LS7A Week 10 (no clicker questions or practice exam questions)

How can humans withstand such a high rate of mutation per genome per generation?

-Because the majority of newly arising mutations occur in noncoding DNA -only 2.5% of genome codes for proteins

Prophase

-Chromosomes condense and become visable -microtubules form around centrosome to form mitotic spindle

Why is the mutation rate per nucleotide per replication for RNA viruses so high?

-RNA is less stable than DNA -RNA doesn't have a proofreading function

In animal cells, what starts cytokinesis?

-a contractile ring (a ring of actin filaments) forms against cell membrane -contracts to pinch the two cells apart

proto-oncogene

-a gene that regulates normal cell division but that can become a cancer-causing oncogene as a result of mutation or recombination -can be mutated by environmental agents

In plant cells, how does cytokinesis start?

-a phragmoplast is formed in the middle of the cell -it guides vesicles containing cell wall components to the middle of the cell and vesicles form cell wall -happens during telophase

chromosome deletion

-a region of the chromosome is missing -result from an error in replication or from the joining of breaks in a chromosome that occur on either side of the deleted region -the larger the deletion, the smaller chance for survival

chromosome duplication

-a region of the chromosome is present twice -small duplications are more likely to stay

cyclin

-a regulatory protein whose levels rise and fall with each round of the cell cycle -most of them activate kinases

in-frame deletion/insertion mutation

-a set of three (a codon) is added or deleted -potentially can cause issues

frame-shift mutation

-a single or not a multiple of 3 nucleotides are added or deleted, which changes the reading frame -a serious mutation

mutagens

-agents that increase the probability of mutation -chemicals, tobacco smoke, uv rays, gamma rays, x-rays

genetic risk factor

-any mutation that increases the risk of a given disease -example: mutations of the BCRA1 gene is a genetic risk factor for breast cancer

How do chromosomal mutations occur?

-by duplications or deletions (duplications are usually less harmful than deletions)

What are some causes for a single strand or double strand break & what are the two repair mechanisms?

-caused by gamma and x rays 1. Homologous recombination 2. Non-homologous end joining

Anaphase

-centromeres split -after full split, the two sister chromatids are now considered full-fledged chromosomes -each one is pulled to opposite sides of cell -depolymerization of microtubules shrink them, allowing the chromatids to be pulled apart

Nonsense mutation

-change of a nucleotide base pair, resulting in a premature stop codon -almost always results in a nonfunctioning protein

Cytokinesis

-division of cytoplasm -starts as mitosis is ending

Base excision repair (BER)

-if one base is damaged, enzymes snip out the base, the the baseless backbone is removed, and a new nucleotide is added -ex: base U is considered damage

How do cancer-causing viruses multiply?

-infect cell and use the machinery of host cell to synthesize proteins encoded in their genome to make more copies of themselves -viruses are assemblages of protein surrounding a core of either DNA or RNA

What is the function of a proto-oncogene?

-makes proteins that promote cell division -ex: growth factors, cell-surface receptors, G proteins, and protein kinases

Telophase

-microtubules of spindle break down -nuclear envelope reforms, creating two new nuclei

somatic mutations

-mutation in a somatic cell -only affects the individual in which they occur -rate of mutation per nucleotide per replication matters more -can increase or decrease cell division

Prometaphase

-nuclear envelope breaks -mitotic spindle attaches to kineotochores (protein complex) on the centromeres of chromosomes -polymerization will help microtubules assemble

Germ-line mutation

-occur in reproductive cells or in the cells that give rise to these reproductive cells -these mutations are passed on to the next gen -rate of mutation per genome per generation matters more

point mutations

-one nucleotide changes resulting in a different base pair -if in a protein coding gene, it can be silent or missense -most frequent type of mutation

What kind of mutations of a proto-oncogene and tumor suppressor would lead to cancer?

-over-activity of proto-oncogene -loss of tumor suppressor activity -a buildup of both mutations is what will lead to cancer cells

What do M cyclin-CDKs do?

-phosphorylate structural proteins in nucleus to break down nuclear envelope -phosphorylate proteins that regulate assembly of microtubules, which promotes the formation of the spindle

What is the p53 gene's role in the cell cycle?

-phosphorylated p53 binds to DNA to block activity of G1/S cyclin-CDK complex -this pauses the cycle to give damaged DNA time to repair

duplication and divergence

-process of creating new genes by duplication followed by change in sequence over evolutionary time -divergence: the slow accumulation of differences between duplicate copies -leads to gene families

Nucleotide excision repair (NER)

-proteins remove a sequence of nucleotides and replaces the sequence -ex: UV causing adjacent nucleotdies to stick together, damaging double helix structure

Cyclin-dependent kinases (CDKs)

-proteins that are always present in the cell but only active when bound to the appropriate cyclin -they phosphorylate target proteins that promote cell divsion

tumor suppressor

-proteins whose normal activities inhibit cell division -ex: participate in cell cycle checkpoints

How often do mutations occur?

-random and spontaneous -unconnected to an organism's need

Non-homologous end joining

-removes damaged sequences and fuses broken ends together -doesn't use template DNA and not as accurate

Mismatch repair

-specific enzymes to remove and replace incorrectly paired nucleotides -this is used where there is no damage, just a mismatched base

When is a mutation actually considered a mutation?

-the actual, permanent damage -was NOT repaired

ploidy

-the number of complete sets of chromosomes in a cell -humans have 23 pairs per set in each cell

inversion

-the reversal of the normal order of a block of genes -usually produces when a region between two breaks in a chromosome is flipped before the breaks are repaired -likely to occur in noncoding DNA

sister chromatid

-the two copies of a chromosome produced in S phase -held together by a centromere, which is where the spindle fibers attach to so the chromosomes can move in cell division

reciprocal translocation

-two different (nonhomologous) chromosomes undergo an exchange of parts -usually occurs in noncoding DNA so breaks don't disrupt cell function

Key characteristics of cancer cells

-uncontrolled cell division -can divide on their own without growth signals -resist signals that inhibit cell division -invade tissue -produce signals to promote new blood vessel growth

Homologous recomination

-uses undamaged section of similar DNA as template -interlaces the damaged and undamaged strands and get them to exchange sequences -end with two complete double-stranded DNA

Model for mitosis cell-cycle checkpoint

1) signals are released by unattached kinetochores and cause MAD to bind to CDC20 2) When all kinetochores are attached MAD releases CDC20 and CDC20 binds to APC 3) the APC/CDC20 complex ubiquitinates Sercurin 4) Securin is destroyed, and separase is released 5) Separase destroys cohesin 6) Chromatids separate and mitosis proceeds to anaphase

Where are the checkpoints in the cell cycle?

1. DNA replication checkpoint at the end of G2 2. Spindle assembly checkpoint before anaphase 3. DNA damage checkpoint before entering S phase

Five stages of mitosis

1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase

Look carefully at the image of the human karyotype shown in Figure 11.3. What is the significance of the small differences between homologous chromosomes? /brainhoney/Resource/10613548,8,0,2,1/Assets/resources/chapter_11/11_72.jpg Photo credit: ISM/Phototake. A. Each homologous chromosome in a pair is from a different parent. B. Some of this person's DNA is mutated, possibly causing disease. C. Chromosomes may not be completely replicated during S phase. D. The differences are a result of the way the material was prepared.

A. Each homologous chromosome in a pair is from a different parent.

When in the cell cycle would you find sister chromatids? A. S and G2 B. G2 C. S D. G1

A. S and G2

Insertion of one nucleotide in a gene will lead to a frameshift mutation. A. True B. False

A. True

Mutagens increase the amount of damage to DNA. A. True B. False

A. True

The development of cancer requires both the _____ of an oncogene and the _____ of a tumor suppressor. B. inhibition; inhibition C. inhibition; activation D. activation; activation

A. activation; inhibition

A chromosomal mutation where a segment breaks off, flips, and then reattaches itself is called a(n): A. inversion. B. reciprocal translocation. C. duplication. D. translocation. E. deletion.

A. inversion

Point mutations that cause amino acid replacements are called: A. nonsynonymous (missense) mutation. B. nonsense mutation. C. synonymous (silent) mutation. D. transition mutation. E. stop mutation.

A. nonsynonymous (missense) mutation.

Several years ago, a man noticed a small mole on his wrist. Years later, the mole grew in size and the man was diagnosed as having metastatic melanoma. This was likely the result of: A. several mutations affecting proto-oncogenes and/or tumor suppressor genes. B. None of the other answer options is correct cancers arise spontaneously, independent of mutations. C. a single mutation inactivating a tumor suppressor gene. D. a single mutation affecting one proto-oncogene in a cell.

A. several mutations affecting proto-oncogenes and/or tumor suppressor genes.

The two molecules of double-stranded DNA in a replicated chromosome are called: A. sister chromatids B. non-sister chromatids C. bivalent chromosomes D. homologous chromosomes

A. sister chromatids

How do new cyclin proteins appear in the cytoplasm? A. All of these choices are correct. B. They are made through protein synthesis. C. They are imported from outside the cell. D. They are recycled.

B. They are made through protein synthesis

A chromosomal mutation in which a segment is missing is called a deletion. A. False B. True

B. True

Which of the following causes breaks in one or both of the sugar-phosphate backbones? A. exposure to oxidizing agents such as household bleach or hydrogen peroxide B. X-rays C. tobacco smoke D. UV radiation

B. X-rays

When a transposable element inserts into a gene, it can: (Select all that apply.) A. cause the gene to duplicate itself. B. cause errors in RNA processing. C. disrupt the open reading frame. D. cause the gene to delete itself. E. interfere with transcription.

B. cause errors in RNA processing. C. disrupt the open reading frame. E. interfere with transcription.

Any DNA "damage" is considered to be a mutation, even if it is immediately corrected by the action of DNA polymerase. A. True B. False

B. false

Which type of repair is a backup for the DNA polymerase proofreading function? A. base excision repair B. mismatch repair C. nucleotide excision repair D. DNA ligase

B. mismatch repair

In which phase of mitosis do chromosomes condense? A. anaphase B. prophase C. metaphase D. telophase

B. prophase

Chronic myelogenous leukemia (CML) is caused when a segment of chromosome 9 and a segment of chromosome 22 both break off and switch places. How is this mutation classified? A. duplication B. reciprocal translocation C. transposition D. inversion E. deletion

B. reciprocal translocation

A point mutation that causes no change in the amino acid sequence of a protein is called a: A. nonsense mutation. B. synonymous (silent) mutation. C. transition mutation. D. stop mutation. E. nonsynonymous (missense) mutation.

B. synonymous (silent) mutation

In which phase of mitosis does the nuclear envelope reform? A. anaphase B. telophase C. metaphase D. prophase

B. telophase

Cell division is regulated by: A. signals that indicate that the cell has reached a sufficient size. B. signals about the nutritional status of the cell. C. All of these choices are correct. D. signals that indicate that DNA has been replicated. E. growth factor signals.

C. All of these choices are correct

Which of the following statements concerning cyclin-dependent kinases (CDKs) is NOT true? A. CDKs are enzymes that attach phosphate groups to other proteins. B. CDKs are active, or "turned on," when complexed with cyclins. C. CDKs are inactive, or "turned off," in the presence of cyclins. D. CDKs are present throughout the cell cycle.

C. CDKs are inactive, or "turned off," in the presence of cyclins.

In which phase of mitosis do sister chromatids separate? A. prophase B. metaphase C. anaphase D. telophase

C. anaphase

In organisms with large genomes, inversions are more likely to be tolerated if the breakpoints occur in: A. open reading frames. B. reciprocal translocations. C. noncoding DNA. D. closed reading frames. E. coding DNA.

C. noncoding DNA

A gene associated with promoting normal cell division is called a(n): A. oncogene. B. tumor suppressor. C. proto-oncogene. D. proto-oncogene or a tumor suppressor.

C. proto-oncogene

What is the difference between mismatch repair and nucleotide excision repair? A. In mismatch repair, the sugar phosphate backbone is fixed, whereas in nucleotide excision repair, several nucleotides are replaced. B. In mismatch repair, several nucleotides are replaced, whereas in nucleotide excision repair the sugar phosphate backbone is fixed. C. In mismatch repair, several nucleotides are replaced, whereas in nucleotide excision repair it is just one. D. In mismatch repair, one nucleotide is replaced, whereas in nucleotide excision repair several nucleotides are replaced.

D. In mismatch repair, one nucleotide is replaced, whereas in nucleotide excision repair several nucleotides are replaced.

Which of the following statements concerning cancer and mutations is CORRECT? A. Usually, a single mutation is all that is required to cause cancer. B. None of the other answer options is correct. C. Cancer can only occur with a mutation in a somatic cell. D. Usually, multiple mutations are required in different genes to cause cancer. E. Cancer can only occur with a mutation in a germ cell.

D. Usually, multiple mutations are required in different genes to cause cancer

What is a cyclin? A. a protein that activates kinases B. a kinase C. a protein whose levels change with the cell cycle D. a protein that activates kinases and a protein whose levels change with the cell cycle

D. a protein that activates kinases and a protein whose levels change with the cell cycle

CDKs are important in the regulation of the cell cycle. They carry out their function by: A. preventing the progression of a cell from one stage of the cell cycle to the next. B. removing phosphate groups from target proteins. C. degrading cyclin proteins. D. adding phosphate groups to target proteins.

D. adding phosphate groups to target proteins

In which phase of mitosis do spindle microtubules shorten? A. metaphase B. telophase C. prophase D. anaphase

D. anaphase

A malignant cancer differs from a benign cancer in that: A. malignant cancers are lethal and benign cancers are not. B. benign cancers are lethal and malignant ones are not. C. malignant cancers are caused by viruses and benign cancers are not. D. malignant cancers invade surrounding tissue and benign cancers do not.

D. malignant cancers invade surrounding tissue and benign cancers do not.

In which phase of mitosis do chromosomes line up at the middle of the cell? A. telophase B. anaphase C. prophase D. metaphase

D. metaphase

The definition of mutation is "any heritable change in the genetic material." The qualifier "heritable" is necessary because: A. changes in the genetic material occur without regard to the needs of the organism. B. changes in the genetic material occur at random along the genome. C. most changes in the genetic material are harmful to the organism. D. most changes in the genetic material are repaired soon after they occur.

D. most changes in the genetic material are repaired soon after they occur

What is the main specialized repair enzyme?

DNA ligase helps repair breaks in backbone by using ATP

_____ is the process where new genes evolve from duplicates of old ones. A. Inversion B. Centromere dosage C. Deletion D. Reciprocal translocation E. Duplication and divergence

E. Duplication and divergence

Which of the following statements regarding tumor suppressors is TRUE? A. Tumor suppressors include PDGF and cyclins. B. None of the other answer options is correct. C. Tumor suppressors promote cell division. D. Tumor suppressors act synergistically with proto-oncogenes. E. Mutations affecting tumor suppressors can contribute to the development of cancers.

E. Mutations affecting tumor suppressors can contribute to the development of cancers.

_____ mutations affect only the individual in which they occur; _____ mutations are passed from parent to offspring. A. Germ-line; heritable B. Germ-line; somatic C. Somatic; point D. Point; germ-line E. Somatic; germ-line

E. Somatic; germ-line

The relatively large number of new mutations that occur in the human genome in each generation is tolerable because: A. we have excellent DNA repair mechanisms. B. compared to other organisms, changes in our proteins have relatively little effect on our cells' structures and functions. C. we have excellent protein repair mechanisms. D. most of the mutations occur in somatic cells, not germ cells. E. most of our genome is noncoding DNA, so few mutations affect our proteins.

E. most of our genome is noncoding DNA, so few mutations affect our proteins

A chromosomal segment that breaks off and attaches to another chromosome is what type of mutation? A. duplication B. inversion C. deletion D. reciprocal translocation E. translocation

E. translocation

Mismatch repair, base excision repair, and nucleotide excision repair are similar in that each: (Select all that apply.) A. repairs multiple mismatched or damaged bases across a region. B. repairs a single mismatched base. C. None of the answer options is correct. D. repairs a short strand of mismatched nucleotides. E. uses an undamaged segment of DNA as the template to repair a damaged segment of DNA.

E. uses an undamaged segment of DNA as the template to repair a damaged segment of DNA

Is it the cyclin or CDK that trigger the required cell cycle events?

It is the cyclin-CDK complex that does this

oncogene

a cancer causing gene

haploid

a cell with one complete set of chromosomes

diploid

a cell with two complete sets of chromosomes

Checkpoint in cell cycle

a control point where stop and go-ahead signals can regulate the cycle

For cancer to actually occur, how should the mutations occur?

a series of mutations occurring sequentially in a single cell line

hotspot

a site in the genome that is especially mutable

What does the G1/S cyclin-CDK complex do?

active at the end of G1 and is necessary for the cell to enter S phase

Why is mutation in the centromere rare?

because an abnormal chromosome is usually lost because it can't be directed properly into the daughter cells during cell division

How can transposable elements lead to mutations?

can be cleaved and inserted into a site in DNA that could potentially lead to a mutation

metaphase

chromosomes line up in middle of cell due to mitotic spindle lengthening or shortening

What happens if a tumor suppressor is mutated to be turned off?

it's absence is what allows cells to divide uncontrollably

What does the S cyclin-CDK do?

necessary to initiate DNA synthesis by activating enzymes and other proteins needed for replication

What does the rate of mutation per genome per generation depend on?

number of cell divisions per generation

Some drugs, like paclitaxel, will rapidly kill growing cells to kill cancer cells. What is the disadvantage?

they can kill non-cancerous cells that are trying to grow