The Mitotic Cell Cycle Flashcards
What are chromosomes made of?
Chromosomes are made of two identical structures called chromatids, which are joined together.
What are sister chromatids?
Sister chromatids are the two identical chromatids of a chromosome, formed when DNA makes an identical copy of itself during interphase.
What holds sister chromatids together?
Sister chromatids are held together by a narrow region called the centromere.
Why are sister chromatids genetically identical?
Each chromatid contains an identical DNA copy, so the genes in both chromatids are the same.
What happens to sister chromatids during cell division?
One chromatid goes into one daughter cell and the other goes into the other daughter cell, making the daughter cells genetically identical.
What is chromatin?
Chromatin is the combination of DNA and proteins that make up chromosomes.
What type of proteins are found in chromosomes, and why?
Chromosomes contain histone proteins, which are basic and interact easily with DNA, which is acidic.
What are two more essential features of chromosomes for nuclear division?
Chromosomes have centromeres (which hold chromatids together) and telomeres (which protect the ends of chromosomes).
What happens during interphase?
During interphase, the cell grows to its normal size, carries out normal functions, and prepares for division. It consists of three phases: G1, S, and G2.
What happens during the S phase of interphase?
The S phase (Synthesis phase) is when DNA replicates, forming two identical chromatids for each chromosome in preparation for cell division.
What happens during the G1 and G2 phases of interphase?
• G1 phase (the gap after cell division and before the S phase): The cell grows, produces RNA, enzymes, and proteins for growth, and decides whether to divide.
• G2 phase (the gap after the S phase and before cell division): The cell continues to grow, checks and repairs new DNA, and prepares for division by producing proteins like tubulin which is needed to make microtubules for the mitotic spindle.
What happens during the M phase?
The M phase (Mitosis) is when the nucleus divides, followed by cytokinesis, where the whole cell splits into two genetically identical cells. In animal cells, this happens by constriction of the cytoplasm, while in plant cells, a new cell wall forms between the nuclei.
Describe the importance of mitosis.
- Growth of multicellular organisms - the two daughter cells formed after mitosis have the same number of chromosomes as the parent cell and are genetically identical. This allows growth of multicellular organisms from unicellular zygotes.
- Replacement of damaged or dead cells and repair of tissues by cell replacement - this is possible using mitosis followed by cell division.
- Asexual reproduction - the production of new individuals of a species by a single parent organism. The offspring is genetically identical to the parents.
- Immune response - the cloning of B and T lymphocytes during the immune response is dependent on mitosis.
Describe the role of telomeres.
The main function of telomeres is to ensure that the ends of the molecule are included in the replication and not left out when DNA is replicated. Telomeres are found at the ends of chromosomes. Telomeres work by making the DNA a bit longer. They have no useful information but allow the copying enzyme to complete copying all the meaningful DNA. The enzyme that performs the role of adding basis to telomeres is called telomerase. The main function of telomeres is therefore to prevent the loss of genes during cell division and to allow continued replication of a cell.
What are benign and malignant tumours?
Benign tumours do not spread from their site of origin. Malignant tumours interfere with the normal functioning of the area where they have started to grow. They may block the intestines, lungs or blood vessels. Cells can break off and spread throughout the blood and lymphatic system to other parts of the body to form secondary growths. The spread of cancers in this way is called metastasis.
Describe the stages in the development of cancer.
- Carcinogens cause mutations, e.g. UV light, tar in tobacco smoke, asbestos, X-rays
- Oncogenes transformed by carcinogens
- Cancerous cells do not respond to signals from other cells so continues to divide by mitosis
- Cancerous cells not removed by immune system, absorb nutrients, rapid mitosis
- Tumour gets bigger, cells change their characteristics and look different under the microscope
- Tumour supplied with blood and lymph vessels. Tumour cells spread in blood and lymph to other parts of the body
- Metastasis. Tumour cells invade other tissues. Secondary cancers form throughout the body.
What is the role of centrosomes in mitosis?
Centrosomes are organelles in animal cells that act as microtubule organizing centers. They produce the spindle, which is needed for separating chromatids during mitosis. However, plant mitosis occurs without centrosomes.
What is the function of the centromere in mitosis?
The centromere holds sister chromatids together and plays a crucial role in their separation. It serves as the attachment site for spindle microtubules and helps pull chromatids to opposite poles during anaphase.
What are kinetochores and what is their function?
Kinetochores are protein structures located at the centromere of each chromatid. They connect the centromere to the spindle microtubules and help pull chromatids toward the spindle poles during mitosis.
How do microtubules contribute to chromatid movement during mitosis?
Microtubules, forming spindle fibers, attach to kinetochores and pull chromatids toward the spindle poles. This movement is achieved by the shortening of microtubules from both the pole end and the kinetochore end.
Why do chromatids have a ‘>’ or ‘<’ shape during anaphase?
As microtubules pull chromatids toward the spindle poles, the kinetochore moves first while the rest of the chromatid drags behind, creating a characteristic ‘>’ or ‘<’ shape.
