chapter 5 - mitotic cell cycle Flashcards
chromosome
threadlike structure containing dna and genes
chromatin
combination of dna (acidic) wound around histones proteins (basic)
2 types of chromatin
heterochromatin and euchromatin
heterochromatin
- tightly coiled (condensed)
- most condensed at metaphase
- densely stained
euchromatin
- loosely coiled
- at interphase (between division)
- not as densely stained
main functions of chromosome in nuclear division
chromosome condensed so dns is tightly packed = easier to separate chromatids at centromere into daughter cells
telomeres
repeated short base sequence at end of chromosome (by telomerase)
• ensure ends of dna are included during dna replication
• copying enzyme cant copy the end of dna so pieces are of info are lost; eventually including loss of vital genes
ageing
specialized cells dont top up their telomeres after dna replication therefore causing loss of genes dns and cell death
centromere
region where chromatids are held together
nucleosome
dna wrapped around histones making 147 base pairs
- made of 8 histone molecules
- linked dna is also held by a histone
mitosis
nuclear division producing 2 genetically identical daughter nuclei each containing the same number of chromosomes as the parent. sister chromatids contain dna with identical genes which is key to precise nuclear division (when each chromatid goes into each daughter cell ut makes them genetically identical)
cell cycle - 3 phases
interphase
nuclear division
cell division
interphase
growth 1 phase:
• prepares for growth and dna synthesis by producing rna, proteins and enzymes
• if there are insufficient growth factors or when cell has reached its max size cell will nor divide and remain in Growth 0
s phase:• synthesis of dna in euchromatin form so each chromosome consist of 2 identical chromatids (short phase)
• chromatin also replicates along with dna so histones are replicated for M phase
growth 2 phase: • gap after S phase and before nuclear divisions prepare for mitosis
• new dna packed and errors are repaired
• sharp increase in the production of tubulin to make microtubules for the formation of mitotic spindle
• nuclear envelope breaks down
mitosis - prophase
prophase • chromosomes condense and become visible • spindle fivers emerge from centrosomes • nuclear envelope breaks down • nucleolus dissapears
mitosis prometaphase
- chromosomes continue to condense
- kinetochores appear at the centromeres
- mitotic spindle microtubules attach to kinetochores
- centrosomes move toward opposite poles
mitosis - metaphase
- mitotic spindle is fully developed centrosomes are at opposite poles of the cell
- chromosomes are lined up at the metaphase plate
- each sister chromatid is attached to a spindle fiber originating poles
mitosis anaphase
- cohesion proteins binding the sister chromatids together break down
- sister chromatids ( now called chromosomes ) are pulled toward opposite poles
- non- kinetochore spindle fibers lengthen, elongating the cell
mitotic telophase
- chromosomes arrive at opposite poles and begin to de-condense
- nuclear envelope material surrounds each set of chromosomes
- the mitotic spindle breaks down
kinetochore
- 2 kinetochore at centromere on each chromatid during metaphase
- made of proteins that bind to dna in centromere and also go microtubules
- microtubules extend from kinetochore to the poles of spindle
importance of mitosis
- growth: clones produced allow growth of mulcellular organism
- replacement of cells and repair of tissues
- asexual reproduction
stem cells
cells that divide repeatedly by mitosis and differentiate into specialized cells or remain as stem cells— 3 diff kinds:
• totipotent: cells that can divide repeatedly to form any other cell in the body
• pluripotent: embryonic stem cells that lead to development of the embryo and later the adult. they are not specialized into placenta
• multi-potent: adult stem cells that are only able to produce a few types of cell
cancer
mutation occurs in genes that control cell division, an oncogene, that results uncontrolled mitosis. cancerous cells divide repeatedly and form a tumour, which is an irregular mass of cells
malignant tumour
tumours that spread through the body, invade other tissues and destroy them. these cells break off from the tumor and form secondary growth, known as metastasis
