how can an uv induced mutation affect dna? course hero

UV exposure doesn’t always lead directly to mutations in the DNA. In fact, UV-A radiation commonly damages DNA in an oxygen-dependent manner that involves photosensitization. This leads to the production of a free radical that then interacts with and oxidizes DNA bases.

Full Answer

How can an UV induced mutation affect DNA?

UV radiation causes two classes of DNA lesions: cyclobutane pyrimidine dimers (CPDs, Figure 1) and 6-4 photoproducts (6-4 PPs, Figure 2). Both of these lesions distort DNA's structure, introducing bends or kinks and thereby impeding transcription and replication.

Would you consider mutations occurring after exposure to UV light spontaneous or induced?

Induced mutations are those that result from an exposure to chemicals, UV rays, x-rays, or some other environmental agent. Spontaneous mutations occur without any exposure to any environmental agent; they are a result of natural reactions taking place within the body.

Are thymine dimers spontaneous mutations?

T-T dimers cause kinks in the DNA strand that prevent both replication and transcription of that part of the DNA. Because they block DNA replication (and therefore prevent cells from reproducing), T-T dimers and other forms of UV damage cannot be inherited, and thus do not constitute mutations.

What is the main damaging effect of UV radiation on DNA?

Although it can damage various molecules in the cell, the most damage occurs when it hits DNA. When an excited oxygen hits DNA, it can cause a guanine to thymine transversion, which means that the purine guanine is replaced by the pyrimidine thymine.

What kind of mutation does UV light cause?

Ultraviolet (UV) light induces specific mutations in the cellular and skin genome such as UV-signature and triplet mutations, the mechanism of which has been thought to involve translesion DNA synthesis (TLS) over UV-induced DNA base damage.

Which is the most efficient way to avoid DNA mutations from UV radiation?

Which is the most efficient way to avoid DNA mutations from UV radiation? Avoid getting X-rays at the doctor's office.

What are two things that can damage DNA after replication?

DNA bases can be damaged by: (1) oxidative processes, (2) alkylation of bases, (3) base loss caused by the hydrolysis of bases, (4) bulky adduct formation, (5) DNA crosslinking, and (6) DNA strand breaks, including single and double stranded breaks. An overview of these types of damage are described below.

What do DNA dimers do?

DNA repair Pyrimidine dimers introduce local conformational changes in the DNA structure, which allow recognition of the lesion by repair enzymes. In most organisms (excluding placental mammals such as humans) they can be repaired by photoreactivation.

What type of mutation is caused by UV radiation quizlet?

UV radiation causes alkylation of guanine bases on the same DNA strand.

How UV light exposure causes DNA mutation quizlet?

UV light damages the DNA of exposed cells by causing bonds to form between adjacent pyrimidine bases, usually thymines, in DNA chains. The thymine dimers inhibit correct replication of the DNA during reproduction of the cell.

How do UV rays cause DNA damage without directly altering the sequence of nucleotides?

UVA (and also UVB) radiation cause indirect damage to DNA via absorption of photons by non-DNA chromophores. This generates reactive oxygen species like singlet oxygen or hydrogen peroxide that oxidize the DNA bases causing mutations.

Which type of molecule in a bacterial cell is damaged by UV radiation?

Ultraviolet (UV) light kills cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up DNA.

How can UV affect our DNA?

DNA is our genetic code, the precious molecule containing all the information necessary to make up a living organism and it is therefore well protected inside a special structure, the nucleus, located deep inside each cell (Figure 1). DNA is composed of two complementary strands that are wound into a double helix (Figure 1). The hereditary message is chemically coded and made up of the four bases, the four ‘building blocks’: adenine (A), thymine (T), guanine (G) and cytosine (C ) (Figure 1).

What is UV Light?

Ultraviolet (UV) light is a type of electromagnetic radiation invisible to most humans and emitted mainly by the sun. However, UV can be released by artificial sources too such as electric arcs and specialized lights (e.g. tanning lamps). The wavelengths of UV rays range between 200 and 400 nm, which are shorter than the wavelengths of violet light (hence the name ultra-violet. Violet is at the higher end of the visible spectrum with a wavelength of around 380–450 nm).

How does DNA repair damage?

When direct DNA damage fuses two base pairs together, the DNA ends up with a bulge in its normal double helix shape. Several enzymes travel around the DNA guarding it and looking for such abnormalities. When they find such a bulge, an abnormal notch, they activate repair proteins that cut out the damaged part of the DNA and put in the correct base pairs. This whole process is called nucleotide excision repair. The effect of indirect DNA damage is harder to detect because transversion does not result in a distorted helix. The mechanism that repairs this kind of damage is called base excision repair. Enzymes called DNA glycosylases remove a base pair misplaced by transversion; other enzymes then open up the DNA’s backbone so that DNA building enzymes can come through and fill the gap with the correct base pair.

How does DNA replication work?

This process happens when the double helix opens up to two single strands so that replication proteins can bind along the DNA backbone and start constructing a new strand according to the instructions they see on the original backbone. Every A base they come across ‘asks’ for a T base — as a pair — and vice versa, while every G they come across ‘screams’ for a C and vice versa. (This happens as A is chemically complementary to T, while G complements chemically C). Since the backbone is no longer ‘smooth’ due to the photoproduct of the pericyclic reaction, it is difficult for the replication proteins to determine what base pairs should be put across the fused, covalently-linked pyrimidines when the altered/ damaged DNA strand needs to be copied and a new DNA strand to be synthesized. This may result in a wrong base being put during the replication process (if the damage is not properly repaired on time). Exactly this base change resulting from the DNA lesion is called mutation.

How does DNA react with UV?

There are different ways UV-excited DNA can react, but the fusion or dimerization of two adjacent bases (the building blocks of the DNA) is the most common. If two pyrimidine bases (thymine or cytosine; two out of the four bases that make up the DNA backbone. The other two are adenine and guanine) are next to each other, their two rings can fuse together forming a covalent link (Figure 2). This type of reaction, called a pericyclic reaction, is possible because of how close their rings are and how their symmetries align (Figure 2). Such a chemical change to the DNA is not a mutation but is rather DNA damage or a DNA lesion. The DNA at a damaged site is no longer truly DNA as it has a different chemical structure to the natural form of DNA and it is a chemical intermediate. This formation of a four-carbon ring between the pyrimidines (see red square on Figure 2) creates a ‘notch’ on the DNA backbone causing problems for essential procedures happening along the DNA backbone.

Where is DNA found in a cell?

Figure 1 : DNA structure. Most DNA is found inside the nucleus of a cell, where it forms the chromosomes. Chromosomes have proteins called histones that bind to DNA and help it get compacted as the DNA molecule gets wound around them. DNA has two strands that twist into the shape of a spiral ladder called a helix. It is made up of four building blocks called nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C ). The nucleotides attach to each other (A with T, and G with C) to form chemical bonds called base pairs, which connect the two DNA strands. Genes are short pieces of DNA that carry specific genetic information. Image source: https://siteman.wustl.edu/glossary/cdr0000045671/

What is the cause of DNA damage?

Part of what makes this type of DNA damage particularly dangerous is that it is caused by excited oxygen molecules, not the UV light itself. Excited oxygen has an unusually long lifespan for a reactive species, so the damage can occur in cells other than skin cells.

What is a mutation in a codon?

A mutation causes a codon to change from UAC to UAU, both of which specify tyrosine. This is an example of

What is the codon AUG?

The codon AUG specifies the amino acid methionine. What would the tRNA anitcodon be that recognizes this codon?

What is the midterm in Earth Science?

earth science midterm - the sun and stars

What happens if a DNA sample from an unknown organism has telomerase?

If a DNA sample from an unknown organism has telomerase, the organism

Why are prokaryotes able to perform transcription and translation at the same time?

Prokaryotes are able to perform transcription and translation at the same time because they lack

Which bond is easier to break?

hydrogen bonds are easier to break allowing for DNA copying of a template

Does tetracycline block translation?

Tetracycline is an antibiotic that blocks the A site on prokaryotic ribosomes, thus preventing translation. Why doesn't it prevent translation in eukaryotic ribosomes?

What is the mechanism of UV light?

Ultraviolet (UV) light induces specific mutations in the cellular and skin genome such as UV-signature and triplet mutations, the mechanism of which has been thought to involve translesion DNA synthesis (TLS) over UV-induced DNA base damage.

Does daylight UV cause mutations?

Daylight UV induces a characteristic UV-specific mutation, a UV-signature mutation occurring preferentially at methyl-CpG sites, which is also observed frequently after exposure to either UVB or UVA, but not to UVC.

Does UVA damage skin?

Indeed, UVA produces oxidative DNA damage not only in cells but also in skin, which, however, does not seem sufficient to induce mutations in the normal skin genome. In contrast, it has been demonstrated that UVA exclusively induces the solar-UV signature mutations in vivo through CPD formation.