Mitosis & Meiosis Flashcards
What is the enzyme that unwinds supercoiled DNA?
Topoisomerase
What are the arms of chromosomes called?
P & Q
What is G0?
Where stable cells that don’t divide are- Not preparing for devision
What dyes stain chromopsomes?
Giemsa: G-Banding, Quinacrine: Q-Banding
What is G1?
(11-12 hours) Cells increase in size and organelles
What is G2?
Shorter growth phase
What is S-Phase?
Cells synthesise a complete copy of DNA and replicates micro-tubule organising structure called centrosome that seperates DNA in M phase.
What are the 3 stages of interphase?
G1, S phase, G2
What are the steps of Mitosis?
Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis
What happens in prophase?
Chromatin condenses into chromosomes, centrosomes nucleate microtubules and move to opposite poles of nucleus
What happens in prometaphase?
Nuclear membrane breaks down, microtubules invade nuclear space, chromatids attach to microtubules, no longer has a nucleus
What happens in metaphase?
Chromosomes line up along equatorial plane
What happens in anaphase
Sister chromatids seperate and are pushed to opposite poles of the cell
What happens in telophase?
Nuclear membranes reform, chromosomes unfold into chromatin
What happens in cytokinesis?
The cytoplase divides to form 2 cells
Drugs that target mitosis?
Taxol & vinca alkaloids prevent mitotic spindle, Ispinesib target spindle poles, Colchicine like drugs target anaphase
In meiosis when is there crossing over of genetic material?
Prophase 1
What happens in prophase 1 of meiosis?
Crossing over occurs to allow for genetic diversity
What happens in metaphase 1 of meiosis?
Random assortment on metaphase plate- resulting in genetic diversity
What happens in meiosis 2?
Sister chromatids seperate, haploid cells produced
Sperm production? (Gametogenesis)
primordial germ cells undergo lots of mitoses
to produce multiple spermatogonia. Meiotic divisions start at puberty and continue during adult life. Cytoplasm divides equally. Millions of mature sperm continuously
produced.
Eggs? (Gametogenesis)
Primordial germ cells undergo 30 mitotic divisions to give rise to oogonia. They enter prophase of meiosis and start by the 8th month of embryonic life. Everything put into suspension-prophase stops. cells enter ovulation 10-50 years later. cytoplasm divided unequally. Meiosis 1 is completed at ovulation. Meiosis 2 only completed if fertilisation occurs. When dividing cytoplasm divides unequally. I egg is produced and 3 polar bodies are produced which die.
What is Non-Disjunction? Give example
Failure of chromosome pairs to separate in Meiosis 1 or sister chromatids to separate properly in meiosis 2. E.g. Downs syndrome
What is monosome? Give example
Loss of a chromosome. E.g. Turners syndrome
What is gonadal mosaicism?
Occurs when precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis)
What is Dcl-2?
A gene which prevents apoptosis, and keeps the cell alive
What does helicase do in DNA replication?
Seperates double-stranded DNA into single strands
What does DNA Polymerase do?
Binds to exposes nitrogenous bases and adds nucleotides to forma DNA molecule
What does ligase do?
An enzyme which can connect two strands of DNA together by forming a bond between the phosphate group of one strand and the deoxyribose group on another
What is telomerase?
the enzyme responsible for protecting chromosome ends from shortening during DNA replication to avoid potentially catastrophic DNA loss. If they get too short repressor genes will stop the cell dividing
What are labile cells?
Cellx that multiply constantly throughout life. High regenerative ability, high rate of turnover, susceptible to toxic effect of ratiation/ drugs. e.g. intestinal epithelium/ haemopoetic cells/ bone marrow.
What are stable cells?
Cells that multiply only when needed. They have good regenative ability and a slow rate of turnover. e.g. hepatocytes, endocrine glands.
What are permanent cells?
Cells unable to replicate in postnatal life. e.g. neutrons/ cardiac ,muscle.
What is hyperplasia?
Increased number of cells.
What is hypoplasia?
Failure of development of an organ.
Metaplasia
Adaptive reversible transformation of one terminally differentiated cell type into another.
