Mutation Repair and DNA Replication.pptx

Chapter 7
Mutation and Mutation Repair

Mutation
• Mutation is a process that produces a gene or chromosome that differs
from the wild type (arbitrary standard for what “normal” is for an
organism).
• It is most commonly defined as a spontaneous permanent change in a
gene or chromosome which usually produces a detectable effect in the
organism concerned and is transmitted to the offsprings.

Mutation Repair
• Mutation repair refers to the various cellular processes that correct
damage or errors in the DNA sequence, ensuring the stability and
integrity of the genetic material.
• DNA can be damaged or altered due to various factors such as
environmental stresses, chemical exposure, radiation, and errors
during DNA replication. These changes, if left uncorrected, can lead to
mutations, which might result in cell malfunction, diseases like cancer,
or genetic disorders.

There are several key mechanisms for
mutation repair in cells
Direct Repair
Mismatch Repair
Base Excision Repair
Nucleotide Excision Repair
Double Stranded Break Repair
Homologous Recombination
Non Homologous End Joining
Translesion Synthesis

Direct Repair
• This is the simplest form of DNA repair where the cell directly
reverses the DNA damage. An example is the direct reversion of UV-
induced thymine dimers by photolyase enzymes in some organisms.

Mismatch Repair
• Corrects errors when DNA is copied.
• Ex- C replaced by A
• Specific proteins scan the new DNA
• Template strand methylated by Dam methylase enzyme
• GATC sequence as the reference point
• A is methylated in the sequences
• GATC endonuclease cuts the segment
• Up to 1000 bp distant repair can be done
• Repair done according to the message coded in the
• template strand
• Mechanism not clear for mammals and higher eukaryotes
• Clinical significance- HNPCC (Hereditary nonpolyposis Colon Cancer)

Base Excision Repair
• This pathway repairs small, non-distorting base lesions caused by
deamination, oxidation, or alkylation. It involves removing the damaged
base, followed by cutting and replacing a short DNA strand section.
• C ,A, G bases in DNA spontaneously form U, hypoxanthine or xanthine
(Thermal lability) respectively-- Depurination
1. They're identified by specific N- glycosylases
2. Remove the base from DNA
3. Apurinic- apyrimidinic endonuclease excise the abasic sugar
4. Polymerase fills the gap
5. Ligase nicks the strands

Nucleotide Excision Repair
• Damaged DNA of up to 30 bases can be repaired
• A stretch of DNA (24-32 bp) flanking the defect is removed
• Cause of damage — UV light- Pyrimidine dimer formation
• Smoking — benzo [a] pyrene –guanine adducts
• Chemotherapeutic agents
• Chemicals
• Exinuclease
• Disease associated- Xeroderma pigmentosum
• 9 proteins involved- XPA- XPG involved in recognition and
• excision

Double Stranded Break Repair
• This is crucial for repairing severe DNA damage. There are two main
pathways:
• Homologous Recombination (HR): A high-fidelity repair process
that uses a sister chromatid as a template for accurate repair.
• Non-Homologous End Joining (NHEJ): A quicker but error-prone
process that joins the broken ends without a template.

Continued…
• 2 proteins are involved in non-homologous rejoining of a ds break
• Ku & DNA-Pk - heterodimers
• Ku first binds to free ends of DNA
• DNA-Pk approximates both the ends
• Base pairing occurs
• Extra tails cut
• Gaps closed by DNA ligase
• Defects if detected in GO/ Gl phase this method
• If defect detected in S, G2 or M phase- Homologous recombination occurs

Translesion Synthesis
• Special DNA polymerases can replicate across damaged DNA,
allowing the replication process to continue past lesions that would
otherwise stall it.

Mutational Consequences
• Types of Mutational Consequences:
• Neutral Mutations: These mutations do not produce any noticeable effects
on the organism. They often occur in non-coding regions of DNA or result
in synonymous changes in coding sequences, where the altered codon still
codes for the same amino acid.
• Beneficial Mutations: These are changes that confer an advantage to the
organism, possibly improving its survival or reproduction. In the long term,
these mutations can contribute to evolutionary adaptations.
• Harmful Mutations: These mutations can be detrimental to the organism,
possibly causing diseases or disorders. For example, mutations in certain
genes can lead to cancers, cystic fibrosis, sickle cell anemia, etc.

Consequences based on Location
• Somatic Mutations: Occur in somatic (body) cells and can lead to
localized effects, such as cancer. These mutations are not heritable.
• Germ-line Mutations: Occur in germ cells (sperm and eggs) and can
be passed on to offspring, potentially leading to inherited genetic
disorders.

Consequences in Gene Expression:
• Loss of Function: Mutations can lead to a gene product (like a
protein) being partially or completely non-functional.
• Gain of Function: In some cases, mutations can result in a new or
enhanced function of a gene product, which can be either beneficial or
harmful.

Population-Level Consequences:
• Genetic Variability: Mutations are a source of genetic diversity in a
population, which is crucial for the process of natural selection and
evolution.
• Genetic Drift and Bottlenecks: In small populations, random
mutations can have a significant impact on the gene pool, leading to
genetic drift.

• Biochemical and Cellular Consequences:
• Enzyme Function: Mutations can alter the function of enzymes, impacting
metabolic pathways.
• Protein Structure: Changes in the primary structure of proteins can affect their
folding and stability, leading to various diseases.
• Developmental Consequences:
• Mutations can affect the normal development of an organism, leading to
congenital abnormalities or developmental disorders.

Types of Mutations
• Mutations are changes in the DNA sequence of a cell's genome and
can be classified into several types based on their nature and effect.
Understanding these different types of mutations is crucial for
grasping how genetic changes can impact organisms.

Point Mutations
• Base Substitution: This is the simplest form of mutation where one
base is replaced by another in the DNA sequence. It includes
• Silent Mutation: The substitution does not change the amino acid due to the
redundancy of the genetic code.
• Missense Mutation: The substitution results in a different amino acid,
potentially altering the protein function.
• Nonsense Mutation: The substitution creates a stop codon, leading to
premature termination of protein synthesis.

Frameshift Mutations/Insertions and
Deletions
• These mutations involve the addition (insertion) or loss (deletion) of
one or more nucleotides in the DNA sequence.
• They can cause a frameshift, altering the reading frame of the gene,
which usually results in a completely different and often nonfunctional
protein.

Duplications
• A segment of the DNA is
duplicated, resulting in multiple
copies of that region.
• Duplications can contribute to
genetic variation within a
population and can be a source of
genetic disorders.

Chromosomal Mutations
• These are larger-scale mutations that involve changes to the structure
or number of entire chromosomes and can have significant effects.
• Types include:
• Deletions: A portion of the chromosome is lost.
• Duplications: Additional copies of a part of the chromosome are made.
• Inversions: A chromosome segment breaks off, flips around, and reattaches.
• Translocations: Segments from two different chromosomes swap places.
• Aneuploidy: Gain or loss of entire chromosomes, leading to a change in the
total number of chromosomes (e.g., Down syndrome).

Repeat Expansion
• This mutation involves the increase in the number of times a short
DNA sequence is repeated.
• It is known to cause certain genetic disorders, such as Huntington's
disease and Fragile X syndrome.

Loss-of-Function and Gain-of-Function
Mutations
• Loss-of-Function: Leads to the reduced or eliminated activity of a
gene product.
• Gain-of-Function: Results in a gene product with enhanced, new, or
constitutive activity.

Somatic and Germline Mutation
• Somatic Mutations: Occur in somatic cells and are not passed to
offspring.
• Germline Mutations: Occur in gametes and can be inherited,
affecting the offspring.

DNA Replication
• The process by which DNA molecule makes its identical copies is known as DNA
replication or DNA replication is the biological process of producing two identical
replicas Of DNA from one original DNA molecule. It takes place in S-phase of
interphase.

Replication in Prokaryotes
• when the circular DNA chromosome of E. coli is copied, replication begins
at a single point, the origin.
• Synthesis occurs at the replication fork, the place at which the DNA helix is
unwound and individual strands are replicated.
• Two replication forks move outward from the origin until they have copied
the whole replicon, that portion of the genome that contains an origin and is
replicated as a unit.
• When the replication forks move around the circle, a structure shaped like
the Greek letter theta is formed.
• Finally, since the bacterial chromosome is a single replicon, the forks meet
on the other side and two separate chromosomes are released.

Replication in Eukaryotes
• Eukaryotic DNA is linear and much longer than procaryotic DNA; E.
coli DNA is about 1,300 gm in length, whereas the 46 chromosomes in
the human nucleus have a total length of 1.8 m (almost 1,400 times
longer).
• Clearly many replication forks must copy eucaryotic DNA
simultaneously so that the molecule/DNA can be duplicated in a
relatively short period, and so many replicons are present that there is
an origin about every 10 to 100 gm along the DNA.
• Replication forks move outward from these sites and eventually meet
forks that have been copying the adjacent DNA stretch. In this fashion
a large molecule is copied quickly.

Mechanism of action of DNA
polymerases: covalent extension of a DNA
primer strand in the 5' 3' direction. The
existing chain terminates at the 3 end with
the nucleotide deoxyguanylate
(deoxyguanosine-5-phosphate). The
diagram shows the DNA polymerase-
catalyzed addition of deoxythymidine
monophosphate (from the precursor
deoxythymidine triphosphate, dTTP) to
the 3'end of the chain with the release of
pyrophosphate (P207).

Steps of DNA Replication
• Step 1: Initiation
• The point at which the replication begins is known as the Origin of Replication
(oriC). Helicase brings about the procedure Of strand separation, which leads to
the formation of the replication fork.
• Step 2: Elongation
• The enzyme DNA Polymerase Ill makes the new strand by reading the nucleotides
on the template strand and specifically adding one nucleotide after the other. If it
reads an Adenine (A) on the template, it will only add a Thymine (T).
• Step 3: Termination
• When Polymerase Ill is adding nucleotides to the lagging strand and creating
Okazaki fragments, it at times leaves a gap or two between the fragments. These
gaps are filled by ligase. It also closes nicks indouble-stranded DNA.

Process of Replication
During replication each enzyme and protein have their own
specific function.
Let us look at the process step by step

Initiation
• Helicase — The point at which the replication begins is known as the
Origin of Replication. Helicase brings about the procedure of strand
separation, which leads to the formation of the replication fork.
• It breaks the hydrogen bond between the base pairs to separate the strand. It
uses energy obtained from ATP Hydrolysis to perform the function.
• SSB Protein — Next step is for the Single-Stranded DNA Binding Protein
to bind to the single-stranded DNA. Its job is to stop the strands from
binding again.
• DNA Primase — Once the strands are separated and ready, replication can
be initiated. For this, a primer is required to bind at the Origin.
• Primers are short sequences of RNA, around 10 nucleotides in length.
• Primase synthesizes the primers.

Elongation
• DNA Polymerase Ill — This enzyme makes the new strand by reading
the nucleotides on the template strand and specifically adding one
nucleotide after the other. If it reads an Adenine (A) on the template, it
will only add a Thymine (T).
• It can only synthesize new strands in the direction of 5' to 3'. It also
helps in proofreading and repairing the new strand. Now you might
think why does Polymerase keep working along the strand and not
randomly float away?
• Its because a ring-shaped protein called as sliding clamp holds the
polymerase into position.

Termination
• DNA Polymerase I — If you remember, we had added a RNA primer at the Origin
to help Polymerase initiate the process. Now as the strand has been made, we need
to remove the primer. This is when Polymerase I comes into the picture. It takes
the help of RNase H to remove the primer and fill in the gaps.
• DNA ligase — When Polymerase Ill is adding nucleotides to the lagging strand
and creating Okazaki fragments, it at times leaves a gap or two between the
fragments. These gaps are filled by ligase. It also closes nicks in double-stranded
DNA.
• The Replication process is finally complete once all the primers are removed and
Ligase has filled in all the remaining gaps. This process gives us two identical sets
of genes, which will then be passed on to two daughter cells. Every cell completes
the entire process in just one hour! The reason for taking such short amount of
time is multiple Origins.
• The cell initiates the process from a number of points and then the pieces are
joined together to create the entire genome!'

Semi-Conservative Replication
• The term "semi-conservative" refers to the way the DNA helix is
replicated. It was first demonstrated by Matthew Meselson and
Franklin Stahl in their famous experiment in 1958.

Process of Semi-Conservative Replication
• Initiation of Replication: The process begins at specific sites on the DNA
molecule called origins of replication. Proteins bind to these sites and
separate the two strands of the helix, creating a replication fork.
• Helicase Enzyme: The enzyme DNA helicase unwinds the double helix,
separating the two strands of DNA. This creates two single strands that
serve as templates for replication.
• Stabilizing the Unwound Strands: Single-strand binding proteins (SSBs)
bind to the single strands of DNA to prevent them from re-annealing or
forming secondary structures.
• Primer Synthesis: An enzyme called primase synthesizes a short RNA
primer complementary to the DNA template. This primer is necessary for
DNA polymerase to start synthesis.

Process Continued…
• Elongation by DNA Polymerase: DNA polymerase adds new nucleotides
complementary to the template strand, starting from the primer. DNA
polymerase can only add nucleotides to the 3’ end of an existing strand, so
the new strand grows in the 5’ to 3’ direction.
• Leading and Lagging Strands: One strand, called the leading strand, is
synthesized continuously towards the replication fork. The other, the
lagging strand, is synthesized discontinuously away from the replication
fork in short fragments called Okazaki fragments.
• Okazaki Fragments on the Lagging Strand: Each Okazaki fragment
begins with its own RNA primer. These fragments are later joined together.
• Removal of RNA Primers: The RNA primers are removed by another
DNA polymerase, and the gaps are filled with DNA nucleotides.

• Ligation: The enzyme DNA ligase joins the Okazaki fragments together, creating
a continuous strand.
• Replication Forks: Replication proceeds bi-directionally from the origin, with
two replication forks moving away from the origin in opposite directions.
• Semi-Conservative Nature: After replication, each of the two new DNA
molecules consists of one original strand and one new strand. This conserves half
of the original DNA molecule in each daughter molecule.
• Proofreading and Error Correction: DNA polymerases have proofreading
ability, allowing them to remove incorrectly paired nucleotides and replace them
with the correct ones, ensuring high fidelity in the replication process.
• Completion of Replication: Once the entire DNA molecule is replicated, the
replication machinery disassembles, resulting in two identical DNA molecules,
each with one old and one new strand.

• Role in Genetic Continuity: Semi-conservative replication ensures genetic
stability and continuity, as each new cell receives an exact copy of the genetic
information.
• Efficiency and Accuracy: The process is remarkably efficient and accurate,
making it possible for cells to replicate large genomes with minimal errors.
• Enzymatic Coordination: The process involves a coordinated effort of multiple
enzymes and proteins, each playing a specific role to ensure accurate and efficient
replication.
• Replication Bubbles: In eukaryotic cells, replication occurs at multiple origins
along the DNA simultaneously, forming 'bubbles' that eventually merge.
• Telomere Replication: Special mechanisms, such as the enzyme telomerase,
replicate the ends of linear chromosomes, known as telomeres, in eukaryotic cells.

Significance of Semi-Conservative
Replication
• This method of replication preserves the sequence of the DNA and
ensures genetic consistency across generations of cells.

Semi-Discontinuous Replication
• Semi-discontinuous replication is a key aspect of DNA replication,
particularly in how the new strands of DNA are synthesized by the
enzyme DNA polymerase. This process is crucial for understanding
the overall mechanism of DNA replication.

Process of Semi-Discontinuous Replication
• DNA Polymerase Directionality: DNA polymerase, the enzyme
responsible for adding nucleotides to the growing DNA chain, can only add
new nucleotides to the 3' end of an existing strand. This directional
limitation of DNA polymerase necessitates the semi-discontinuous nature of
DNA replication.
• Formation of Replication Forks: The replication process begins at specific
sites called origins of replication, where the DNA double helix is unwound
by the enzyme helicase, forming a Y-shaped structure known as the
replication fork.
• Leading and Lagging Strands: The opening of the double helix results in
two single DNA strands: the leading strand and the lagging strand. The
leading strand is oriented so that its 3' end faces the replication fork and can
be synthesized continuously. In contrast, the lagging strand has its 3' end
facing away from the replication fork.

• Continuous Synthesis on the Leading Strand: DNA polymerase synthesizes the leading
strand continuously in the 5' to 3' direction, following the movement of the replication
fork.
• Discontinuous Synthesis on the Lagging Strand: The lagging strand is synthesized in
short segments known as Okazaki fragments. This is because the 5' to 3' synthesis
direction is opposite to the direction in which the replication fork is moving.
• Initiation of Okazaki Fragments: Each Okazaki fragment begins with a short RNA
primer, laid down by the enzyme primase. The DNA polymerase then extends these
primers, adding DNA nucleotides.
• Removal of RNA Primers: Once an Okazaki fragment is synthesized, its RNA primer is
removed and replaced with DNA. In eukaryotes, this task is performed by RNase H
(which removes the RNA primer) and DNA polymerase δ or ε (which fills in the gap).
• Ligation of Okazaki Fragments: The enzyme DNA ligase connects the Okazaki
fragments, creating a continuous DNA strand on the lagging side.

• Replication Fork Progression: As the replication fork progresses, this
process of synthesizing Okazaki fragments on the lagging strand is repeated
numerous times.
• Coordination Between Leading and Lagging Strands: The replication of
both strands is highly coordinated. Although the leading strand is
synthesized continuously and the lagging strand discontinuously, both are
extended at a similar rate.
• Proofreading and Error Correction: DNA polymerases involved in
replication possess proofreading abilities to correct mistakes, ensuring high
fidelity in DNA replication.
• Role of Clamp Proteins: Clamp proteins (like the sliding clamp) keep the
DNA polymerase bound to the DNA, increasing the efficiency of
replication.

• Telomere Replication in Eukaryotes: Specialized mechanisms, like
the enzyme telomerase, replicate the ends of chromosomes (telomeres)
in eukaryotic cells, as conventional DNA replication machinery cannot
replicate these regions completely.
• Replication Complexes: In eukaryotic cells, DNA replication occurs
within specialized structures called replication factories, where
multiple proteins and enzymes work in concert.
• Challenges in Replicating Linear DNA: In eukaryotes, replicating
the very ends of linear chromosomes poses a challenge, but this is
addressed by the unique structure of telomeres and the action of
telomerase.

• Cell Cycle Regulation: The entire process is tightly regulated within
the cell cycle to ensure DNA is replicated only once per cell division.
• Enzyme Coordination and Timings: The process involves a complex
interplay of various enzymes, each initiating its activity at precisely
the right time to ensure efficient and accurate replication.
• Replication Speed: DNA replication is a remarkably rapid process,
with human cells replicating approximately 50 nucleotides per second.
• Importance in Genetic Stability: Semi-discontinuous replication is
crucial for maintaining genetic stability and integrity, as it ensures
accurate and complete replication of the DNA in every cell cycle.

Enzymes and Proteins Involved In DNA
Replication
DNA Helicase :
• Helicase enzyme opens up the DNA double helix by breaking hydrogen bond between two strands
of DNA and provide single template strand.
• DNA-B is a primary replicative Helicase it binds and move on lagging strand in 5' to 3' direction
unwinding the duplex as it goes.
• Helicase requires ATP as energy source
Single Stranded Binding Proteins (SSB proteins) :
• SSB proteins binds to both separated single stranded DNA and prevent the DNA double helix from
re-annealing after helicase unwinds.
• SSB proteins are maintaining the strand separation and facilitating the synthesis of the nascent
strand.
Topoisomerase :
• DNA Topoisomerase is a nuclease enzyme that break a phosphodiester bond in a DNA strand.
• The function of Topoisomerase is relaxes the DNA from its super coiled nature.

Continued…
DNA Gyrase :
• This enzyme is used to make sure the double stranded areas out side of the
replication fork do not supercoil, DNA Gyrase is one type of topoisomerase.
Primase :
• Primase provides a starting point of RNA (or DNA) for DNA polymerase to begin
synthesise of the new DNA strand.
• Because DNA polymerase requires free 3'-OH group for bind to DNA for starting
replication.
DNA Polymerase :
• DNA dependent DNA polymerase enzyme that can synthesise a new strand on a
DNA tamplate.
• DNA polymerase has different types in Prokaryotes and Eukaryotes.

Prokaryotic DNA Polymerase
Prokaryotes has 3 types of DNA polymerase, these are
DNA polymerase I -
• It is made up of one subunits. It has 3' to 5' and 5' to 3' exonuclease activity.
• Function - DNA repair, Gap filling and synthesis of new lagging strand.
DNA polymerase II -
• It is made up of 7 subunits. It has only 3' to 5' exonuclease activity.
• Function - DNA repair and DNA proof reading.
DNA polymerase III -
• It is made up of at least 10 subunits. It has 3' to 5' exonuclease activity.
• Function - This is the main replication enzyme in Prokaryotes.

Eukaryotic DNA Polymerase
• Eukaryotes has 5 types of DNA polymerase which are DNA polymerase α, β, γ, δ and ε.
• DNA polymerase α -
• It has no any exonuclease activity.
• Function - DNA replication in the nucleus.
• DNA polymerase β -
• It has no any exonuclease activity.
• Function - DNA replication and base excision repair.
• DNA polymerase γ -
• It has 3' to 5' exonuclease activity.
• Function - DNA replication in Mitochondria.
• DNA polymerase δ -
• Function - Synthesis of lagging strand during DNA replication.
• DNA polymerase ε -
• Function - Synthesis of leading strand during DNA replication.

Enzymes and Proteins Continued…
Beta Clamp Proteins :
• Beta clamps are the protein which prevents elongating DNA polymerase from
dissociating from the DNA parent strand.
• It helps hold the DNA polymerase in place on the DNA.
DNA Ligase :
• DNA Ligase Catalyse the joining of ends of two DNA chains by forming phosphodiester
bond between 3'-OH group at one end of DNA strand and and 5'-Phosphate group at the
end of other DNA strand.
• DNA ligase joins the Okazaki fragments of two lagging strand.
Telomerase :
• Lengthens the telomeric DNA by adding repetitive nucleotide sequence to the ends of
eukaryotic chromosomes.
• This allows germ cells and stem cells to avoid the Hayflick limit on cell division.

Telomere
• Telomeres are the repetitive nucleotide sequences at the ends of
eukaryotic chromosomes. They protect the chromosome ends from
deterioration or fusion with neighboring chromosomes, thus
maintaining the integrity and stability of the genetic material.

Basic Structure and Function of Telomeres
• Telomeres: They are repetitive nucleotide sequences at the ends of
eukaryotic chromosomes. In humans, the sequence is typically
TTAGGG, repeated thousands of times.
• Protective Cap: Telomeres function as protective caps, preventing
chromosomes from fraying or fusing with each other.
• Chromosome Stability: They maintain chromosomal integrity and
stability during cell division.

Telomere Shortening During Replication
• End Replication Problem: Due to the linear nature of chromosomes
and the mechanism of DNA replication, the very ends of chromosomes
cannot be completely replicated.
• Progressive Shortening: With each cell division, telomeres shorten
because DNA polymerase cannot replicate the extreme 3’ end of the
lagging strand.

Telomerase and Its Function
• Enzyme Composition: Telomerase is a ribonucleoprotein enzyme
composed of a protein component and an RNA component, which
serves as a template for telomere extension.
• Adding Telomere Sequences: It adds TTAGGG repeats to the ends of
chromosomes, compensating for the shortening that occurs during
DNA replication.

Telomerase Activity in Different Cell Types
• Somatic Cells: Most somatic (body) cells have low or no telomerase
activity, leading to progressive telomere shortening with age.
• Germline, Stem, and Cancer Cells: These cells often have active
telomerase, allowing them to maintain telomere length and divide
indefinitely.

Telomeres and Aging
• Cellular Aging: Telomere shortening in somatic cells is associated
with aging and age-related decline.
• Senescence and Apoptosis: Critically short telomeres can trigger
cellular senescence (aging) or apoptosis (programmed cell death),
acting as a biological clock.

Telomeres and Cancer
• Unlimited Division: Cancer cells often reactivate telomerase,
allowing them to bypass senescence and continue dividing.
• Target for Cancer Therapies: Telomerase is a potential target for
cancer therapies; inhibiting it could limit the ability of cancer cells to
multiply.

Measurement of Telomere Length
• Indicator of Biological Age: Telomere length is considered an
indicator of biological aging and has been a subject of extensive
research in aging and age-related diseases.
• Techniques: Various techniques, like qPCR and Southern blotting, are
used to measure telomere length.

Telomere Maintenance in Stem Cells
• Stem Cell Function: High telomerase activity in stem cells is crucial
for their self-renewal and regenerative capacity.
• Role in Tissue Repair: This activity is important for ongoing tissue
repair and regeneration throughout an organism's life.

Ethical and Medical Implications
• Aging and Life Extension: Research on telomerase has implications
in potential life extension technologies and treatments for age-related
diseases.
• Ethical Considerations: Such research raises ethical questions about
the desirability and consequences of extending human lifespan.

Future Research Directions
• Aging and Disease: Ongoing research is focused on understanding the
precise role of telomeres and telomerase in aging and age-related
diseases.
• Therapeutic Potential: There's significant interest in targeting
telomerase in cancer therapy and in potentially using telomerase
activators to delay aging.

References
• https://www.ncbi.nlm.nih.gov/books/NBK21114/
• https://bio.libretexts.org/Bookshelves/Biochemistry/Fundamentals_of_Biochemistry_(Jakubowski_and_Flatt)
/03%3A_Unit_III-
_Information_Pathway/24%3A_DNA_Metabolism/24.02%3A_DNA_Mutations_Damage_and_Repair
• https://bio.libretexts.org/Bookshelves/Genetics/Working_with_Molecular_Genetics_(Hardison)/Unit_II%3A_
Replication_Maintenance_and_Alteration_of_the_Genetic_Material/7%3A_Mutation_and_Repair_of_DNA
• http://www.nature.com/scitable/topicpage/genetic-mutation-441
• https://link.springer.com/chapter/10.1007/978-981-16-7041-1_9
• https://pubmed.ncbi.nlm.nih.gov/33693881/
• https://openstax.org/books/biology-2e/pages/14-6-dna-repair
• https://www.nature.com/articles/s41576-021-00376-2

• https://pubmed.ncbi.nlm.nih.gov/27362223/
• https://bio.libretexts.org/Courses/Lumen_Learning/Biology_for_Non_Majors_I_(
Lumen)/10%3A_DNA_Transcription_and_Translation/10.11%3A_Introduction_t
o_DNA_Mutations
• https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Concep
ts_in_Biology_(OpenStax)/09%3A_Molecular_Biology/9.02%3A_DNA_Replicat
ion
• https://brilliant.org/wiki/mutation-and-dna-repair/
• https://jackwestin.com/resources/mcat-content/repair-of-dna/repair-of-mutations
• https://genomebiology.biomedcentral.com/articles/10.1186/s13059-018-1509-y
• https://www.sciencedaily.com/releases/2023/12/231221012721.htm
• http://www2.csudh.edu/nsturm/CHEMXL153/DNAMutationRepair.htm
• https://www.khanacademy.org/science/ap-biology/gene-expression-and-
regulation/replication/a/molecular-mechanism-of-dna-replication
• https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Biology
_(Kimball)/05%3A_DNA/5.13%3A_DNA_Repair

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