Lecture 31

Question 1

What is a mutation? Mutations can be either ______ or ______.

Answer 1

spontaneous or induced

Question 2

Spontaneous mutations

Answer 2

Spontaneous mutations occur without external intervention. The bulk of spontaneous mutations result from errors in the pairing of bases by DNA polymerase during DNA replication. In general, there is a 1 chance in 1,000,000 that a gene will mutate when the cell divides, the mutation rate is 1/1,000,000 or 10–6 , which is relatively rare.

Question 3

The occurrence of random mutations at low frequency is an essential aspect of the _______________, for evolution requires that genetic diversity be generated randomly and at a low rate.

Answer 3

-adaptation of species to their environment. This is possible bc prokaryotes divide and their exponential grwoth ensure that genetic diversity can be generated randomly and at a low rate (formation of mutations)

Question 4

Most mutations are harmful or neutral and are likely removed from the gene pool when the individual cell dies. However, a few mutations may be beneficial to a population of bacteria that is reguarly exposed to ________. Cells carrying mutated genes that aid with antibiotic resistance are more likely to be passed down to future generations.

Answer 4

antibiotics

Question 5

Not all mutations are spontaneous, some are ______, meaning they are what?

Answer 5

induced, meaning that they are due to agents in the environment and include mutations made deliberately by humans

Question 6

Rates of mutation can be increased by using ______. What is this?

Answer 6

mutagens, which is an agent that causes mutations (chemicals, radiation), and can increase the mutation rate

Question 7

A mutagen usually increases the spontaneous rate of mutation, which is about in in 10^6 by a factor of what?

Answer 7

10 to 1000 times. In other words, in the presence of a mutagen, the normal rate of mutations becomes a rate of 10^-5 to 10^-3 (1/10000 to 1/1000) per replicated gene

Question 8

Mutations that change only one base pair are called? These mutations are caused by _________ .

Answer 8

point mutations, caused by base pair substitutions

Question 9

The most common type of mutation?

Answer 9

point mutation, base pair substitution

Question 10

Different types of base pair substitutions?

Answer 10

missense, nonsense, silent mutations

Question 11

silent mutations

Answer 11

silent mutations result when there is no change in the amino acid that is coded. this is usually due to the degeneracy of the code with a chnage in the base pair corresponding to the third position of the mRNA codon.

Question 12

If the base substitution results in an amino acid substitution in the synthesized protein, this change in the DNA is known as a what?

Answer 12

missense mutation

Question 13

What is the possible change with a missense mutation?

Answer 13

There is a possible phenotype change. Possible because in some cases, even if the amino acid is changed, the function of the protein may not change if the amino acid is in a non-vital portion of the protein, or is chemically very similar to the original amino (a basic amino acid to a basic amino acid). However, the effects of some missense mutations can be dramatic.

Question 14

when a base pair substitution results in the formation of a stop or nonsense codon? What is produced because of this mutation?

Answer 14

nonsense mutation, produces truncated protein. Effect on phenotype very likely. Unless the nonsense mutation is very near the end of the gene, the incomplete product will be completely inactive.

Question 15

Besides base pair mutations, there are also changes in the DNA called ________ . And define. This mutation can shift the_________ frame. Frameshift mutations almost always result in what?

Answer 15

Frameshift mutations, there are changes in the DNA where one or a few nucleotide pairs are deleted or inserted into the DNA. This mutation can shift the ‘translational reading frame,’ that is the 3 by 3 grouping of nucleotides recognized as codons by the tRNAs during translation.

Almost always result in a long strech of altered amino acids and the production of an inactive protein from the mutated gene

Question 16

chemical mutagens: nucleotide base analogs

Answer 16

chemical mutagens: nucleotide base analogs are molecules that resemble the purine and pyrimidine bases of DNA in structure yet display faulty pairing properties. DNA replication errors will occur at higher frequencies at these sites due to incorrect base pairing, the result is the incorporation of a mismatched base into the new strand of DNA and thus introduction of mutation.

Question 17

chemical mutations: work to push apart base pairs

Answer 17

Other chemical mutagens function as intercalating agents, these mutagens become inserted between two DNA base pairs and push them apart. Eg. Acridines dyes and ethidium bromide (often used to detect DNA in gel electrophoresis) are planar molecules that act as intercalating agents. During replication, this abnormal conformation can lead to single base insertions or deletions. Thus they typically induce frameshift mutations.

Question 18

nonionizing radiation: like what type? and what does it cause?

Answer 18

UV radiation is due primarily to its effect on DNA – pyrimidine dimers are formed in which C and T bases on the same strand of DNA become covalently bonded to each other. This will greatly impede DNA polymerase activity or greatly increases its misreading the sequence at this point causing mutation.

Question 19

Ionizing radiation as a mutagen – types and what this type of radiation causes?

Answer 19

gamma rays, X-rays, cosmic rays (short wavelength radiation)

These rays cause water and other substances to ionize, resulting in the formation of free radicals, such as hydroxyl radicals. These free radicals will react with and damage macromolecules (such as DNA) in the cell, causing double or single-stranded breaks, leading to rearrangements or large deletions.

Question 20

Another method of genetic alteration in a cell besides mutations is __________, which is what?

Answer 20

genetic recombination, which typically generates much larger genetic changes than mutations. Entire genes, sets of genes, or even larger segments of DNA can be transferred between chromosomes or other genetic elements (structures that carry genetic information, like plasmids).

Question 21

Recombination

Answer 21

defined as the physical exchange of DNA between genetic elements

Question 22

homologous recombination

Answer 22

a process that results in the genetic exchange between homologous DNA sequences from two different sources

For homologous recombination to make new genotypes, it is essential that two homologous sequences be related/homologous but genetically distinct. Genetic recombination in prokaryotes occurs after fragments of homologous DNA from a donor chromosome are transferred to a recipient or host cell .

Question 23

Three different processes to acquire or transfer these fragments of homologous DNA from a donor to a recipient

Answer 23

transformation, transduction or conjugation

Question 24

Note that homologous recombination is a complex process that requires __________, any non-incorporated DNA is degraded. One of the key proteins involved is the _______protein, it is essential in nearly every homologous recombination pathway. RecA-like proteins have been identified in all bacteria examined, as well as Archaea and most Eukarya.

Answer 24

~25 proteins/enzymes

RecA protein