bio 2107 chapter 14

transition mutation

A point mutation in which a pyrimidine is susbstituted for a pyrimidine, or a purine is substituted for a purine.

frameshift mutations: A. Cause insertion or deletion of a single amino acid B. Result in premature stop codons C. Change entire amino acid sequence downstream of mutation D. Cause cancer E. All the above

C. Change entire amino acid sequence downstream of mutation

nonsense mutation

- A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. - result in premature stop codons

duplications can lead to new genes

- Gene duplication can provide new targets for selection to act upon, without compromising the function of the original gene. - can acquire mutations that gradually lead to new, yet similar function to the original gene. - results in the creation of gene families, a collection of genes that share similar functional protein domains, but have diverged to have different functions.

Do point mutations matter?

- If an error occurs but the codon still codes for the same amino acid, the result is a fully functional protein. This is a - When the amino acid sequence is changed due to the mutation, the protein may fold in correctly, causing it to no longer function. This is a nonsynonymous or missense mutation

base excision repair

- In this example, a molecule of uracil is mistakenly incorporated into a new DNA strand instead of cytosine. - Since uracil is found in mRNA but not DNA ,the uracil needs to be removed. - In base excision repair, a enzyme specialized to remove one particular base acts to remove that base when that base is in the wrong place.

mismatch repair

- Mismatched bases are recognized, and a repair enzyme breaks the backbone downstream. - Another enzyme removes successive nucleotides, including the mismatched base. - DNA polymerase comes in and adds the missing bases, using the intact strand as a template.

reciprocal translocation

- Reciprocal translocations join segments from nonhomologous chromosomes. - In the formation of a reciprocal translocation, both chromosomes are broken and the terminal segments are exchanged before the breaks are repaired. In large genomes, the breaks are likely to occur in noncoding DNA, so the breaks themselves do not usually disrupt gene function.

nucleotide excision repair

- Similar process to mismatch repair. - But mismatch repair operates on a single mispaired base, whereas nucleotide excision repair recognizes multiple mismatched bases in a region of the DNA. - The region that is excised and replaced can extend for thousands of nucleotides.

transportable elements

- Transposable elements are DNA sequences that can move from one position to another in the genome. - Transposons can insert into a gene and disrupt its function.

inversions

- When the normal order of a block of genes is reversed, the result is an inversion. - typically form when the region between two breaks in a chromosome is flipped before the breaks are repaired.

chromasomal level deletions

- when a region of the chromosome is missing. - A deletion may result from a replication error or the joining of breaks that may have occurred on either side of the deleted region. - Because chromosomes occur in homologous pairs, a deletion in one chromosome can persist in a population. However, in general the larger the deletion, the smaller the chance of survival.

nonsynonymous mutation

A mutation in a gene that changes the amino acid sequence of the protein that gene encodes.

point mutation

1. Here you see a T-A base pair temporarily become a mismatched T-G base pair because DNA polymerase mistakenly inserts a G opposite the T. In this case, the proofreading function of DNA polymerase failed to catch the error. 2. During the next replication, the G in the new template strand specifies a C in the daughter strand (matched correctly). 3. One base pair (T-A) is replaced by a different base pair (C-G), and a nucleotide substitution or point mutation has occurred.

duplication

A chromosome in which a region is present twice instead of once is said to contain a duplication.

The relatively large number of new mutations that occur in the human genome each generation is tolerable because: A. We have excellent repair mechanisms B. Most of the mutations occur in somatic cells, not germ cells C. Most of our genome is non-coding DNA, so few mutations affect our proteins D. We have excellent protein repair mechanisms E. Compared to other organisms, changes in our proteins have relatively little affect on our cells' structure and function

C. Most of our genome is non-coding DNA, so few mutations affect our proteins

Large scale mutations in chromosomes: A. Are typically seen in elderly B. Usually fixed by DNA polymerase C. Sometimes caused by errors in meiosis D. Can be caused by DNA methylation

C. Sometimes caused by errors in meiosis

Cancer is usually due to: A. Exposure to chemicals and radiation B. Mutation in stem cells C. Series of mutations that occur throughout an affected tissue or organ D. Series of mutations that occur in a single lineage of somatic cells E. Series of mutations that occur in multiple lineages of germ cells

D. Series of mutations that occur in a single lineage of somatic cells

Any DNA damage is considered to me a mutation, even if it's immediately corrected by DNA polymerase True/False

False. Only a mutation when in both strands

how do organisms reduce the frequency of errors during replication?

If proofreading doesn't catch an error, then mismatch repair enzymes can come in and repair the damage.

how do mutations occur?

Mutations caused by mutagens: - X-rays can cause breaks in the sugar-phosphate backbone, either in one strand or both. - UV light can cause adjacent pyrimidines to cross link, forming thymine dimers most commonly. - Bleach or hydrogen peroxide can cause a loss of a base, resulting in a gap in one strand of the DNA. - Tobacco smoke can add bulky side groups to the bases, resulting in improper base pairing.

frame shift muatations

The transcript has a single base insertion that shifts the reading frame. When the transcript is translated, the shift in the reading frame results in an amino acid sequence very different from the nonmutant sequence.

. The enzyme _____ repairs breaks in the DNA sugar-phosphate backbone. a. DNA ligase b. uracyl glycosylase c. None of the other answer options is correct. d. .AP endonuclease e. DNA polymerase

a. DNA ligase

The enzyme _____ repairs 99% of mismatched bases immediately during replication. a. DNA polymerase b. DNA ligase c. uracyl glycosylase d. AP endonuclease e. None of the answer options is correct.

a. DNA polymerase

Why do data on observable mutant phenotypes underestimate the actual frequency of mutation? (Select all that apply.) a. Many mutations are in noncoding regions of the genome. b. Most mutations result in death of the individual or an inability to reproduce. c. Some mutations in protein-coding regions of the genome are synonymous mutations.

a. Many mutations are in noncoding regions of the genome. c. Some mutations in protein-coding regions of the genome are synonymous mutations.

A family can share a genetic risk of developing cancer if: a. a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor. b. a somatic cell mutation in one of the genes implicated in the cancer occurred in an ancestor. c. All of these choices are correct. d. the cancer is caused by somatic cell mutations. e. the cancer is caused by germ-line mutations.

a. a germ-line mutation in one of the genes implicated in the cancer occurred in an ancestor.

Which of the following would not occur when a transposable element inserts into a gene? a. cause the gene to duplicate itself. b. disrupt the open reading frame. c. cause errors in RNA processing. d. interfere with transcription.

a. cause the gene to duplicate itself.

synonymous mutation (silent mutation)

altered codon specifies the same amino acid

Why do mutations associated with cancer almost always occur sequentially instead of simultaneously? a. Each mutation increases cellular growth rate, allowing more cells to have a higher chance of the next mutation. b. All of these choices are correct. c. The mutations are extremely unlikely to occur in the same cell at the same time. d. Each mutation adds to the growth advantage of the ones occurring previously.

b. All of these choices are correct.

Insertions and deletions of single nucleotides: a. cause cancer. b. cause frameshift mutations. c. shorten chromosomes. d. add or delete amino acids to or from the normal polypeptide. e. cause missense mutations.

b. cause frameshift mutations.

Point mutations that cause amino acid replacements are called: a. synonymous (silent) mutation. b. transition mutation. c. nonsynonymous (missense) mutation. d. stop mutation. e. nonsense mutation.

c. nonsynonymous (missense) mutation.

somatic cells

cells of the body

Reciprocal translocations can affect gene dosage because: a. reciprocal translocation involves the duplication of one set of genes and the deletion of another set of genes. b. None of the answer options is correct. c. the genes involved in the translocation are nonfunctional. d. the two chromosomes involved in the translocation always assort together during meiosis. e. the two chromosomes involved in the translocation may not assort together during meiosis.

e. the two chromosomes involved in the translocation may not assort together during meiosis.

somatic mutation and cancer

most cancers result from mutations in somatic cells

germ cells

reproductive cells

Stop Mutation

substitution, resulting in a stop codon