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exam study
cellular reproduction
| Question | Answer |
|---|---|
| How does cell division in prokaryotes take place? | Cell division in prokaryotes takes place in two stages, which together make up a simple cell cycle. Copy the DNA. This process is called replication. Split the cell in two to form daughter cells. This process is called binary fission. |
| How is hereditary information stored in a prokaryote? | The hereditary information in a prokaryote is stored in DNA (same as any other organism). The prokaryotic chromosome is a single circle of DNA. |
| How does DNA replication begin in prokaryotes? | DNA replication begins with the unzipping of the double-stranded DNA at a point called the origin of replication. A new double helix is formed by adding complementary nucleotides to the exposed DNA strands that have been unzipped. |
| What reproductive mechanisms do bacteria use to increase genetic variation? | conjugation: acquire DNA from other bacteria (pili) transformation: acquire DNA from surroundings transduction: acquire DNA from viruses |
| How is DNA packaged in eukaryotic cells? | DNA in eukaryotic cells is linear and packaged into a compact chromosome. |
| What are mitosis and meiosis? | Mitosis is a cell division mechanism that occurs in somatic cells. Meiosis is a cell division mechanism that occurs in germ cells. |
| What are the phases of the eukaryotic cell cycle? | Interphase (G₁, S, and G₂ phases) Mitosis (M phase) Cytokinesis (C phase) |
| What are homologous chromosomes and sister chromatids? | Homologous chromosomes contain the same genes but they may have different variations of those genes, which are called alleles. |
| What are homologous chromosomes and sister chromatids? (continued) | One homologous chromosome is obtained from each parent. Sister chromatids are exactly the same and are a result of DNA replication. |
| What is a karyotype? | Condensed chromosomes first become visible. The nuclear envelope begins to disintegrate. The nucleolus disappears. Centrioles separate in the centre of the cell and migrate to opposite ends (“poles”) of the cell. |
| What is a karyotype? (continued) | The centrioles start to form a network of spindle fibres. Each cable in the spindle is made of microtubules. |
| What happens during Metaphase of mitosis? | The chromosomes attached to microtubules of the spindle are aligned in the centre of the cell. The centromeres are aligned along an imaginary plane that divides the cell in half; this is known as the equatorial plane. |
| What happens during Anaphase of mitosis? | Sister chromatids separate. Enzymes break the cohesin and the kinetochores. The microtubules of the spindle are dismantled, starting at the poles. This pulls the chromatids toward the poles. |
| What happens during Telophase of mitosis? | The spindle is dismantled. A nuclear envelope forms around the set of chromosomes at each pole. The chromosomes begin to become uncondensed. The nucleolus reappears. |
| What is cytokinesis? | Cytokinesis occurs at the end of mitosis and is a division of the cytoplasm into roughly equal halves. |
| What is cytokinesis? (continued) | In animals, cytokinesis occurs by actin filaments contracting and pinching the cell in two. This action is evident as a cleavage furrow that appears between the daughter cells. |
| What are the three principal checkpoints in the cell cycle? | G₁, G₂, and M checkpoints. |
| What is cancer? | Cancer is a growth disorder of cells. It begins when apparently normal cells grow uncontrollably and spread to other parts of the body. The result is a growing cluster of cells called a tumor. |
| What is the difference between benign and malignant tumors? | Benign tumors are surrounded by a healthy layer of cells (also known as encapsulated) and do not spread to other areas. |
| What is the difference between benign and malignant tumors? (continued) | Malignant tumors are not encapsulated and are invasive. Cells from malignant tumors leave and spread to different areas of the body to form new tumors. These cells are called metastases. |
| What causes cancer? | Cancer is caused by a gene disorder in somatic tissue in which damaged genes fail to properly control the cell cycle. Mutations cause damage to genes. |
| What causes cancer? (continued) | They may result from chemical or environmental exposure, such as UV rays. Viral exposure may also alter DNA. |
| What are proto-oncogenes and tumor-suppressor genes? | Proto-oncogenes These genes encode proteins that stimulate cell division. Mutations to these genes can cause cells to divide excessively. When mutated, these genes become oncogenes. |
| What are proto-oncogenes and tumor-suppressor genes? (continued) | Tumor-suppressor genes These genes normally turn off cell division in healthy cells. When mutated, these genes allow uncontrolled cell division. |
| Why does meiosis occur? | To produce gametes (sperm or eggs). Gametes are haploid cells (have half the normal amount of DNA). |
| What happens in meiosis I and meiosis II? | Meiosis I separates the homologous pairs. Meiosis II separates the sister chromatids. |
| What are the stages of Meiosis I? | Prophase I Homologues pair up and exchange segments. Metaphase I The paired homologous chromosomes align at the equatorial plane. |
| What are the stages of Meiosis I? (continued) | Anaphase I Homologues separate from the pairing and move to opposite poles. Telophase I Individual chromosomes gather at each of the two poles. |
| What are the stages of Meiosis II? | Prophase II After a brief interphase with no DNA replication, new spindle fibres form. Metaphase II The sister chromatids align at the equatorial plane. |
| What are the stages of Meiosis II? (continued) | Anaphase II Sister chromatids separate from the pairing and move to opposite poles. Telophase II Individual chromosomes gather at each of the two poles, and a new nuclear envelope forms. |
| What are the three mechanisms that produce genetic variation? | Independent assortment Crossing over Random fertilization—one of 8 million different sperm can fertilize the egg. |
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oliviavanwort
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