BIO 317: Unit 1

Ch. 2

What are the two classifications of all living things?

Prokaryotes and Eukaryotes.

What is a prokaryote?

A unicellular organism that have two domains: bacteria (eubacteria or true bacteria) and archaea. They do not have a nucleus or membrane-bound organelles, so genetic material is in close contact with other cellular components, affecting gene expression control. The cell diameter is small, with only one circular DNA molecule that floats in the cytoplasm. They reproduce via binary fission.

What is a eukaryote?

A multicellular organism that has compartmentalized structures with components bound by intracellular membranes (organelles), containing a nucleus with lots of linear-stranded DNA. This DNA is tightly packed into chromosomes via histone proteins (combined structure called chromatin). The cell usually has a larger diameter. They can reproduce via sexual (meiosis/fertilization) or asexual (mitosis) reproduction.

What is the complex called that contains DNA and histones?

Chromatin

Are viruses considered prokaryotic or eukaryotic? Why?

They are neither. This is because they do not have the structure of a cell. They are relatively simple structures composed of an outer protein coat surrounding nucleic acid (either DNA/RNA). They only reproduce in host cells.

Why are viruses useful?

They can help study molecular processes because of the simplicity and small genome that the cell contains. For example, bacteriophage (infect bacteria) are used to study gene expression, recombination, and molecular evolution.

What is the criteria for any cell to reproduce successfully?

1. its genetic information must be copied.

2. the copies must be separated from each other.

3. the cell must divide.

How do prokaryotes reproduce?

Binary fission

What is binary fission?

It is the method of reproduction for prokaryotes. It is relatively simple. A singular circular chromosome is replicated, resulting in two origins of replication. They are anchored on opposite sides of the cell via proteins, and then the cell divides to produce identical daughter cell copies of the original chromosome.

Do prokaryotes or eukaryotes have a higher rate of replication?

Prokaryotes

How do eukaryotes reproduce?

It is a complex process. They either go through sexual (meiosis/fertilization) or asexual (mitosis) reproduction.

Multiple chromosomes have to be replicated and sorted equally and precisely into two daughter cells, which is assisted by the nuclear matrix. There are two protein fibers (nuclear lamina and internal matrix protein) that help linear chromosomes sort equally into daughter cells.

What is a somatic cell?

Any cell except for reproductive cells.

What is a diploid cell?

Contains two sets of each chromosome (human diploid cell: 2n = 46).

What is a haploid cell?

Contains one set of each chromosome (human haploid cell: n = 23).

Diploid cells have:

two sets of chromosomes.

What is a centromere?

The physical location (DNA sequence) on a chromosome where the kinetochore and spindle microtubules attach.

What are kinetochores?

This is composed of proteins that assemble on the centromere to provide a site for the spindle microtubules to attach.

What are telomeres?

Protective tips of a linear chromosome (one on each end).

What is the origin(s) of replication?

Where the DNA synthesis begins; a eukaryotic chromosome has many origins, while prokaryotic chromosomes (after replication) typically only have one.

What would be the result if a chromosome did not have a kinetochore?

The spindle microtubules would not be able to attach to pull the sister chromatids apart, so one daughter cell would be missing a chromosome.

What is the life/cell cycle?

Interphase (G1, Go, S, G2) and M (mitosis) phase.

What is interphase?

An extended period between cell divisions where the cell grows, and DNA synthesis and chromosome replication occurs. It is the longest part of the cell cycle.

What are phase checkpoints?

Key transition points that regulate cell-cycle progression. Passed only when key requirements are met or else the cell will be arrested. There are three: G1/S, G2/M, and spindle-assembly checkpoint.

What happens during the G1/S checkpoint?

This is the most important checkpoint, as after this, the cell is committed to dividing. There is a confirmation that there are enough protein and cell materials to complete DNA replication.

What happens during the G2/M checkpoint?

Cell checks to see if DNA is completely replicated and undamaged before entering mitosis.

What is Go?

A non-dividing phase, where the cell exits active cell division cycle. They do so if they lack the required growth factors or nutrients to pass the G1/S checkpoint. This is reversible though, they can reenter the cell cycle.

What does the M phase consist of?

Mitosis and cytokinesis

What is mitosis?

The separation of sister chromatids via 5 steps: prophase, prometaphase, metaphase, anaphase, telophase.

What is cytokinesis?

The second part of the M phase, where there is complete separation of the cytoplasm.

What is prophase?

The first step to mitosis, in which chromosomes condense. Each chromosome possesses two chromatids (due to replication during S phase). The mitotic spindle forms and stretch from centrosome.

What is prometaphase?

This is the second stage of mitosis. The nuclear membrane disintegrates. Spindle microtubules attach to chromatids at the kinetochore.

What is a centrosome?

A small, non-membrane-bound organelle found in animal cells that acts as the main microtubule-organizing center. It organizes cell structure and guides the creation of the mitotic spindle needed to separate chromosomes during cell division.

What is metaphase?

The third step of mitosis. Chromosomes line up on the metaphase plate.

What is anaphase?

The fourth stage of mitosis. Sister chromatids separate and move toward opposite poles. The two replicated chromosomes, upon their split, become unreplicated chromosomes (singular).

What is telophase?

The final step of mitosis, in which chromosomes arrive at spindle poles. The nuclear membrane re-forms and the chromosomes relax.

What is cytokinesis?

The step that follows telophase in the M phase, but it is not apart of mitosis. The cytoplasm separates here.

What are spindle microtubules composed of?

Composed of alpha and beta subunits that polymerize.

How do spindle microtubules do their job? What assists them?

During anaphase, when sister chromatids are being pulled apart, molecular motors disassemble tubulin molecules and generate forces that pull the chromosome toward the spindle pole (where centrosomes are located) via tension at the kinetochores.

What does the spindle-assembly checkpoint do?

During metaphase, this ensures that each chromosome is aligned on the metaphase plate and attached to spindle microtubules from opposite poles.

What is true about the genetic variation in asexual reproduction?

There is none. The daughter cells are genetically identical to the mother cells.

What is meiosis?

The production of haploid gametes via meiocytes. The process follows the same order as mitosis: prophase, metaphase, anaphase, telophase; however, the process is repeated twice, as the cell undergoes a chromosomal reduction to produce a haploid gamete.

What is fertilization?

The fusion of haploid gametes. This can come from the same individual (self-fertilization) or two different (cross-fertilization or crossing).

True or False: Meiosis can begin only in diploid cells.

True.

What are the cells that undergo meiosis called?

Meiocytesh

What are meiocytes?

The diploid cells that undergo meiosis.

What is polyploidy?

More than two sets of chromosomes in a cell (3n, 4n, etc.).

Describe meiosis I.

Separation of homologous chromosome pairs, and reduction of the chromosome number by half to produce haploid cells. This follows these steps: prophase I, metaphase I, anaphase I, telophase I, and then interkinesis. This is also known as the reduction division phase.

Describe meiosis II.

Separation of sister chromatids (similar to mitosis; however, occurs in haploid cell), also known as equational division. This follows these steps: prophase II, metaphase II, anaphase II, and telophase II.

What happens during prophase I?

Chromosomes condense and homologous chromosomes pair up, forming a tetrad/bivalent and begin synapsis. The synaptonemal complex develops to fix homologs together. This allows for crossing over to occur at the chiasma.

There are 5 subsections where each step described above occurs specifically: leptotene, zygotene, pachytene, diplotene, and diakinesis.

What is synapsis?

Close pairing of homologs, forming bivalents (or tetrads).

What are bivalents/tetrads?

The formation of closely associated four-sister chromatids of two homologs during prophase I of meiosis.

What is crossing over?

The exchange of genetic material from the sister chromatid of one chromosome to the sister chromatid of the other synapsed chromosome (between non-sister chromatids). This is the first mechanism of generating genetic variation in newly formed gametes, which occurs during prophase I.

What is the chiasma?

The physical location where two non-sister chromatids cross during prophase I.

What is leptotene?

The first substep of prophase I, in which chromosomes contract and become visible.

What is zygotene?

This is the second substep of prophase I, in which chromosomes continue to condense and homologs pair up and begin synapsis.

What is pachytene?

This is the third substep of prophase I, in which chromosomes become shorter and thicker, and the synaptonemal complex develops between the homologs.

What is the synaptonemal complex?

A complex that forms during pachytene (the third substep of prophase I), in which a group of proteins work like glue to fix homologs to each other to form a stable tetrad.

What is diplotene?

This is the fourth substep of prophase I, in which centromeres of paired chromosomes move apart; the two homologs remain attached at each chiasma.

What is diakinesis?

The fifth substep of prophase I, in which chromosomal condensation continues, the nuclear membrane breaks down, and the spindle forms and attaches to microtubules.

How many bivalents are there in a human cell during prophase I?

23

What happens during metaphase I?

There is random alignment of homologs along the metaphase plate.

What happens during anaphase I?

Separation of homologs, and the random distribution of chromosomes into two newly divided cells (second mechanism of generating genetic variation in newly formed gametes - random/independent assortment).

What happens during telophase I? What follows?

Chromosomes arrive at the spindle poles and the cytoplasm divides. Interkinesis follows, with the nuclear membrane reforming and chromosomes decondensing.

What happens during prophase II?

Chromosomes re-condense; spindle re-forms; nuclear envelope breaks down.

What happens during metaphase II?

Replicated chromosomes line up on the metaphase plate.

What happens during anaphase II?

Sister chromatids separate and pulled to opposite poles.

What happens during telophase II?

Chromosomes decondense; spindle breaks down; nuclear envelope re-forms.

True or False: Some cells forgo telophase I and interkinesis, jumping straigh to metaphase II during meiosis.

True. This is true of some cells so they can avoid decondensing and recondensing chromosomes.

How can you determine the number of possible combinations that can result from meiosis?

2^n (n = the number of bivalent or homologs)

How can you determine the number of ways chromosomes can line up during metaphase I?

2^n ½ (n = the number of bivalent or homologs). ******** stopped here and added quiz and test questions

Which of the following occurs during the prometaphase of mitosis?

Spindle fibers attach to kinetochores.

Genetically speaking, prokaryotes are different from eukaryotes because:

prokaryotes usually have one main circular chromosome, whereas eukaryotes have multiple linear chromosomes.

Which structural component of a eukaryotic chromosome is the attachment point for spindle microtubules during the M phase?

Kinetochore

In female animals, the cell capable of being fertilized is the:

ovum.

Which of the following processes is unique to plants (and not found in animals)?

Double fertilization

In which stage of meiosis do bivalents become aligned in the middle of the cell?

Metaphase I

Which of the following crosses would produce a 1:1 ratio of phenotypes in the next generation?

 

Aa x aa

If an AABbCcdd individual is crossed to an AaBbccDD individual, what is the probability that the first offspring will be of the AaBbCcDd genotype?

1/8

Individuals with aa genotype are affected by a recessive disorder, whereas AA and Aa individuals have a normal phenotype.  A man with genotype Aa and a woman with genotype Aa are planning on having four children.  What is the probability that exactly two of their four children will be affected?

0.211

If genes assort independently, a testcrossed dihybrid characteristically produces progeny phenotypes in the ratio:

 

1 : 1 : 1 : 1

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b, respectively. What is the probability of producing an offspring with the AB phenotype from a cross of AaBb x AaBb?

9/16

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b, respectively. What is the probability of producing an "AB" gamete from an AaBb individual?

1/4

The sex determination system used by Drosophila is called:

the X:A sex determination system.

An XXY chromosome constitution produces _____ development in humans and _____ development in fruit flies.

male ; female

How many Barr bodies are present in an individual with Klinefelter syndrome (XXYY)?

1

A researcher discovers a new unicellular organism with a prokaryotic-like cell (no nucleus, single circular chromosome) whose RNA polymerase is structurally similar to that of eukaryotes. Based on the classification framework described in this chapter, which domain would this organism most likely belong to?

Archaea

Genetically speaking, prokaryotes are different from eukaryotes because:

prokaryotes usually have one main circular chromosome, whereas eukaryotes have multiple linear chromosomes.

Which of the following occurs during prophase?

Mitotic spindles form

Which of the following is NOT associated with binary fission?

Centrosomes

During the cell cycle, DNA is replicated during the ___ phase, and nuclear division occurs during the ___ phase.

S ; M

During which subphase of interphase does the cell undergo DNA synthesis to duplicate its genetic material?

S phase

Which of the following occur during prometaphase of mitosis?

Spindle microtubules attach to chromatids. Nuclear membrane disintegrates.

Mice (Mus musculus) have 40 chromosomes per diploid cell (2n = 40). How many double-stranded DNA molecules and how many chromosomes are there in a mouse cell that is in the G2 stage of the cell cycle?

80 DNA molecules and 40 chromosomes.

Which of the following processes is unique to plants (and not found in animals)?

Double fertilization

In which stage of meiosis do bivalents become aligned in the middle of the cell?

Metaphase I

What is the term for the structure that results from the pairing of two homologs during prophase I?

tetrad/bivalent

Sexual reproduction in eukaryotes universally consists of which two foundational processes?

Meiosis and fertilization

During prophase I, ______ protects centromeric cohesin from being cleaved by seperase, ensuring that ____ remain together until meiosis II.

shugoshin ; sister chromatids

A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX (females) and XY (males). What is the total number of telomeres in a rat cell in G2?

168

Nuclear membrane disintegrates during which phase?

Prometaphase