Biol 2107K Chapter 11

Polar bodies are:

haploid cells.

Prophase of meiosis I has some important differences from prophase of mitosis. These differences include: ___________pair, and _________ occurs.

homologous chromosomes; crossing over

Sexual reproduction results:

in a new generation that is not genetically identical to its parents. in offspring that are not genetically identical. from combining genetic material from two gametes. in a new generation with the same number of chromosomes as each parent.

The process of cytokinesis involves components of the cytoskeleton. It is most similar to what other cytoskeletal function?

muscle contraction

During meiosis crossing over takes place between:

non-sister chromatids.

Cancer-causing genes found in some viruses are called:

oncogenes.

Crossing over occurs during which step in meiosis?

prophase I

Sister chromatids are best described as two DNA molecules that have ____________.

virtually identical sequences of nucleotides.

Is the alignment of chromosomes at metaphase of meiosis II most similar to the alignment of chromosomes during metaphase of mitosis.

yes

Chiasma

(plural, chiasmata) A crosslike structure within a bivalent constituting a physical manifestation of crossing over.

At the start of mitosis, how many centromeres are present in a human cell?

46

Oncogene

A cancer-causing gene.

What would be the consequence if a cell underwent mitosis but not cytokinesis?

A cell that undergoes mitosis but not cytokinesis will become a single cell with two nuclei (and therefore with twice the normal amount of DNA); this type of cell is called a multinucleate cell.

Centrosome

A compact structure that is the microtubule organizing center for animal cells.

Centromere

A constriction that physically holds sister chromatids together; the site of the attachment of the spindle fibers that move the chromosome in cell division.

Why don't plant cells use a contractile ring to divide their daughter cells?

A contractile ring can't "pinch" a cell wall.

Tumor Suppressors

A family of genes that encode proteins whose normal activities inhibit cell division. (p53)

Meiotic Cell Division

A form of cell division that includes only one round of DNA replication but two rounds of nuclear division; meiotic cell division makes sexual reproduction possible.

Cyclin-dependant Kinase

A kinase that is always present within the cell but active only when bound to the appropriate cyclin.

What do you predict would be the consequence of a mutation in FtsZ that disrupts the function of the protein it encodes?

A mutation that disrupts the function of the FtsZ protein will block cell division.

Cyclin

A regulatory protein whose levels rise and fall with each round of the cell cycle.

Gametes

A reproductive haploid cell; gametes fuse in pairs to form a diploid zygote. In many species, there are two types of gametes: eggs in females, sperm in males.

Polar body

A small cell produced by the asymmetric first meiotic division of the primary oocyte.

Karyotype

A standard arrangement of chromosomes, showing the number and shapes of the chromosomes representative of a species.

Mitotic Spindle

A structure in the cytosol made up predominantly of microtubules that pull the chromosomes into separate daughter cells.

Under experimental conditions, we can delete the gene for the motor protein involved in contraction of the contractile ring during animal cell cytokinesis. Which of the following results might you predict?

Additional rounds of the cell cycle continue producing a multinucleate cell.

In what way is cytokinesis in plant cells similar to binary fission in a bacterium?

Cell wall material is deposited to separate the daughter cells.

Non-sister Chromatids

Chromatids of different members of a pair of homologous chromosomes; although they carry the same complement of genes, they are not genetically identical.

Muscle cells in the mammalian heart are multinucleate, meaning that multiple nuclei are present in the cytoplasm of a large cell. Predict what is different about the cell cycle in a muscle cell.

Cytokinesis does not occur.

What are some steps in prokaryotic binary fission?

DNA is replicated bidirectionally from a single point on the circular chromosome. The cell continues to grow outward symmetrically, separating the two chromosomes. The two replicated chromosomes remain attached to the plasma membrane. Cell wall material is laid down at the midpoint to separate the two daughter cells.

What is true regarding binary fission?

DNA replication during binary fission is a bidirectional process, occurring in opposite directions.

Contractile Ring

In animal cells, a ring of actin filaments that forms at the equator of the cell perpendicular to the axis of what was the spindle at the beginning of cytokinesis.

Explain how cytokinesis differs between animal and plant cells.

In animal cells, cytokinesis involves a contractile ring made of actin. This contractile ring forms against the inner face of the cell membrane at the equator of the cell. When the ring contracts, the cytoplasm is pinched in half, forming two new daughter cells. In plant cells, cytokinesis involves the growth of a new cell wall called a cell plate in the middle of the dividing cell. The new plate fuses with the original cell wall at the perimeter of the cell and two new daughter cells are formed.

Pragmoplast

In dividing plant cells, a structure formed by overlapping microtubules that guide vesicles containing cell wall components to the middle of the cell.

Cytokinesis

In eukaryotic cells, the division of the cytoplasm into two separate cells.

Mitosis

In eukaryotic cells, the division of the nucleus, in which the chromosomes are separated into two nuclei.

In a human cell at the end of prophase I, how many chromatids, centromeres, and bivalents are present?

In human cells at the end of prophase I, there are 92 chromatids, 46 centromeres, and 23 bivalents.

List three ways in which meiosis I differs from mitosis.

In meiosis I, homologous chromosomes pair, undergo crossing over, and segregate from each other. These events do not occur in mitosis. In mitosis, centromeres divide and sister chromatids separate, events that do not take place in meiosis I.

Describe the roles of cyclins and cyclin-dependent kinases in the cell cycle.

In the cell cycle, cyclins bind to and activate cyclin-dependent kinases (CDKs). Once activated, the CDKs then phosphorylate target proteins involved in promoting cell division.

What is true about gamete formation in mammals?

In the female, the separation of cytoplasm is unequal during meiosis. The cytoplasm is diminished during development of sperm, and a flagellum is formed to give sperm locomotion. Only one of the four cells resulting from meiosis goes on to become an egg, which becomes a zygote upon fertilization by a sperm cell. Only one of the four cells resulting from meiosis goes on to become an oocyte.

What is true regarding the protein CDK?

It binds to cyclin. It functions as a kinase. It functions to control the cell cycle. It is transcribed and translated from a gene present in DNA.

Why does meiosis result in more genetic variation than can be explained by mutation alone?

It creates unique DNA sequence.

What describes the result(s) of crossing over that takes place in meiosis I?

The formation of a DNA molecule that is part maternal and part paternal. The formation of a chromatid that is part maternal and part paternal. Homologous chromosomes are held together. The formation of a chiasma.

Bivalent

The four-stranded structure consisting of two pairs of sister chromatids aligned along their length and held together by chiasmata.

Can you think of two ways in which the function of p53 can be disrupted?

The function of the p53 protein can be disrupted by a mutation in the p53 gene. Alternatively, certain viral proteins, such as the E6 protein of HPV discussed in Case 2: Cancer, can interfere with the function of the p53 protein.

The prokaryotic protein FtsZ is evolutionarily related to eukaryotic tubulin. What does this mean?

The gene sequence for FtsZ is similar to tubulin. The amino acid sequence for FtsZ is similar to tubulin. The overall protein structure of FtsZ is similar to tubulin. The two proteins evolved from a common ancestral protein. The two proteins evolved from a common ancestral protein.

Synapsis

The gene-for-gene pairing of homologous chromosomes in prophase I of meiosis.

Proto-oncogene

The normal cellular gene counterpart to an oncogene, which is similar to a viral oncogene but can cause cancer only when mutated.

Crossover

The physical breakage, exchange of parts, and reunion between non-sister chromatids.

Cell division

The process by which cells make more cells.

Binary Fission

The process by which cells of bacteria or archaeons divide.

The microtubules that form the mitotic spindle extend out from the centrosome. Where would you expect to find the plus (fast assembling) end of a spindle microtubule?

away from the centrosome, at the kinetochore

What reproduces by binary fission?

bacteria archaea chloroplasts mitochondria

Prokaryotic cells divide by

binary fission

How does meiosis generate genetic diversity?

both crossing over and random alignment at metaphase I

During meiosis, the main source of diversity is due to:

crossing over of chromosomes during metaphase I

The amount of _____ is fairly constant throughout the cell cycle, but the amount of _____ varies.

cyclin-dependent kinase/DNA

Eukaryotic cells divide by

Mitosis & Cytokinesis

Reductional Division

An alternative name for meiosis I, since this division reduces the number of chromosomes by half.

How do oncogenes differ from tumor suppressor genes?

An oncogene causes cancer by producing an excess of protein activity that pushes the cell to divide. A tumor suppressor like p53 functions oppositely: Its normal function is to prevent cell division and its absence is what allows the cell to divide uncontrollably.

Describe what an oncogene, a proto-oncogene, and a tumor suppressor gene do.

An oncogene is a gene that causes cancer. A proto-oncogene is a gene that has the potential to cause cancer when mutated. A tumor suppressor gene blocks specific steps in the development of cancer.

Equational Division

Another name for meiosis II because cells in meiosis II have the same number of chromosomes at the beginning and at the end of the process.

Sex Chromosome

Any of the chromosomes associated with sex.

Haploid

Describes a cell with one complete set of chromosomes.

Diploid

Describes a cell with two complete sets of chromosomes.

What is the significance of the small differences between homologous chromosomes?

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

Meiosis II

Equational division, the second stage of meiotic cell division, in which the number of chromosomes is unchanged.

Name two ways in which meiotic cell division creates genetic diversity, and explain how each occurs.

Genetic diversity is created in meiotic cell division by the crossing over of chromosomes and random alignment of bivalents in metaphase I. In crossing over, homologous chromosomes of maternal origin and paternal origin exchange DNA segments, thus creating genetic diversity. Random alignment of bivalents leads to a chromosome set that is a random mix of maternal and paternal homologs.

Why would a compound that interferes with bacterial cell wall synthesis be useful for treating a bacterial infection?

It would limit the spread of the infection through cell division.

Describe how chromosomes behave in meiosis. State when chromosomes are duplicated (forming sister chromatids) and when they are not duplicated.

Meiosis basically consists of two consecutive cell division cycles called meiosis I and meiosis II. Prior to meiosis, chromosomes are duplicated, forming sister chromatids. In meiosis I, homologous chromosomes pair, cross over, and separate into two different daughter cells. During meiosis II, sister chromatids separate into two more daughter cells. The result of this process is four haploid daughter cells, each having unique genetic information.

Compare and contrast mitotic cell division and meiotic cell division in terms of number of products, number of cell divisions, and the processes unique to each.

Mitosis is preceded by one round of DNA synthesis and produces two genetically identical daughter cells, each with 46 chromosomes, in one round of division. Meiosis is also preceded by one round of DNA synthesis, but consists of two rounds of cell division to produce four genetically different daughter cells, with 23 chromosomes each.

The contractile ring that leads to cytokinesis in animal cells has been shown to be made primarily of actin filaments (microfilaments). Which motor protein would you predict is involved in contraction of the ring?

Myosin

Checkpoint

One of multiple regulatory mechanism that coordinate the temporal sequence of events in the cell cycle.

What would happen if a chromosome only connected to the mitotic spindle at one of its kinetochores?

One of the daughter cells would have an extra copy of that chromosome. The sister chromatids would not separate. The chromosome would not line up properly at metaphase.

Homologous Chromosomes

Pairs of chromosomes, matching in size and appearance, that carry the same set of genes; one of each pair was received from the mother, the other from the father.

Compare and contrast the ways in which prokaryotic cells and eukaryotic cells divide.

Prokaryotic cells reproduce through a process called binary fission. During this process, the cell replicates its DNA, increases in size, and divides into two daughter cells, each having one copy of the parental DNA. Eukaryotic cells go through a similar process, albeit more complex, called mitotic cell division. In this process, cells first replicate their chromosomes in the nucleus. The nuclear envelope then dissolves and each pair of chromosomes is divided by connecting to the mitotic spindle. Once the two full sets of chromosomes are separated, a nuclear envelope forms around each one. The cell then goes through a process called cytokinesis, where it is split into two new daughter cells. Binary fission is like mitosis in many ways although it differs in a few key aspects: (1) The size and shape of the genetic material; bacteria have a single circular chromosome, whereas eukaryotic cells generally have multiple linear chromosomes. (2) The DNA of prokaryotes is attached to the plasma membrane, allowing separation of DNA into the daughter cells by cell growth. Eukaryotic cells have to first dissolve the nuclear membrane and then reform it to separate DNA.

Meiosis I

Reductional division, the first stage of meiotic cell division, in which the number of chromosomes is halved.

When in the cell cycle would you find sister chromatids?

S and G2

Which DNA sequences are more alike: a pair of sister chromatids or a pair of homologous chromosomes?

Sister chromatids are the result of DNA replication during S phase, and so they have identical DNA sequences (with the exception of a few changes due to rare mutations). The two homologous chromosomes are inherited from two different parents. The DNA sequences of these chromosomes are therefore similar, but not identical.

What is true about the eukaryotic cell cycle?

Some cells pause between M phase and S phase for more than a year. The M phase consists of two events: mitosis and cytokinesis. There are three phases of interphase: the S phase and two gap phases. There are two stages to the cell cycle: M phase and interphase.

How must spindle microtubules attach to chromosomes during prometaphase of meiosis I?

Spindle microtubules from one pole must attach to both kinetochores in a pair of sister chromatids.

Name the five steps of mitosis.

The five steps in mitosis are: (1) prophase (chromosomes condense, centrosomes radiate spindle microtubules and migrate to opposite poles), (2) prometaphase (microtubules of the mitotic spindle attach to chromosomes), (3) metaphase (chromosomes align in center of cell), (4) anaphase (sister chromatids separate and travel to opposite poles), and (5) telophase (nuclear envelope re-forms and chromosomes decondense).

Paramecium is a single-cell eukaryotic organism that can reproduce by mitotic cell division. Prior to the M phase of the cell cycle, what must occur?

The cell must replicate its chromosomes.

If a cell has a mutation in the p53 gene such that the p53 protein is no longer able to be phosphorylated, ________

The cell would proceed through the cell cycle even in the presence of DNA damage.

What would happen to the daughter cells if the G2 phase of the parent cell is shortened?

The cells would be smaller than normal.

Cell Cycle

The collective name for the steps that make up eukaryotic cell division.

Zygote

The diploid cell formed by the fusion of two gametes.

The genetic constitution of each cell after telophase II is different from the others. What two processes during meiosis result in these differences?

The products of meiosis are different from each other as a result of two key processes: (1) crossing over, which occurs at essentially random positions along the chromosomes and creates unique combinations of genetic differences that may be present in the maternal and paternal chromosomes, and (2) random orientation of the homologous chromosomes on the spindle in metaphase I, so each nucleus receives a random combination of maternal and paternal homologs.

Kinetochore

The protein complexes on a chromatid where spindle fibers attach.

Asexual Reproduction

The reproduction of cells or single-celled organisms by cell division; offspring are clones of the parent.

Sister Chromatids

The two copies of a chromosome produced by DNA replication.

Why are the X and Y chromosomes not considered homologous?

They do not carry the same set of genes, and mammalian males carry two very different sex chromosomes.

Give three examples of checkpoints that the cell monitors before proceeding through the cell cycle.

Three examples of checkpoints during the cell cycle are (1) the spindle assembly checkpoint, which is active before anaphase and ensures that all chromosomes are attached to the spindles; (2) the DNA damage checkpoint, which is active in the G1 phase and checks for DNA damage; and (3) the DNA replication checkpoint, which is active in G2 and makes sure all the DNA is replicated.

Describe three situations in which mitotic cell division occurs.

Three situations in which mitotic cell division occurs are in the development of multicellular organisms, maintenance and repair of organs and tissues, and asexual reproduction of unicellular eukaryotes.

During what step in meiosis do the daughter cells become haploid?

anaphase I

When do sister chromatids separate in meiosis?

anaphase II

A zygote is:

diploid.

At the end of mitosis the daughter cells are ____________, whereas at the end of meiosis the daughter cells are ____________.

diploid; haploid

What has the MOST similarity in nucleotide sequences?

sister chromatids

Synapsis is best described as:

the pairing of homologous chromosomes in prophase I.