Genetics-Cell Cycle

What are the three traditional disciplines in the study of genetics?

Transmission genetics, molecular genetics, population genetics.

Name 3 model organisms used in genetics and what type of biology they model.

• E. coli – molecular genetics and basic cellular processes.

• Drosophila melanogaster (fruit fly) – development and genetics.

• Mus musculus (mouse) – human disease and mammalian biology.

Name 3 differences between DNA of prokaryotes and eukaryotes.

1. Prokaryotic DNA is circular; eukaryotic is linear.

2. Prokaryotes lack histones; eukaryotic DNA is wrapped around histones.

3. Prokaryotes have one origin of replication; eukaryotes have multiple origins.

Why is DNA packing important in eukaryotes?

It allows long DNA molecules to fit inside the nucleus and regulates gene expression

What cells go through the cell cycle?

Eukaryotic cells.

What does homology mean for genes, and how is it determined?

Homology refers to genes derived from a common ancestor; determined by comparing DNA or protein sequences.

What is the normal time for a cell to complete a cell cycle?

It varies by cell type; typical mammalian cells take ~24 hours; there is no universal normal time.

What stage of the cell cycle deals with nuclear division?

M phase (mitosis)

What are the 3 stages of interphase and their events?

• G1: Cell growth and preparation for DNA replication.

• S: DNA replication.

• G2: Preparation for mitosis, organelle replication.

What is the resting (quiescent) stage? Give examples.

G0 phase; cells like neurons or muscle cells exit the cycle but remain functional.

What are the stages of the cell cycle?

G1, S, G2, M, and G0.

What are the major cell cycle checkpoints and what do they check?

• G1 checkpoint: Checks for DNA damage before S phase.

• G2 checkpoint: Ensures DNA replication is complete and accurate.

• M checkpoint: Ensures chromosomes are attached to spindle before separation.

What is cytokinesis, and how does it differ in animals vs plants?

Cytokinesis divides cytoplasm; animals form a cleavage furrow, plants form a cell plate.

What happens at the restriction point in the cell cycle?

Cell commits to division; regulated by Rb protein, cyclins, CDKs.

What do chromosomes look like in G1, G2, and PMAT?

• G1: Single chromatid, uncondensed.

• G2: Replicated but uncondensed.

• PMAT: Condensed into X-shaped chromosomes.

What are the essential structural elements of eukaryotic chromosomes?

Centromere (CEN), telomere, kinetochore.

How can you identify chromosomes in a karyotype?

Size, banding pattern, centromere position.

What are microtubules made of and their function?

Tubulin; they form spindle fibers that attach to centromeres and move chromosomes

During which subphase do microtubules grow and shrink?

Grow during prophase/prometaphase; shrink during anaphase.

How do Rb, CDK, and cyclins determine cell division?

Cyclins activate CDKs; CDKs phosphorylate Rb, releasing E2F to promote division. Mutations can lead to cancer.

What is cancer? Does it usually arise from a single mutation?

Uncontrolled cell growth; usually arises from multiple mutations; tumor suppressors prevent this.

What are “beads on a string”?

Nucleosomes (beads) of DNA wrapped around histones connected by linker DNA (string).

What are nucleosomes made of?

DNA wrapped around histone proteins (H2A, H2B, H3, H4).

By what factor does DNA get packed to fit into a nucleus?

Approximately 10,000-fold