately 1 error per 10^3 to 10^4 inserted bases. There are also proofreading mechanisms during DNA synthesis that reduce the error rate to about 1 error per 10^6 to 10^7 base pairs.
Furthermore, postreplication mismatch repair processes further reduce the error rate to around 1 error per 10^9 to 10^10 base pairs.

Question 21

How does postreplication mismatch repair reduce the error rate in DNA replication?

Answer 21

Postreplication mismatch repair is a mechanism that detects and corrects errors after DNA replication. It helps reduce the error rate in DNA replication to approximately 1 error per 10^9 to 10^10 base pairs.

Question 22

How does primase initiate synthesis without a primer, and what is its role in DNA replication?

Answer 22

Primase initiates synthesis without a primer by synthesizing a short RNA primer complementary to the DNA template. The RNA primer provides a starting point for DNA polymerases to bind and begin DNA synthesis.

Question 23

How does the presence of magnesium ions (Mg2+) contribute to the DNA synthesis reaction?

Answer 23

Magnesium ions (Mg2+) play a crucial role in DNA synthesis. They stabilize the negatively charged phosphate groups of the dNTPs, facilitating the bonding reaction between the incoming nucleotide and the growing DNA chain. Mg2+ ions also help in the proper positioning of the dNTP within the active site of DNA polymerases.

Question 24

What are the specific proofreading mechanisms employed by DNA polymerases during DNA synthesis?

Answer 24

DNA polymerases employ proofreading mechanisms to ensure accuracy during DNA synthesis. These mechanisms include exonuclease activity, where the polymerase can remove mismatched nucleotides from the growing DNA chain and replace them with the correct ones.

Question 25

What are the specific functions of each protein in the DNA Replicase system or Replisomes?

Answer 25

DNA polymerases: Catalyze the synthesis of new DNA strands by adding nucleotides. Primase: Initiates the synthesis of RNA primers. DNA helicase: Unwinds the double-stranded DNA to create a replication fork. DNA ligase: Joins the Okazaki fragments on the lagging strand during DNA replication. Single-stranded binding proteins: Stabilize and protect the single-stranded DNA regions during replication.

Question 26

How does the catalytic activity of DNA polymerases promote the formation of bonds in the DNA backbone?

Answer 26

DNA polymerases have an active site that can catalyze the formation of phosphodiester bonds between nucleotides. They use the energy from the incoming deoxynucleoside 5'-triphosphate (dNTP) to join the 3'-hydroxyl group of the growing DNA chain with the 5'-phosphate group of the incoming nucleotide, thereby forming the bond in the DNA backbone.

Question 27

What's the site of DNA replication

Answer 27

Replication fork It is formed by the newly synthesized daughter helices and resembles a two-pronged fork.

Question 28

How are the leading and lagging strands synthesized during DNA replication?

Answer 28

The leading strand is synthesized continuously during DNA replication, while the lagging strand is synthesized in small fragments called Okazaki fragments.

Question 29

What is the direction of DNA synthesis by DNA polymerases?

Answer 29

DNA polymerases synthesize DNA in the 5' to 3' direction. They cannot synthesize DNA in the opposite direction (3' to 5').

Question 30

How are Okazaki fragments joined together during replication?

Answer 30

together during replication by an enzyme called DNA ligase. DNA ligase catalyzes the formation of covalent bonds between the fragments, resulting in a continuous daughter strand.

Question 31

What is the difference between the leading and lagging strands?

Answer 31

The leading strand is synthesized continuously in the same direction as the replication fork, while the lagging strand is synthesized discontinuously in the opposite direction. The leading strand is synthesized without interruption, while the lagging strand is synthesized in fragments.

Question 32

How does the discontinuous assembly of the lagging strand

Answer 32

The discontinuous assembly of the lagging strand enables overall growth because the fragments are still synthesized in the 5' to 3' direction at the nucleotide level. When the fragments are joined together, they form a continuous strand.

Question 33

What is the role of DNA ligase in DNA replication?

Answer 33

DNA ligase plays a crucial role in DNA replication by sealing breaks in double-stranded DNA molecules. It catalyzes the formation of phosphodiester bonds between the 3'-hydroxyl group of one DNA chain and the 5'-phosphoryl group of the other, resulting in the connection of DNA fragments.

Question 34

What energy source drives the bond formation catalyzed by DNA ligase in different organisms?

Answer 34

ATP is typically used as the energy source, while in bacteria, NAD+ is commonly utilized.

Question 35

What can DNA ligase seal in double-stranded DNA molecules?

Answer 35

DNA ligase can seal breaks in double-stranded DNA molecules. It is not able to link two molecules of single-stranded DNA or circularize single-stranded DNA. Its main function is to join the ends of DNA strands during replication or repair processes.

Question 36

Can you explain the mechanism of DNA ligase in joining Okazaki fragments during DNA replication?

Answer 36

DNA ligase joins Okazaki fragments during DNA replication by catalyzing the formation of phosphodiester bonds between the adjacent fragments. It seals the nicks (unjoined ends) in the DNA backbone, resulting in the formation of a continuous daughter strand.

Question 37

Can you explain the role of single-stranded binding proteins (SSBs) in DNA replication?

Answer 37

Single-stranded binding proteins (SSBs) stabilize and protect single-stranded DNA regions during DNA replication. They bind to the exposed single-stranded DNA, preventing it from forming secondary structures and being degraded by nucleases. SSBs also help to keep the DNA strands separated, allowing for efficient replication.

Question 38

What are the functions of helicase in DNA replication, and how does it contribute to the unwinding of the DNA double helix?

Answer 38

Helicase plays a crucial role in DNA replication by unwinding the double-stranded DNA at the replication fork. It uses energy from ATP hydrolysis to break the hydrogen bonds between the base pairs, separating the DNA strands and creating the single-stranded DNA templates needed for DNA synthesis.

Question 39

What is the function of topoisomerases in DNA replication, and how do they relieve torsional stress during replication?

Answer 39

Topoisomerases are enzymes involved in DNA replication that help relieve torsional stress and prevent DNA supercoiling. They achieve this by cutting and rejoining the DNA strands, allowing for controlled rotation of the DNA during replication.

Question 40

What are topoisomerases and what role do they play in DNA processes?

Answer 40

Topoisomerases are enzymes that are involved in DNA processes such as replication, transcription, and recombination. They help regulate the degree of supercoiling in DNA, which is the twisting and winding of the DNA strands.

Question 41

What is the difference between negative and positive supercoiling of DNA?

Answer 41

Negative supercoiling refers to the underwinding of DNA, which prepares it for processes like replication. Positive supercoiling, on the other hand, condenses DNA but makes strand separation more difficult.

Question 42

How do Type I and Type II topoisomerases differ in their actions on DNA?

Answer 42

Type I topoisomerases cleave one strand of DNA and relax supercoiled DNA. Type II topoisomerases cleave both strands of DNA and utilize ATP energy to introduce negative supercoils into DNA.

Question 43

What are some antibiotics that target bacterial topoisomerase II (DNA gyrase)?

Answer 43

Antibiotics such as novobiocin, nalidixic acid, and ciprofloxacin target bacterial topoisomerase II (DNA gyrase). Novobiocin blocks the binding of ATP to gyrase, while nalidixic acid and ciprofloxacin interfere with the breakage and rejoining of DNA chains.

Question 44

How does camptothecin inhibit human topoisomerase I and what effect does it have on DNA?

Answer 44

Camptothecin inhibits human topoisomerase I by stabilizing the form of the enzyme covalently linked to DNA. This prevents DNA re-ligation and leads to DNA damage, ultimately causing apoptosis (programmed cell death).

Question 45

What are autonomously replicating sequences (ARS) or replicators, and where have they been extensively studied?

Answer 45

Autonomously replicating sequences (ARS) or replicators are specific sequences in DNA that act as origins of replication. They have been extensively studied in eukaryotes, particularly in yeast

Question 46

What is the function of the origin recognition complex (ORC) in initiating DNA replication?

Answer 46

The origin recognition complex (ORC) is a multisubunit protein complex that plays a crucial role in initiating DNA replication. It binds to several sequences within the replicator and helps recruit other proteins involved in replication.

Question 47

How does the rate of replication fork movement differ between eukaryotes and E. coli?

Answer 47

The rate of replication fork movement in eukaryotes is slower compared to E. coli. Eukaryotes replicate at a rate of approximately 50 nucleotides per second, which is only one-twentieth of the rate observed in E. coli.

Question 48

How long would it take to replicate an average human chromosome from a single origin at the rate observed in eukaryotes?

Answer 48

Replicating an average human chromosome from a single origin at the rate observed in eukaryotes (~50 nucleotides per second)

Question 49

What are some potential applications or implications of understanding the mechanisms of topoisomerases and DNA replication?

Answer 49

Understanding the mechanisms of topoisomerases and DNA replication has several implications and applications. It helps in understanding genetic processes, developing antibiotics that target bacterial topoisomerases, studying diseases related to DNA replication errors, and exploring potential therapeutic strategies for cancer treatment. Additionally, knowledge of DNA replication is crucial for advancements in genetic engineering, biotechnology, and synthetic biology

Question 50

What are the specific mechanisms by which Type I and Type II topoisomerases cleave and reseal DNA strands?

Answer 50

Type I topoisomerases cleave one strand of the DNA, forming a transient covalent bond between the enzyme and the DNA. The DNA strand is then passed through the break, and the enzyme reseals the nicked DNA strand. Type II topoisomerases cleave both strands of the DNA, creating a double-stranded break. They form a covalent protein-DNA intermediate, allowing them to pass another segment of DNA through the break. Finally, the enzyme reseals the double-stranded break.

Question 51

What are some of the key sequences recognized by the origin recognition complex (ORC) during DNA replication initiation in eukaryotes?

Answer 51

The origin recognition complex (ORC) recognizes specific sequences within the replicator during DNA replication initiation in eukaryotes. These sequences, known as origin recognition sites, vary among species but generally contain conserved DNA motifs that serve as binding sites for ORC.

Question 52

How do different types of autonomously replicating sequences (ARS) or replicators function, and what factors determine their efficiency and specificity?

Answer 52

The slower rate of replication fork movement in eukaryotes compared to E. coli can be attributed to multiple factors, such as the larger size and complexity of eukaryotic genomes, the need for coordination with chromatin structure, and the requirement for more complex protein-protein interactions during replication.

Question 53

What are the potential long-term consequences of DNA replication errors caused by topoisomerase dysfunction?

Answer 53

DNA replication errors caused by topoisomerase dysfunction can have various long-term consequences. They can lead to mutations, genomic instability, and the development of genetic diseases or predisposition to certain cancers. Additionally, errors in DNA replication can result in impaired cellular function and contribute to aging processes.

Question 54

How does replication of human chromosomes occur?(direction)

Answer 54

Replication of human chromosomes occurs bidirectionally from multiple origins, with each origin initiating the replication process in both directions.

Question 55

Why are multiple origins of replication necessary in eukaryotic cells?

Answer 55

Multiple origins of replication are necessary in eukaryotic cells because eukaryotic chromosomes are larger than bacterial chromosomes. Having multiple origins allows for simultaneous replication of different regions of the chromosome, making the replication process more efficient and faster.

Question 56

What are the different types of DNA polymerases found in eukaryotes?

Answer 56

DNA polymerases found in eukaryotes include α, β, γ, δ, and ɛ.

Question 57

Which DNA polymerase is responsible for chromosome replication in mammalian cells?

Answer 57

DNA polymerase α is responsible for chromosome replication in mammalian cells.

Question 58

What is the speed of polymerization of DNA polymerase α compared to bacterial enzymes?

Answer 58

The speed of polymerization of DNA polymerase α is slower compared to bacterial enzymes. It can polymerize about 100 nucleotides per second, whereas bacterial enzymes can polymerize about 10 times faster.

Question 59

What are the subunits of mammalian DNA polymerase α and what are their functions?

Answer 59

Mammalian DNA polymerase α consists of four subunits. One subunit has a primase activity, and the largest subunit (with a molecular weight of approximately 180,000) contains the polymerization activity.

Question 60

Why is DNA polymerase α not suitable for high-fidelity DNA replication?

Answer 60

DNA polymerase α lacks proofreading exonuclease activity, which means it cannot correct errors during DNA replication. This makes it unsuitable for high-fidelity DNA replication.

Question 61

What is the role of proliferating cell nuclear antigen (PCNA) in DNA replication?

Answer 61

Proliferating cell nuclear antigen (PCNA) is a protein that associates with DNA polymerase α and stimulates its activity during DNA replication.

Question 62

Which DNA polymerase is involved in extending the primers synthesized by DNA polymerase α? And it's function

Answer 62

The primers synthesized by DNA polymerase α are extended by the multi-subunit DNA polymerase δ. δ is the main enzyme responsible for synthesizing the lagging strand during DNA replication. It participates in both leading and lagging strand synthesis and possesses 3' to 5' exonuclease proofreading activity.

Question 63

What are the specific functions of DNA polymerases β, γ, and ɛ in mammalian cells?

Answer 63

DNA polymerase β is involved in DNA repair processes, DNA polymerase γ is responsible for mitochondrial DNA synthesis, and DNA polymerase ɛ is primarily used for leading strand synthesis. It has high fidelity and proofreading capabilities. Pol ε also participates in DNA repair processes.

Question 64

In what situations does DNA polymerase ɛ replace DNA polymerase δ?

Answer 64

DNA polymerase ɛ can replace DNA polymerase δ in some situations, such as during DNA repair processes.

Question 65

How does DNA polymerase δ contribute to both leading and lagging strand synthesis?

Answer 65

DNA polymerase δ contributes to both leading and lagging strand synthesis in a complex comparable to the dimeric bacterial DNA polymerase III.

Question 66

How does the replication machinery in eukaryotes compare to that of bacteria?

Answer 66

The replication machinery in eukaryotes is similar to that of bacteria, but there are some differences due to the larger size and complexity of eukaryotic genomes.

Question 67

What are the differences between DNA polymerase α and DNA polymerase III in bacteria?

Answer 67

DNA polymerase α and DNA polymerase III in bacteria have different subunit compositions and functions, with DNA polymerase α being responsible for priming and DNA polymerase III being the main enzyme involved in DNA synthesis.

Question 68

Which DNA polymerase is involved in DNA repair processes?

Answer 68

DNA polymerase β is involved in DNA repair processes.

Question 69

What is the role of DNA polymerase γ in eukaryotic cells?

Answer 69

DNA polymerase γ is specifically involved in mitochondrial DNA synthesis.

Question 70

How does DNA polymerase δ proofread and correct errors during DNA synthesis?

Answer 70

DNA polymerase δ has a proofreading exonuclease activity, which allows it to remove mismatched nucleotides and correct errors during DNA synthesis.

Question 71

In mammalian cells, there are ____ DNA polymerases: namely

Answer 71

five α, β, γ, δ, and ɛ.

Question 72

What's the feature of DNA polymerase α

Answer 72

DNA polymerase α is the major enzyme responsible for chromosome replication but has lower speed and lacks proofreading activity. DNA polymerase α synthesizes short primers for Okazaki fragments on the lagging & leading strand and is stimulated by proliferating cell nuclear antigen (PCNA). Polymerase about 100 neuclotide per second (in bacteria is about×10)

Question 73

Features of DNA polymerase δ

Answer 73

DNA polymerase δ, which has proofreading activity, extends the primers synthesized by DNA polymerase α and carries out both leading and lagging strand synthesis.

Question 74

Features of DNA polymerase β, DNA polymerase γ, and DNA polymerase ɛ

Answer 74

DNA polymerase β is involved in DNA repair, DNA polymerase γ is responsible for mitochondrial DNA synthesis, and DNA polymerase ɛ is used for leading strand and may function at the replication fork, similar to bacterial DNA polymerase I, by removing the primers of Okazaki fragments on the lagging strand.

Question 75

DNA polymerase δ is replaced by DNA polymerase___ in certain situations, such as

Answer 75

DNA polymerase δ is replaced by DNA polymerase ɛ in certain situations, such as during DNA repair processes.

Question 76

______ is a compound that inhibits the DNA polymerase of the herpes simplex virus. And how

Answer 76

Acyclovir It is phosphorylated by a virally encoded thymidine kinase and binds to the viral enzyme with high affinity.

Question 77

___ is used to treat herpes simplex

Answer 77

Acyclovir is a compound that was developed by a scientist named Gertrude Elion

Question 78

Acyclovir is made up of a molecule called _____, which is a building block of DNA, attached to an incomplete ____ . This structure allows acyclovir to be recognized and modified by a specific enzyme called _______ which is produced by the herpes virus.

Answer 78

guanine ribose ring. thymidine kinase,

Question 79

When acyclovir enters a virus-infected cell, the viral thymidine kinase enzyme attaches a phosphate group to it, forming a modified version called acyclo-GMP. This modified molecule is then further modified by cellular enzymes into acyclo-GTP.

Answer 79

Acyclo-GTP has a higher affinity or attraction to the viral thymidine kinase enzyme compared to the cellular thymidine kinase. This means that it mainly gets converted into acyclo-GTP in the virus-infected cells

Question 80

Acyclo-GTP acts in two ways to inhibit the herpes DNA polymerase. They are?

Answer 80

First, it competes with the normal building blocks of DNA, called nucleotides, when they try to bind to the DNA polymerase. This competition makes it difficult for the herpes DNA polymerase to continue replicating the viral DNA. Second, acyclo-GTP lacks a specific chemical group called a 3' hydroxyl, which is needed for adding more nucleotides to the growing DNA chain. Without this hydroxyl group, acyclo-GTP acts as a "chain terminator"

Question 81

After replication there's a process called DNA methylation whats it

Answer 81

After DNA replication, there is a process called DNA methylation that occurs. This process involves adding a chemical modification called a methyl group to the DNA molecule at a specific position called C5 of cytosine.

Question 82

This methylation process is catalyzed or facilitated by an enzyme called

Answer 82

DNA methyltransferase (abbreviated as Dam).

Question 83

Whats Gene silencing

Answer 83

DNA methylation is a common mechanism associated with gene silencing, which means it turns off or reduces the activity of certain genes.

Question 84

Transcriptional regulation of tissue specific genes during cellular differentiation also results from

Answer 84

DNA methylation.

Question 85

Function of DNA methylation

Answer 85

DNA methylation helps regulate the activity of tissue-specific genes, ensuring that the right genes are expressed in the right cells at the right time.

Question 86

example is X-chromosomal inactivation, which happens in female mammals to balance the gene expression between the two X chromosomes. It also contributes to genomic imprinting, which is the selective silencing of either the maternal or paternal alleles (gene copies).

Question 87

Methylation occurs in

Answer 87

CG rich areas in the promoter region The promoter region is a region of DNA near the beginning of a gene that helps control its expression or activity.

Question 88

The changes in gene expression that result from methylation can be passed down from one generation to another, but sometimes these inherited marks or imprints can be erased and rewritten during the process.

Question 89

Epigenetic information refers

Answer 89

to these inherited marks or modifications that can change how genes are expressed. They are often described as "writings with nature's pencil"

Question 90

What's ROS and how it affects methylation

Answer 90

Reactive oxygen species (ROS), which are molecules that can cause damage to cells ROS can lead to a process called hypermethylation, which involves excessive methylation of certain areas of the DNA

Question 91

Methylation is influenced by factors such as

Answer 91

Methylation is influenced by factors like cancer, reactive oxygen species, cellular senescence, and can have implications for age-related diseases like type 2 diabetes

Question 92

Unrepaired DNA damage is known as a

Answer 92

lesion

Question 93

Most serious lesion is

Answer 93

change in base sequence of DNA It could be replicated and become permanent

Question 94

What's mutation

Answer 94

Mutation is the permanent change in DNA base sequence It could be addition, substitutions or deletion

Question 95

What's silent mutation

Answer 95

Silent mutation is when it affects non essential DNA or has negligible effect on gene function

Question 96

 In mammals accumulation of mutation is strongly correlated with .

Answer 96

cancer

Question 97

These DNA repair mechanisms are like a quality control system that ensures that only about 1 in every 1000 damaged DNA molecules becomes a permanent mutation or change in our genetic code.

Question 98

The replication process should be carried out with 

Answer 98

High fidelity, otherwise the information is altered

Question 99

Stages of DNA repair

Answer 99

General repair Proof reading Exonucleolytic proof reading Nucleotide Excision repair Strand Directed Mismatch Repair

Question 100

What's epigenome

Answer 100

The epigenome refers to the chemical modifications and proteins that can control the activity of genes without changing the underlying DNA sequence.

Question 101

Deregulation of epigenome has been recognized as a fundamental mechanism of carcinogenesi

Question 102

Hypermethylation of CG islands have been observed to silence

Answer 102

oncosuppressor genes. Stuffs that can prevent cancer

Question 103

Another type of deregulation involves changes in histone modifications, specifically _____&______

Answer 103

acetylation and methylation

Question 104

What are histones

Answer 104

Histones are proteins that help package and organize DNA in the nucleus of cells

Question 105

Inhibition of epigenetic regulators like ____&_____ are being looked upon as potential target for chemotherapy

Answer 105

DNA methyl transferase (DMT) and histone decaetylase (HDAC)

Question 106

What's exonucleolytic proofreading What's Exonucleases

Answer 106

mechanism ensures that mistakes in DNA replication, such as incorrect base pairing, are detected and corrected promptly. DNA polymerase possesses a specific activity called 3' to 5' exonuclease activity. Exonucleases are enzymes that can remove nucleotides from the ends of DNA strands.

Question 107

_______ is a mechanism that cells use to prevent unwanted mutations in DNA caused by UV radiation

Answer 107

Nucleotide Excision Repair (NER)

Question 108

Eg of mutations caused by UV radiation is?

Answer 108

Thymine dimers are abnormal formations of two adjacent thymine bases in the DNA strand that can occur due to UV exposure.

Question 109

There are___major proteins involved in NER in mammalian cells

Answer 109

9 XPA, XPB, XPC, XPD, XPE, XPF, and XPG. their names are based on the diseases associated with deficiencies in those proteins

Question 110

The names of NER is derived from

Answer 110

These names are derived from a genetic disorder called xeroderma pigmentosum, which is characterized by extreme sensitivity to UV radiation and a high risk of skin cancer.

Question 111

NER occurs alongside the replication process, ensuring the accurate repair of damaged DNA and reducing the risk of mutations.

Question 112

CSA and CSB are enzymes that are deficient in another genetic disorder called ____, which is associated with developmental and neurological abnormalities

Answer 112

Cockayne syndrome

Question 113

The original template DNA strand contains certain methylated residues, specifically

Answer 113

N6-methyl adenine and 5-methyl cytosine.

Question 114

while the newly synthesized DNA strand may initially be free of methylation, it can acquire methyl groups from the original template strand or undergo dynamic changes in methylation patterns during replication and other cellular processes.

Question 115

The wrong base is removed by the endonuclease activity of the ___ It removes _____to_____ nucleotides around the wrong base

Answer 115

XPG 24-32 nucleotides

Question 116

What's Strand Directed Mismatch Repair The detection & looping of E coli is removed by

Answer 116

When a miss match or mistake I identified a loop is made and the segment is removed And correct one is added by ligase and SSB's MutS, MutC, MutH

Question 117

What's Base Excision repair

Answer 117

Base Excision repair is the process by which cells fixes depurination damage Depurination causes certain bases in DNA, specifically cytosine, adenine, and guanine, to change into different bases called uracil, hypoxanthine, and xanthine, respectively.

Question 118

How does Base Excision repair fix depurination

Answer 118

enzymes called N-glycosylases that can remove these abnormal bases from the DNA molecule. After the abnormal base is removed, there is a gap in the DNA where the sugar molecule used to be. To fill in this gap, another enzyme called apurinic endonuclease removes the sugar. Then, a repair DNA polymerase (DNAP) comes in and adds the correct base to fill the gap. Finally, a ligase enzyme seals the DNA strand back together.

Question 119

What's Xeroderma Pigmentosum (XP)

Answer 119

is an inherited disease that affects the skin.

Question 120

XP is caused by And there are_____ XP genes

Answer 120

defects in the nucleotide excision repair (NER) mechanism, which is responsible for fixing DNA damage. There are seven XP genes (A to G) involved in the NER mechanism. Mutations in any one of these XP genes can lead to the development of XP. Exposure to ultraviolet (UV) light, particularly sunlight, can cause the formation of thymine dimers in the DNA. In XP patients, the repair mechanism is impaired, and these mutations accumulate, increasing the risk of cancer.

Question 121

XP patients are highly sensitive to UV rays and may experience skin problems like blisters when exposed to sunlight. Avoiding sunlight and using sunscreen can be beneficial for XP patients. XP patients have a significantly higher risk of developing skin cancer compared to normal individuals (1000-fold greater risk).

Question 122

XP is a genetic disease that affects the skin and is inherited in

Answer 122

an autosomal recessive manner.

Question 123

It is possible to diagnose XP before birth through

Answer 123

prenatal testing.

Question 124

What's Ataxia Telangiectasia (AT)

Answer 124

Ataxia Telangiectasia (AT) is a genetic disease that's caused by a change in a specific gene called ataxia telangiectasia mutated (ATM), which is found on chromosome 11q.

Question 125

What are the symptoms of Ataxia Telangiectasia

Answer 125

People with AT have an increased sensitivity to UV light, making their skin more prone to damage from the sun. Cerebellar ataxia is a common symptom of AT, causing problems with balance and coordination. Telangiectasia refers to small blood vessels that can be seen in the eyes and skin of individuals with AT. People with AT have a higher risk of developing lympho-reticular neoplasms, which are cancers affecting the lymph nodes and immune system.

Question 126

AT affects approximately

Answer 126

1 in every 40,000 individuals.

Question 127

Replication is ________, each strand acting as template for a new daughter strand.

Answer 127

semiconservative

Question 128

Replication is carried out in three identifiable phases:

Answer 128

initiation, elongation, and termination

Question 129

The reaction starts at the origin and usually proceeds bidirectionally meaning

Answer 129

The reaction starts at the origin and usually proceeds bidirectionally. DNA is synthesized in the 5’ to 3’ direction by DNA polymerases.

Question 130

The fidelity of DNA replication is maintained by (

Answer 130

1) base selection by the polymerase, (2) a 3’to 5’proofreading exonuclease activity that is part of most DNA polymerases, (3) specific repair systems for mismatches left behind after replication.

Question 131

DNA synthesis is done 5to 3 and proff reading is done 3 to5

Question 132

In E. coli, DNA polymerase _____ is the primary replication enzyme.

Answer 132

III

Question 133

DNA polymerase 1 aid in replication, recombination and repair by?

Answer 133

DNA polymerase I synthesizes DNA in the 5' to 3' direction during replication. It has a 3' to 5' exonuclease activity for proofreading and removing mismatched nucleotides. The enzyme also exhibits a 5' to 3' exonuclease activity involved in nick translation during repair and recombination. DNA polymerase I removes RNA primers synthesized by primase during replication and fills in the resulting gaps with DNA. It plays a role in DNA repair, specifically base excision repair (BER), by filling in single-stranded gaps left after damaged bases are excised

Question 134

What's Fanconi's Anemia:

Answer 134

This condition is associated with defects in specific genes located on chromosomes 20q and 9q. It affects the repair of DNA cross-links, which can lead to an increased occurrence of cancer.

Question 135

What's Bloom's Syndrome: Bloom's Syndrome

Answer 135

is caused by a gene located on chromosome 15q. It involves defects in DNA ligase or helicase, which are enzymes involved in DNA repair. Individuals with Bloom's Syndrome have a higher risk of developing lymphoreticular malignancies.

Question 136

What's Cockayne Syndrome:

Answer 136

Cockayne Syndrome is characterized by a defect in the NER mechanism, similar to XP. In this case, a specific transcription factor called TFIIH is defective. This condition is associated with stunted growth and mental retardation.

Question 137

What's Hereditary Polyposis Colon Cancer (Lynch syndrome):

Answer 137

Lynch syndrome is caused by a defective gene on chromosome 2. The defect affects hMSH1 and hMSH2 genes, which are involved in mismatch repair. Individuals with Lynch syndrome have a higher risk of developing colon cancer due to problems in DNA repair.