Name: dna changes from point mutations to uv damage
Uploaded: 2026-08-26T08:19:55.800Z
Duration: 2 min 27 s
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Mutations

- [Istruttore] Le mutazioni puntiformi,

in cui un singolo
nucleotide viene modificato,

possono produrre una
proteina totalmente normale

o completamente non
funzionale, a seconda del tipo.

Questi includono mutazioni
silenti, missense,

nonsense e frameshift.

Le mutazioni silenti,
come suggerisce il nome,

non incidono sulla sequenza
aminoacidica della proteina.

Ad esempio, se il codone
CCA viene modificato in CCG,

continuer&#xE0; a codificare per
la prolina dell&#x27;amminoacido

e la proteina funzioner&#xE0; normalmente.

Le mutazioni missenso, d&#x27;altra parte,

comportano la sostituzione di
un amminoacido con un altro,

come l&#x27;arginina invece della prolina,

che pu&#xF2; causare il
malfunzionamento della proteina.

Le mutazioni nonsense si verificano quando

si cambia un codone per un
amminoacido in uno di stop.

Ci&#xF2; segnala alla cellula di
interrompere la traduzione,

risultante in una proteina
troncata prematuramente

che spesso non &#xE8; funzionale.

Le mutazioni frameshift avvengono
se il riquadro di lettura,

raggruppati i gruppi di
tre nucleotidi in codoni,

viene spostato, spesso per
l&#x27;inserimento o la cancellazione

di uno o pi&#xF9; nucleotidi.

Ci&#xF2; si traduce in una
serie di nuovi codoni

che codificano per diversi aminoacidi,

creando una proteina anormale.

mutazioni

Le mutazioni sono cambiamenti nella sequenza del DNA. Questi cambiamenti possono verificarsi spontaneamente durante la replicazione del DNA oppure essere indotti da fattori ambientali. Le mutazioni possono essere caratterizzate in diversi modi: in base al fatto che alterino la sequenza amminoacidica della proteina e al modo in cui lo fanno, in base all&#x2019;estensione del DNA interessato e in base al fatto che colpiscano cellule somatiche o germinali.
Conseguenze delle mutazioni puntiformi a livello molecolare
Le mutazioni che interessano un singolo nucleotide sono chiamate mutazioni puntiformi. Quando le mutazioni puntiformi insorgono all&#x2019;interno dei geni, le conseguenze possono variare in gravit&#xE0; a seconda del modo in cui alterano la sequenza amminoacidica codificata. Una mutazione silente non modifica la sequenza amminoacidica ed &#xE8; spesso neutra. Una mutazione missenso modifica un singolo amminoacido e gli effetti possono essere gravi se il cambiamento altera la funzione della proteina. Una mutazione nonsenso introduce un codone di stop, tronca la proteina e probabilmente la rende non funzionale. Le inserzioni o delezioni di nucleotidi possono causare mutazioni frameshift se alterano la cornice di lettura, influenzando tutti i codoni a valle e spesso compromettendo gravemente la funzione della proteina.
Le alterazioni cromosomiche sono mutazioni su larga scala
Il tipo pi&#xF9; drastico di mutazione, l&#x2019;alterazione cromosomica, modifica la struttura o il numero dei cromosomi. I cambiamenti strutturali possono comprendere delezioni, duplicazioni, inversioni e traslocazioni di ampi segmenti di DNA all&#x2019;interno di un singolo cromosoma. Le anomalie numeriche, come l&#x2019;aneuploidia, comportano l&#x2019;acquisizione o la perdita di interi cromosomi. Le mutazioni cromosomiche sono generalmente molto pi&#xF9; gravi delle mutazioni puntiformi perch&#xE9; interessano numerosi geni ed elementi regolatori. Le alterazioni cromosomiche possono essere rilevate mediante l&#x2019;analisi del cariotipo della cellula interessata.
Solo le mutazioni germinali sono ereditarie
Le mutazioni possono insorgere in qualsiasi cellula, ma solo le mutazioni germinali&#x2014;quelle presenti nelle cellule uovo e negli spermatozoi&#x2014;possono essere trasmesse alla prole. Le malattie ereditarie sono un sottotipo di disturbi genetici causati da mutazioni germinali deleterie. Possono essere autosomiche, coinvolgendo i cromosomi da 1 a 22, oppure legate al sesso, coinvolgendo il cromosoma X o Y. Un esempio di malattia ereditaria &#xE8; la fibrosi cistica (CF), che colpisce principalmente i polmoni. &#xC8; causata da una delezione nel gene CFTR che rimuove un singolo amminoacido dalla proteina CFTR. La CF &#xE8; una malattia autosomica recessiva, il che significa che una persona con una copia mutata del gene e una copia normale non svilupper&#xE0; la malattia. D&#x2019;altra parte, malattie come la malattia di Huntington, un disturbo neurodegenerativo, sono autosomiche dominanti, il che significa che &#xE8; necessaria una sola copia mutata del gene affinch&#xE9; la malattia si sviluppi.
Alcune mutazioni sono causate da fattori ambientali
Sia le mutazioni somatiche sia le mutazioni germinali possono insorgere spontaneamente, ma possono anche essere indotte da agenti ambientali noti come mutageni. Questi comprendono le radiazioni ambientali o sostanze chimiche che danneggiano il DNA. Un mutageno ambientale ben caratterizzato &#xE8; la radiazione ultravioletta (UV). La radiazione UV induce la formazione di legami covalenti tra basi di timina adiacenti sullo stesso filamento di DNA, creando dimeri di timina che deformano la struttura del DNA. Il Sole &#xE8; una fonte naturale di radiazione UV. I pi&#xF9; dannosi raggi UV-C sono assorbiti dall&#x2019;atmosfera, mentre i raggi UV-A e UV-B raggiungono la superficie terrestre. Le fonti artificiali di esposizione ai raggi UV comprendono i lettini abbronzanti, che trasmettono principalmente raggi UV-A e quantit&#xE0; minori di UV-B.
Fortunatamente, le cellule possiedono meccanismi per riparare il DNA danneggiato, ma talvolta il danno non viene riparato prima della divisione cellulare, in particolare nelle cellule in rapida divisione, come le cellule cutanee, e le mutazioni possono accumularsi. Quando queste mutazioni interessano geni che regolano la crescita e la divisione cellulare, possono contribuire allo sviluppo del cancro.

Mutazioni

Overview

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

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dna changes from point mutations to uv damage

Mutations are changes in the DNA sequence. They can happen by chance during DNA copying, or they can be caused by environmental factors such as radiation and chemicals. Scientists also describe mutations by how much DNA they affect, how they change a protein, and whether they happen in body cells or germline cells.

Some mutations affect only one nucleotide, which is a point mutation. When a point mutation falls inside a gene, the outcome depends on how the amino acid sequence changes. A silent mutation leaves the amino acid the same and usually has no effect. A missense mutation changes one amino acid, and the result can be serious if the protein no longer works well.

Other point mutations can stop protein production early. A nonsense mutation creates a stop codon, which truncates the protein and often makes it nonfunctional. A frameshift mutation happens when nucleotides are inserted or deleted in protein-coding DNA. This shifts the reading frame and changes all downstream codons.

Some mutations are large-scale chromosomal alterations. These changes affect the physical structure of a chromosome and can include deletion, duplication, inversion, or the addition of DNA from another chromosome. Because they can involve many genes and regulatory elements, they are usually more serious than point mutations. Cells with these changes can be identified by karyotyping.

Only germline mutations are inherited. These mutations are present in egg and sperm cells and can pass to offspring, while somatic mutations stay outside the germline. Hereditary diseases are caused by harmful germline mutations. They can be autosomal, on chromosomes 1 through 22, or sex-linked, on the X or Y chromosome.

Cystic fibrosis is one example of a hereditary disease. It affects the lungs and is caused by a deletion in the CFTR gene that removes a single amino acid from the CFTR protein. It is autosomal recessive, so one normal copy can prevent disease. Huntington's disease is another example, and it is autosomal dominant, which means one mutated copy is enough for the disorder to develop.

Mutations can also come from mutagens, which are external agents that damage DNA. Ultraviolet, or UV, radiation is a well-known mutagen. It has more energy than visible light and can create thymine dimers when bases on the same DNA strand bond with each other. The sun is a natural source of UV radiation, and tanning beds are artificial sources that mainly emit UV-A with some UV-B.

Cells can repair DNA damage, but repair is not always complete before cell division. This matters most in rapidly dividing cells such as skin cells. If the damage affects genes that help control cell growth and division, it can contribute to cancer.

DNA Changes From Point Mutations to UV Damage

dna-changes-from-point-mutations-to-uv-damage

the dna helix

How DNA Stores Genetic Information

DNA stores genetic information that is passed from one generation to the next in organisms and most viruses. It is built from two strands of nucleotides that twist together into a double helix. The story of how scientists uncovered this structure developed step by step over nearly a century. Each DNA strand is made of nucleotides. A nucleotide contains the sugar deoxyribose, a phosphate group, and one of four nitrogen bases: adenine (A), guanine (G), cytosine (C), or thymine (T). Adenine and...

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Chromatin and Histones in DNA Packing

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organization of genes

Genes, Introns, and Regulatory DNA

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karyotyping

Chromosome Stains for Detecting Disorders

Chromosome staining helps scientists find genetic disorders by showing the number and physical features of chromosomes. These features appear after DNA condenses into chromosomes during mitosis. Cytogeneticists then stop mitosis and stain the chromosomes to study their banding pattern. The pattern reveals details such as chromosome number, shape, and type. A chromosome description like this is called a karyotype. To create one, scientists take an image of the stained chromosomes and identify...

replication in prokaryotes

How Prokaryotic DNA Is Copied

Prokaryotic DNA is copied through a coordinated process with three main stages: initiation, elongation, and termination. It begins when initiator proteins bind to the single origin of replication, or ori, on the cell’s circular chromosome. The DNA then copies around the circle in both directions, starting from two replication forks, and this produces two DNA molecules. Several proteins work together to open and protect the DNA during replication. Topoisomerase cuts one side of the...

replication in eukaryotes

Eukaryotic DNA Copying and Telomeres

Eukaryotic DNA copying is tightly regulated and must duplicate many linear chromosomes before cell division. The process is highly conserved and uses many proteins with specialized roles. It moves through initiation, elongation, and termination, and it ends with two complete sets of chromosomes in the nucleus. Eukaryotic replication shares basic steps with prokaryotic DNA replication, but the larger genome and linear chromosomes require more proteins. Replication begins at multiple origins of...

proofreading

DNA Polymerase Fixes Replication Errors

DNA polymerase helps copy DNA and fix mistakes during replication. It adds nucleotides in a sequence that matches the template DNA strand. The enzyme also has a higher affinity for the correct base, which helps keep DNA replication accurate. As new genomic DNA is made, it is synthesized in the 5’ to 3’ direction. In many cells, DNA polymerases have different jobs in this process. DNA polymerase delta and DNA polymerase epsilon can proofread when nuclear DNA is being copied. These polymerases...

mismatch repair

DNA Mismatch Repair in Replication

DNA mismatch repair fixes copying errors that happen during DNA replication. When DNA polymerase makes a mistake, the cell can detect a wrong base pair, such as A with G or T with C, and replace it with the correct nucleotide. This repair system works in both prokaryotes and eukaryotes and depends on several proteins. The Mutator protein family plays a central role in this process. In bacteria such as Escherichia coli, MutS first binds the mismatch. MutL then helps identify which strand is the...

nucleotide excision repair

DNA Damage Repair by Excision

DNA damage repair by excision protects cells from mutagens that can change DNA. Exposure to environmental mutagens can create bulky lesions that bend the double helix or block transcription. If these changes are not repaired, they can lead to mutations and may contribute to cancer or disease, depending on which DNA sequences are affected. Nucleotide excision repair, or NER, is the process that detects and removes this kind of damage. Specialized proteins scan the DNA for a damaged region, then...

mutations

Mutations are changes in the DNA sequence. They can happen by chance during DNA copying, or they can be caused by environmental factors such as radiation and chemicals. Scientists also describe mutations by how much DNA they affect, how they change a protein, and whether they happen in body cells or germline cells. Some mutations affect only one nucleotide, which is a point mutation. When a point mutation falls inside a gene, the outcome depends on how the amino acid sequence changes. A silent...

transcription

Transcription and Gene Control

Transcription and gene control explain how cells make RNA from DNA and decide which genes are active. RNA polymerase copies a DNA sequence into RNA, and this is the first step in making a protein from a gene. Many other proteins and control sequences help make messenger RNA, or mRNA, correctly. In eukaryotes, the DNA is first copied into a primary RNA, also called pre-mRNA. This RNA can then be processed into mature mRNA, which serves as the template for protein synthesis. In prokaryotes such...

translation

Protein Synthesis and mRNA Decoding

Protein synthesis begins when ribosomes decode messenger RNA (mRNA) and build a chain of amino acids. This final step of gene expression is called translation. The finished chain is a polypeptide, which can later become a functional protein. Proteins are often called the building blocks of life because they make up much of the body, from muscle fibers to hairs and immune system parts. The instructions for each protein are encoded in genes found in the DNA of every cell. In biology, the central...

bacterial transformation

Griffith’s Mouse Experiment and DNA

Bacterial transformation explains how DNA can move into bacteria and change their traits. Frederick Griffith first noticed this in 1928 while studying pneumonia-causing Streptococcus pneumoniae in mice. He compared one pathogenic strain with one non-pathogenic strain and found that only the pathogenic strain killed the host mice. Griffith made an unexpected discovery when he killed the pathogenic bacteria and mixed their remains with live, non-pathogenic bacteria. The mixture killed the mice,...

key terms and concepts

Explore how point mutations, chromosomal alterations, and UV exposure change DNA. Learn which mutations are inherited and how some can lead to disease.

DNA Changes From Point Mutations to UV Damage | JoVE K12

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Compare and contrast existing models, identify patterns, and use structural and functional evidence to analyze the characteristics of life. Engage in argument about the designation of viruses as non-living based on these characteristics.
EXPLANATION: Students begin to develop patterns of living and non-living organisms in kindergarten and build on detailed characteristics of different classifications of living organisms throughout elementary and middle school. Biology 1 discussions introduce viral particles and viral cycles, building on student understanding of living organisms to engage in an argument regarding the classification of a viral particle as either living or non-living.

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Evaluate comparative models of various cell types with a focus on organic molecules that make up cellular structures.
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Organization of Genes

Overview

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Karyotyping

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Overview

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Overview

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Transcription

Overview
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Translation

Lesson: Translation
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Overview
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siRNA - Small Interfering RNAs

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piRNA - Piwi-interacting RNAs

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Phosphorylation

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Integrate evidence to develop a structural model of a DNA molecule. Using the model, develop and communicate an explanation for how DNA serves as a template for self-replication and encodes biological information.
EXPLANATION: Discussions of DNA in earlier grades have been limited to discussions of genes and the role of genes in the appearance and activities of an organism. Biology 1 represents a student's introduction to a molecular model of a DNA as well as the organization of DNA into genes and genes subsequently into chromosomes. Students should address interactions between genes in proteins which regulate both the shape and reproduction of DNA molecules. It is important to note that not all segments of DNA are transcribed for proteins. Portions of DNA are involved in regulating the expression of genes or affect the structure of the chromosomes (replication origin, centromeres, and telomeres).

DNA Changes From Point Mutations to UV Damage

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