(Physiology) - Cell division and Chromosome Flashcards
Mastery
What is a gene?
what are they made up of
whats another name
Chromosomes and how they prepare for cell divison
when do they replicate
what do they look like in G2
segments of DNA and units of hereditary traits
Centromere in the centre, chromosome on top and sister chromatids on bottoms
SISTER CHROMATIDS
Chromosomes replicate and condense
replicated in S phase, from one chromatid to a pair of sister
in G2 it is a whole chromosome
Somatic cells and Gametes
Somatic cell
most cells have 46 chromosomes (diploid)
* two sets of 23
* One set from each parent
Gametes (sperm and egg cells) haploid
* 1 set of chromosomes (23)
* Result of Meiosis
SINGLE CHROMATID AND SINGLE CHROMATID ONE FROM MOM ONE FROM DAD
Cell division cycle
broad view of interphase and Mitosis
How long
Process
Interphase- G1, S, G2 phase
in interphase chromosomes are duplicated and cell organelles are made
In mitosis, chromatids split and each cell is equal and identical
In G1 cell is growing, and organelles multiply, metabolically active, 8 hours
S phase is getting ready for next division, replicating and synthesizing DNA, 8 hours
G2 phase, cell grows and centrioles replicate- microtubules
Go through mitosis
What kind of cells divide repeatedly
what cells are alive but don’t divide
what cells divide sometimes
Some cells divide repeatedly Using stem cells
Eg. Skin, Blood cells, cheek cells
Some cells stay alive but don’t divide
Eg. Muscle and nerve (called G0 cells)
cells never leave G1 and never go thru mitosis, but can still function
Other cells divide infrequently
Eg. bone
Mitotic division
PPMAT+C
Prophase:
- Chromatin condenses into chromosomes,
- nuclear membrane degenerates
- Centrosomes move apart
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Prometaphase:
- Nuclear envelope disappears
- Spindles from chromatids to centrosomes
- Kinetochore proteins appear
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Metaphase:
- Centromeres of chromosomes line up at the metaphase plate
- Mitotic spindles start to form
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Anaphase:
- Centromeres of chromosomes split
- Sister chromatids move toward opposite poles of the cell, pulled apart
- Kinetochore microtubules move chromatids toward opposite ends of the cell
- Nonkinetechore microtubules
Overlap and push against each other, elongating the cell
———————————————————
Telophase:
- Mitotic spindles dissolve
- Chromosomes become chromatin
- New nuclear membrane forms
———————————————————
Cytokinesis
- Division of cytoplasm Occurs with telophase
- Cleavage furrow pinches cell in two
(actin-myosin drawstring)
AFTER CELLS ENTER INTERPHASE
cell control system
how to pass first one
External factors that can trigger cell division
dont want them to divide if they arent ready or if we dont need
two main checkpoints
G1 checkpoint
after mitosis, at the end of G1
can pass if DNA is undamaged, cell is big enough and enough nutrients
G2 checkpoint
end of G2, decide if we go into mitosis again
PASSING THRU G2 PHASE
Two regulatory proteins involved
in cell cycle control
Cyclins and cyclin-dependent kinases (Cdks)
Come tgth to bind and from MPF, Triggers mitosis
hormones can trigger second
GROWTH FACTOR
messenger response which can help pass G1 or G2 checkpoint
RULES OF CELL DIVISION
Density-dependent Inhibition
* Crowded cells stop dividing
Anchorage dependence
* Cells must be attached to substratum to divide
Cancer cells
No density-dependent inhibition
Do not respond to body’s control mechanisms,
WONT STOP DIVIDING
override checkpoints
No anchorage dependence
Form tumours
Apoptosis and Necrosis
Apoptosis
“Programmed cell death”
Protective process
* E.g. with cell dysfunction
* May protect us from
cancers
——————————————————–
Necrosis
Cell death triggered by
inflammation
Meiosis overview
Meiosis chromosomes and what it produces
Meiosis I: Reduces chromosomes from
diploid to haploid
Meiosis II: Produces four haploid daughter cells
——————————————————–
23 from mom 23 from dad
Meiosis 1 and 2
each one doubles in the S phase
but we split before doubling again
First Stage of Meiosis
ON EXAM
Crossing over. exchange of DNA only in prophase 1, Chromosomes of the same genes find each other, increases variablity
HAPPENS IN PROPHASE 1
ON EXAMMMMM
Stages of Meiosis actually, like what is happening in cell division
Prophase 1:
- 6 chromosomes 3 pairs
- centrioles split and nuclear membrane
- condense DNA
- DNA find matching set
- CROSSING OVER
—————————————————
Metaphase 1:
- Homologous pairs line up on midplate, mismatched pairs
—————————————————
Anaphase 1:
- Split CHROMOSOMES, instead of chromatids, 3 this way 3 the other
- daughter cells will get 3 chromosomes
—————————————————
Then cytokinesis and telophase, instead of going back down into chromatin and recreating nuclear membrane, next stage
—————————————————
Prophase 2:
- break down nuclear membrane and condense DNA
—————————————————
Metaphase 2:
-Line up chromosomes on mid plate
- already hapliod
—————————————————
Anaphase 2:
- get split
—————————————————
Telophase 2:
-split up cells and go back into messy chromatin and only 3 chromsomes in each of the daughters, but we started with 6
- EACH DAUGHTER CELL IS UNIQUE
MITOSIS VS MEIOSIS
Mitosis:
Produces 2 identical daughter cells.
Occurs in body (somatic) cells for growth and repair.
One division.
Daughter cells are diploid (same number of chromosomes as parent).
Meiosis:
Produces 4 genetically different cells (gametes: sperm or eggs).
Occurs in reproductive cells for sexual reproduction.
CHROMOSOMES FIND EACH OTHER TO CROSS OVER
Two divisions.
Daughter cells are haploid (half the number of chromosomes).
What is it called when in prophase 1 of meiosis, Chromosomes look for each other and CROSS over
Independent assortment
Each pair of chromosomes sorts its maternal and paternal homologues
into daughter cells independently of the other pairs
they would be unique, because of crossing over
Genetic variability
Independent assortment, random fertilization and crossing over produce a zygote with any of about 64 trillion diploid combinations
Meiosis Malfunction
Chromosomes mishaps types
Abnormal chromosome count
* The failure of homologous pairs to separate during MEIOSIS 1
* The failure of sister chromatids to separate during MEIOSIS 2
XXY (Klinefelter’s syndrome),
XO- Turner’s, no second X
Down syndrome is caused by trisomy 21
* An extra copy of chromosome 21
* Karyotype
Types of Genetic malfunctions
TIDD
Deletion - have no gene
duplication- double set of gene
Inversions - out of order and on wrong locus
Reciprocal Translocation - Chromosome 5 meeting number 4 by accident
