Cell Division, Chromatin, and Cell Cycle Regulation in Biology

What process do bacteria use to divide?

Binary fission.

What is the name of the starting point for bacterial chromosome replication?

Origin of replication (Ori).

During binary fission, in what direction does replication proceed?

Bidirectionally around the circular chromosome.

What structure forms to divide a bacterial cell into two cells?

Septum.

What protein assembles into a ring at the midpoint of a bacterial cell during division?

FtsZ protein.

What happens to bacteria that have a mutated FtsZ gene?

They cannot properly form a septum and fail to divide.

Why is bacterial DNA replication sometimes called 'theta replication'?

Because the replication process forms a structure resembling the Greek letter theta (θ).

What is chromatin composed of?

DNA and histone proteins.

Define a nucleosome.

A unit of chromatin consisting of DNA wrapped around histone proteins.

What are the proteins that help hold radial DNA loops in place?

Scaffold (SMC) proteins.

What protein complex aids chromosome condensation?

Condesin.

Differentiate between heterochromatin and euchromatin.

Heterochromatin is tightly packed and inactive; euchromatin is loosely packed and active.

According to the ENCODE project, approximately what percentage of the human genome is active?

About 80%.

What does ENCODE stand for?

Encyclopedia of DNA Elements.

Define ploidy.

The number of sets of chromosomes in a cell.

How many chromosomes are found in a human diploid cell?

46 chromosomes.

What is the difference between homologous chromosomes and sister chromatids?

Homologous chromosomes have the same genes but different parental origins; sister chromatids are identical copies.

What is a karyotype?

A display of all chromosomes arranged by size and shape.

What holds sister chromatids together after DNA replication?

Cohesin proteins.

At what point in the cell cycle are chromosomes replicated?

S phase.

List the five main phases of the eukaryotic cell cycle.

G1, S, G2, mitosis (M), cytokinesis.

Which phase is typically the longest in the cell cycle?

G1 phase.

What happens during the S phase?

DNA is replicated.

What occurs during the G2 phase?

Preparation for mitosis; organelles and proteins needed for division are produced.

What is the function of centrioles during the cell cycle?

They help organize the spindle apparatus.

During which phase does the spindle apparatus begin to assemble?

Prophase.

Name the five stages of mitosis in order.

Prophase, prometaphase, metaphase, anaphase, telophase.

During which phase do chromosomes first become visible?

Prophase.

What happens to the nuclear envelope during prophase?

It breaks down.

During which phase do chromosomes attach to spindle fibers?

Prometaphase.

What structure connects spindle fibers to chromosomes?

Kinetochore.

What causes chromosomes to move during prometaphase?

Microtubules attach to kinetochores and exert pulling forces.

What is the metaphase plate?

An imaginary plane where chromosomes align during metaphase.

During which phase do sister chromatids separate?

Anaphase.

What is the difference between anaphase A and anaphase B?

Anaphase A involves movement of chromatids to poles; anaphase B involves separation of spindle poles.

What happens to the spindle apparatus during telophase?

It disassembles.

What reappears in each nucleus during telophase?

Nuclear envelope and nucleolus.

What is cytokinesis?

Division of the cytoplasm into two daughter cells.

How does cytokinesis differ in animal and plant cells?

Animal cells form a cleavage furrow; plant cells form a cell plate.

What cytoskeletal component forms the cleavage furrow in animal cells?

Actin filaments.

What structure forms between nuclei in plant cells during cytokinesis?

Cell plate.

In which organisms does mitosis occur within the nucleus before cytokinesis?

Fungi and some protists.

Name the three main checkpoints of the cell cycle.

G1/S checkpoint, G2/M checkpoint, spindle (M) checkpoint.

What is the main decision point where the cell commits to divide?

G1/S checkpoint (restriction point).

What proteins regulate passage through the checkpoints?

Cyclins and cyclin-dependent kinases (Cdks).

What role do growth factors play in cell cycle regulation?

They signal cells to divide by activating Cdks.

What is the function of Platelet-Derived Growth Factor (PDGF)?

Stimulates cell division in connective tissue and promotes wound healing.

What are the two major categories of genes that can cause cancer when mutated?

Proto-oncogenes and tumor suppressor genes.

How many copies of a proto-oncogene must be mutated for cancer to occur?

One copy.

What is the role of the p53 gene in preventing cancer?

It halts the cell cycle when DNA is damaged and can trigger apoptosis if the damage is irreparable.