Honors Biology Chapter 14 section 6

What is a frameshift mutation?

Frameshift mutations are insertions or deletions of nucleotides may result in a shift in the reading frame or insertion of a stop codon.

How do the nucleotides get repaired after proofreading?

If it is the right base, the next nucleotide is added. If an incorrect base has been added, the enzyme makes a cut at the phosphodiester bond and releases the wrong nucleotide.

What happens if mismatches do not work?

If this remains uncorrected, it may lead to more permanent damage.

How is the wrong base identified in prokaryotes?

In E. coli, after replication, the nitrogenous base adenine acquires a methyl group; the parental DNA strand will have methyl groups, whereas the newly synthesized strand lacks them. Thus, DNA polymerase is able to remove the wrongly incorporated bases from the newly synthesized, non-methylated strand.

How is the wrong base identified in eukaryotes?

In eukaryotes, the mechanism is not very well understood, but it is believed to involve recognition of unsealed nicks in the new strand, as well as a short-term continuing association of some of the replication proteins with the new daughter strand after replication has completed.

What occurs during proofreading?

In proofreading, the DNA pol reads the newly added base before adding the next one, so a correction can be made. The polymerase checks whether the newly added base has paired correctly with the base in the template strand.

What is an induced mutation?

Induced mutations are those that result from an exposure to chemicals, UV rays, x-rays, or some other environmental agent.

What role does DNA polymerase play in mutations?

Most of the mistakes during DNA replication are promptly corrected by DNA polymerase by proofreading the base that has been just added.

What are mutations?

Mutations are variations in the nucleotide sequence of a genome

What are insertions and deletions?

Mutations can also be the result of the addition of a base, known as an insertion, or the removal of a base, also known as deletion.

What is a point mutation?

Point mutations are those mutations that affect a single base pair. These include silent, nonsense and missense mutations.

What is a mismatch repair?

Some errors are not corrected during replication, but are instead corrected after replication is completed; this type of repair is known as mismatch repair

What is a silent mutation?

Some mutations are not expressed; these are known as silent mutations.Silent point mutations have no effect on the protein sequence.

What is translocation?

Sometimes a piece of DNA from one chromosome may get translocated to another chromosome or to another region of the same chromosome; this is also known as translocation.

What is a spontaneous mutation?

Spontaneous mutations occur without any exposure to any environmental agent; they are a result of natural reactions taking place within the body.

What are the two types of mutations?

Such mutations may be of two types: induced or spontaneous.

How are nucleotides repaired during mismatch?

The enzymes recognize the incorrectly added nucleotide and excise it; this is then replaced by the correct base.

What are substitutions?

The most common nucleotide mutations are substitutions, in which one base is replaced by another. These can be of two types, either transitions or transversions

What is proofreading done by?

This is performed by the exonuclease action of DNA pol III.

What is a transition substitution?

Transition substitution refers to a purine or pyrimidine being replaced by a base of the same kind; for example, a purine such as adenine may be replaced by the purine guanine.

What is a transversion substitution?

Transversion substitution refers to a purine being replaced by a pyrimidine, or vice versa; for example, cytosine, a pyrimidine, is replaced by adenine, a purine.

What can result from genetic mutations?

Xeroderma pigmentosa is a condition in which thymine dimerization from exposure to UV is not repaired. Exposure to sunlight results in skin lesions.

How are nucleotides removed and replaced?

enzymes replace incorrect bases by making a cut on both the 3' and 5' ends of the incorrect base. The segment of DNA is removed and replaced with the correctly paired nucleotides by the action of DNA pol. Once the bases are filled in, the remaining gap is sealed with a phosphodiester linkage catalyzed by DNA ligase. This repair mechanism is often employed when UV exposure causes the formation of pyrimidine dimers.

What is a missense mutation ?

missense point mutations result in an amino acid substitutions

What is a nonsense mutation?

nonsense point mutations substitute stop codons for an amino acids