Cell Cycle Flashcards
What are the stages of the cell cycle?
Interphase
Cell division
What are the stages of Interphase?
G0: Cycle arrest (cell is inactive + resting)
G1: Organelles and proteins are replicated
C1: Checkpoint (cycle can be halted and repairs made)
S: Chromosomes are replicated
G2: Cell is checked and repairs made
C2: Checkpoint (cycle can be halted and repairs made)
Wha are the stages of cell division?
P: Chromosome condense, nuclear membrane dissolves and centrioles move toward the poles
pm: The spindle apparatus appears, attaches to the centromeres and moves the chromosomes
M: Chromosomes line up along the equator of the cell
A: Spindle fibres contract, splitting the centromere and pulling the chromosomes apart to form two sister chromatids which move to opposite sides of the cell
T: Chromosomes decondense, nuclear membrane reforms and the cell pinches
Cytokinesis: Organelles move to the sides, the cytoplasm splits and 2 new identical daughter cells are formed
How do quadrivalent pairs join?
During Meiosis I:
Short sections of telomeres (pairing centres) unique to homologous pairs connect to proteins on the nuclear envelope to form nuclear-chromosome complexes
NC-complexes joins to the cytoskeleton which moves the bivalent pairs together
Complementary regions on each chromosome (same alleles) form a synaptonemal complex
What do quadrivalent pairs allow?
Recombination -
Chiasmata: swapping of genetic material
Random separation of chromosomes
What are the stages of DNA replication?
DNA is unwound by helicase
DNA polymerase joins complementary free nucleotides in the 5’ to 3’ direction by phosphodiester bonds
On the lagging strand, primase creates primers to initiate a sequence for DNA polymerase forming Okazaki fragments
Ligase joins the fragments to create a true 3’ to 5’ strand
What are the stages of spermatogenesis?
After puberty:
The (germ cell) spermatogonium undergoes Mitosis to form two identical spermatocytes
One spermatocyte will become a spermatogonium (maintain supply)
Primary spermatocyte undergoes meiosis I to form 2 secondary spermatocytes
Secondary spermatocytes undergoes meiosis II to form 4 spermatids (haploid)
Spermatids mature to form sperm
What are the stages of oogenesis?
Before birth:
The (germ cell) oogonium undergoes Mitosis to form two identical oocytes
One oocyte will become a oogonium (maintain supply)
Primary oocyte starts meiosis I but is paused during Prophase I until birth
After puberty:
Primary oocyte finishes meiosis I to form a secondary oocyte and a polar body
Secondary oocyte starts meiosis II but is paused during Metaphase II until fertilised
After fertilisation:
Secondary oocyte finishes meiosis II to form an ovum (fertilised egg) (haploid) and a polar body
As soon as the genetic material combines a zygote is formed
What does aneuploidy mean and what are its causes?
Abnormal number of chromosomes
Non-disjunction:
Centromere does not split (daughter cell results with both sister chromatids)
Anaphase lag:
Spindle apparatus fails to attach to a centromere or contracts too slowly (daughter cell results with missing chromosomes)
What is the difference between non-mosaicism and mosaicism and Describe the cell lines that arise after aneuploidy
Non-mosaicism: 1 cell line (first post-zygotic divisions)
Mosaicism: >1 cell line (later cell divisions)
What prevents aneuploidy?
Cell cycle checkpoints
Must be inactive/irregular to allow aneuploidy
State the number of chromosome pairs, chromosomes and chromatids during: Interphase (Normal) After Replication Mitosis (P, M, A, T) Meiosis (Meiosis I, Meiosis II)
Interphase: 23 chromosome pairs, 46 chromosomes, 46 chromatids
After replication: 23 chromosome pairs, 46 chromosomes, 92 chromatids
Mitosis:
P and M: 23 chromosome pairs, 46 chromosomes, 92 chromatids
A and T: 46 chromosome pairs, 92 chromosomes, 92 chromatids
Meiosis:
Meiosis I: 0 chromosome pairs, 23 chromosomes, 46 chromatids
Meiosis II: 0 chromosome pairs, 23 chromosomes, 23 chromatids
