Chapter 11 & 12 Flashcards
Mitosis and meiosis are eukaryotic ________
nuclear division in stem cells, the mechanisms that lead to the distribution of DNA to new nuclei in forthcoming daughter cells
Mitosis is used by multicelled organisms for _____, repair, and _____ reproduction by repeated division of somatic cells
growth; asexual
Meiosis occurs only in particular somatic cells called _____ cells.
Germ cells; they divide to form gamates (sex cells)
Somatic cells=
diploid= 2n (mitosis); for humans 2(23)= 46 chromosomes
that is they have 2 of each type of chromosome
gamates=
haploid= n (meiosis); 23 chromosomes in a sperm/egg
only 1 chromosome of each type
before division, each threadlike chromosome is duplicated to form 2 sister chromatids held together by a _____
centromere
The centromere is the region where….
duplicated chromosomes will attach to the microtubules of the spindle during nuclear division
The cell cycle is….
a reoccurring sequence of events that extends from the time of a cell’s formation until each division is completed
most of cell’s existence (90%) is in the ___
interphase
what happens during interphase ?
Cell’s mass increases, the cytoplasmic components approx. double in number, AND DNA IS DUPLICATED
Interphase has three stages: G1, S1, G2
explain what happens in each
G1: most of the carbohydrates, lipids, and proteins for a cell’s own use and for export are assembled. CELL GROWTH
S phase: the cell copies its DNA and synthesizes proteins used in organizing condensed chromosomes. DNA SYNTHESIS
G2: proteins that will drive mitosis to completion are produced. PREPARE FOR DIVISION, chromatin duplicated
Apotosis have chances to form into tumors there they….
commit cell suicide or program cell death
G= Gap for growth
S= synthesis of DNA
Stages of Mitosis:
- Prophase
- Metaphase
- Anaphase
- Telephase
-Prophase: Prepare for division! Chromatin condenses to chromosomes consisting of two sister chromatids.
Nuclear envelope disappears.
Metaphase: Meet in the midline.
Chromosomes align at equatorial plane. In this stage, chromosomes are at the most condensed
Anaphase: Alone and apart :(
Sister chromatids seprate to move to the poles, spindle fibers pull apart
Centromeres divide.
Telephase: Torn and towed away T_T
Chromatin expands. Cytoplasm divides.
Phase in which nuclear membrane reforms around the chromosomes. Chromosomes decondense and arrive @ opposite poles
spindle apparatus
is crucial to mitosis/ meiosis. Seperate and move sister chromosomes to where they need to go (which is the nuclei) to opposite pole
Function of centrioles?
centrioles are short stacks of microtubular fibers) organize tubulin subunits to form microtubular fibers.
Microtubular fibers are made of tubulins
transition to metaphase?
spindle apparatus forms
chromatin
Chromatin is the uncondensed DNA that is present in the cell during interphase (the cell’s normal “growth and development” stage). Think of this as unraveled DNA that is laying around in the nucleus. Because it is unraveled, transcription machinery can get to it and use it to transcribe mRNA. mRNA will then leave the nucleus and go on to help in making proteins.
chromosomes
Chromosomes are super condensed DNA that is present in the cell during mitosis (cell division). Imagine if all that chromatin “packed up” and wrapped itself nice and neat, kind of like when we wrap up electrical cords of adapters or appliances. Chromosomes are structures of highly condensed DNA that make it easy for the cell to divide and distribute its DNA into the two new daughter cells that will be formed from the existing cell. Chromosomes can contain one or two CHROMATIDS, which I’ll talk about next.
chromatids
Chromatids are one half of a mitotic chromosome. You know how most chromosomes look like X’s? Well, one half of that “X”, the “>” half, is a chromatid. Chromatids are usually identical. Why does a chromosome have two, then? One chromatid will be taken into one of the new daughter cells in mitosis, and the other chromatid will be taken to the other. The cell itself has machinery that literally rip apart chromosomes at their center, letting each new cell take one chromatid with it.
It is important to know that the instant an “X” chromosome ( two chromatids) is ripped apart, the two chromatids become two individual chromosomes. As the new daughter cells (with their one chromatid each) grow, they will replicate that chromatid during interphase and restore the “X” chromosome that we see in mitosis. Until then, though, cells only have the “>” part of the chromosome (which is all they need).
Once again, remember that a chromosome can have one OR two chromatids. Chromatids are identical, and two chromatids exist on chromosomes because one chromatid needs to go into each new daughter cell.
cytokinesis begins…
towards the start of anaphase and ends towards the end of telephase
Cytoplasmic division of animal cells
squeezed in the in the middle to separate the two daughter cells- a process called cleavage or furrowing
end result of meiosis
4 genetically different haploid gamates
end result of mitosis
2 daughter cells, chromosomally identical to parent.
2 diploid cells
meiosis produces gamates that have one of each pair of homologous chromosomes
during meiosis homologous chromosomes…
line up unequally
difference between anaphase I and anaphase II
Anaphase I: homologous chromosomes seperate from each other
Anaphase II: sister chromosomes seperate from each other
humans have 2^n possible genetically different gamates
2^23. over 8 million possible genetically different gamates
crossing over
when non sister chromatids exchange segments in a process called crossing over. This is one source of genetic variation
after crossing over, nonsister chromatids begin to partially separate but remain attached by
chiasmata
variation present at fertilization is from 3 sources:
- crossing over occurs during prophase I–> gives rise to 8 million possible gamates
- random alignments at metaphase I lead to millions of combonations of maternal and paternal chromosomes in each gamate
- at fertalization, all of the genetically diverse gamates producedm chance will determine which two will meet
Similarities in Meiosis and Mitosis
- a cell proceeds from interphase for both
- the cell duplicates DNA for both
- Each duplicated chromosome consists of 2 sister chromatids linked at the centromere
- microtubules of the spindle apparatus move the chromosomes in prescribed directions
Differences in meiosis and mitosis
meiosis function is gamate formation, occurs in germ cells (adult stem cells), 2 nuclear divisions, results in 4 genetically different gamates, haploid n
Mitosis function is for growth, repair, asexual reproduction, occurs in somatic (diploid) cells, 1 nuclear division, results in 2 genetically identical diploid cells, 2n
Prokaryotic conjunction is a mechanism by which….
a copy of a plasmid is transferred from a donor bacteria to a recipient bacteria
A plasmid is a
small, self-replicating circle of DNA with a few genes, usually these genes confer a survival advantage such as resistance to antibiotics.
some plasmid genes give instruction for prokaryotic conjunction
Prokayotes reproduce by….
Binary fission.
end result: prokaryotes that are genetically identical, asexual
Transformation
importing pieces of DNA
transductions:
prokaryote does not transport DNA, but is brought over by virus (vector). Prokaryote gets info from outside the cell
conjunction
donor prokaryote copy of plasmid of transferred by donor to recipient
