5.0 The Mitotic Cell Cycle Flashcards
Structure of the Chromosome
1. DNA:
- chromosome composed of a long molecule of DNA
- double-stranded helix made up of nucleotides - each nucleotide consists of a sugar, phosphate group, and nitrogenous base
- sequence of these bases encodes genetic information
- highly organized and condensed to fit within the nucleus
2. HISTONE PROTEINS:
- DNA is tightly wrapped around histone proteins forms nucleosome
- Each nucleosome consists of a segment of DNA wound around a core of eight histone proteins
- nucleosomes further coil and fold to create a more compact structure, allowing the long DNA molecule to be efficiently packaged within the chromosome
- This complex of DNA and histone proteins is referred to as chromatin
3. SISTER CHROMATIDS:
- After DNA replication, chromosome consists of two identical DNA molecules, forming a sister chromatid
- joined together by the centromere
- sister chromatids remain connected until they are separated into individual chromosomes during mitosis or meiosis
4. CENTROMERES:
- a constricted region of the chromosome where the two sister chromatids are most tightly connected
- essential for the proper segregation of chromosomes during cell division
- serves as the attachment point for spindle fibers (spindle fibre connects to kniteochore)
- ensures that sister chromatids are pulled apart and distributed to each daughter cell equally.
5. TELOMERES:
- repetitive nucleotide sequences located at the ends of chromosomes
- protect ends of the chromosome from degradation and prevent them from being mistaken for DNA breaks that need repair
- vital role in maintaining the stability of the chromosome and prevent the loss of essential genetic information during DNA replication
- They also contribute to the regulation of cellular aging, as they shorten with each round of cell division
importance of mitosis
- replacement of cells (NOT REPAIR)
- repair of tissue
- repair of tissue by cell replacement
- growth / increase in cell numbers
- asexual reproduction / vegetative
- maintaining same number of chromosomes : Ensures genetic stability / new cells can retain function
- genetically identical to parents
- produces daughter cells that are genetically identical
- Cloning of B and T-lymphocytes during immune response
mitotic cycle
INTERPHASE:
1. G1:
- 46 chromosomes and chromatids
- producing RNA, proteins and enzymes
2. S PHASE:
- synthesis of DNA
- each chromosome consists of two identical chromatids
- 46 chromosomes and 92
chromatids
- Chromatin also replicates along with DNA so histones are replicated
2. G2:
- New DNA checked, and errors are repaired
- Sharp increase in the production of tubulin to make microtubules for the formation of mitotic spindle
- Nuclear envelope envelopes nucleus
MITOSIS:
- refer to picture
CYTOKINESIS:
- division of cytoplasm between daughter cells, last stage of cell division
- refer to picture
NOTE:
- nuclear envelope breaks down into vesicles during prophase and reassembles when the vesicles fuse to form the envelope back at telophase
Role of Telomeres
- repeated short base sequence at end of chromosome (by telomerase)
- permit continued replication
- prevent loss of genes
- protect ends of chromosomes from being, degraded (reduction in length of chromosome)
Importance of Stem Cells
DEFINITION:
- cells that divide repeatedly by mitosis, and differentiate into specialized cells or remain as stem cells.
TYPES:
- Totipotent: cells that can divide repeatedly to form any other cell in the body, e.g.: zygote
- Pluripotent: embryotic stem cells that lead to development of the embryo and later the adult. They are not specialized into placenta.
- Multipotent: Adult stem cells that are only able to produce a few types of cells e.g. stem cells in bone marrow. Their telomeres don’t shorten as telomerase is present and active. Its activity is diminished after birth, except in reproductive and adult stem cells
FUNCTION:
➤ Divides to give continuous supply of stem cells For:
1. Cell replacement
2. Tissue repair
3. Growth
Uncontrolled Cell Division
- Cells divide repeatedly
- Cell cycle checkpoints not controlled
- Short interphase :
- DNA replication is error-prone
- Very little growth
Cytokinesis
ANIMAL cells:
- Cell membrane drawn together
➤ By contractile ring of microfilaments
➤ Forms a cleavage furrow
➤ Creating a drawstring effect
➤ Cell membrane fuses to divide cell into two
PLANT cells:
➤ Vesicles transported to equator
➤ To form cell plate at equator
➤ Cell wall laid down
➤ So cytoplasm divided into two
➤ Organelles are shared out
What causes uncontrolled cell division / cancer
- Mutation in genes that controls cell division
➤ Oncogenes (mutated gene that causes cancer) is switched on
➤ Proto-oncogene (normal gene) converted to an oncogene
➤ Tumor suppressor genes switched off
➤ Cancer cells pass on mutations and oncogenes to daughter cells
➤ Cancer cells can escape DNA repair during interphase as well
➤ Result in accumulated mutations
Accumulated mutations in cancer cells can cause:
➤ Immune system does not recognize the cells as foreign and destroy it ➡ avoid detection of immune
system
➤ No programmed cell death
➤ Has telomerase ➡ can divide indefinitely
➤ Do not respond to extra / intracellular signals to stop dividing
➤ Mitosis is no longer inhibited by cell-to-cell contact
➤ No contact inhibition
➤ Loss of function / cell specialization
➤ Form mass of undifferentiated cells = tumor
Tumor Formation
- Mutagens (carcinogens) cause mutations in gene which controls cell division (oncogenes are switched on)
- Cancerous cells escape cell death and immune system due to self antigens
- Cell undergoes rapid and uncontrolled mitosis : grows into mass of unspecialized cells (tumor)
- Tumor continues to grow which displaces and compresses surrounding tissue
- Growth of blood capillaries into tumor (angiogenesis)
- has high demand of nutrients ,lack of nutrients for other non-cancerous cells
Types of Tumors
BENIGN:
- does not spread from their site of origin
- warts, ovarian cysts, brain tumors
MALIGNANT:
- can spread throughout body
- can undergo metastasis
- through blood and lymphatic system
- invade and destroys other tissues in other areas
- can result in secondary growth
